Sample records for ice shelf antarctic

  1. Breakup of Pack Ice, Antarctic Ice Shelf

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Breakup of Pack Ice along the periphery of the Antarctic Ice Shelf (53.5S, 3.0E) produced this mosaic of ice floes off the Antarctic Ice Shelf. Strong offshore winds, probably associated with strong katabatic downdrafts from the interior of the continent, are seen peeling off the edges of the ice shelf into long filamets of sea ice, icebergs, bergy bits and growlers to flow northward into the South Atlantic Ocean. 53.5S, 3.0E

  2. Breakup of Pack Ice, Antarctic Ice Shelf

    NASA Image and Video Library

    1991-09-18

    STS048-152-007 (12-18 Sept 1991) --- The periphery of the Antarctic ice shelf and the Antarctic Peninsula were photographed by the STS 48 crew members. Strong offshore winds, probably associated with katabatic winds from the interior of the continent, are peeling off the edges of the ice shelf into ribbons of sea ice, icebergs, bergy bits and growlers into the cold waters of the circum-Antarctic southern ocean.

  3. Ross Ice Shelf, Antarctic Ice and Clouds

    NASA Technical Reports Server (NTRS)

    1991-01-01

    In this view of Antarctic ice and clouds, (56.5S, 152.0W), the Ross Ice Shelf of Antarctica is almost totally clear, showing stress cracks in the ice surface caused by wind and tidal drift. Clouds on the eastern edge of the picture are associated with an Antarctic cyclone. Winds stirred up these storms have been known to reach hurricane force.

  4. Sensitivity of an Antarctic Ice Sheet Model to Sub-Ice-Shelf Melting

    NASA Astrophysics Data System (ADS)

    Lipscomb, W. H.; Leguy, G.; Urban, N. M.; Berdahl, M.

    2017-12-01

    Theory and observations suggest that marine-based sectors of the Antarctic ice sheet could retreat rapidly under ocean warming and increased melting beneath ice shelves. Numerical models of marine ice sheets vary widely in sensitivity, depending on grid resolution and the parameterization of key processes (e.g., calving and hydrofracture). Here we study the sensitivity of the Antarctic ice sheet to ocean warming and sub-shelf melting in standalone simulations of the Community Ice Sheet Model (CISM). Melt rates either are prescribed based on observations and high-resolution ocean model output, or are derived from a plume model forced by idealized ocean temperature profiles. In CISM, we vary the model resolution (between 1 and 8 km), Stokes approximation (shallow-shelf, depth-integrated higher-order, or 3D higher-order) and calving scheme to create an ensemble of plausible responses to sub-shelf melting. This work supports a broader goal of building statistical and reduced models that can translate large-scale Earth-system model projections to changes in Antarctic ocean temperatures and ice sheet discharge, thus better quantifying uncertainty in Antarctic-sourced sea-level rise.

  5. Antarctic ice discharge due to warm water intrusion into shelf cavities

    NASA Astrophysics Data System (ADS)

    Winkelmann, R.; Reese, R.; Albrecht, T.; Mengel, M.; Asay-Davis, X.

    2017-12-01

    Ocean-induced melting below ice shelves is the dominant driver for mass loss from the Antarctic Ice Sheet at present. Observations show that many Antarctic ice shelves are thinning which reduces their buttressing potential and can lead to increased ice discharge from the glaciers upstream. Melt rates from Antarctic ice shelves are determined by the temperature and salinity of the ambient ocean. In many parts, ice shelves are shielded by clearly defined density fronts which keep relatively warm Northern water from entering the cavity underneath the ice shelves. Projections show that a redirection of coastal currents might allow these warmer waters to intrude into ice shelf cavities, for instance in the Weddell Sea, and thereby cause a strong increase in sub-shelf melt rates. Using the Potsdam Ice-shelf Cavity mOdel (PICO), we assess how such a change would influence the dynamic ice loss from Antarctica. PICO is implemented as part of the Parallel Ice Sheet Model (PISM) and mimics the vertical overturning circulation in ice-shelf cavities. The model is capable of capturing the wide range of melt rates currently observed for Antarctic ice shelves and reproduces the typical pattern of comparably high melting near the grounding line and lower melting or refreezing towards the calving front. Based on regional observations of ocean temperatures, we use PISM-PICO to estimate an upper limit for ice discharge resulting from the potential erosion of ocean fronts around Antarctica.

  6. Antarctic Ice Shelf Loss Comes From Underneath

    NASA Image and Video Library

    2017-12-08

    Calving front of an ice shelf in West Antarctica. The traditional view on ice shelves, the floating extensions of seaward glaciers, has been that they mostly lose ice by shedding icebergs. A new study by NASA and university researchers has found that warm ocean waters melting the ice sheets from underneath account for 55 percent of all ice shelf mass loss in Antarctica. This image was taken during the 2012 Antarctic campaign of NASA's Operation IceBridge, a mission that provided data for the new ice shelf study. Read more: www.nasa.gov/topics/earth/features/earth20130613.html Credit: NASA/GSFC/Jefferson Beck NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  7. Marine ice regulates the future stability of a large Antarctic ice shelf

    PubMed Central

    Kulessa, Bernd; Jansen, Daniela; Luckman, Adrian J.; King, Edward C.; Sammonds, Peter R.

    2014-01-01

    The collapses of the Larsen A and B ice shelves on the Antarctic Peninsula in 1995 and 2002 confirm the impact of southward-propagating climate warming in this region. Recent mass and dynamic changes of Larsen B’s southern neighbour Larsen C, the fourth largest ice shelf in Antarctica, may herald a similar instability. Here, using a validated ice-shelf model run in diagnostic mode, constrained by satellite and in situ geophysical data, we identify the nature of this potential instability. We demonstrate that the present-day spatial distribution and orientation of the principal stresses within Larsen C ice shelf are akin to those within pre-collapse Larsen B. When Larsen B’s stabilizing frontal portion was lost in 1995, the unstable remaining shelf accelerated, crumbled and ultimately collapsed. We hypothesize that Larsen C ice shelf may suffer a similar fate if it were not stabilized by warm and mechanically soft marine ice, entrained within narrow suture zones. PMID:24751641

  8. Rapid glass sponge expansion after climate-induced Antarctic ice shelf collapse.

    PubMed

    Fillinger, Laura; Janussen, Dorte; Lundälv, Tomas; Richter, Claudio

    2013-07-22

    Over 30% of the Antarctic continental shelf is permanently covered by floating ice shelves, providing aphotic conditions for a depauperate fauna sustained by laterally advected food. In much of the remaining Antarctic shallows (<300 m depth), seasonal sea-ice melting allows a patchy primary production supporting rich megabenthic communities dominated by glass sponges (Porifera, Hexactinellida). The catastrophic collapse of ice shelves due to rapid regional warming along the Antarctic Peninsula in recent decades has exposed over 23,000 km(2) of seafloor to local primary production. The response of the benthos to this unprecedented flux of food is, however, still unknown. In 2007, 12 years after disintegration of the Larsen A ice shelf, a first biological survey interpreted the presence of hexactinellids as remnants of a former under-ice fauna with deep-sea characteristics. Four years later, we revisited the original transect, finding 2- and 3-fold increases in glass sponge biomass and abundance, respectively, after only two favorable growth periods. Our findings, along with other long-term studies, suggest that Antarctic hexactinellids, locked in arrested growth for decades, may undergo boom-and-bust cycles, allowing them to quickly colonize new habitats. The cues triggering growth and reproduction in Antarctic glass sponges remain enigmatic. Copyright © 2013 Elsevier Ltd. All rights reserved.

  9. Understanding Ice Shelf Basal Melting Using Convergent ICEPOD Data Sets: ROSETTA-Ice Study of Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

    Bell, R. E.; Frearson, N.; Tinto, K. J.; Das, I.; Fricker, H. A.; Siddoway, C. S.; Padman, L.

    2017-12-01

    The future stability of the ice shelves surrounding Antarctica will be susceptible to increases in both surface and basal melt as the atmosphere and ocean warm. The ROSETTA-Ice program is targeted at using the ICEPOD airborne technology to produce new constraints on Ross Ice Shelf, the underlying ocean, bathymetry, and geologic setting, using radar sounding, gravimetry and laser altimetry. This convergent approach to studying the ice-shelf and basal processes enables us to develop an understanding of the fundamental controls on ice-shelf evolution. This work leverages the stratigraphy of the ice shelf, which is detected as individual reflectors by the shallow-ice radar and is often associated with surface scour, form close to the grounding line or pinning points on the ice shelf. Surface accumulation on the ice shelf buries these reflectors as the ice flows towards the calving front. This distinctive stratigraphy can be traced across the ice shelf for the major East Antarctic outlet glaciers and West Antarctic ice streams. Changes in the ice thickness below these reflectors are a result of strain and basal melting and freezing. Correcting the estimated thickness changes for strain using RIGGS strain measurements, we can develop decadal-resolution flowline distributions of basal melt. Close to East Antarctica elevated melt-rates (>1 m/yr) are found 60-100 km from the calving front. On the West Antarctic side high melt rates primarily develop within 10 km of the calving front. The East Antarctic side of Ross Ice Shelf is dominated by melt driven by saline water masses that develop in Ross Sea polynyas, while the melting on the West Antarctic side next to Hayes Bank is associated with modified Continental Deep Water transported along the continental shelf. The two sides of Ross Ice Shelf experience differing basal melt in part due to the duality in the underlying geologic structure: the East Antarctic side consists of relatively dense crust, with low amplitude

  10. Challenges for understanding Antarctic surface hydrology and ice-shelf stability

    NASA Astrophysics Data System (ADS)

    Kingslake, J.; Bell, R. E.; Banwell, A. F.; Boghosian, A.; Spergel, J.; Trusel, L. D.

    2017-12-01

    It is widely hypothesized that surface meltwater can contribute to ice mass loss in Antarctica through its impact on ice-shelf stability. Meltwater potentially expedites ice-shelf calving by flowing into and enlarging existing crevasses, and could even trigger ice-shelf disintegration via stresses generated by melt ponds. When ice shelves collapse, the adjacent grounded ice accelerates and thins, which contributes to sea-level rise. How these mechanisms mediate the interactions between the atmosphere, the ocean and the ice sheet is the subject of long-standing research efforts. The drainage of water across the surface of the Antarctic Ice Sheet and its ice shelves is beginning to be recognized as another important aspect of the system. Recent studies have revealed that surface meltwater drainage is more widespread than previously thought and that surface hydrological systems in Antarctica may expand and proliferate this century. Contrasting hypotheses regarding the impact of the proliferation of drainage systems on ice-shelf stability have emerged. Surface drainage could deliver meltwater to vulnerable area or export meltwater from ice shelves entirely. Which behavior dominates may have a large impact on the future response of the Antarctic Ice Sheet to atmospheric warming. We will discuss these recent discoveries and hypotheses, as well as new detailed studies of specific areas where hydrological systems are well developed, such as Amery and Nimrod Ice Shelves. We will highlight analogies that can be drawn with Greenlandic (near-)surface hydrology and, crucially, where hydrological systems on the two ice sheets are very different, leading to potentially important gaps in our understanding. Finally, we will look ahead to the key questions that we argue will need to be if we are to determine the role Antarctic surface hydrology could play in the future of the ice sheet. These include: Where does meltwater pond today and how will this change this century? What

  11. Recent Antarctic Peninsula warming relative to Holocene climate and ice-shelf history.

    PubMed

    Mulvaney, Robert; Abram, Nerilie J; Hindmarsh, Richard C A; Arrowsmith, Carol; Fleet, Louise; Triest, Jack; Sime, Louise C; Alemany, Olivier; Foord, Susan

    2012-09-06

    Rapid warming over the past 50 years on the Antarctic Peninsula is associated with the collapse of a number of ice shelves and accelerating glacier mass loss. In contrast, warming has been comparatively modest over West Antarctica and significant changes have not been observed over most of East Antarctica, suggesting that the ice-core palaeoclimate records available from these areas may not be representative of the climate history of the Antarctic Peninsula. Here we show that the Antarctic Peninsula experienced an early-Holocene warm period followed by stable temperatures, from about 9,200 to 2,500 years ago, that were similar to modern-day levels. Our temperature estimates are based on an ice-core record of deuterium variations from James Ross Island, off the northeastern tip of the Antarctic Peninsula. We find that the late-Holocene development of ice shelves near James Ross Island was coincident with pronounced cooling from 2,500 to 600 years ago. This cooling was part of a millennial-scale climate excursion with opposing anomalies on the eastern and western sides of the Antarctic Peninsula. Although warming of the northeastern Antarctic Peninsula began around 600 years ago, the high rate of warming over the past century is unusual (but not unprecedented) in the context of natural climate variability over the past two millennia. The connection shown here between past temperature and ice-shelf stability suggests that warming for several centuries rendered ice shelves on the northeastern Antarctic Peninsula vulnerable to collapse. Continued warming to temperatures that now exceed the stable conditions of most of the Holocene epoch is likely to cause ice-shelf instability to encroach farther southward along the Antarctic Peninsula.

  12. STS-48 ESC Earth observation of ice pack, Antarctic Ice Shelf

    NASA Technical Reports Server (NTRS)

    1991-01-01

    STS-48 Earth observation taken aboard Discovery, Orbiter Vehicle (OV) 103, is of the breakup of pack ice along the periphery of the Antarctic Ice Shelf. Strong offshore winds, probably associated with katabatic downdrafts from the interior of the continent, are seen peeling off the edges of the ice shelf into long filaments of sea ice, icebergs, bergy bits, and growlers to flow northward into the South Atlantic Ocean. These photos are used to study ocean wind, tide and current patterns. Similar views photographed during previous missions, when analyzed with these recent views may yield information about regional ice drift and breakup of ice packs. The image was captured using an electronic still camera (ESC), was stored on a removable hard disk or small optical disk, and was converted to a format suitable for downlink transmission. The ESC documentation was part of Development Test Objective (DTO) 648, Electronic Still Photography.

  13. Future sea-level rise from tidewater and ice-shelf tributary glaciers of the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Schannwell, C.; Barrand, N. E.; Radic, V.

    2016-12-01

    Iceberg calving and increased ice discharge from ice-shelf tributary glaciers contribute significant amounts to global sea-level rise (SLR) from the Antarctic Peninsula (AP). Owing to ongoing ice dynamical changes (collapse of buttressing ice shelves), these contributions have accelerated in recent years. As the AP is one of the fastest warming regions on Earth, further ice dynamical adjustment (increased ice discharge) is expected over the next two centuries. Here the first regional SLR projection of the AP from both iceberg calving and increased ice discharge from ice-shelf tributary glaciers in response to ice-shelf collapse is presented. The British Antarctic Survey Antarctic Peninsula Ice Sheet Model (BAS-APISM), previously shown to be suitable for the unique topographic setting from the AP, is forced by temperature output from 13 global climate models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5). In response to the high greenhouse gas emission scenario (Representative Concentration Pathway (RCP)8.5), simulations project contribution to SLR of 28±16 to 32±16 mm by 2300, partitioned approximately equally between contributions from tidewater glaciers and ice-shelf tributary glaciers. In the RCP4.5 scenario, sea-level rise projections to 2300 are dominated by tidewater glaciers ( ˜8-18 mm). In this cooler scenario, 2.4±1 mm is added to global sea levels from ice-shelf tributary drainage basins as fewer ice-shelves are projected to collapse. Sea-level projections from ice-shelf tributary glaciers are dominated by drainage basins feeding George VI Ice Shelf, accounting for ˜70% of simulated SLR. Combined total ice dynamical SLR projections to 2300 from the AP vary between 11±2 and 32±16 mm sea-level equivalent (SLE), depending on the emission scenario used. These simulations suggest that omission of tidewater glaciers could lead to a substantial underestimation of the ice-sheet's contribution to regional SLR. Iceberg calving and

  14. Intercomparison of Antarctic ice-shelf, ocean, and sea-ice interactions simulated by MetROMS-iceshelf and FESOM 1.4

    NASA Astrophysics Data System (ADS)

    Naughten, Kaitlin A.; Meissner, Katrin J.; Galton-Fenzi, Benjamin K.; England, Matthew H.; Timmermann, Ralph; Hellmer, Hartmut H.; Hattermann, Tore; Debernard, Jens B.

    2018-04-01

    An increasing number of Southern Ocean models now include Antarctic ice-shelf cavities, and simulate thermodynamics at the ice-shelf/ocean interface. This adds another level of complexity to Southern Ocean simulations, as ice shelves interact directly with the ocean and indirectly with sea ice. Here, we present the first model intercomparison and evaluation of present-day ocean/sea-ice/ice-shelf interactions, as simulated by two models: a circumpolar Antarctic configuration of MetROMS (ROMS: Regional Ocean Modelling System coupled to CICE: Community Ice CodE) and the global model FESOM (Finite Element Sea-ice Ocean Model), where the latter is run at two different levels of horizontal resolution. From a circumpolar Antarctic perspective, we compare and evaluate simulated ice-shelf basal melting and sub-ice-shelf circulation, as well as sea-ice properties and Southern Ocean water mass characteristics as they influence the sub-ice-shelf processes. Despite their differing numerical methods, the two models produce broadly similar results and share similar biases in many cases. Both models reproduce many key features of observations but struggle to reproduce others, such as the high melt rates observed in the small warm-cavity ice shelves of the Amundsen and Bellingshausen seas. Several differences in model design show a particular influence on the simulations. For example, FESOM's greater topographic smoothing can alter the geometry of some ice-shelf cavities enough to affect their melt rates; this improves at higher resolution, since less smoothing is required. In the interior Southern Ocean, the vertical coordinate system affects the degree of water mass erosion due to spurious diapycnal mixing, with MetROMS' terrain-following coordinate leading to more erosion than FESOM's z coordinate. Finally, increased horizontal resolution in FESOM leads to higher basal melt rates for small ice shelves, through a combination of stronger circulation and small-scale intrusions of

  15. Meltwater produced by wind-albedo interaction stored in an East Antarctic ice shelf

    NASA Astrophysics Data System (ADS)

    Lenaerts, J. T. M.; Lhermitte, S.; Drews, R.; Ligtenberg, S. R. M.; Berger, S.; Helm, V.; Smeets, C. J. P. P.; Broeke, M. R. Van Den; van de Berg, W. J.; van Meijgaard, E.; Eijkelboom, M.; Eisen, O.; Pattyn, F.

    2017-01-01

    Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves causing grounded glaciers to accelerate and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line, which in the recent past has led to the disintegration of the most northerly ice shelves. Here, we provide observational and model evidence that this process also occurs over an East Antarctic ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the Antarctic Peninsula, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal East Antarctica high temperatures are caused by persistent katabatic winds originating from the ice sheet’s interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining >3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared with its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in situ observation of supraglacial flow and englacial storage of meltwater suggests that ice-shelf grounding zones in East Antarctica, like their Antarctic Peninsula counterparts, are vulnerable to hydrofracturing.

  16. Observed platelet ice distributions in Antarctic sea ice: An index for ocean-ice shelf heat flux

    NASA Astrophysics Data System (ADS)

    Langhorne, P. J.; Hughes, K. G.; Gough, A. J.; Smith, I. J.; Williams, M. J. M.; Robinson, N. J.; Stevens, C. L.; Rack, W.; Price, D.; Leonard, G. H.; Mahoney, A. R.; Haas, C.; Haskell, T. G.

    2015-07-01

    Antarctic sea ice that has been affected by supercooled Ice Shelf Water (ISW) has a unique crystallographic structure and is called platelet ice. In this paper we synthesize platelet ice observations to construct a continent-wide map of the winter presence of ISW at the ocean surface. The observations demonstrate that, in some regions of coastal Antarctica, supercooled ISW drives a negative oceanic heat flux of -30 Wm-2 that persists for several months during winter, significantly affecting sea ice thickness. In other regions, particularly where the thinning of ice shelves is believed to be greatest, platelet ice is not observed. Our new data set includes the longest ice-ocean record for Antarctica, which dates back to 1902 near the McMurdo Ice Shelf. These historical data indicate that, over the past 100 years, any change in the volume of very cold surface outflow from this ice shelf is less than the uncertainties in the measurements.

  17. Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf.

    PubMed

    Garabato, Alberto C Naveira; Forryan, Alexander; Dutrieux, Pierre; Brannigan, Liam; Biddle, Louise C; Heywood, Karen J; Jenkins, Adrian; Firing, Yvonne L; Kimura, Satoshi

    2017-02-09

    The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change. The increased freshwater output from Antarctica is important in determining sea level rise, the fate of Antarctic sea ice and its effect on the Earth's albedo, ongoing changes in global deep-ocean ventilation, and the evolution of Southern Ocean ecosystems and carbon cycling. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models.

  18. Validation of the Antarctic Snow Accumulation and Ice Discharge Basal Stress Boundary in the South Eastern Region of the Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Nelson, C. B.; King, K.

    2015-12-01

    The largest ice shelf in Antarctic, Ross Ice Shelf, was investigated over the years of (1970-2015). Near the basal stress boundary between the ice shelf and the West Antarctic ice sheet, ice velocity ranges from a few meters per year to several hundred meters per year in ice streams. Most of the drainage from West Antarctica into the Ross Ice Shelf flows down two major ice streams, each of which discharges more than 20 km3 of ice each year. Along with velocity changes, the warmest water below parts of the Ross Ice Shelf resides in the lowest portion of the water column because of its high salinity. Vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm water into contact with the ice shelf. This process can cause melting over a period of time and eventually cause breakup of ice shelf. With changes occurring over many years a validation is needed for the Antarctic Snow Accumulation and Ice Discharge (ASAID) basal stress boundary created in 2003. After the 2002 Larsen B Ice Shelf disintegration, nearby glaciers in the Antarctic Peninsula accelerated up to eight times their original speed over the next 18 months. Similar losses of ice tongues in Greenland have caused speed-ups of two to three times the flow rates in just one year. Rapid changes occurring in regions surrounding Antarctica are causing concern in the polar science community to research changes occurring in coastal zones over time. During the research, the team completed study on the Ross Ice Shelf located on the south western coast of the Antarctic. The study included a validation of the ABSB vs. the natural basal stress boundary (NBSB) along the Ross Ice Shelf. The ASAID BSB was created in 2003 by a team of researchers headed by National Aeronautics and Space Administration Goddard Space Flight Center (NASA GSFC), with an aim of studying coastal deviations as it pertains to the mass balance of the entire continent. The point data file was aimed at creating a replica of the

  19. Neoglacial Antarctic sea-ice expansion driven by mid-Holocene retreat of the Ross Ice Shelf.

    NASA Astrophysics Data System (ADS)

    Bendle, J. A.; Newton, K.; Mckay, R. M.; Crosta, X.; Etourneau, J.; Anya, A. B.; Seki, O.; Golledge, N. R.; Bertler, N. A. N.; Willmott, V.; Schouten, S.; Riesselman, C. R.; Masse, G.; Dunbar, R. B.

    2017-12-01

    Recent decades have seen expanding Antarctic sea-ice coverage, coeval with thinning West Antarctic Ice Sheet (WAIS) ice shelves and the rapid freshening of surface and bottom waters along the Antarctic margin. The mid-Holocene Neoglacial transition represents the last comparable baseline shift in sea-ice behaviour. The drivers and feedbacks involved in both the recent and Holocene events are poorly understood and characterised by large proxy-model mismatches. We present new records of compound specific fatty acid isotope analyses (δ2H-FA), highly-branched isoprenoid alkenes (HBIs) TEX86L temperatures, grain-size, mass accumulations rates (MARs) and image analyses from a 171m Holocene sediment sequence from Site U1357 (IODP leg 318). In combination with published records we reconstruct Holocene changes in glacial meltwater, sedimentary inputs and sea-ice. The early Holocene (11 to 10 ka) is characterised by large fluctuations in inputs of deglacial meltwater and sediments and seismic evidence of downlapping material from the south, suggesting a dominating influence from glacial retreat of the local outlet glaciers. From 10 to 8 ka there is decreasing meltwater inputs, an onlapping drift and advection of material from the east. After ca. 8 ka positively correlated δ2H-FA and MARs infer that pulses of glacial melt correlate to stronger easterly currents, driving erosion of material from upstream banks and that the Ross Ice Shelf (RIS) becomes a major influence. A large mid-Holocene meltwater pulse (preceded by warming TEX86L temperatures) is evident between ca. 6 to 4.5 ka, culminating in a rapid and permanent increase in sea-ice from 4.5 ka. This is coeval with cosmogenic nuclide evidence for a rapid thinning of the Antarctic ice sheet during the mid-Holocene (Hein et al., 2016). We suggest this represents a final major pulse of deglaciation from the Ross Ice Shelf, which initiates the Neoglacial, driving cool surface waters along the coast and greater sea-ice

  20. Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line.

    PubMed

    Drews, R; Pattyn, F; Hewitt, I J; Ng, F S L; Berger, S; Matsuoka, K; Helm, V; Bergeot, N; Favier, L; Neckel, N

    2017-05-09

    Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskers' size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability.

  1. Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line

    PubMed Central

    Drews, R.; Pattyn, F.; Hewitt, I. J.; Ng, F. S. L.; Berger, S.; Matsuoka, K.; Helm, V.; Bergeot, N.; Favier, L.; Neckel, N.

    2017-01-01

    Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskers' size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability. PMID:28485400

  2. Continued rapid glacier recession following the 1995 collapse of the Prince Gustav Ice Shelf on the Antarctic Peninsula (Invited)

    NASA Astrophysics Data System (ADS)

    Glasser, N. F.; Scambos, T. A.

    2009-12-01

    We use optical satellite imagery (ASTER and Landsat) to document changes in the Prince Gustav Ice Shelf (PGIS) and its tributary glaciers before and after its 1995 collapse. Interpretation of a pre-collapse Landsat 4-5 TM image acquired in February 1988 shows that the ice shelf was fed primarily by Sjogren Glacier from the Antarctic Peninsula and by Rhoss Glacier from James Ross Island (JRI). In 1988, the PGIS contained numerous structural discontinuities (rifts and crevasses), which collectively indicate that ice-shelf break-up had commenced at least seven years before collapse. Meltwater ponds and streams were also common across its surface. After the ice shelf collapsed, Rhoss Glacier became a tidewater glacier and has since experienced rapid and continued recession. Between January 2001 and December 2006 (six to eleven years after the collapse of the PGIS), the front of Rhoss Glacier receded a total of 13.6 km. We conclude that where tributary glaciers become tidewater glaciers they react to ice-shelf removal by rapid and continued recession and that the response time of glaciers on the Antarctic Peninsula to ice-shelf removal is measured on annual to decadal timescales. This rapid recession, coupled with previously documented tributary glacier thinning and acceleration, indicates that Antarctic Peninsula glaciers are extremely sensitive to ice-shelf collapse.

  3. Antarctic ice shelf potentially stabilized by export of meltwater in surface river.

    PubMed

    Bell, Robin E; Chu, Winnie; Kingslake, Jonathan; Das, Indrani; Tedesco, Marco; Tinto, Kirsty J; Zappa, Christopher J; Frezzotti, Massimo; Boghosian, Alexandra; Lee, Won Sang

    2017-04-19

    Meltwater stored in ponds and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers and ice streams, thereby raising sea level globally. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks-interconnected streams, ponds and rivers-on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf's meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica-contrary to present Antarctic ice-sheet models, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.

  4. Antarctic Ice Shelf Potentially Stabilized by Export of Meltwater in Surface River

    NASA Technical Reports Server (NTRS)

    Bell, Robin E.; Chu, Winnie; Kingslake, Jonathan; Das, Indrani; Tedesco, Marco; Tinto, Kirsty J.; Zappa, Christopher J.; Frezzotti, Massimo; Boghosian, Alexandra; Lee, Won Sang

    2017-01-01

    Meltwater stored in ponds and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers and ice streams, thereby raising sea level globally. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks-interconnected streams, ponds and rivers-on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf's meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica-contrary to present Antarctic ice-sheet models, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.

  5. Antarctic ice-sheet loss driven by basal melting of ice shelves.

    PubMed

    Pritchard, H D; Ligtenberg, S R M; Fricker, H A; Vaughan, D G; van den Broeke, M R; Padman, L

    2012-04-25

    Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves, potentially limiting their ability to buttress the flow of grounded tributary glaciers. Indeed, recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. But the extent and magnitude of ice-shelf thickness change, the underlying causes of such change, and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary control of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow. The highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen seas, and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic ice-sheet mass balance, and hence global sea level, on annual to decadal timescales.

  6. Impact of surface melt and ponding on the stability of Larsen C Ice Shelf, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Kulessa, Bernd; Luckman, Adrian; Hubbard, Bryn; Bevan, Suzanne; O'Leary, Martin; Ashmore, David; Kuipers Munneke, Peter; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Holland, Paul; McGrath, Daniel; Brisbourne, Alex; Rutt, Ian

    2017-04-01

    Several ice shelves on the Antarctic Peninsula have disintegrated rapidly in recent decades, and surface meltwater is strongly implicated as a driver. The Larsen C Ice Shelf is the largest ice shelf on the peninsula and one of the largest in Antarctica, and is subject to pronounced surface melting and meltwater ponding, especially in the northern sectors and landward inlets. As part of the MIDAS project we have investigated the structure and physical properties of the firn and ice layers in the 2014/15 and 2015/16 austral summers, using a combination of radar and seismic geophysical surveys together with hot water drilling and borehole optical televiewing and temperature measurements. We found that Larsen C's firn column and ice temperatures are modified strongly by surface melting and ponding, including the presence of massive ice bodies in the Cabinet and Whirlwind inlets. Numerical modelling reveals that these modifications have been altering ice shelf deformation, flow and fracture significantly. The findings from our MIDAS project thus suggest that the response of Antarctic ice shelves to climatic warming is more complex than previously thought.

  7. The effects of sub-ice-shelf melting on dense shelf water formation and export in idealized simulations of Antarctic margins

    NASA Astrophysics Data System (ADS)

    Marques, Gustavo; Stern, Alon; Harrison, Matthew; Sergienko, Olga; Hallberg, Robert

    2017-04-01

    Dense shelf water (DSW) is formed in coastal polynyas around Antarctica as a result of intense cooling and brine rejection. A fraction of this water reaches ice shelves cavities and is modified due to interactions with sub-ice-shelf melt water. This modified water mass contributes to the formation of Antarctic Bottom Water, and consequently, influences the large-scale ocean circulation. Here, we investigate the role of sub-ice-shelf melting in the formation and export of DSW using idealized simulations with an isopycnal ocean model (MOM6) coupled with a sea ice model (SIS2) and a thermodynamic active ice shelf. A set of experiments is conducted with variable horizontal grid resolutions (0.5, 1.0 and 2.0 km), ice shelf geometries and atmospheric forcing. In all simulations DSW is spontaneously formed in coastal polynyas due to the combined effect of the imposed atmospheric forcing and the ocean state. Our results show that sub-ice-shelf melting can significantly change the rate of dense shelf water outflows, highlighting the importance of this process to correctly represent bottom water formation.

  8. Antarctic ice shelf potentially stabilized by export of meltwater in surface river

    NASA Astrophysics Data System (ADS)

    Bell, Robin E.; Chu, Winnie; Kingslake, Jonathan; Das, Indrani; Tedesco, Marco; Tinto, Kirsty J.; Zappa, Christopher J.; Frezzotti, Massimo; Boghosian, Alexandra; Lee, Won Sang

    2017-04-01

    Meltwater stored in ponds and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers and ice streams, thereby raising sea level globally. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks—interconnected streams, ponds and rivers—on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf’s meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica—contrary to present Antarctic ice-sheet models, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.

  9. Antarctic sub-shelf melt rates via SIMPEL

    NASA Astrophysics Data System (ADS)

    Reese, Ronja; Albrecht, Torsten; Winkelmann, Ricarda

    2017-04-01

    Ocean-induced melting below ice-shelves is currently suspected to be the dominant cause of mass loss from the Antarctic Ice Sheet (e.g. Depoorter et al. 2013). Although thinning of ice shelves does not directly contribute to sea-level rise, it may have a significant indirect impact through the potential of ice shelves to buttress their adjacent ice sheet. Hence, an appropriate representation of sub-shelf melt rates is essential for modelling the evolution of ice sheets with marine terminating outlet glaciers. Due to computational limits of fully-coupled ice and ocean models, sub-shelf melt rates are often parametrized in large-scale or long-term simulations (e.g. Matin et al. 2011, Pollard & DeConto 2012). These parametrizations usually depend on the depth of the ice shelf base or its local slope but do not include the physical processes in ice shelf cavities. Here, we present the Sub Ice shelf Melt Potsdam modEL (SIMPEL) which mimics the first-order large-scale circulation in ice shelf cavities based on an ocean box model (Olbers & Hellmer, 2010), implemented in the Parallel Ice Sheet Model (Bueler & Brown 2009, Winkelmann et al. 2011, www.pism-docs.org). In SIMPEL, ocean water is transported at depth towards the grounding line where sub-shelf melt rates are highest, and then rises along the shelf base towards the calving front where refreezing can occur. Melt rates are computed by a description of ice-ocean interaction commonly used in high-resolution models (McPhee 1992, Holland & Jenkins 1999). This enables the model to capture a wide-range of melt rates, comparable to the observed range for Antarctic ice shelves (Rignot et al. 2013).

  10. Larsen Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Warmer surface temperatures over just a few months in the Antarctic can splinter an ice shelf and prime it for a major collapse, NASA and university scientists report in the latest issue of the Journal of Glaciology. Using satellite images of tell-tale melt water on the ice surface and a sophisticated computer simulation of the motions and forces within an ice shelf, the scientists demonstrated that added pressure from surface water filling crevasses can crack the ice entirely through. The process can be expected to become more widespread if Antarctic summer temperatures increase. This true-color image from Landsat 7, acquired on February 21, 2000, shows pools of melt water on the surface of the Larsen Ice Shelf, and drifting icebergs that have split from the shelf. The upper image is an overview of the shelf's edge, while the lower image is displayed at full resolution of 30 meters (98 feet) per pixel. The labeled pond in the lower image measures roughly 1.6 by 1.6 km (1.0 x 1.0 miles). Full text of Press Release More Images and Animations Image courtesy Landsat 7 Science Team and NASA GSFC

  11. An unusual early Holocene diatom event north of the Getz Ice Shelf (Amundsen Sea): Implications for West Antarctic Ice Sheet development

    NASA Astrophysics Data System (ADS)

    Esper, O.; Gersonde, R.; Hillenbrand, C.; Kuhn, G.; Smith, J.

    2011-12-01

    Modern global change affects not only the polar north but also, and to increasing extent, the southern high latitudes, especially the Antarctic regions covered by the West Antarctic Ice Sheet (WAIS). Consequently, knowledge of the mechanisms controlling past WAIS dynamics and WAIS behaviour at the last deglaciation is critical to predict its development in a future warming world. Geological and palaeobiological information from major drainage areas of the WAIS, like the Amundsen Sea Embayment, shed light on the history of the WAIS glaciers. Sediment records obtained from a deep inner shelf basin north of Getz Ice Shelf document a deglacial warming in three phases. Above a glacial diamicton and a sediment package barren of microfossils that document sediment deposition by grounded ice and below an ice shelf or perennial sea ice cover (possibly fast ice), respectively, a sediment section with diatom assemblages dominated by sea ice taxa indicates ice shelf retreat and seasonal ice-free conditions. This conclusion is supported by diatom-based summer temperature reconstructions. The early retreat was followed by a phase, when exceptional diatom ooze was deposited around 12,500 cal. years B.P. [1]. Microscopical inspection of this ooze revealed excellent preservation of diatom frustules of the species Corethron pennatum together with vegetative Chaetoceros, thus an assemblage usually not preserved in the sedimentary record. Sediments succeeding this section contain diatom assemblages indicating rather constant Holocene cold water conditions with seasonal sea ice. The deposition of the diatom ooze can be related to changes in hydrographic conditions including strong advection of nutrients. However, sediment focussing in the partly steep inner shelf basins cannot be excluded as a factor enhancing the thickness of the ooze deposits. It is not only the presence of the diatom ooze but also the exceptional preservation and the species composition of the diatom assemblage

  12. Wilkins Ice Shelf

    NASA Image and Video Library

    2009-04-20

    The Wilkins Ice Shelf, as seen by NASA Terra spacecraft, on the western side of the Antarctic Peninsula, experienced multiple disintegration events in 2008. By the beginning of 2009, a narrow ice bridge was all that remained to connect the ice shelf to ice fragments fringing nearby Charcot Island. That bridge gave way in early April 2009. Days after the ice bridge rupture, on April 12, 2009, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite acquired this image of the southern base of the ice bridge, where it connected with the remnant ice shelf. Although the ice bridge has played a role in stabilizing the ice fragments in the region, its rupture doesn't guarantee the ice will immediately move away. http://photojournal.jpl.nasa.gov/catalog/PIA11991

  13. Community dynamics of nematodes after Larsen ice-shelf collapse in the eastern Antarctic Peninsula.

    PubMed

    Hauquier, Freija; Ballesteros-Redondo, Laura; Gutt, Julian; Vanreusel, Ann

    2016-01-01

    Free-living marine nematode communities of the Larsen B embayment at the eastern Antarctic Peninsula were investigated to provide insights on their response and colonization rate after large-scale ice-shelf collapse. This study compares published data on the post-collapse situation from 2007 with new material from 2011, focusing on two locations in the embayment that showed highly divergent communities in 2007 and that are characterized by a difference in timing of ice-shelf breakup. Data from 2007 exposed a more diverse community at outer station B.South, dominated by the genus Microlaimus. On the contrary, station B.West in the inner part of Larsen B was poor in both numbers of individuals and genera, with dominance of a single Halomonhystera species. Re-assessment of the situation in 2011 showed that communities at both stations diverged even more, due to a drastic increase in Halomonhystera at B.West compared to relatively little change at B.South. On a broader geographical scale, it seems that B.South gradually starts resembling other Antarctic shelf communities, although the absence of the genus Sabatieria and the high abundance of Microlaimus still set it apart nine years after the main Larsen B collapse. In contrast, thriving of Halomonhystera at B.West further separates its community from other Antarctic shelf areas.

  14. Iceberg B-15, Ross Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Iceberg B-15 broke from the Ross Ice Shelf in Antarctica in late March. Among the largest ever observed, the new iceberg is approximately 170 miles long x 25 miles wide. Its 4,250 square-mile area is nearly as large as the state of Connecticut. The iceberg was formed from glacial ice moving off the Antarctic continent and calved along pre-existing cracks in the Ross Ice Shelf near Roosevelt Island. The calving of the iceberg essentially moves the northern boundary of the ice shelf about 25 miles to the south, a loss that would normally take the ice shelf as long as 50-100 years to replace. This infrared image was acquired by the DMSP (Defense Meteorological Satellite Program) F-13 satellite on April 13, 2000. For more images see Antarctic Meteorological Research Center Image courtesy of the University of Wisconsin - Madison, Space Science and Engineering Center, Antarctic Meteorological Research Center

  15. Antarctic sub-shelf melt rates via PICO

    NASA Astrophysics Data System (ADS)

    Reese, Ronja; Albrecht, Torsten; Mengel, Matthias; Asay-Davis, Xylar; Winkelmann, Ricarda

    2018-06-01

    Ocean-induced melting below ice shelves is one of the dominant drivers for mass loss from the Antarctic Ice Sheet at present. An appropriate representation of sub-shelf melt rates is therefore essential for model simulations of marine-based ice sheet evolution. Continental-scale ice sheet models often rely on simple melt-parameterizations, in particular for long-term simulations, when fully coupled ice-ocean interaction becomes computationally too expensive. Such parameterizations can account for the influence of the local depth of the ice-shelf draft or its slope on melting. However, they do not capture the effect of ocean circulation underneath the ice shelf. Here we present the Potsdam Ice-shelf Cavity mOdel (PICO), which simulates the vertical overturning circulation in ice-shelf cavities and thus enables the computation of sub-shelf melt rates consistent with this circulation. PICO is based on an ocean box model that coarsely resolves ice shelf cavities and uses a boundary layer melt formulation. We implement it as a module of the Parallel Ice Sheet Model (PISM) and evaluate its performance under present-day conditions of the Southern Ocean. We identify a set of parameters that yield two-dimensional melt rate fields that qualitatively reproduce the typical pattern of comparably high melting near the grounding line and lower melting or refreezing towards the calving front. PICO captures the wide range of melt rates observed for Antarctic ice shelves, with an average of about 0.1 m a-1 for cold sub-shelf cavities, for example, underneath Ross or Ronne ice shelves, to 16 m a-1 for warm cavities such as in the Amundsen Sea region. This makes PICO a computationally feasible and more physical alternative to melt parameterizations purely based on ice draft geometry.

  16. Firn structure of Larsen C Ice Shelf, Antarctic Peninsula, from in-situ geophysical surveys

    NASA Astrophysics Data System (ADS)

    Kulessa, B.; Brisbourne, A.; Kuipers Munneke, P.; Bevan, S. L.; Luckman, A. J.; Hubbard, B. P.; Ashmore, D.; Holland, P.; Jansen, D.; King, E. C.; O'Leary, M.; McGrath, D.

    2015-12-01

    Rising surface temperatures have been causing firn layers on Antarctic Peninsula ice shelves to compact, a process that is strongly implicated in ice shelf disintegration. Firn compaction is expected to warm the ice column and given sufficiently wet and compacted firn layers, to allow meltwater to penetrate into surface crevasses and thus enhance the potential for hydrofracture. On Larsen C Ice Shelf a compacting firn layer has previously been inferred from airborne radar and satellite data, with strongly reduced air contents in Larsen C's north and north-west. The hydrological processes governing firn compaction, and the detailed firn structures they produce, have so far remained uncertain however. Using integrated seismic refraction, MASW (Multi-Channel Analysis of Surface Waves), seismoelectric and ground-penetrating radar (GPR) data, we reveal vertical and horizontal changes in firn structure across Larsen C Ice Shelf. Particular attention is paid to the spatial prevalence of refrozen meltwaters within firn, such as the massive subsurface ice layer discovered recently by the NERC-funded MIDAS project in Cabinet Inlet in Larsen C's extreme northwest. Such ice layers or lenses are particularly dramatic manifestations of increased ice shelf densities and temperatures, and contrast sharply with the relatively uncompacted firn layers present in the ice shelf's southeast. We consider our observations in the context of a one-dimensional firn model for Larsen C Ice Shelf that includes melt percolation and refreezing, and discuss temporal changes in firn layer structures due to surface melt and ponding.

  17. Unravelling InSAR observed Antarctic ice-shelf flexure using 2-D elastic and viscoelastic modelling

    NASA Astrophysics Data System (ADS)

    Wild, Christian T.; Marsh, Oliver J.; Rack, Wolfgang

    2018-04-01

    Ice-shelf grounding zones link the Antarctic ice-sheets to the ocean. Differential interferometric synthetic aperture radar (DInSAR) is commonly used to monitor grounding-line locations, but also contains information on grounding-zone ice thickness, ice properties and tidal conditions beneath the ice shelf. Here, we combine in-situ data with numerical modelling of ice-shelf flexure to investigate 2-D controls on the tidal bending pattern on the Southern McMurdo Ice Shelf. We validate our results with 9 double-differential TerraSAR-X interferograms. It is necessary to make adjustments to the tidal forcing to directly compare observations with model output and we find that when these adjustments are small (< 1.5 cm) a viscoelastic model matches better, while an elastic model is more robust overall. Within landward embayments, where lateral stresses from surrounding protrusions damp the flexural response, a 2-D model captures behaviour that is missed in simple 1-D models. We conclude that improvements in current tide models are required to allow for the full exploitation of DInSAR in grounding-zone glaciology.

  18. Antarctic ice shelf thickness from CryoSat-2 radar altimetry

    NASA Astrophysics Data System (ADS)

    Chuter, Stephen; Bamber, Jonathan

    2016-04-01

    The Antarctic ice shelves provide buttressing to the inland grounded ice sheet, and therefore play a controlling role in regulating ice dynamics and mass imbalance. Accurate knowledge of ice shelf thickness is essential for input-output method mass balance calculations, sub-ice shelf ocean models and buttressing parameterisations in ice sheet models. Ice shelf thickness has previously been inferred from satellite altimetry elevation measurements using the assumption of hydrostatic equilibrium, as direct measurements of ice thickness do not provide the spatial coverage necessary for these applications. The sensor limitations of previous radar altimeters have led to poor data coverage and a lack of accuracy, particularly the grounding zone where a break in slope exists. We present a new ice shelf thickness dataset using four years (2011-2014) of CryoSat-2 elevation measurements, with its SARIn dual antennae mode of operation alleviating the issues affecting previous sensors. These improvements and the dense across track spacing of the satellite has resulted in ˜92% coverage of the ice shelves, with substantial improvements, for example, of over 50% across the Venable and Totten Ice Shelves in comparison to the previous dataset. Significant improvements in coverage and accuracy are also seen south of 81.5° for the Ross and Filchner-Ronne Ice Shelves. Validation of the surface elevation measurements, used to derive ice thickness, against NASA ICESat laser altimetry data shows a mean bias of less than 1 m (equivalent to less than 9 m in ice thickness) and a fourfold decrease in standard deviation in comparison to the previous continental dataset. Importantly, the most substantial improvements are found in the grounding zone. Validation of the derived thickness data has been carried out using multiple Radio Echo Sounding (RES) campaigns across the continent. Over the Amery ice shelf, where extensive RES measurements exist, the mean difference between the datasets is 3

  19. Massive subsurface ice formed by refreezing of ice-shelf melt ponds

    PubMed Central

    Hubbard, Bryn; Luckman, Adrian; Ashmore, David W.; Bevan, Suzanne; Kulessa, Bernd; Kuipers Munneke, Peter; Philippe, Morgane; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Tison, Jean-Louis; O'Leary, Martin; Rutt, Ian

    2016-01-01

    Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km across, several kilometres long and tens of metres deep, located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and radar measurements with remote sensing and firn modelling to investigate the layer, found to be ∼10 °C warmer and ∼170 kg m−3 denser than anticipated in the absence of ponding and hitherto used in models of ice-shelf fracture and flow. Surface ponding and ice layers such as the one we report are likely to form on a wider range of Antarctic ice shelves in response to climatic warming in forthcoming decades. PMID:27283778

  20. Ice-Shelf Melting Around Antarctica

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Jacobs, S.; Mouginot, J.; Scheuchl, B.

    2013-07-01

    We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines.

  1. Future sea-level rise from tidewater and ice-shelf tributary glaciers of the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Schannwell, Clemens; Barrand, Nicholas E.; Radić, Valentina

    2016-11-01

    Iceberg calving and increased ice discharge from ice-shelf tributary glaciers contribute significant amounts to global sea-level rise (SLR) from the Antarctic Peninsula (AP). Owing to ongoing ice dynamical changes (collapse of buttressing ice shelves), these contributions have accelerated in recent years. As the AP is one of the fastest warming regions on Earth, further ice dynamical adjustment (increased ice discharge) is expected over the next two centuries. In this paper, the first regional SLR projection of the AP from both iceberg calving and increased ice discharge from ice-shelf tributary glaciers in response to ice-shelf collapse is presented. An ice-sheet model forced by temperature output from 13 global climate models (GCMs), in response to the high greenhouse gas emission scenario (RCP8.5), projects AP contribution to SLR of 28 ± 16 to 32 ± 16 mm by 2300, partitioned approximately equally between contributions from tidewater glaciers and ice-shelf tributary glaciers. In the RCP4.5 scenario, sea-level rise projections to 2300 are dominated by tidewater glaciers (∼8-18 mm). In this cooler scenario, 2.4 ± 1 mm is added to global sea levels from ice-shelf tributary drainage basins as fewer ice-shelves are projected to collapse. Sea-level projections from ice-shelf tributary glaciers are dominated by drainage basins feeding George VI Ice Shelf, accounting for ∼70% of simulated SLR. Combined total ice dynamical SLR projections to 2300 from the AP vary between 11 ± 2 and 32 ± 16 mm sea-level equivalent (SLE), depending on the emission scenario used. These simulations suggest that omission of tidewater glaciers could lead to a substantial underestimation of the ice-sheet's contribution to regional SLR.

  2. Ice-shelf melting around Antarctica

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Jacobs, S.

    2008-12-01

    The traditional view on the mass balance of Antarctic ice shelves is that they loose mass principally from iceberg calving with bottom melting a much lower contributing factor. Because ice shelves are now known to play a fundamental role in ice sheet evolution, it is important to re-evaluate their wastage processes from a circumpolar perspective using a combination of remote sensing techniques. We present area average rates deduced from grounding line discharge, snow accumulation, firn depth correction and ice shelf topography. We find that ice shelf melting accounts for roughly half of ice-shelf ablation, with a total melt water production of 1027 Gt/yr. The attrition fraction due to in-situ melting varies from 9 to 90 percent around Antarctica. High melt producers include the Ronne, Ross, Getz, Totten, Amery, George VI, Pine Island, Abbot, Dotson/Crosson, Shackleton, Thwaites and Moscow University Ice Shelves. Low producers include the Larsen C, Princess Astrid and Ragnhild coast, Fimbul, Brunt and Filchner. Correlation between melt water production and grounding line discharge is low (R2 = 0.65). Correlation with thermal ocean forcing from the ocean are highest in the northern parts of West Antarctica where regressions yield R2 of 0.93-0.97. Melt rates in the Amundsen Sea exhibit a quadratic sensitivity to thermal ocean forcing. We conclude that ice shelf melting plays a dominant role in ice shelf mass balance, with a potential to change rapidly in response to altered ocean heat transport onto the Antarctic continental shelf.

  3. Mass Balance of the Northern Antarctic Peninsula and its Ongoing Response to Ice Shelf Loss

    NASA Astrophysics Data System (ADS)

    Scambos, T. A.; Berthier, E.; Haran, T. M.; Shuman, C. A.; Cook, A. J.; Bohlander, J. A.

    2012-12-01

    An assessment of the most rapidly changing areas of the Antarctic Peninsula (north of 66°S) shows that ice mass loss for the region is dominated by areas affected by eastern-Peninsula ice shelf losses in the past 20 years. Little if any of the mass loss is compensated by increased snowfall in the northwestern or far northern areas. We combined satellite stereo-image DEM differencing and ICESat-derived along-track elevation changes to measure ice mass loss for the Antarctic Peninsula north of 66°S between 2001-2010, focusing on the ICESat-1 period of operation (2003-2009). This mapping includes all ice drainages affected by recent ice shelf loss in the northeastern Peninsula (Prince Gustav, Larsen Inlet, Larsen A, and Larsen B) as well as James Ross Island, Vega Island, Anvers Island, Brabant Island and the adjacent west-flowing glaciers. Polaris Glacier (feeding the Larsen Inlet, which collapsed in 1986) is an exception, and may have stabilized. Our method uses ASTER and SPOT-5 stereo-image DEMs to determine dh/dt for elevations below 800 m; at higher elevations ICESat along-track elevation differencing is used. To adjust along-track path offsets between its 2003-2009 campaigns, we use a recent DEM of the Peninsula to establish and correct for cross-track slope (Cook et al., 2012, doi:10.5194/essdd-5-365-2012; http://nsidc.org/data/nsidc-0516.html) . We reduce the effect of possible seasonal variations in elevation by using only integer-year repeats of the ICESat tracks for comparison. Mass losses are dominated by the major glaciers that had flowed into the Prince Gustav (Boydell, Sjorgren, Röhss), Larsen A (Edgeworth, Bombardier, Dinsmoor, Drygalski), and Larsen B (Hektoria, Jorum, and Crane) embayments. The pattern of mass loss emphasizes the significant and multi-decadal response to ice shelf loss. Areas with shelf losses occurring 30 to 100s of years ago seem to be relatively stable or losing mass only slowly (western glaciers, northernmost areas). The

  4. Monitoring Antarctic ice sheet surface melting with TIMESAT algorithm

    NASA Astrophysics Data System (ADS)

    Ye, Y.; Cheng, X.; Li, X.; Liang, L.

    2011-12-01

    Antarctic ice sheet contributes significantly to the global heat budget by controlling the exchange of heat, moisture, and momentum at the surface-atmosphere interface, which directly influence the global atmospheric circulation and climate change. Ice sheet melting will cause snow humidity increase, which will accelerate the disintegration and movement of ice sheet. As a result, detecting Antarctic ice sheet melting is essential for global climate change research. In the past decades, various methods have been proposed for extracting snowmelt information from multi-channel satellite passive microwave data. Some methods are based on brightness temperature values or a composite index of them, and others are based on edge detection. TIMESAT (Time-series of Satellite sensor data) is an algorithm for extracting seasonality information from time-series of satellite sensor data. With TIMESAT long-time series brightness temperature (SSM/I 19H) is simulated by Double Logistic function. Snow is classified to wet and dry snow with generalized Gaussian model. The results were compared with those from a wavelet algorithm. On this basis, Antarctic automatic weather station data were used for ground verification. It shows that this algorithm is effective in ice sheet melting detection. The spatial distribution of melting areas(Fig.1) shows that, the majority of melting areas are located on the edge of Antarctic ice shelf region. It is affected by land cover type, surface elevation and geographic location (latitude). In addition, the Antarctic ice sheet melting varies with seasons. It is particularly acute in summer, peaking at December and January, staying low in March. In summary, from 1988 to 2008, Ross Ice Shelf and Ronnie Ice Shelf have the greatest interannual variability in amount of melting, which largely determines the overall interannual variability in Antarctica. Other regions, especially Larsen Ice Shelf and Wilkins Ice Shelf, which is in the Antarctic Peninsula

  5. Duality of Ross Ice Shelf systems: crustal boundary, ice sheet processes and ocean circulation from ROSETTA-Ice surveys

    NASA Astrophysics Data System (ADS)

    Tinto, K. J.; Siddoway, C. S.; Padman, L.; Fricker, H. A.; Das, I.; Porter, D. F.; Springer, S. R.; Siegfried, M. R.; Caratori Tontini, F.; Bell, R. E.

    2017-12-01

    Bathymetry beneath Antarctic ice shelves controls sub-ice-shelf ocean circulation and has a major influence on the stability and dynamics of the ice sheets. Beneath the Ross Ice Shelf, the sea-floor bathymetry is a product of both tectonics and glacial processes, and is influenced by the processes it controls. New aerogeophysical surveys have revealed a fundamental crustal boundary bisecting the Ross Ice Shelf and imparting a duality to the Ross Ice Shelf systems, encompassing bathymetry, ocean circulation and ice flow history. The ROSETTA-Ice surveys were designed to increase the resolution of Ross Ice Shelf mapping from the 55 km RIGGS survey of the 1970s to a 10 km survey grid, flown over three years from New York Air National Guard LC130s. Radar, LiDAR, gravity and magnetic instruments provide a top to bottom profile of the ice shelf and the underlying seafloor, with 20 km resolution achieved in the first two survey seasons (2015 and 2016). ALAMO ocean-profiling floats deployed in the 2016 season are measuring the temperature and salinity of water entering and exiting the sub-ice water cavity. A significant east-west contrast in the character of the magnetic and gravity fields reveals that the lithospheric boundary between East and West Antarctica exists not at the base of the Transantarctic Mountains (TAM), as previously thought, but 300 km further east. The newly-identified boundary spatially coincides with the southward extension of the Central High, a rib of shallow basement identified in the Ross Sea. The East Antarctic side is characterized by lower amplitude magnetic anomalies and denser TAM-type lithosphere compared to the West Antarctic side. The crustal structure imparts a fundamental duality on the overlying ice and ocean, with deeper bathymetry and thinner ice on the East Antarctic side creating a larger sub-ice cavity for ocean circulation. The West Antarctic side has a shallower seabed, more restricted ocean access and a more complex history of

  6. Ross Ice Shelf airstream driven by polar vortex cyclone

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2012-07-01

    The powerful air and ocean currents that flow in and above the Southern Ocean, circling in the Southern Hemisphere's high latitudes, form a barrier to mixing between Antarctica and the rest of the planet. Particularly during the austral winter, strong westerly winds isolate the Antarctic continent from heat, energy, and mass exchange, bolstering the scale of the annual polar ozone depletion and driving the continent's record-breaking low temperatures. Pushing through this wall of high winds, the Ross Ice Shelf airstream (RAS) is responsible for a sizable amount of mass and energy exchange from the Antarctic inland areas to lower latitudes. Sitting due south of New Zealand, the roughly 470,000-square-kilometer Ross Ice Shelf is the continent's largest ice shelf and a hub of activity for Antarctic research. A highly variable lower atmospheric air current, RAS draws air from the inland Antarctic Plateau over the Ross Ice Shelf and past the Ross Sea. Drawing on modeled wind patterns for 2001-2005, Seefeldt and Cassano identify the primary drivers of RAS.

  7. Improving Our Understanding of Antarctic Sea Ice with NASA's Operation IceBridge and the Upcoming ICESat-2 Mission

    NASA Technical Reports Server (NTRS)

    Petty, Alek A.; Markus, Thorsten; Kurtz, Nathan T.

    2017-01-01

    Antarctic sea ice is a crucial component of the global climate system. Rapid sea ice production regimes around Antarctica feed the lower branch of the Southern Ocean overturning circulation through intense brine rejection and the formation of Antarctic Bottom Water (e.g., Orsi et al. 1999; Jacobs 2004), while the northward transport and subsequent melt of Antarctic sea ice drives the upper branch of the overturning circulation through freshwater input (Abernathy et al. 2016). Wind-driven trends in Antarctic sea ice (Holland Kwok 2012) have likely increased the transport of freshwater away from the Antarctic coastline, significantly altering the salinity distribution of the Southern Ocean (Haumann et al. 2016). Conversely, weaker sea ice production and the lack of shelf water formation over the Amundsen and Bellingshausen shelf seas promote intrusion of warm Circumpolar Deep Water onto the continental shelf and the ocean-driven melting of several ice shelves fringing the West Antarctic Ice Sheet (e.g., Jacobs et al. 2011; Pritchard et al. 2012; Dutrieux et al. 2014). Sea ice conditions around Antarctica are also increasingly considered an important factor impacting local atmospheric conditions and the surface melting of Antarctic ice shelves (e.g., Scambos et al. 2017). Sea ice formation around Antarctica is responsive to the strong regional variability in atmospheric forcing present around Antarctica, driving this bimodal variability in the behavior and properties of the underlying shelf seas (e.g., Petty et al. 2012; Petty et al. 2014).

  8. Impacts of the Larsen-C Ice Shelf calving event

    NASA Astrophysics Data System (ADS)

    Hogg, Anna E.; Gudmundsson, G. Hilmar

    2017-08-01

    A giant iceberg has calved off the Larsen-C Ice Shelf, the largest remaining ice shelf on the Antarctic Peninsula, reducing its total area by ~10%. Whilst calving events are a natural phenomenon and thus not necessarily indicative of changing environmental conditions, such events can impact ice-shelf stability.

  9. Channelized melting drives thinning under Dotson ice shelf, Western Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Gourmelen, N.; Goldberg, D.; Snow, K.; Henley, S. F.; Bingham, R. G.; Kimura, S.; Hogg, A.; Shepherd, A.; Mouginot, J.; Lenaerts, J.; Ligtenberg, S.; Van De Berg, W. J.

    2017-12-01

    The majority of meteoric ice that forms in West Antarctica leaves the ice sheet through floating ice shelves, many of which have been thinning substantially over the last 25 years. A significant proportion of ice-shelf thinning has been driven by submarine melting facilitated by increased access of relatively warm (>0.6oC) modified Circumpolar Deep Water to sub-shelf cavities. Ice shelves play a significant role in stabilising the ice sheet from runaway retreat and regulating its contribution to sea level change. Ice-shelf melting has also been implicated in sustaining high primary productivity in Antarctica's coastal seas. However, these processes vary regionally and are not fully understood. Under some ice shelves, concentrated melting leads to the formation of inverted channels. These channels guide buoyant melt-laden outflow, which can lead to localised melting of the sea ice cover. The channels may also potentially lead to heightened crevassing, which in turn affects ice-shelf stability. Meanwhile, numerical studies suggest that buttressing loss is sensitive to the location of ice removal within an ice-shelf. Thus it is important that we observe spatial patterns, as well as magnitudes, of ice-shelf thinning, in order to improve understanding of the ocean drivers of thinning and of their impacts on ice-shelf stability. Here we show from high-resolution altimetry measurements acquired between 2010 to 2016 that Dotson Ice Shelf, West Antarctica, thins in response to basal melting focussed along a single 5 km-wide and 60 km-long channel extending from the ice shelf's grounding zone to its calving front. The coupled effect of geostrophic circulation and ice-shelf topography leads to the observed concentration of basal melting. Analysis of previous datasets suggests that this process has been ongoing for at least the last 25 years. If focused thinning continues at present rates, the channel would melt through within 40-50 years, almost two centuries before it is

  10. The role of ice shelves in the Holocene evolution of the Antarctic ice sheet

    NASA Astrophysics Data System (ADS)

    Bernales, Jorge; Rogozhina, Irina; Thomas, Maik

    2014-05-01

    Using the continental-scale ice sheet-shelf model SICOPOLIS (Greve, 1997 [1]; Sato and Greve, 2012 [2]), we assess the influence of ice shelves on the Holocene evolution and present-day geometry of the Antarctic ice sheet. We have designed a series of paleoclimate simulations driven by a time-evolved climate forcing that couples the surface temperature record from the Vostok ice core with precipitation pattern using an empirical relation of Dahl-Jensen et al., (1998) [3]. Our numerical experiments show that the geometry of ice shelves is determined by the evolution of climate and ocean conditions over time scales of 15 to 25 kyr. This implies that the initial configuration of ice shelves at the Last Glacial Maximum (LGM, about 21 kyr before present) has a significant effect on the modelled Early Holocene volume of ice shelves (up to 20%) that gradually diminishes to a negligible level for the present-day ice shelf configuration. Thus, the present-day geometry of the Antarctic ice shelves can be attained even if an ice-shelf-free initial condition is chosen at the LGM. However, the grounded ice volume, thickness and dynamic states are found to be sensitive to the ice shelf dynamics over a longer history spanning several tens of thousands of years. A presence of extensive marine ice at the LGM, supported by sediment core reconstructions (e.g. Naish et al., 2009 [4]), has a clear buttressing effect on the grounded ice that remains significant over a period of 30 to 50 kyr. If ice-shelf-free conditions are prescribed at the LGM, the modelled Early Holocene and present-day grounded ice volumes are underestimated by up to 10%, as opposed to simulations incorporating ice shelf dynamics over longer periods. The use of ice-shelf-free LGM conditions thus results in 50 to over 200 meters thinner ice sheet across much of East Antarctica. References [1] Greve, R. (1997). Application of a polythermal three-dimensional ice sheet model to the Greenland ice sheet: response to

  11. Long-term monitoring of glacier dynamics of Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Friedl, Peter; Seehaus, Thorsten; Wendt, Anja; Braun, Matthias

    2017-04-01

    The Antarctic Peninsula is one of the world`s most affected regions by Climate Change. Dense and long time series of remote sensing data enable detailed studies of the rapid glaciological changes in this area. We present results of a study on Fleming Glacier, which was the major tributary glacier of former Wordie Ice Shelf, located at the south-western side of the Antarctic Peninsula. Since the ice shelf disintegrated in a series of events starting in the 1970s, only disconnected tidewater glaciers have remained today. As a reaction to the loss of the buttressing force of the ice shelf, Fleming Glacier accelerated and dynamically thinned. However, all previous studies conducted at Wordie Bay covered only relatively short investigation periods and ended in 2008 the latest. Hence it was not well known how long the process of adaption to the changing boundary conditions exactly lasts and how it is characterized in detail. We provide long time series (1994 - 2016) of glaciological parameters (i.e. ice extent, velocity, grounding line position, ice elevation) for Fleming Glacier obtained from multi-mission remote sensing data. For this purpose large datasets of previously active (e.g. ERS, Envisat, ALOS PALSAR, Radarsat-1) as well as currently recording SAR sensors (e.g. Sentinel-1, TerraSAR-X, TanDEM-X) were processed and combined with data from other sources (e.g. optical images, laser altimeter and ice thickness data). The high temporal resolution of our dataset enables us to present a detailed history of 22 years of glacial dynamics at Fleming Glacier after the disintegration of Wordie Ice Shelf. We found strong evidence for a rapid grounding line retreat of up to 13 km between 2008 and 2011, which led to a further amplification of dynamic ice thinning. Today Fleming Glacier seems to be far away from approaching a new equilibrium. Our data show that the current glacier dynamics of Fleming Glacier are not primarily controlled by the loss of the ice shelf anymore, but

  12. Teleseismic Earthquake Signals Observed on an Ice Shelf

    NASA Astrophysics Data System (ADS)

    Baker, M. G.; Aster, R. C.; Anthony, R. E.; Wiens, D.; Nyblade, A.; Bromirski, P. D.; Stephen, R. A.; Gerstoft, P.

    2015-12-01

    The West Antarctic Rift System (WARS) is one of Earth's largest continental extension zones. Study of the WARS is complicated by the presence of the West Antarctic Ice Sheet, the Ross Ice Shelf, and the Ross Sea. Recent deployments of broadband seismographs in the POLENET project have allowed passive seismic techniques, such as receiver function analysis and surface wave dispersion, to be widely utilized to infer crustal and mantle velocity structure across much of the WARS and West Antarctica. However, a large sector of the WARS lies beneath the Ross Ice Shelf. In late 2014, 34 broadband seismographs were deployed atop the ice shelf to jointly study deep Earth structure and the dynamics of the ice shelf. Ice shelf conditions present strong challenges to broadband teleseismic imaging: 1) The presence of complicating signals in the microseism through long-period bands due to the influence of ocean gravity waves; 2) The strong velocity contrasts at the ice-water and water-sediment interfaces on either side of the water layer give rise to large amplitude reverberations; 3) The water layer screens S-waves or P-to-S phases originating from below the water layer. We present an initial analysis of the first teleseismic earthquake arrivals collected on the ice shelf at the end of the 2014 field season from a limited subset of these stations.

  13. Glacial morphology and depositional sequences of the Antarctic Continental Shelf

    USGS Publications Warehouse

    ten Brink, Uri S.; Schneider, Christopher

    1995-01-01

    Proposes a simple model for the unusual depositional sequences and morphology of the Antarctic continental shelf. It considers the regional stratal geometry and the reversed morphology to be principally the results of time-integrated effects of glacial erosion and sedimentation related to the location of the ice grounding line. The model offers several guidelines for stratigraphic interpretation of the Antarctic shelf and a Northern Hemisphere shelf, both of which were subject to many glacial advances and retreats. -Authors

  14. Ice Shelves and Landfast Ice on the Antarctic Perimeter: Revised Scope of Work

    NASA Technical Reports Server (NTRS)

    Scambos, Ted

    2002-01-01

    Ice shelves respond quickly and profoundly to a warming climate. Within a decade after mean summertime temperature reaches approx. O C and persistent melt pending is observed, a rapid retreat and disintegration occurs. This link was documented for ice shelves in the Antarctic Peninsula region (the Larsen 'A', 'B' and Wilkins Ice shelves) by the results of a previous grant under ADRO-1. Modeling of ice flow and the effects of meltwater indicated that melt pending accelerates shelf breakup by increasing fracture penetration. SAR data supplemented an AVHRR- and SSM/I-based image analysis of extent and surface characteristic changes. This funded grant is a revised, scaled-down version of an earlier proposal under the ADRO-2 NRA. The overall objective remains the same: we propose to build on the previous study by examining other ice shelves of the Antarctic and incorporate an examination of the climate-related characteristics of landfast ice. The study now considers just a few shelf and fast ice areas for study, and is funded for two years. The study regions are the northeastern Ross Ice Shelf, the Larsen 'B' and 'C' shelves, fast ice and floating shelf ice in the Pine Island Glacier area, and fast ice along the Wilkes Land coast. Further, rather than investigating a host of shelf and fast ice processes, we will home in on developing a series of characteristics associated with climate change over shelf and fast ice areas. Melt pending and break-up are the end stages of a response to a warming climate that may begin with increased melt event frequency (which changes both albedo and emissivity temporarily), changing firn backscatter (due to percolation features), and possibly increased rifting of the shelf surface. Fast ice may show some of these same processes on a seasonal timescale, providing insight into shelf evolution.

  15. Role of CO2-forced Antarctic shelf freshening on local shelf warming in an eddying global climate model

    NASA Astrophysics Data System (ADS)

    Goddard, P.; Dufour, C.; Yin, J.; Griffies, S. M.; Winton, M.

    2017-12-01

    Ocean warming near the Antarctic ice shelves has critical implications for future ice sheet mass loss and global sea level rise. A global climate model (GFDL CM2.6) with an eddying ocean is used to quantify and better understand the mechanisms contributing to ocean warming on the Antarctic continental shelf in an idealized 2xCO2 experiment. The results indicate that the simulated shelf region warming varies in magnitude at different locations. Relatively large warm anomalies occur both in the upper 100 m and at depth, which are controlled by different mechanisms. Here, we focus on the deep shelf warming and its relationship to shelf freshening. Under CO2-forcing, enhanced runoff from Antarctica, more regional precipitation, and reduction of sea ice contribute to the shelf freshening. The freshening increases the lateral density gradient of the Antarctic Slope Front, which can limit along-isopycnal onshore transport of heat from the Circumpolar Deep Water across the shelf break. Thus, the magnitude and location of the freshening anomalies govern the magnitude and location of onshore heat transport and deep warm anomalies. Additionally, the freshening increases vertical stratification on the shelf. The enhanced stratification reduces vertical mixing of heat associated with diffusion and gravitational instabilities, further contributing to the build-up of temperature anomalies at depth. Freshening is a crucial driver of the magnitude and location of the warming; however, other drivers influence the warming such as CO2-forced weakening of the easterly wind stress and associated shoaling of isotherms. Understanding the relative role of freshening in the inhomogeneous ocean warming of the Antarctic continental shelf would lead to better projections of future ice sheet mass loss, especially near the most vulnerable calving fronts.

  16. Fracture propagation and stability of ice shelves governed by ice shelf heterogeneity

    NASA Astrophysics Data System (ADS)

    Borstad, Chris; McGrath, Daniel; Pope, Allen

    2017-05-01

    Tabular iceberg calving and ice shelf retreat occurs after full-thickness fractures, known as rifts, propagate across an ice shelf. A quickly evolving rift signals a threat to the stability of Larsen C, the Antarctic Peninsula's largest ice shelf. Here we reveal the influence of ice shelf heterogeneity on the growth of this rift, with implications that challenge existing notions of ice shelf stability. Most of the rift extension has occurred in bursts after overcoming the resistance of suture zones that bind together neighboring glacier inflows. We model the stresses in the ice shelf to determine potential rift trajectories. Calving perturbations to ice flow will likely reach the grounding line. The stability of Larsen C may hinge on a single suture zone that stabilizes numerous upstream rifts. Elevated fracture toughness of suture zones may be the most important property that allows ice shelves to modulate Antarctica's contribution to sea level rise.

  17. Changes in ice dynamics along the northern Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Seehaus, Thorsten; Marinsek, Sebastian; Cook, Alison; Van Wessem, Jan-Melchior; Braun, Matthias

    2017-04-01

    The climatic conditions along the Antarctic Peninsula have undergone considerable changes during the last 50 years. A period of pronounced air temperature rise, increasing ocean temperatures as well as changes in the precipitation pattern have been reported by various authors. Consequently, the glacial systems showed changes including widespread retreat, surface lowering as well as variations in flow speeds. During the last decades numerous ice shelves along the Antarctic Peninsula retreated, started to break-up or disintegrated completely. The loss of the buttressing effect caused tributary glaciers to accelerate with increasing ice discharge along the Antarctic Peninsula. Quantification of the mass changes is still subject to considerable errors although numbers derived from the different methods are converging. The aim is to study the reaction of glaciers at the northern Antarctic Peninsula to the changing climatic conditions and the readjustments of tributary glaciers to ice shelf disintegration, as well as to better quantify the ice mass loss and its temporal changes. We analysed time series of various satellite sensors (ERS-1/2 SAR, ENVISAT ASAR, RADARSAT-1, ALOS PALSAR, TerraSAR-X/TanDEM-X, ASTER, Landsat) to detect changes in ice dynamics of 74 glacier basins along the northern Antarctic Peninsula (<65°). Intensity feature tracking techniques were applied on data stacks from different SAR satellites over the last 20 years to infer temporal trends in glacier surface velocities. In combination with ice thickness reconstructions and modeled climatic mass balance fields regional imbalances were calculated. Variations in ice front position were mapped based on optical and SAR satellite data sets. Along the west coast of the northern Antarctic Peninsula an increase in flow speeds by 40% between 1992 and 2014 was observed, whereas glaciers on the east side (north of former Prince-Gustav Ice Shelf) showed a strong deceleration. Nearly all former ice shelf

  18. Regional Changes in the Sea Ice Cover and Ice Production in the Antarctic

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2011-01-01

    Coastal polynyas around the Antarctic continent have been regarded as sea ice factories because of high ice production rates in these regions. The observation of a positive trend in the extent of Antarctic sea ice during the satellite era has been intriguing in light of the observed rapid decline of the ice extent in the Arctic. The results of analysis of the time series of passive microwave data indicate large regional variability with the trends being strongly positive in the Ross Sea, strongly negative in the Bellingshausen/Amundsen Seas and close to zero in the other regions. The atmospheric circulation in the Antarctic is controlled mainly by the Southern Annular Mode (SAM) and the marginal ice zone around the continent shows an alternating pattern of advance and retreat suggesting the presence of a propagating wave (called Antarctic Circumpolar Wave) around the circumpolar region. The results of analysis of the passive microwave data suggest that the positive trend in the Antarctic sea ice cover could be caused primarily by enhanced ice production in the Ross Sea that may be associated with more persistent and larger coastal polynyas in the region. Over the Ross Sea shelf, analysis of sea ice drift data from 1992 to 2008 yields a positive rate-of-increase in the net ice export of about 30,000 km2 per year. For a characteristic ice thickness of 0.6 m, this yields a volume transport of about 20 km3/year, which is almost identical, within error bars, to our estimate of the trend in ice production. In addition to the possibility of changes in SAM, modeling studies have also indicated that the ozone hole may have a role in that it causes the deepening of the lows in the western Antarctic region thereby causing strong winds to occur offthe Ross-ice shelf.

  19. Changes in ice dynamics and mass balance of the Antarctic ice sheet.

    PubMed

    Rignot, Eric

    2006-07-15

    The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 degrees C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

  20. Ice-dammed lateral lake and epishelf lake insights into Holocene dynamics of Marguerite Trough Ice Stream and George VI Ice Shelf, Alexander Island, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Davies, Bethan J.; Hambrey, Michael J.; Glasser, Neil F.; Holt, Tom; Rodés, Angél; Smellie, John L.; Carrivick, Jonathan L.; Blockley, Simon P. E.

    2017-12-01

    We present new data regarding the past dynamics of Marguerite Trough Ice Stream, George VI Ice Shelf and valley glaciers from Ablation Point Massif on Alexander Island, Antarctic Peninsula. This ice-free oasis preserves a geological record of ice stream lateral moraines, ice-dammed lakes, ice-shelf moraines and valley glacier moraines, which we dated using cosmogenic nuclide ages. We provide one of the first detailed sediment-landform assemblage descriptions of epishelf lake shorelines. Marguerite Trough Ice Stream imprinted lateral moraines against eastern Alexander Island at 120 m at Ablation Point Massif. During deglaciation, lateral lakes formed in the Ablation and Moutonnée valleys, dammed against the ice stream in George VI Sound. Exposure ages from boulders on these shorelines yielded ages of 13.9 to 9.7 ka. Following recession of the ice stream, George VI Ice Shelf formed in George VI Sound. An epishelf lake formed at 15-20 m asl in Ablation and Moutonnée valleys, dated from 9.4 to 4.6 ka, suggesting that the lake was stable and persistent for some 5000 years. Lake-level lowering occurred after this, with the lake level at 12 m at 3.1 ± 0.4 ka and at 5 m asl today. A readvance of the valley glaciers on Alexander Island at 4.4 ± 0.7 ka is recorded by valley glacier moraines overlying epishelf lake sediments. We speculate that the glacier readvance, which occurred during a period of warmth, may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of George VI Ice Shelf.

  1. Changes in ice dynamics along the northern Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Seehaus, T.; Braun, M.; Cook, A.; Marinsek, S.

    2016-12-01

    The climatic conditions along the Antarctic Peninsula have undergone considerable changes during the last 50 years. Numerous ice shelves along the Antarctic Peninsula retreated, started to break-up or disintegrated. The loss of the buttressing effect caused tributary glaciers to accelerate with increasing ice discharge along the Antarctic Peninsula. The aim is to study the reaction of glaciers at the northern Antarctic Peninsula to the changing climatic conditions and the readjustments of tributary glaciers to ice shelf disintegration, as well as to better quantify the ice mass loss and its temporal changes.We analysed time series of various SAR satellite sensors to detect changes in ice flow speed and surface elevation. Intensity feature tracking techniques were applied on data stacks from different SAR satellites over the last 20 years to infer changes in glacier surface velocities. High resolution bi-static TanDEM-X data was used to derive digital elevation models by differential SAR interferometry. In combination with ASTER and SPOT stereo images, changes in surface elevations were determined. Altimeter data from ICESat, CryoSat-2 and NASA operation IceBridge ATM were used for vertical referencing and quality assessment of the digital elevation models. Along the west coast of the northern Antarctic Peninsula an increase in flow speeds by 40% between 1992 and 2014 was observed, whereas glaciers on the east side (north of former Prince-Gustav Ice Shelf) showed a strong deceleration. In total an ice discharge of 17.93±6.22 Gt/a was estimated for 74 glaciers on the Antarctic Peninsula north of 65°S. Most of the former ice shelf tributaries showed similar reactions to ice shelf disintegration. At the Sjögren-Inlet a total ice mass loss of -37.5±8.2 Gt and a contribution to sea level rise of 20.9±5.2 Gt were found in the period 1993-2014. The average surface lowering rate in the period 2012-2014 amounts to -2.2 m/a. At Dinsmoor-Bombardier-Edgeworth glacier

  2. West Antarctic Ice Sheet retreat driven by Holocene warm water incursions

    PubMed Central

    Hillenbrand, Claus-Dieter; Smith, James A.; Hodell, David A.; Greaves, Mervyn; Poole, Christopher R.; Kender, Sev; Williams, Mark; Andersen, Thorbjørn Joest; Jernas, Patrycja E.; Klages, Johann P.; Roberts, Stephen J.; Gohl, Karsten; Larter, Robert D.; Kuhn, Gerhard

    2017-01-01

    Glaciological and oceanographic observations coupled with numerical models show that warm Circumpolar Deep Water (CDW) upwelling onto the West Antarctic continental shelf causes melting of the undersides of floating ice shelves. Because these ice shelves buttress glaciers feeding into them, their ocean-induced thinning is driving Antarctic ice-sheet loss today. Here we present the first multi-proxy data based reconstruction of variability in CDW inflow to the Amundsen Sea sector, the most vulnerable part of the West Antarctic Ice Sheet, during the last 11,000 years. The chemical composition of foraminifer shells and benthic foraminifer assemblages in marine sediments indicate that enhanced CDW upwelling, controlled by the latitudinal position of the Southern Hemisphere westerly winds, forced deglaciation of this sector both until 7,500 years ago, when an ice-shelf collapse may have caused rapid ice-sheet thinning further upstream, and since the 1940s. These results increase confidence in the predictive capability of current ice-sheet models. PMID:28682333

  3. Channelized Melting Drives Thinning Under a Rapidly Melting Antarctic Ice Shelf

    NASA Astrophysics Data System (ADS)

    Gourmelen, Noel; Goldberg, Dan N.; Snow, Kate; Henley, Sian F.; Bingham, Robert G.; Kimura, Satoshi; Hogg, Anna E.; Shepherd, Andrew; Mouginot, Jeremie; Lenaerts, Jan T. M.; Ligtenberg, Stefan R. M.; van de Berg, Willem Jan

    2017-10-01

    Ice shelves play a vital role in regulating loss of grounded ice and in supplying freshwater to coastal seas. However, melt variability within ice shelves is poorly constrained and may be instrumental in driving ice shelf imbalance and collapse. High-resolution altimetry measurements from 2010 to 2016 show that Dotson Ice Shelf (DIS), West Antarctica, thins in response to basal melting focused along a single 5 km-wide and 60 km-long channel extending from the ice shelf's grounding zone to its calving front. If focused thinning continues at present rates, the channel will melt through, and the ice shelf collapse, within 40-50 years, almost two centuries before collapse is projected from the average thinning rate. Our findings provide evidence of basal melt-driven sub-ice shelf channel formation and its potential for accelerating the weakening of ice shelves.

  4. The safety band of Antarctic ice shelves

    NASA Astrophysics Data System (ADS)

    Fürst, Johannes Jakob; Durand, Gaël; Gillet-Chaulet, Fabien; Tavard, Laure; Rankl, Melanie; Braun, Matthias; Gagliardini, Olivier

    2016-05-01

    The floating ice shelves along the seaboard of the Antarctic ice sheet restrain the outflow of upstream grounded ice. Removal of these ice shelves, as shown by past ice-shelf recession and break-up, accelerates the outflow, which adds to sea-level rise. A key question in predicting future outflow is to quantify the extent of calving that might precondition other dynamic consequences and lead to loss of ice-shelf restraint. Here we delineate frontal areas that we label as `passive shelf ice’ and that can be removed without major dynamic implications, with contrasting results across the continent. The ice shelves in the Amundsen and Bellingshausen seas have limited or almost no `passive’ portion, which implies that further retreat of current ice-shelf fronts will yield important dynamic consequences. This region is particularly vulnerable as ice shelves have been thinning at high rates for two decades and as upstream grounded ice rests on a backward sloping bed, a precondition to marine ice-sheet instability. In contrast to these ice shelves, Larsen C Ice Shelf, in the Weddell Sea, exhibits a large `passive’ frontal area, suggesting that the imminent calving of a vast tabular iceberg will be unlikely to instantly produce much dynamic change.

  5. Edge of Ice Shelf

    NASA Image and Video Library

    2017-12-08

    Edge of an ice shelf in Adelaide Island, off the Antarctic Peninsula. Credit: NASA / Maria-Jose Vinas NASA's Operation IceBridge is an airborne science mission to study Earth's polar ice. For more information about IceBridge, visit: www.nasa.gov/icebridge NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  6. Pathways of basal meltwater from Antarctic ice shelves: A model study

    NASA Astrophysics Data System (ADS)

    Kusahara, Kazuya; Hasumi, Hiroyasu

    2014-09-01

    We investigate spreading pathways of basal meltwater released from all Antarctic ice shelves using a circumpolar coupled ice shelf-sea ice-ocean model that reproduces major features of the Southern Ocean circulation, including the Antarctic Circumpolar Current (ACC). Several independent virtual tracers are used to identify detailed pathways of basal meltwaters. The spreading pathways of the meltwater tracers depend on formation sites, because the meltwaters are transported by local ambient ocean circulation. Meltwaters from ice shelves in the Weddell and Amundsen-Bellingshausen Seas in surface/subsurface layers are effectively advected to lower latitudes with the ACC. Although a large portion of the basal meltwaters is present in surface and subsurface layers, a part of the basal meltwaters penetrates into the bottom layer through active dense water formation along the Antarctic coastal margins. The signals at the seafloor extend along the topography, showing a horizontal distribution similar to the observed spreading of Antarctic Bottom Water. Meltwaters originating from ice shelves in the Weddell and Ross Seas and in the Indian sector significantly contribute to the bottom signals. A series of numerical experiments in which thermodynamic interaction between the ice shelf and ocean is neglected regionally demonstrates that the basal meltwater of each ice shelf impacts sea ice and/or ocean thermohaline circulation in the Southern Ocean. This article was corrected on 10 OCT 2014. See the end of the full text for details.

  7. Fun at Antarctic grounding lines: Ice-shelf channels and sediment transport

    NASA Astrophysics Data System (ADS)

    Drews, Reinhard; Mayer, Christoph; Eisen, Olaf; Helm, Veit; Ehlers, Todd A.; Pattyn, Frank; Berger, Sophie; Favier, Lionel; Hewitt, Ian H.; Ng, Felix; Fürst, Johannes J.; Gillet-Chaulet, Fabien; Bergeot, Nicolas; Matsuoka, Kenichi

    2017-04-01

    Meltwater beneath the polar ice sheets drains, in part, through subglacial conduits. Landforms created by such drainages are abundant in areas formerly covered by ice sheets during the last glacial maximum. However, observations of subglacial conduit dynamics under a contemporary ice sheet are lacking. We present results from ice-penetrating radar to infer the existence of subglacial conduits upstream of the grounding line of Roi Baudouin Ice Shelf, Antarctica. The conduits are aligned with ice-shelf channels, and underlain by esker ridges formed from sediment deposition due to reduced water outflow speed near the grounding line. In turn, the eskers modify local ice flow to initiate the bottom topography of the ice-shelf channels, and create small surface ridges extending onto the shelf. Relict features on the shelf are interpreted to indicate a history of these interactions and variability of past subglacial drainages. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation, and ice-shelf stability. To investigate the role of sediment transport beneath ice sheets further, we model the sheet-shelf system of the Ekstömisen catchment, Antarctica. A 3D finite element model (Elmer/ICE) is used to solve the transients full Stokes equation for isotropic, isothermal ice with a dynamic grounding line. We initialize the model with surface topography from the TanDEM-X satellites and by inverting simultaneously for ice viscosity and basal drag using present-day surface velocities. Results produce a flow field which is consitent with sattelite and on-site observations. Solving the age-depth relationship allows comparison with radar isochrones from airborne data, and gives information about the atmospheric/dynamic history of this sector. The flow field will eventually be used to identify potential sediment sources and sinks which we compare with more than 400 km of

  8. Obliquity-paced Pliocene West Antarctic ice sheet oscillations.

    PubMed

    Naish, T; Powell, R; Levy, R; Wilson, G; Scherer, R; Talarico, F; Krissek, L; Niessen, F; Pompilio, M; Wilson, T; Carter, L; DeConto, R; Huybers, P; McKay, R; Pollard, D; Ross, J; Winter, D; Barrett, P; Browne, G; Cody, R; Cowan, E; Crampton, J; Dunbar, G; Dunbar, N; Florindo, F; Gebhardt, C; Graham, I; Hannah, M; Hansaraj, D; Harwood, D; Helling, D; Henrys, S; Hinnov, L; Kuhn, G; Kyle, P; Läufer, A; Maffioli, P; Magens, D; Mandernack, K; McIntosh, W; Millan, C; Morin, R; Ohneiser, C; Paulsen, T; Persico, D; Raine, I; Reed, J; Riesselman, C; Sagnotti, L; Schmitt, D; Sjunneskog, C; Strong, P; Taviani, M; Vogel, S; Wilch, T; Williams, T

    2009-03-19

    Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch ( approximately 5-3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming. Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, approximately 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to approximately 3 degrees C warmer than today and atmospheric CO(2) concentration was as high as approximately 400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt under conditions of elevated CO(2).

  9. Characterisation of the nematode community of a low-activity cold seep in the recently ice-shelf free Larsen B area, Eastern Antarctic Peninsula.

    PubMed

    Hauquier, Freija; Ingels, Jeroen; Gutt, Julian; Raes, Maarten; Vanreusel, Ann

    2011-01-01

    Recent climate-induced ice-shelf disintegration in the Larsen A (1995) and B (2002) areas along the Eastern Antarctic Peninsula formed a unique opportunity to assess sub-ice-shelf benthic community structure and led to the discovery of unexplored habitats, including a low-activity methane seep beneath the former Larsen B ice shelf. Since both limited particle sedimentation under previously permanent ice coverage and reduced cold-seep activity are likely to influence benthic meiofauna communities, we characterised the nematode assemblage of this low-activity cold seep and compared it with other, now seasonally ice-free, Larsen A and B stations and other Antarctic shelf areas (Weddell Sea and Drake Passage), as well as cold-seep ecosystems world-wide. The nematode community at the Larsen B seep site differed significantly from other Antarctic sites in terms of dominant genera, diversity and abundance. Densities in the seep samples were high (>2000 individuals per 10 cm(2)) and showed below-surface maxima at a sediment depth of 2-3 cm in three out of four replicates. All samples were dominated by one species of the family Monhysteridae, which was identified as a Halomonhystera species that comprised between 80 and 86% of the total community. The combination of high densities, deeper density maxima and dominance of one species is shared by many cold-seep ecosystems world-wide and suggested a possible dependence upon a chemosynthetic food source. Yet stable (13)C isotopic signals (ranging between -21.97±0.86‰ and -24.85±1.89‰) were indicative of a phytoplankton-derived food source. The recent ice-shelf collapse and enhanced food input from surface phytoplankton blooms were responsible for the shift from oligotrophic pre-collapse conditions to a phytodetritus-based community with high densities and low diversity. The parthenogenetic reproduction of the highly dominant Halomonhystera species is rather unusual for marine nematodes and may be responsible for the

  10. Environmental controls on micro fracture processes in shelf ice

    NASA Astrophysics Data System (ADS)

    Sammonds, Peter

    2013-04-01

    The recent retreat and collapse of the ice shelves on the Antarctic Peninsula has been associated with regional atmospheric warming, oceanic warming, increased summer melt and shelf flexure. Although the cause of collapse is a matter of active discussion, the process is that of fracture of a creep-brittle material, close to its melting point. The environmental controls on how fracturing initiates, at a micro-scale, strongly determine the macroscopic disintegration of ice shelves. In particular the shelf temperature profile controls the plasticity of the ice shelf; the densification of shelf ice due to melting and re-freezing affects the crack tip stress intensity; the accretion of marine ice at the bottom of the shelf imposes a thermal/mechanical discontinuity; saline environments control crack tip stress corrosion; cyclic loading promotes sub-critical crack propagation. These strong environmental controls on shelf ice fracture means that assessing shelf stability is a non-deterministic problem. How these factors may be parameterized in ice shelf models, through the use of fracture mechanisms maps, is discussed. The findings are discussed in relation to the stability of Larsen C.

  11. West Antarctic Ice Sheet retreat driven by Holocene warm water incursions.

    PubMed

    Hillenbrand, Claus-Dieter; Smith, James A; Hodell, David A; Greaves, Mervyn; Poole, Christopher R; Kender, Sev; Williams, Mark; Andersen, Thorbjørn Joest; Jernas, Patrycja E; Elderfield, Henry; Klages, Johann P; Roberts, Stephen J; Gohl, Karsten; Larter, Robert D; Kuhn, Gerhard

    2017-07-05

    Glaciological and oceanographic observations coupled with numerical models show that warm Circumpolar Deep Water (CDW) incursions onto the West Antarctic continental shelf cause melting of the undersides of floating ice shelves. Because these ice shelves buttress glaciers feeding into them, their ocean-induced thinning is driving Antarctic ice-sheet retreat today. Here we present a multi-proxy data based reconstruction of variability in CDW inflow to the Amundsen Sea sector, the most vulnerable part of the West Antarctic Ice Sheet, during the Holocene epoch (from 11.7 thousand years ago to the present). The chemical compositions of foraminifer shells and benthic foraminifer assemblages in marine sediments indicate that enhanced CDW upwelling, controlled by the latitudinal position of the Southern Hemisphere westerly winds, forced deglaciation of this sector from at least 10,400 years ago until 7,500 years ago-when an ice-shelf collapse may have caused rapid ice-sheet thinning further upstream-and since the 1940s. These results increase confidence in the predictive capability of current ice-sheet models.

  12. Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water

    PubMed Central

    van Wijk, Esmee

    2018-01-01

    Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise. PMID:29675467

  13. Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water.

    PubMed

    Silvano, Alessandro; Rintoul, Stephen Rich; Peña-Molino, Beatriz; Hobbs, William Richard; van Wijk, Esmee; Aoki, Shigeru; Tamura, Takeshi; Williams, Guy Darvall

    2018-04-01

    Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise.

  14. Centuries of intense surface melt on Larsen C Ice Shelf

    NASA Astrophysics Data System (ADS)

    Bevan, Suzanne L.; Luckman, Adrian; Hubbard, Bryn; Kulessa, Bernd; Ashmore, David; Kuipers Munneke, Peter; O'Leary, Martin; Booth, Adam; Sevestre, Heidi; McGrath, Daniel

    2017-12-01

    Following a southward progression of ice-shelf disintegration along the Antarctic Peninsula (AP), Larsen C Ice Shelf (LCIS) has become the focus of ongoing investigation regarding its future stability. The ice shelf experiences surface melt and commonly features surface meltwater ponds. Here, we use a flow-line model and a firn density model (FDM) to date and interpret observations of melt-affected ice layers found within five 90 m boreholes distributed across the ice shelf. We find that units of ice within the boreholes, which have densities exceeding those expected under normal dry compaction metamorphism, correspond to two climatic warm periods within the last 300 years on the Antarctic Peninsula. The more recent warm period, from the 1960s onwards, has generated distinct sections of dense ice measured in two boreholes in Cabinet Inlet, which is close to the Antarctic Peninsula mountains - a region affected by föhn winds. Previous work has classified these layers as refrozen pond ice, requiring large quantities of mobile liquid water to form. Our flow-line model shows that, whilst preconditioning of the snow began in the late 1960s, it was probably not until the early 1990s that the modern period of ponding began. The earlier warm period occurred during the 18th century and resulted in two additional sections of anomalously dense ice deep within the boreholes. The first, at 61 m in one of our Cabinet Inlet boreholes, consists of ice characteristic of refrozen ponds and must have formed in an area currently featuring ponding. The second, at 69 m in a mid-shelf borehole, formed at the same time on the edge of the pond area. Further south, the boreholes sample ice that is of an equivalent age but which does not exhibit the same degree of melt influence. This west-east and north-south gradient in the past melt distribution resembles current spatial patterns of surface melt intensity.

  15. Obliquity-paced Pliocene West Antarctic ice sheet oscillations

    USGS Publications Warehouse

    Naish, T.; Powell, R.; Levy, R.; Wilson, G.; Scherer, R.; Talarico, F.; Krissek, L.; Niessen, F.; Pompilio, M.; Wilson, T.; Carter, L.; DeConto, R.; Huybers, P.; McKay, R.; Pollard, D.; Ross, J.; Winter, D.; Barrett, P.; Browne, G.; Cody, R.; Cowan, E.; Crampton, J.; Dunbar, G.; Dunbar, N.; Florindo, F.; Gebhardt, C.; Graham, I.; Hannah, M.; Hansaraj, D.; Harwood, D.; Helling, D.; Henrys, S.; Hinnov, L.; Kuhn, G.; Kyle, P.; Laufer, A.; Maffioli, P.; Magens, D.; Mandernack, K.; McIntosh, W.; Millan, C.; Morin, R.; Ohneiser, C.; Paulsen, T.; Persico, D.; Raine, I.; Reed, J.; Riesselman, C.; Sagnotti, L.; Schmitt, D.; Sjunneskog, C.; Strong, P.; Taviani, M.; Vogel, S.; Wilch, T.; Williams, T.

    2009-01-01

    Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages1, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles2. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch (5–3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming3. Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to 3 °C warmer than today4 and atmospheric CO2 concentration was as high as 400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model7 that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt8 under conditions of elevated CO2.

  16. Ice Shelf-Ocean Interactions Near Ice Rises and Ice Rumples

    NASA Astrophysics Data System (ADS)

    Lange, M. A.; Rückamp, M.; Kleiner, T.

    2013-12-01

    The stability of ice shelves depends on the existence of embayments and is largely influenced by ice rises and ice rumples, which act as 'pinning-points' for ice shelf movement. Of additional critical importance are interactions between ice shelves and the water masses underlying them in ice shelf cavities, particularly melting and refreezing processes. The present study aims to elucidate the role of ice rises and ice rumples in the context of climate change impacts on Antarctic ice shelves. However, due to their smaller spatial extent, ice rumples react more sensitively to climate change than ice rises. Different forcings are at work and need to be considered separately as well as synergistically. In order to address these issues, we have decided to deal with the following three issues explicitly: oceanographic-, cryospheric and general topics. In so doing, we paid particular attention to possible interrelationships and feedbacks in a coupled ice-shelf-ocean system. With regard to oceanographic issues, we have applied the ocean circulation model ROMBAX to ocean water masses adjacent to and underneath a number of idealized ice shelf configurations: wide and narrow as well as laterally restrained and unrestrained ice shelves. Simulations were performed with and without small ice rises located close to the calving front. For larger configurations, the impact of the ice rises on melt rates at the ice shelf base is negligible, while for smaller configurations net melting rates at the ice-shelf base differ by a factor of up to eight depending on whether ice rises are considered or not. We employed the thermo-coupled ice flow model TIM-FD3 to simulate the effects of several ice rises and one ice rumple on the dynamics of ice shelf flow. We considered the complete un-grounding of the ice shelf in order to investigate the effect of pinning points of different characteristics (interior or near calving front, small and medium sized) on the resulting flow and stress fields

  17. NASA finds Shrimp Under Antarctic Ice [Video

    NASA Image and Video Library

    2017-12-08

    At a depth of 600 feet beneath the West Antarctic ice sheet, a small shrimp-like creature managed to brighten up an otherwise gray polar day in late November 2009. This critter is a three-inch long Lyssianasid amphipod found beneath the Ross Ice Shelf, about 12.5 miles away from open water. NASA scientists were using a borehole camera to look back up towards the ice surface when they spotted this pinkish-orange creature swimming beneath the ice. Credit: NASA

  18. Mounting evidence for intense ocean interaction with the Pine Island Glacier Ice Shelf

    NASA Astrophysics Data System (ADS)

    Bindschadler, R.; Holland, D.; Vaughan, D.; Vornberger, P.

    2008-12-01

    The spatial signature of thinning and acceleration of the Pine Island Glacier has led to the inference that these changes originate at the seaward end of the glacier, possibly within or under the ice shelf (Payne et al., 2004; Shepherd et al., 2004). We present new analyses resulting from both new and archived satellite imagery of the ice shelf that supports this inference and provides new insights into strong seasonal and intra- annual characters of ocean-ice shelf interaction. Strong longitudinal variations in both thickness and surface elevation measured by British Antarctic Survey airborne radars (Vaughan et al., 2006) have wavelengths that correspond roughly to the annual motion of the ice shelf. These could be caused by seasonal variations in flow speed, but such variations of flow speed have never been reported and are not seen in the most recent continuous GPS observations of the ice shelf. We suggest that these strong variations in ice thickness, as large as 200 meters in an average thickness of 600 meters, are caused by seasonal variations in the properties of the water circulating underneath the ice shelf. One likely explanation is that the dominant water mass reaching the deepest parts of the ice shelf alternates between cold High Salinity Shelf Water in the winter and warm Circumpolar Deep Water in the summer. Evidence for recent strengthening of the sub- shelf circulation is the sudden occurrence of three persistent polynyas immediately adjacent to the ice front. These are located in precisely the locations expected from modeled sub-shelf circulation (Payne et al., 2007). This mode was never observed in any satellite imagery prior to the 1999-2000 austral summer (data of 7 summers since 1973 were available), but has occurred in 7 of the 9 summers since and persists throughout the summer. Payne, A.J., A. Vieli, A.P. Shepherd, D.J. Wingham and E. Rignot, 2004. Recent dramatic thinning of largest West Antarctic ice stream triggered by oceans, Geophysical

  19. Landcover Mapping of the McMurdo Ice Shelf Using Landsat and WorldView Image Data

    NASA Astrophysics Data System (ADS)

    Hansen, E. K.; Macdonald, G.; Mayer, D. P.; MacAyeal, D. R.

    2016-12-01

    Ice shelves bound approximately half of the Antarctic coast and act to buttress the glaciers that feed them. The collapse of the Larsen B Ice Shelf on the Antarctic Peninsula highlights the importance of processes at the surface for an ice shelf's stability. The McMurdo Ice Shelf is unique among Antarctic ice shelves in that it exists in a relatively warm climate zone and is thus more vulnerable to climate change than colder ice shelves at similar latitudes. However, little is known quantitatively about the surface cover types across the ice shelf, impeding the study of its hydrology and of the origins of its features. In particular, no work has been done linking field observations of supraglacial channels to shelf-wide surface hydrology. We will present the first satellite-derived multiscale landcover map of the McMurdo Ice Shelf based on Landsat 8 and WorldView-2 image data. Landcover types are extracted using supervised classification methods referenced to field observations. Landsat 8 provides coverage of the entire ice shelf ( 5,000 km2) at 30 m/pixel, sufficient to distinguish glacial ice, debris cover, and large supraglacial lakes. WorldView data cover a smaller area— 300 km2 at 2 m/pixel—and thus allow detailed mapping of features that are not spatially resolved by Landsat, such as supraglacial channels and small fractures across the ice shelf's surface. We take advantage of the higher resolution of WorldView-2 data to calculate the area of mid-summer surface water in channels and melt ponds within a detailed study area and use this as the basis for a spectral mixture model in order to estimate the total surface water area across the ice shelf. We intend to use the maps to guide strategic planning of future field research into the seasonal surface hydrology and climate stability of the McMurdo Ice Shelf.

  20. Ocean Wave-to-Ice Energy Transfer Determined from Seafloor Pressure and Ice Shelf Seismic Observations

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Wiens, D.; Aster, R. C.; Nyblade, A.

    2017-12-01

    Ice shelves play an important role in buttressing land ice from reaching the sea, thus restraining the rate of sea level rise. Long-period gravity wave impacts excite vibrations in ice shelves that may trigger tabular iceberg calving and/or ice shelf collapse events. Three kinds of seismic plate waves were continuously observed by broadband seismic arrays on the Ross Ice Shelf (RIS) and on the Pine Island Glacier (PIG) ice shelf: (1) flexural-gravity waves, (2) flexural waves, and (3) extensional Lamb waves, suggesting that all West Antarctic ice shelves are subjected to similar gravity wave excitation. Ocean gravity wave heights were estimated from pressure perturbations recorded by an ocean bottom differential pressure gauge at the RIS front, water depth 741 m, about 8 km north of an on-ice seismic station that is 2 km from the shelf front. Combining the plate wave spectrum, the frequency-dependent energy transmission and reflection at the ice-water interface were determined. In addition, Young's modulus and Poisson's ratio of the RIS are estimated from the plate wave motions, and compared with the widely used values. Quantifying these ice shelf parameters from observations will improve modeling of ice shelf response to ocean forcing, and ice shelf evolution.

  1. Antarctic sea ice losses drive gains in benthic carbon drawdown.

    PubMed

    Barnes, D K A

    2015-09-21

    Climate forcing of sea-ice losses from the Arctic and West Antarctic are blueing the poles. These losses are accelerating, reducing Earth's albedo and increasing heat absorption. Subarctic forest (area expansion and increased growth) and ice-shelf losses (resulting in new phytoplankton blooms which are eaten by benthos) are the only significant described negative feedbacks acting to counteract the effects of increasing CO2 on a warming planet, together accounting for uptake of ∼10(7) tonnes of carbon per year. Most sea-ice loss to date has occurred over polar continental shelves, which are richly, but patchily, colonised by benthic animals. Most polar benthos feeds on microscopic algae (phytoplankton), which has shown increased blooms coincident with sea-ice losses. Here, growth responses of Antarctic shelf benthos to sea-ice losses and phytoplankton increases were investigated. Analysis of two decades of benthic collections showed strong increases in annual production of shelf seabed carbon in West Antarctic bryozoans. These were calculated to have nearly doubled to >2x10(5) tonnes of carbon per year since the 1980s. Annual production of bryozoans is median within wider Antarctic benthos, so upscaling to include other benthos (combined study species typically constitute ∼3% benthic biomass) suggests an increased drawdown of ∼2.9x10(6) tonnes of carbon per year. This drawdown could become sequestration because polar continental shelves are typically deeper than most modern iceberg scouring, bacterial breakdown rates are slow, and benthos is easily buried. To date, most sea-ice losses have been Arctic, so, if hyperboreal benthos shows a similar increase in drawdown, polar continental shelves would represent Earth's largest negative feedback to climate change. Copyright © 2015 Elsevier Ltd. All rights reserved.

  2. Antarctic Ice-Sheet Mass Balance from Satellite Altimetry 1992 to 2001

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Brenner, Anita C.; Cornejo, Helen; Giovinetto, Mario; Saba, Jack L.; Yi, Donghui

    2003-01-01

    A major uncertainty in understanding the causes of the current rate of sea level rise is the potential contributions from mass imbalances of the Greenland and Antarctic ice sheets. Estimates of the current mass balance of the Antarctic ice sheet are derived from surface- elevation changes obtained from 9 years of ERS - 1 & 2 radar altimeter data. Elevation time-series are created from altimeter crossovers among 90-day data periods on a 50 km grid to 81.5 S. The time series are fit with a multivariate linear/sinusoidal function to give the average rate of elevation change (dH/dt). On the major Rome-Filchner, Ross, and Amery ice shelves, the W d t are small or near zero. In contrast, the ice shelves of the Antarctic Peninsula and along the West Antarctic coast appear to be thinning significantly, with a 23 +/- 3 cm per year surface elevation decrease on the Larsen ice shelf and a 65 +/- 4 cm per year decrease on the Dotson ice shelf. On the grounded ice, significant elevation decreases are obtained over most of the drainage basins of the Pine Island and Thwaites glaciers in West Antarctica and inland of Law Dome in East Antarctica. Significant elevation increases are observed within about 200 km of the coast around much of the rest of the ice sheet. Farther inland, the changes are a mixed pattern of increases and decreases with increases of a few centimeters per year at the highest elevations of the East Antarctic plateau. The derived elevation changes are combined with estimates of the bedrock uplift from several models to provide maps of ice thickness change. The ice thickness changes enable estimates of the ice mass balances for the major drainage basins, the overall mass balance, and the current contribution of the ice sheet to global sea level change.

  3. Seasonal Forcing of Summer Dissolved Inorganic Carbon and Chlorophyll a on the Western Shelf of the Antarctic Peninsula

    DTIC Science & Technology

    2010-03-30

    Click Here for Full Article Seasonal forcing of summer dissolved inorganic carbon and chlorophyll a on the western shelf of the Antarctic Peninsula... season characterized by decreased spring sea ice cover or nearshore accumulation of phytoplankton in association with sea ice. The impact of these wind...Stammerjohn, and O. Schofield (2010), Seasonal forcing of summer dissolved inorganic carbon and chlorophyll a on the western shelf of the Antarctic

  4. Seismicity within a propagating ice shelf rift: the relationship between icequake locations and ice shelf structure

    USGS Publications Warehouse

    Heeszel, David S.; Fricker, Helen A.; Bassis, Jeremy N.; O'Neel, Shad; Walter, Fabian

    2014-01-01

    Iceberg calving is a dominant mass loss mechanism for Antarctic ice shelves, second only to basal melting. An important known process involved in calving is the initiation and propagation of through-penetrating fractures called rifts; however, the mechanisms controlling rift propagation remain poorly understood. To investigate the mechanics of ice-shelf rifting, we analyzed seismicity associated with a propagating rift tip on the Amery Ice Shelf, using data collected during the Austral summers of 2004-2007. We investigated seismicity associated with fracture propagation using a suite of passive seismological techniques including icequake locations, back projection, and moment tensor inversion. We confirm previous results that show that seismicity is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of one to three hours. However, even during periods of quiescence, we find significant seismic deformation around the rift tip. Moment tensors, calculated for a subset of the largest icequakes (MW > -2.0) located near the rift tip, show steeply dipping fault planes, horizontal or shallowly plunging stress orientations, and often have a significant volumetric component. They also reveal that much of the observed seismicity is limited to the upper 50 m of the ice shelf. This suggests a complex system of deformation that involves the propagating rift, the region behind the rift tip, and a system of rift-transverse crevasses. Small-scale variations in the mechanical structure of the ice shelf, especially rift-transverse crevasses and accreted marine ice, play an important role in modulating the rate and location of seismicity associated with propagating ice shelf rifts.

  5. Breakup of the Larsen Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Recent Moderate-resolution Imaging Spectroradiometer (MODIS) satellite imagery analyzed at the University of Colorado's National Snow and Ice Data Center revealed that the northern section of the Larsen B ice shelf, a large floating ice mass on the eastern side of the Antarctic Peninsula, has shattered and separated from the continent. This particular image was taken on March 5, 2002. The shattered ice formed a plume of thousands of icebergs adrift in the Weddell Sea. A total of about 3,250 square kilometers of shelf area disintegrated in a 35-day period beginning on January 31, 2002. Over the last five years, the shelf has lost a total of 5,700 square kilometers and is now about 40 percent the size of its previous minimum stable extent. Ice shelves are thick plates of ice, fed by glaciers, that float on the ocean around much of Antarctica. The Larsen B shelf was about 220 meters thick. Based on studies of ice flow and sediment thickness beneath the ice shelf, scientists believe that it existed for at least 400 years prior to this event and likely existed since the end of the last major glaciation 12,000 years ago. For reference, the area lost in this most recent event dwarfs Rhode Island (2,717 square kilometers) in size. In terms of volume, the amount of ice released in this short time is 720 billion tons--enough ice for about 12 trillion 10-kilogram bags. This is the largest single event in a series of retreats by ice shelves along the peninsula over the last 30 years. The retreats are attributed to a strong climate warming in the region. The rate of warming is approximately 0.5 degrees Celsius per decade, and the trend has been present since at least the late 1940s. Overall in the peninsula, the extent of seven ice shelves has declined by a total of about 13,500 square kilometers since 1974. This value excludes areas that would be expected to calve under stable conditions. Ted Scambos, a researcher with the National Snow and Ice Data Center (NSIDC) at

  6. Recent dynamic changes on Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Friedl, Peter; Seehaus, Thorsten C.; Wendt, Anja; Braun, Matthias H.; Höppner, Kathrin

    2018-04-01

    The Antarctic Peninsula is one of the world's regions most affected by climate change. Several ice shelves have retreated, thinned or completely disintegrated during recent decades, leading to acceleration and increased calving of their tributary glaciers. Wordie Ice Shelf, located in Marguerite Bay at the south-western side of the Antarctic Peninsula, completely disintegrated in a series of events between the 1960s and the late 1990s. We investigate the long-term dynamics (1994-2016) of Fleming Glacier after the disintegration of Wordie Ice Shelf by analysing various multi-sensor remote sensing data sets. We present a dense time series of synthetic aperture radar (SAR) surface velocities that reveals a rapid acceleration of Fleming Glacier in 2008 and a phase of further gradual acceleration and upstream propagation of high velocities in 2010-2011.The timing in acceleration correlates with strong upwelling events of warm circumpolar deep water (CDW) into Wordie Bay, most likely leading to increased submarine melt. This, together with continuous dynamic thinning and a deep subglacial trough with a retrograde bed slope close to the terminus probably, has induced unpinning of the glacier tongue in 2008 and gradual grounding line retreat between 2010 and 2011. Our data suggest that the glacier's grounding line had retreated by ˜ 6-9 km between 1996 and 2011, which caused ˜ 56 km2 of the glacier tongue to go afloat. The resulting reduction in buttressing explains a median speedup of ˜ 1.3 m d-1 ( ˜ 27 %) between 2008 and 2011, which we observed along a centre line extending between the grounding line in 1996 and ˜ 16 km upstream. Current median ice thinning rates (2011-2014) along profiles in areas below 1000 m altitude range between ˜ 2.6 to 3.2 m a-1 and are ˜ 70 % higher than between 2004 and 2008. Our study shows that Fleming Glacier is far away from approaching a new equilibrium and that the glacier dynamics are not primarily controlled by the loss of the

  7. Simple model of melange and its influence on rapid ice retreat in a large-scale Antarctic ice sheet model.

    NASA Astrophysics Data System (ADS)

    Pollard, D.; Deconto, R. M.

    2017-12-01

    Theory, modeling and observations point to the prospect of runaway grounding-line retreat and marine ice loss from West Antarctica and major East Antarctic basins, in response to climate warming. These rapid retreats are associated with geologic evidence of past high sea-level stands, and pose a threat of drastic sea-level rise in the future.Rapid calving of ice from deep grounding lines generates substantial downstream melange (floating ice debris). It is unknown whether this melange has a significant effect on ice dynamics during major Antarctic retreats, through clogging of seaways and back pressure at the grounding line. Observations in Greenland fjords suggest that melange can have a significant buttressing effect, but the lateral scales of Antarctic basins are an order of magnitude larger (100's km compared to 10's km), with presumably much less influence of confining margins.Here we attempt to include melange as a prognostic variable in a 3-DAntarctic ice sheet-shelf model. Continuum mechanics is used as aheuristic representation of discrete particle physics. Melange is createdby ice calving and cliff failure. Its dynamics are treated similarly to ice flow, but with little or no resistance to divergence. Melange providesback pressure where adjacent to grounded tidewater ice faces or ice-shelf edges. We examine the influence of the new melange component during rapid Antarctic retreat in warm-Pliocene and future warming scenarios.

  8. Ice Shelves and Landfast Ice on the Antarctic Perimeter: Revised Scope of Work

    NASA Technical Reports Server (NTRS)

    Abdalati, Waleed (Technical Monitor); Scambos, Ted

    2004-01-01

    Ice shelves respond quickly and profoundly to a warming climate. Within a decade after mean summertime temperature reaches approximately 0 deg C and persistent melt ponding is observed, a rapid retreat and disintegration begins. This link was documented for ice shelves in the Antarctic Peninsula region (the Larsen 'A', B', and Wilkins Ice shelves) in the results of a previous grant under ADRO-1. Modeling of shelf ice flow and the effects of meltwater indicated that melt ponding accelerates shelf breakup by increasing fracturing. The ADRO-2 funding (topic of this report) supported further inquiry into the evolution of ice shelves under warming conditions, and the post-breakup effects on their feeder glaciers. Also, this grant considered fast ice and sea ice characteristics, to the extent that they provide information regarding shelf stability. A major component of this work was in the form of NSIDC image data support and in situ sea ice research on the Aurora Australis 'ARISE' cruise of September 9 2003 through October 28 2003.

  9. Subglacial meltwater channels on the Antarctic continental shelf

    NASA Astrophysics Data System (ADS)

    Kirkham, J. D.; Hogan, K.; Dowdeswell, J. A.; Larter, R. D.; Arnold, N. S.; Nitsche, F. O.; Golledge, N. R.

    2017-12-01

    Extensive submarine channel networks exist on the Antarctic continental shelf. The genesis of the channels has been attributed to the flow of subglacial meltwater beneath a formerly more expansive Antarctic Ice Sheet (AIS), implying that there was an active subglacial hydrological system beneath the past AIS which influenced its ice flow dynamics and mass-loss behaviour. However, the dimensions of the channels are inconsistent with the minimal quantities of meltwater produced under the AIS at present; consequently, their formative mechanism, and its implications for past ice-sheet dynamics, remain unresolved. Here, analysis of >100,000 km2 of multibeam bathymetric data is used to produce the most comprehensive inventory of Antarctic submarine channelised landforms to date. Over 2700 bedrock channels are mapped across four locations on the inner continental shelves of the Bellingshausen and Amundsen Seas. Morphometric analysis reveals highly similar distributions of channel widths, depths, cross-sectional areas and geometric properties, with subtle differences present between channels located in the Bellingshausen Sea compared to those situated in the Amundsen Sea region. The channels are 75-3400 m wide, 3-280 m deep, 160-290,000 m2 in cross-sectional area, and exhibit V-shaped cross-sectional geometries that are typically eight times as wide as they are deep. The features are comparable, but substantially larger, than the system of channels known as the Labyrinth in the McMurdo Dry Valleys whose genesis has been attributed to catastrophic outburst floods, sourced from subglacial lakes, during the middle Miocene. A similar process origin is proposed for the channels observed on the Antarctic continental shelf, formed through the drainage of relict subglacial lake basins, including some 59 identified using submarine geomorphological evidence and numerical modelling calculations. Water is predicted to accumulate in the subglacial lakes over centuries to millennia and

  10. What's Cooler Than Being Cool? Icefin: Robotic Exploration Beneath Antarctic Ice Shelves

    NASA Astrophysics Data System (ADS)

    Lawrence, J.; Schmidt, B. E.; Meister, M. R.; Glass, J. B.; Bowman, J. S.; Stockton, A. M.; Dichek, D.; Hurwitz, B.; Ramey, C.; Spears, A.; Walker, C. C.

    2017-12-01

    The 2017-18 Antarctic field season marks the first of three under the RISEUP project (Ross Ice Shelf & Europa Underwater Probe, NASA PSTAR program grant NNX16AL07G, PI B. E. Schmidt). RISEUP expands our efforts to understand the physical processes governing ice-ocean interactions from beneath the McMurdo Ice Shelf (MIS) to the Ross Ice Shelf (RIS), utilizing the modular autonomous or remotely operable submersible vehicle (AUV/ROV) Icefin. The remote, aphotic regions below Antarctic shelves present a unique opportunity- they are both poorly understood terrestrial environments and analogs for similar systems hypothesized to be present on other bodies in our solar system, such as Europa and Enceladus. By developing new robotic technologies to access and explore ice shelf cavities we are advancing our understanding of how temperature, pressure, and salinity influence the ice-ocean interface, the limits of habitable environments on Earth, and what biological processes and adaptations enable the life discovered by the RISP and WISSARD programs during initial exploration beneath the RIS. These investigations further our understanding of ocean world habitability and support planned and proposed planetary missions (e.g. Europa Clipper, Europa Lander) via improved constraint of marine ice accretion processes, organic entrainment, and interface habitability. Custom built at Georgia Tech and first deployed during the 2014/15 Antarctic season, Icefin is 3.5 m, 125 kg modular vehicle that now carries a full suite of oceanographic sensors (including conductivity, temperature, depth, dissolved O2, dissolved organic matter, turbidity, pH, eH, and sonar) that can be deployed through boreholes as small as 25 cm in diameter. Here we present continued analysis of basal ice and oceanographic observations in the McMurdo Sound region from 2012-2015 with, pending anticipated field work, comparisons to preliminary data from the 2017/18 field season beneath both the McMurdo and Ross Ice

  11. Increased West Antarctic and unchanged East Antarctic ice discharge over the last 7 years

    NASA Astrophysics Data System (ADS)

    Gardner, Alex S.; Moholdt, Geir; Scambos, Ted; Fahnstock, Mark; Ligtenberg, Stefan; van den Broeke, Michiel; Nilsson, Johan

    2018-02-01

    Ice discharge from large ice sheets plays a direct role in determining rates of sea-level rise. We map present-day Antarctic-wide surface velocities using Landsat 7 and 8 imagery spanning 2013-2015 and compare to earlier estimates derived from synthetic aperture radar, revealing heterogeneous changes in ice flow since ˜ 2008. The new mapping provides complete coastal and inland coverage of ice velocity north of 82.4° S with a mean error of < 10 m yr-1, resulting from multiple overlapping image pairs acquired during the daylight period. Using an optimized flux gate, ice discharge from Antarctica is 1929 ± 40 Gigatons per year (Gt yr-1) in 2015, an increase of 36 ± 15 Gt yr-1 from the time of the radar mapping. Flow accelerations across the grounding lines of West Antarctica's Amundsen Sea Embayment, Getz Ice Shelf and Marguerite Bay on the western Antarctic Peninsula, account for 88 % of this increase. In contrast, glaciers draining the East Antarctic Ice Sheet have been remarkably constant over the period of observation. Including modeled rates of snow accumulation and basal melt, the Antarctic ice sheet lost ice at an average rate of 183 ± 94 Gt yr-1 between 2008 and 2015. The modest increase in ice discharge over the past 7 years is contrasted by high rates of ice sheet mass loss and distinct spatial patters of elevation lowering. The West Antarctic Ice Sheet is experiencing high rates of mass loss and displays distinct patterns of elevation lowering that point to a dynamic imbalance. We find modest increase in ice discharge over the past 7 years, which suggests that the recent pattern of mass loss in Antarctica is part of a longer-term phase of enhanced glacier flow initiated in the decades leading up to the first continent-wide radar mapping of ice flow.

  12. Numerical modelling and data assimilation of the Larsen B ice shelf, Antarctic Peninsula.

    PubMed

    Vieli, Andreas; Payne, Antony J; Du, Zhijun; Shepherd, Andrew

    2006-07-15

    In this study, the flow and rheology of pre-collapse Larsen B ice shelf are investigated by using a combination of flow modelling and data assimilation. Observed shelf velocities from satellite interferometry are used to constrain an ice shelf model by using a data assimilation technique based on the control method. In particular, the ice rheology field and the velocities at the inland shelf boundary are simultaneously optimized to get a modelled flow and stress field that is consistent with the observed flow. The application to the Larsen B ice shelf shows that a strong weakening of the ice in the shear zones, mostly along the margins, is necessary to fit the observed shelf flow. This pattern of bands with weak ice is a very robust feature of the inversion, whereas the ice rheology within the main shelf body is found to be not well constrained. This suggests that these weak zones play a major role in the control of the flow of the Larsen B ice shelf and may be the key to understanding the observed pre-collapse thinning and acceleration of Larsen B. Regarding the sensitivity of the stress field to rheology, the consistency of the model with the observed flow seems crucial for any further analysis such as the application of fracture mechanics or perturbation model experiments.

  13. Future Antarctic bed topography and its implications for ice sheet dynamics

    NASA Astrophysics Data System (ADS)

    Adhikari, S.; Ivins, E. R.; Larour, E.; Seroussi, H.; Morlighem, M.; Nowicki, S.

    2014-06-01

    The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has generally been losing its mass since the Last Glacial Maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace, primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that past loading is relatively less important than future loading for the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years AD 2100 and 2500, respectively, and that the East Antarctic Ice Sheet is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay will approach roughly 45 mm yr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is generally associated with the flattening of reverse bed slope, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote stability in marine portions of the ice sheet in the future.

  14. Future Antarctic bed topography and its implications for ice sheet dynamics

    NASA Astrophysics Data System (ADS)

    Adhikari, S.; Ivins, E.; Larour, E.; Seroussi, H.; Morlighem, M.; Nowicki, S.

    2014-01-01

    The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A~recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) is generally losing its mass since the last glacial maximum (LGM). In a sustained warming climate, the AIS is predicted to retreat at a greater pace primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that the past loading is relatively less important than future loading on the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years 2100 and 2500 AD, respectively, and that the East Antarctic Ice Sheet (EAIS) is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay approaches roughly 45 mm yr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is associated with the flattening of reverse bed, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote the stability to marine portions of the ice sheet in future.

  15. Future Antarctic Bed Topography and Its Implications for Ice Sheet Dynamics

    NASA Technical Reports Server (NTRS)

    Adhikari, Surendra; Ivins, Erik R.; Larour, Eric Y.; Seroussi, Helene L.; Morlighem, Mathieu; Nowicki, S.

    2014-01-01

    The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has generally been losing its mass since the Last Glacial Maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace, primarily via melting beneath the ice shelves.We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS.We find that past loading is relatively less important than future loading for the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years AD 2100 and 2500, respectively, and that the East Antarctic Ice Sheet is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay will approach roughly 45mmyr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is generally associated with the flattening of reverse bed slope, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote stability in marine portions of the ice sheet in the future.

  16. AVHRR imagery reveals Antarctic ice dynamics

    NASA Technical Reports Server (NTRS)

    Bindschadler, Robert A.; Vornberger, Patricia L.

    1990-01-01

    A portion of AVHRR data taken on December 5, 1987 at 06:15 GMT over a part of Antarctica is used here to show that many of the most significant dynamic features of ice sheets can be identified by a careful examination of AVHRR imagery. The relatively low resolution of this instrument makes it ideal for obtaining a broad view of the ice sheets, while its wide swath allows coverage of areas beyond the reach of high-resolution imagers either currently in orbit or planned. An interpretation is given of the present data, which cover the area of ice streams that drain the interior of the West Antarctic ice sheet into the Ross Ice Shelf.

  17. Sea ice and oceanic processes on the Ross Sea continental shelf

    NASA Technical Reports Server (NTRS)

    Jacobs, S. S.; Comiso, J. C.

    1989-01-01

    The spatial and temporal variability of Antarctic sea ice concentrations on the Ross Sea continental shelf have been investigated in relation to oceanic and atmospheric forcing. Sea ice data were derived from Nimbus 7 scanning multichannel microwave radiometer (SMMR) brightness temperatures from 1979-1986. Ice cover over the shelf was persistently lower than above the adjacent deep ocean, averaging 86 percent during winter with little month-to-month of interannual variability. The large spring Ross Sea polynya on the western shelf results in a longer period of summer insolation, greater surface layer heat storage, and later ice formation in that region the following autumn.

  18. Chacterization of Teleseismic Earthquakes Observed on an Ice Shelf

    NASA Astrophysics Data System (ADS)

    Baker, M. G.; Aster, R. C.; Anthony, R. E.; Wiens, D.; Nyblade, A.; Bromirski, P. D.; Stephen, R. A.; Gerstoft, P.

    2016-12-01

    Broadband seismographs deployed atop large tabular icebergs and ice shelves record a rich superposition of atmospheric, oceanic, and solid earth signals. We characterize these signals, including body and surface wave arrivals from approximately 200 global earthquakes, using a 34-station broadband array spanning the Ross Ice Shelf, Antarctica. Teleseismic earthquake arrivals are essential for constructing models of crustal and upper mantle structure, and observations on the ice shelf are key to resolving the structure of the underlying West Antarctic Rift System. To test the plausibility of passive imaging in this unique environment, we examine seasonal and spatial dependence of signal-to-noise ratios of body wave arrivals and the impact of ice shelf dynamics on surface wave dispersion. We also note unusual phase mechanics arising from the floating platform geometry.

  19. Evaluation of Ice sheet evolution and coastline changes from 1960s in Amery Ice Shelf using multi-source remote sensing images

    NASA Astrophysics Data System (ADS)

    Qiao, G.; Ye, W.; Scaioni, M.; Liu, S.; Feng, T.; Liu, Y.; Tong, X.; Li, R.

    2013-12-01

    Global change is one of the major challenges that all the nations are commonly facing, and the Antarctica ice sheet changes have been playing a critical role in the global change research field during the past years. Long time-series of ice sheet observations in Antarctica would contribute to the quantitative evaluation and precise prediction of the effects on global change induced by the ice sheet, of which the remote sensing technology would make critical contributions. As the biggest ice shelf and one of the dominant drainage systems in East Antarctic, the Amery Ice Shelf has been making significant contributions to the mass balance of the Antarctic. Study of Amery Ice shelf changes would advance the understanding of Antarctic ice shelf evolution as well as the overall mass balance. At the same time, as one of the important indicators of Antarctica ice sheet characteristics, coastlines that can be detected from remote sensing imagery can help reveal the nature of the changes of ice sheet evolution. Most of the scientific research on Antarctica with satellite remote sensing dated from 1970s after LANDSAT satellite was brought into operation. It was the declassification of the cold war satellite reconnaissance photographs in 1995, known as Declassified Intelligence Satellite Photograph (DISP) that provided a direct overall view of the Antarctica ice-sheet's configuration in 1960s, greatly extending the time span of Antarctica surface observations. This paper will present the evaluation of ice-sheet evolution and coastline changes in Amery Ice Shelf from 1960s, by using multi-source remote sensing images including the DISP images and the modern optical satellite images. The DISP images scanned from negatives were first interior-oriented with the associated parameters, and then bundle block adjustment technology was employed based on the tie points and control points, to derive the mosaic image of the research region. Experimental results of coastlines generated

  20. West-Antarctic Ice Streams: Analog to Ice Flow in Channels on Mars

    NASA Technical Reports Server (NTRS)

    Lucchitta, B. K.

    1997-01-01

    Sounding of the sea floor in front of the Ross Ice Shelf in Antarctica recently revealed large persistent patterns of longitudinal megaflutes and drumlinoid forms, which are interpreted to have formed at the base of ice streams during the list glacial advance. The flutes bear remarkable resemblance to longitudinal grooves and highly elongated streamlined islands found on the floors of some large martian channels, called outflow channels. ln addition, other similarities exist between Antarctic ice streams and outflow channels. Ice streams are 30 to 80 km wide and hundreds of kilometers long, as are the martian channels. Ice stream beds are below sea level. Floors of many martian outflow channels lie below martian datum, which may have been close to or below past martian sea levels. The Antarctic ice stream bed gradient is flat and locally may go uphill, and surface slopes are exceptionally low. So are gradients of martian channels. The depth to the bed in ice streams is 1 to 1.5 km. At bankful stage, the depth of the fluid in outflow channels would have been 1 to 2 km. These similarities suggest that the martian outflow channels, whose origin is commonly attributed to gigantic catastrophic floods, were locally filled by ice that left a conspicuous morphologic imprint. Unlike the West-Antarctic-ice streams, which discharge ice from an ice sheet, ice in the martian channels came from water erupting from the ground. In the cold martian environment, this water, if of moderate volume, would eventually freeze. Thus it may have formed icings on springs, ice dams and jams on constrictions in the channel path, or frozen pools. Given sufficient thickness and downhill surface gradient, these ice masses would have moved; and given the right conditions, they could have moved like Antarctic ice streams.

  1. Greenhouse to Icehouse Antarctic Paleoclimate and Ice History from George V Land and Adélie Land Shelf Sediments

    NASA Astrophysics Data System (ADS)

    Williams, T.; Escutia, C.; De Santis, L.; O'Brien, P.; Pekar, S. F.; Brinkhuis, H.; Domack, E. W.

    2013-12-01

    Along the George V and Adélie Land continental shelf of East Antarctica, shallowly-buried strata contain a record of Antarctica's climate and ice history from the lush forests of the Eocene greenhouse to the dynamic ice sheet margins of the Neogene. Short piston cores and dredges have recovered Early Cretaceous and Eocene organic-rich sediment at the seabed, and in 2010, IODP Expedition 318 recovered earliest Oligocene and early Pliocene subglacial and proglacial diamictites. However, challenging ice and drilling conditions from the JOIDES Resolution on the shelf resulted in poor core recovery and sites had to be abandoned before the stratigraphic targets could be reached. Therefore, in a new IODP drilling proposal submitted earlier this year, we propose to use the MeBo sea bed drill for improved core recovery and easier access to the shelf, and drill a stratigraphic transect of shallow (~80m) holes. To investigate the evolution of the Antarctic ice sheet in this sector, we target strata above and below regional erosional and downlap surfaces to date and characterize major episodes of ice sheet advance and retreat. These direct records of ice extent on the shelf can be set in the context of Southern Ocean records of temperature, ice-rafted debris (IRD) and latitudinal fluctuations of the opal belt, and hence we can relate ice sheet evolution to paleoclimate conditions. Targets include possible late Eocene precursor glaciations, the Eocene/Oligocene boundary erosion surface, Oligocene and Miocene ice extents, and ice margin fluctuations in the Pliocene. At the Cretaceous and Eocene proposed sites, marine and terrestrial temperature proxies and palynological records will provide information on high-latitude paleoenvironments and pole-equator temperature gradients. Here we present existing data from the area and the proposed new drill sites. The ice and climate history of the George V and Adélie Land margin can provide warm-world scenarios to help understand ice

  2. Oceanic Controls of North American East Coast Sea Level Rise and Ocean Warming of the Antarctic Shelf

    NASA Astrophysics Data System (ADS)

    Goddard, Paul

    Sea level rise (SLR) threatens coastal communities, infrastructure, and ecosystems. Worldwide, stakeholders critically depend on SLR projections with the associated uncertainty for risk assessments, decision-making and coastal planning. Recent research suggests that the Antarctic ice sheet mass loss during the 21st century may contribute up to an additional one meter of global SLR by year 2100. While uncertainty still exists, this value would double the 'likely' (> 66% probability) range of global SLR (0.52-0.98 m) by the year 2100, as found by Chapter 13 on Sea Level Change in the Fifth Assessment Report by the Intergovernmental Panel on Climate Change. Here, we present three studies that assess mechanisms relevant to 21st century local, regional, and global SLR. Appendix A examines the effect of large-scale oceanic and atmospheric circulation variability on extreme sea levels along the East Coast of North America. Appendices B and C analyze ocean warming on the Antarctic shelf and its implications for future ice shelf basal melt and Antarctic Ice Sheet mass loss. These studies will contribute to more accurate projections of local, regional, and global SLR. In Appendix A, we analyze long-term tide gauge records from the North American eastern seaboard and find an extreme SLR event during 2009-2010. Within this two-year period, coastal sea levels spiked between Montauk, New York and Southern Canada by up to 128 mm. This two-year spike is unprecedented in the tide gauge record and found to be a 1-in-850 year event. We show that a 30% reduction in strength of the Atlantic meridional overturning circulation (AMOC) and a strong negative North Atlantic Oscillation (NAO) index caused the extreme SLR event. Climate models project that the AMOC will weaken and NAO variability will remain high over the 21st century. Consequently, extreme SLR events on the Northeast Coast could become more frequent during the 21st century in response to climate change and SLR. In Appendix B

  3. Continent-Wide Estimates of Antarctic Strain Rates from Landsat 8-Derived Velocity Grids and Their Application to Ice Shelf Studies

    NASA Astrophysics Data System (ADS)

    Alley, K. E.; Scambos, T.; Anderson, R. S.; Rajaram, H.; Pope, A.; Haran, T.

    2017-12-01

    Strain rates are fundamental measures of ice flow used in a wide variety of glaciological applications including investigations of bed properties, calculations of basal mass balance on ice shelves, application to Glen's flow law, and many other studies. However, despite their extensive application, strain rates are calculated using widely varying methods and length scales, and the calculation details are often not specified. In this study, we compare the results of nominal and logarithmic strain-rate calculations based on a satellite-derived velocity field of the Antarctic ice sheet generated from Landsat 8 satellite data. Our comparison highlights the differences between the two commonly used approaches in the glaciological literature. We evaluate the errors introduced by each code and their impacts on the results. We also demonstrate the importance of choosing and specifying a length scale over which strain-rate calculations are made, which can have large local impacts on other derived quantities such as basal mass balance on ice shelves. We present strain-rate data products calculated using an approximate viscous length-scale with satellite observations of ice velocity for the Antarctic continent. Finally, we explore the applications of comprehensive strain-rate maps to future ice shelf studies, including investigations of ice fracture, calving patterns, and stability analyses.

  4. Retreat of northern margins of George VI and Wilkins Ice Shelves, Antarctic Peninsula

    USGS Publications Warehouse

    Lucchitta, B.K.; Rosanova, C.E.

    1998-01-01

    The George VI and Wilkins Ice Shelves are considered at risk of disintegration due to a regional atmospheric warming trend on the Antarctic Peninsula. Retreat of the northern margin of the George VI Ice Shelf has been observed previously, but the Wilkins Ice Shelf was thought to be stable. We investigated the positions of the northern fronts of these shelves from the literature and looked for changes on 1974 Landsat and 1992 and 1995 European remote-sensing satellite (ERS) synthetic aperture radar images. Our investigation shows that the northern George VI Ice Shelf lost a total of 906 km2 between 1974 and 1992, and an additional 87 km2 by 1995. The northern margin of the Wilkins Ice Shelf lost 796 km2 between 1990 and 1992, and another 564 km2 between 1992 and 1995. Armadas of tabular icebergs were visible in front of this shelf in the ERS images. These two ice shelves mark the southernmost documented conspicuous retreat of ice-shelf margins.

  5. Basal crevasses and suture zones in the Larsen C Ice Shelf, Antarctica: Implications for ice shelf stability in a warming climate

    NASA Astrophysics Data System (ADS)

    McGrath, Daniel J.

    Understanding ice shelf structure and processes is paramount to future predictions of sea level rise, as nearly 75% of the ice flux from the Antarctic Ice Sheet (AIS) passes through these gates. The breakup of an ice shelf removes the longitudinal back stress acting on the grounded inland ice and leads to flow acceleration, dynamic thinning and frontal retreat, processes that can be sustained for more than a decade. Increased ice discharge to the ocean contributes to global sea level rise. This dissertation investigates basal crevasses and suture zones, two key structural components of ice shelves, in order to understand how the structure of an ice shelf influences its stability in a warming climate. Ground penetrating radar, high-resolution satellite imagery and a variety of modeling approaches are utilized to assess these features on the Larsen C Ice Shelf but in a manner that considers their influence on ice shelf stability around the AIS. Basal crevasses are large-scale (~66% of ice thickness and ten's of kms in length) and abundant features that are significant structural weaknesses. The viscoplastic deformation of the ice shelf in response to the perturbed hydrostatic balance leads to the formation of both surface depressions and crevasses, hence weakening the ice shelf further. Basal crevasses increase the local ice-ocean interface by ~30%, thereby increasing basal roughness and altering ice-ocean interactions. Ice-shelf fractures frequently terminate where they encounter suture zones, regions of material heterogeneity that form at the lateral bounds of meteoric inflows to ice shelves. The termination of a 25 km-long rift in the Churchill Peninsula suture zone is investigated and found to contain ~60 m of accreted marine ice. Steady-state basal melting/freezing rates are determined for the ice shelf and applied to a flowline model to examine the along-flow evolution of ice shelf structure. The thickening surface wedge of locally accumulated meteoric ice

  6. The effects of ocean circulation on ocean-ice interaction and potential feedbacks in an idealized shelf cavity

    NASA Astrophysics Data System (ADS)

    Bishop, S. P.; Thompson, A. F.; Schodlok, M.

    2016-02-01

    The West Antarctic ice sheet is melting at unprecedented rates, which will impact global sea level rise. The ocean may be playing the dominant role in this ice melt through the upwelling of warm and salty Circumpolar Deep Water (CDW) in regions such as Pine Island Glacier (PIG). There is evidence that the Antarctic Slope Front at the continental shelf constrains shoreward transport of CDW by mesoscale eddies. However, little is known about the ocean-ice interaction and potential feedbacks that take place once this water is advected into ice shelf cavities. In this talk we use MITgcm to simulate an idealized setup of the PIG ice shelf cavity, similar to the setup in De Rydt et al. 2014, to understand the effects of ocean circulation and potential feedbacks of ice-shelf melt on the ocean circulation. To do this we run the model in two different configurations with and without a wind-driven current at the northern edge of the ice shelf and annually updating the geometry of the ice shelf based on the parameterized ice-shelf melt. Eddy heat and potential vorticity fluxes are diagnosed and presented for each of the simulations and compared with control simulations where the ice-shelf cavity is not modified. Results show high ice shelf melt during the first year with maximum values in excess of 60 meters near the grounding line, but settle to tens of meters during the following years.

  7. Export of Ice-Cavity Water from Pine Island Ice Shelf, West Antarctica

    NASA Astrophysics Data System (ADS)

    Thurnherr, Andreas; Jacobs, Stanley; Dutrieux, Pierre

    2013-04-01

    Stability of the West Antarctic Ice Sheet is sensitive to changes in melting at the bottom of floating ice shelves that form the seaward extensions of Antarctic glaciers flowing into the ocean. Not least because observations in the cavities beneath ice shelves are difficult, heat fluxes and melt rates have been inferred from oceanographic measurements obtained near the ice edge (calving fronts). Here, we report on a set of hydrographic and velocity data collected in early 2009 near the calving front of the Amundsen Sea's fast-moving and (until recently) accelerating Pine Island Glacier and its associated ice shelf. CTD profiles collected along the southern half of the meridionally-trending ice front show clear evidence for export of ice-cavity water. That water was carried in the upper ocean along the ice front by a southward current that is possibly related to a striking clockwise gyre that dominated the (summertime) upper-ocean circulation in Pine Island Bay. Signatures of ice-cavity water appear unrelated to current direction along most of the ice front, suggesting that cross-frontal exchange is dominated by temporal variability. However, repeated hydrographic and velocity measurements in a small "ice cove" at the southern end of the calving front show a persistent strong (mean velocity peaking near 0.5 ms-1) outflow of ice-cavity water in the upper 500 m. While surface features (boils) suggested upwelling from deep below the ice shelf, vertical velocity measurements reveal 1) that the mean upwelling within the confines of the cove was too weak to feed the observed outflow, and 2) that large high-frequency internal waves dominated the vertical motion of water inside the cove. These observations indicate that water exchange between the Pine Island Ice Shelf cavity and the Amundsen sea is strongly asymmetric with weak broad inflow at depth and concentrated surface-intensified outflow of melt-laden deep water at the southern edge of the calving front. The lack of

  8. Meteorological Drivers of West Antarctic Ice Sheet and Ice Shelf Surface Melt

    NASA Astrophysics Data System (ADS)

    Scott, R. C.; Nicolas, J. P.; Bromwich, D. H.; Norris, J. R.; Lubin, D.

    2017-12-01

    We identify synoptic patterns and surface energy balance components driving warming and surface melting on the West Antarctic Ice Sheet (WAIS) and ice shelves using reanalysis and satellite remote sensing data from 1973-present. We have developed a synoptic climatology of atmospheric circulation patterns during the summer melt season using k-means cluster and composite analysis of daily 700-mb geopotential height and near-surface air temperature and wind fields from the ECMWF ERA-Interim reanalysis. Surface melt occurrence is detected in satellite passive microwave brightness temperature observations (K-band, horizontal polarization) beginning with the NASA Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR) and continuing with its more familiar descendants SMMR, SSM/I and SSMIS. To diagnose synoptic precursors and physical processes driving surface melt we combine the circulation climatology and multi-decadal records of cloud cover with surface radiative fluxes from the Extended AVHRR Polar Pathfinder (APP-x) project. We identify three distinct modes of regional summer West Antarctic warming since 1979 involving anomalous ridging over West Antarctica (WA) and the Amundsen Sea (AS). During the 1970s, ESMR data reveal four extensive melt events on the Ross Sea sector of the WAIS also linked to AS blocking. We therefore define an Amundsen Sea Blocking Index (ASBI). The ASBI and synoptic circulation pattern occurrence frequencies are correlated with the tropical Pacific (ENSO) and high latitude Southern Annular Mode (SAM) indices and the West Antarctic melt index. Surface melt in WA is favored by enhanced downwelling infrared and turbulent sensible heat fluxes associated with intrusions of warm, moist marine air. Consistent with recent findings from the Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE), marine advection to the Ross sector is favored by El Niño conditions in the tropical Pacific and a negative SAM. We also find

  9. Investigating ice shelf mass loss processes from continuous satellite altimetry

    NASA Astrophysics Data System (ADS)

    Fricker, H. A.

    2017-12-01

    The Antarctic Ice Sheet continually gains mass through snowfall over its large area and, to remain approximately in equilibrium, it sheds most of this excess mass through two processes, basal melting and iceberg calving, that both occur in the floating ice shelves surrounding the continent. Small amounts of mass are also lost by surface melting, which occurs on many ice shelves every summer to varying degrees, and has been linked to ice-shelf collapse via hydrofracture on ice shelves that have been pre-weakened. Ice shelves provide mechanical support to `buttress' seaward flow of grounded ice, so that ice-shelf thinning and retreat result in enhanced ice discharge to the ocean. Ice shelves are susceptible to changes in forcing from both the atmosphere and the ocean, which both change on a broad range of timescales to modify mass gains and losses at the surface and base, and from internal instabilities of the ice sheet itself. Mass loss from iceberg calving is episodic, with typical intervals between calving events on the order of decades. Since ice shelves are so vast, the only viable way to monitor them is with satellites. Here, we discuss results from satellite radar and laser altimeter data from one NASA satellite (ICESat), and four ESA satellites (ERS-1, ERS-2, Envisat, CryoSat-2) to obtain estimates of ice-shelf surface height since the early 1990s. The continuous time series show accelerated losses in total Antarctic ice-shelf volume from 1994 to 2017, and allow us to investigate the processes causing ice-shelf mass change. For Larsen C, much of the variability comes from changing atmospheric conditions affecting firn state. In the Amundsen Sea, the rapid thinning is a combination of accelerated ocean-driven thinning and ice dynamics. This long-term thinning signal is, however, is strongly modulated by ENSO-driven interannual variability. However, observations of ocean variability around Antarctica are sparse, since these regions are often covered in sea ice

  10. Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models

    NASA Astrophysics Data System (ADS)

    Levermann, A.; Winkelmann, R.; Nowicki, S.; Fastook, J. L.; Frieler, K.; Greve, R.; Hellmer, H. H.; Martin, M. A.; Meinshausen, M.; Mengel, M.; Payne, A. J.; Pollard, D.; Sato, T.; Timmermann, R.; Wang, W. L.; Bindschadler, R. A.

    2014-08-01

    The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02-0.14 m; 90% range: 0.0-0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04-0.21 m; 90% range: 0.01-0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these

  11. Edwardsiella andrillae, a new species of sea anemone from Antarctic ice.

    PubMed

    Daly, Marymegan; Rack, Frank; Zook, Robert

    2013-01-01

    Exploration of the lower surface of the Ross Ice Shelf in Antarctica by the Submersible Capable of under-Ice Navigation and Imaging (SCINI) remotely operated vehicle discovered a new species of sea anemone living in this previously undocumented ecosystem. This discovery was a significant outcome of the Coulman High Project's geophysical and environmental fieldwork in 2010-2011 as part of the ANDRILL (ANtarctic geologic DRILLing) program. Edwardsiella andrillae n. sp., lives with most of its column in the ice shelf, with only the tentacle crown extending into the seawater below. In addition to being the only Antarctic representative of the genus, Edwardsiella andrillae is distinguished from all other species of the genus in the number of tentacles and in the size and distribution of cnidae. The anatomy and histology of Edwardsiella andrillae present no features that explain how this animal withstands the challenges of life in such an unusual habitat.

  12. Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene.

    PubMed

    Kingslake, J; Scherer, R P; Albrecht, T; Coenen, J; Powell, R D; Reese, R; Stansell, N D; Tulaczyk, S; Wearing, M G; Whitehouse, P L

    2018-06-01

    To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model parameters 1 . Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so) 2-4 . Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today's grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance 5 . Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity-parameters that are difficult to measure and to incorporate into ice-sheet models.

  13. Strong sensitivity of Pine Island ice-shelf melting to climatic variability.

    PubMed

    Dutrieux, Pierre; De Rydt, Jan; Jenkins, Adrian; Holland, Paul R; Ha, Ho Kyung; Lee, Sang Hoon; Steig, Eric J; Ding, Qinghua; Abrahamsen, E Povl; Schröder, Michael

    2014-01-10

    Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice-shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate.

  14. Analogue modelling of the influence of ice shelf collapse on the flow of ice sheets grounded below sea-level

    NASA Astrophysics Data System (ADS)

    Corti, Giacomo; Zeoli, Antonio

    2016-04-01

    The sudden breakup of ice shelves is expected to result in significant acceleration of inland glaciers, a process related to the removal of the buttressing effect exerted by the ice shelf on the tributary glaciers. This effect has been tested in previous analogue models, which however applied to ice sheets grounded above sea level (e.g., East Antarctic Ice Sheet; Antarctic Peninsula and the Larsen Ice Shelf). In this work we expand these previous results by performing small-scale laboratory models that analyse the influence of ice shelf collapse on the flow of ice streams draining an ice sheet grounded below sea level (e.g., the West Antarctic Ice Sheet). The analogue models, with dimensions (width, length, thickness) of 120x70x1.5cm were performed at the Tectonic Modelling Laboratory of CNR-IGG of Florence, Italy, by using Polydimethilsyloxane (PDMS) as analogue for the flowing ice. This transparent, Newtonian silicone has been shown to well approximate the rheology of natural ice. The silicone was allowed to flow into a water reservoir simulating natural conditions in which ice streams flow into the sea, terminating in extensive ice shelves which act as a buttress for their glaciers and slow their flow. The geometric scaling ratio was 10(-5), such that 1cm in the models simulated 1km in nature; velocity of PDMS (a few mm per hour) simulated natural velocities of 100-1000 m/year. Instability of glacier flow was induced by manually removing a basal silicone platform (floating on water) exerting backstresses to the flowing analogue glacier: the simple set-up adopted in the experiments isolates the effect of the removal of the buttressing effect that the floating platform exerts on the flowing glaciers, thus offering insights into the influence of this parameter on the flow perturbations resulting from a collapse event. The experimental results showed a significant increase in glacier velocity close to its outlet following ice shelf breakup, a process similar to what

  15. Variable Basal Melt Rates of Antarctic Peninsula Ice Shelves, 1994-2016

    NASA Astrophysics Data System (ADS)

    Adusumilli, Susheel; Fricker, Helen Amanda; Siegfried, Matthew R.; Padman, Laurie; Paolo, Fernando S.; Ligtenberg, Stefan R. M.

    2018-05-01

    We have constructed 23-year (1994-2016) time series of Antarctic Peninsula (AP) ice-shelf height change using data from four satellite radar altimeters (ERS-1, ERS-2, Envisat, and CryoSat-2). Combining these time series with output from atmospheric and firn models, we partitioned the total height-change signal into contributions from varying surface mass balance, firn state, ice dynamics, and basal mass balance. On the Bellingshausen coast of the AP, ice shelves lost 84 ± 34 Gt a-1 to basal melting, compared to contributions of 50 ± 7 Gt a-1 from surface mass balance and ice dynamics. Net basal melting on the Weddell coast was 51 ± 71 Gt a-1. Recent changes in ice-shelf height include increases over major AP ice shelves driven by changes in firn state. Basal melt rates near Bawden Ice Rise, a major pinning point of Larsen C Ice Shelf, showed large increases, potentially leading to substantial loss of buttressing if sustained.

  16. Evidence for a palaeo-subglacial lake on the Antarctic continental shelf

    PubMed Central

    Kuhn, Gerhard; Hillenbrand, Claus-Dieter; Kasten, Sabine; Smith, James A.; Nitsche, Frank O.; Frederichs, Thomas; Wiers, Steffen; Ehrmann, Werner; Klages, Johann P.; Mogollón, José M.

    2017-01-01

    Subglacial lakes are widespread beneath the Antarctic Ice Sheet but their control on ice-sheet dynamics and their ability to harbour life remain poorly characterized. Here we present evidence for a palaeo-subglacial lake on the Antarctic continental shelf. A distinct sediment facies recovered from a bedrock basin in Pine Island Bay indicates deposition within a low-energy lake environment. Diffusive-advection modelling demonstrates that low chloride concentrations in the pore water of the corresponding sediments can only be explained by initial deposition of this facies in a freshwater setting. These observations indicate that an active subglacial meltwater network, similar to that observed beneath the extant ice sheet, was also active during the last glacial period. It also provides a new framework for refining the exploration of these unique environments. PMID:28569750

  17. Polynya dynamics and associated atmospheric forcing at the Ronne Ice Shelf

    NASA Astrophysics Data System (ADS)

    Ebner, Lars; Heinemann, Günther

    2014-05-01

    The Ronne Ice Shelf is known as one of the most active regions of polynya developments around the Antarctic continent. Low temperatures are prevailing throughout the whole year, particularly in winter. It is generally recognized that polynya formations are primarily forced by offshore winds and secondarily by ocean currents. Many authors have addressed this issue previously at the Ross Ice Shelf and Adélie Coast and connected polynya dynamics to strong katabatic surge events. Such investigations of atmospheric dynamics and simultaneous polynya occurrence are still severely underrepresented for the southwestern part of the Weddell Sea and especially for the Ronne Ice Shelf. Due to the very flat terrain gradients of the ice shelf katabatic winds are of minor importance in that area. Other atmospheric processes must therefore play a crucial role for polynya developments at the Ronne Ice Shelf. High-resolution simulations have been carried out for the Weddell Sea region using the non-hydrostatic NWP model COSMO from the German Meteorological Service (DWD). For the austral autumn and winter (March to August) 2008 daily forecast simulations were conducted with the consideration of daily sea-ice coverage deduced from the passive microwave system AMSR-E. These simulations are used to analyze the synoptic and mesoscale atmospheric dynamics of the Weddell Sea region and find linkages to polynya occurrence at the Ronne Ice Shelf. For that reason, the relation between the surface wind speed, the synoptic pressure gradient in the free atmosphere and polynya area is investigated. Seven significant polynya events are identified for the simulation period, three in the autumn and four in the winter season. It can be shown that in almost all cases synoptic cyclones are the primary polynya forcing systems. In most cases the timely interaction of several passing cyclones in the northern and central Weddell Sea leads to maintenance of a strong synoptic pressure gradient above the

  18. The internal structure of the Brunt Ice Shelf, Antarctica from ice-penetrating radar

    NASA Astrophysics Data System (ADS)

    King, Edward; De Rydt, Jan; Gudmundsson, Hilmar

    2016-04-01

    The Brunt Ice Shelf is a small feature on the Coats Land Coast of the Weddell Sea, Antarctica. It is unusual among Antarctic ice shelves because the ice crossing the grounding line from the ice sheet retains no structural integrity, so the ice shelf comprises icebergs of continental ice cemented together by sea ice, with the whole blanketed by in-situ snowfall. The size and distribution of the icebergs is governed by the thickness profile along the grounding line. Where bedrock troughs discharge thick ice to the ice shelf, the icebergs are large and remain close together with little intervening sea ice. Where bedrock ridges mean the ice crossing the grounding line is thin, the icebergs are small and widely-scattered with large areas of sea ice between them. To better understand the internal structure of the Brunt Ice Shelf and how this might affect the flow dynamics we conducted ice-penetrating radar surveys during December 2015 and January 2016. Three different ground-based radar systems were used, operating at centre frequencies of 400, 50 and 10 MHz respectively. The 400 MHz system gave detailed firn structure and accumulation profiles as well as time-lapse profiles of the active propagation of a crevasse. The 50 MHz system provided intermediate-level detail of iceberg distribution and thickness as well as information on the degree of salt water infiltration into the accumulating snow pack. The 10 MHz system used a high-power transmitter in an attempt to measure ice thickness beneath salt-impregnated ice. In this poster we will present example data from each of the three radar systems which will demonstrate the variability of the internal structure of the ice shelf. We will also present preliminary correlations between the internal structure and the surface topography from satellite data.

  19. Sea ice and oceanic processes on the Ross Sea continental shelf

    NASA Astrophysics Data System (ADS)

    Jacobs, S. S.; Comiso, J. C.

    1989-12-01

    We have investigated the spatial and temporal variability of Antarctic sea ice concentrations on the Ross Sea continental shelf, in relation to oceanic and atmospheric forcing. Sea ice data were derived from Nimbus 7 scanning multichannel microwave radiometer (SMMR) brightness temperatures from 1979-1986. Ice cover over the shelf was persistently lower than above the adjacent deep ocean, averaging 86% during winter with little month-to-month or interannual variability. The large spring Ross Sea polynya on the western shelf results in a longer period of summer insolation, greater surface layer heat storage, and later ice formation in that region the following autumn. Newly identified Pennell and Ross Passage polynyas near the continental shelf break appear to be maintained in part by divergence above a submarine bank and by upwelling of warmer water near the slope front. Warmer subsurface water enters the shelf region year-round and will retard ice growth and enhance heat flux to the atmosphere when entrained in the strong winter vertical circulation. Temperatures at 125-m depth on a mooring near the Ross Ice Shelf during July 1984 averaged 0.15°C above freezing, sufficient to support a vertical heat flux above 100 W/m2. Monthly average subsurface ocean temperatures along the Ross Ice Shelf lag the air temperature cycle and begin to rise several weeks before spring ice breakout. The coarse SMMR resolution and dynamic ice shelf coastlines can compromise the use of microwave sea ice data near continental boundaries.

  20. Response of Antarctic ice shelf melt to SAM trend and possible feedbacks with the ice-dynamics

    NASA Astrophysics Data System (ADS)

    Donat-Magnin, Marion; Jourdain, Nicolas C.; Gallée, Hubert; Spence, Paul; Cornford, Stephen L.; Le Sommer, Julien; Durand, Gaël

    2017-04-01

    The observed positive trend in the Southern Annular Mode (SAM) may warm the Southern Ocean sub-surface through decreased Ekman downward pumping. Subsequent change in ice-shelves melt has been suggested to trigger glacier acceleration in West Antarctica. Here we use a regional ocean model configuration of the Amundsen Sea that includes interactive ice-shelf cavities. Our results show that the inclusion of ice-shelves changes the ocean response to the projected SAM trend, i.e. it typically inhibits a part of the SAM-induced subsurface warming. Heat budget analysis has been used to propose responsible mechanisms. Regarding Thwaites and Pine Island, sub ice-shelf melt increases above 400m by approximately 40% for Thwaites and 10% for Pine Island and decreases by up to 10% below in response to ocean temperature changes driven by the projected SAM trend. The melt sensitivity to poleward shifting winds is nonetheless small compared to the sensitivity to an ice-sheet instability, i.e. to a projected change in the shape of ice-shelf cavities. For instance, the sub ice-shelf melt are doubled near the grounding line of some glaciers in response to the largest grounding line retreat projected for 2100. Large increase in basal melt close to the grounding line could largely impact instability and glacier acceleration. Our work suggests the need for including ice shelves into ocean models, and to couple ocean models to ice-sheet models in climate projections.

  1. Edwardsiella andrillae, a New Species of Sea Anemone from Antarctic Ice

    PubMed Central

    Daly, Marymegan; Rack, Frank; Zook, Robert

    2013-01-01

    Exploration of the lower surface of the Ross Ice Shelf in Antarctica by the Submersible Capable of under-Ice Navigation and Imaging (SCINI) remotely operated vehicle discovered a new species of sea anemone living in this previously undocumented ecosystem. This discovery was a significant outcome of the Coulman High Project’s geophysical and environmental fieldwork in 2010-2011 as part of the ANDRILL (ANtarctic geologic DRILLing) program. Edwardsiella andrillae n. sp., lives with most of its column in the ice shelf, with only the tentacle crown extending into the seawater below. In addition to being the only Antarctic representative of the genus, Edwardsiella andrillae is distinguished from all other species of the genus in the number of tentacles and in the size and distribution of cnidae. The anatomy and histology of Edwardsiella andrillae present no features that explain how this animal withstands the challenges of life in such an unusual habitat. PMID:24349517

  2. The Antarctic Ice.

    ERIC Educational Resources Information Center

    Radok, Uwe

    1985-01-01

    The International Antarctic Glaciological Project has collected information on the East Antarctic ice sheet since 1969. Analysis of ice cores revealed climatic history, and radar soundings helped map bedrock of the continent. Computer models of the ice sheet and its changes over time will aid in predicting the future. (DH)

  3. Modelling present-day basal melt rates for Antarctic ice shelves using a parametrization of buoyant meltwater plumes

    NASA Astrophysics Data System (ADS)

    Lazeroms, Werner M. J.; Jenkins, Adrian; Hilmar Gudmundsson, G.; van de Wal, Roderik S. W.

    2018-01-01

    Basal melting below ice shelves is a major factor in mass loss from the Antarctic Ice Sheet, which can contribute significantly to possible future sea-level rise. Therefore, it is important to have an adequate description of the basal melt rates for use in ice-dynamical models. Most current ice models use rather simple parametrizations based on the local balance of heat between ice and ocean. In this work, however, we use a recently derived parametrization of the melt rates based on a buoyant meltwater plume travelling upward beneath an ice shelf. This plume parametrization combines a non-linear ocean temperature sensitivity with an inherent geometry dependence, which is mainly described by the grounding-line depth and the local slope of the ice-shelf base. For the first time, this type of parametrization is evaluated on a two-dimensional grid covering the entire Antarctic continent. In order to apply the essentially one-dimensional parametrization to realistic ice-shelf geometries, we present an algorithm that determines effective values for the grounding-line depth and basal slope in any point beneath an ice shelf. Furthermore, since detailed knowledge of temperatures and circulation patterns in the ice-shelf cavities is sparse or absent, we construct an effective ocean temperature field from observational data with the purpose of matching (area-averaged) melt rates from the model with observed present-day melt rates. Our results qualitatively replicate large-scale observed features in basal melt rates around Antarctica, not only in terms of average values, but also in terms of the spatial pattern, with high melt rates typically occurring near the grounding line. The plume parametrization and the effective temperature field presented here are therefore promising tools for future simulations of the Antarctic Ice Sheet requiring a more realistic oceanic forcing.

  4. Future Antarctic bed topography and its implications for ice sheet dynamics

    NASA Astrophysics Data System (ADS)

    Adhikari, Surendra; Ivins, Erik; Larour, Eric; Seroussi, Helene; Morlighem, Mathieu; Nowicki, Sophie

    2014-05-01

    A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has been generally losing its mass since the last glacial maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that the past loading is relatively less important than future loading on the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years 2100 and 2500 AD, respectively, and that the East Antarctic Ice Sheet (EAIS) is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector of WAIS in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay approaches roughly 45 mm/yr in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is associated with the flattening of reverse bed, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote the stability to marine portions of the ice sheet in the future.

  5. Dynamic Antarctic ice sheet during the early to mid-Miocene

    PubMed Central

    DeConto, Robert M.; Pollard, David; Levy, Richard H.

    2016-01-01

    Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate–ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet–climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52–0.66‰, or a sea level equivalent change of 30–36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability. PMID:26903645

  6. Response of the Antarctic ice sheet to ocean forcing using the POPSICLES coupled ice sheet-ocean model

    NASA Astrophysics Data System (ADS)

    Martin, D. F.; Asay-Davis, X.; Price, S. F.; Cornford, S. L.; Maltrud, M. E.; Ng, E. G.; Collins, W.

    2014-12-01

    We present the response of the continental Antarctic ice sheet to sub-shelf-melt forcing derived from POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010. Simulations are performed at 0.1 degree (~5 km) ocean resolution and ice sheet resolution as fine as 500 m using adaptive mesh refinement. A comparison of fully-coupled and comparable standalone ice-sheet model results demonstrates the importance of two-way coupling between the ice sheet and the ocean. The POPSICLES model couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). BISICLES makes use of adaptive mesh refinement to fully resolve dynamically-important regions like grounding lines and employs a momentum balance similar to the vertically-integrated formulation of Schoof and Hindmarsh (2009). Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests like MISMIP3D (Pattyn et al., 2013) and realistic configurations (Favier et al. 2014). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). A companion presentation, "Present-day circum-Antarctic simulations using the POPSICLES coupled land ice-ocean model" in session C027 describes the ocean-model perspective of this work, while we focus on the response of the ice sheet and on details of the model. The figure shows the BISICLES-computed vertically-integrated ice velocity field about 1 month into a 20-year coupled Antarctic run. Groundling lines are shown in green.

  7. The Tweeting Ice Shelf: geophysics and outreach

    NASA Astrophysics Data System (ADS)

    Van Liefferinge, Brice; Berger, Sophie; Drews, Reinhard; Pattyn, Frank

    2015-04-01

    Over the last decade the Antarctic and Greenland ice sheets have contributed about one third of the annual sea level rise (Hanna et al., 2013). However, it remains difficult to reconcile global mass balance estimates obtained from different satellite-based methods. A typical approach is to balance the mass input from atmospheric modelling with the outgoing mass flux at the ice-sheet boundary (Shepherd et al., 2012). The flux calculations at the boundary rely on satellite-derived surface velocities, which are currently only available as snapshots in time, and which need ground truth for validation. Here, we report on continuous, year-round measurements that aim at improving the input-output method in several aspects and carefully map the flow speed allowing for detecting seasonal variability. For this purpose, we set up in December 2014 three stand-alone single-frequency GPSes on the Roi Baudouin ice shelf (East Antarctica). The GPSes are installed across a surface depression (typical for large ice-shelf channels), where subglacial melting is expected. This setup allows us to investigate how these channels behave, i.e., if they become wider, whether or not they enhance the ice flow, and, in combination with an installed phase-sensitive radar, what amount of melting occurs below the channels in contact with the ocean. The GPS data are transmitted on a daily basis. Ice-shelf velocity is derived from the raw hourly location following the methods described in den Ouden et al. (2010), Dunse et al. (2012), and Ahlstrøm et al. (2013). However, a reference station has not been used for the correction. Basic processing involves outliers removal, smoothing, time-series analysis and comparison with tidal models. The project comes alongside an outreach event: on a weekly basis, the ice shelf 'tweets' its position, motion and relays other information with respect to the project. The GPS systems can be followed on Twitter via @TweetinIceShelf as well as the Tweeting Ice Shelf

  8. RTopo-2: A global high-resolution dataset of ice sheet topography, ice shelf cavity geometry and ocean bathymetry

    NASA Astrophysics Data System (ADS)

    Timmermann, Ralph; Schaffer, Janin

    2016-04-01

    The RTopo-1 data set of Antarctic ice sheet/shelf geometry and global ocean bathymetry has proven useful not only for modelling studies of ice-ocean interaction in the southern hemisphere. Following the spirit of this data set, we introduce a new product (RTopo-2) that contains consistent maps of global ocean bathymetry, upper and lower ice surface topographies for Greenland and Antarctica, and global surface height on a spherical grid with now 30 arc seconds resolution. We used the General Bathymetric Chart of the Oceans (GEBCO_2014) as the backbone and added the International Bathymetric Chart of the Arctic Ocean version 3 (IBCAOv3) and the International Bathymetric Chart of the Southern Ocean (IBCSO) version 1. To achieve a good representation of the fjord and shelf bathymetry around the Greenland continent, we corrected data from earlier gridded products in the areas of Petermann Glacier, Hagen Bræ and Helheim Glacier assuming that sub-ice and fjord bathymetries roughly follow plausible Last Glacial Maximum ice flow patterns. For the continental shelf off northeast Greenland and the floating ice tongue of Nioghalvfjerdsfjorden Glacier at about 79°N, we incorporated a high-resolution digital bathymetry model including all available multibeam survey data for the region. Radar data for ice surface and ice base topographies of the floating ice tongues of Nioghalvfjerdsfjorden Glacier and Zachariæ Isstrøm have been obtained from the data centers of Technical University of Denmark (DTU), Operation Icebridge (NASA/NSF) and Alfred Wegener Institute (AWI). For the Antarctic ice sheet/ice shelves, RTopo-2 largely relies on the Bedmap-2 product but applies corrections for the geometry of Getz, Abbot and Fimbul ice shelf cavities. The data set is available in full and in regional subsets in NetCDF format from the PANGAEA database.

  9. Compression experiments on artificial, alpine and marine ice: implications for ice-shelf/continental interactions

    NASA Astrophysics Data System (ADS)

    Dierckx, Marie; Goossens, Thomas; Samyn, Denis; Tison, Jean-Louis

    2010-05-01

    Antarctic ice shelves are important components of continental ice dynamics, in that they control grounded ice flow towards the ocean. As such, Antarctic ice shelves are a key parameter to the stability of the Antarctic ice sheet in the context of global change. Marine ice, formed by sea water accretion beneath some ice shelves, displays distinct physical (grain textures, bubble content, ...) and chemical (salinity, isotopic composition, ...) characteristics as compared to glacier ice and sea ice. The aim is to refine Glen's flow relation (generally used for ice behaviour in deformation) under various parameters (temperature, salinity, debris, grain size ...) to improve deformation laws used in dynamic ice shelf models, which would then give more accurate and / or realistic predictions on ice shelf stability. To better understand the mechanical properties of natural ice, deformation experiments were performed on ice samples in laboratory, using a pneumatic compression device. To do so, we developed a custom built compression rig operated by pneumatic drives. It has been designed for performing uniaxial compression tests at constant load and under unconfined conditions. The operating pressure ranges from about 0.5 to 10 Bars. This allows modifying the experimental conditions to match the conditions found at the grounding zone (in the 1 Bar range). To maintain the ice at low temperature, the samples are immersed in a Silicone oil bath connected to an external refrigeration system. During the experiments, the vertical displacement of the piston and the applied force is measured by sensors which are connected to a digital acquisition system. We started our experiments with artificial ice and went on with continental ice samples from glaciers in the Alps. The first results allowed us to acquire realistic mechanical data for natural ice. Ice viscosity was calculated for different types of artificial ice, using Glen's flow law, and showed the importance of impurities

  10. Responses of Basal Melting of Antarctic Ice Shelves to the Climatic Forcing of the Last Glacial Maximum and CO2 Doubling

    NASA Astrophysics Data System (ADS)

    Abe-Ouchi, A.; Obase, T.

    2017-12-01

    Basal melting of the Antarctic ice shelves is an important factor in determining the stability of the Antarctic ice sheet. This study used the climatic outputs of an atmosphere?ocean general circulation model to force a circumpolar ocean model that resolves ice shelf cavity circulation to investigate the response of Antarctic ice shelf melting to different climatic conditions, i.e., to an increase (doubling) of CO2 and the Last Glacial Maximum conditions. We also conducted sensitivity experiments to investigate the role of surface atmospheric change, which strongly affects sea ice production, and the change of oceanic lateral boundary conditions. We found that the rate of change of basal melt due to climate warming is much greater (by an order of magnitude) than due to cooling. This is mainly because the intrusion of warm water onto the continental shelves, linked to sea ice production and climate change, is crucial in determining the basal melt rate of many ice shelves. Sensitivity experiments showed that changes of atmospheric heat flux and ocean temperature are both important for warm and cold climates. The offshore wind change together with atmospheric heat flux change strongly affected the production of sea ice and high-density water, preventing warmer water approaching the ice shelves under a colder climate. These results reflect the importance of both water mass formation in the Antarctic shelf seas and subsurface ocean temperature in understanding the long-term response to climate change of the melting of Antarctic ice shelves.

  11. Ocean as the main driver of Antarctic ice sheet retreat during the Holocene

    NASA Astrophysics Data System (ADS)

    Crosta, Xavier; Crespin, Julien; Swingedouw, Didier; Marti, Olivier; Masson-Delmotte, Valérie; Etourneau, Johan; Goosse, Hugues; Braconnot, Pascale; Yam, Ruth; Brailovski, Irena; Shemesh, Aldo

    2018-07-01

    Ocean-driven basal melting has been shown to be the main ablation process responsible for the recession of many Antarctic ice shelves and marine-terminating glaciers over the last decades. However, much less is known about the drivers of ice shelf melt prior to the short instrumental era. Based on diatom oxygen isotope (δ18Odiatom; a proxy for glacial ice discharge in solid or liquid form) records from western Antarctic Peninsula (West Antarctica) and Adélie Land (East Antarctica), higher ocean temperatures were suggested to have been the main driver of enhanced ice melt during the Early-to-Mid Holocene while atmosphere temperatures were proposed to have been the main driver during the Late Holocene. Here, we present a new Holocene δ18Odiatom record from Prydz Bay, East Antarctica, also suggesting an increase in glacial ice discharge since 4500 years before present ( 4.5 kyr BP) as previously observed in Antarctic Peninsula and Adélie Land. Similar results from three different regions around Antarctica thus suggest common driving mechanisms. Combining marine and ice core records along with new transient accelerated simulations from the IPSL-CM5A-LR climate model, we rule out changes in air temperatures during the last 4.5 kyr as the main driver of enhanced glacial ice discharge. Conversely, our simulations evidence the potential for significant warmer subsurface waters in the Southern Ocean during the last 6 kyr in response to enhanced summer insolation south of 60°S and enhanced upwelling of Circumpolar Deep Water towards the Antarctic shelf. We conclude that ice front and basal melting may have played a dominant role in glacial discharge during the Late Holocene.

  12. Modelling West Antarctic ice sheet growth and collapse through the past five million years.

    PubMed

    Pollard, David; DeConto, Robert M

    2009-03-19

    The West Antarctic ice sheet (WAIS), with ice volume equivalent to approximately 5 m of sea level, has long been considered capable of past and future catastrophic collapse. Today, the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams. Grounding lines are several hundred metres below sea level and the bed deepens upstream, raising the prospect of runaway retreat. Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms. Its variation since the Last Glacial Maximum is best known, with grounding lines advancing to the continental-shelf edges around approximately 15 kyr ago before retreating to near-modern locations by approximately 3 kyr ago. Prior collapses during the warmth of the early Pliocene epoch and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes, and by the discovery of open-ocean diatoms in subglacial sediments. Until now, however, little direct evidence of such behaviour has been available. Here we use a combined ice sheet/ice shelf model capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing to simulate Antarctic ice sheet variations over the past five million years. Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands. Transitions between glacial, intermediate and collapsed states are relatively rapid, taking one to several thousand years. Our simulation is in good agreement with a new sediment record (ANDRILL AND-1B) recovered from the western Ross Sea, indicating a long-term trend from more frequently collapsed to more glaciated states, dominant 40-kyr cyclicity in the Pliocene, and major retreats at

  13. Multidecadal warming of Antarctic waters.

    PubMed

    Schmidtko, Sunke; Heywood, Karen J; Thompson, Andrew F; Aoki, Shigeru

    2014-12-05

    Decadal trends in the properties of seawater adjacent to Antarctica are poorly known, and the mechanisms responsible for such changes are uncertain. Antarctic ice sheet mass loss is largely driven by ice shelf basal melt, which is influenced by ocean-ice interactions and has been correlated with Antarctic Continental Shelf Bottom Water (ASBW) temperature. We document the spatial distribution of long-term large-scale trends in temperature, salinity, and core depth over the Antarctic continental shelf and slope. Warming at the seabed in the Bellingshausen and Amundsen seas is linked to increased heat content and to a shoaling of the mid-depth temperature maximum over the continental slope, allowing warmer, saltier water greater access to the shelf in recent years. Regions of ASBW warming are those exhibiting increased ice shelf melt. Copyright © 2014, American Association for the Advancement of Science.

  14. Chronicling ice shelf history in the sediments left behind

    NASA Astrophysics Data System (ADS)

    Rosenheim, B. E.; Subt, C.; Shevenell, A.; Guitard, M.; Vadman, K. J.; DeCesare, M.; Wellner, J. S.; Bart, P. J.; Lee, J. I.; Domack, E. W.; Yoo, K. C.; Hayes, J. M.

    2017-12-01

    Collapsing and retreating ice shelves leave unmistakable sediment sequences on the Antarctic margin. These sequences tell unequivocal stories of collapse or retreat through a typical progression of sub-ice shelf diamicton (marking the past positions of grounding lines), sequentially overlain by a granulated facies from beneath the ice shelf, ice rafted debris from the calving line, and finally open marine sediment. The timelines to these stories, however, are troublesome. Difficulties in chronicling these stories recorded in sediment have betrayed their importance to our understanding of a warming world in many cases. The difficulties involve the concerted lack of preservation/production of calcium carbonate tests from the water column above and admixture of relict organic material from older sources of carbon. Here, we summarize our advances in the last decade of overcoming difficulties associated with the paucity of carbonate and creating chronologies of ice shelf retreat into the deglacial history of Antarctica by exploiting the range of thermochemical stability in organic matter (Ramped PyrOx) from these sediment sequences. We describe our success in comparing Ramped PyrOx 14C dates with foraminiferal dates, the relationship between sediment facies and radiocarbon age spectrum, and our ability to push limits of dating sediments deposited underneath ice shelves. With attention to the caveats of recent dating developments, we summarize expectations that geologist should have when coring the Antarctic margins to discern deglacial history. Perhaps most important among these expectations is the ability to design coring expeditions without regard to our ability to date calcium carbonate microfossils within the cores, in essence removing suspense of knowing whether cores taken from crucial paleo ice channels and other bathymetric features will ultimately yield a robust chronology for its sedimentary sequence.

  15. Antarctic Circumpolar Current Dynamics and Their Relation to Antarctic Ice Sheet and Perennial Sea-Ice Variability in the Central Drake Passage During the Last Climate Cycle

    NASA Astrophysics Data System (ADS)

    Kuhn, G.; Wu, S.; Hass, H. C.; Klages, J. P.; Zheng, X.; Arz, H. W.; Esper, O.; Hillenbrand, C. D.; Lange, C.; Lamy, F.; Lohmann, G.; Müller, J.; McCave, I. N. N.; Nürnberg, D.; Roberts, J.; Tiedemann, R.; Timmermann, A.; Titschack, J.; Zhang, X.

    2017-12-01

    The evolution of the Antarctic Ice Sheet during the last climate cycle and the interrelation to global atmospheric and ocean circulation remains controversial and plays an important role for our understanding of ice sheet response to modern global warming. The timing and sequence of deglacial warming is relevant for understanding the variability and sensitivity of the Antarctic Ice Sheet to climatic changes, and the continuing rise of atmospheric greenhouse gas concentrations. The Antarctic Ice Sheet is a pivotal component of the global water budget. Freshwater fluxes from the ice sheet may affect the Antarctic Circumpolar Current (ACC), which is strongly impacted by the westerly wind belt in the Southern Hemisphere (SHWW) and constricted to its narrowest extent in the Drake Passage. The flow of ACC water masses through Drake Passage is, therefore, crucial for advancing our understanding of the Southern Ocean's role in global meridional overturning circulation and global climate change. In order to address orbital and millennial-scale variability of the Antarctic ice sheet and the ACC, we applied a multi-proxy approach on a sediment core from the central Drake Passage including grain size, iceberg-rafted debris, mineral dust, bulk chemical and mineralogical composition, and physical properties. In combination with already published and new sediment records from the Drake Passage and Scotia Sea, as well as high-resolution data from Antarctic ice cores (WDC, EDML), we now have evidence that during glacial times a more northerly extent of the perennial sea-ice zone decreased ACC current velocities in the central Drake Passage. During deglaciation the SHWW shifted southwards due to a decreasing temperature gradient between subtropical and polar latitudes caused by sea ice and ice sheet decline. This in turn caused Southern Hemisphere warming, a more vigorous ACC, stronger Southern Ocean ventilation, and warm Circumpolar Deep Water (CDW) upwelling on Antarctic shelves

  16. Physical basis for a thick ice shelf in the Arctic Basin during the penultimate glacial maximum

    NASA Astrophysics Data System (ADS)

    Gasson, E.; DeConto, R.; Pollard, D.; Clark, C.

    2017-12-01

    A thick ice shelf covering the Arctic Ocean during glacial stages was discussed in a number of publications in the 1970s. Although this hypothesis has received intermittent attention, the emergence of new geophysical evidence for ice grounding in water depths of up to 1 km in the central Arctic Basin has renewed interest into the physical plausibility and significance of an Arctic ice shelf. Various ice shelf configurations have been proposed, from an ice shelf restricted to the Amerasian Basin (the `minimum model') to a complete ice shelf cover in the Arctic. Attempts to simulate an Arctic ice shelf have been limited. Here we use a hybrid ice sheet / shelf model that has been widely applied to the Antarctic ice sheet to explore the potential for thick ice shelves forming in the Arctic Basin. We use a climate forcing appropriate for MIS6, the penultimate glacial maximum. We perform a number of experiments testing different ice sheet / shelf configurations and compare the model results with ice grounding locations and inferred flow directions. Finally, we comment on the potential significance of an Arctic ice shelf to the global glacial climate system.

  17. Antarctic Glaciological Data at NSIDC: field data, temperature, and ice velocity

    NASA Astrophysics Data System (ADS)

    Bauer, R.; Bohlander, J.; Scambos, T.; Berthier, E.; Raup, B.; Scharfen, G.

    2003-12-01

    An extensive collection of many Antarctic glaciological parameters is available for the polar science community upon request. The National Science Foundation's Office of Polar Programs funds the Antarctic Glaciological Data Center (AGDC) at the National Snow and Ice Data Center (NSIDC) to archive and distribute Antarctic glaciological and cryospheric system data collected by the U.S. Antarctic Program. AGDC facilitates data exchange among Principal Investigators, preserves recently collected data useful to future research, gathers data sets from past research, and compiles continent-wide information useful for modeling and field work planning. Data sets are available via our web site, http://nsidc.org/agdc/. From here, users can access extensive documentation, citation information, locator maps, derived images and references, and the numerical data. More than 50 Antarctic scientists have contributed data to the archive. Among the compiled products distributed by AGDC are VELMAP and THERMAP. THERMAP is a compilation of over 600 shallow firn temperature measurements ('10-meter temperatures') collected since 1950. These data provide a record of mean annual temperature, and potentially hold a record of climate change on the continent. The data are represented with maps showing the traverse route, and include data sources, measurement technique, and additional measurements made at each site, i.e., snow density and accumulation. VELMAP is an archive of surface ice velocity measurements for the Antarctic Ice Sheet. The primary objective of VELMAP is to assemble a historic record of outlet glaciers and ice shelf ice motion over the Antarctic. The collection includes both PI-contributed measurements and data generated at NSIDC using Landsat and SPOT satellite imagery. Tabular data contain position, speed, bearing, and data quality information, and related references. Two new VELMAP data sets are highlighted: the Mertz Glacier and the Institute Ice Stream. Mertz Glacier ice

  18. Pigments in sediments beneath recently collapsed ice shelves: The case of Larsen A and B shelves, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Sañé, E.; Isla, E.; Grémare, A.; Gutt, J.; Vétion, G.; DeMaster, D. J.

    2011-01-01

    In March 2002, 3200 km 2 of the Larsen B ice shelf collapsed off the Eastern Antarctic Peninsula (EAP). In the austral summer of 2006, sea floor sediment was recovered beneath the extinct Larsen B ice shelf and in a region off the Northern Antarctic Peninsula (NAP), which has been free of ice shelves for more than 1000 yr. To assess changes in the chemical composition of the sediment after ice shelf collapses, chlorophylls and pheophytins were measured in sediment cores at six stations. This is the first time that chlorophyll pigments have been analysed in sediment samples from regions under recently collapsed ice shelves. Five years after the ice shelf collapse, Chla and Chlc concentrations were similar in the interfacial sediment (upper 1 cm) of NAP and EAP regions. However, in EAP Chla and Chlc concentrations decreased more rapidly with depth in the sediment column and were negligible below 2 cm depth. The high Chla to Pheoa ratios indicated that sedimentary pigments found in EAP had undergone limited degradation suggesting that they were locally produced rather than laterally advected. Complementary information from excess 210Pb activity and diatom valve distributions provided further evidence that the pigment fluxes to the seabed in EAP took place only after the ice shelf collapse.

  19. Initiation and long-term instability of the East Antarctic Ice Sheet.

    PubMed

    Gulick, Sean P S; Shevenell, Amelia E; Montelli, Aleksandr; Fernandez, Rodrigo; Smith, Catherine; Warny, Sophie; Bohaty, Steven M; Sjunneskog, Charlotte; Leventer, Amy; Frederick, Bruce; Blankenship, Donald D

    2017-12-13

    Antarctica's continental-scale ice sheets have evolved over the past 50 million years. However, the dearth of ice-proximal geological records limits our understanding of past East Antarctic Ice Sheet (EAIS) behaviour and thus our ability to evaluate its response to ongoing environmental change. The EAIS is marine-terminating and grounded below sea level within the Aurora subglacial basin, indicating that this catchment, which drains ice to the Sabrina Coast, may be sensitive to climate perturbations. Here we show, using marine geological and geophysical data from the continental shelf seaward of the Aurora subglacial basin, that marine-terminating glaciers existed at the Sabrina Coast by the early to middle Eocene epoch. This finding implies the existence of substantial ice volume in the Aurora subglacial basin before continental-scale ice sheets were established about 34 million years ago. Subsequently, ice advanced across and retreated from the Sabrina Coast continental shelf at least 11 times during the Oligocene and Miocene epochs. Tunnel valleys associated with half of these glaciations indicate that a surface-meltwater-rich sub-polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming. Cooling since the late Miocene resulted in an expanded polar EAIS and a limited glacial response to Pliocene warmth in the Aurora subglacial basin catchment. Geological records from the Sabrina Coast shelf indicate that, in addition to ocean temperature, atmospheric temperature and surface-derived meltwater influenced East Antarctic ice mass balance under warmer-than-present climate conditions. Our results imply a dynamic EAIS response with continued anthropogenic warming and suggest that the EAIS contribution to future global sea-level projections may be under-estimated.

  20. Initiation and long-term instability of the East Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Gulick, Sean P. S.; Shevenell, Amelia E.; Montelli, Aleksandr; Fernandez, Rodrigo; Smith, Catherine; Warny, Sophie; Bohaty, Steven M.; Sjunneskog, Charlotte; Leventer, Amy; Frederick, Bruce; Blankenship, Donald D.

    2017-12-01

    Antarctica’s continental-scale ice sheets have evolved over the past 50 million years. However, the dearth of ice-proximal geological records limits our understanding of past East Antarctic Ice Sheet (EAIS) behaviour and thus our ability to evaluate its response to ongoing environmental change. The EAIS is marine-terminating and grounded below sea level within the Aurora subglacial basin, indicating that this catchment, which drains ice to the Sabrina Coast, may be sensitive to climate perturbations. Here we show, using marine geological and geophysical data from the continental shelf seaward of the Aurora subglacial basin, that marine-terminating glaciers existed at the Sabrina Coast by the early to middle Eocene epoch. This finding implies the existence of substantial ice volume in the Aurora subglacial basin before continental-scale ice sheets were established about 34 million years ago. Subsequently, ice advanced across and retreated from the Sabrina Coast continental shelf at least 11 times during the Oligocene and Miocene epochs. Tunnel valleys associated with half of these glaciations indicate that a surface-meltwater-rich sub-polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming. Cooling since the late Miocene resulted in an expanded polar EAIS and a limited glacial response to Pliocene warmth in the Aurora subglacial basin catchment. Geological records from the Sabrina Coast shelf indicate that, in addition to ocean temperature, atmospheric temperature and surface-derived meltwater influenced East Antarctic ice mass balance under warmer-than-present climate conditions. Our results imply a dynamic EAIS response with continued anthropogenic warming and suggest that the EAIS contribution to future global sea-level projections may be under-estimated.

  1. Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

    USGS Publications Warehouse

    Holland, P. R.; Brisbourne, A.; Corr, H. F. J.; Mcgrath, Daniel; Purdon, K.; Paden, J.; Fricker, H. A.; Paolo, F. S.; Fleming, A.H.

    2015-01-01

    The catastrophic collapses of Larsen A and B ice shelves on the eastern Antarctic Peninsula have caused their tributary glaciers to accelerate, contributing to sea-level rise and freshening the Antarctic Bottom Water formed nearby. The surface of Larsen C Ice Shelf (LCIS), the largest ice shelf on the peninsula, is lowering. This could be caused by unbalanced ocean melting (ice loss) or enhanced firn melting and compaction (englacial air loss). Using a novel method to analyse eight radar surveys, this study derives separate estimates of ice and air thickness changes during a 15-year period. The uncertainties are considerable, but the primary estimate is that the surveyed lowering (0.066 ± 0.017 m yr−1) is caused by both ice loss (0.28 ± 0.18 m yr−1) and firn-air loss (0.037 ± 0.026 m yr−1). The ice loss is much larger than the air loss, but both contribute approximately equally to the lowering because the ice is floating. The ice loss could be explained by high basal melting and/or ice divergence, and the air loss by low surface accumulation or high surface melting and/or compaction. The primary estimate therefore requires that at least two forcings caused the surveyed lowering. Mechanisms are discussed by which LCIS stability could be compromised in the future. The most rapid pathways to collapse are offered by the ungrounding of LCIS from Bawden Ice Rise or ice-front retreat past a "compressive arch" in strain rates. Recent evidence suggests that either mechanism could pose an imminent risk.

  2. Estimation of Antarctic Land-Fast Sea Ice Algal Biomass and Snow Thickness From Under-Ice Radiance Spectra in Two Contrasting Areas

    NASA Astrophysics Data System (ADS)

    Wongpan, P.; Meiners, K. M.; Langhorne, P. J.; Heil, P.; Smith, I. J.; Leonard, G. H.; Massom, R. A.; Clementson, L. A.; Haskell, T. G.

    2018-03-01

    Fast ice is an important component of Antarctic coastal marine ecosystems, providing a prolific habitat for ice algal communities. This work examines the relationships between normalized difference indices (NDI) calculated from under-ice radiance measurements and sea ice algal biomass and snow thickness for Antarctic fast ice. While this technique has been calibrated to assess biomass in Arctic fast ice and pack ice, as well as Antarctic pack ice, relationships are currently lacking for Antarctic fast ice characterized by bottom ice algae communities with high algal biomass. We analyze measurements along transects at two contrasting Antarctic fast ice sites in terms of platelet ice presence: near and distant from an ice shelf, i.e., in McMurdo Sound and off Davis Station, respectively. Snow and ice thickness, and ice salinity and temperature measurements support our paired in situ optical and biological measurements. Analyses show that NDI wavelength pairs near the first chlorophyll a (chl a) absorption peak (≈440 nm) explain up to 70% of the total variability in algal biomass. Eighty-eight percent of snow thickness variability is explained using an NDI with a wavelength pair of 648 and 567 nm. Accounting for pigment packaging effects by including the ratio of chl a-specific absorption coefficients improved the NDI-based algal biomass estimation only slightly. Our new observation-based algorithms can be used to estimate Antarctic fast ice algal biomass and snow thickness noninvasively, for example, by using moored sensors (time series) or mapping their spatial distributions using underwater vehicles.

  3. An Antarctic stratigraphic record of step-wise ice-sheet growth through the Eocene-Oligocene transition

    NASA Astrophysics Data System (ADS)

    Passchier, S.; Ciarletta, D. J.; Miriagos, T.; Bijl, P.; Bohaty, S. M.

    2016-12-01

    The Antarctic cryosphere plays a critical role in the ocean-atmosphere system, but its early evolution is still poorly known. With a near-field record from Prydz Bay, Antarctica, we conclude that Antarctic continental ice-sheet growth commenced with the EOT-1 "precursor" glaciation, during a time of Subantarctic surface ocean cooling and a decline in atmospheric pCO2. Prydz Bay lies downstream of a major East Antarctic ice-sheet drainage system and the Gamburtsev Mountains, a likely nucleation point for the first ice sheets. Its sedimentary records uniquely constrain the timing of ice-sheet advance onto the continental shelf. We investigate a detrital record extracted from three Ocean Drilling Program drill holes in Prydz Bay within a new depositional and chronological framework spanning the late Eocene to early Oligocene ( 36-33 Ma). The chemical index of alteration (CIA) and the S-index, calculated from the major element geochemistry of bulk samples, yield estimates of chemical weathering intensities and mean annual temperature (MAT) on the East Antarctic continent. We document evidence for late Eocene mountain glaciation along with transient warm events at 35.8-34.8 Ma. These data and our sedimentological analyses confirm the presence of ephemeral mountain glaciers on East Antarctica during the late Eocene between 35.9 and 34.4 Ma. Furthermore, we document the stepwise climate cooling of the Antarctic hinterland from 34.4 Ma as the ice sheet advanced towards the edges of the continent during EOT-1. The youngest part of our data set correlates to the time interval of the Oi-1 glaciation, when the ice-sheet in Prydz Bay extended to the outer shelf. Cooling and ice growth on Antarctica was spatially variable and ice sheets formed under declining pCO2. These results point to complex ice sheet - atmosphere - ocean - solid-earth feedbacks.

  4. Ice shelf thickness change from 2010 to 2017

    NASA Astrophysics Data System (ADS)

    Hogg, A.; Shepherd, A.; Gilbert, L.; Muir, A. S.

    2017-12-01

    Floating ice shelves fringe 74 % of Antarctica's coastline, providing a direct link between the ice sheet and the surrounding oceans. Over the last 25 years, ice shelves have retreated, thinned, and collapsed catastrophically. While change in the mass of floating ice shelves has only a modest steric impact on the rate of sea-level rise, their loss can affect the mass balance of the grounded ice-sheet by influencing the rate of ice flow inland, due to the buttressing effect. Here we use CryoSat-2 altimetry data to map the detailed pattern of ice shelf thickness change in Antarctica. We exploit the dense spatial sampling and repeat coverage provided by the CryoSat-2 synthetic aperture radar interferometric mode (SARIn) to investigate data acquired between 2010 to the present day. We find that ice shelf thinning rates can exhibit large fluctuations over short time periods, and that the improved spatial resolution of CryoSat-2 enables us to resolve the spatial pattern of thinning with ever greater detail in Antarctica. In the Amundsen Sea, ice shelves at the terminus of the Pine Island and Thwaites glaciers have thinned at rates in excess of 5 meters per year for more than two decades. We observe the highest rates of basal melting near to the ice sheet grounding line, reinforcing the importance of high resolution datasets. On the Antarctic Peninsula, in contrast to the 3.8 m per decade of thinning observed since 1992, we measure an increase in the surface elevation of the Larsen-C Ice-Shelf during the CryoSat-2 period.

  5. The sources of Antarctic bottom water in a global ice ocean model

    NASA Astrophysics Data System (ADS)

    Goosse, Hugues; Campin, Jean-Michel; Tartinville, Benoı̂t

    Two mechanisms contribute to the formation of Antarctic bottom water (AABW). The first, and probably the most important, is initiated by the brine released on the Antarctic continental shelf during ice formation which is responsible for an increase in salinity. After mixing with ambient water at the shelf break, this salty and dense water sinks along the shelf slope and invades the deepest part of the global ocean. For the second one, the increase of surface water density is due to strong cooling at the ocean-atmosphere interface, together with a contribution from brine release. This induces deep convection and the renewal of deep waters. The relative importance of these two mechanisms is investigated in a global coupled ice-ocean model. Chlorofluorocarbon (CFC) concentrations simulated by the model compare favourably with observations, suggesting a reasonable deep water ventilation in the Southern Ocean, except close to Antarctica where concentrations are too high. Two artificial passive tracers released at surface on the Antarctic continental shelf and in the open-ocean allow to show clearly that the two mechanisms contribute significantly to the renewal of AABW in the model. This indicates that open-ocean convection is overestimated in our simulation. Additional experiments show that the amount of AABW production due to the export of dense shelf waters is quite sensitive to the parameterisation of the effect of downsloping and meso-scale eddies. Nevertheless, shelf waters always contribute significantly to deep water renewal. Besides, increasing the P.R. Gent, J.C. McWilliams [Journal of Physical Oceanography 20 (1990) 150-155] thickness diffusion can nearly suppress the AABW formation by open-ocean convection.

  6. Ice shelf basal melt rates around Antarctica from simulations and observations

    NASA Astrophysics Data System (ADS)

    Schodlok, M. P.; Menemenlis, D.; Rignot, E. J.

    2016-02-01

    We introduce an explicit representation of Antarctic ice shelf cavities in the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) ocean retrospective analysis; and compare resulting basal melt rates and patterns to independent estimates from satellite observations. Two simulations are carried out: the first is based on the original ECCO2 vertical discretization; the second has higher vertical resolution particularly at the depth range of ice shelf cavities. The original ECCO2 vertical discretization produces higher than observed melt rates and leads to a misrepresentation of Southern Ocean water mass properties and transports. In general, thicker levels at the base of the ice shelves lead to increased melting because of their larger heat capacity. This strengthens horizontal gradients and circulation within and outside the cavities and, in turn, warm water transports from the shelf break to the ice shelves. The simulation with more vertical levels produces basal melt rates (1735 ± 164 Gt/a) and patterns that are in better agreement with observations. Thinner levels in the sub-ice-shelf cavities improve the representation of a fresh/cold layer at the ice shelf base and of warm/salty water near the bottom, leading to a sharper pycnocline and reduced vertical mixing underneath the ice shelf. Improved water column properties lead to more accurate melt rates and patterns, especially for melt/freeze patterns under large cold-water ice shelves. At the 18 km grid spacing of the ECCO2 model configuration, the smaller, warm-water ice shelves cannot be properly represented, with higher than observed melt rates in both simulations.

  7. Ice velocity and SAR backscatter record for the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Scheuchl, B.; Mouginot, J.; Rignot, E. J.; Small, D.; Khazendar, A.; Seroussi, H. L.; Kellndorfer, J. M.

    2017-12-01

    The Antarctic Peninsula has undergone some dramatic changes in the last three decades. The latest high-profile change was the calving of iceberg A68 off the Larsen-C ice shelf, which resulted in the ice shelf to have the smallest extent since the beginning of satellite observations. A first indication of the beginning of the formation of the iceberg was reported based on 2008 ice velocity data by Khazendar et al. 2011 (GRL). With two long term funded missions as well as other available sensors, there is a wealth of data being collected not seen before. The European Sentinel-1 constellation provides InSAR coverage of the area every 6 days. In addition, lower resolution wide swath data are being collected over the Weddell sea and cover the shelf frequently. Landsat-8 thermal infrared imagery proved another valuable data source in monitoring the progression. USGS has committed Landsat-8 for frequent acquisitions in Antarctica during periods with available daylight. Here we take a longer term view of the Antarctic Peninsula and will provide a satellite data record of ice velocity data generated using SAR and optical data. In difference to our MEaSUREs Antarctica-wide 1 km annual product, this regional time series will be provided at 50 m posting to facilitate research that requires higher resolution velocity maps. We also use suitable InSAR data to determine the grounding line for the region. SAR backscatter can vary dramatically in the region, particularly in Austral summer. Low backscatter is an indication for surface melt, and in the case of Larsen-C, this can engulf the entire ice shelf at times. We will generate a calibrated backscatter time series using a precision DEM of the region. The maps will provide the temporal and spatial extent of surface melt and will be compared with results from the Regional Climate Model (RACMO) and, where available, with weather station data. We also use double difference interferograms, to chronicle the progression of the Larsen

  8. Palaeoglaciology of the Alexander Island ice cap, western Antarctic Peninsula, reconstructed from marine geophysical and core data

    NASA Astrophysics Data System (ADS)

    Graham, Alastair G. C.; Smith, James A.

    2012-03-01

    The glacial history of the continental shelf northwest of Alexander Island is not well known, due mainly to a lack of targeted marine data on Antarctica's palaeo-ice sheets in their inter-ice-stream areas. Recently it has been argued that the region was ice-free at the Last Glacial Maximum (LGM) and thus a potential site for glacial refugia. In this paper, multibeam swath bathymetry, sub-bottom profiles and sediment cores are used to map the Alexander Island sector of the Antarctic Peninsula margin, in order to reconstruct the shelf's palaeoglaciology. Sea-floor bedforms provide evidence that an independent ice cap persisted on Alexander Island through the LGM and deglaciation. We show that this ice cap drained via two major, previously-undescribed tidewater outlets (Rothschild and Charcot Glaciers) sourced from an ice dome centred over the west of the island and near-shore areas. The glaciers grounded along deep, fjord-like cross-shelf troughs to within at least ˜10-20 km of the shelf edge, and probably reached the shelf break. Only one small outer-shelf zone appears to have remained free of ice throughout an otherwise extensive LGM. During retreat, grounding-line geomorphology indicates periodic stabilisation of Charcot Glacier on the mid-shelf after 13,500 cal yrs BP, while Rothschild Glacier retreated across its mid-shelf by 14,450 cal yrs BP. The timing of these events is in phase with retreat in nearby Marguerite Trough, and we take this as evidence of a common history and forcing with the Antarctic Peninsula Ice Sheet. The fine details of ice flow documented by our new reconstruction highlight the importance of capturing complex ice flow patterns in models (e.g. in inter-stream areas), for understanding how region-specific parts of Antarctica may change in the future. Moreover, the reconstruction shows that glacial refugia, if present, cannot have been extensive on the Alexander Island shelf at the LGM as indicated by previous biological studies; instead

  9. An AirSAR 2004 view from the DC-8 as it approaches the Larsen Ice Shelf, which is part of the Antarctic Peninsula

    NASA Image and Video Library

    2004-03-13

    An AirSAR 2004 view from the DC-8 as it approaches the Larsen Ice Shelf, which is part of the Antarctic Peninsula. AirSAR 2004 is a three-week expedition in Central and South America by an international team of scientists that is using an all-weather imaging tool, called the Airborne Synthetic Aperture Radar (AirSAR), located onboard NASA's DC-8 airborne laboratory. Scientists from many parts of the world are combining ground research with NASA's AirSAR technology to improve and expand on the quality of research they are able to conduct. These photos are from the DC-8 aircraft while flying an AirSAR mission over Antarctica. The Antarctic Peninsula is more similar to Alaska and Patagonia than to the rest of the Antarctic continent. It is drained by fast glaciers, receives abundant precipitation, and melts significantly in the summer months. In recent decades, the Peninsula has experienced significant atmospheric warming (about 2 degrees C since 1950), which has triggered a vast and spectacular retreat of its floating ice shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia ice fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with the Airborne Synthetic Aperture Radar developed by scientists from NASA’s Jet Propulsion Laboratory. AirSAR will provide a baseline model and unprecedented mapping of the region. This data will make it possible to determine whether the warming trend is slowing, continuing or accelerating. AirSAR will also provide reliable information on ice shelf thickness to measure the contribution of the glaciers to sea level.

  10. Flexural-response of the McMurdo Ice Shelf to surface lake filling and drainage

    NASA Astrophysics Data System (ADS)

    Banwell, A. F.; MacAyeal, D. R.; Willis, I.; Macdonald, G. J.; Goodsell, B.

    2017-12-01

    Antarctic ice-shelf instability and break-up, as exhibited by the Larsen B ice shelf in 2002, remains one of the most difficult glaciological processes to observe directly. It is, however, vital to do so because ice-shelf breakup has the potential to influence the buttressing controls on inland ice discharge, and thus to affect sea level. Several mechanisms enabling Larsen B style breakup have previously been proposed, including the ability of surface lakes to introduce ice-shelf fractures when they fill and drain. During the austral summer of 2016/2017, we monitored the filling and draining of four surface lakes on the McMurdo Ice Shelf, Antarctica, and the effect of these processes on ice-shelf flexure. Water-depth data from pressure sensors reveal that two lakes filled to >2 m in depth and subsequently drained over multiple week timescales, which had a simultaneous effect on vertical ice deflection in the area. Differential GPS data from 12 receivers over three months show that vertical deflection varies as a function of distance from the maximum load change (i.e. at the lake centre). Using remote sensing techniques applied to both Landsat 8 and Worldview imagery, we also quantify the meltwater volume in these two lakes through the melt season, which, together with the vertical deflection data, are used to constrain key flexural parameter values in numerical models of ice-shelf flexure.

  11. Foehn and temperature-based melt patterns over the Larsen C Ice Shelf as simulated by the MAR regional climate model

    NASA Astrophysics Data System (ADS)

    Datta, R.; Tedesco, M.; Agosta, C.; Fettweis, X.; Kuipers Munneke, P.; van den Broeke, M. R.

    2017-12-01

    Surface melting has been implicated in the collapse of Antarctic Peninsula ice shelves, most dramatically in the Larsen A (1995) and Larsen B (2002) ice shelves. In July of this year, a rift in the remaining Larsen C ice shelf broke away one of the largest icebergs ever recorded. Ice-shelf retreat is likely related to strong atmospheric warming in this area, by means of hydrofracturing and possibly by the warming atmosphere itself. According the hydrofracture mechanism, meltwater produced during anomalously warm summers infiltrates and deepens pre-existent crevasses, leading to the eventual break-up of the ice shelf. In addition to region-wide warming, melting in the East Antarctic Peninsula can be caused by frequent intrusions of westerly foehn winds. The remaining Larsen C ice shelf, as well as glaciers previously feeding to the former Larsen B ice shelf, are therefore vulnerable to both (a) the atmospheric circulation patterns that influence foehn wind frequency and intensity and (b) regional interannual temperature trends. We discuss spatial patterns of meltwater production in the northeast basin of the Antarctic Peninsula as modeled by the Modèle Atmosphérique Régionale (MAR) at a 10km resolution between 2001 and 2014. The timeseries associated with these patterns are used to identify interannual changes in the frequency of foehn-induced melt, and compare foehn-induced melting to melt associated with regional warming. Melt occurrence in MAR is evaluated against multiple satellite datasets and near-surface automatic weather station data from three sites. Finally, we discuss the seasonal depth to which meltwater percolates into the snowpack (as modeled by MAR) because of the potential influence of meltwater on both warming and densification of the ice shelf.

  12. Dating Antarctic ice sheet collapse: Proposing a molecular genetic approach

    NASA Astrophysics Data System (ADS)

    Strugnell, Jan M.; Pedro, Joel B.; Wilson, Nerida G.

    2018-01-01

    Sea levels at the end of this century are projected to be 0.26-0.98 m higher than today. The upper end of this range, and even higher estimates, cannot be ruled out because of major uncertainties in the dynamic response of polar ice sheets to a warming climate. Here, we propose an ecological genetics approach that can provide insight into the past stability and configuration of the West Antarctic Ice Sheet (WAIS). We propose independent testing of the hypothesis that a trans-Antarctic seaway occurred at the last interglacial. Examination of the genomic signatures of bottom-dwelling marine species using the latest methods can provide an independent window into the integrity of the WAIS more than 100,000 years ago. Periods of connectivity facilitated by trans-Antarctic seaways could be revealed by dating coalescent events recorded in DNA. These methods allow alternative scenarios to be tested against a fit to genomic data. Ideal candidate taxa for this work would need to possess a circumpolar distribution, a benthic habitat, and some level of genetic structure indicated by phylogeographical investigation. The purpose of this perspective piece is to set out an ecological genetics method to help resolve when the West Antarctic Ice Shelf last collapsed.

  13. New details about the LGM extent and subsequent retreat of the West Antarctic Ice Sheet from the easternmost Amundsen Sea Embayment shelf

    NASA Astrophysics Data System (ADS)

    Klages, J. P.; Hillenbrand, C. D.; Kuhn, G.; Smith, J. A.; Graham, A. G. C.; Nitsche, F. O.; Frederichs, T.; Arndt, J. E.; Gebhardt, C.; Robin, Z.; Uenzelmann-Neben, G.; Gohl, K.; Jernas, P.; Wacker, L.

    2017-12-01

    In recent years several previously undiscovered grounding-zone wedges (GZWs) have been described within the Abbot-Cosgrove palaeo-ice stream trough on the easternmost Amundsen Sea Embayment shelf. These GZWs document both the Last Glacial Maximum (LGM; 26.5-19 cal. ka BP) grounding-line extent and the subsequent episodic retreat within this trough that neighbors the larger Pine Island-Thwaites trough to the west. Here we combine bathymetric, seismic, and geologic data showing that 1) the grounding line in Abbot Trough did not reach the continental shelf break at any time during the last glacial period, and 2) a prominent stacked GZW constructed from six individual wedges lying upon another was deposited 100 km upstream from the LGM grounding-line position. The available data allow for calculating volumes for most of these individual GZWs and for the entire stack. Sediment cores were recovered seawards from the outermost GZW in the trough, and from the individual wedges of the stacked GZW in order to define the LGM grounding-line extent, and provide minimum grounding-line retreat ages for the respective positions on the stacked GZW. We present implications of a grounded-ice free outer shelf throughout the last glacial period. Furthermore, we assess the significance of the grounding-line stillstand period recorded by the stacked GZW in Abbot Trough for the timing of post-LGM retreat of the West Antarctic Ice Sheet from the Amundsen Sea Embayment shelf.

  14. Ice Sheet History from Antarctic Continental Margin Sediments: The ANTOSTRAT Approach

    USGS Publications Warehouse

    Barker, P.F.; Barrett, P.J.; Camerlenghi, A.; Cooper, A. K.; Davey, F.J.; Domack, E.W.; Escutia, C.; Kristoffersen, Y.; O'Brien, P.E.

    1998-01-01

    The Antarctic Ice Sheet is today an important part of the global climate engine, and probably has been so for most of its long existence. However, the details of its history are poorly known, despite the measurement and use, over two decades, of low-latitude proxies of ice sheet volume. An additional way of determining ice sheet history is now available, based on understanding terrigenous sediment transport and deposition under a glacial regime. It requires direct sampling of the prograded wedge of glacial sediments deposited at the Antarctic continental margin (and of derived sediments on the continental rise) at a small number of key sites, and combines the resulting data using numerical models of ice sheet development. The new phase of sampling is embodied mainly in a suite of proposals to the Ocean Drilling Program, generated by separate regional proponent groups co-ordinated through ANTOSTRAT (the Antarctic Offshore Acoustic Stratigraphy initiative). The first set of margin sites has now been drilled as ODP Leg 178 to the Antarctic Peninsula margin, and a first, short season of inshore drilling at Cape Roberts, Ross Sea, has been completed. Leg 178 and Cape Roberts drilling results are described briefly here, together with an outline of key elements of the overall strategy for determining glacial history, and of the potential contributions of drilling other Antarctic margins investigated by ANTOSTRAT. ODP Leg 178 also recovered continuous ultra-high-resolution Holocene biogenic sections at two sites within a protected, glacially-overdeepened basin (Palmer Deep) on the inner continental shelf of the Antarctic Peninsula. These and similar sites from around the Antarctic margin are a valuable resource when linked with ice cores and equivalent sections at lower latitude sites for studies of decadal and millenial-scale climate variation.

  15. DEM, tide and velocity over sulzberger ice shelf, West Antarctica

    USGS Publications Warehouse

    Baek, S.; Shum, C.K.; Lee, H.; Yi, Y.; Kwoun, Oh-Ig; Lu, Z.; Braun, Andreas

    2005-01-01

    Arctic and Antarctic ice sheets preserve more than 77% of the global fresh water and could raise global sea level by several meters if completely melted. Ocean tides near and under ice shelves shifts the grounding line position significantly and are one of current limitations to study glacier dynamics and mass balance. The Sulzberger ice shelf is an area of ice mass flux change in West Antarctica and has not yet been well studied. In this study, we use repeat-pass synthetic aperture radar (SAR) interferometry data from the ERS-1 and ERS-2 tandem missions for generation of a high-resolution (60-m) Digital Elevation Model (DEM) including tidal deformation detection and ice stream velocity of the Sulzberger Ice Shelf. Other satellite data such as laser altimeter measurements with fine foot-prints (70-m) from NASA's ICESat are used for validation and analyses. The resulting DEM has an accuracy of-0.57??5.88 m and is demonstrated to be useful for grounding line detection and ice mass balance studies. The deformation observed by InSAR is found to be primarily due to ocean tides and atmospheric pressure. The 2-D ice stream velocities computed agree qualitatively with previous methods on part of the Ice Shelf from passive microwave remote-sensing data (i.e., LANDSAT). ?? 2005 IEEE.

  16. Eddy-resolving simulations of the Fimbul Ice Shelf cavity circulation: Basal melting and exchange with open ocean

    NASA Astrophysics Data System (ADS)

    Hattermann, T.; Smedsrud, L. H.; Nøst, O. A.; Lilly, J. M.; Galton-Fenzi, B. K.

    2014-10-01

    Melting at the base of floating ice shelves is a dominant term in the overall Antarctic mass budget. This study applies a high-resolution regional ice shelf/ocean model, constrained by observations, to (i) quantify present basal mass loss at the Fimbul Ice Shelf (FIS); and (ii) investigate the oceanic mechanisms that govern the heat supply to ice shelves in the Eastern Weddell Sea. The simulations confirm the low melt rates suggested by observations and show that melting is primarily determined by the depth of the coastal thermocline, regulating deep ocean heat fluxes towards the ice. Furthermore, the uneven distribution of ice shelf area at different depths modulates the melting response to oceanic forcing, causing the existence of two distinct states of melting at the FIS. In the simulated present-day state, only small amounts of Modified Warm Deep Water enter the continental shelf, and ocean temperatures beneath the ice are close to the surface freezing point. The basal mass loss in this so-called state of "shallow melting" is mainly controlled by the seasonal inflow of solar-heated surface water affecting large areas of shallow ice in the upper part of the cavity. This is in contrast to a state of "deep melting", in which the thermocline rises above the shelf break depth, establishing a continuous inflow of Warm Deep Water towards the deep ice. The transition between the two states is found to be determined by a complex response of the Antarctic Slope Front overturning circulation to varying climate forcings. A proper representation of these frontal dynamics in climate models will therefore be crucial when assessing the evolution of ice shelf basal melting along this sector of Antarctica.

  17. Rheology of the Ronne Ice Shelf, Antarctica, Inferred from Satellite Radar Interferometry Data using an Inverse Control Method

    NASA Technical Reports Server (NTRS)

    Larour, E.; Rignot, E.; Joughin, I.; Aubry, D.

    2005-01-01

    The Antarctic Ice Sheet is surrounded by large floating ice shelves that spread under their own weight into the ocean. Ice shelf rigidity depends on ice temperature and fabrics, and is influenced by ice flow and the delicate balance between bottom and surface accumulation. Here, we use an inverse control method to infer the rigidity of the Ronne Ice Shelf that best matches observations of ice velocity from satellite radar interferometry. Ice rigidity, or flow law parameter B, is shown to vary between 300 and 900 kPa a(sup 1/3). Ice is softer along the side margins due to frictional heating, and harder along the outflow of large glaciers, which advect cold continental ice. Melting at the bottom surface of the ice shelf increases its rigidity, while freezing decreases it. Accurate numerical modelling of ice shelf flow must account for this spatial variability in mechanical characteristics.

  18. Ice Bridge Antarctic Sea Ice

    NASA Image and Video Library

    2009-10-21

    Sea ice is seen out the window of NASA's DC-8 research aircraft as it flies 2,000 feet above the Bellingshausen Sea in West Antarctica on Wednesday, Oct., 21, 2009. This was the fourth science flight of NASA’s Operation Ice Bridge airborne Earth science mission to study Antarctic ice sheets, sea ice, and ice shelves. Photo Credit: (NASA/Jane Peterson)

  19. Simulating a Dynamic Antarctic Ice Sheet in the Early to Middle Miocene

    NASA Astrophysics Data System (ADS)

    Gasson, E.; DeConto, R.; Pollard, D.; Levy, R. H.

    2015-12-01

    There are a variety of sources of geological data that suggest major variations in the volume and extent of the Antarctic ice sheet during the early to middle Miocene. Simulating such variability using coupled climate-ice sheet models is problematic due to a strong hysteresis effect caused by height-mass balance feedback and albedo feedback. This results in limited retreat of the ice sheet once it has reached the continental size, as likely occurred prior to the Miocene. Proxy records suggest a relatively narrow range of atmospheric CO2 during the early to middle Miocene, which exacerbates this problem. We use a new climate forcing which accounts for ice sheet-climate feedbacks through an asynchronous GCM-RCM coupling, which is able to better resolve the narrow Antarctic ablation zone in warm climate simulations. When combined with recently suggested mechanisms for retreat into subglacial basins due to ice shelf hydrofracture and ice cliff failure, we are able to simulate large-scale variability of the Antarctic ice sheet in the Miocene. This variability is equivalent to a seawater oxygen isotope signal of ~0.5 ‰, or a sea level equivalent change of ~35 m, for a range of atmospheric CO2 between 280 - 500 ppm.

  20. Recent Ice Loss from the Fleming and Other Glaciers, Wordie Bay, West Antarctic Peninsula

    NASA Technical Reports Server (NTRS)

    Rignot, E.; Casassa, G.; Gogineni, S.; Kanagaratnam, P.; Krabill, W.; Pritchard, H.; Rivera, A.; Thomas, R.; Turner, J.; Vaughan, D.

    2005-01-01

    Satellite radar interferometry data from 1995 to 2004, and airborne ice thickness data from 2002, reveal that the glaciers flowing into former Wordie Ice Shelf, West Antarctic Peninsula, discharge 6.8 +/- 0.3 km(exp 3)/yr of ice, which is 84 +/- 30 percent larger than a snow accumulation of 3.7 +/- 0.8 km(exp 3)/yr over a 6,300 km(exp 2) drainage basin. Airborne and ICESat laser altimetry elevation data reveal glacier thinning at rates up to 2 m/yr. Fifty km from its ice front, Fleming Glacier flows 50 percent faster than it did in 1974 prior to the main collapse of Wordie Ice Shelf. We conclude that the glaciers accelerated following ice shelf removal, and have been thinning and losing mass to the ocean over the last decade. This and other observations suggest that the mass loss from the northern part of the Peninsula is not negligible at present.

  1. Patterns of variability in steady- and non steady-state Ross Ice Shelf flow

    NASA Astrophysics Data System (ADS)

    Campbell, A. J.; Hulbe, C. L.; Scambos, T. A.; Klinger, M. J.; Lee, C. K.

    2016-12-01

    Ice shelves are gateways through which climate change can be transmitted from the ocean or atmosphere to a grounded ice sheet. It is thus important to separate patterns of ice shelf change driven internally (from the ice sheet) and patterns driven externally (by the ocean or atmosphere) so that modern observations can be viewed in an appropriate context. Here, we focus on the Ross Ice Shelf (RIS), a major component of the West Antarctic Ice Sheet system and a feature known to experience variable ice flux from tributary ice streams and glaciers, for example, ice stream stagnation and glacier surges. We perturb a model of the Ross Ice Shelf with periodic influx variations, ice rise and ice plain grounding events, and iceberg calving in order to generate transients in the ice shelf flow and thickness. Characteristic patterns associated with those perturbations are identified using empirical orthogonal functions (EOFs). The leading EOFs reveal shelf-wide pattern of response to local perturbations that can be interpreted in terms of coupled mass and momentum balance. For example, speed changes on Byrd Glacier cause both thinning and thickening in a broad region that extends to Roosevelt Island. We calculate decay times at various locations for various perturbations and find that mutli-decadal to century time scales are typical. Unique identification of responses to particular forcings may thus be difficlult to achieve and flow divergence cannot be assumed to be constant when interpreting observed changes in ice thickness. In reality, perturbations to the ice shelf do not occur individually, rather the ice shelf contains a history of boundary perturbations. To explore the degree individual perturbations are seperable from their ensemble, EOFs from individual events are combined in pairs and compared against experiments with the same periodic perturbations pairs. Residuals between these EOFs reveal the degree interaction between between disctinct perturbations.

  2. A shift in the biogenic silica of sediment in the Larsen B continental shelf, off the Eastern Antarctic Peninsula, resulting from climate change.

    PubMed

    Sañé, Elisabet; Isla, Enrique; Bárcena, María Ángeles; DeMaster, David J

    2013-01-01

    In 2002, section B of the Larsen ice shelf, off of the Eastern Antarctic Peninsula, collapsed and created the opportunity to study whether the changes at the sea surface left evidence in the sedimentary record. Biogenic silica is major constituent of Antarctic marine sediment, and its presence in the sediment column is associated with diatom production in the euphotic zone. The abundance of diatom valves and the number of sponge spicules in the biogenic silica was analyzed to determine how the origin of the biogenic silica in the upper layers of the sediment column responded to recent environmental changes. Diatom valves were present only in the upper 2 cm of sediment, which roughly corresponds to the period after the collapse of the ice shelf. In contrast, sponge spicules, a more robust form of biogenic silica, were also found below the upper 2 cm layer of the sediment column. Our results indicate that in this region most of the biogenic silica in the sedimentary record originated from sponge spicules rather than diatoms during the time when the sea surface was covered by the Larsen ice shelf. Since the collapse of the ice shelf, the development of phytoplankton blooms and the consequent influx of diatom debris to the seabed have shifted the biogenic silica record to one dominated by diatom debris, as occurs in most of the Antarctic marine sediment. This shift provides further evidence of the anthropogenic changes to the benthic habitats of the Antarctic and will improve the interpretation of the sedimentary record in Polar Regions where these events occur.

  3. Evidence against a late Wisconsinan ice shelf in the Gulf of Maine

    USGS Publications Warehouse

    Oldale, R.N.; Williams, R.S.; Colman, Steven M.

    1990-01-01

    Proposals for the formation of a late Wisconsinan ice shelf in the Gulf of Maine during the retreat of the Laurentide Ice Sheet are considered to be inappropriate. An Antarctic-type ice shelf does not fit the field data that indicate temperate glacial, terrestrial, and marine climates for the region between 18 ka and 12 ka. A temperate ice shelf has no modern analogues and may be physically impossible. The preponderance of stratified drift in the Gulf of Maine region supports temperate climates during late Wisconsinan time. It also indicates that glacial meltwater, rather than ice in either an ice sheet or ice shelf, was the primary transport mechanism of glacial sediment and the source for the glaciomarine mud. For these reasons we have proposed glacial analogues for the deglaciation of the Gulf of Maine that consist of temperate or subpolar marine-based glaciers, characterized by depositional environments dominated by meltwater discharge directly to the sea or the sea by way of subaerial meltwater streams. These analogues include Alaskan fjord glaciers, glaciers on the Alaskan continental shelf that discharged meltwater directly into the sea in the not too distant past, and Austfonna (Nordaustandet, Svalbard, Norway) that is presently discharging meltwater in the sea along a grounded ice wall. This last example is the best modern-day analogue for the depositional environment for most of the glaciomarine mud in the Gulf of Maine and deglaciation of the Gulf. 

  4. Morphology and stratal geometry of the Antarctic continental shelf: Insights from models

    USGS Publications Warehouse

    Cooper, Alan K.; Barker, Peter F.; Brancolini, Giuliano

    1997-01-01

    Reconstruction of past ice-sheet fluctuations from the stratigraphy of glaciated continental shelves requires understanding of the relationships among the stratal geometry, glacial and marine sedimentary processes, and ice dynamics. We investigate the formation of the morphology and the broad stratal geometry of topsets on the Antarctic continental shelf with numerical models. Our models assume that the stratal geometry and morphology are principally the results of time-integrated effects of glacial erosion and sedimentation related to the location of the seaward edge of the grounded ice. The location of the grounding line varies with time almost randomly across the shelf. With these simple assumptions, the models can successfully mimic salient features of the morphology and the stratal geometry. The models suggest that the current shelf has gradually evolved to its present geometry by many glacial advances and retreats of the grounding line to different locations across the shelf. The locations of the grounding line do not appear to be linearly correlated with either fluctuations in the 5 l s O record (which presumably represents changes in the global ice volume) or with the global sea-level curve, suggesting that either a more complex relationship exists or local effects dominate. The models suggest that erosion of preglacial sediments is confined to the inner shelf, and erosion decreases and deposition increases toward the shelf edge. Some of the deposited glacial sediments must be derived from continental erosion. The sediments probably undergo extensive transport and reworking obliterating much of the evidence for their original depositional environment. The flexural rigidity and the tectonic subsidence of the underlying lithosphere modify the bathymetry of the shelf, but probably have little effect on the stratal geometry. Our models provide several guidelines for the interpretation of unconformities, the nature of preserved topset deposits, and the

  5. Accelerating ice loss from the fastest Greenland and Antarctic glaciers

    NASA Astrophysics Data System (ADS)

    Thomas, R.; Frederick, E.; Li, J.; Krabill, W.; Manizade, S.; Paden, J.; Sonntag, J.; Swift, R.; Yungel, J.

    2011-05-01

    Ice discharge from the fastest glaciers draining the Greenland and Antarctic ice sheets - Jakobshavn Isbrae (JI) and Pine Island Glacier (PIG)- continues to increase, and is now more than double that needed to balance snowfall in their catchment basins. Velocity increase probably resulted from decreased buttressing from thinning (and, for JI, breakup) of their floating ice tongues, and from reduced basal drag as grounding lines on both glaciers retreat. JI flows directly into the ocean as it becomes afloat, and here creep rates are proportional to the cube of bed depth. Rapid thinning of the PIG ice shelf increases the likelihood of its breakup, and subsequent rapid increase in discharge velocity. Results from a simple model indicate that JI velocities should almost double to >20 km a-1 by 2015, with velocities on PIG increasing to >10 km a-1 after breakup of its ice shelf. These high velocities would probably be sustained over many decades as the glaciers retreat within their long, very deep troughs. Resulting sea-level rise would average about 1.5 mm a-1.

  6. Accelerating Ice Loss from the Fastest Greenland and Antarctic Glaciers

    NASA Technical Reports Server (NTRS)

    Thomas, R.; Frederick, E.; Li, J.; Krabill, W.; Manizade, S.; Paden, J.; Sonntag, J.; Swift, R.; Yungel, J.

    2011-01-01

    Ice discharge from the fastest glaciers draining the Greenland and Antarctic ice sheets . Jakobshavn Isbrae (JI) and Pine Island Glacier (PIG). continues to increase, and is now more than double that needed to balance snowfall in their catchment basins. Velocity increase probably resulted from decreased buttressing from thinning (and, for JI, breakup) of their floating ice tongues, and from reduced basal drag as grounding lines on both glaciers retreat. JI flows directly into the ocean as it becomes afloat, and here creep rates are proportional to the cube of bed depth. Rapid thinning of the PIG ice shelf increases the likelihood of its breakup, and subsequent rapid increase in discharge velocity. Results from a simple model indicate that JI velocities should almost double to >20 km/a by 2015, with velocities on PIG increasing to >10 km/a after breakup of its ice shelf. These high velocities would probably be sustained over many decades as the glaciers retreat within their long, very deep troughs. Resulting sea ]level rise would average about 1.5 mm/a.

  7. Interannual Variability in Amundsen Sea Ice-Shelf Height Change Linked to ENSO

    NASA Astrophysics Data System (ADS)

    Paolo, F. S.; Fricker, H. A.; Padman, L.

    2015-12-01

    Atmospheric and sea-ice conditions around Antarctica, particularly in the Amundsen and Bellingshausen seas, respond to climate dynamics in the tropical Pacific Ocean on interannual time scales including the El Nino-Southern Oscillation (ENSO). It has been hypothesized that the mass balance of the Antarctic Ice Sheet, including its floating ice shelves, also responds to this climate signal; however, this has not yet been unambiguously demonstrated. We apply multivariate singular spectrum analysis (MSSA) to our 18-year (1994-2012) time series of ice-shelf height in the Amundsen Sea (AS) region. This advanced spectral method distinguishes between regular deterministic behavior ("cycles") at sub-decadal time scale and irregular behavior ("noise") at shorter time scales. Although the long-term trends of AS ice-shelf height changes are much larger than the range of interannual variability, the short-term rate of change dh/dt can vary about the trend by more than 50%. The mode of interannual variability in the AS ice-shelf height is strongly correlated with the low-frequency mode of ENSO (periodicity of ~4.5 years) as represented by the Southern Oscillation Index. The ice-shelf height in the AS is expected to respond to changes in precipitation and inflows of warm subsurface Circumpolar Deep Water (CDW) into the ocean cavities under the ice shelves, altering basal melt rates. Since both of these processes affecting ice-shelf mass balance respond to changes in wind fields for different ENSO states, we expect some correlation between them. We will describe the spatial structure of AS ice-shelf height response to ENSO, and attempt to distinguish the precipitation signal from basal mass balance due to changing CDW inflows.

  8. Cenozoic ice sheet history from East Antarctic Wilkes Land continental margin sediments

    USGS Publications Warehouse

    Escutia, C.; De Santis, L.; Donda, F.; Dunbar, R.B.; Cooper, A. K.; Brancolini, Giuliano; Eittreim, S.L.

    2005-01-01

    The long-term history of glaciation along the East Antarctic Wilkes Land margin, from the time of the first arrival of the ice sheet to the margin, through the significant periods of Cenozoic climate change is inferred using an integrated geophysical and geological approach. We postulate that the first arrival of the ice sheet to the Wilkes Land margin resulted in the development of a large unconformity (WL-U3) between 33.42 and 30 Ma during the early Oligocene cooling climate trend. Above WL-U3, substantial margin progradation takes place with early glacial strata (e.g., outwash deposits) deposited as low-angle prograding foresets by temperate glaciers. The change in geometry of the prograding wedge across unconformity WL-U8 is interpreted to represent the transition, at the end of the middle Miocene "climatic optimum" (14-10 Ma), from a subpolar regime with dynamic ice sheets (i.e., ice sheets come and go) to a regime with persistent but oscillatory ice sheets. The steep foresets above WL-U8 likely consist of ice proximal sediments (i.e., water-lain till and debris flows) deposited when grounded ice-sheets extended into the shelf. On the continental rise, shelf progradation above WL-U3 results in an up-section increase in the energy of the depositional environment (i.e., seismic facies indicative of more proximal turbidite and of bottom contour current deposition from the deposition of the lower WL-S5 sequence to WL-S7). Maximum rates of sediment delivery to the rise occur during the development of sequences WL-S6 and WL-S7, which we infer to be of middle Miocene age. During deposition of the two uppermost sequences, WL-S8 and WL-S9, there is a marked decrease in the sediment supply to the lower continental rise and a shift in the depocenters to more proximal areas of the margin. We believe WL-S8 records sedimentation during the final transition from a dynamic to a persistent but oscillatory ice sheet in this margin (14-10 Ma). Sequence WL-S9 forms under a polar

  9. A Self-Organizing Map Based Evaluation of the Antarctic Mesoscale Prediction System Using Observations from a 30-m Instrumented Tower on the Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Nigro, M. A.; Cassano, J. J.; Wille, J.; Bromwich, D. H.; Lazzara, M. A.

    2015-12-01

    An accurate representation of the atmospheric boundary layer in numerical weather prediction models is important for predicting turbulence and energy exchange in the atmosphere. This study uses two years of observations from a 30-m automatic weather station (AWS) installed on the Ross Ice Shelf, Antarctica to evaluate forecasts from the Antarctic Mesoscale Prediction System (AMPS), a numerical weather prediction system based on the polar version of the Weather Research and Forecasting (Polar WRF) model that uses the MYJ planetary boundary layer scheme and that primarily supports the extensive aircraft operations of the U.S. Antarctic Program. The 30-m AWS has six levels of instrumentation, providing vertical profiles of temperature, wind speed, and wind direction. The observations show the atmospheric boundary layer over the Ross Ice Shelf is stable approximately 80% of the time, indicating the influence of the permanent ice surface in this region. The observations from the AWS are further analyzed using the method of self-organizing maps (SOM) to identify the range of potential temperature profiles that occur over the Ross Ice Shelf. The SOM analysis identified 30 patterns, which range from strong inversions to slightly unstable profiles. The corresponding AMPS forecasts were evaluated for each of the 30 patterns to understand the accuracy of the AMPS near surface layer under different atmospheric conditions. The results indicate that under stable conditions AMPS with MYJ under predicts the inversion strength by as much as 7.4 K over the 30-m depth of the tower and over predicts the near surface wind speed by as much as 3.8 m s-1. Conversely, under slightly unstable conditions, AMPS predicts both the inversion strength and near surface wind speeds with reasonable accuracy.

  10. Ice Front at Venable Ice Shelf

    NASA Image and Video Library

    2013-06-13

    This photo, taken onboard the Chilean Navy P3 aircraft, shows the ice front of Venable Ice Shelf, West Antarctica, in October 2008. It is an example of a small-size ice shelf that is a large melt water producer.

  11. Amery Ice Shelf's 'Loose Tooth' Gets Looser

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Amery Ice Shelf is an important dynamic system responsible for draining about 16% of the grounded East Antarctic ice sheet through only 2% of its coastline. Most of the mass input to the system occurs from the Lambert and several other glaciers. Mass loss from the system occurs through basal melting and iceberg calving. These images from the Multi-angle Imaging SpectroRadiometer (MISR) portray the ice shelf front on October 6, 2001 (top) and September 29, 2002 (bottom), and illustrate changes that took place over the year elapsed between the two views.

    Two longitudinal rifts, oriented roughly parallel to the direction of ice flow and measuring about 25 and 15 kilometers in length, are apparent near the seaward edge of the ice shelf. Between them, a transverse fracture extends eastward from the base of the western rift. This rift system is colloquially named the Amery 'loose tooth.' Over the course of the one-year interval between these two MISR images, the ice front has advanced approximately 1.6 - 1.7 kilometers, and the transverse fracture and a three-way fissure at the juncture of the rifts have widened. When the transverse fracture eventually reaches the eastern rift, a large iceberg (25 kilometers x 25 kilometers) will be released.

    These false-color multi-angle composites combine red-band data from MISR's 60o forward, nadir, and 60o aftward viewing cameras, displayed as red, green and blue, respectively. Different colors represent angular reflectance variations. Since generally smooth surfaces predominantly forward-scatter sunlight, these appear in shades of blue. Rough surfaces tend to backward-scatter sunlight, and these appear in shades of red or orange. Low clouds appear bright purple, since they exhibit both forward and backward-scattering. Using this technique, textural variations among ice types are revealed, and clouds can be easily distinguished from ice. Illumination conditions on the two dates are nearly identical.

    Understanding the

  12. The evolution of a coupled ice shelf-ocean system under different climate states

    NASA Astrophysics Data System (ADS)

    Grosfeld, Klaus; Sandhäger, Henner

    2004-07-01

    Based on a new approach for coupled applications of an ice shelf model and an ocean general circulation model, we investigate the evolution of an ice shelf-ocean system and its sensitivity to changed climatic boundary conditions. Combining established 3D models into a coupled model system enabled us to study the reaction and feedbacks of each component to changes at their interface, the ice shelf base. After calculating the dynamics for prescribed initial ice shelf and bathymetric geometries, the basal mass balance determines the system evolution. In order to explore possible developments for given boundary conditions, an idealized geometry has been chosen, reflecting basic features of the Filchner-Ronne Ice Shelf, Antarctica. The model system is found to be especially sensitive in regions where high ablation or accretion rates occur. Ice Shelf Water formation as well as the build up of a marine ice body, resulting from accretion of marine ice, is simulated, indicating strong interaction processes. To improve consistency between modeled and observed ice shelf behavior, we incorporate the typical cycle of steady ice front advance and sudden retreat due to tabular iceberg calving in our time-dependent simulations. Our basic hypothesis is that iceberg break off is associated with abrupt crack propagation along elongated anomalies of the inherent stress field of the ice body. This new concept yields glaciologically plausible results and represents an auspicious basis for the development of a thorough calving criterion. Experiments under different climatic conditions (ocean warming of 0.2 and 0.5 °C and doubled surface accumulation rates) show the coupled model system to be sensitive especially to ocean warming. Increased basal melt rates of 100% for the 0.5 °C ocean warming scenario and an asymmetric development of ice shelf thicknesses suggest a high vulnerability of ice shelf regions, which represent pivotal areas between the Antarctic Ice Sheet and the Southern

  13. Thickening and Thinning of Antarctic Ice Shelves and Tongues and Mass Balance Estimates

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Li, Jun; Giovinetto, Mario; Robbins, John; Saba, Jack L.; Yi, Donghui

    2011-01-01

    Previous analysis of elevation changes for 1992 to 2002 obtained from measurements by radar altimeters on ERS-l and 2 showed that the shelves in the Antarctic Peninsula (AP) and along the coast of West Antarctica (WA), including the eastern part of the Ross Ice Shelf, were mostly thinning and losing mass whereas the Ronne Ice shelf also in WA was mostly thickening. The estimated total mass loss for the floating ice shelves and ice tongues from ice draining WA and the AP was 95 Gt/a. In contrast, the floating ice shelves and ice tongues from ice draining East Antarctica (EA), including the Filchner, Fimbul, Amery, and Western Ross, were mostly thickening with a total estimated mass gain of 142 Gt/a. Data from ICESat laser altimetry for 2003-2008 gives new surface elevation changes (dH/dt) with some similar values for the earlier and latter periods, including -27.6 and -26.9 cm a-Ion the West Getz ice shelf and -42.4 and - 27.2 cm/a on the East Getz ice shelf, and some values that indicate more thinning in the latter period, including -17.9 and -36.2 cm/a on the Larsen C ice shelf, -35.5 and -76.0 cm/a on the Pine Island Glacier floating, -60.5 and -125.7 .cm/a on the Smith Glacier floating, and -34.4 and -108.9 cm/a on the Thwaites Glacier floating. Maps of measured dH/dt and estimated thickness change are produced along with mass change estimates for 2003 - 2008.

  14. Instability of the Antarctic Ross Sea Embayment as climate warms

    NASA Astrophysics Data System (ADS)

    Hughes, Terence; Zhao, Zihong; Hintz, Raymond; Fastook, James

    2017-06-01

    Collapse of the Antarctic Ice Sheet since the Last Glacial Maximum 18,000 years ago is most pronounced in the Ross Sea Embayment, which is partly ice-free during Antarctic summers, thereby breaching the O-ring of ice shelves and sea ice surrounding Antarctica that stabilizes the ice sheet. The O-ring may have vanished during Early Holocene (5000 to 3000 B.C.), Roman (1 to 400 A.D.), and Medieval (900 to 1300 A.D.) warm periods and reappeared during the Little Ice Age (1300 to 1900 A.D.). We postulate further collapse in the embayment during the post-1900 warming may be forestalled because East Antarctic outlet glaciers "nail" the Ross Ice Shelf to the Transantarctic Mountains so it can resist the push from West Antarctic ice streams. Our hypothesis is examined for Byrd Glacier and a static ice shelf using three modeling experiments having plastic, viscous, and viscoplastic solutions as more data and improved modeling became available. Observed crevasse patterns were not reproduced. A new research study is needed to model a dynamic Ross Ice Shelf with all its feeder ice streams, outlet glaciers, and ice calving dynamics in three dimensions over time to fully test our hypothesis. The required model must allow accelerated calving if further warming melts sea ice and discerps the ice shelf. Calving must then successively pull the outlet glacier "nails" so collapse of the marine West Antarctic Ice Sheet proceeds to completion.

  15. Ice Bridge Antarctic Sea Ice

    NASA Image and Video Library

    2009-10-21

    An iceberg is seen out the window of NASA's DC-8 research aircraft as it flies 2,000 feet above the Amundsen Sea in West Antarctica on Wednesday, Oct., 21, 2009. This was the fourth science flight of NASA’s Operation Ice Bridge airborne Earth science mission to study Antarctic ice sheets, sea ice, and ice shelves. Photo Credit: (NASA/Jane Peterson)

  16. Tidal Modulation of Ice-shelf Flow: a Viscous Model of the Ross Ice Shelf

    NASA Technical Reports Server (NTRS)

    Brunt, Kelly M.; MacAyeal, Douglas R.

    2014-01-01

    Three stations near the calving front of the Ross Ice Shelf, Antarctica, recorded GPS data through a full spring-neap tidal cycle in November 2005. The data revealed a diurnal horizontal motion that varied both along and transverse to the long-term average velocity direction, similar to tidal signals observed in other ice shelves and ice streams. Based on its periodicity, it was hypothesized that the signal represents a flow response of the Ross Ice Shelf to the diurnal tides of the Ross Sea. To assess the influence of the tide on the ice-shelf motion, two hypotheses were developed. The first addressed the direct response of the ice shelf to tidal forcing, such as forces due to sea-surface slopes or forces due to sub-ice-shelf currents. The second involved the indirect response of ice-shelf flow to the tidal signals observed in the ice streams that source the ice shelf. A finite-element model, based on viscous creep flow, was developed to test these hypotheses, but succeeded only in falsifying both hypotheses, i.e. showing that direct tidal effects produce too small a response, and indirect tidal effects produce a response that is not smooth in time. This nullification suggests that a combination of viscous and elastic deformation is required to explain the observations.

  17. Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the Last Glacial Termination.

    PubMed

    Fogwill, C J; Turney, C S M; Golledge, N R; Etheridge, D M; Rubino, M; Thornton, D P; Baker, A; Woodward, J; Winter, K; van Ommen, T D; Moy, A D; Curran, M A J; Davies, S M; Weber, M E; Bird, M I; Munksgaard, N C; Menviel, L; Rootes, C M; Ellis, B; Millman, H; Vohra, J; Rivera, A; Cooper, A

    2017-01-05

    Reconstructing the dynamic response of the Antarctic ice sheets to warming during the Last Glacial Termination (LGT; 18,000-11,650 yrs ago) allows us to disentangle ice-climate feedbacks that are key to improving future projections. Whilst the sequence of events during this period is reasonably well-known, relatively poor chronological control has precluded precise alignment of ice, atmospheric and marine records, making it difficult to assess relationships between Antarctic ice-sheet (AIS) dynamics, climate change and sea level. Here we present results from a highly-resolved 'horizontal ice core' from the Weddell Sea Embayment, which records millennial-scale AIS dynamics across this extensive region. Counterintuitively, we find AIS mass-loss across the full duration of the Antarctic Cold Reversal (ACR; 14,600-12,700 yrs ago), with stabilisation during the subsequent millennia of atmospheric warming. Earth-system and ice-sheet modelling suggests these contrasting trends were likely Antarctic-wide, sustained by feedbacks amplified by the delivery of Circumpolar Deep Water onto the continental shelf. Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections. With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise.

  18. Outlet Glacier-Ice Shelf-Ocean Interactions: Is the Tail Wagging the Dog?

    NASA Astrophysics Data System (ADS)

    Parizek, B. R.; Walker, R. T.; Rinehart, S. K.

    2009-12-01

    While the massive interior regions of the Antarctic and Greenland Ice Sheets are presently ``resting quietly", the lower elevations of many outlet glaciers are experiencing dramatic adjustments due to changes in ice dynamics and/or surface mass balance. Oceanic and/or atmospheric forcing in these marginal regions often leads to mass deficits for entire outlet basins. Therefore, coupling the wagging tail of ice-ocean interactions with the vast ice-sheet reservoirs is imperative for accurate assessments of future sea-level rise. To study ice-ocean dynamic processes, we couple an ocean-plume model that simulates ice-shelf basal melting rates based on temperature and salinity profiles combined with plume dynamics associated with the geometry of the ice-shelf cavity (following Jenkins, 1991 and Holland and Jenkins, 1999) with a two-dimensional, isothermal model of outlet glacier-ice shelf flow (as used in Alley et al., 2007; Walker et al., 2008; Parizek et al., in review). Depending on the assigned temperature and salinity profiles, the ocean model can simulate both water-mass end-members: either cold High Salinity Shelf Water (HSSW) or relatively warm Circumpolar Deep Water (CDW), as well as between-member conditions. Notably, the coupled system exhibits sensitivity to the initial conditions. In particular, melting concentrated near the grounding line has the greatest effect in forcing grounding-line retreat. Retreat is further enhanced by a positive feedback between the ocean and ice, as the focused melt near the grounding line leads to an increase in the local slope of the basal ice, thereby enhancing buoyancy-driven plume flow and subsequent melt rates.

  19. Sea-level response to abrupt ocean warming of Antarctic ice shelves

    NASA Astrophysics Data System (ADS)

    Pattyn, Frank

    2016-04-01

    Antarctica's contribution to global sea-level rise increases steadily. A fundamental question remains whether the ice discharge will lead to marine ice sheet instability (MISI) and collapse of certain sectors of the ice sheet or whether ice loss will increase linearly with the warming trends. Therefore, we employ a newly developed ice sheet model of the Antarctic ice sheet, called f.ETISh (fast Elementary Thermomechanical Ice Sheet model) to simulate ice sheet response to abrupt perturbations in ocean and atmospheric temperature. The f.ETISh model is a vertically integrated hybrid (SSA/SIA) ice sheet model including ice shelves. Although vertically integrated, thermomechanical coupling is ensured through a simplified representation of ice sheet thermodynamics based on an analytical solution of the vertical temperature profile, including strain heating and horizontal advection. The marine boundary is represented by a flux condition either coherent with power-law basal sliding (Pollard & Deconto (2012) based on Schoof (2007)) or according to Coulomb basal friction (Tsai et al., 2015), both taking into account ice-shelf buttressing. Model initialization is based on optimization of the basal friction field. Besides the traditional MISMIP tests, new tests with respect to MISI in plan-view models have been devised. The model is forced with stepwise ocean and atmosphere temperature perturbations. The former is based on a parametrised sub-shelf melt (limited to ice shelves), while the latter is based on present-day mass balance/surface temperature and corrected for elevation changes. Surface melting is introduced using a PDD model. Results show a general linear response in mass loss to ocean warming. Nonlinear response due to MISI occurs under specific conditions and is highly sensitive to the basal conditions near the grounding line, governed by both the initial conditions and the basal sliding/deformation model. The Coulomb friction model leads to significantly higher

  20. NASA MISR Tracks Growth of Rift in the Larsen C Ice Shelf

    NASA Image and Video Library

    2017-04-11

    A rift in Antarctica's Larsen C ice shelf has grown to 110 miles (175 km) long, making it inevitable that an iceberg larger than Rhode Island will soon calve from the ice shelf. Larsen C is the fourth largest ice shelf in Antarctica, with an area of almost 20,000 square miles (50,000 square kilometers). The calving event will remove approximately 10 percent of the ice shelf's mass, according to the Project for Impact of Melt on Ice Shelf Dynamics and Stability (MIDAS), a UK-based team studying the ice shelf. Only 12 miles (20 km) of ice now separates the end of the rift from the ocean. The rift has grown at least 30 miles (50 km) in length since August, but appears to be slowing recently as Antarctica returns to polar winter. Project MIDAS reports that the calving event might destabilize the ice shelf, which could result in a collapse similar to what occurred to the Larsen B ice shelf in 2002. The Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard NASA's Terra satellite captured views of Larsen C on August 22, 2016, when the rift was 80 miles (130 km) in length; December 8, 2016, when the rift was approximately 90 miles (145 km) long; and April 6, 2017. The MISR instrument has nine cameras, which view the Earth at different angles. The overview image, from December 8, shows the entire Antarctic Peninsula -- home to Larsen A, B, and C ice shelves -- in natural color (similar to how it would appear to the human eye) from MISR's vertical-viewing camera. Combining information from several MISR cameras pointed at different angles gives information about the texture of the ice. The accompanying GIF depicts the inset area shown on the larger image and displays data from all three dates in false color. These multiangular views -- composited from MISR's 46-degree backward-pointing camera, the nadir (vertical-viewing) camera, and the 46-degree forward-pointing camera -- represent variations in ice texture as changes in color, such that areas of rough ice appear

  1. Abbot Ice Shelf, the Amundsen Sea Continental Margin and the Southern Boundary of the Bellingshausen Plate Seaward of West Antarctica

    NASA Astrophysics Data System (ADS)

    Cochran, J. R.; Tinto, K. J.; Bell, R. E.

    2014-12-01

    The Abbot Ice Shelf extends 450 km along the coast of West Antarctica between 103°W and 89°W and straddles the boundary between the Bellingshausen Sea continental margin, which overlies a former subduction zone, and Amundsen Sea rifted continental margin. Inversion of NASA Operation IceBridge airborne gravity data for sub-ice bathymetry shows that the western part of the ice shelf, as well as Cosgrove Ice Shelf to the south, are underlain by a series of east-west trending rift basins. The eastern boundary of the rifted terrain coincides with the eastern boundary of rifting between Antarctica and Zealandia and the rifts formed during the early stages of this rifting. Extension in these rifts is minor as rifting quickly jumped north of Thurston Island. The southern boundary of the Cosgrove Rift is aligned with the southern boundary of a sedimentary basin under the Amundsen Embayment continental shelf to the west, also formed by Antarctica-Zealandia rifting. The shelf basin has an extension factor, β, of 1.5 - 1.7 with 80 -100 km of extension occurring in an area now ~250 km wide. Following this extension early in the rifting process, rifting centered to the north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf has been tectonically quiescent and has primarily been shaped though subsidence, sedimentation and the passage of the West Antarctic Ice Sheet back and forth across it. The former Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to its incorporation into the Antarctic Plate at ~62 Ma. During the latter part of its existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence between the Bellingshausen and Antarctic plates east of 102°W. Seismic reflection and gravity data show that this convergence is expressed by an area of intensely deformed sediments beneath the continental slope from 102°W to 95°W and

  2. Multi-Decadal Averages of Basal Melt for Ross Ice Shelf, Antarctica Using Airborne Observations

    NASA Astrophysics Data System (ADS)

    Das, I.; Bell, R. E.; Tinto, K. J.; Frearson, N.; Kingslake, J.; Padman, L.; Siddoway, C. S.; Fricker, H. A.

    2017-12-01

    Changes in ice shelf mass balance are key to the long term stability of the Antarctic Ice Sheet. Although the most extensive ice shelf mass loss currently is occurring in the Amundsen Sea sector of West Antarctica, many other ice shelves experience changes in thickness on time scales from annual to ice age cycles. Here, we focus on the Ross Ice Shelf. An 18-year record (1994-2012) of satellite radar altimetry shows substantial variability in Ross Ice Shelf height on interannual time scales, complicating detection of potential long-term climate-change signals in the mass budget of this ice shelf. Variability of radar signal penetration into the ice-shelf surface snow and firn layers further complicates assessment of mass changes. We investigate Ross Ice Shelf mass balance using aerogeophysical data from the ROSETTA-Ice surveys using IcePod. We use two ice-penetrating radars; a 2 GHz unit that images fine-structure in the upper 400 m of the ice surface and a 360 MHz radar to identify the ice shelf base. We have identified internal layers that are continuous along flow from the grounding line to the ice shelf front. Based on layer continuity, we conclude that these layers must be the horizons between the continental ice of the outlet glaciers and snow accumulation once the ice is afloat. We use the Lagrangian change in thickness of these layers, after correcting for strain rates derived using modern day InSAR velocities, to estimate multidecadal averaged basal melt rates. This method provides a novel way to quantify basal melt, avoiding the confounding impacts of spatial and short-timescale variability in surface accumulation and firn densification processes. Our estimates show elevated basal melt rates (> -1m/yr) around Byrd and Mullock glaciers within 100 km from the ice shelf front. We also compare modern InSAR velocity derived strain rates with estimates from the comprehensive ground-based RIGGS observations during 1973-1978 to estimate the potential magnitude of

  3. The frequency response of a coupled ice sheet-ice shelf-ocean system to climate forcing variability

    NASA Astrophysics Data System (ADS)

    Goldberg, D.; Snow, K.; Jordan, J. R.; Holland, P.; Arthern, R. J.

    2017-12-01

    Changes at the West Antarctic ice-ocean boundary in recent decades has triggered significant increases in the regions contribution to global sea-level rise, coincident with large scale, and in some cases potentially unstable, grounding line retreat. Much of the induced change is thought to be driven by fluctuations in the oceanic heat available at the ice-ocean boundary, transported on-shelf via warm Circumpolar Deep Water (CDW). However, the processes in which ocean heat drives ice-sheet loss remains poorly understood, with observational studies routinely hindered by the extreme environment notorious to the Antarctic region. In this study we apply a novel synchronous coupled ice-ocean model, developed within the MITgcm, and are thus able to provide detailed insight into the impacts of short time scale (interannual to decadal) climate variability and feedbacks within the ice-ocean system. Feedbacks and response are assessed in an idealised ice-sheet/ocean-cavity configuration in which the far field ocean condition is adjusted to emulate periodic climate variability patterns. We reveal a non-linear response of the ice-sheet to periodic variations in thermocline depth. These non-linearities illustrate the heightened sensitivity of fast flowing ice-shelves to periodic perturbations in heat fluxes occurring at interannual and decadal time scales. The results thus highlight how small perturbations in variable climate forcing, like that of ENSO, may trigger large changes in ice-sheet response.

  4. Latest Word on Retreat of the West Antarctic Ice Sheet

    NASA Technical Reports Server (NTRS)

    Bindschadler, R.

    2000-01-01

    The West Antarctic ice sheet during the Last Glacial Maximum (LGM) is estimated to have been three times its present volume and to have extended close to the edge of the continental shelf Holocene retreat of this ice sheet in the Ross Sea began between 11,000 and 12,000 years ago. This history implies an average contribution of this ice sheet to sea level of 0.9 mm/a. Evidence of dateable past grounding line positions in the Ross sector are broadly consistent with a linear retreat model. However, inferred rates of retreat for some of these grounding line positions are not consistent with a linear retreat model. More rapid retreat approximately 7600 years ago and possible near-stability in the Ross Sea sector at present suggest a slow rate of initial retreat followed by a more rapid-than-average retreat during the late Holocene, returning to a near-zero rate of retreat currently. This model is also consistent with the mid-Holocene high stand observations of eustatic sea level. Recent compilation of Antarctic bed elevations (BEDMAP) illustrates that the LGM and present grounding lines occur in the shallowest waters, further supporting the model of a middle phase of rapid retreat bracketed by an older and a more recent phase of modest retreat. Extension of these hypotheses into the future make subsequent behavior of the West Antarctic ice sheet more difficult to predict but suggest that if it loses its hold on the present shallow bed, the final retreat of the ice sheet could be very rapid.

  5. Uncertainty quantification of Antarctic contribution to sea-level rise using the fast Elementary Thermomechanical Ice Sheet (f.ETISh) model

    NASA Astrophysics Data System (ADS)

    Bulthuis, Kevin; Arnst, Maarten; Pattyn, Frank; Favier, Lionel

    2017-04-01

    Uncertainties in sea-level rise projections are mostly due to uncertainties in Antarctic ice-sheet predictions (IPCC AR5 report, 2013), because key parameters related to the current state of the Antarctic ice sheet (e.g. sub-ice-shelf melting) and future climate forcing are poorly constrained. Here, we propose to improve the predictions of Antarctic ice-sheet behaviour using new uncertainty quantification methods. As opposed to ensemble modelling (Bindschadler et al., 2013) which provides a rather limited view on input and output dispersion, new stochastic methods (Le Maître and Knio, 2010) can provide deeper insight into the impact of uncertainties on complex system behaviour. Such stochastic methods usually begin with deducing a probabilistic description of input parameter uncertainties from the available data. Then, the impact of these input parameter uncertainties on output quantities is assessed by estimating the probability distribution of the outputs by means of uncertainty propagation methods such as Monte Carlo methods or stochastic expansion methods. The use of such uncertainty propagation methods in glaciology may be computationally costly because of the high computational complexity of ice-sheet models. This challenge emphasises the importance of developing reliable and computationally efficient ice-sheet models such as the f.ETISh ice-sheet model (Pattyn, 2015), a new fast thermomechanical coupled ice sheet/ice shelf model capable of handling complex and critical processes such as the marine ice-sheet instability mechanism. Here, we apply these methods to investigate the role of uncertainties in sub-ice-shelf melting, calving rates and climate projections in assessing Antarctic contribution to sea-level rise for the next centuries using the f.ETISh model. We detail the methods and show results that provide nominal values and uncertainty bounds for future sea-level rise as a reflection of the impact of the input parameter uncertainties under

  6. On thin ice/in hot water: Rapid drawdown of Wordie Ice Shelf glaciers in the decades after collapse in response to a changing ocean

    NASA Astrophysics Data System (ADS)

    Walker, C. C.; Gardner, A. S.

    2016-12-01

    Over the past 50 years, several Antarctic Peninsula ice shelves have retreated or collapsed completely. One such collapse was the Wordie Ice Shelf (WIS), located in Marguerite Bay, which began to disintegrate around 1989. We use several observational datasets to show that the glaciers that used to maintain WIS have experienced a surprising acceleration in flow ( 500m/yr) that began 2008, nearly 20 years after the onset of WIS collapse. During the same period, airborne altimetry from NASA Operation IceBridge shows the glaciers experienced a drawdown at their calving fronts between 4 and 9 m/yr, a near-doubling in rate of elevation change from the 1990's and early-2000's. The time lag between WIS collapse and rapid glacier drawdown suggests that these recent changes are unrelated to loss of buttressing. We identify possible links to changes in ocean conditions using in-situ Palmer Station Long-Term Ecological Research (PAL LTER) ocean CTD-gridded observations (Martinson et al., 2008) taken along the continental shelf on the west Antarctic Peninsula (WAP) since 1993. We use ECCO2 simulations and atmospheric reanalysis data to characterize changes in atmospheric forcing. We also measure changes in ice shelf area using historic archives and Landsat imagery for 50 glacier systems along the WAP from 1945 to present. Surface structural changes in the WIS system, e.g., melt ponds, sea/fast ice presence, and crevasse density/orientation, are also examined. We conclude that recent changes in WIS tributaries likely resulted from a significant increase in upwelling of warm, salty Upper Circumpolar Deep Water (UCDW) due to enhanced wind forcing following coincident global atmospheric oscillation events, namely a positive Southern Annular Mode and a moderate La Nina event. This enabled enhanced incursions of UCDW into Marguerite Bay between 2008-2014, in part due to the deep Marguerite Trough that connects the bay to the continental shelf break, along which the southern boundary

  7. Ice in Channels and Ice-Rock Mixtures in Valleys on Mars: Did They Slide on Deformable Rubble Like Antarctic Ice Streams?

    NASA Technical Reports Server (NTRS)

    Lucchitta, B. K.

    1997-01-01

    Recent studies of ice streams in Antarctica reveal a mechanism of basal motion that may apply to channels and valleys on Mars. The mechanism is sliding of the ice on deformable water-saturated till under high pore pressures. It has been suggested by Lucchitta that ice was present in outflow channels on Mars and gave them their distinctive morphology. This ice may have slid like Antarctic ice streams but on rubbly weathering products rather than till. However, to generate water under high pore pressures, elevated heatflow is needed to melt the base of the ice. Either volcanism or higher heatflow more than 2 b.y. ago could have raised the basal temperature. Regarding valley networks, higher heatflow 3 b.y. ago could have allowed sliding of ice-saturated overburden at a few hundred meters depth. If the original, pristine valleys were somewhat deeper than they are now, they could have formed by the same mechanism. Recent sounding of the seafloor in front of the Ross Ice Shelf in Antarctica reveals large persistent patterns of longitudinal megaflutes and drumlinoid forms, which bear remarkable resemblance to longitudinal grooves and highly elongated streamlined islands found on the floors of martian outflow channels. The flutes are interpreted to have formed at the base of ice streams during the last glacial advance. Additional similarities of Antarctic ice streams with martian outflow channels are apparent. Antarctic ice streams are 30 to 80 km wide and hundreds of kilometers long. Martian outflow channels have similar dimensions. Ice stream beds are below sea level. Carr determined that most common floor elevations of martian outflow channels lie below martian datum, which may have been close to or below past martian sea levels. The Antarctic ice stream bed gradient is flat and locally may go uphill, and surface slopes are exceptionally. Martian channels also have floor gradients that are shallow or go uphill locally and have low surface gradients. The depth to the

  8. Examining Differences in Arctic and Antarctic Sea Ice Change

    NASA Astrophysics Data System (ADS)

    Nghiem, S. V.; Rigor, I. G.; Clemente-Colon, P.; Neumann, G.; Li, P.

    2015-12-01

    The paradox of the rapid reduction of Arctic sea ice versus the stability (or slight increase) of Antarctic sea ice remains a challenge in the cryospheric science research community. Here we start by reviewing a number of explanations that have been suggested by different researchers and authors. One suggestion is that stratospheric ozone depletion may affect atmospheric circulation and wind patterns such as the Southern Annular Mode, and thereby sustaining the Antarctic sea ice cover. The reduction of salinity and density in the near-surface layer may weaken the convective mixing of cold and warmer waters, and thus maintaining regions of no warming around the Antarctic. A decrease in sea ice growth may reduce salt rejection and upper-ocean density to enhance thermohalocline stratification, and thus supporting Antarctic sea ice production. Melt water from Antarctic ice shelves collects in a cool and fresh surface layer to shield the surface ocean from the warmer deeper waters, and thus leading to an expansion of Antarctic sea ice. Also, wind effects may positively contribute to Antarctic sea ice growth. Moreover, Antarctica lacks of additional heat sources such as warm river discharge to melt sea ice as opposed to the case in the Arctic. Despite of these suggested explanations, factors that can consistently and persistently maintains the stability of sea ice still need to be identified for the Antarctic, which are opposed to factors that help accelerate sea ice loss in the Arctic. In this respect, using decadal observations from multiple satellite datasets, we examine differences in sea ice properties and distributions, together with dynamic and thermodynamic processes and interactions with land, ocean, and atmosphere, causing differences in Arctic and Antarctic sea ice change to contribute to resolving the Arctic-Antarctic sea ice paradox.

  9. Modeling the growth and decay of the Antarctic Peninsula Ice Sheet

    NASA Astrophysics Data System (ADS)

    Payne, A. J.; Sugden, D. E.; Clapperton, C. M.

    1989-03-01

    A model of the growth and decay of the Antarctic Peninsula Ice Sheet during the last glacial/interglacial cycle is used to identify the main controls on ice sheet behavior. Using as input glaciological assumptions derived by W. F. Budd and I. N. Smith (1982, Annals of Glaciology3, 42-49), bedrock topography, isostatic compensation, and mass balance relationships, the model is driven by sea-level change over the last 40,000 yr in association with assumed changes in the rate of melting beneath ice shelves. An ice sheet dome over 3.5 km thick grows on the offshore shelf and straits west of the Antarctic Peninsula and reaches a maximum at 18,000 yr B.P. Collapse begins at 14,000 yr B.P. but becomes rapid and continuous after 10,000 yr B.P. The present stable ice cover is achieved at 6500 yr B.P. Ice growth and decay are characterized by thresholds which separate periods of steady state from periods of rapid transition; the thresholds usually relate to topography. Tests show that ice sheet behavior is most sensitive to sea-level change, basal marine melting, and accumulation and is less sensitive to isostasy, spatial variation in accumulation, calving rates, and ice flow parameterization. Tests of the model against field evidence show good agreement in places, as well as discrepancies which require further work.

  10. Morphological evidence and direct estimates of rapid melting beneath Totten Glacier Ice Shelf, East Antarctica

    NASA Astrophysics Data System (ADS)

    Greenbaum, Jamin; Schroeder, Dustin; Grima, Cyril; Habbal, Feras; Dow, Christine; Roberts, Jason; Gwyther, David; van Ommen, Tas; Siegert, Martin; Blankenship, Donald

    2017-04-01

    Shelf in West Antarctica and the Petermann Glacier Ice Shelf in Greenland have shown that basal terraces associated with large basal channels are an indication of rapidly melting ice shelves. In this context, these new results identify an East Antarctic example of rapid basal melting processes and demonstrate that airborne radar can be used to identify basal characteristics and processes relevant to ice shelf stability.

  11. Looking Into and Through the Ross Ice Shelf - ROSETTA-ICE

    NASA Astrophysics Data System (ADS)

    Bell, R. E.

    2015-12-01

    Our current understanding of the structure and stability of the Ross Ice Shelf is based on satellite studies of the ice surface and the 1970's RIGGS program. The study of the flowlines evident in the MODIS imagery combined with surface geophysics has revealed a complex history with ice streams Mercer, Whillans and Kamb changing velocity over the past 1000 years. Here, we present preliminary IcePod and IceBridge radar data acquired in December 2014 and November 2013 across the Ross Ice Shelf that show clearly, for the first time, the structure of the ice shelf and provide insights into ice-ocean interaction. The three major layers of the ice shelf are (1) the continental meteoric ice layer), ice formed on the grounded ice sheet that entered the ice shelf where ice streams and outlet glaciers crossed the grounding line (2) the locally accumulating meteoric ice layer, ice and snow that forms from snowfall on the floating ice shelf and (3) a basal marine ice layer. The locally accumulating meteoric ice layer contains well-defined internal layers that are generally parallel to the ice surface and thickens away from the grounding line and reaches a maximum thickness of 220m along the line crossing Roosevelt Island. The continental meteoric layer is located below a broad irregular internal reflector, and is characterized by irregular internal layers. These internal layers are often folded, likely a result of deformation as the ice flowed across the grounding line. The basal marine ice layer, up to 50m thick, is best resolved in locations where basal crevasses are present, and appears to thicken along the flow at rates of decimeters per year. Each individual flowband of the ice shelf contains layers that are distinct in their structure. For example, the thickness of the locally accumulated layer is a function of both the time since crossing the grounding line and the thickness of the incoming ice. Features in the meteoric ice, such as distinct folds, can be traced between

  12. Calving fluxes and basal melt rates of Antarctic ice shelves.

    PubMed

    Depoorter, M A; Bamber, J L; Griggs, J A; Lenaerts, J T M; Ligtenberg, S R M; van den Broeke, M R; Moholdt, G

    2013-10-03

    Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000 gigatonnes per year. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front. So far, however, no study has reliably quantified the calving flux and the basal mass balance (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained. Here we estimate the mass balance components for all ice shelves in Antarctica, using satellite measurements of calving flux and grounding-line flux, modelled ice-shelf snow accumulation rates and a regional scaling that accounts for unsurveyed areas. We obtain a total calving flux of 1,321 ± 144 gigatonnes per year and a total basal mass balance of -1,454 ± 174 gigatonnes per year. This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves. We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering and enhanced discharge. We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing.

  13. The effect of basal channels on oceanic ice-shelf melting

    NASA Astrophysics Data System (ADS)

    Millgate, Thomas; Holland, Paul R.; Jenkins, Adrian; Johnson, Helen L.

    2013-12-01

    The presence of ice-shelf basal channels has been noted in a number of Antarctic and Greenland ice shelves, but their impact on basal melting is not fully understood. Here we use the Massachusetts Institute of Technology general circulation model to investigate the effect of ice-shelf basal channels on oceanic melt rate for an idealized ice shelf resembling the floating tongue of Petermann Glacier in Greenland. The introduction of basal channels prevents the formation of a single geostrophically balanced boundary current; instead the flow is diverted up the right-hand (Coriolis-favored) side of each channel, with a return flow in the opposite direction on the left-hand side. As the prescribed number of basal channels is increased the mean basal melt rate decreases, in agreement with previous studies. For a small number of relatively wide channels the subice flow is found to be a largely geostrophic horizontal circulation. The reduction in melt rate is then caused by an increase in the relative contribution of weakly melting channel crests and keels. For a larger number of relatively narrow channels, the subice flow changes to a vertical overturning circulation. This change in circulation results in a weaker sensitivity of melt rates to channel size. The transition between the two regimes is governed by the Rossby radius of deformation. Our results explain why basal channels play an important role in regulating basal melting, increasing the stability of ice shelves.

  14. Sea-level response to melting of Antarctic ice shelves on multi-centennial timescales with the fast Elementary Thermomechanical Ice Sheet model (f.ETISh v1.0)

    NASA Astrophysics Data System (ADS)

    Pattyn, Frank

    2017-08-01

    The magnitude of the Antarctic ice sheet's contribution to global sea-level rise is dominated by the potential of its marine sectors to become unstable and collapse as a response to ocean (and atmospheric) forcing. This paper presents Antarctic sea-level response to sudden atmospheric and oceanic forcings on multi-centennial timescales with the newly developed fast Elementary Thermomechanical Ice Sheet (f.ETISh) model. The f.ETISh model is a vertically integrated hybrid ice sheet-ice shelf model with vertically integrated thermomechanical coupling, making the model two-dimensional. Its marine boundary is represented by two different flux conditions, coherent with power-law basal sliding and Coulomb basal friction. The model has been compared to existing benchmarks. Modelled Antarctic ice sheet response to forcing is dominated by sub-ice shelf melt and the sensitivity is highly dependent on basal conditions at the grounding line. Coulomb friction in the grounding-line transition zone leads to significantly higher mass loss in both West and East Antarctica on centennial timescales, leading to 1.5 m sea-level rise after 500 years for a limited melt scenario of 10 m a-1 under freely floating ice shelves, up to 6 m for a 50 m a-1 scenario. The higher sensitivity is attributed to higher ice fluxes at the grounding line due to vanishing effective pressure. Removing the ice shelves altogether results in a disintegration of the West Antarctic ice sheet and (partially) marine basins in East Antarctica. After 500 years, this leads to a 5 m and a 16 m sea-level rise for the power-law basal sliding and Coulomb friction conditions at the grounding line, respectively. The latter value agrees with simulations by DeConto and Pollard (2016) over a similar period (but with different forcing and including processes of hydrofracturing and cliff failure). The chosen parametrizations make model results largely independent of spatial resolution so that f.ETISh can potentially be

  15. The effect of changing wind forcing on Antarctic ice shelf melting in high-resolution, global sea ice-ocean simulations with the Accelerated Climate Model for Energy (ACME)

    NASA Astrophysics Data System (ADS)

    Asay-Davis, Xylar; Price, Stephen; Petersen, Mark; Wolfe, Jonathan

    2017-04-01

    The capability for simulating sub-ice shelf circulation and submarine melting and freezing has recently been added to the U.S. Department of Energy's Accelerated Climate Model for Energy (ACME). With this new capability, we use an eddy permitting ocean model to conduct two sets of simulations in the spirit of Spence et al. (GRL, 41, 2014), who demonstrate increased warm water upwelling along the Antarctic coast in response to poleward shifting and strengthening of Southern Ocean westerly winds. These characteristics, symptomatic of a positive Southern Annular Mode (SAM), are projected to continue into the 21st century under anthropogenic climate change (Fyfe et al., J. Clim., 20, 2007). In our first simulation, we force the climate model using the standard CORE interannual forcing dataset (Large and Yeager; Clim. Dyn., 33, 2009). In our second simulation, we force our climate model using an altered version of CORE interannual forcing, based on the latter half of the full time series, which we take as a proxy for a future climate state biased towards a positive SAM. We compare ocean model states and sub-ice shelf melt rates with observations, exploring sources of model biases as well as the effects of the two forcing scenarios.

  16. Glider observations of the Dotson Ice Shelf outflow

    NASA Astrophysics Data System (ADS)

    Miles, Travis; Lee, Sang Hoon; Wåhlin, Anna; Ha, Ho Kyung; Kim, Tae Wan; Assmann, Karen M.; Schofield, Oscar

    2016-01-01

    The Amundsen Sea is one of the most productive polynyas in the Antarctic per unit area and is undergoing rapid changes including a reduction in sea ice duration, thinning ice sheets, retreat of glaciers and the potential collapse of the Thwaites Glacier in Pine Island Bay. A growing body of research has indicated that these changes are altering the water mass properties and associated biogeochemistry within the polynya. Unfortunately difficulties in accessing the remote location have greatly limited the amount of in situ data that has been collected. In this study data from a Teledyne-Webb Slocum glider was used to supplement ship-based sampling along the Dotson Ice Shelf (DIS). This autonomous underwater vehicle revealed a detailed view of a meltwater laden outflow from below the western flank of the DIS. Circumpolar Deep Water intruding onto the shelf drives glacial melt and the supply of macronutrients that, along with ample light, supports the large phytoplankton blooms in the Amundsen Sea Polynya. Less well understood is the source of micronutrients, such as iron, necessary to support this bloom to the central polynya where chlorophyll concentrations are highest. This outflow region showed decreasing optical backscatter with proximity to the bed indicating that particulate matter was sourced from the overlying glacier rather than resuspended sediment. This result suggests that particulate iron, and potentially phytoplankton primary productivity, is intrinsically linked to the magnitude and duration of sub-glacial melt from Circumpolar Deep Water intrusions onto the shelf.

  17. Is the Wilkins Ice Shelf a Firn Aquifer? Spaceborne Observation of Subsurface Winter Season Liquid Meltwater Storage on the Antarctic Peninsula using Multi-Frequency Active and Passive Microwave Remote Sensing

    NASA Astrophysics Data System (ADS)

    Miller, J.; Scambos, T.; Forster, R. R.; Long, D. G.; Ligtenberg, S.; van den Broeke, M.; Vaughan, D. G.

    2015-12-01

    Near-surface liquid meltwater on ice shelves has been inferred to influence ice shelf stability if it induces hydrofracture and is linked to disintegration events on the Larsen B and the Wilkins ice shelves on the Antarctic Peninsula during the summer months. While the initial Wilkins disintegration event occurred in March of 2009, two smaller disintegration events followed in May and in July of that year. It has long been assumed meltwater refreezes soon after surface melt processes cease. Given this assumption, an earlier hypothesis for the two winter season disintegration events was hydrofracture via a brine infiltration layer. Two lines of evidence supported this hypothesis 1) early airborne radar surveys did not record a reflection from the bottom of the ice shelf, and 2) a shallow core drilled in 1972 on the Wilkins encountered liquid water at a depth of ~7 m. The salinity of the water and the temperature at the base of the core, however, were not described. The recent discovery of winter season liquid meltwater storage on the Greenland ice sheet has changed perceptions on meltwater longevity at depth in firn. Evidence of Greenland's firn aquifer includes liquid meltwater encountered in shallow firn cores at 5 m depth and a lack of reflections from the base of the ice sheet in airborne surveys. Thus, previous lines of evidence suggesting brine infiltration may alternatively suggest the presence of a perennial firn aquifer. We recently demonstrated the capability for observation of Greenland's firn aquifer from space using multi-frequency active and passive microwave remote sensing. This research exploits the retrieval technique developed for Greenland to provide the first spaceborne mappings of winter season liquid meltwater storage on the Wilkins. We combine L-band brightness temperature and backscatter data from the MIRAS instrument (1.4 GHz) aboard ESA's Soil Moisture and Ocean Salinity mission and the radar (1.3 GHZ) and radiometer(1.4 GHz) aboard NASA

  18. Glacial removal of late Cenozoic subglacially emplaced volcanic edifices by the West Antarctic ice sheet

    USGS Publications Warehouse

    Behrendt, John C.; Blankenship, D.D.; Damaske, D.; Cooper, A. K.

    1995-01-01

    Local maxima of the horizontal gradient of pseudogravity from closely spaced aeromagnetic surveys over the Ross Sea, northwestern Ross Ice Shelf, and the West Antarctic ice sheet, reveal a linear magnetic rift fabric and numerous subcircular, high-amplitude anomalies. Geophysical data indicate two or three youthful volcanic edifices at widely separated areas beneath the sea and ice cover in the West Antarctic rift system. In contrast, we suggest glacial removal of edifices of volcanic sources of many more anomalies. Magnetic models, controlled by marine seismic reflection and radar ice-sounding data, allow us to infer that glacial removal of the associated late Cenozoic volcanic edifices (probably debris, comprising pillow breccias, and hyaloclastites) has occurred essentially concomitantly with their subglacial eruption. "Removal' of unconsolidated volcanic debris erupted beneath the ice is probably a more appropriate term than "erosion', given its fragmented, ice-contact origin. The exposed volcanoes may have been protected from erosion by the surrounding ice sheet because of more competent rock or high elevation above the ice sheet. -from Authors

  19. Coastal-change and glaciological map of the Amery Ice Shelf area, Antarctica: 1961–2004

    USGS Publications Warehouse

    Foley, Kevin M.; Ferrigno, Jane G.; Swithinbank, Charles; Williams, Richard S.; Orndorff, Audrey L.

    2013-01-01

    Reduction in the area and volume of Earth’s two polar ice sheets is intricately linked to changes in global climate and to the resulting rise in sea level. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council. On the basis of these recommendations, the U.S. Geological Survey used its archive of satellite images to document changes in the cryospheric coastline of Antarctica and analyze the glaciological features of the coastal regions. Amery Ice Shelf, lying between 67.5° and 75° East longitude and 68.5° and 73.2° South latitude, is the largest ice shelf in East Antarctica. The latest measurements of the area of the ice shelf range between 62,620 and 71,260 square kilometers. The ice shelf is fed primarily by Lambert, Mellor, and Fisher Glaciers; its thickness ranges from 3,000 meters in the center of the grounding line to less than 300 meters at the ice front. Lambert Glacier is considered to be the largest glacier in the world, and its drainage basin is more than 1 million square kilometers in area. It is possible to see some coastal change on the outlet glaciers along the coast, but most of the noticeable change occurs on the Amery Ice Shelf front.

  20. Twenty-three years of height changes on Antarctic Peninsula ice shelves

    NASA Astrophysics Data System (ADS)

    Adusumilli, S.; Siegfried, M. R.; Paolo, F. S.; Fricker, H. A.; Padman, L.

    2017-12-01

    Over the past few decades, several ice shelves in the Antarctic Peninsula (AP), the northernmost region of Antarctica, have collapsed or undergone significant retreat. While the disintegration of these ice shelves appears to be linked primarily to hydrofracture initiated by widespread surface melting, it has also been proposed that some of these ice shelves could have weakened prior to collapse due to increased basal melt rates induced by thermal ocean forcing. To determine the long-term evolution of ice shelves in this region, we compiled data from four radar altimeters (ERS-1, ERS-2, Envisat, and CryoSat-2) spanning twenty-three years (1994-2017). Over Larsen C, the largest AP ice shelf, a surface lowering of around 1 m between 1992 and 2009 has been partially offset by a height increase of around 0.75 m between 2009 and 2017. We use four independent, repeat airborne laser altimetry surveys from NASA's Operation IceBridge to confirm the recent height increase, and a firn densification model (IMAU-FDM) forced by a regional atmospheric model (RACMO), to show that the recent height increase is primarily due to density changes in the firn column. In contrast, George VI Ice Shelf in the Bellingshausen Sea remains in a state of continuous thinning through excess basal melting attributed to higher fluxes of ocean heat under the ice shelf. Changes such as these, which can occur on seasonal to decadal timescales, can potentially impact the dynamics of the grounded ice sheet behind the floating ice shelves, consequently affecting sea-level rise. Therefore, it is vital to continue the long-term, uninterrupted monitoring of ice shelves through the modern satellite and airborne altimetry missions, and lengthen our existing time series to investigate the climate drivers causing changes in the ice shelves from above (accumulation and density changes) and below (basal melting).

  1. Geostatistical Methods For Determination of Roughness, Topography, And Changes of Antarctic Ice Streams From SAR And Radar Altimeter Data

    NASA Technical Reports Server (NTRS)

    Herzfeld, Ute C.

    2002-01-01

    The central objective of this project has been the development of geostatistical methods fro mapping elevation and ice surface characteristics from satellite radar altimeter (RA) and Syntheitc Aperture Radar (SAR) data. The main results are an Atlas of elevation maps of Antarctica, from GEOSAT RA data and an Atlas from ERS-1 RA data, including a total of about 200 maps with 3 km grid resolution. Maps and digital terrain models are applied to monitor and study changes in Antarctic ice streams and glaciers, including Lambert Glacier/Amery Ice Shelf, Mertz and Ninnis Glaciers, Jutulstraumen Glacier, Fimbul Ice Shelf, Slessor Glacier, Williamson Glacier and others.

  2. Green icebergs formed by freezing of organic-rich seawater to the base of Antarctic ice shelves

    NASA Technical Reports Server (NTRS)

    Warren, Stephen G.; Roesler, Collin S.; Morgan, Vincent I.; Brandt, Richard E.; Goodwin, Ian D.; Allison, Ian

    1993-01-01

    Samples of Antarctic seawater, basal ice, and green ice from ice cliffs and green icebergs are analyzed in order to examine green icebergs formed by the freezing of organic-rich seawater to the base of Antarctic ice shelves. Spectral reflectance of a green iceberg measured near 67 deg S, 62 deg E confirms that the color is inherent in the ice, not an artifact of the illumination. A constituent that absorbs blue photons is identified by spectrophotometric analysis of core samples from this iceberg and from the Amery basal ice, and of seawater samples from Prydz Bay off the Amery Ice Shelf. Analysis of the samples by fluorescence spectroscopy indicates that the blue absorption, and hence the inherent green color, is due to the presence of marine-derived organic matter in the green iceberg, basal ice, and seawater. Thick accumulations of green ice, in icebergs, and at the base of ice shelves indicate that high concentrations of organic matter exist in seawater for centuries at the depth of basal freezing.

  3. Larsen B Ice Shelf

    Atmospheric Science Data Center

    2013-04-16

    article title:  Unique Views of a Shattered Ice Shelf     View Larger Image ... views of the breakup of the northern section of the Larsen B ice shelf are shown in this image pair from the Multi-angle Imaging ...

  4. Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets.

    PubMed

    Pritchard, Hamish D; Arthern, Robert J; Vaughan, David G; Edwards, Laura A

    2009-10-15

    Many glaciers along the margins of the Greenland and Antarctic ice sheets are accelerating and, for this reason, contribute increasingly to global sea-level rise. Globally, ice losses contribute approximately 1.8 mm yr(-1) (ref. 8), but this could increase if the retreat of ice shelves and tidewater glaciers further enhances the loss of grounded ice or initiates the large-scale collapse of vulnerable parts of the ice sheets. Ice loss as a result of accelerated flow, known as dynamic thinning, is so poorly understood that its potential contribution to sea level over the twenty-first century remains unpredictable. Thinning on the ice-sheet scale has been monitored by using repeat satellite altimetry observations to track small changes in surface elevation, but previous sensors could not resolve most fast-flowing coastal glaciers. Here we report the use of high-resolution ICESat (Ice, Cloud and land Elevation Satellite) laser altimetry to map change along the entire grounded margins of the Greenland and Antarctic ice sheets. To isolate the dynamic signal, we compare rates of elevation change from both fast-flowing and slow-flowing ice with those expected from surface mass-balance fluctuations. We find that dynamic thinning of glaciers now reaches all latitudes in Greenland, has intensified on key Antarctic grounding lines, has endured for decades after ice-shelf collapse, penetrates far into the interior of each ice sheet and is spreading as ice shelves thin by ocean-driven melt. In Greenland, glaciers flowing faster than 100 m yr(-1) thinned at an average rate of 0.84 m yr(-1), and in the Amundsen Sea embayment of Antarctica, thinning exceeded 9.0 m yr(-1) for some glaciers. Our results show that the most profound changes in the ice sheets currently result from glacier dynamics at ocean margins.

  5. Ocean-Forced Ice-Shelf Thinning in a Synchronously Coupled Ice-Ocean Model

    NASA Astrophysics Data System (ADS)

    Jordan, James R.; Holland, Paul R.; Goldberg, Dan; Snow, Kate; Arthern, Robert; Campin, Jean-Michel; Heimbach, Patrick; Jenkins, Adrian

    2018-02-01

    The first fully synchronous, coupled ice shelf-ocean model with a fixed grounding line and imposed upstream ice velocity has been developed using the MITgcm (Massachusetts Institute of Technology general circulation model). Unlike previous, asynchronous, approaches to coupled modeling our approach is fully conservative of heat, salt, and mass. Synchronous coupling is achieved by continuously updating the ice-shelf thickness on the ocean time step. By simulating an idealized, warm-water ice shelf we show how raising the pycnocline leads to a reduction in both ice-shelf mass and back stress, and hence buttressing. Coupled runs show the formation of a western boundary channel in the ice-shelf base due to increased melting on the western boundary due to Coriolis enhanced flow. Eastern boundary ice thickening is also observed. This is not the case when using a simple depth-dependent parameterized melt, as the ice shelf has relatively thinner sides and a thicker central "bulge" for a given ice-shelf mass. Ice-shelf geometry arising from the parameterized melt rate tends to underestimate backstress (and therefore buttressing) for a given ice-shelf mass due to a thinner ice shelf at the boundaries when compared to coupled model simulations.

  6. Ice Stream Slowdown Will Drive Long-Term Thinning of the Ross Ice Shelf, With or Without Ocean Warming

    NASA Astrophysics Data System (ADS)

    Campbell, Adam J.; Hulbe, Christina L.; Lee, Choon-Ki

    2018-01-01

    As time series observations of Antarctic change proliferate, it is imperative that mathematical frameworks through which they are understood keep pace. Here we present a new method of interpreting remotely sensed change using spatial statistics and apply it to the specific case of thickness change on the Ross Ice Shelf. First, a numerical model of ice shelf flow is used together with empirical orthogonal function analysis to generate characteristic patterns of response to specific forcings. Because they are continuous and scalable in space and time, the patterns allow short duration observations to be placed in a longer time series context. Second, focusing only on changes that are statistically significant, the synthetic response surfaces are used to extract magnitude and timing of past events from the observational data. Slowdown of Kamb and Whillans Ice Streams is clearly detectable in remotely sensed thickness change. Moreover, those past events will continue to drive thinning into the future.

  7. Effects of ice shelf basal melt variability on evolution of Thwaites Glacier

    NASA Astrophysics Data System (ADS)

    Hoffman, M. J.; Fyke, J. G.; Price, S. F.; Asay-Davis, X.; Perego, M.

    2017-12-01

    , it does not alter the eventual mass loss and sea level rise at centennial scales. The potential differences are significant enough to highlight the need for further observations to constrain the amplitude and period of the modes of climate and ocean variability relevant to Antarctic ice shelf melting.

  8. Advances in modelling subglacial lakes and their interaction with the Antarctic ice sheet.

    PubMed

    Pattyn, Frank; Carter, Sasha P; Thoma, Malte

    2016-01-28

    Subglacial lakes have long been considered hydraulically isolated water bodies underneath ice sheets. This view changed radically with the advent of repeat-pass satellite altimetry and the discovery of multiple lake discharges and water infill, associated with water transfer over distances of more than 200 km. The presence of subglacial lakes also influences ice dynamics, leading to glacier acceleration. Furthermore, subglacial melting under the Antarctic ice sheet is more widespread than previously thought, and subglacial melt rates may explain the availability for water storage in subglacial lakes and water transport. Modelling of subglacial water discharge in subglacial lakes essentially follows hydraulics of subglacial channels on a hard bed, where ice sheet surface slope is a major control on triggering subglacial lake discharge. Recent evidence also points to the development of channels in deformable sediment in West Antarctica, with significant water exchanges between till and ice. Most active lakes drain over short time scales and respond rapidly to upstream variations. Several Antarctic subglacial lakes exhibit complex interactions with the ice sheet due to water circulation. Subglacial lakes can therefore-from a modelling point of view-be seen as confined small oceans underneath an imbedded ice shelf. © 2015 The Author(s).

  9. Icebergs, sea ice, blue carbon and Antarctic climate feedbacks

    PubMed Central

    Fleming, Andrew; Sands, Chester J.; Quartino, Maria Liliana; Deregibus, Dolores

    2018-01-01

    Sea ice, including icebergs, has a complex relationship with the carbon held within animals (blue carbon) in the polar regions. Sea-ice losses around West Antarctica's continental shelf generate longer phytoplankton blooms but also make it a hotspot for coastal iceberg disturbance. This matters because in polar regions ice scour limits blue carbon storage ecosystem services, which work as a powerful negative feedback on climate change (less sea ice increases phytoplankton blooms, benthic growth, seabed carbon and sequestration). This resets benthic biota succession (maintaining regional biodiversity) and also fertilizes the ocean with nutrients, generating phytoplankton blooms, which cascade carbon capture into seabed storage and burial by benthos. Small icebergs scour coastal shallows, whereas giant icebergs ground deeper, offshore. Significant benthic communities establish where ice shelves have disintegrated (giant icebergs calving), and rapidly grow to accumulate blue carbon storage. When 5000 km2 giant icebergs calve, we estimate that they generate approximately 106 tonnes of immobilized zoobenthic carbon per year (t C yr−1). However, their collisions with the seabed crush and recycle vast benthic communities, costing an estimated 4 × 104 t C yr−1. We calculate that giant iceberg formation (ice shelf disintegration) has a net potential of approximately 106 t C yr−1 sequestration benefits as well as more widely known negative impacts. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’. PMID:29760118

  10. Icebergs, sea ice, blue carbon and Antarctic climate feedbacks.

    PubMed

    Barnes, David K A; Fleming, Andrew; Sands, Chester J; Quartino, Maria Liliana; Deregibus, Dolores

    2018-06-28

    Sea ice, including icebergs, has a complex relationship with the carbon held within animals (blue carbon) in the polar regions. Sea-ice losses around West Antarctica's continental shelf generate longer phytoplankton blooms but also make it a hotspot for coastal iceberg disturbance. This matters because in polar regions ice scour limits blue carbon storage ecosystem services, which work as a powerful negative feedback on climate change (less sea ice increases phytoplankton blooms, benthic growth, seabed carbon and sequestration). This resets benthic biota succession (maintaining regional biodiversity) and also fertilizes the ocean with nutrients, generating phytoplankton blooms, which cascade carbon capture into seabed storage and burial by benthos. Small icebergs scour coastal shallows, whereas giant icebergs ground deeper, offshore. Significant benthic communities establish where ice shelves have disintegrated (giant icebergs calving), and rapidly grow to accumulate blue carbon storage. When 5000 km 2 giant icebergs calve, we estimate that they generate approximately 10 6 tonnes of immobilized zoobenthic carbon per year (t C yr -1 ). However, their collisions with the seabed crush and recycle vast benthic communities, costing an estimated 4 × 10 4  t C yr -1 We calculate that giant iceberg formation (ice shelf disintegration) has a net potential of approximately 10 6  t C yr -1 sequestration benefits as well as more widely known negative impacts.This article is part of the theme issue 'The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change'. © 2018 The Authors.

  11. Direct evidence of warm water access to the Totten Glacier sub-ice shelf cavity

    NASA Astrophysics Data System (ADS)

    Orsi, A. H.; Rintoul, S. R.; Silvano, A.; van Wijk, E.; Pena-Molino, B.; Rosenberg, M. A.

    2015-12-01

    The Totten Glacier holds enough ice to raise global sea level by 3.5 m, is thinning according to (some) satellite data, and is grounded well below sea level on a retrograde bed and hence is potentially unstable. Basal melt driven by ocean heat flux has been linked to ice shelf thinning elsewhere in Antarctica, but no oceanographic measurements had been made near the Totten. In January 2015 the RSV Aurora Australis was the first ship to reach the Totten calving front. Observations from ship-board CTD, moorings and profiling floats provide direct confirmation that warm water reaches the ice shelf cavity. Warm water is present near the sea floor at every station deeper than 300 m depth, with maximum temperatures at mid-shelf >0.5°C. Mooring data confirm that the warm water is present year-round. A deep (>1100 m) channel at the calving front allows warm water (-0.4°C, >2°C above the local freezing point) to access the ice shelf cavity. The contrast between the oceanographic conditions near the Totten and near the Mertz Glacier is stark, although they are separated by only 30 degrees of longitude. East Antarctic ice shelves have often been assumed to behave in a similar manner and to be invulnerable to ocean change; these measurements suggest these assumptions need to be reconsidered.

  12. Marine pelagic ecosystems: the West Antarctic Peninsula

    PubMed Central

    Ducklow, Hugh W; Baker, Karen; Martinson, Douglas G; Quetin, Langdon B; Ross, Robin M; Smith, Raymond C; Stammerjohn, Sharon E; Vernet, Maria; Fraser, William

    2006-01-01

    The marine ecosystem of the West Antarctic Peninsula (WAP) extends from the Bellingshausen Sea to the northern tip of the peninsula and from the mostly glaciated coast across the continental shelf to the shelf break in the west. The glacially sculpted coastline along the peninsula is highly convoluted and characterized by deep embayments that are often interconnected by channels that facilitate transport of heat and nutrients into the shelf domain. The ecosystem is divided into three subregions, the continental slope, shelf and coastal regions, each with unique ocean dynamics, water mass and biological distributions. The WAP shelf lies within the Antarctic Sea Ice Zone (SIZ) and like other SIZs, the WAP system is very productive, supporting large stocks of marine mammals, birds and the Antarctic krill, Euphausia superba. Ecosystem dynamics is dominated by the seasonal and interannual variation in sea ice extent and retreat. The Antarctic Peninsula is one among the most rapidly warming regions on Earth, having experienced a 2°C increase in the annual mean temperature and a 6°C rise in the mean winter temperature since 1950. Delivery of heat from the Antarctic Circumpolar Current has increased significantly in the past decade, sufficient to drive to a 0.6°C warming of the upper 300 m of shelf water. In the past 50 years and continuing in the twenty-first century, the warm, moist maritime climate of the northern WAP has been migrating south, displacing the once dominant cold, dry continental Antarctic climate and causing multi-level responses in the marine ecosystem. Ecosystem responses to the regional warming include increased heat transport, decreased sea ice extent and duration, local declines in ice-dependent Adélie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition and changes in krill recruitment, abundance and availability to predators. The climate/ecological gradients

  13. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier [Sub-ice shelf sediments record 20 th century retreat history of Pine Island Glacier

    DOE PAGES

    Smith, J. A.; Andersen, T. J.; Shortt, M.; ...

    2016-11-23

    The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreatmore » is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Furthermore our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.« less

  14. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier [Sub-ice shelf sediments record 20 th century retreat history of Pine Island Glacier

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Smith, J. A.; Andersen, T. J.; Shortt, M.

    The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreatmore » is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Furthermore our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.« less

  15. Ice-Shelf Melt Response to Changing Winds and Glacier Dynamics in the Amundsen Sea Sector, Antarctica

    NASA Astrophysics Data System (ADS)

    Donat-Magnin, Marion; Jourdain, Nicolas C.; Spence, Paul; Le Sommer, Julien; Gallée, Hubert; Durand, Gaël.

    2017-12-01

    It has been suggested that the coastal Southern Ocean subsurface may warm over the 21st century in response to strengthening and poleward shifting winds, with potential adverse effects on West Antarctic glaciers. However, using a 1/12° ocean regional model that includes ice-shelf cavities, we find a more complex response to changing winds in the Amundsen Sea. Simulated offshore subsurface waters get colder under strengthened and poleward shifted winds representative of the SAM projected trend. The buoyancy-driven circulation induced by ice-shelf melt transports this cold offshore anomaly onto the continental shelf, leading to cooling and decreased melt below 450 m. In the vicinity of ice-shelf fronts, Ekman pumping contributes to raise the isotherms in response to changing winds. This effect overwhelms the horizontal transport of colder offshore waters at intermediate depths (between 200 and 450 m), and therefore increases melt rates in the upper part of the ice-shelf cavities, which reinforces the buoyancy-driven circulation and further contributes to raise the isotherms. Then, prescribing an extreme grounding line retreat projected for 2100, the total melt rates simulated underneath Thwaites and Pine Island are multiplied by 2.5. Such increase is explained by a larger ocean/ice interface exposed to CDW, which is then amplified by a stronger melt-induced circulation along the ice draft. Our main conclusions are that (1) outputs from ocean models that do not represent ice shelf cavities (e.g., CMIP5 models) should not be directly used to predict the thermal forcing of future ice shelf cavities; (2) coupled ocean/ice sheet models with a velocity-dependent melt formulation are needed for future projections of glaciers experiencing a significant grounding line retreat.

  16. Using Satellite-derived Ice Concentration to Represent Antarctic Coastal Polynyas in Ocean Climate Models

    NASA Technical Reports Server (NTRS)

    Stoessel, Achim; Markus, Thorsten

    2003-01-01

    The focus of this paper is on the representation of Antarctic coastal polynyas in global ice-ocean general circulation models (OGCMs), in particular their local, regional, and high-frequency behavior. This is verified with the aid of daily ice concentration derived from satellite passive microwave data using the NASATeam 2 (NT2) and the bootstrap (BS) algorithms. Large systematic regional and temporal discrepancies arise, some of which are related to the type of convection parameterization used in the model. An attempt is made to improve the fresh-water flux associated with melting and freezing in Antarctic coastal polynyas by ingesting (assimilating) satellite ice concentration where it comes to determining the thermodynamics of the open-water fraction of a model grid cell. Since the NT2 coastal open-water fraction (polynyas) tends to be less extensive than the simulated one in the decisive season and region, assimilating NT2 coastal ice concentration yields overall reduced net freezing rates, smaller formation rates of Antarctic Bottom Water, and a stronger southward flow of North Atlantic Deep Water across 30 S. Enhanced net freezing rates occur regionally when NT2 coastal ice concentration is assimilated, concomitant with a more realistic ice thickness distribution and accumulation of High-Salinity Shelf Water. Assimilating BS rather than NT2 coastal ice concentration, the differences to the non-assimilated simulation are generally smaller and of opposite sign. This suggests that the model reproduces coastal ice concentration in closer agreement with the BS data than with the NT2 data, while more realistic features emerge when NT2 data are assimilated.

  17. Sensitivity of Totten Glacier Ice Shelf extent and grounding line to oceanic forcing

    NASA Astrophysics Data System (ADS)

    Pelle, T.; Morlighem, M.; Choi, Y.

    2017-12-01

    Totten Glacier is a major outlet glacier of the East Antarctic Ice Sheet and has been shown to be vulnerable to ocean-induced melt in both its past and present states. The intrusion of warm, circumpolar deep water beneath the Totten Glacier Ice Shelf (TGIS) has been observed to accelerate ice shelf thinning and promote iceberg calving, a primary mechanism of mass discharge from Totten. As such, accurately simulating TGIS's ice front dynamics is crucial to the predictive capabilities of ice sheet models in this region. Here, we study the TGIS using the Ice Sheet System Model (ISSM) and test the applicability of three calving laws: Crevasse Formation calving, Eigen calving, and Tensile Stress calving. We simulate the evolution of Totten Glacier through 2100 under enhanced oceanic forcing in order to investigate both future changes in ice front dynamics and possible thresholds of instability. In addition, we artificially retreat Totten's ice front position and allow the model to proceed dynamically in order to analyze the response of the glacier to calving events. Our analyses show that Tensile Stress calving most accurately reproduces Totten Glacier's observed ice front position. Furthermore, unstable grounding line retreat is projected when Totten is simulated under stronger oceanic thermal forcing scenarios and when the calving front is significantly retreated.

  18. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica.

    PubMed

    Cochran, James R; Tinto, Kirsty J; Bell, Robin E

    2015-05-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, β , of 1.5-1.7 with 80-100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. Abbot Ice Shelf is underlain by E-W rift basins created at ∼90 Ma Amundsen shelf shaped by subsidence, sedimentation, and passage of the ice sheet Bellingshausen plate boundary is located near the base of continental slope and rise.

  19. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica

    PubMed Central

    Cochran, James R; Tinto, Kirsty J; Bell, Robin E

    2015-01-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, β, of 1.5–1.7 with 80–100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. Key Points: Abbot Ice Shelf is underlain by E-W rift basins created at ∼90 Ma Amundsen shelf shaped by subsidence, sedimentation, and passage of the ice sheet Bellingshausen plate boundary is located near the base of continental slope and rise PMID:26709352

  20. Polar zoobenthos blue carbon storage increases with sea ice losses, because across-shelf growth gains from longer algal blooms outweigh ice scour mortality in the shallows.

    PubMed

    Barnes, David K A

    2017-12-01

    One of the major climate-forced global changes has been white to blue to green; losses of sea ice extent in time and space around Arctic and West Antarctic seas has increased open water and the duration (though not magnitude) of phytoplankton blooms. Blueing of the poles has increases potential for heat absorption for positive feedback but conversely the longer phytoplankton blooms have increased carbon export to storage and sequestration by shelf benthos. However, ice shelf collapses and glacier retreat can calve more icebergs, and the increased open water allows icebergs more opportunities to scour the seabed, reducing zoobenthic blue carbon capture and storage. Here the size and variability in benthic blue carbon in mega and macrobenthos was assessed in time and space at Ryder and Marguerite bays of the West Antarctic Peninsula (WAP). In particular the influence of the duration of primary productivity and ice scour are investigated from the shallows to typical shelf depths of 500 m. Ice scour frequency dominated influence on benthic blue carbon at 5 m, to comparable with phytoplankton duration by 25 m depth. At 500 m only phytoplankton duration was significant and influential. WAP zoobenthos was calculated to generate ~10 7 , 4.5 × 10 6 and 1.6 × 10 6 tonnes per year (between 2002 and 2015) in terms of production, immobilization and sequestration of carbon respectively. Thus about 1% of annual primary productivity has sequestration potential at the end of the trophic cascade. Polar zoobenthic blue carbon capture and storage responses to sea ice losses, the largest negative feedback on climate change, has been underestimated despite some offsetting of gain by increased ice scouring with more open water. Equivalent survey of Arctic and sub-Antarctic shelves, for which new projects have started, should reveal the true extent of this feedback and how much its variability contributes to uncertainty in climate models. © 2017 John Wiley & Sons Ltd.

  1. Seasonal Outflow of Ice Shelf Water Across the Front of the Filchner Ice Shelf, Weddell Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Darelius, E.; Sallée, J. B.

    2018-04-01

    The ice shelf water (ISW) found in the Filchner Trough, located in the southern Weddell Sea, Antarctica, is climatically important; it descends into the deep Weddell Sea contributing to bottom water formation, and it blocks warm off-shelf waters from accessing the Filchner ice shelf cavity. Yet the circulation of ISW within the Filchner Trough and the processes determining its exchange across the ice shelf front are to a large degree unknown. Here mooring records from the ice shelf front are presented, the longest of which is 4 years long. They show that the coldest (Θ =- 2.3∘C) ISW, which originates from the Ronne Trough in the west, exits the cavity across the western part of the ice shelf front during late austral summer and early autumn. The supercooled ISW escaping the cavity flows northward with a velocity of about 0.03 m/s. During the rest of the year, there is no outflow at the western site: the current is directed eastward, parallel to the ice shelf front, and the temperatures at the mooring site are slightly higher (Θ =- 2.0∘C). The eastern records show a more persistent outflow of ISW.

  2. Impact of increasing antarctic glacial freshwater release on regional sea-ice cover in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Merino, Nacho; Jourdain, Nicolas C.; Le Sommer, Julien; Goosse, Hugues; Mathiot, Pierre; Durand, Gael

    2018-01-01

    The sensitivity of Antarctic sea-ice to increasing glacial freshwater release into the Southern Ocean is studied in a series of 31-year ocean/sea-ice/iceberg model simulations. Glaciological estimates of ice-shelf melting and iceberg calving are used to better constrain the spatial distribution and magnitude of freshwater forcing around Antarctica. Two scenarios of glacial freshwater forcing have been designed to account for a decadal perturbation in glacial freshwater release to the Southern Ocean. For the first time, this perturbation explicitly takes into consideration the spatial distribution of changes in the volume of Antarctic ice shelves, which is found to be a key component of changes in freshwater release. In addition, glacial freshwater-induced changes in sea ice are compared to typical changes induced by the decadal evolution of atmospheric states. Our results show that, in general, the increase in glacial freshwater release increases Antarctic sea ice extent. But the response is opposite in some regions like the coastal Amundsen Sea, implying that distinct physical mechanisms are involved in the response. We also show that changes in freshwater forcing may induce large changes in sea-ice thickness, explaining about one half of the total change due to the combination of atmospheric and freshwater changes. The regional contrasts in our results suggest a need for improving the representation of freshwater sources and their evolution in climate models.

  3. How ice shelf morphology controls basal melting

    NASA Astrophysics Data System (ADS)

    Little, Christopher M.; Gnanadesikan, Anand; Oppenheimer, Michael

    2009-12-01

    The response of ice shelf basal melting to climate is a function of ocean temperature, circulation, and mixing in the open ocean and the coupling of this external forcing to the sub-ice shelf circulation. Because slope strongly influences the properties of buoyancy-driven flow near the ice shelf base, ice shelf morphology plays a critical role in linking external, subsurface heat sources to the ice. In this paper, the slope-driven dynamic control of local and area-integrated melting rates is examined under a wide range of ocean temperatures and ice shelf shapes, with an emphasis on smaller, steeper ice shelves. A 3-D numerical ocean model is used to simulate the circulation underneath five idealized ice shelves, forced with subsurface ocean temperatures ranging from -2.0°C to 1.5°C. In the sub-ice shelf mixed layer, three spatially distinct dynamic regimes are present. Entrainment of heat occurs predominately under deeper sections of the ice shelf; local and area-integrated melting rates are most sensitive to changes in slope in this "initiation" region. Some entrained heat is advected upslope and used to melt ice in the "maintenance" region; however, flow convergence in the "outflow" region limits heat loss in flatter portions of the ice shelf. Heat flux to the ice exhibits (1) a spatially nonuniform, superlinear dependence on slope and (2) a shape- and temperature-dependent, internally controlled efficiency. Because the efficiency of heat flux through the mixed layer decreases with increasing ocean temperature, numerical simulations diverge from a simple quadratic scaling law.

  4. Glacial-marine sediments record ice-shelf retreat during the late Holocene in Beascochea Bay on the western margin of the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Hardin, L. A.; Wellner, J. S.

    2010-12-01

    Beascochea Bay has an overall rapid rate of sedimentation due to retreating fast-flowing ice, and thus contains high-resolution records of Antarctica’s glacial and climate history. Beascochea Bay is a 16 km long by 8 km wide bay located on the western margin of the Antarctica Peninsula, centered between Anvers Island and Renaud Island, but open to the Bellingshausen Sea. Currently, three tidewater glaciers draining the Bruce Plateau of Graham Land enter into the fjords of Beascochea Bay, releasing terrigenous sediments which have left a record of the fluctuations of the Antarctic Peninsula Ice Cap since the grounded ice decoupled from the seafloor after the last glacial maximum. These three glaciers have played a significant role in providing sediment to the main basin, allowing a detailed sediment facies analysis to be conducted from eight sediment cores which were collected during the austral summer of 2007. Pebbly silty clay sediment cores, along with 3.5 kHz seismic data and multibeam swath bathymetry data, are integrated to reconstruct a glacial retreat timeline for the middle to late Holocene, which can be compared to the recent retreat rates over the last century. Paleoenvironment of deposition is determined by mapping lateral facies changes from the side fjords (proximal) to the outer basin (distal), as each region records the transition from glacial-marine sediments to open-marine sediments. As the ice retreated from the outer basin to the inner basin, and most recently leaving the side fjords, each facies deposited can be age-constrained by radiocarbon, 210Pb, and 137Cs dating methods. A distinct 137Cs signal is readily seen in two kasten cores from a side fjord and the inner basin of Beascochea Bay. This dating method revealed an average sedimentation rate of 2.7 mm per year for approximately the last century, which is comparable to 210Pb rates obtained in other studies. Lithology variations in each sediment core record indications of ice-shelf

  5. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier.

    PubMed

    Smith, J A; Andersen, T J; Shortt, M; Gaffney, A M; Truffer, M; Stanton, T P; Bindschadler, R; Dutrieux, P; Jenkins, A; Hillenbrand, C-D; Ehrmann, W; Corr, H F J; Farley, N; Crowhurst, S; Vaughan, D G

    2017-01-05

    The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line-which marks the boundary between grounded ice and floating ice shelf-is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Thus our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.

  6. Thermohaline variability and Antarctic bottom water formation at the Ross Sea shelf break

    NASA Astrophysics Data System (ADS)

    Budillon, Giorgio; Castagno, Pasquale; Aliani, Stefano; Spezie, Giancarlo; Padman, Laurie

    2011-10-01

    We use hydrological and current meter data collected in the Ross Sea, Antarctica between 1995 and 2006 to describe the spatial and temporal variability of water masses involved in the production of Antarctic Bottom Water (AABW). Data were collected in two regions of known outflows of dense shelf water in this region; the Drygalski Trough (DT) and the Glomar-Challenger Trough (GCT). Dense shelf water just inshore of the shelf break is dominated by High Salinity Shelf Water (HSSW) in the DT and Ice Shelf Water (ISW) in the GCT. The HSSW in the northern DT freshened by ˜0.06 in 11 y, while the ISW in the northern GCT freshened by ˜0.04 in 8 y and warmed by ˜0.04 °C in 11 y, dominated by a rapid warming during austral summer 2001/02. The Antarctic Slope Front separating the warm Circumpolar Deep Water (CDW) from the shelf waters is more stable near GCT than near DT, with CDW and mixing products being found on the outer DT shelf but not on the outer GCT shelf. The different source waters and mixing processes at the two sites lead to production of AABW with different thermohaline characteristics in the central and western Ross Sea. Multi-year time series of hydrography and currents at long-term moorings within 100 km of the shelf break in both troughs confirm the interannual signals in the dense shelf water and reveal the seasonal cycle of water mass properties. Near the DT the HSSW salinities experienced maxima in March/April and minima in September/October. The ISW in the GCT is warmest in March/April and coolest between August and October. Mooring data also demonstrate significant high-frequency variability associated with tides and other processes. Wavelet analysis of near-bottom moored sensors sampling the dense water cascade over the continental slope west of the GCT shows intermittent energetic pulses of cold, dense water with periods from ˜32 h to ˜5 days.

  7. Dibble Ice Shelf

    NASA Image and Video Library

    2013-06-13

    This photo, aken onboard a National Science Foundation/NASA chartered Twin Otter aircraft, shows the ice front of Dibble Ice Shelf, East Antarctica, a significant melt water producer from the Wilkes Land region, East Antarctica.

  8. The paradox of a long grounding during West Antarctic Ice Sheet retreat in Ross Sea.

    PubMed

    Bart, Philip J; Krogmeier, Benjamin J; Bart, Manon P; Tulaczyk, Slawek

    2017-04-28

    Marine geological data show that the West Antarctic Ice Sheet (WAIS) advanced to the eastern Ross Sea shelf edge during the Last Glacial Maximum (LGM) and eventually retreated ~1000 km to the current grounding-line position on the inner shelf. During the early deglacial, the WAIS deposited a voluminous stack of overlapping grounding zone wedges (GZWs) on the outer shelf of the Whales Deep Basin. The large sediment volume of the GZW cluster suggests that the grounding-line position of the paleo-Bindschadler Ice Stream was relatively stationary for a significant time interval. We used an upper bound estimate of paleo-sediment flux to investigate the lower bound duration over which the ice stream would have deposited sediment to account for the GZW volume. Our calculations show that the cluster represents more than three millennia of ice-stream sedimentation. This long duration grounding was probably facilitated by rapid GZW growth. The subsequent punctuated large-distance (~200 km) grounding-line retreat may have been a highly non-linear ice sheet response to relatively continuous external forcing such as gradual climate warming or sea-level rise. These findings indicate that reliable predictions of future WAIS retreat may require incorporation of realistic calculations of sediment erosion, transport and deposition.

  9. Changes in glacier dynamics in the northern Antarctic Peninsula since 1985

    NASA Astrophysics Data System (ADS)

    Seehaus, Thorsten; Cook, Alison J.; Silva, Aline B.; Braun, Matthias

    2018-02-01

    The climatic conditions along the northern Antarctic Peninsula have shown significant changes within the last 50 years. Here we present a comprehensive analysis of temporally and spatially detailed observations of the changes in ice dynamics along both the east and west coastlines of the northern Antarctic Peninsula. Temporal evolutions of glacier area (1985-2015) and ice surface velocity (1992-2014) are derived from a broad multi-mission remote sensing database for 74 glacier basins on the northern Antarctic Peninsula ( < 65° S along the west coast and north of the Seal Nunataks on the east coast). A recession of the glaciers by 238.81 km2 is found for the period 1985-2015, of which the glaciers affected by ice shelf disintegration showed the largest retreat by 208.59 km2. Glaciers on the east coast north of the former Prince Gustav Ice Shelf extent in 1986 receded by only 21.07 km2 (1985-2015) and decelerated by about 58 % on average (1992-2014). A dramatic acceleration after ice shelf disintegration with a subsequent deceleration is observed at most former ice shelf tributaries on the east coast, combined with a significant frontal retreat. In 2014, the flow speed of the former ice shelf tributaries was 26 % higher than before 1996. Along the west coast the average flow speeds of the glaciers increased by 41 %. However, the glaciers on the western Antarctic Peninsula revealed a strong spatial variability of the changes in ice dynamics. By applying a hierarchical cluster analysis, we show that this is associated with the geometric parameters of the individual glacier basins (hypsometric indexes, maximum surface elevation of the basin, flux gate to catchment size ratio). The heterogeneous spatial pattern of ice dynamic evolutions at the northern Antarctic Peninsula shows that temporally and spatially detailed observations as well as further monitoring are necessary to fully understand glacier change in regions with such strong topographic and climatic variances.

  10. Modelling and parameterizing the influence of tides on ice-shelf melt rates

    NASA Astrophysics Data System (ADS)

    Jourdain, N.; Molines, J. M.; Le Sommer, J.; Mathiot, P.; de Lavergne, C.; Gurvan, M.; Durand, G.

    2017-12-01

    Significant Antarctic ice sheet thinning is observed in several sectors of Antarctica, in particular in the Amundsen Sea sector, where warm circumpolar deep waters affect basal melting. The later has the potential to trigger marine ice sheet instabilities, with an associated potential for rapid sea level rise. It is therefore crucial to simulate and understand the processes associated with ice-shelf melt rates. In particular, the absence of tides representation in ocean models remains a caveat of numerous ocean hindcasts and climate projections. In the Amundsen Sea, tides are relatively weak and the melt-induced circulation is stronger than the tidal circulation. Using a regional 1/12° ocean model of the Amundsen Sea, we nonetheless find that tides can increase melt rates by up to 36% in some ice-shelf cavities. Among the processes that can possibly affect melt rates, the most important is an increased exchange at the ice/ocean interface resulting from the presence of strong tidal currents along the ice drafts. Approximately a third of this effect is compensated by a decrease in thermal forcing along the ice draft, which is related to an enhanced vertical mixing in the ocean interior in presence of tides. Parameterizing the effect of tides is an alternative to the representation of explicit tides in an ocean model, and has the advantage not to require any filtering of ocean model outputs. We therefore explore different ways to parameterize the effects of tides on ice shelf melt. First, we compare several methods to impose tidal velocities along the ice draft. We show that getting a realistic spatial distribution of tidal velocities in important, and can be deduced from the barotropic velocities of a tide model. Then, we explore several aspects of parameterized tidal mixing to reproduce the tide-induced decrease in thermal forcing along the ice drafts.

  11. Green icebergs formed by freezing of organic-rich seawater to the base of Antarctic ice shelves

    NASA Astrophysics Data System (ADS)

    Warren, Stephen G.; Roesler, Collin S.; Morgan, Vincent I.; Brandt, Richard E.; Goodwin, Ian D.; Allison, Ian

    1993-01-01

    Although most icebergs are blue, green icebergs are seen occasionally in the Antarctic ocean. Chemical and isotopic analysis of samples from green icebergs indicate that the ice consists of desalinated frozen seawater, as does the basal ice from the Amery Ice Shelf. Spectral reflectance of a green iceberg measured near 67°S, 62°E, confirms that the color is inherent to the ice, not an artifact of the illumination. Pure ice appears blue owing to its absorption of red photons. Addition of a constituent that absorbs blue photons can shift the peak reflectance from blue to green. Such a constituent was identified by spectrophotometric analysis of core samples from this iceberg and from the Amery basal ice, and of seawater samples from Prydz Bay off the Amery Ice Shelf. Analysis of the samples by fluorescence spectroscopy indicates that the blue absorption, and hence the inherent green color, is due to the presence of marine-derived organic matter in the green iceberg, basal ice, and seawater. Thick accumulations of green ice, in icebergs and at the base of ice shelves, indicate that high concentrations of organic matter exist in seawater for centuries at the depth of basal freezing.

  12. Present-day Circum-Antarctic Simulations using the POPSICLES Coupled Ice Sheet-Ocean Model

    NASA Astrophysics Data System (ADS)

    Asay-Davis, X.; Martin, D. F.; Price, S. F.; Maltrud, M. E.; Collins, W.

    2014-12-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010. Simulations are performed at 0.1o (~5 km) ocean resolution and with adaptive ice-sheet model resolution as fine as 500 m. We compare time-averaged melt rates below a number of major ice shelves with those reported by Rignot et al. (2013) as well as other recent studies. We also present seasonal variability and decadal trends in submarine melting from several Antarctic regions. Finally, we explore the influence on basal melting and system dynamics resulting from two different choices of climate forcing: a "normal-year" climatology and the CORE v. 2 forcing data (Large and Yeager 2008).POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh (2009) to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3D; Pattyn et al., 2013) and realistic configurations (Favier et al. 2014).A companion presentation, "Response of the Antarctic Ice Sheet to ocean forcing using the POPSICLES coupled ice sheet-ocean model" in session C024 covers the ice-sheet response to these melt rates in the coupled simulation

  13. Seasonal-to-Interannual Variability in Antarctic Sea-Ice Dynamics, and Its Impact on Surface Fluxes and Water Mass Production

    NASA Technical Reports Server (NTRS)

    Drinkwater, Mark R.

    1999-01-01

    Strong seasonal and interannual signals in Antarctic bottom-water outflow remain unexplained yet are highly correlated with anomalies in net sea-ice growth in coastal polynyas. The mechanisms responsible for driving salination and replenishment and rejuvenation of the dense shelf "source" waters likely also generate pulses of bottom water outflow. The objective of this research is to investigate time-scales of variability in the dynamics of sea-ice in the Southern Ocean in order to determine the primary sites for production of dense shelf waters. We are using a merged satellite/buoy sea-ice motion data set for the period 1978-present day to compute the dynamics of opening and closing of coastal polynyas over the continental shelf. The Ocean Circulation and Climate Advanced Model (OCCAM) ocean general circulation model with coupled sea-ice dynamics is presently forced using National Center for Environmental Prediction (NCEP) data to simulate fluxes and the salination impact of the ocean shelf regions. This work is relevant in the context of measuring the influence of polar sea-ice dynamics upon polar ocean characteristics, and thereby upon global thermohaline ocean circulation. Interannual variability in simulated net freezing rate in the Southern Weddell Sea is shown for the period 1986-1993. There is a pronounced maximum of ice production in 1988 and minimum in 1991 in response to anomalies in equatorward meridional wind velocity. This follows a similar approximate 8-year interannual cycle in Sea Surface Temperature (SST) and satellite-derived ice-edge anomalies reported elsewhere as the "Antarctic Circumpolar Wave." The amplitude of interannual fluctuations in annual net ice production are about 40% of the mean value, implying significant interannual variance in brine rejection and upper ocean heat loss. Southward anomalies in wind stress induce negative anomalies in open water production, which are observed in passive microwave satellite images. Thus, cycles of

  14. Comparison of Ice-shelf Creep Flow Simulations with Ice-front Motion of Filchner-Ronne Ice Shelf, Antarctica, Detected by SAR Interferometry

    NASA Technical Reports Server (NTRS)

    Hulbe, C. L.; Rignot, E.; MacAyeal, D. R.

    1998-01-01

    Comparison between numerical model ice-shelf flow simulations and synthetic aperture radar (SAR) interferograms is used to study the dynamics at the Hemmen Ice Rise (HIR) and Lassiter Coast (LC) corners of the iceberg-calving front of the Filchner-Ronne Ice Shelf (FRIS).

  15. Coastal-change and glaciological map of the Ronne Ice Shelf area, Antarctica, 1974-2002

    USGS Publications Warehouse

    Ferrigno, Jane G.; Foley, K.M.; Swithinbank, C.; Williams, R.S.; Dalide, L.M.

    2005-01-01

    Changes in the area and volume of polar ice sheets are intricately linked to changes in global climate, and the resulting changes in sea level may severely impact the densely populated coastal regions on Earth. Melting of the West Antarctic part alone of the Antarctic ice sheet could cause a sea-level rise of approximately 6 meters (m). The potential sea-level rise after melting of the entire Antarctic ice sheet is estimated to be 65 m (Lythe and others, 2001) to 73 m (Williams and Hall, 1993). In spite of its importance, the mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is poorly known; it is not known for certain whether the ice sheet is growing or shrinking. In a review paper, Rignot and Thomas (2002) concluded that the West Antarctic part of the Antarctic ice sheet is probably becoming thinner overall; although it is thickening in the west, it is thinning in the north. Joughin and Tulaczyk (2002), on the basis of analysis of ice-flow velocities derived from synthetic aperture radar, concluded that most of the Ross ice streams (ice streams on the east side of the Ross Ice Shelf) have a positive mass balance, whereas Rignot and others (in press) infer even larger negative mass balance for glaciers flowing northward into the Amundsen Sea, a trend suggested by Swithinbank and others (2003a,b, 2004). The mass balance of the East Antarctic part of the Antarctic ice sheet is unknown, but thought to be in near equilibrium. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), in subsequent recommendations by the Scientific Committee on Antarctic Research (SCAR) (1989, 1993), and by the National Science Foundation's (1990) Division of Polar Pro-grams. On the basis of these recommendations, the U.S. Geo-logical Survey (USGS) decided that the archive of early 1970s Landsat 1, 2, and 3 Multispectral Scanner

  16. Balance of the West Antarctic Ice Sheet

    NASA Technical Reports Server (NTRS)

    2002-01-01

    For several decades, measurements of the West Antarctic Ice Sheet showed it to be retreating rapidly. But new data derived from satellite-borne radar sensors show the ice sheet to be growing. Changing Antarctic ice sheets remains an area of high scientific interest, particularly in light of recent global warming concerns. These new findings are significant because scientists estimate that sea level would rise 5-6 meters (16-20 feet) if the ice sheet collapsed into the sea. Do these new measurements signal the end of the ice sheet's 10,000-year retreat? Or, are these new satellite data simply much more accurate than the sparse ice core and surface measurements that produced the previous estimates? Another possibility is that the ice accumulation may simply indicate that the ice sheet naturally expands and retreats in regular cycles. Cryologists will grapple with these questions, and many others, as they examine the new data. The image above depicts the region of West Antarctica where scientists measured ice speed. The fast-moving central ice streams are shown in red. Slower tributaries feeding the ice streams are shown in blue. Green areas depict slow-moving, stable areas. Thick black lines depict the areas that collect snowfall to feed their respective ice streams. Reference: Ian Joughin and Slawek Tulaczyk Science Jan 18 2002: 476-480. Image courtesy RADARSAT Antarctic Mapping Project

  17. Variability of sea salts in ice and firn cores from Fimbul Ice Shelf, Dronning Maud Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Paulina Vega, Carmen; Isaksson, Elisabeth; Schlosser, Elisabeth; Divine, Dmitry; Martma, Tõnu; Mulvaney, Robert; Eichler, Anja; Schwikowski-Gigar, Margit

    2018-05-01

    Major ions were analysed in firn and ice cores located at Fimbul Ice Shelf (FIS), Dronning Maud Land - DML, Antarctica. FIS is the largest ice shelf in the Haakon VII Sea, with an extent of approximately 36 500 km2. Three shallow firn cores (about 20 m deep) were retrieved in different ice rises, Kupol Ciolkovskogo (KC), Kupol Moskovskij (KM), and Blåskimen Island (BI), while a 100 m long core (S100) was drilled near the FIS edge. These sites are distributed over the entire FIS area so that they provide a variety of elevation (50-400 m a.s.l.) and distance (3-42 km) to the sea. Sea-salt species (mainly Na+ and Cl-) generally dominate the precipitation chemistry in the study region. We associate a significant sixfold increase in median sea-salt concentrations, observed in the S100 core after the 1950s, to an enhanced exposure of the S100 site to primary sea-salt aerosol due to a shorter distance from the S100 site to the ice front, and to enhanced sea-salt aerosol production from blowing salty snow over sea ice, most likely related to the calving of Trolltunga occurred during the 1960s. This increase in sea-salt concentrations is synchronous with a shift in non-sea-salt sulfate (nssSO42-) toward negative values, suggesting a possible contribution of fractionated aerosol to the sea-salt load in the S100 core most likely originating from salty snow found on sea ice. In contrast, there is no evidence of a significant contribution of fractionated sea salt to the ice-rises sites, where the signal would be most likely masked by the large inputs of biogenic sulfate estimated for these sites. In summary, these results suggest that the S100 core contains a sea-salt record dominated by the proximity of the site to the ocean, and processes of sea ice formation in the neighbouring waters. In contrast, the ice-rises firn cores register a larger-scale signal of atmospheric flow conditions and a less efficient transport of sea-salt aerosols to these sites. These findings are a

  18. Endmembers of Ice Shelf Melt

    NASA Astrophysics Data System (ADS)

    Boghosian, A.; Child, S. F.; Kingslake, J.; Tedesco, M.; Bell, R. E.; Alexandrov, O.; McMichael, S.

    2017-12-01

    Studies of surface melt on ice shelves have defined a spectrum of meltwater behavior. On one end the storage of meltwater in persistent surface ponds can trigger ice shelf collapse as in the 2002 event leading to the disintegration of the Larsen B Ice Shelf. On the other, meltwater export by rivers can stabilize an ice shelf as was recently shown on the Nansen Ice Shelf. We explore this dichotomy by quantifying the partitioning between stored and transported water on two glaciers adjacent to floating ice shelves, Nimrod (Antarctica) and Peterman (Greenland). We analyze optical satellite imagery (LANDSAT, WorldView), airborne imagery (Operation IceBridge, Trimetrogon Aerial Phototography), satellite radar (Sentinel-1), and digital elevation models (DEMs) to categorize surface meltwater fate and map the evolution of ice shelf hydrology and topographic features through time. On the floating Peterman Glacier tongue a sizable river exports water to the ocean. The surface hydrology of Nimrod Glacier, geometrically similar to Peterman but with ten times shallower surface slope, is dominated by storage in surface lakes. In contrast, the Nansen has the same surface slope as Nimrod but transports water through surface rivers. Slope alone is not the sole control on ice shelf hydrology. It is essential to track the storage and transport volumes for each of these systems. To estimate water storage and transport we analyze high resolution (40 cm - 2 m) modern and historical DEMs. We produce historical (1957 onwards) DEMs with structure-from-motion photogrammetry. The DEMs are used to constrain water storage potential estimates of observed basins and water routing/transport potential. We quantify the total volume of water stored seasonally and interannually. We use the normalize difference water index to map meltwater extent, and estimate lake water depth from optical data. We also consider the role of stored water in subsurface aquifers in recharging surface water after

  19. Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Diez, A.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Anthony, R. E.; Aster, R. C.; Cai, C.; Nyblade, A.; Wiens, D. A.

    2016-05-01

    An L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency band from 4 to 18 Hz is dominated by Rayleigh and Love waves propagating from the north that, based on daily temporal variations, we conclude were generated by field camp activity. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile within the firn and ice to ˜150 m depth. The derived density profile allows estimation of the pore close-off depth and the firn-air content thickness. Separate inversions of Rayleigh and Love wave dispersion curves give different shear wave velocity profiles within the firn. We attribute this difference to an effective anisotropy due to fine layering. The layered structure of firn, ice, water and the seafloor results in a characteristic dispersion curve below 7 Hz. Forward modelling the observed Rayleigh wave dispersion curves using representative firn, ice, water and sediment structures indicates that Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. The forward modelling shows that analysis of seismic data from an ice shelf provides the possibility of resolving ice shelf thickness, water column thickness and the physical properties of the ice shelf and underlying seafloor using passive-source seismic data.

  20. Ice shelf structure from dispersion curve analysis of passive-source seismic data, Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Diez, A.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Anthony, R. E.; Aster, R. C.; Cai, C.; Nyblade, A.; Wiens, D.

    2015-12-01

    An L-shaped array of three-component short period seismic stations was deployed at the Ross Ice Shelf, Antarctica approximately 100 km south of the ice edge, near 180° longitude, from November 18 through 28, 2014. Polarization analysis of data from these stations clearly shows propagating waves from below the ice shelf for frequencies below 2 Hz. Energy above 2 Hz is dominated by Rayleigh and Love waves propagating from the north. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile, from which we derive a density profile. The derived shear wave velocity profiles differ within the firn for the inversions using Rayleigh and Love wave dispersion curves. This difference is attributed to an effective anisotropy due to fine layering. The layered structure of firn, ice, water, and ocean floor results in a characteristic dispersion curve pattern below 7 Hz. We investigate the observed structures in more detail by forward modeling of Rayleigh wave dispersion curves for representative firn, ice, water, sediment structures. Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. Our results show that the analysis of high frequency Rayleigh waves on an ice shelf has the ability to resolve ice shelf thickness, water column thickness, and the physical properties of the underlying ocean floor using passive-source seismic data.

  1. The role of cooperative iceberg capsize during ice-shelf disintegration

    NASA Astrophysics Data System (ADS)

    Wilder, W. G.; Burton, J. C.; Amundson, J. M.; Cathles, L. M.; Zhang, W. W.

    2011-12-01

    The physical processes responsible for the sudden, rapid collapse of Antarctic ice-shelves (Larsen B, in 2002; Wilkins, in 2008) are poorly understood. Observations are limited to a handful of satellite images. Thus we have undertaken a series of laboratory-scale experiments using a water-filled tank and "ice" made from buoyant plastic blocks to investigate these processes. Previous experiments have quantified how gravitational potential energy of single-iceberg capsize is converted to other forms of energy [described in Burton et al., submitted], including hydrodynamic forms that may feed back on the ice shelf to cause additional calving. The new experiments reported here examine the energetics of hydrodynamically coupled icebergs that exhibit collective behaviors qualitatively similar to features observed in satellite imagery. Our results suggest that there is a critical proximity at which icebergs will capsize in the same direction an overwhelming majority of the time (cooperative capsize), and a significant part of the gravitational potential energy is converted into translational kinetic energy. We speculate that the residual translational energy observed in our experiments may explain the significant expansion rate (~1 meter/second) of collapsing Antarctic ice-shelves. Burton, J. C., J. M. Amundson, D. S. Abbot, A. Boghosian, L. M. Cathles, S. Correa-Legisos, K. N. Darnell, N. Guttenberg, D. M. Holland, and D. R. MacAyeal. submitted. Laboratory investigations of iceberg-capsize dynamics, energy dissipation and tsunamigenesis. J. Geophys. Res.

  2. Regionally Optimized GRACE Processing and Inter-comparison on the Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Mohajerani, Y.; Velicogna, I.; Sutterley, T. C.; Rignot, E. J.

    2017-12-01

    The Antarctic ice sheet is losing mass at an accelerating rate, with a sea level contribution that changed from 0.08mm/yr from 1992 to 2001 to 0.4mm/yr from 2002 to 2011. While most of this contribution comes from West Antarctica, Totten Glacier has the largest discharge of ice in East Antarctica, with a sea level rise potential of 3.9 m. Furthermore, the drainage basin of Totten Glacier, along the neighboring Moscow University Glacier are below sea level, extending hundreds of kilometers inland. Therefore, obtaining regional estimates of both western and eastern Antarctic basins are of critical importance. The GRACE (Gravity Recovery and Climate Experiment) satellite has been providing mass balance time-series from geoid changes since 2002. Several mascon and harmonic GRACE solutions are available from different processing centers. Here, we evaluate the various solutions across the ice sheet and a new set of regionally optimized mascons to study the mass balance of Totten and Moscow University glaciers. We obtain a trend of -16.5±4.1Gt/yr with an acceleration of -2.0±1.8Gt/yr2 for the two glaciers for the period April 2002 to December 2016 using the Ivins et al (2013) GIA model (errors include leakage, GIA, and regression errors). We compare the results with the Mass Budget Method that combines ice discharge (D) and surface mass balance (SMB) from two models: 1) RACMO2.3, and 2) MAR3.6.4. MBM/RACMO2.3 shows the best agreement with the GRACE estimates. Within the common period from April 2002 to December 2015, the MBM/RACMO2.3 and MAR3.6.4 results are -15.6±1.8Gt/yr and -6.7±1.5Gt/yr respectively, while the GRACE time-series has a trend of -14.8±2.7 Gt/yr. We extend the study to the Getz Ice Shelf, the third largest ice shelf in West Antarctica after Ronne and Ross West ice shelves. We compare our gravity-derived mass estimates, the mass budget estimates, and the volume changes from altimetry data to compare the estimates and obtain a multi-sensor assessment

  3. Marine evidence of a deconvolving Antarctic Ice Sheet during post-LGM retreat of the Ross Sea sector

    NASA Astrophysics Data System (ADS)

    Prothro, L. O.; Yokoyama, Y.; Simkins, L. M.; Anderson, J. B.; Majewski, W.; Yamane, M.; Ohkouchi, N.

    2017-12-01

    Predictive models of ice sheet and sea level change are dependent on observational data of ice-sheet behavior for model testing and tuning. The geologic record contains a wealth of information about ice-sheet dynamics, with fewer logistical, spatial, and temporal limitations than are involved in data acquisition along contemporary ice margins. However, past ice-sheet behavior is still largely uncertain or contested due to issues with obtaining meaningful radiocarbon dates. We minimize bias from glacially-reworked carbon and limitations from unknown geomorphic context and uncertainty in sediment facies identification by using careful sedimentary analyses within a geomorphic framework, as well as selection of appropriate dating methods. Our study area, the Ross Sea sector of Antarctica, is the primary drainage outlet for 25% of the continent's grounded ice. During the Last Glacial Maximum, the low-profile, marine-based West Antarctic Ice Sheet (WAIS) and the steeper profile, largely land-based East Antarctic Ice Sheet (EAIS) converged in the Ross Sea to flow out to or near the continental shelf edge. Geomorphic and sedimentary data reveal that during their subsequent retreat to form the Ross Sea Embayment, the two ice sheets behaved differently, with the WAIS rapidly retreating tens of kilometers followed by extended pauses, while the EAIS retreated steadily, with shorter (decadal- to century-long) pauses. This behavior leads us to believe that the two ice sheets may have contributed diachronously to sea level. By acquiring accurate timing of grounding line retreat, we are able to calculate volumes of ice lost throughout deglaciation, as well as associated sea level contributions. In addition, we attempt to rectify the contradicting marine and terrestrial interpretations of retreat patterns from the Ross Sea continental shelf.

  4. Antarctic Ice Mass Balance from GRACE

    NASA Astrophysics Data System (ADS)

    Boening, C.; Firing, Y. L.; Wiese, D. N.; Watkins, M. M.; Schlegel, N.; Larour, E. Y.

    2014-12-01

    The Antarctic ice mass balance and rates of change of ice mass over the past decade are analyzed based on observations from the Gravity Recovery and Climate Experiment (GRACE) satellites, in the form of JPL RL05M mascon solutions. Surface mass balance (SMB) fluxes from ERA-Interim and other atmospheric reanalyses successfully account for the seasonal GRACE-measured mass variability, and explain 70-80% of the continent-wide mass variance at interannual time scales. Trends in the residual (GRACE mass - SMB accumulation) mass time series in different Antarctic drainage basins are consistent with time-mean ice discharge rates based on radar-derived ice velocities and thicknesses. GRACE also resolves accelerations in regional ice mass change rates, including increasing rates of mass gain in East Antarctica and accelerating ice mass loss in West Antarctica. The observed East Antarctic mass gain is only partially explained by anomalously large SMB events in the second half of the record, potentially implying that ice discharge rates are also decreasing in this region. Most of the increasing mass loss rate in West Antarctica, meanwhile, is explained by decreasing SMB (principally precipitation) over this time period, part of the characteristic decadal variability in regional SMB. The residual acceleration of 2+/-1 Gt/yr, which is concentrated in the Amundsen Sea Embayment (ASE) basins, represents the contribution from increasing ice discharge rates. An Ice Sheet System Model (ISSM) run with constant ocean forcing and stationary grounding lines both underpredicts the largest trends in the ASE and produces negligible acceleration or interannual variability in discharge, highlighting the potential importance of ocean forcing for setting ice discharge rates at interannual to decadal time scales.

  5. Decadal-Scale Response of the Antarctic Ice sheet to a Warming Ocean using the POPSICLES Coupled Ice Sheet-Ocean model

    NASA Astrophysics Data System (ADS)

    Martin, D. F.; Asay-Davis, X.; Cornford, S. L.; Price, S. F.; Ng, E. G.; Collins, W.

    2015-12-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period from 1990 to 2010. We use the CORE v. 2 interannual forcing data to force the ocean model. Simulations are performed at 0.1o(~5 km) ocean resolution with adaptive ice sheet resolution as fine as 500 m to adequately resolve the grounding line dynamics. We discuss the effect of improved ocean mixing and subshelf bathymetry (vs. the standard Bedmap2 bathymetry) on the behavior of the coupled system, comparing time-averaged melt rates below a number of major ice shelves with those reported in the literature. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and the consequent dynamic response of the grounded ice sheet.POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program, and the BISICLES ice-sheet model. POP2x includes sub-ice-shelf circulation using partial top cells and the commonly used three-equation boundary layer physics. Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP) and other continental-scale simulations and melt-rate observations. BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d) and realistic configurations.The figure shows the BISICLES-computed vertically-integrated grounded ice velocity field 5 years into a 20-year coupled full-continent Antarctic-Southern-Ocean simulation. Submarine melt rates are painted onto the surface of the floating ice shelves. Grounding lines are shown in green.

  6. Ice-shelf Dynamics Near the Front of Filchner-Ronne Ice Shelf, Antarctica, Revealed by SAR Interferometry

    NASA Technical Reports Server (NTRS)

    Rignot, E.; MacAyeal, D. R.

    1998-01-01

    Fifteen synthetic-aperture radar (SAR) images of the Ronne Ice Shelf, Antarctica, obtained by the European Space Agency (ESA)'s Earth Remote Sensing satellites (ERS) 1 & 2 are used to study ice-shelf dynamics near two ends of the iceberg-calving front.

  7. Numerical model of ice melange expansion during abrupt ice-shelf collapse

    NASA Astrophysics Data System (ADS)

    Guttenberg, N.; Abbot, D. S.; Amundson, J. M.; Burton, J. C.; Cathles, L. M.; Macayeal, D. R.; Zhang, W.

    2010-12-01

    Satellite imagery of the February 2008 Wilkins Ice-Shelf Collapse event reveals that a large percentage of the involved ice shelf was converted to capsized icebergs and broken fragments of icebergs over a relatively short period of time, possibly less than 24 hours. The extreme violence and short time scale of the event, and the considerable reduction of gravitational potential energy between upright and capsized icebergs, suggests that iceberg capsize might be an important driving mechanism controlling both the rate and spatial extent of ice shelf collapse. To investigate this suggestion, we have constructed an idealized, 2-dimensional model of a disintegrating ice shelf composed of a large number (N~100 to >1000) of initially well-packed icebergs of rectangular cross section. The model geometry consists of a longitudinal cross section of the idealized ice shelf from grounding line (or the upstream extent of ice-shelf fragmentation) to seaward ice front, and includes the region beyond the initial ice front to cover the open, ice-free water into which the collapsing ice shelf expands. The seawater in which the icebergs float is treated as a hydrostatic fluid in the computation of iceberg orientation (e.g., the evaluation of buoyancy forces and torques), thereby eliminating the complexities of free-surface waves, but net horizontal drift of the icebergs is resisted by a linear drag law designed to energy dissipation by viscous forces and surface-gravity-wave radiation. Icebergs interact via both elastic and inelastic contacts (typically a corner of one iceberg will scrape along the face of its neighbor). Ice-shelf collapse in the model is embodied by the mass capsize of a large proportion of the initially packed icebergs and the consequent advancement of the ice front (leading edge). Model simulations are conducted to examine (a) the threshold of stability (e.g., what density of initially capsizable icebergs is needed to allow a small perturbation to the system

  8. Ice shelf structure and stability: Larsen C Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Hubbard, B. P.; Ashmore, D.; Bevan, S. L.; Booth, A. D.; Holland, P.; Jansen, D.; Kuipers Munneke, P.; Kulessa, B.; Luckman, A. J.; Sevestre, H.; O'Leary, M.

    2017-12-01

    We report on recent empirical investigations of the internal structure and stability (or otherwise) of Larsen C Ice Shelf (LCIS), Antarctica, focusing on research carried out for the MIDAS research project between 2014 and 2017. Borehole- and surface geophysics-based fieldwork carried out in austral springs 2014 and 2015 revealed that ephemeral surface ponds, preferentially located within the major inlets within the northern sector of the ice shelf, result in the formation of several tens of metres of (relatively dense) subsurface ice within what would otherwise have been a progressively densifying snow and firn column. Five boreholes were drilled throughout the sector and logged by optical televiewer, showing this refrozen ice to be extensive and of variable composition depending on its process of formation. Mapping the depth-distribution of the resulting ice types and associating each with a simple flow-line model of ice motion and accumulation indicates that this area of LCIS has experienced substantial melting for some centuries but that surface ponding has only occurred in recent decades, possibly restricted to the past 20 years. We also present near-surface temperature data that reveal surprising temporal patterns in foehn wind activity and intensity. Finally, we report on the geometrical extension and widening of a rift that was responsible for calving a 5,800 km^2 iceberg from the LCIS in July 2017. The nature of rift propagation through `suture' ice bands, widely considered to be composed of marine ice, is contrasted with that of its propagation through meteoric ice.

  9. Simulations of coupled, Antarctic ice-ocean evolution using POP2x and BISICLES (Invited)

    NASA Astrophysics Data System (ADS)

    Price, S. F.; Asay-Davis, X.; Martin, D. F.; Maltrud, M. E.; Hoffman, M. J.

    2013-12-01

    We present initial results from Antarctic, ice-ocean coupled simulations using large-scale ocean circulation and land ice evolution models. The ocean model, POP2x is a modified version of POP, a fully eddying, global-scale ocean model (Smith and Gent, 2002). POP2x allows for circulation beneath ice shelf cavities using the method of partial top cells (Losch, 2008). Boundary layer physics, which control fresh water and salt exchange at the ice-ocean interface, are implemented following Holland and Jenkins (1999), Jenkins (1999), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008; Kimura et al., 2013) and with results from other idealized ice-ocean coupling test cases (e.g., Goldberg et al., 2012). The land ice model, BISICLES (Cornford et al., 2012), includes a 1st-order accurate momentum balance (L1L2) and uses block structured, adaptive-mesh refinement to more accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. For idealized test cases focused on marine-ice sheet dynamics, BISICLES output compares very favorably relative to simulations based on the full, nonlinear Stokes momentum balance (MISMIP-3d; Pattyn et al., 2013). Here, we present large-scale (southern ocean) simulations using POP2x with fixed ice shelf geometries, which are used to obtain and validate modeled submarine melt rates against observations. These melt rates are, in turn, used to force evolution of the BISICLES model. An offline-coupling scheme, which we compare with the ice-ocean coupling work of Goldberg et al. (2012), is then used to sequentially update the sub-shelf cavity geometry seen by POP2x.

  10. Impact of sea-ice melt on dimethyl sulfide (sulfoniopropionate) inventories in surface waters of Marguerite Bay, West Antarctic Peninsula.

    PubMed

    Stefels, Jacqueline; van Leeuwe, Maria A; Jones, Elizabeth M; Meredith, Michael P; Venables, Hugh J; Webb, Alison L; Henley, Sian F

    2018-06-28

    The Southern Ocean is a hotspot of the climate-relevant organic sulfur compound dimethyl sulfide (DMS). Spatial and temporal variability in DMS concentration is higher than in any other oceanic region, especially in the marginal ice zone. During a one-week expedition across the continental shelf of the West Antarctic Peninsula (WAP), from the shelf break into Marguerite Bay, in January 2015, spatial heterogeneity of DMS and its precursor dimethyl sulfoniopropionate (DMSP) was studied and linked with environmental conditions, including sea-ice melt events. Concentrations of sulfur compounds, particulate organic carbon (POC) and chlorophyll a in the surface waters varied by a factor of 5-6 over the entire transect. DMS and DMSP concentrations were an order of magnitude higher than currently inferred in climatologies for the WAP region. Particulate DMSP concentrations were correlated most strongly with POC and the abundance of haptophyte algae within the phytoplankton community, which, in turn, was linked with sea-ice melt. The strong sea-ice signal in the distribution of DMS(P) implies that DMS(P) production is likely to decrease with ongoing reductions in sea-ice cover along the WAP. This has implications for feedback processes on the region's climate system.This article is part of the theme issue 'The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change'. © 2018 The Author(s).

  11. Ice shelf fracture parameterization in an ice sheet model

    NASA Astrophysics Data System (ADS)

    Sun, Sainan; Cornford, Stephen L.; Moore, John C.; Gladstone, Rupert; Zhao, Liyun

    2017-11-01

    Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ˜ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

  12. Antarctic glacier-tongue velocities from Landsat images: First results

    USGS Publications Warehouse

    Lucchitta, Baerbel K.; Mullins, K.F.; Allison, A.L.; Ferrigno, Jane G.

    1993-01-01

    We measured the velocities of six glacier tongues and a few tongues within ice shelves distributed around the Antarctic coastline by determining the displacement of crevasse patterns seen on sequential Landsat images. The velocities range from less than 0.2 km a−1 for East Antarctic ice-shelf tongues to more than 2.5 km a−1 for the Thwaites Glacier Tongue. All glacier tongues show increases in velocity toward their distal margins. In general, the tongues of glaciers draining the West Antarctic ice sheet have moved significantly faster than those in East Antarctica. This observation may be significant in light of the hypothesized possible disintegration of the West Antarctic ice sheet.

  13. Arctic and Antarctic Sea Ice Changes and Impacts (Invited)

    NASA Astrophysics Data System (ADS)

    Nghiem, S. V.

    2013-12-01

    The extent of springtime Arctic perennial sea ice, important to preconditioning summer melt and to polar sunrise photochemistry, continues its precipitous reduction in the last decade marked by a record low in 2012, as the Bromine, Ozone, and Mercury Experiment (BROMEX) was conducted around Barrow, Alaska, to investigate impacts of sea ice reduction on photochemical processes, transport, and distribution in the polar environment. In spring 2013, there was further loss of perennial sea ice, as it was not observed in the ocean region adjacent to the Alaskan north coast, where there was a stretch of perennial sea ice in 2012 in the Beaufort Sea and Chukchi Sea. In contrast to the rapid and extensive loss of sea ice in the Arctic, Antarctic sea ice has a trend of a slight increase in the past three decades. Given the significant variability in time and in space together with uncertainties in satellite observations, the increasing trend of Antarctic sea ice may arguably be considered as having a low confidence level; however, there was no overall reduction of Antarctic sea ice extent anywhere close to the decreasing rate of Arctic sea ice. There exist publications presenting various factors driving changes in Arctic and Antarctic sea ice. After a short review of these published factors, new observations and atmospheric, oceanic, hydrological, and geological mechanisms contributed to different behaviors of sea ice changes in the Arctic and Antarctic are presented. The contribution from of hydrologic factors may provide a linkage to and enhance thermal impacts from lower latitudes. While geological factors may affect the sensitivity of sea ice response to climate change, these factors can serve as the long-term memory in the system that should be exploited to improve future projections or predictions of sea ice changes. Furthermore, similarities and differences in chemical impacts of Arctic and Antarctic sea ice changes are discussed. Understanding sea ice changes and

  14. Could a new ice core offer an insight into the stability of the West Antarctic Ice Sheet during the last interglacial?

    NASA Astrophysics Data System (ADS)

    Mulvaney, R.; Hindmarsh, R. C.

    2013-12-01

    Vaughan et al., in their 2011 paper 'Potential Seaways across West Antarctica' (Geochem. Geophys. Geosyst., 12, Q10004, doi:10.1029/2011GC003688), offer the intriguing prospect that substantial ice loss from the West Antarctic Ice Sheet during the previous interglacial period might have resulted in the opening of a seaway between the Weddell Sea and the Amundsen Sea. One of their potential seaways passes between the south western corner of the present Ronne Ice Shelf and the Pine Island Bay, through what is currently the course of the Rutford Ice Stream, between the Ellsworth Mountains and the Fletcher Promontory. To investigate whether this seaway could have existed (and to recover a paleoclimate and ice sheet history from the Weddell Sea), a team from the British Antarctic Survey and the Laboratoire de Glaciologie et Géophysique de l'Environnement drilled an ice core from a close to a topographic dome in the ice surface on the Fletcher Promontory in January 2012, reaching the bedrock at 654.3m depth from the surface. The site was selected to penetrate directly through the centre of a Raymond cupola observed in internal radar reflections from the ice sheet, with the intention that this would ensure we obtained the oldest ice available from the Fletcher Promontory. The basal ice sheet temperature measured was -18°C, implying the oldest ice would not have melted away from the base, while the configuration of the Raymond cupola in the radar horizons suggested stability in the ice dome topography during the majority of the Holocene. Our hypothesis is that chemical analysis of the ice core will reveal whether the site was ever relatively close to open sea water or ice shelf in the Rutford channel 20 km distant, rather than the current 700 km distance to sea ice/open water in either the Weddell Sea or the Amundsen Sea. While we do not yet have the chemistry data to test this hypothesis, in this poster we will discuss whether there is in reality any potential local

  15. Ice Streams as the Critical Link Between the Interior Ice Reservoir of the Antarctic Ice Sheet and the Global Climate System - a WISSARD Perspective (Invited)

    NASA Astrophysics Data System (ADS)

    Tulaczyk, S. M.; Beem, L.; Walter, J. I.; Hossainzadeh, S.; Mankoff, K. D.

    2010-12-01

    Fast flowing ice streams represent crucial features of the Antarctic ice sheet because they provide discharge ‘valves’ for the interior ice reservoir and because their grounding lines are exposed to ocean thermal forcing. Even with no/little topographic control ice flow near the perimeter of a polar ice sheet self-organizes into discrete, fast-flowing ice streams. Within these features basal melting (i.e. lubrication for ice sliding) is sustained through elevated basal shear heating in a region of thin ice that would otherwise be characterized by basal freezing and slow ice motion. Because faster basal ice motion is typically associated with faster subglacial erosion, ice streams tend to localize themselves over time by carving troughs into underlying rocks and sediments. Debris generated by this erosional activity is carried to the continental shelf and/or continental slope where it may be deposited at very high rates, rivaling these associated with deposition by some of the largest rivers on Earth. In terms of their hydrologic and geological functions, Antarctic ice streams play pretty much the same role as rivers do on non-glaciated continents. However, understanding of their dynamics is still quite rudimentary, largely because of the relative inaccessibility of the key basal and marine boundaries of ice streams where pertinent measurements need to be made. The present elevated interest in predicting future contribution of Antarctica to global sea level changes is driving ambitious research programs aimed at scientific exploration of these poorly investigated environments that will play a key role in defining the response of the ice sheet to near future climate changes. We will review one of these programs, the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) with particular focus on its planned contributions to understanding of ice stream dynamics.

  16. Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Berger, Sophie; Drews, Reinhard; Helm, Veit; Sun, Sainan; Pattyn, Frank

    2017-11-01

    Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e. the difference between refreezing and melting. Here, we present an improved technique - based on satellite observations - to capture the small-scale variability in the BMB of ice shelves. As a case study, we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica, and derive its yearly averaged BMB at 10 m horizontal gridding. We use mass conservation in a Lagrangian framework based on high-resolution surface velocities, atmospheric-model surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which preserves abrupt changes in flow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. Our BMB field exhibits much spatial detail and ranges from -14.7 to 8.6 m a-1 ice equivalent. Highest melt rates are found close to the grounding line where the pressure melting point is high, and the ice shelf slope is steep. The BMB field agrees well with on-site measurements from phase-sensitive radar, although independent radar profiling indicates unresolved spatial variations in firn density. We show that an elliptical surface depression (10 m deep and with an extent of 0.7 km × 1.3 km) lowers by 0.5 to 1.4 m a-1, which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice shelf channels advect passively (i.e. no melting nor refreezing) toward the ice shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have

  17. The Role of Basal Channels in Ice Shelf Calving.

    NASA Astrophysics Data System (ADS)

    Dow, C. F.; Lee, W. S.; Greenbaum, J. S.; Greene, C. A.; Blankenship, D. D.; Poinar, K.; Forrest, A.; Young, D. A.; Zappa, C. J.

    2017-12-01

    Increased rates of ice shelf break-up drives acceleration of grounded glacial ice into the ocean, resulting in sea-level rise. Ice shelves are vulnerable to thinning, which make them more susceptible to calving. Here, we examine basal channels under three ice shelves that locally thin the ice and drive formation of transverse ice shelf fractures. The basal channels also cause surface depressions due to hydrostatic buoyancy effects and can draw in surface water to form rivers. These rivers exacerbate thinning by surface melting and hydraulic loading, and can accelerate rifting when they flow into the transverse fractures. Our investigation focuses on Nansen Ice Shelf in the Ross Sea Embayment, East Antarctica. We use ice-sounding radar and single-beam laser altimeter data from two aerogeophysical campaigns conducted in 2011 and 2014, ice surface DEM reconstruction, and satellite imagery analysis, to examine the role of a substantial basal channel in the stability of this ice shelf. Nansen Ice Shelf calved two large icebergs totaling 214 km2 in area in April 2016. The transverse fracture that eventually rifted to form these icebergs initiated directly over the basal channel in 1987. In years when surface water formed on Nansen Ice Shelf, a river flowed into the transverse fracture. In November 2016, we identified a new fracture over the basal channel during in-situ data collection. We compare the Nansen Ice Shelf fractures with those at other vulnerable ice-shelf systems, including Petermann Glacier in Greenland and Totten Glacier in East Antarctica, to evaluate the role that basal channels may play in simultaneous basal and surface weakening and their consequent effect on ice-shelf rifting and stability.

  18. Post-LGM grounding line and calving front translations of the West Antarctic Ice Sheet in the Whales Deep paleo-ice-stream trough, eastern Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    McGlannan, A. J.; Bart, P. J.; Chow, J.

    2016-12-01

    A large-area (2500 km2) multibeam survey of the Whales Deep paleo-ice-stream trough, eastern Ross Sea, Antarctica was acquired during NBP1502B. This sector of the continental shelf is important as it was covered by grounded and floating ice, which drained the central part of an expanded West Antarctic Ice Sheet (WAIS) during the last glacial cycle. The seafloor geomorphology shows a well-defined cluster of four back stepping grounding zone wedges (GZWs) that were deposited in a partly overlapping fashion on the middle continental shelf during WAIS retreat. These observations permit two end-member possibilities for how the WAIS grounding line and calving front vacated the trough. In the first scenario, each GZW represents successive landward shifts of the grounding line and calving front. In the second scenario, each GZW represents a large-scale retreat and re-advance of grounded and floating ice. To determine which of these two end-member scenarios most accurately describes WAIS retreat from this sector of Ross Sea, we evaluated a grid of kasten and piston cores. The core stations were selected on the basis of backstepping GZWs along the trough axis. Our core data analyses included an integration of visual core descriptions, x-ray images, grain size, water content, total organic carbon, shear strengths, and diatom assemblage data. Core data reveal a single transgressive succession from proximal diamict overlain by sub-ice-shelf and/or open-marine sediments. These data strongly support the first scenario, suggesting that an ice shelf remained continuously intact during the time that the grounding line successively moved from the shelf edge to the middle shelf by small-scale landward translations until the end of the fourth grounding event. Sedimentologic and diatom-assemblage data from the inner shelf show that only the last middle shelf grounding event ended with a long-distance retreat of grounded and then floating ice to south of the modern calving front.

  19. Bacteria beneath the West Antarctic ice sheet.

    PubMed

    Lanoil, Brian; Skidmore, Mark; Priscu, John C; Han, Sukkyun; Foo, Wilson; Vogel, Stefan W; Tulaczyk, Slawek; Engelhardt, Hermann

    2009-03-01

    Subglacial environments, particularly those that lie beneath polar ice sheets, are beginning to be recognized as an important part of Earth's biosphere. However, except for indirect indications of microbial assemblages in subglacial Lake Vostok, Antarctica, no sub-ice sheet environments have been shown to support microbial ecosystems. Here we report 16S rRNA gene and isolate diversity in sediments collected from beneath the Kamb Ice Stream, West Antarctic Ice Sheet and stored for 15 months at 4 degrees C. This is the first report of microbes in samples from the sediment environment beneath the Antarctic Ice Sheet. The cells were abundant ( approximately 10(7) cells g(-1)) but displayed low diversity (only five phylotypes), likely as a result of enrichment during storage. Isolates were cold tolerant and the 16S rRNA gene diversity was a simplified version of that found in subglacial alpine and Arctic sediments and water. Although in situ cell abundance and the extent of wet sediments beneath the Antarctic ice sheet can only be roughly extrapolated on the basis of this sample, it is clear that the subglacial ecosystem contains a significant and previously unrecognized pool of microbial cells and associated organic carbon that could potentially have significant implications for global geochemical processes.

  20. Toward Surface Mass Balance Modeling over Antarctic Peninsula with Improved Snow/Ice Physics within WRF

    NASA Astrophysics Data System (ADS)

    Villamil-Otero, G.; Zhang, J.; Yao, Y.

    2017-12-01

    The Antarctic Peninsula (AP) has long been the focus of climate change studies due to its rapid environmental changes such as significantly increased glacier melt and retreat, and ice-shelf break-up. Progress has been continuously made in the use of regional modeling to simulate surface mass changes over ice sheets. Most efforts, however, focus on the ice sheets of Greenland with considerable fewer studies in Antarctica. In this study the Weather Research and Forecasting (WRF) model, which has been applied to the Antarctic region for weather modeling, is adopted to capture the past and future surface mass balance changes over AP. In order to enhance the capabilities of WRF model simulating surface mass balance over the ice surface, we implement various ice and snow processes within the WRF and develop a new WRF suite (WRF-Ice). The WRF-Ice includes a thermodynamic ice sheet model that improves the representation of internal melting and refreezing processes and the thermodynamic effects over ice sheet. WRF-Ice also couples a thermodynamic sea ice model to improve the simulation of surface temperature and fluxes over sea ice. Lastly, complex snow processes are also taken into consideration including the implementation of a snowdrift model that takes into account the redistribution of blowing snow as well as the thermodynamic impact of drifting snow sublimation on the lower atmospheric boundary layer. Intensive testing of these ice and snow processes are performed to assess the capability of WRF-Ice in simulating the surface mass balance changes over AP.

  1. Investigation of Antarctic Sea Ice Concentration by Means of Selected Algorithms

    DTIC Science & Technology

    1992-05-08

    Changes in areal extent and concentration of sea ice around Antarctica may serve as sensitive indicators of global warming . A comparison study was...occurred from July, 1987 through June, 1990. Antarctic Ocean, Antarctic regions, Global warming , Sea ice-Antarctic regions.

  2. Summer Drivers of Atmospheric Variability Affecting Ice Shelf Thinning in the Amundsen Sea Embayment, West Antarctica

    NASA Astrophysics Data System (ADS)

    Deb, Pranab; Orr, Andrew; Bromwich, David H.; Nicolas, Julien P.; Turner, John; Hosking, J. Scott

    2018-05-01

    Satellite data and a 35-year hindcast of the Amundsen Sea Embayment summer climate using the Weather Research and Forecasting model are used to understand how regional and large-scale atmospheric variability affects thinning of ice shelves in this sector of West Antarctica by melting from above and below (linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge). El Niño episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge. The location of the Amundsen Sea Low and the polarity of the Southern Annular Mode (SAM) have negligible impact on surface melting, although a positive SAM and eastward shift of the Amundsen Sea Low cause anomalous westerlies over the continental shelf edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic ice shelves.

  3. Measurements of ethane in Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    Verhulst, K. R.; Fosse, E. K.; Aydin, K. M.; Saltzman, E. S.

    2011-12-01

    Ethane is one of the most abundant hydrocarbons in the atmosphere. The major ethane sources are fossil fuel production and use, biofuel combustion, and biomass-burning emissions and the primary loss pathway is via reaction with OH. A paleoatmospheric ethane record would be useful as a tracer of biomass-burning emissions, providing a constraint on past changes in atmospheric methane and methane isotopes. An independent biomass-burning tracer would improve our understanding of the relationship between biomass burning and climate. The mean annual atmospheric ethane level at high southern latitudes is about 230 parts per trillion (ppt), and Antarctic firn air measurements suggest that atmospheric ethane levels in the early 20th century were considerably lower (Aydin et al., 2011). In this study, we present preliminary measurements of ethane (C2H6) in Antarctic ice core samples with gas ages ranging from 0-1900 C.E. Samples were obtained from dry-drilled ice cores from South Pole and Vostok in East Antarctica, and from the West Antarctic Ice Sheet Divide (WAIS-D). Gases were extracted from the ice by melting under vacuum in a glass vessel sealed by indium wire and were analyzed using high resolution GC/MS with isotope dilution. Ethane levels measured in ice core samples were in the range 100-220 ppt, with a mean of 157 ± 45 ppt (n=12). System blanks contribute roughly half the amount of ethane extracted from a 300 g ice core sample. These preliminary data exhibit a temporal trend, with higher ethane levels from 0-900 C.E., followed by a decline, reaching a minimum between 1600-1700 C.E. These trends are consistent with variations in ice core methane isotopes and carbon monoxide isotopes (Ferretti et al., 2005, Wang et al., 2010), which indicate changes in biomass burning emissions over this time period. These preliminary data suggest that Antarctic ice core bubbles contain paleoatmospheric ethane levels. With further improvement of laboratory techniques it appears

  4. Mass Balance of the West Antarctic Ice-Sheet from ICESat Measurements

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Li, Jun; Robins, John; Saba, Jack L.; Yi, Donghui

    2011-01-01

    Mass balance estimates for 2003-2008 are derived from ICESat laser altimetry and compared with estimates for 1992-2002 derived from ERS radar altimetry. The net mass balance of 3 drainage systems (Pine Island, Thwaites/Smith, and the coast of Marie Bryd) for 2003-2008 is a loss of 100 Gt/yr, which increased from a loss of 70 Gt/yr for the earlier period. The DS including the Bindschadler and MacAyeal ice streams draining into the Ross Ice Shelf has a mass gain of 11 Gt/yr for 2003-2008, compared to an earlier loss of 70 Gt/yr. The DS including the Whillans and Kamb ice streams has a mass gain of 12 Gt/yr, including a significant thickening on the upper part of the Kamb DS, compared to a earlier gain of 6 Gt/yr (includes interpolation for a large portion of the DS). The other two DS discharging into the Ronne Ice Shelf and the northern Ellsworth Coast have a mass gain of 39 Gt/yr, compared to a gain of 4 Gt/yr for the earlier period. Overall, the increased losses of 30 Gt/yr in the Pine Island, Thwaites/Smith, and the coast of Marie Bryd DSs are exceeded by increased gains of 59 Gt/yr in the other 4 DS. Overall, the mass loss from the West Antarctic ice sheet has decreased to 38 Gt/yr from the earlier loss of 67 Gt/yr, reducing the contribution to sea level rise to 0.11 mm/yr from 0.19 mm/yr

  5. Evolution of the early Antarctic ice ages

    NASA Astrophysics Data System (ADS)

    Liebrand, Diederik; de Bakker, Anouk T. M.; Beddow, Helen M.; Wilson, Paul A.; Bohaty, Steven M.; Ruessink, Gerben; Pälike, Heiko; Batenburg, Sietske J.; Hilgen, Frederik J.; Hodell, David A.; Huck, Claire E.; Kroon, Dick; Raffi, Isabella; Saes, Mischa J. M.; van Dijk, Arnold E.; Lourens, Lucas J.

    2017-04-01

    Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ˜110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ˜85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ˜110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (˜28.0 My to ˜26.3 My ago) and across the Oligocene-Miocene Transition (˜23.0 My ago). However, the high-amplitude glacial-interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical—indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions.

  6. Evolution of the early Antarctic ice ages

    PubMed Central

    de Bakker, Anouk T. M.; Beddow, Helen M.; Wilson, Paul A.; Bohaty, Steven M.; Pälike, Heiko; Batenburg, Sietske J.; Hilgen, Frederik J.; Hodell, David A.; Huck, Claire E.; Kroon, Dick; Raffi, Isabella; Saes, Mischa J. M.; van Dijk, Arnold E.; Lourens, Lucas J.

    2017-01-01

    Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ∼110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ∼85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ∼110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago) and across the Oligocene−Miocene Transition (∼23.0 My ago). However, the high-amplitude glacial−interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical—indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions. PMID:28348211

  7. Hemispheric atmospheric variations and oceanographic impacts associated with katabatic surges across the Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Bromwich, David H.; Carrasco, Jorge F.; Liu, Zhong; Tzeng, Ren-Yow

    1993-07-01

    Numerical simulations and surface-based observations show that katabatic winds persistently converge toward and blow across the Siple Coast part of West Antarctica onto the Ross Ice Shelf. About 14% of the time during winter (April to August 1988), thermal infrared satellite images reveal the horizontal propagation of this negatively buoyant katabatic airstream for about 1000 km across the ice shelf to its northwestern edge, a trajectory that nearly parallels the Transantarctic Mountains. This takes place when the pressure field supports such airflow, and is caused by synoptic scale cyclones that decay near and/or over Marie Byrd Land. The northwestward propagation of the katabatic winds is accompanied by other changes in the hemispheric long wave pattern. An upper level ridge develops over Wilkes Land, resulting in an enhancement of the split jet in the Pacific Ocean. Then, more frequent and/or intensified synoptic scale cyclones are steered toward Marie Byrd Land where they become nearly stationary to the northeast of the climatological location. The resulting isobaric configuration accelerates the katabatic winds crossing Siple Coast and supports their horizontal propagation across the Ross Ice Shelf. An immediate impact of this katabatic airflow, that crosses from the ice shelf to the Ross Sea, is expansion of the persistent polynya that is present just to the east of Ross Island. This polynya is a conspicuous feature on passive microwave images of Antarctic sea ice and plays a central role in the salt budget of water masses over the Ross Sea continental shelf. The impact of this katabatic airflow upon mesoscale cyclogenesis over the South Pacific Ocean is also discussed.

  8. Ice-shelf Dynamics Near the Front of Filchner-Ronne Ice Shelf, Antarctica, Revealed by SAR Interferometry: Model/Interferogram Comparison

    NASA Technical Reports Server (NTRS)

    MacAyeal, D. R.; Rignot, E.; Hulbe, C. L.

    1998-01-01

    We compare Earth Remote Sensing (ERS) satellite synthetic-aperture radar (SAR) interferograms with artificial interferograms constructed using output of a finite-element ice-shelf flow model to study the dynamics of Filchner-Ronne Ice Shelf (FRIS) near Hemmen Ice Rise (HIR) where the iceberg-calving front itersects Berkener Island (BI).

  9. Structural Uncertainty in Antarctic sea ice simulations

    NASA Astrophysics Data System (ADS)

    Schneider, D. P.

    2016-12-01

    The inability of the vast majority of historical climate model simulations to reproduce the observed increase in Antarctic sea ice has motivated many studies about the quality of the observational record, the role of natural variability versus forced changes, and the possibility of missing or inadequate forcings in the models (such as freshwater discharge from thinning ice shelves or an inadequate magnitude of stratospheric ozone depletion). In this presentation I will highlight another source of uncertainty that has received comparatively little attention: Structural uncertainty, that is, the systematic uncertainty in simulated sea ice trends that arises from model physics and mean-state biases. Using two large ensembles of experiments from the Community Earth System Model (CESM), I will show that the model is predisposed towards producing negative Antarctic sea ice trends during 1979-present, and that this outcome is not simply because the model's decadal variability is out-of-synch with that in nature. In the "Tropical Pacific Pacemaker" ensemble, in which observed tropical Pacific SST anomalies are prescribed, the model produces very realistic atmospheric circulation trends over the Southern Ocean, yet the sea ice trend is negative in every ensemble member. However, if the ensemble-mean trend (commonly interpreted as the forced response) is removed, some ensemble members show a sea ice increase that is very similar to the observed. While this results does confirm the important role of natural variability, it also suggests a strong bias in the forced response. I will discuss the reasons for this systematic bias and explore possible remedies. This an important problem to solve because projections of 21st -Century changes in the Antarctic climate system (including ice sheet surface mass balance changes and related changes in the sea level budget) have a strong dependence on the mean state of and changes in the Antarctic sea ice cover. This problem is not unique to

  10. Dating glacimarine sediments from the continental shelf in the Amundsen Sea using a multi-tool box: Implications for West Antarctic ice-sheet extent and retreat during the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Hillenbrand, C. D.; Smith, J.; Klages, J. P.; Kuhn, G.; Maher, B.; Moreton, S.; Wacker, L.; Frederichs, T.; Wiers, S.; Jernas, P.; Anderson, J. B.; Ehrmann, W. U.; Graham, A. G. C.; Gohl, K.; Larter, R. D.

    2016-02-01

    Satellite data and in-situ measurements show that today considerable mass loss is occurring from the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS). The observational record only spans the past four decades, and until recently the long-term context of the current deglaciation was poorly constrained. This information is, however, crucial for understanding WAIS dynamics, evaluating the role of forcing mechanisms for ice-sheet melting, and testing and calibrating ice-sheet models that attempt to predict future WAIS behavior and its impact on global sea level. Over the past decade several multinational marine expeditions and terrestrial fieldwork campaigns have targeted the Amundsen Sea shelf and its hinterland to reconstruct the WAIS configuration during the Last Glacial Maximum (LGM) and its subsequent deglacial history. The resulting studies succeeded in shedding light on the maximum WAIS extent at the LGM and the style, pattern and speed of its retreat and thinning thereafter. Despite this progress, however, significant uncertainties and discrepancies between marine and terrestrial reconstructions remain, which may arise from difficulties in dating sediment cores from the Antarctic shelf, especially their deglacial sections. Resolving these issues is crucial for understanding the WAIS' contribution to post-LGM sea-level rise, its sensitivity to different forcing mechanisms and its future evolution. Here we present chronological constraints on WAIS advance in the Amundsen Sea and its retreat from 20 ka BP into the Holocene that were obtained by various techniques, such as 14C dating of large ( 10 mg) and small (<<1 mg) sample aliquots of calcareous microfossils, 14C dating of acid-insoluble organic matter combusted at low (300 °C) and high (800 °C) temperatures and dating of sediment cores by using geomagnetic paleointensity. We will compare the different age constraints and discuss their reliability, applicability and implications for WAIS history.

  11. Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth

    NASA Astrophysics Data System (ADS)

    Cook, Carys P.; van de Flierdt, Tina; Williams, Trevor; Hemming, Sidney R.; Iwai, Masao; Kobayashi, Munemasa; Jimenez-Espejo, Francisco J.; Escutia, Carlota; González, Jhon Jairo; Khim, Boo-Keun; McKay, Robert M.; Passchier, Sandra; Bohaty, Steven M.; Riesselman, Christina R.; Tauxe, Lisa; Sugisaki, Saiko; Galindo, Alberto Lopez; Patterson, Molly O.; Sangiorgi, Francesca; Pierce, Elizabeth L.; Brinkhuis, Henk; Klaus, Adam; Fehr, Annick; Bendle, James A. P.; Bijl, Peter K.; Carr, Stephanie A.; Dunbar, Robert B.; Flores, José Abel; Hayden, Travis G.; Katsuki, Kota; Kong, Gee Soo; Nakai, Mutsumi; Olney, Matthew P.; Pekar, Stephen F.; Pross, Jörg; Röhl, Ursula; Sakai, Toyosaburo; Shrivastava, Prakash K.; Stickley, Catherine E.; Tuo, Shouting; Welsh, Kevin; Yamane, Masako

    2013-09-01

    Warm intervals within the Pliocene epoch (5.33-2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century and atmospheric CO2 concentrations similar to today. Estimates for global sea level highstands during these times imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene.

  12. Antarctic sea ice thickness data archival and recovery at the Australian Antarctic Data Centre

    NASA Astrophysics Data System (ADS)

    Worby, A. P.; Treverrow, A.; Raymond, B.; Jordan, M.

    2007-12-01

    A new effort is underway to establish a portal for Antarctic sea ice thickness data at the Australian Antarctic Data Centre (http://aadc-maps.aad.gov.au/aadc/sitd/). The intention is to provide a central online access point for a wide range of sea ice data sets, including sea ice and snow thickness data collected using a range of techniques, and sea ice core data. The recommendation to establish this facility came from the SCAR/CliC- sponsored International Workshop on Antarctic Sea Ice Thickness, held in Hobart in July 2006. It was recognised, in particular, that satellite altimetry retrievals of sea ice and snow cover thickness rely on large-scale assumptions of the sea ice and snow cover properties such as density, freeboard height, and snow stratigraphy. The synthesis of historical data is therefore particularly important for algorithm development. This will be closely coordinated with similar efforts in the Arctic. A small working group was formed to identify suitable data sets for inclusion in the archive. A series of standard proformas have been designed for converting old data, and to help standardize the collection of new data sets. These proformas are being trialled on two Antarctic sea ice research cruises in September - October 2007. The web-based portal allows data custodians to remotely upload and manage their data, and for all users to search the holdings and extract data relevant to their needs. This presentation will report on the establishment of the data portal, recent progress in identifying appropriate data sets and making them available online. maps.aad.gov.au/aadc/sitd/

  13. Coastal-Change and Glaciological Map of the Northern Ross Ice Shelf Area, Antarctica: 1962-2004

    USGS Publications Warehouse

    Ferrigno, Jane G.; Foley, Kevin M.; Swithinbank, Charles; Williams, Richard S.

    2007-01-01

    Changes in the area and volume of polar ice sheets are intricately linked to changes in global climate, and the resulting changes in sea level could severely impact the densely populated coastal regions on Earth. Melting of the West Antarctic part alone of the Antarctic ice sheet would cause a sea-level rise of approximately 6 meters (m). The potential sea-level rise after melting of the entire Antarctic ice sheet is estimated to be 65 m (Lythe and others, 2001) to 73 m (Williams and Hall, 1993). The mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is highly complex, responding differently to different conditions in each region (Vaughan, 2005). In a review paper, Rignot and Thomas (2002) concluded that the West Antarctic ice sheet is probably becoming thinner overall; although it is thickening in the west, it is thinning in the north. Thomas and others (2004), on the basis of aircraft and satellite laser altimetry surveys, believe the thinning may be accelerating. Joughin and Tulaczyk (2002), on the basis of analysis of ice-flow velocities derived from synthetic aperture radar, concluded that most of the Ross ice streams (ice streams on the east side of the Ross Ice Shelf) have a positive mass balance, whereas Rignot and others (2004) infer even larger negative mass balance for glaciers flowing northward into the Amundsen Sea, a trend suggested by Swithinbank and others (2003a,b; 2004). The mass balance of the East Antarctic ice sheet is thought by Davis and others (2005) to be strongly positive on the basis of the change in satellite altimetry measurements made between 1992 and 2003. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), in subsequent recommendations by the Scientific Committee on Antarctic Research (SCAR) (1989, 1993), and by the National Science Foundation?s (1990) Division of Polar

  14. Geological and geomorphological insights into Antarctic ice sheet evolution.

    PubMed

    Sugden, David E; Bentley, Michael J; O Cofaigh, Colm

    2006-07-15

    Technical advances in the study of ice-free parts of Antarctica can provide quantitative records that are useful for constraining and refining models of ice sheet evolution and behaviour. Such records improve our understanding of system trajectory, influence the questions we ask about system stability and help to define the ice-sheet processes that are relevant on different time-scales. Here, we illustrate the contribution of cosmogenic isotope analysis of exposed bedrock surfaces and marine geophysical surveying to the understanding of Antarctic ice sheet evolution on a range of time-scales. In the Dry Valleys of East Antarctica, 3He dating of subglacial flood deposits that are now exposed on mountain summits provide evidence of an expanded and thicker Mid-Miocene ice sheet. The survival of surface boulders for approximately 14Myr, the oldest yet measured, demonstrates exceptionally low rates of subsequent erosion and points to the persistence and stability of the dry polar desert climate since that time. Increasingly, there are constraints on West Antarctic ice sheet fluctuations during Quaternary glacial cycles. In the Sarnoff Mountains of Marie Byrd Land in West Antarctica, 10Be and 26Al cosmogenic isotope analysis of glacial erratics and bedrock reveal steady thinning of the ice sheet from 10400 years ago to the present, probably as a result of grounding line retreat. In the Antarctic Peninsula, offshore analysis reveals an extensive ice sheet at the last glacial maximum. Based on radiocarbon dating, deglaciation began by 17000cal yr BP and was complete by 9500cal yr BP. Deglaciation of the west and east sides of the Antarctic Peninsula ice sheet occurred at different times and rates, but was largely complete by the Early Holocene. At that time ice shelves were less extensive on the west side of the Antarctic Peninsula than they are today. The message from the past is that individual glacier drainage basins in Antarctica respond in different and distinctive

  15. Calving and rifting on McMurdo Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Banwell, Alison; Willis, Ian; MacAyeal, Douglas; Goodsell, Becky; Macdonald, Grant; Mayer, David; Powell, Anthony

    2017-04-01

    On March 2, 2016, a series of small en échelon tabular icebergs calved from the seaward front of the McMurdo Ice Shelf, and a previously inactive ice-shelf rift suddenly widened and propagated by 3km, 25% of its previous length, setting the stage for future calving of an approximately 8 km2 segment of the ice shelf. Immediately prior to these events, perhaps within 24 hours, all remaining land-fast sea ice buttressing the ice shelf broke up and drifted away. The events were witnessed by time-lapse cameras at nearby Scott Base giving a unique opportunity to document the timing of the events and conditions leading up to them. In addition, the events can be put into context using nearby seismic and automatic weather station data, satellite imagery, and ground observation made 8 months later. Although the observations cannot be used definitively to identify the exact trigger of calving and rifting, the seismic records reveal superimposed sets of long-period (>10 s) sea swell, propagating into McMurdo Sound from distant storm sources in the Pacific Ocean, at the time of, and immediately prior to, the break-up of sea ice and associated ice shelf calving and rifting. This conspicuous presence suggests that sea swell should be studied further as a proximal cause of ice-shelf calving and rifting; if proven, it suggests that ice-shelf stability is tele-connected with far-field storm conditions at lower latitudes, adding a global dimension to the physics of potential ice-shelf breakup.

  16. Rapid drawdown of Antarctica's Wordie Ice Shelf glaciers in response to ENSO/Southern Annular Mode-driven warming in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Walker, C. C.; Gardner, A. S.

    2017-10-01

    Here we investigate the largest acceleration in ice flow across all of Antarctica between ∼2008 InSAR and 2014 Landsat velocity mappings. This occurred in glaciers that used to feed into the Wordie Ice Shelf on the west Antarctic Peninsula, which rapidly disintegrated in ∼1989. Between 2008 and 2014, these glaciers experienced at least a threefold increase in surface elevation drawdown relative to the 2002-2008 time period. After ∼20 yrs of relative stability, it is unlikely that the ice shelf collapse played a role in the large response. Instead, we find that the rapid acceleration and surface drawdown is linked to enhanced melting at the ice-ocean boundary, attributable to changes in winds driven by global atmospheric circulation patterns, namely the El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM), linking changes in grounded ice to atmospheric-driven ocean warming.

  17. Spawning of Massive Antarctic Iceberg Captured by NASA

    NASA Image and Video Library

    2017-07-14

    Between July 10 and 12, 2017, the Larsen C Ice Shelf in West Antarctica calved one of the largest icebergs in history (named "A-68"), weighing approximately one trillion tons. The rift in the ice shelf that spawned the iceberg has been present on the shelf since at least the beginning of the Landsat era (approximately the 1970s), but remained relatively dormant until around 2012, when it was observed actively moving through a suture zone in the ice shelf (Jansen et al., 2015). Suture zones are wide bands of ice that extend from glacier grounding lines (the boundary between a floating ice shelf and ice resting on bedrock) to the sea comprised of a frozen mixture of glacial ice and sea water, traditionally considered to be stabilizing features in ice shelves. When the Antarctic entered its annual dark period in late April, scientists knew the rift only had a few more miles to go before it completely calved the large iceberg. However, due to the lack of sunlight during the Antarctic winter, visible imagery is generally not available each year between May and August. This frame is from an animation that shows the ice shelf as imaged by the NASA/NOAA satellite Suomi NPP, which features the VIIRS (Visible Infrared Imaging Radiometer Suite) instrument. VIIRS has a day/night panchromatic band capable of collecting nighttime imagery of Earth with a spatial resolution of 2,460 feet (750 meters). An image from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra satellite shows the last cloud-free, daytime image of the ice shelf on April 6; the MODIS thermal imagery band is shown on April 29. The images from May 9 to July 14 show available cloud-free imagery from Suomi NPP. Luckily, despite several cloudy days leading up to the break, the weather mostly cleared on July 11, allowing scientists to see the newly formed iceberg on July 12. The animation is available at https://photojournal.jpl.nasa.gov/catalog/PIA21785

  18. Impact of ice-shelf sediment content on the dynamics of plumes under melting ice shelves

    NASA Astrophysics Data System (ADS)

    Wells, A.

    2015-12-01

    When a floating ice shelf melts into an underlying warm salty ocean, the resulting fresh meltwater can rise in a buoyant Ice-Shelf-Water plume under the ice. In certain settings, ice flowing across the grounding line carries a basal layer of debris rich ice, entrained via basal freezing around till in the upstream ice sheet. Melting of this debris-laden ice from floating ice shelves provides a flux of dense sediment to the ocean, in addition to the release of fresh buoyant meltwater. This presentation considers the impact of the resulting suspended sediment on the dynamics of ice shelf water plumes, and identifies two key flow regimes depending on the sediment concentration frozen into the basal ice layer. For large sediment concentration, melting of the debris-laden ice shelf generates dense convectively unstable waters that drive convective overturning into the underlying ocean. For lower sediment concentration, the sediment initially remains suspended in a buoyant meltwater plume rising along the underside of the ice shelf, before slowly depositing into the underlying ocean. A theoretical plume model is used to evaluate the significance of the negatively buoyant sediment on circulation strength and the feedbacks on melting rate, along with the expected depositional patterns under the ice shelf.

  19. New Crustal Boundary Revealed Beneath the Ross Ice Shelf, Antarctica, through ROSETTA-Ice Integrated Aerogeophysics, Geology, and Ocean Research

    NASA Astrophysics Data System (ADS)

    Tinto, K. J.; Siddoway, C. S.; Bell, R. E.; Lockett, A.; Wilner, J.

    2017-12-01

    Now submerged within marine plateaus and rises bordering Antarctica, Australia and Zealandia, the East Gondwana accretionary margin was a belt of terranes and stitched by magmatic arcs, later stretched into continental ribbons separated by narrow elongate rifts. This crustal architecture is known from marine geophysical exploration and ocean drilling of the mid-latitude coastal plateaus and rises. A concealed sector of the former East Gondwana margin that underlies the Ross Ice Shelf (RIS), Antarctica, is the focus of ROSETTA-ICE, a new airborne data acquisition campaign that explores the crustal makeup, tectonic boundaries and seafloor bathymetry beneath RIS. Gravimeters and a magnetometer are deployed by LC130 aircraft surveying along E-W lines spaced at 10 km, and N-S tie lines at 55 km, connect 1970s points (RIGGS) for controls on ocean depth and gravity. The ROSETTA-ICE survey, 2/3 completed thus far, provides magnetic anomalies, Werner depth-to-basement solutions, a new gravity-based bathymetric model at 20-km resolution, and a new crustal density map tied to the 1970s data. Surprisingly, the data reveal that the major lithospheric boundary separating East and West Antarctica lies 300 km east of the Transantarctic Mountains, beneath the floating RIS. The East and West regions have contrasting geophysical characteristics and bathymetry, with relatively dense lithosphere, low amplitude magnetic anomalies, and deep bathymetry on the East Antarctica side, and high amplitude magnetic anomalies, lower overall density and shallower water depths on the West Antarctic side. The Central High, a basement structure cored at DSDP Site 270 and seismically imaged in the Ross Sea, continues beneath RIS as a faulted but coherent crustal ribbon coincident with the tectonic boundary. The continuity of Gondwana margin crustal architecture discovered beneath the West Antarctic Ice Sheet requires a revision of the existing tectonic framework. The sub-RIS narrow rift basins and

  20. Mass balance of the Antarctic ice sheet.

    PubMed

    Wingham, D J; Shepherd, A; Muir, A; Marshall, G J

    2006-07-15

    The Antarctic contribution to sea-level rise has long been uncertain. While regional variability in ice dynamics has been revealed, a picture of mass changes throughout the continental ice sheet is lacking. Here, we use satellite radar altimetry to measure the elevation change of 72% of the grounded ice sheet during the period 1992-2003. Depending on the density of the snow giving rise to the observed elevation fluctuations, the ice sheet mass trend falls in the range -5-+85Gtyr-1. We find that data from climate model reanalyses are not able to characterise the contemporary snowfall fluctuation with useful accuracy and our best estimate of the overall mass trend-growth of 27+/-29Gtyr-1-is based on an assessment of the expected snowfall variability. Mass gains from accumulating snow, particularly on the Antarctic Peninsula and within East Antarctica, exceed the ice dynamic mass loss from West Antarctica. The result exacerbates the difficulty of explaining twentieth century sea-level rise.

  1. Microbial mercury methylation in Antarctic sea ice.

    PubMed

    Gionfriddo, Caitlin M; Tate, Michael T; Wick, Ryan R; Schultz, Mark B; Zemla, Adam; Thelen, Michael P; Schofield, Robyn; Krabbenhoft, David P; Holt, Kathryn E; Moreau, John W

    2016-08-01

    Atmospheric deposition of mercury onto sea ice and circumpolar sea water provides mercury for microbial methylation, and contributes to the bioaccumulation of the potent neurotoxin methylmercury in the marine food web. Little is known about the abiotic and biotic controls on microbial mercury methylation in polar marine systems. However, mercury methylation is known to occur alongside photochemical and microbial mercury reduction and subsequent volatilization. Here, we combine mercury speciation measurements of total and methylated mercury with metagenomic analysis of whole-community microbial DNA from Antarctic snow, brine, sea ice and sea water to elucidate potential microbially mediated mercury methylation and volatilization pathways in polar marine environments. Our results identify the marine microaerophilic bacterium Nitrospina as a potential mercury methylator within sea ice. Anaerobic bacteria known to methylate mercury were notably absent from sea-ice metagenomes. We propose that Antarctic sea ice can harbour a microbial source of methylmercury in the Southern Ocean.

  2. The response of grounded ice to ocean temperature forcing in a coupled ice sheet-ice shelf-ocean cavity model

    NASA Astrophysics Data System (ADS)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.

    2010-12-01

    Ice shelves provide a pathway for the heat content of the ocean to influence continental ice sheets. Changes in the rate or location of basal melting can alter their geometry and effect changes in stress conditions at the grounding line, leading to a grounded ice response. Recent observations of ice streams and ice shelves in the Amundsen Sea sector of West Antarctica have been consistent with this story. On the other hand, ice dynamics in the grounding zone control flux into the shelf and thus ice shelf geometry, which has a strong influence on the circulation in the cavity beneath the shelf. Thus the coupling between the two systems, ocean and ice sheet-ice shelf, can be quite strong. We examine the response of the ice sheet-ice shelf-ocean cavity system to changes in ocean temperature using a recently developed coupled model. The coupled model consists a 3-D ocean model (GFDL's Generalized Ocean Layered Dynamics model, or GOLD) to a two-dimensional ice sheet-ice shelf model (Goldberg et al, 2009), and allows for changing cavity geometry and a migrating grounding line. Steady states of the coupled system are found even under considerable forcing. The ice shelf morphology and basal melt rate patterns of the steady states exhibit detailed structure, and furthermore seem to be unique and robust. The relationship between temperature forcing and area-averaged melt rate is influenced by the response of ice shelf morphology to thermal forcing, and is found to be sublinear in the range of forcing considered. However, results suggest that area-averaged melt rate is not the best predictor of overall system response, as grounding line stability depends on local aspects of the basal melt field. Goldberg, D N, D M Holland and C G Schoof, 2009. Grounding line movement and ice shelf buttressing in marine ice sheets, Journal of Geophysical Research-Earth Surfaces, 114, F04026.

  3. The association of Antarctic krill Euphausia superba with the under-ice habitat.

    PubMed

    Flores, Hauke; van Franeker, Jan Andries; Siegel, Volker; Haraldsson, Matilda; Strass, Volker; Meesters, Erik Hubert; Bathmann, Ulrich; Wolff, Willem Jan

    2012-01-01

    The association of Antarctic krill Euphausia superba with the under-ice habitat was investigated in the Lazarev Sea (Southern Ocean) during austral summer, autumn and winter. Data were obtained using novel Surface and Under Ice Trawls (SUIT), which sampled the 0-2 m surface layer both under sea ice and in open water. Average surface layer densities ranged between 0.8 individuals m(-2) in summer and autumn, and 2.7 individuals m(-2) in winter. In summer, under-ice densities of Antarctic krill were significantly higher than in open waters. In autumn, the opposite pattern was observed. Under winter sea ice, densities were often low, but repeatedly far exceeded summer and autumn maxima. Statistical models showed that during summer high densities of Antarctic krill in the 0-2 m layer were associated with high ice coverage and shallow mixed layer depths, among other factors. In autumn and winter, density was related to hydrographical parameters. Average under-ice densities from the 0-2 m layer were higher than corresponding values from the 0-200 m layer collected with Rectangular Midwater Trawls (RMT) in summer. In winter, under-ice densities far surpassed maximum 0-200 m densities on several occasions. This indicates that the importance of the ice-water interface layer may be under-estimated by the pelagic nets and sonars commonly used to estimate the population size of Antarctic krill for management purposes, due to their limited ability to sample this habitat. Our results provide evidence for an almost year-round association of Antarctic krill with the under-ice habitat, hundreds of kilometres into the ice-covered area of the Lazarev Sea. Local concentrations of postlarval Antarctic krill under winter sea ice suggest that sea ice biota are important for their winter survival. These findings emphasise the susceptibility of an ecological key species to changing sea ice habitats, suggesting potential ramifications on Antarctic ecosystems induced by climate change.

  4. The Association of Antarctic Krill Euphausia superba with the Under-Ice Habitat

    PubMed Central

    Flores, Hauke; van Franeker, Jan Andries; Siegel, Volker; Haraldsson, Matilda; Strass, Volker; Meesters, Erik Hubert; Bathmann, Ulrich; Wolff, Willem Jan

    2012-01-01

    The association of Antarctic krill Euphausia superba with the under-ice habitat was investigated in the Lazarev Sea (Southern Ocean) during austral summer, autumn and winter. Data were obtained using novel Surface and Under Ice Trawls (SUIT), which sampled the 0–2 m surface layer both under sea ice and in open water. Average surface layer densities ranged between 0.8 individuals m−2 in summer and autumn, and 2.7 individuals m−2 in winter. In summer, under-ice densities of Antarctic krill were significantly higher than in open waters. In autumn, the opposite pattern was observed. Under winter sea ice, densities were often low, but repeatedly far exceeded summer and autumn maxima. Statistical models showed that during summer high densities of Antarctic krill in the 0–2 m layer were associated with high ice coverage and shallow mixed layer depths, among other factors. In autumn and winter, density was related to hydrographical parameters. Average under-ice densities from the 0–2 m layer were higher than corresponding values from the 0–200 m layer collected with Rectangular Midwater Trawls (RMT) in summer. In winter, under-ice densities far surpassed maximum 0–200 m densities on several occasions. This indicates that the importance of the ice-water interface layer may be under-estimated by the pelagic nets and sonars commonly used to estimate the population size of Antarctic krill for management purposes, due to their limited ability to sample this habitat. Our results provide evidence for an almost year-round association of Antarctic krill with the under-ice habitat, hundreds of kilometres into the ice-covered area of the Lazarev Sea. Local concentrations of postlarval Antarctic krill under winter sea ice suggest that sea ice biota are important for their winter survival. These findings emphasise the susceptibility of an ecological key species to changing sea ice habitats, suggesting potential ramifications on Antarctic ecosystems induced by climate

  5. Expanding Antarctic Sea Ice: Anthropogenic or Natural Variability?

    NASA Astrophysics Data System (ADS)

    Bitz, C. M.

    2016-12-01

    Antarctic sea ice extent has increased over the last 36 years according to the satellite record. Concurrent with Antarctic sea-ice expansion has been broad cooling of the Southern Ocean sea-surface temperature. Not only are Southern Ocean sea ice and SST trends at odds with expectations from greenhouse gas-induced warming, the trend patterns are not reproduced in historical simulations with comprehensive global climate models. While a variety of different factors may have contributed to the observed trends in recent decades, we propose that it is atmospheric circulation changes - and the changes in ocean circulation they induce - that have emerged as the most likely cause of the observed Southern Ocean sea ice and SST trends. I will discuss deficiencies in models that could explain their incorrect response. In addition, I will present results from a series of experiments where the Antarctic sea ice and ocean are forced by atmospheric perturbations imposed within a coupled climate model. Figure caption: Linear trends of annual-mean SST (left) and annual-mean sea-ice concentration (right) over 1980-2014. SST is from NOAA's Optimum Interpolation SST dataset (version 2; Reynolds et al. 2002). Sea-ice concentration is from passive microwave observations using the NASA Team algorithm. Only the annual means are shown here for brevity and because the signal to noise is greater than in the seasonal means. Figure from Armour and Bitz (2015).

  6. Mapping and Assessing Variability in the Antarctic Marginal Ice Zone, the Pack Ice and Coastal Polynyas

    NASA Astrophysics Data System (ADS)

    Stroeve, Julienne; Jenouvrier, Stephanie

    2016-04-01

    Sea ice variability within the marginal ice zone (MIZ) and polynyas plays an important role for phytoplankton productivity and krill abundance. Therefore mapping their spatial extent, seasonal and interannual variability is essential for understanding how current and future changes in these biological active regions may impact the Antarctic marine ecosystem. Knowledge of the distribution of different ice types to the total Antarctic sea ice cover may also help to shed light on the factors contributing towards recent expansion of the Antarctic ice cover in some regions and contraction in others. The long-term passive microwave satellite data record provides the longest and most consistent data record for assessing different ice types. However, estimates of the amount of MIZ, consolidated pack ice and polynyas depends strongly on what sea ice algorithm is used. This study uses two popular passive microwave sea ice algorithms, the NASA Team and Bootstrap to evaluate the distribution and variability in the MIZ, the consolidated pack ice and coastal polynyas. Results reveal the NASA Team algorithm has on average twice the MIZ and half the consolidated pack ice area as the Bootstrap algorithm. Polynya area is also larger in the NASA Team algorithm, and the timing of maximum polynya area may differ by as much as 5 months between algorithms. These differences lead to different relationships between sea ice characteristics and biological processes, as illustrated here with the breeding success of an Antarctic seabird.

  7. Ross Ice Shelf

    Atmospheric Science Data Center

    2013-04-16

    ... Larger Image According to researchers funded by the National Science Foundation, several penguin colonies near the Ross Ice Shelf, ... Hut Point Peninsula. For a press release from the National Science Foundation containing additional details and MISR imagery ...

  8. The Last Interglacial History of the Antarctic Ice sheet

    NASA Astrophysics Data System (ADS)

    Bradley, Sarah; Siddall, Mark; Milne, Glenn A.; Masson-Delmotte, Valerie; Wolff, Eric; Hindmarsh, Richard C. A.

    2014-05-01

    In this paper we present a summary of the work which was conducted as part of the 'PAST4FUTURE -WP4.1: Sea Level and Ice sheets' project. The overall aim of this study was to understand the response of the Antarctic Ice sheet (AIS) to climate forcing during the Last interglacial (LIG) and its contribution to the observed higher than present sea level during this period. The study involved the application and development of a novel technique which combined East Antarctic stable isotope ice core data with the output from a Glacial Isostatic Adjustment (GIA) model [Bradley et al., 2012]. We investigated if the stable isotope ice core data are sensitive to detecting isostatically driven changes in the surface elevation driven by changes in the ice-loading history of the AIS and if so, could we address some key questions relating to the LIG history of the AIS. Although it is believed that the West Antarctic Ice sheet (WAIS) reduced in size during the LIG compared to the Holocene, major uncertainties and unknowns remain unresolved: Did the WAIS collapse? What would the contribution of such a collapse be the higher than present LIG eustatic sea level (ESL)? We will show that a simulated collapse of the WAIS does not generate a significant elevation driven signal at the EAIS LIG ice core sites, and as such, these ice core records cannot be used to assess WAIS stability over this period. However, we will present 'treasure maps' [Bradley et al., 2012] to identify regions of the AIS where results from geological studies and/or new paleoclimate data may be sensitive to detecting a WAIS collapse. These maps can act as a useful tool for the wider science community/field scientists as a guide to highlight sites suitable to constrain the evolution of the WAIS during the LIG. Studies have proposed that the surface temperature across the East Antarctic Ice Sheet (EAIS) was significantly warmer, 2-5°C during the LIG compared to present [Lang and Wolff, 2011]. These higher

  9. Downslope föhn winds over the Antarctic Peninsula and their effect on the Larsen ice shelves

    NASA Astrophysics Data System (ADS)

    Grosvenor, D. P.; King, J. C.; Choularton, T. W.; Lachlan-Cope, T.

    2014-09-01

    Mesoscale model simulations are presented of a westerly föhn event over the Antarctic Peninsula mountain ridge and onto the Larsen C ice shelf, just south of the recently collapsed Larsen B ice shelf. Aircraft observations showed the presence of föhn jets descending near the ice shelf surface with maximum wind speeds at 250-350 m in height. Surface flux measurements suggested that melting was occurring. Simulated profiles of wind speed, temperature and wind direction were very similar to the observations. However, the good match only occurred at a model time corresponding to ~9 h before the aircraft observations were made since the model föhn jets died down after this. This was despite the fact that the model was nudged towards analysis for heights greater than ~1.15 km above the surface. Timing issues aside, the otherwise good comparison between the model and observations gave confidence that the model flow structure was similar to that in reality. Details of the model jet structure are explored and discussed and are found to have ramifications for the placement of automatic weather station (AWS) stations on the ice shelf in order to detect föhn flow. Cross sections of the flow are also examined and were found to compare well to the aircraft measurements. Gravity wave breaking above the mountain crest likely created a~situation similar to hydraulic flow and allowed föhn flow and ice shelf surface warming to occur despite strong upwind blocking, which in previous studies of this region has generally not been considered. Our results therefore suggest that reduced upwind blocking, due to wind speed increases or stability decreases, might not result in an increased likelihood of föhn events over the Antarctic Peninsula, as previously suggested. The surface energy budget of the model during the melting periods showed that the net downwelling short-wave surface flux was the largest contributor to the melting energy, indicating that the cloud clearing effect of f

  10. Tsunami and infragravity waves impacting Antarctic ice shelves

    NASA Astrophysics Data System (ADS)

    Bromirski, P. D.; Chen, Z.; Stephen, R. A.; Gerstoft, P.; Arcas, D.; Diez, A.; Aster, R. C.; Wiens, D. A.; Nyblade, A.

    2017-07-01

    The responses of the Ross Ice Shelf (RIS) to the 16 September 2015 8.3 (Mw) Chilean earthquake tsunami (>75 s period) and to oceanic infragravity (IG) waves (50-300 s period) were recorded by a broadband seismic array deployed on the RIS from November 2014 to November 2016. Here we show that tsunami and IG-generated signals within the RIS propagate at gravity wave speeds (˜70 m/s) as water-ice coupled flexural-gravity waves. IG band signals show measureable attenuation away from the shelf front. The response of the RIS to Chilean tsunami arrivals is compared with modeled tsunami forcing to assess ice shelf flexural-gravity wave excitation by very long period (VLP; >300 s) gravity waves. Displacements across the RIS are affected by gravity wave incident direction, bathymetry under and north of the shelf, and water layer and ice shelf thicknesses. Horizontal displacements are typically about 10 times larger than vertical displacements, producing dynamical extensional motions that may facilitate expansion of existing fractures. VLP excitation is continuously observed throughout the year, with horizontal displacements highest during the austral winter with amplitudes exceeding 20 cm. Because VLP flexural-gravity waves exhibit no discernable attenuation, this energy must propagate to the grounding zone. Both IG and VLP band flexural-gravity waves excite mechanical perturbations of the RIS that likely promote tabular iceberg calving, consequently affecting ice shelf evolution. Understanding these ocean-excited mechanical interactions is important to determine their effect on ice shelf stability to reduce uncertainty in the magnitude and rate of global sea level rise.

  11. Oceanographic Influences on Ice Shelves and Drainage in the Amundsen Sea

    NASA Astrophysics Data System (ADS)

    Minzoni, R. T.; Anderson, J. B.; Majewski, W.; Yokoyama, Y.; Fernandez, R.; Jakobsson, M.

    2016-12-01

    Marine sediment cores collected during the IB OdenSouthern Ocean 2009-2010 cruise are used to reconstruct the Holocene history of the Cosgrove Ice Shelf, which today occupies Ferrero Bay, a large embayment of eastern Pine Island Bay. Detailed sedimentology, geochemistry, and micropaleontology of cores, in conjunction with subbottom profiles, reveal an unexpected history of recession. Presence of planktic foraminifera at the base of Kasten Core-15 suggests an episode of enhanced circulation beneath a large ice shelf that covered the Amundsen Sea during the Early Holocene, and relatively warm water incursion has been interpreted as a potential culprit for major recession and ice mass loss by 10.7 cal kyr BP from radiocarbon dating. Fine sediment deposition and low productivity throughout the Mid Holocene indicate long-lived stability of the Cosgrove Ice Shelf in Ferrero Bay, despite regional warming evident from ice core data and ice shelf loss in the Antarctic Peninsula. High productivity and diatom abundance signify opening of Ferrero Bay and recession of the Cosgrove Ice Shelf to its present day configuration by 2.0 cal kyr BP. This coincides with deglaciation of an island near Canisteo Peninsula according to published cosmogenic exposure ages. Presence of benthic foraminifera imply that warm deep water influx beneath the extended Cosgrove Ice Shelf was a mechanism for under-melting the ice shelf and destabilizing the grounding line. Major ice shelf recession may also entail continental ice mass loss from the eastern sector of the Amundsen Sea during the Late Holocene. Oceanographic forcing remains a key concern for the current stability of the Antarctic Ice Sheet, especially along the tidewater margins of West Antarctica. Ongoing work on diatom and foraminiferal assemblages of the Late Holocene in Ferrero Bay and other fjord settings will improve our understanding of recent oceanographic changes and their potential influence on ice shelves and outlet glaciers

  12. The role of glacial and tectonic genesis in forming of the Antarctic Peninsula's shelf topography

    NASA Astrophysics Data System (ADS)

    Greku, Rudolf; Greku, Tatyana

    2015-04-01

    The influence of endogenous and exogenous factors on the topography of the West Antarctic shelf is shown. 1. The gravity tomography models [Atlas…] show that the non-geotectonic depressions about 300 m of depth extends to the south from the Bransfield Rift along the western and eastern shelves of the Antarctic Peninsula (AP) up to 69 °S. This is due to the glacial tectonic, which was caused by lithostatic pressure of ice mass and the corresponding deviatoric stress (as а horizontal stretching) in a period of an intense glaciation. Ice mass increases towards the south, therefore the deviatoric stretch and the width of the shelves increases also. 2. Besides such external factors, deep tomography data were taken into account. Results of tomographic modelling show the structure of the AP along its crest and along several cross sections. The AP body, as a single structure, is submerged into the lithospheres of the Pacific Ocean and the Weddell Sea to the depth of 150 km. Some layers of its deepened part are displaced concerning the AP's crest axis. The largest of these shifts are observed up to 50 km from the axis to the east at the latitude of 63°S at the depths of 6-7 km, then a shift up to 100 km to the west at 66°S at the depth of 9 km and at 67°S to the east up to 150 km at the depth of 13 km. 3. After breakup of the ice shelf to the west of the AP, the outflow of ice weight from the main ice board on the Peninsula increased. The consumption of the ice is evaluated now by the discharge of glaciers. Informative data for that are the satellite radar altimetry and interferometry. Several pairs of the ERS1/2 images of 1995-2008 were processed for the area of the Vernadsky Ukrainian Antarctic Station. These 100km x 100km images show 4 glaciers (Deloncle, Girard, Waddington and Collins) along transverse faults. The Collins glacier is the most active one. It starts at the crest of the Bruce Plateau АР at the height of 1450 m. Three smaller glaciers provide an

  13. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica

    NASA Astrophysics Data System (ADS)

    Cochran, James R.; Tinto, Kirsty J.; Bell, Robin E.

    2015-05-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, β, of 1.5-1.7 with 80-100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. The copyright line for this article was changed on 5 JUN 2015 after original online publication.

  14. A 25-year Record of Antarctic Ice Sheet Elevation and Mass Change

    NASA Astrophysics Data System (ADS)

    Shepherd, A.; Muir, A. S.; Sundal, A.; McMillan, M.; Briggs, K.; Hogg, A.; Engdahl, M.; Gilbert, L.

    2017-12-01

    Since 1992, the European Remote-Sensing (ERS-1 and ERS-2), ENVISAT, and CryoSat-2 satellite radar altimeters have measured the Antarctic ice sheet surface elevation, repeatedly, at approximately monthly intervals. These data constitute the longest continuous record of ice sheet wide change. In this paper, we use these observations to determine changes in the elevation, volume and mass of the East Antarctic and West Antarctic ice sheets, and of parts of the Antarctic Peninsula ice sheet, over a 25-year period. The root mean square difference between elevation rates computed from our survey and 257,296 estimates determined from airborne laser measurements is 54 cm/yr. The longevity of the satellite altimeter data record allows to identify and chart the evolution of changes associated with meteorology and ice flow, and we estimate that 3.6 % of the continental ice sheet, and 21.7 % of West Antarctica, is in a state of dynamical imbalance. Based on this partitioning, we estimate the mass balance of the East and West Antarctic ice sheet drainage basins and the root mean square difference between these and independent estimates derived from satellite gravimetry is less than 5 Gt yr-1.

  15. Modeling the basal melting and marine ice accretion of the Amery Ice Shelf

    NASA Astrophysics Data System (ADS)

    Galton-Fenzi, B. K.; Hunter, J. R.; Coleman, R.; Marsland, S. J.; Warner, R. C.

    2012-09-01

    The basal mass balance of the Amery Ice Shelf (AIS) in East Antarctica is investigated using a numerical ocean model. The main improvements of this model over previous studies are the inclusion of frazil formation and dynamics, tides and the use of the latest estimate of the sub-ice-shelf cavity geometry. The model produces a net basal melt rate of 45.6 Gt year-1 (0.74 m ice year-1) which is in good agreement with reviewed observations. The melting at the base of the ice shelf is primarily due to interaction with High Salinity Shelf Water created from the surface sea-ice formation in winter. The temperature difference between the coldest waters created in the open ocean and the in situ freezing point of ocean water in contact with the deepest part of the AIS drives a melt rate that can exceed 30 m of ice year-1. The inclusion of frazil dynamics is shown to be important for both melting and marine ice accretion (refreezing). Frazil initially forms in the supercooled water layer adjacent to the base of the ice shelf. The net accretion of marine ice is 5.3 Gt year-1, comprised of 3.7 Gt year-1 of frazil accretion and 1.6 Gt year-1 of direct basal refreezing.

  16. Holocene Accumulation and Ice Flow near the West Antarctic Ice Sheet Divide Ice Core Site

    NASA Technical Reports Server (NTRS)

    Koutnik, Michelle R.; Fudge, T.J.; Conway, Howard; Waddington, Edwin D.; Neumann, Thomas A.; Cuffey, Kurt M.; Buizert, Christo; Taylor, Kendrick C.

    2016-01-01

    The West Antarctic Ice Sheet Divide Core (WDC) provided a high-resolution climate record from near the Ross-Amundsen Divide in Central West Antarctica. In addition, radar-detected internal layers in the vicinity of the WDC site have been dated directly from the ice core to provide spatial variations in the age structure of the region. Using these two data sets together, we first infer a high-resolution Holocene accumulation-rate history from 9.2 thousand years of the ice-core timescale and then confirm that this climate history is consistent with internal layers upstream of the core site. Even though the WDC was drilled only 24 kilometers from the modern ice divide, advection of ice from upstream must be taken into account. We evaluate histories of accumulation rate by using a flowband model to generate internal layers that we compare to observed layers. Results show that the centennially averaged accumulation rate was over 20 percent lower than modern at 9.2 thousand years before present (B.P.), increased by 40 percent from 9.2 to 2.3 thousand years B.P., and decreased by at least 10 percent over the past 2 thousand years B.P. to the modern values; these Holocene accumulation-rate changes in Central West Antarctica are larger than changes inferred from East Antarctic ice-core records. Despite significant changes in accumulation rate, throughout the Holocene the regional accumulation pattern has likely remained similar to today, and the ice-divide position has likely remained on average within 5 kilometers of its modern position. Continent-scale ice-sheet models used for reconstructions of West Antarctic ice volume should incorporate this accumulation history.

  17. Modelling the bathymetry of the Antarctic continental shelf

    USGS Publications Warehouse

    ten Brink, Uri S.; Rogers, William P.; Kirkham, R.M.

    1992-01-01

    Continental shelves are typically covered by relatively shallow waters (<200 m) which deepen gradually from the coast to the shelf edge. The continental shelf around Antarctica is deeper than normal (400-700m) and is characterized in many areas by a nearshore trough (up to 1 km deep) that gradually shallows toward the shelf edge. We examine the cause for the unusual shelf bathymetry of Antarctica by 2-D numerical models that simulate the bathymetry along seismic line ODP-119 in Prydz Bay. Line ODP-119 was chosen because it is tied to to 5 ODP boreholes, and because the margin underwent little recent tectonic activity or changes in the glacial drainage pattern. The numerical models incorporate several factors that are likely to influence the bathymetry, such as the load of the ice cap, the isostatic response of the lithosphere, thermal and tectnoic subsidence of the margin, sea level changes, and the patterns of erosion and sedimentation across the margin. The models show that the observed bathymetry can be produced almost entirely by the sum of the outer-shelf sediment loading and inner-shelf unloading and by the load of the slope sediments. A simple statistical mdoel demonstrates that this distribution pattern of erosion and deposition can be generated by multiple cycles of ice sheet advances across the shelf, whereby in each cycle a thin (a few tens of meters) uniform layer of sediments is eroded from under the ice sheet and is redeposited seaward of the grounding line.

  18. Antarctic Sea-Ice Freeboard and Estimated Thickness from NASA's ICESat and IceBridge Observations

    NASA Technical Reports Server (NTRS)

    Yi, Donghui; Kurtz, Nathan; Harbeck, Jeremy; Manizade, Serdar; Hofton, Michelle; Cornejo, Helen G.; Zwally, H. Jay; Robbins, John

    2016-01-01

    ICESat completed 18 observational campaigns during its lifetime from 2003 to 2009. Data from all of the 18 campaign periods are used in this study. Most of the operational periods were between 34 and 38 days long. Because of laser failure and orbit transition from 8-day to 91-day orbit, there were four periods lasting 57, 16, 23, and 12 days. IceBridge data from 2009, 2010, and 2011 are used in this study. Since 2009, there are 19 Airborne Topographic Mapper (ATM) campaigns, and eight Land, Vegetation, and Ice Sensor (LVIS) campaigns over the Antarctic sea ice. Freeboard heights are derived from ICESat, ATM and LVIS elevation and waveform data. With nominal densities of snow, water, and sea ice, combined with snow depth data from AMSR-E/AMSR2 passive microwave observation over the southern ocean, sea-ice thickness is derived from the freeboard. Combined with AMSR-E/AMSR2 ice concentration, sea-ice area and volume are also calculated. During the 2003-2009 period, sea-ice freeboard and thickness distributions show clear seasonal variations that reflect the yearly cycle of the growth and decay of the Antarctic pack ice. We found no significant trend of thickness or area for the Antarctic sea ice during the ICESat period. IceBridge sea ice freeboard and thickness data from 2009 to 2011 over the Weddell Sea and Amundsen and Bellingshausen Seas are compared with the ICESat results.

  19. Victoria Land, Ross Sea, and Ross Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    On December 19, 2001, MODIS acquired data that produced this image of Antarctica's Victoria Land, Ross Ice Shelf, and the Ross Sea. The coastline that runs up and down along the left side of the image denotes where Victoria Land (left) meets the Ross Ice Shelf (right). The Ross Ice Shelf is the world's largest floating body of ice, approximately the same size as France. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  20. Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge

    NASA Astrophysics Data System (ADS)

    Bakker, Pepijn; Clark, Peter U.; Golledge, Nicholas R.; Schmittner, Andreas; Weber, Michael E.

    2017-01-01

    Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean-atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations.

  1. NASA Launches Eighth Year of Antarctic Ice Change Airborne Survey

    NASA Image and Video Library

    2017-12-08

    At the southern end of the Earth, a NASA plane carrying a team of scientists and a sophisticated instrument suite to study ice is returning to surveying Antarctica. For the past eight years, Operation IceBridge has been on a mission to build a record of how polar ice is evolving in a changing environment. The information IceBridge has gathered in the Antarctic, which includes data on the thickness and shape of snow and ice, as well as the topography of the land and ocean floor beneath the ocean and the ice, has allowed scientists to determine that the West Antarctic Ice Sheet may be in irreversible decline. Researchers have also used IceBridge data to evaluate climate models of Antarctica and map the bedrock underneath Antarctic ice. Read more:http://go.nasa.gov/2dxczkd NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  2. Antarctic lakes (above and beneath the ice sheet): Analogues for Mars

    NASA Technical Reports Server (NTRS)

    Rice, J. W., Jr.

    1992-01-01

    The perennial ice covered lakes of the Antarctic are considered to be excellent analogues to lakes that once existed on Mars. Field studies of ice covered lakes, paleolakes, and polar beaches were conducted in the Bunger Hills Oasis, Eastern Antarctica. These studies are extended to the Dry Valleys, Western Antarctica, and the Arctic. Important distinctions were made between ice covered and non-ice covered bodies of water in terms of the geomorphic signatures produced. The most notable landforms produced by ice covered lakes are ice shoved ridges. These features form discrete segmented ramparts of boulders and sediments pushed up along the shores of lakes and/or seas. Sub-ice lakes have been discovered under the Antarctic ice sheet using radio echo sounding. These lakes occur in regions of low surface slope, low surface accumulations, and low ice velocity, and occupy bedrock hollows. The presence of sub-ice lakes below the Martian polar caps is possible. The discovery of the Antarctic sub-ice lakes raises possibilities concerning Martian lakes and exobiology.

  3. Simulations of Antarctic ice shelves and the Southern Ocean in the POP2x ocean model coupled with the BISICLES ice-sheet model

    NASA Astrophysics Data System (ADS)

    Asay-Davis, Xylar; Martin, Daniel; Price, Stephen; Maltrud, Mathew

    2014-05-01

    We present initial results from Antarctic, ice-ocean coupled simulations using large-scale ocean circulation and ice-sheet evolution models. This presentation focuses on the ocean model, POP2x, which is a modified version of POP, a fully eddying, global-scale ocean model (Smith and Gent, 2002). POP2x allows for circulation beneath ice shelf cavities using the method of partial top cells (Losch, 2008). Boundary layer physics, which control fresh water and salt exchange at the ice-ocean interface, are implemented following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013) and with results from other idealized ice-ocean coupling test cases (e.g., Goldberg et al., 2012). A companion presentation, 'Fully resolved whole-continent Antarctica simulations using the BISICLES AMR ice sheet model coupled with the POP2x Ocean Model', concentrates more on the ice-sheet model, BISICLES (Cornford et al., 2012), which includes a 1st-order accurate momentum balance (L1L2) and uses block structured, adaptive-mesh refinement to more accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. For idealized test cases focused on marine-ice sheet dynamics, BISICLES output compares very favorably relative to simulations based on the full, nonlinear Stokes momentum balance (MISMIP-3d; Pattyn et al., 2013). Here, we present large-scale (Southern Ocean) simulations using POP2x at 0.1 degree resolution with fixed ice shelf geometries, which are used to obtain and validate modeled submarine melt rates against observations. These melt rates are, in turn, used to force evolution of the BISICLES model. An offline-coupling scheme, which we compare with the ice-ocean coupling work of Goldberg et al. (2012), is then used to

  4. The Response of Ice Sheets to Climate Variability

    NASA Astrophysics Data System (ADS)

    Snow, K.; Goldberg, D. N.; Holland, P. R.; Jordan, J. R.; Arthern, R. J.; Jenkins, A.

    2017-12-01

    West Antarctic Ice Sheet loss is a significant contributor to sea level rise. While the ice loss is thought to be triggered by fluctuations in oceanic heat at the ice shelf bases, ice sheet response to ocean variability remains poorly understood. Using a synchronously coupled ice-ocean model permitting grounding line migration, this study evaluates the response of an ice sheet to periodic variations in ocean forcing. Resulting oscillations in grounded ice volume amplitude is shown to grow as a nonlinear function of ocean forcing period. This implies that slower oscillations in climatic forcing are disproportionately important to ice sheets. The ice shelf residence time offers a critical time scale, above which the ice response amplitude is a linear function of ocean forcing period and below which it is quadratic. These results highlight the sensitivity of West Antarctic ice streams to perturbations in heat fluxes occurring at decadal time scales.

  5. Variability of Antarctic Sea Ice 1979-1998

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Comiso, Josefino C.; Parkinson, Claire L.; Cavalieri, Donald J.; Gloersen, Per; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    The principal characteristics of the variability of Antarctic sea ice cover as previously described from satellite passive-microwave observations are also evident in a systematically-calibrated and analyzed data set for 20.2 years (1979-1998). The total Antarctic sea ice extent (concentration > 15 %) increased by 13,440 +/- 4180 sq km/year (+1.18 +/- 0.37%/decade). The area of sea ice within the extent boundary increased by 16,960 +/- 3,840 sq km/year (+1.96 +/- 0.44%/decade). Regionally, the trends in extent are positive in the Weddell Sea (1.5 +/- 0.9%/decade), Pacific Ocean (2.4 +/- 1.4%/decade), and Ross (6.9 +/- 1.1 %/decade) sectors, slightly negative in the Indian Ocean (-1.5 +/- 1.8%/decade, and strongly negative in the Bellingshausen-Amundsen Seas sector (-9.5 +/- 1.5%/decade). For the entire ice pack, small ice increases occur in all seasons with the largest increase during autumn. On a regional basis, the trends differ season to season. During summer and fall, the trends are positive or near zero in all sectors except the Bellingshausen-Amundsen Seas sector. During winter and spring, the trends are negative or near zero in all sectors except the Ross Sea, which has positive trends in all seasons. Components of interannual variability with periods of about 3 to 5 years are regionally large, but tend to counterbalance each other in the total ice pack. The interannual variability of the annual mean sea-ice extent is only 1.6% overall, compared to 5% to 9% in each of five regional sectors. Analysis of the relation between regional sea ice extents and spatially-averaged surface temperatures over the ice pack gives an overall sensitivity between winter ice cover and temperature of -0.7% change in sea ice extent per K. For summer, some regional ice extents vary positively with temperature and others negatively. The observed increase in Antarctic sea ice cover is counter to the observed decreases in the Arctic. It is also qualitatively consistent with the

  6. Assessment of East Antarctic ice flow directions, ice grounding events, and glacial thermal regime across the middle Miocene climate transition from the ANDRILL-SMS and CRP drill holes

    NASA Astrophysics Data System (ADS)

    Passchier, S.; Hauptvogel, D.; Hansen, M.; Falk, C.; Martin, L.

    2010-12-01

    Here we present a synthesis of early and middle Miocene ice sheet development based on facies analyses and multiple compositional studies on the AND-2A and CRP drillcores from the Ross Sea, ca. 10 km off the coast of East Antarctica. The middle Miocene is characterized by one of the three largest shifts in deep-sea oxygen isotope records. During this time the East Antarctic ice sheet became dry-based at high elevation in the Transantarctic Mountains and advanced across the Ross Sea continental shelf to create widespread glacial unconformities. However, detailed proxy records also indicate that ice development was complex and may have occurred in a stepwise fashion, instead of one major episode. Our analyses of “grounded ice” diamictites from both the CRP and AND-2A cores show a significant change in composition across the middle Miocene transition. More detailed analyses of the stratigraphic distribution of facies, heavy mineral provenance, particle size, and major and trace element geochemistry in AND-2A show that relatively large polythermal ice-sheets similar in size to the modern were already present between 17.6 and 17.1 Ma. These results are in agreement with proxy records suggesting that Antarctic ice volumes were larger than today’s volume during the Mi-1b glaciation. Between 17.1 and 15.6-14.9 Ma, a predominance of iceberg debris sourced from the Ferrar Group in the Transantarctic Mountains suggests vigorous glacial erosion and fjord incision by East Antarctic outlet glaciers. The facies characteristics and comparison with compositional data from Neogene tills in the Transantarctic Mountains further suggest that the East Antarctic ice sheet may have been smaller than today during the Miocene climatic optimum (~17-15 Ma) with ice possibly reaching sea level only near the central Transantarctic Mountains. Advance of the grounding line and the development of glacial flow patterns compatible with a larger ice sheet than the modern commenced between 15

  7. Links between Patagonian Ice Sheet fluctuations and Antarctic dust variability during the last glacial period (MIS 4-2)

    NASA Astrophysics Data System (ADS)

    Kaiser, Jérôme; Lamy, Frank

    2010-06-01

    Antarctic and Greenland ice-core records reveal large fluctuations of dust input on both orbital and millennial time-scales with potential global climate implications. At least during glacial periods, the Antarctic dust fluctuations appear to be largely controlled by environmental changes in southern South America. We compare dust flux records from two Antarctic ice-cores to variations in the composition of the terrigenous supply at ODP Site 1233 located off southern Chile and known to record fluctuations in the extent of the northern part of the Patagonian ice-sheet (NPIS) during the last glacial period (Marine Isotope Stage, MIS, 4 to 2). Within age uncertainties, millennial-scale glacial advances (retreats) of the NPIS correlate to Antarctic dust maxima (minima). In turn, NPIS fluctuations were closely related to offshore sea surface temperature (SST) changes. This pattern suggests a causal link involving changes in temperature, in rock flour availability, in latitudinal extensions of the westerly winds and in foehn winds in the southern Pampas and Patagonia. We further suggest that the long-term trend of dust accumulation is partly linked to the sea-level related changes in the size if the Patagonian source area due to the particular morphology of the Argentine shelf. We suggest that sea-level drops at the beginning of MIS 4 and MIS 2 were important for long-term dust increases, while changes in the Patagonian dust source regions primarily control the early dust decrease during the MIS 4/3 transition and Termination 1.

  8. Century-scale simulations of the response of the West Antarctic Ice Sheet to a warming climate

    DOE PAGES

    Cornford, S. L.; Martin, D. F.; Payne, A. J.; ...

    2015-03-23

    We use the BISICLES adaptive mesh ice sheet model to carry out one, two, and three century simulations of the fast-flowing ice streams of the West Antarctic Ice Sheet. Each of the simulations begins with a geometry and velocity close to present day observations, and evolves according to variation in meteoric ice accumulation, ice shelf melting, and mesh resolution. Future changes in accumulation and melt rates range from no change, through anomalies computed by atmosphere and ocean models driven by the E1 and A1B emissions scenarios, to spatially uniform melt rates anomalies that remove most of the ice shelves overmore » a few centuries. We find that variation in the resulting ice dynamics is dominated by the choice of initial conditions, ice shelf melt rate and mesh resolution, although ice accumulation affects the net change in volume above flotation to a similar degree. Given sufficient melt rates, we compute grounding line retreat over hundreds of kilometers in every major ice stream, but the ocean models do not predict such melt rates outside of the Amundsen Sea Embayment until after 2100. Sensitivity to mesh resolution is spurious, and we find that sub-kilometer resolution is needed along most regions of the grounding line to avoid systematic under-estimates of the retreat rate, although resolution requirements are more stringent in some regions – for example the Amundsen Sea Embayment – than others – such as the Möller and Institute ice streams.« less

  9. Amundsen Sea simulation with optimized ocean, sea ice, and thermodynamic ice shelf model parameters

    NASA Astrophysics Data System (ADS)

    Nakayama, Y.; Menemenlis, D.; Schodlok, M.; Heimbach, P.; Nguyen, A. T.; Rignot, E. J.

    2016-12-01

    Ice shelves and glaciers of the West Antarctic Ice Sheet are thinning and melting rapidly in the Amundsen Sea (AS). This is thought to be caused by warm Circumpolar Deep Water (CDW) that intrudes via submarine glacial troughs located at the continental shelf break. Recent studies, however, point out that the depth of thermocline, or thickness of Winter Water (WW, potential temperature below -1 °C located above CDW) is critical in determining the melt rate, especially for the Pine Island Glacier (PIG). For example, the basal melt rate of PIG, which decreased by 50% during summer 2012, has been attributed to thickening of WW. Despite the possible importance of WW thickness on ice shelf melting, previous modeling studies in this region have focused primarily on CDW intrusion and have evaluated numerical simulations based on bottom or deep CDW properties. As a result, none of these models have shown a good representation of WW for the AS. In this study, we adjust a small number of model parameters in a regional Amundsen and Bellingshausen Seas configuration of the Massachusetts Institute of Technology general circulation model (MITgcm) to better fit the available observations during the 2007-2010 period. We choose this time period because summer observations during these years show small interannual variability in the eastern AS. As a result of adjustments, our model shows significantly better match with observations than previous modeling studies, especially for WW. Since density of sea water depends largely on salinity at low temperature, this is crucial for assessing the impact of WW on PIG melt rate. In addition, we conduct several sensitivity studies, showing the impact of surface heat loss on the thickness and properties of WW. We also discuss some preliminary results pertaining to further optimization using the adjoint method. Our work is a first step toward improved representation of ice-shelf ocean interactions in the ECCO (Estimating the Circulation and

  10. Bathymetric and oceanic controls on Abbot Ice Shelf thickness and stability

    NASA Astrophysics Data System (ADS)

    Cochran, J. R.; Jacobs, S. S.; Tinto, K. J.; Bell, R. E.

    2014-05-01

    Ice shelves play key roles in stabilizing Antarctica's ice sheets, maintaining its high albedo and returning freshwater to the Southern Ocean. Improved data sets of ice shelf draft and underlying bathymetry are important for assessing ocean-ice interactions and modeling ice response to climate change. The long, narrow Abbot Ice Shelf south of Thurston Island produces a large volume of meltwater, but is close to being in overall mass balance. Here we invert NASA Operation IceBridge (OIB) airborne gravity data over the Abbot region to obtain sub-ice bathymetry, and combine OIB elevation and ice thickness measurements to estimate ice draft. A series of asymmetric fault-bounded basins formed during rifting of Zealandia from Antarctica underlie the Abbot Ice Shelf west of 94° W and the Cosgrove Ice Shelf to the south. Sub-ice water column depths along OIB flight lines are sufficiently deep to allow warm deep and thermocline waters observed near the western Abbot ice front to circulate through much of the ice shelf cavity. An average ice shelf draft of ~200 m, 15% less than the Bedmap2 compilation, coincides with the summer transition between the ocean surface mixed layer and upper thermocline. Thick ice streams feeding the Abbot cross relatively stable grounding lines and are rapidly thinned by the warmest inflow. While the ice shelf is presently in equilibrium, the overall correspondence between draft distribution and thermocline depth indicates sensitivity to changes in characteristics of the ocean surface and deep waters.

  11. Simulation of the Greenland Ice Sheet over two glacial-interglacial cycles: investigating a sub-ice-shelf melt parameterization and relative sea level forcing in an ice-sheet-ice-shelf model

    NASA Astrophysics Data System (ADS)

    Bradley, Sarah L.; Reerink, Thomas J.; van de Wal, Roderik S. W.; Helsen, Michiel M.

    2018-05-01

    Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM) the Greenland ice sheet (GrIS) expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS) and Innuitian Ice Sheet (IIS), it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial-interglacial cycles (240 ka BP to the present day) using the ice-sheet-ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL) forcing generated by a glacial isostatic adjustment (GIA) model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG) and LGM the ice sheet added 1.46 and -2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (˜ 1.26 m) than most previous studies whereas the contribution to the LIG highstand is lower (˜ 0.7 m). The spatial and temporal behaviour of the northern margin was highly variable in all simulations

  12. Influence of West Antarctic Ice Sheet collapse on Antarctic surface climate

    NASA Astrophysics Data System (ADS)

    Steig, Eric J.; Huybers, Kathleen; Singh, Hansi A.; Steiger, Nathan J.; Ding, Qinghua; Frierson, Dargan M. W.; Popp, Trevor; White, James W. C.

    2015-06-01

    Climate model simulations are used to examine the impact of a collapse of the West Antarctic Ice Sheet (WAIS) on the surface climate of Antarctica. The lowered topography following WAIS collapse produces anomalous cyclonic circulation with increased flow of warm, maritime air toward the South Pole and cold-air advection from the East Antarctic plateau toward the Ross Sea and Marie Byrd Land, West Antarctica. Relative to the background climate, areas in East Antarctica that are adjacent to the WAIS warm, while substantial cooling (several °C) occurs over parts of West Antarctica. Anomalously low isotope-paleotemperature values at Mount Moulton, West Antarctica, compared with ice core records in East Antarctica, are consistent with collapse of the WAIS during the last interglacial period, Marine Isotope Stage 5e. More definitive evidence might be recoverable from an ice core record at Hercules Dome, East Antarctica, which would experience significant warming and positive oxygen isotope anomalies if the WAIS collapsed.

  13. Shelf–ocean exchange and hydrography west of the Antarctic Peninsula: a review

    PubMed Central

    2018-01-01

    The West Antarctic Peninsula (WAP) is a highly productive marine ecosystem where extended periods of change have been observed in the form of glacier retreat, reduction of sea-ice cover and shifts in marine populations, among others. The physical environment on the shelf is known to be strongly influenced by the Antarctic Circumpolar Current flowing along the shelf slope and carrying warm, nutrient-rich water, by cold waters flooding into the northern Bransfield Strait from the Weddell Sea, by an extensive network of glaciers and ice shelves, and by strong seasonal to inter-annual variability in sea-ice formation and air–sea interactions, with significant modulation by climate modes like El Niño–Southern Oscillation and the Southern Annular Mode. However, significant gaps have remained in understanding the exchange processes between the open ocean and the shelf, the pathways and fate of oceanic water intrusions, the shelf heat and salt budgets, and the long-term evolution of the shelf properties and circulation. Here, we review how recent advances in long-term monitoring programmes, process studies and newly developed numerical models have helped bridge these gaps and set future research challenges for the WAP system. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’. PMID:29760109

  14. Core drilling through the ross ice shelf (antarctica) confirmed Basal freezing.

    PubMed

    Zotikov, I A; Zagorodnov, V S; Raikovsky, J V

    1980-03-28

    New techniques that have been used to obtain a continuous ice core through the whole 416-meter thickness of the Ross Ice Shelf at Camp J-9 have demonstrated that the bottom 6 meters of the ice shelf consists of sea ice. The rate of basal freezing that is forming this ice is estimated by different methods to be 2 centimeters of ice per year. The sea ice is composed of large vertical crystals, which form the waffle-like lower boundary of the shelf. A distinct alignment of the crystals throughout the sea ice layer suggests the presence of persistent long-term currents beneath the ice shelf.

  15. Iron Supply and Demand in an Antarctic Shelf Ecosystem

    NASA Astrophysics Data System (ADS)

    McGillicuddy, D. J., Jr.; Sedwick, P.; Dinniman, M. S.; Arrigo, K. R.; Bibby, T. S.; Greenan, B. J. W.; Hofmann, E. E.; Klinck, J. M., II; Smith, W.; Mack, S. L.; Marsay, C. M.; Sohst, B. M.; van Dijken, G.

    2016-02-01

    The Ross Sea sustains a rich ecosystem and is the most productive sector of the Southern Ocean. Most of this production occurs within a polynya during the November-February period, when the availability of dissolved iron (dFe) is thought to exert the major control on phytoplankton growth. Here we combine new data on the distribution of dFe, high-resolution model simulations of ice melt and regional circulation, and satellite-based estimates of primary production to quantify iron supply and demand over the Ross Sea continental shelf. Our analysis suggests that the largest sources of dFe to the euphotic zone are wintertime mixing and melting sea ice, with a lesser input from intrusions of Circumpolar Deep Water, and a small amount from melting glacial ice. Together these sources are in approximate balance with the annual biological dFe demand inferred from satellite-based productivity algorithms, although both the supply and demand estimates have large uncertainties. Our findings illustrate the complexities of iron cycling in the Southern Ocean, highlighting the heterogeneity of the underlying processes along the Antarctic continental margin. Explicit representation of these complexities, and the temporal variability in both proximate and ultimate sources of iron, will be necessary to understand how a changing climate will affect this important ecosystem and its influence on biogeochemical cycles. Reduction of the present uncertainties in iron supply and demand will require coupled observational and modeling systems capable of resolving the wide range of physical, biological, and chemical processes involved.

  16. Air-sea interaction regimes in the sub-Antarctic Southern Ocean and Antarctic marginal ice zone revealed by icebreaker measurements

    NASA Astrophysics Data System (ADS)

    Yu, Lisan; Jin, Xiangze; Schulz, Eric W.; Josey, Simon A.

    2017-08-01

    This study analyzed shipboard air-sea measurements acquired by the icebreaker Aurora Australis during its off-winter operation in December 2010 to May 2012. Mean conditions over 7 months (October-April) were compiled from a total of 22 ship tracks. The icebreaker traversed the water between Hobart, Tasmania, and the Antarctic continent, providing valuable in situ insight into two dynamically important, yet poorly sampled, regimes: the sub-Antarctic Southern Ocean and the Antarctic marginal ice zone (MIZ) in the Indian Ocean sector. The transition from the open water to the ice-covered surface creates sharp changes in albedo, surface roughness, and air temperature, leading to consequential effects on air-sea variables and fluxes. Major effort was made to estimate the air-sea fluxes in the MIZ using the bulk flux algorithms that are tuned specifically for the sea-ice effects, while computing the fluxes over the sub-Antarctic section using the COARE3.0 algorithm. The study evidenced strong sea-ice modulations on winds, with the southerly airflow showing deceleration (convergence) in the MIZ and acceleration (divergence) when moving away from the MIZ. Marked seasonal variations in heat exchanges between the atmosphere and the ice margin were noted. The monotonic increase in turbulent latent and sensible heat fluxes after summer turned the MIZ quickly into a heat loss regime, while at the same time the sub-Antarctic surface water continued to receive heat from the atmosphere. The drastic increase in turbulent heat loss in the MIZ contrasted sharply to the nonsignificant and seasonally invariant turbulent heat loss over the sub-Antarctic open water.Plain Language SummaryThe icebreaker Aurora Australis is a research and supply vessel that is regularly chartered by the Australian <span class="hlt">Antarctic</span> Division during the southern summer to operate in waters between Hobart, Tasmania, and Antarctica. The vessel serves as the main lifeline to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018ISPAr42.3.2625L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018ISPAr42.3.2625L"><span>Compiling Techniques for East <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Velocity Mapping Based on Historical Optical Imagery</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, X.; Li, R.; Qiao, G.; Cheng, Y.; Ye, W.; Gao, T.; Huang, Y.; Tian, Y.; Tong, X.</p> <p>2018-05-01</p> <p><span class="hlt">Ice</span> flow velocity over long time series in East Antarctica plays a vital role in estimating and predicting the mass balance of <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet and its contribution to global sea level rise. However, there is no <span class="hlt">Antarctic</span> <span class="hlt">ice</span> velocity product with large space scale available showing the East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> flow velocity pattern before the 1990s. We proposed three methods including parallax decomposition, grid-based NCC image matching, feature and gird-based image matching with constraints for estimation of surface velocity in East Antarctica based on ARGON KH-5 and LANDSAT imagery, showing the feasibility of using historical optical imagery to obtain <span class="hlt">Antarctic</span> <span class="hlt">ice</span> motion. Based on these previous studies, we presented a set of systematic method for developing <span class="hlt">ice</span> surface velocity product for the entire East Antarctica from the 1960s to the 1980s in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910063773&hterms=1087&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3D%2526%25231087','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910063773&hterms=1087&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3D%2526%25231087"><span><span class="hlt">Antarctic</span> Sea <span class="hlt">ice</span> variations and seasonal air temperature relationships</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Weatherly, John W.; Walsh, John E.; Zwally, H. J.</p> <p>1991-01-01</p> <p>Data through 1987 are used to determine the regional and seasonal dependencies of recent trends of <span class="hlt">Antarctic</span> temperature and sea <span class="hlt">ice</span>. Lead-lag relationships involving regional sea <span class="hlt">ice</span> and air temperature are systematically evaluated, with an eye toward the <span class="hlt">ice</span>-temperature feedbacks that may influence climatic change. Over the 1958-1087 period the temperature trends are positive in all seasons. For the 15 years (l973-l987) for which <span class="hlt">ice</span> data are available, the trends are predominantly positive only in winter and summer, and are most strongly positive over the <span class="hlt">Antarctic</span> Peninsula. The spatially aggregated trend of temperature for this latter period is small but positive, while the corresponding trend of <span class="hlt">ice</span> coverage is small but negative. Lag correlations between seasonal anomalies of the two variables are generally stronger with <span class="hlt">ice</span> lagging the summer temperatures and with <span class="hlt">ice</span> leading the winter temperatures. The implication is that summer temperatures predispose the near-surface waters to above-or below-normal <span class="hlt">ice</span> coverage in the following fall and winter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20120015900&hterms=export&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dexport','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20120015900&hterms=export&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dexport"><span>Variability and Trends in Sea <span class="hlt">Ice</span> Extent and <span class="hlt">Ice</span> Production in the Ross Sea</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Comiso, Josefino; Kwok, Ronald; Martin, Seelye; Gordon, Arnold L.</p> <p>2011-01-01</p> <p>Salt release during sea <span class="hlt">ice</span> formation in the Ross Sea coastal regions is regarded as a primary forcing for the regional generation of <span class="hlt">Antarctic</span> Bottom Water. Passive microwave data from November 1978 through 2008 are used to examine the detailed seasonal and interannual characteristics of the sea <span class="hlt">ice</span> cover of the Ross Sea and the adjacent Bellingshausen and Amundsen seas. For this period the sea <span class="hlt">ice</span> extent in the Ross Sea shows the greatest increase of all the <span class="hlt">Antarctic</span> seas. Variability in the <span class="hlt">ice</span> cover in these regions is linked to changes in the Southern Annular Mode and secondarily to the <span class="hlt">Antarctic</span> Circumpolar Wave. Over the Ross Sea <span class="hlt">shelf</span>, analysis of sea <span class="hlt">ice</span> drift data from 1992 to 2008 yields a positive rate of increase in the net <span class="hlt">ice</span> export of about 30,000 sq km/yr. For a characteristic <span class="hlt">ice</span> thickness of 0.6 m, this yields a volume transport of about 20 cu km/yr, which is almost identical, within error bars, to our estimate of the trend in <span class="hlt">ice</span> production. The increase in brine rejection in the Ross <span class="hlt">Shelf</span> Polynya associated with the estimated increase with the <span class="hlt">ice</span> production, however, is not consistent with the reported Ross Sea salinity decrease. The locally generated sea <span class="hlt">ice</span> enhancement of Ross Sea salinity may be offset by an increase of relatively low salinity of the water advected into the region from the Amundsen Sea, a consequence of increased precipitation and regional glacial <span class="hlt">ice</span> melt.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JGRC..118.5899R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JGRC..118.5899R"><span>Airborne thickness and freeboard measurements over the McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica, and implications for <span class="hlt">ice</span> density</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rack, Wolfgang; Haas, Christian; Langhorne, Pat J.</p> <p>2013-11-01</p> <p>We present airborne measurements to investigate the thickness of the western McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in the western Ross Sea, Antarctica. Because of basal accretion of marine <span class="hlt">ice</span> and brine intrusions conventional radar systems are limited in detecting the <span class="hlt">ice</span> thickness in this area. In November 2009, we used a helicopter-borne laser and electromagnetic induction sounder (EM bird) to measure several thickness and freeboard profiles across the <span class="hlt">ice</span> <span class="hlt">shelf</span>. The maximum electromagnetically detectable <span class="hlt">ice</span> thickness was about 55 m. Assuming hydrostatic equilibrium, the simultaneous measurement of <span class="hlt">ice</span> freeboard and thickness was used to derive bulk <span class="hlt">ice</span> densities ranging from 800 to 975 kg m-3. Densities higher than those of pure <span class="hlt">ice</span> can be largely explained by the abundance of sediments accumulated at the surface and present within the <span class="hlt">ice</span> <span class="hlt">shelf</span>, and are likely to a smaller extent related to the overestimation of <span class="hlt">ice</span> thickness by the electromagnetic induction measurement related to the presence of a subice platelet layer. The equivalent thickness of debris at a density of 2800 kg m-3 is found to be up to about 2 m thick. A subice platelet layer below the <span class="hlt">ice</span> <span class="hlt">shelf</span>, similar to what is observed in front of the <span class="hlt">ice</span> <span class="hlt">shelf</span> below the sea <span class="hlt">ice</span>, is likely to exist in areas of highest thickness. The thickness and density distribution reflects a picture of areas of basal freezing and supercooled <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Water emerging from below the central <span class="hlt">ice</span> <span class="hlt">shelf</span> cavity into McMurdo Sound.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120013495','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120013495"><span>Mass Gains of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet Exceed Losses</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zwally, H. Jay; Li, Jun; Robbins, John; Saba, Jack L.; Yi, Donghui; Brenner, Anita; Bromwich, David</p> <p>2012-01-01</p> <p>During 2003 to 2008, the mass gain of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet from snow accumulation exceeded the mass loss from <span class="hlt">ice</span> discharge by 49 Gt/yr (2.5% of input), as derived from ICESat laser measurements of elevation change. The net gain (86 Gt/yr) over the West <span class="hlt">Antarctic</span> (WA) and East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets (WA and EA) is essentially unchanged from revised results for 1992 to 2001 from ERS radar altimetry. Imbalances in individual drainage systems (DS) are large (-68% to +103% of input), as are temporal changes (-39% to +44%). The recent 90 Gt/yr loss from three DS (Pine Island, Thwaites-Smith, and Marie-Bryd Coast) of WA exceeds the earlier 61 Gt/yr loss, consistent with reports of accelerating <span class="hlt">ice</span> flow and dynamic thinning. Similarly, the recent 24 Gt/yr loss from three DS in the <span class="hlt">Antarctic</span> Peninsula (AP) is consistent with glacier accelerations following breakup of the Larsen B and other <span class="hlt">ice</span> shelves. In contrast, net increases in the five other DS of WA and AP and three of the 16 DS in East Antarctica (EA) exceed the increased losses. Alternate interpretations of the mass changes driven by accumulation variations are given using results from atmospheric-model re-analysis and a parameterization based on 5% change in accumulation per degree of observed surface temperature change. A slow increase in snowfall with climate waRMing, consistent with model predictions, may be offsetting increased dynamic losses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C41C1232H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C41C1232H"><span>Reconciliation of <span class="hlt">Antarctic</span> marine and terrestrial geologic records: climate and <span class="hlt">ice</span>-sheet variability in the mid-Miocene</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Halberstadt, A. R. W.; DeConto, R.; Gasson, E.; Kowalewski, D. E.; Levy, R. H.; Naish, T.; Chorley, H.</p> <p>2017-12-01</p> <p>The mid-Miocene Climatic Optimum ( 17-15 Ma) serves as a possible analog for future <span class="hlt">Antarctic</span> conditions, as atmospheric CO2 concentrations were similar to those projected for the next few decades. During the subsequent mid-Miocene Climatic Transition, the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (AIS) developed from a more variable <span class="hlt">ice</span> sheet to a continental, marine-terminating <span class="hlt">ice</span> sheet resembling the modern configuration. Near-shore marine records from the Ross Sea (ANDRILL-2A; Levy et al., 2016) imply highly dynamic AIS behavior in the mid-Miocene. Reconstructed environmental conditions during this time period range from full glaciation of the area to a warm interglacial environment. Multiple AIS expansions during the mid-Miocene are interpreted from geophysical evidence including seismic surveys correlated to drill core data (Chow & Bart, 2003). These marine records are seemingly at odds with sedimentary and geomorphic studies in the McMurdo Dry Valleys (MDVs) that suggest the East <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet was mostly invariable since the mid-Miocene (Sugden & Denton, 2004). Well-preserved landforms, observed by Marchant et al. (2013) and others, lack any indication of surface modification from glacial advance or wet cryoturbation, suggesting that hyper-arid cold-desert conditions have persisted in the MDVs since the mid-Miocene. This long-term landform stability in the MDVs implying a stable <span class="hlt">ice</span> sheet is seemingly inconsistent with the highly dynamic AIS behavior reconstructed by Levy et al. (2016). Here, we use a Regional Climate Model (cf. Gasson et al., 2016) with a range of greenhouse gas concentrations, orbital configurations, <span class="hlt">ice</span> sheet and <span class="hlt">shelf</span> geometries, and sea surface conditions to reconcile the apparent dichotomy between marine and terrestrial records. Preliminary results reveal lapse-rate-corrected temperatures in the MDVs that generally remained below freezing in the austral summer, even under the warmest Miocene simulations (840 ppmv atmospheric CO2, `warm' austral</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.S52A..01B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.S52A..01B"><span>Chilean Tsunami Rocks the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bromirski, P. D.; Gerstoft, P.; Chen, Z.; Stephen, R. A.; Diez, A.; Arcas, D.; Wiens, D.; Aster, R. C.; Nyblade, A.</p> <p>2016-12-01</p> <p>The response of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (RIS) to the September 16, 2015 9.3 Mb Chilean earthquake tsunami (> 75 s period) and infragravity (IG) waves (50 - 300 s period) were recorded by a broadband seismic array deployed on the RIS from November 2014 to November 2015. The array included two linear transects, one approximately orthogonal to the <span class="hlt">shelf</span> front extending 430 km southward toward the grounding zone, and an east-west transect spanning the RIS roughly parallel to the front about 100 km south of the <span class="hlt">ice</span> edge (https://scripps.ucsd.edu/centers/iceshelfvibes/). Signals generated by both the tsunami and IG waves were recorded at all stations on floating <span class="hlt">ice</span>, with little ocean wave-induced energy reaching stations on grounded <span class="hlt">ice</span>. Cross-correlation and dispersion curve analyses indicate that tsunami and IG wave-generated signals propagate across the RIS at gravity wave speeds (about 70 m/s), consistent with coupled water-<span class="hlt">ice</span> flexural-gravity waves propagating through the <span class="hlt">ice</span> <span class="hlt">shelf</span> from the north. Gravity wave excitation at periods > 100 s is continuously observed during the austral winter, providing mechanical excitation of the RIS throughout the year. Horizontal displacements are typically about 3 times larger than vertical displacements, producing extensional motions that could facilitate expansion of existing fractures. The vertical and horizontal spectra in the IG band attenuate exponentially with distance from the front. Tsunami model data are used to assess variability of excitation of the RIS by long period gravity waves. Substantial variability across the RIS roughly parallel to the front is observed, likely resulting from a combination of gravity wave amplitude variability along the front, signal attenuation, incident angle of the wave forcing at the front that depends on wave generation location as well as bathymetry under and north of the <span class="hlt">shelf</span>, and water layer and <span class="hlt">ice</span> <span class="hlt">shelf</span> thickness and properties.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20601510','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20601510"><span>Proteorhodopsin-bearing bacteria in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Koh, Eileen Y; Atamna-Ismaeel, Nof; Martin, Andrew; Cowie, Rebecca O M; Beja, Oded; Davy, Simon K; Maas, Elizabeth W; Ryan, Ken G</p> <p>2010-09-01</p> <p>Proteorhodopsins (PRs) are widespread bacterial integral membrane proteins that function as light-driven proton pumps. <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> supports a complex community of autotrophic algae, heterotrophic bacteria, viruses, and protists that are an important food source for higher trophic levels in <span class="hlt">ice</span>-covered regions of the Southern Ocean. Here, we present the first report of PR-bearing bacteria, both dormant and active, in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> from a series of sites in the Ross Sea using gene-specific primers. Positive PR sequences were generated from genomic DNA at all depths in sea <span class="hlt">ice</span>, and these sequences aligned with the classes Alphaproteobacteria, Gammaproteobacteria, and Flavobacteria. The sequences showed some similarity to previously reported PR sequences, although most of the sequences were generally distinct. Positive PR sequences were also observed from cDNA reverse transcribed from RNA isolated from sea <span class="hlt">ice</span> samples. This finding indicates that these sequences were generated from metabolically active cells and suggests that the PR gene is functional within sea <span class="hlt">ice</span>. Both blue-absorbing and green-absorbing forms of PRs were detected, and only a limited number of blue-absorbing forms were found and were in the midsection of the sea <span class="hlt">ice</span> profile in this study. Questions still remain regarding the protein's ecological functions, and ultimately, field experiments will be needed to establish the ecological and functional role of PRs in the sea <span class="hlt">ice</span> ecosystem.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/1239510-sph-non-newtonian-model-ice-sheet-ice-shelf-dynamics','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1239510-sph-non-newtonian-model-ice-sheet-ice-shelf-dynamics"><span>SPH non-Newtonian Model for <span class="hlt">Ice</span> Sheet and <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Dynamics</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Tartakovsky, Alexandre M.; Pan, Wenxiao; Monaghan, Joseph J.</p> <p>2012-07-07</p> <p>We propose a new three-dimensional smoothed particle hydrodynamics (SPH) non-Newtonian model to study coupled <span class="hlt">ice</span> sheet and <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics. Most existing <span class="hlt">ice</span> sheet numerical models use a grid-based Eulerian approach, and are usually restricted to shallow <span class="hlt">ice</span> sheet and <span class="hlt">ice</span> <span class="hlt">shelf</span> approximations of the momentum conservation equation. SPH, a fully Lagrangian particle method, solves the full momentum conservation equation. SPH method also allows modeling of free-surface flows, large material deformation, and material fragmentation without employing complex front-tracking schemes, and does not require re-meshing. As a result, SPH codes are highly scalable. Numerical accuracy of the proposed SPH model ismore » first verified by simulating a plane shear flow with a free surface and the propagation of a blob of <span class="hlt">ice</span> along a horizontal surface. Next, the SPH model is used to investigate the grounding line dynamics of <span class="hlt">ice</span> sheet/<span class="hlt">shelf</span>. The steady position of the grounding line, obtained from our SPH simulations, is in good agreement with laboratory observations for a wide range of bedrock slopes, <span class="hlt">ice</span>-to-fluid density ratios, and flux. We examine the effect of non-Newtonian behavior of <span class="hlt">ice</span> on the grounding line dynamics. The non-Newtonian constitutive model is based on Glen's law for a creeping flow of a polycrystalline <span class="hlt">ice</span>. Finally, we investigate the effect of a bedrock geometry on a steady-state position of the grounding line.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1714546A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1714546A"><span>Structure of the <span class="hlt">shelf</span> and slope waters of the <span class="hlt">Antarctic</span> Seas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Artamonova, Ksenia; Antipov, Nikolay; Gangnus, Ivan; Maslennikov, Vyacheslav</p> <p>2015-04-01</p> <p>The main objective of present work is to consider characteristics of <span class="hlt">shelf</span> and slope waters in the Commonwealth, Ross, Amundson and Bellingshausen Seas. Data of Russian surveys led during the <span class="hlt">Antarctic</span> summer of 2006 - 2014 on RV "Academic Fedorov"and "Academic Treshnikov"was analyzed. Distribution of temperature, salinity, dissolved oxygen, silicate, phosphates and nitrates in the water masses of the Commonwealth and Amundsen seas was shown. Significant differences in the structures of the <span class="hlt">shelf</span> and slope waters of the seas were observed. A water structure at the oceanological sections of the Commonwealth Sea was constituted by the <span class="hlt">Antarctic</span> Surface Water (AASW) with enough high concentration of silicate, nitrate nitrogen and phosphates compare with other areas of the World Ocean; the Upper Circumpolar Deep Water (UCDW) characterized by a minimum of the oxygen content, and a maximum of nutrient concentrations; The Lower Circumpolar Deep Water (LCDW) primary characterized by a salinity maximum and a minimum of nutritive salts as well; and the <span class="hlt">Antarctic</span> Bottom water (AABW). It was shown that the local cold, salt and dense <span class="hlt">Antarctic</span> <span class="hlt">Shelf</span> water (ASW) formed in the <span class="hlt">shelf</span> area of the Commonwealth Sea. The characteristics of ASW were defined. The ASW mixed with the CDW and their mixture (The Bottom Water of the Prydz Bay (BWPB)) moved down along the slope, and reached the bottom.The characteristics of the BWPB were analyzed. The BWPB was defined by higher content of dissolved oxygen (more 5.5 ml/l) and lower contents of biogenic elements (silicon - low 120 µМ, phosphates - low 2.35 µМ and nitrates - low 29 µМ) in the bottom layer at the slope compared with the Circumpolar Deep Water (CDW) characteristics. Interannual variability of characteristics of the water masses was observed on the repeated oceanological section along 70° E in the Commonwealth Sea. It was shown that characteristics and structure of the BWPB undergo appreciable changes year by year. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMGC43E1001D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMGC43E1001D"><span>Glacial History of the NE <span class="hlt">Antarctic</span> Peninsula over centennial to millennial timescales</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Davies, B. J.; Glasser, N. F.; Hambrey, M.; Carrivick, J.; Smellie, J.</p> <p>2010-12-01</p> <p>A detailed glacier inventory of 232 glaciers was undertaken of the northeast <span class="hlt">Antarctic</span> Peninsula and James Ross Island for the first time. Glacier inventories provide representative, detailed and natural indications of the impacts of climate change. Documenting the continued response of <span class="hlt">ice</span> <span class="hlt">shelf</span> feeder glaciers after the collapse of the Prince Gustav <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in 1997 is especially important for predicting future glacier behaviour in this region. James Ross Island has a relatively long history of glacier observations, and offers a unique opportunity to assess the ongoing impacts of a changing climate in a very sensitive part of the global system. This work classified and mapped the glaciers of James Ross Island and the northern <span class="hlt">Antarctic</span> Peninsula for the first time, documenting change in extent and behaviour in 1988, 2001 and 2009, and characterising glacier response to <span class="hlt">ice</span> <span class="hlt">shelf</span> collapse. Glacier altitude, aspect, area, slope and rate of recession were among the indices' measured. James Ross Island is approximately 78% <span class="hlt">ice</span>-covered, with <span class="hlt">ice</span>-free terrain exhibiting characteristic permafrost and thermokarst landforms, including rock glaciers and <span class="hlt">ice</span>-cored moraine. The island is dominated by the cold-based Mount Haddington <span class="hlt">Ice</span> Cap, which feeds numerous polythermal elongate tidewater valley glaciers. The tidewater glaciers typically form extensive medial, lateral and terminal moraines. Initial inventory results show that <span class="hlt">ice-shelf</span> feeder tidewater glaciers on the APIS have stabilised since the 1997 collapse of the Prince Gustav <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, although recession continues. Of the non-<span class="hlt">ice-shelf</span> tidewater glaciers, glacier recession has accelerated in the decade since 2001. Land-based valley glacier retreat has accelerated post 2001, in line with continued atmospheric warming. Climate relationships can be determined from altitude-aspect relationships, with glaciers on the drier eastern side of James Ross Island retreating fastest. Glacier mass balances are strongly</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140010302','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140010302"><span><span class="hlt">Ice-Shelf</span> Flexure and Tidal Forcing of Bindschadler <span class="hlt">Ice</span> Stream, West Antarctica</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Walker, Ryan T.; Parizek, Bryron R.; Alley, Richard B.; Brunt, Kelly M.; Anandakrishnan, Sridhar</p> <p>2014-01-01</p> <p>Viscoelastic models of <span class="hlt">ice-shelf</span> flexure and <span class="hlt">ice</span>-stream velocity perturbations are combined into a single efficient flowline model to study tidal forcing of grounded <span class="hlt">ice</span>. The magnitude and timing of icestream response to tidally driven changes in hydrostatic pressure and/or basal drag are found to depend significantly on bed rheology, with only a perfectly plastic bed allowing instantaneous velocity response at the grounding line. The model can reasonably reproduce GPS observations near the grounding zone of Bindschadler <span class="hlt">Ice</span> Stream (formerly <span class="hlt">Ice</span> Stream D) on semidiurnal time scales; however, other forcings such as tidally driven <span class="hlt">ice-shelf</span> slope transverse to the flowline and flexurally driven till deformation must also be considered if diurnal motion is to be matched</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoRL..4411519C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..4411519C"><span>Regional Changes in Icescape Impact <span class="hlt">Shelf</span> Circulation and Basal Melting</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cougnon, E. A.; Galton-Fenzi, B. K.; Rintoul, S. R.; Legrésy, B.; Williams, G. D.; Fraser, A. D.; Hunter, J. R.</p> <p>2017-11-01</p> <p><span class="hlt">Ice</span> <span class="hlt">shelf</span> basal melt is the dominant contribution to mass loss from <span class="hlt">Antarctic</span> <span class="hlt">ice</span> shelves. However, the sensitivity of basal melt to changes in icescape (grounded icebergs, <span class="hlt">ice</span> shelves, and sea <span class="hlt">ice</span>) and related ocean circulation is poorly understood. Here we simulate the impact of the major 2010 calving event of the Mertz Glacier Tongue (MGT), East Antarctica, and related redistribution of sea <span class="hlt">ice</span> and icebergs on the basal melt rate of the local <span class="hlt">ice</span> shelves. We find that the position of the grounded tabular iceberg B9B controls the water masses that reach the nearby <span class="hlt">ice</span> <span class="hlt">shelf</span> cavities. After the calving of the MGT and the removal of B9B, warmer water is present both within the MGT cavity and on the continental <span class="hlt">shelf</span> driving a 57% increase of the deep MGT basal melting. Major changes in icescape influence the oceanic heat flux responsible for basal <span class="hlt">ice</span> <span class="hlt">shelf</span> melting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890018779','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890018779"><span><span class="hlt">Ice</span> sheet radar altimetry</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zwally, J.</p> <p>1988-01-01</p> <p>The surface topography of the Greenland and <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets between 72 degrees north and south was mapped using radar altimetry data from the U.S. Navy GEOSAT. The glaciological objectives of this activity were to study the dynamics of the <span class="hlt">ice</span> flow, changes in the position of floating <span class="hlt">ice-shelf</span> fronts, and ultimately to measure temporal changes in <span class="hlt">ice</span> surface elevation indicative of <span class="hlt">ice</span> sheet mass balance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4655561','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4655561"><span>Collapse of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet after local destabilization of the Amundsen Basin</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Feldmann, Johannes; Levermann, Anders</p> <p>2015-01-01</p> <p>The future evolution of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet represents the largest uncertainty in sea-level projections of this and upcoming centuries. Recently, satellite observations and high-resolution simulations have suggested the initiation of an <span class="hlt">ice</span>-sheet instability in the Amundsen Sea sector of West Antarctica, caused by the last decades’ enhanced basal <span class="hlt">ice-shelf</span> melting. Whether this localized destabilization will yield a full discharge of marine <span class="hlt">ice</span> from West Antarctica, associated with a global sea-level rise of more than 3 m, or whether the <span class="hlt">ice</span> loss is limited by <span class="hlt">ice</span> dynamics and topographic features, is unclear. Here we show that in the Parallel <span class="hlt">Ice</span> Sheet Model, a local destabilization causes a complete disintegration of the marine <span class="hlt">ice</span> in West Antarctica. In our simulations, at 5-km horizontal resolution, the region disequilibrates after 60 y of currently observed melt rates. Thereafter, the marine <span class="hlt">ice</span>-sheet instability fully unfolds and is not halted by topographic features. In fact, the <span class="hlt">ice</span> loss in Amundsen Sea sector shifts the catchment's <span class="hlt">ice</span> divide toward the Filchner–Ronne and Ross <span class="hlt">ice</span> shelves, which initiates grounding-line retreat there. Our simulations suggest that if a destabilization of Amundsen Sea sector has indeed been initiated, Antarctica will irrevocably contribute at least 3 m to global sea-level rise during the coming centuries to millennia. PMID:26578762</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T13F..06T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T13F..06T"><span>Turning up the Heat on the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (From Below): Challenges and Near-Term Opportunities for Measuring <span class="hlt">Antarctic</span> Geothermal Fluxes (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tulaczyk, S. M.; Hossainzadeh, S.</p> <p>2010-12-01</p> <p><span class="hlt">Antarctic</span> heat flow plays an important role in determining the rate of meltwater production at the base of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet. Basal meltwater represents a key control on <span class="hlt">ice</span> sheet mass balance, <span class="hlt">Antarctic</span> geochemical fluxes into the Southern Ocean, and subglacial microbial habitats. However, direct measurements of heat flow are difficult in glaciated terrains. Vertical temperature profiles determined in <span class="hlt">ice</span> boreholes are influenced by thermal energy fluxes associated with basal melting/freezing and have to be used with caution when calculating geothermal flux rates. Two published continent-wide geophysical estimates of <span class="hlt">Antarctic</span> geothermal fluxes provide valuable databases but are not fully consistent with each other and need to be verified by direct subglacial measurements. Planned drilling into <span class="hlt">Antarctic</span> subglacial environments will offer the opportunity to perform such measurements. Determination of temperature gradients in sedimentary sequences resting at the bottom of subglacial lakes will offer particularly useful insights. Temperature profiles in such environments will not be thermally or mechanically disturbed as it may be the case in till layers proximal to a sliding <span class="hlt">ice</span> base. We will review plans for making such measurements as part of the WISSARD (Whillans <span class="hlt">Ice</span> Stream Subglacial Access Research Drilling) project, which is scheduled to penetrate the West <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet in 2012-13 and 2013-14.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950053174&hterms=3G&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3D3G','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950053174&hterms=3G&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3D3G"><span>Present-day <span class="hlt">Antarctic</span> <span class="hlt">ice</span> mass changes and crustal motion</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>James, Thomas S.; Ivins, Erik R.</p> <p>1995-01-01</p> <p>The peak vertical velocities predicted by three realistic, but contrasting, present-day scenarios of <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet mass balance are found to be of the order of several mm/a. One scenario predicts local uplift rates in excess of 5 mm/a. These rates are small compared to the peak <span class="hlt">Antarctic</span> vertical velocities of the <span class="hlt">ICE</span>-3G glacial rebound model, which are in excess of 20 mm/a. If the Holocene <span class="hlt">Antarctic</span> deglaciation history protrayed in <span class="hlt">ICE</span>-3G is realistic, and if regional upper mantle viscosity is not an order of magnitude below 10(exp 21) Pa(dot)s, then a vast geographical region in West Antarctica is uplifting at a rate that could be detected by a future Global Positioning System (GPS) campaign. While present-day scenarios predict small vertical crustal velocities, their overall continent-ocean mass exchange is large enough to account for a substantial portion of the observed secular polar motion (omega m(arrow dot)) and time-varying zonal gravity field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19990100907&hterms=3G&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3D3G','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19990100907&hterms=3G&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3D3G"><span>Present-day <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Mass Changes and Crustal Motion</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>James, Thomas S.; Ivins, Erik R.</p> <p>1995-01-01</p> <p>The peak vertical velocities predicted by three realistic, but contrasting, present-day scenarios of <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet mass balance are found to be of the order of several mm/a. One scenario predicts local uplift rates in excess of 5 mm/a. These rates are small compared to the peak <span class="hlt">Antarctic</span> vertical velocities of the <span class="hlt">ICE</span>-3G glacial rebound model, which are in excess of 20 mm/a. If the Holocene <span class="hlt">Antarctic</span> deglaciation history portrayed in <span class="hlt">ICE</span>-3G is realistic, and if regional upper mantle viscosity is not an order of magnitude below 10(exp 21) pa s, then a vast geographical region in West Antarctica is uplifting at a rate that could be detected by a future Global Positioning System (GPS) campaign. While present-day scenarios predict small vertical crustal velocities, their overall continent-ocean mass exchange is large enough to account for a substantial portion of the observed secular polar motion ((Omega)m(bar)) and time-varying zonal gravity field J(sub 1).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25143114','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25143114"><span>A microbial ecosystem beneath the West <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Christner, Brent C; Priscu, John C; Achberger, Amanda M; Barbante, Carlo; Carter, Sasha P; Christianson, Knut; Michaud, Alexander B; Mikucki, Jill A; Mitchell, Andrew C; Skidmore, Mark L; Vick-Majors, Trista J</p> <p>2014-08-21</p> <p>Liquid water has been known to occur beneath the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet for more than 40 years, but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale. Here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial <span class="hlt">Antarctic</span> lake. Subglacial Lake Whillans (SLW) lies beneath approximately 800 m of <span class="hlt">ice</span> on the lower portion of the Whillans <span class="hlt">Ice</span> Stream (WIS) in West Antarctica and is part of an extensive and evolving subglacial drainage network. The water column of SLW contained metabolically active microorganisms and was derived primarily from glacial <span class="hlt">ice</span> melt with solute sources from lithogenic weathering and a minor seawater component. Heterotrophic and autotrophic production data together with small subunit ribosomal RNA gene sequencing and biogeochemical data indicate that SLW is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea. Our results confirm that aquatic environments beneath the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet support viable microbial ecosystems, corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes that can mobilize elements from the lithosphere and influence Southern Ocean geochemical and biological systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Natur.547...49L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Natur.547...49L"><span>Climate change drives expansion of <span class="hlt">Antarctic</span> <span class="hlt">ice</span>-free habitat</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Jasmine R.; Raymond, Ben; Bracegirdle, Thomas J.; Chadès, Iadine; Fuller, Richard A.; Shaw, Justine D.; Terauds, Aleks</p> <p>2017-07-01</p> <p><span class="hlt">Antarctic</span> terrestrial biodiversity occurs almost exclusively in <span class="hlt">ice</span>-free areas that cover less than 1% of the continent. Climate change will alter the extent and configuration of <span class="hlt">ice</span>-free areas, yet the distribution and severity of these effects remain unclear. Here we quantify the impact of twenty-first century climate change on <span class="hlt">ice</span>-free areas under two Intergovernmental Panel on Climate Change (IPCC) climate forcing scenarios using temperature-index melt modelling. Under the strongest forcing scenario, <span class="hlt">ice</span>-free areas could expand by over 17,000 km2 by the end of the century, close to a 25% increase. Most of this expansion will occur in the <span class="hlt">Antarctic</span> Peninsula, where a threefold increase in <span class="hlt">ice</span>-free area could drastically change the availability and connectivity of biodiversity habitat. Isolated <span class="hlt">ice</span>-free areas will coalesce, and while the effects on biodiversity are uncertain, we hypothesize that they could eventually lead to increasing regional-scale biotic homogenization, the extinction of less-competitive species and the spread of invasive species.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28658207','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28658207"><span>Climate change drives expansion of <span class="hlt">Antarctic</span> <span class="hlt">ice</span>-free habitat.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lee, Jasmine R; Raymond, Ben; Bracegirdle, Thomas J; Chadès, Iadine; Fuller, Richard A; Shaw, Justine D; Terauds, Aleks</p> <p>2017-07-06</p> <p><span class="hlt">Antarctic</span> terrestrial biodiversity occurs almost exclusively in <span class="hlt">ice</span>-free areas that cover less than 1% of the continent. Climate change will alter the extent and configuration of <span class="hlt">ice</span>-free areas, yet the distribution and severity of these effects remain unclear. Here we quantify the impact of twenty-first century climate change on <span class="hlt">ice</span>-free areas under two Intergovernmental Panel on Climate Change (IPCC) climate forcing scenarios using temperature-index melt modelling. Under the strongest forcing scenario, <span class="hlt">ice</span>-free areas could expand by over 17,000 km 2 by the end of the century, close to a 25% increase. Most of this expansion will occur in the <span class="hlt">Antarctic</span> Peninsula, where a threefold increase in <span class="hlt">ice</span>-free area could drastically change the availability and connectivity of biodiversity habitat. Isolated <span class="hlt">ice</span>-free areas will coalesce, and while the effects on biodiversity are uncertain, we hypothesize that they could eventually lead to increasing regional-scale biotic homogenization, the extinction of less-competitive species and the spread of invasive species.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C42A..08S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C42A..08S"><span>Geometric controls of the flexural gravity waves on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sergienko, O. V.</p> <p>2017-12-01</p> <p>Long-period ocean waves, formed locally or at distant sources, can reach sub-<span class="hlt">ice-shelf</span> cavities and excite coupled motion in the cavity and the <span class="hlt">ice</span> <span class="hlt">shelf</span> - flexural gravity waves. Three-dimensional numerical simulations of the flexural gravity waves on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> show that propagation of these waves is strongly controlled by the geometry of the system - the cavity shape, its water-column thickness and the <span class="hlt">ice-shelf</span> thickness. The results of numerical simulations demonstrate that propagation of the waves is spatially organized in beams, whose orientation is determined by the direction of the of the open ocean waves incident on the <span class="hlt">ice-shelf</span> front. As a result, depending on the beams orientation, parts of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> experience significantly larger flexural stresses compared to other parts where the flexural gravity beams do not propagate. Very long-period waves can propagate farther away from the <span class="hlt">ice-shelf</span> front exciting flexural stresses in the vicinity of the grounding line.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFMOS13C1208P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFMOS13C1208P"><span>Tidal Impacts on Oceanographic and Sea-<span class="hlt">ice</span> Processes in the Southern Ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Padman, L.; Muench, R. D.; Howard, S.; Mueller, R.</p> <p>2008-12-01</p> <p>We review recent field and modeling results that demonstrate the importance of tides in establishing the oceanographic and sea-<span class="hlt">ice</span> conditions in the boundary regions of the Southern Ocean. The tidal component dominates the total oceanic kinetic energy throughout much of the circum-<span class="hlt">Antarctic</span> seas. This domination is especially pronounced over the continental slope and <span class="hlt">shelf</span> including the sub-<span class="hlt">ice-shelf</span> cavities. Tides provide most of the energy that forces diapycnal mixing under <span class="hlt">ice</span> shelves and thereby contributes to basal melting. The resulting <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Water is a significant component of the <span class="hlt">Antarctic</span> Bottom Water (AABW) filling much of the deep global ocean. Tides exert significant divergent forcing on sea <span class="hlt">ice</span> along glacial <span class="hlt">ice</span> fronts and coastal regions, contributing to creation and maintenance of the coastal polynyas where much of the High Salinity <span class="hlt">Shelf</span> Water component of AABW is formed. Additional tidally forced <span class="hlt">ice</span> divergence along the <span class="hlt">shelf</span> break and upper slope significantly impacts area-averaged <span class="hlt">ice</span> growth and upper-ocean salinity. Tidally forced cross- slope advection, and mixing by the benthic stress associated with tidal currents along the <span class="hlt">shelf</span> break and upper slope, strongly influence the paths, volume fluxes and hydrographic properties of benthic outflows of dense water leaving the continental <span class="hlt">shelf</span>. These outflows provide primary source waters for the AABW. These results confirm that general ocean circulation and coupled ocean/<span class="hlt">ice</span>/atmosphere climate models must incorporate the impacts of tides.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSHE44B1508G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSHE44B1508G"><span>Seismic Imaging of Circumpolar Deep Water Exchange across the <span class="hlt">Shelf</span> Break of the <span class="hlt">Antarctic</span> Peninsula</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gunn, K.; White, N.; Larter, R. D.; Falder, M.; Caulfield, C. C. P.</p> <p>2016-02-01</p> <p>The western <span class="hlt">Antarctic</span> Peninsula is an area of recent extreme atmospheric warming. In the adjacent ocean, there is particular interest in on-<span class="hlt">shelf</span> movement of Circumpolar Deep Water as a possible link to changing climate by affecting <span class="hlt">ice</span> <span class="hlt">shelf</span> processes. Here, we investigate on-<span class="hlt">shelf</span> intrusions using two-dimensional seismic imaging of the water column which has vertical and horizontal resolutions of 10 m. 8 seismic profiles were acquired in February 2015 using the RRS James Clark Ross. These profiles traverse the <span class="hlt">shelf</span> break and cross two bathymetric features, the Marguerite and Biscoe troughs, which may play a role in water exchange processes. Seismic data were acquired using two Generator-Injector air guns fired every 10 s with a pressure of 2000 psi. Reflections were recorded on a 2.4 km streamer of 192 receivers spaced every 12.5 m. Observed reflections in the processed records are caused by rapid changes of temperature ( 80%) and salinity ( 20%), delineating water masses of different properties. 13 XCTDs and XBTs plus a 38 kHz echo-sounder profile were simultaneously acquired along seismic profiles and used for calibration. Preliminary results show the top of the Winter Water layer as a bright reflection at 50-120 m depth across the entire survey, corresponding to temperatures ≤ -1°C. Curved, discontinuous, eddy-like reflections, also seen on echo-sounder profiles, are attributed to modified Upper Circumpolar Deep Water with temperatures ≥ 1.34°C. A warm core eddy, 11 km long and 220 m high, is visible 2 km inland of the <span class="hlt">shelf</span> break. Pure Upper Circumpolar Deep Water of temperatures ≥ 1.80°C is aligned with weak but discernible, lens-shaped reflections. Eddy-like structures and the overall reflective morphology yield useful insights into <span class="hlt">shelf</span> exchange processes, suggestive of three potential mechanisms: (i) topography controlled flow; (ii) an '<span class="hlt">ice</span>-pump' mechanism; and (iii) mesoscale eddies.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C11C0775W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C11C0775W"><span>Seismic Excitation of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> by Whillans <span class="hlt">Ice</span> Stream Stick-Slip Events</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wiens, D.; Pratt, M. J.; Aster, R. C.; Nyblade, A.; Bromirski, P. D.; Stephen, R. A.; Gerstoft, P.; Diez, A.; Cai, C.; Anthony, R. E.; Shore, P.</p> <p>2015-12-01</p> <p>Rapid variations in the flow rate of upstream glaciers and <span class="hlt">ice</span> streams may cause significant deformation of <span class="hlt">ice</span> shelves. The Whillans <span class="hlt">Ice</span> Stream (WIS) represents an extreme example of rapid variations in velocity, with motions near the grounding line consisting almost entirely of once or twice-daily stick-slip events with a displacement of up to 0.7 m (Winberry et al, 2014). Here we report observations of compressional waves from the WIS slip events propagating hundreds of kilometers across the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (RIS) detected by broadband seismographs deployed on the <span class="hlt">ice</span> <span class="hlt">shelf</span>. The WIS slip events consist of rapid basal slip concentrated at three high friction regions (often termed sticky-spots or asperities) within a period of about 25 minutes (Pratt et al, 2014). Compressional displacement pulses from the second and third sticky spots are detected across the entire RIS up to about 600 km away from the source. The largest pulse results from the third sticky spot, located along the northwestern grounding line of the WIS. Propagation velocities across the <span class="hlt">ice</span> <span class="hlt">shelf</span> are significantly slower than the P wave velocity in <span class="hlt">ice</span>, as the long period displacement pulse is also sensitive to velocities of the water and sediments beneath the <span class="hlt">ice</span> <span class="hlt">shelf</span>. Particle motions are, to the limit of resolution, entirely within the horizontal plane and roughly radial with respect to the WIS sticky-spots, but show significant complexity, presumably due to differences in <span class="hlt">ice</span> velocity, thickness, and the thickness of water and sediment beneath. Study of this phenomenon should lead to greater understanding of how the <span class="hlt">ice</span> <span class="hlt">shelf</span> responds to sudden forcing around the periphery.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSHE44B1515S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSHE44B1515S"><span>Spatial and temporal variation of <span class="hlt">Shelf</span> Water and its connection with <span class="hlt">Antarctic</span> Bottom Water in Prydz Bay, East Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sun, Y.; Shi, J.; Yuan, X.</p> <p>2016-02-01</p> <p>Hydrographic surveys from 1981 to 2015, instrumented seal data from 2004 to 2014, and mooring data were used to reveal spatial and temporal variation of <span class="hlt">Shelf</span> Water (SW) and the connection between SW and <span class="hlt">Antarctic</span> Bottom Water (AABW) in Prydz Bay. The basic spatial pattern of the SW properties was presented and 5 subregions were distinguished based on the pattern and the topography. The change of water masses and the processes on the <span class="hlt">shelf</span> are investigated in these subregions. A high salinity SW(S>34.6) is observed in the central and northern part of the Amery Basin in summer, which is like to be caused by the Circumpolar Deep Water (CDW) intrusion, and the eddy activities could be the primary impact to the CDW intrusion. There could be less CDW intrusion in winter because of the <span class="hlt">ice</span> cover in this subregion, which is supported by the mooring in Prydz Bay Channel. A high salinity SW is observed near the Mackenzie polynya in winter, which is caused by brine rejection in <span class="hlt">ice</span> production process. But the high salinity SW seems unlikely to form the overflow denser SW and locally form AABW. A dense water mass with low salinity, low temperature and high oxygen was observed on the <span class="hlt">shelf</span> break in the 70.5°E section, which could be caused by the <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Water (ISW) export from Amery <span class="hlt">Shelf</span>. According to the hydrographic data, the dense water can form overflow DSW and flow downslope to west, which can be observed in the bottom of slope near 1500m in the 70°E section. The water will form AABW if it can flow downslope to the deep basin and keep mixing with CDW, suggesting a new type of DSW overflow in Prydz Bay.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26417090','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26417090"><span>No barrier to emergence of bathyal king crabs on the <span class="hlt">Antarctic</span> <span class="hlt">shelf</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Aronson, Richard B; Smith, Kathryn E; Vos, Stephanie C; McClintock, James B; Amsler, Margaret O; Moksnes, Per-Olav; Ellis, Daniel S; Kaeli, Jeffrey; Singh, Hanumant; Bailey, John W; Schiferl, Jessica C; van Woesik, Robert; Martin, Michael A; Steffel, Brittan V; Deal, Michelle E; Lazarus, Steven M; Havenhand, Jonathan N; Swalethorp, Rasmus; Kjellerup, Sanne; Thatje, Sven</p> <p>2015-10-20</p> <p>Cold-water conditions have excluded durophagous (skeleton-breaking) predators from the <span class="hlt">Antarctic</span> seafloor for millions of years. Rapidly warming seas off the western <span class="hlt">Antarctic</span> Peninsula could now facilitate their return to the continental <span class="hlt">shelf</span>, with profound consequences for the endemic fauna. Among the likely first arrivals are king crabs (Lithodidae), which were discovered recently on the adjacent continental slope. During the austral summer of 2010 ‒ 2011, we used underwater imagery to survey a slope-dwelling population of the lithodid Paralomis birsteini off Marguerite Bay, western <span class="hlt">Antarctic</span> Peninsula for environmental or trophic impediments to shoreward expansion. The population density averaged ∼ 4.5 individuals × 1,000 m(-2) within a depth range of 1,100 ‒ 1,500 m (overall observed depth range 841-2,266 m). Images of juveniles, discarded molts, and precopulatory behavior, as well as gravid females in a trapping study, suggested a reproductively viable population on the slope. At the time of the survey, there was no thermal barrier to prevent the lithodids from expanding upward and emerging on the outer <span class="hlt">shelf</span> (400- to 550-m depth); however, near-surface temperatures remained too cold for them to survive in inner-<span class="hlt">shelf</span> and coastal environments (<200 m). Ambient salinity, composition of the substrate, and the depth distribution of potential predators likewise indicated no barriers to expansion of lithodids onto the outer <span class="hlt">shelf</span>. Primary food resources for lithodids--echinoderms and mollusks--were abundant on the upper slope (550-800 m) and outer <span class="hlt">shelf</span>. As sea temperatures continue to rise, lithodids will likely play an increasingly important role in the trophic structure of subtidal communities closer to shore.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4620881','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4620881"><span>No barrier to emergence of bathyal king crabs on the <span class="hlt">Antarctic</span> <span class="hlt">shelf</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Aronson, Richard B.; Smith, Kathryn E.; Vos, Stephanie C.; McClintock, James B.; Amsler, Margaret O.; Moksnes, Per-Olav; Ellis, Daniel S.; Kaeli, Jeffrey; Singh, Hanumant; Bailey, John W.; Schiferl, Jessica C.; van Woesik, Robert; Martin, Michael A.; Steffel, Brittan V.; Deal, Michelle E.; Lazarus, Steven M.; Havenhand, Jonathan N.; Swalethorp, Rasmus; Kjellerup, Sanne; Thatje, Sven</p> <p>2015-01-01</p> <p>Cold-water conditions have excluded durophagous (skeleton-breaking) predators from the <span class="hlt">Antarctic</span> seafloor for millions of years. Rapidly warming seas off the western <span class="hlt">Antarctic</span> Peninsula could now facilitate their return to the continental <span class="hlt">shelf</span>, with profound consequences for the endemic fauna. Among the likely first arrivals are king crabs (Lithodidae), which were discovered recently on the adjacent continental slope. During the austral summer of 2010‒2011, we used underwater imagery to survey a slope-dwelling population of the lithodid Paralomis birsteini off Marguerite Bay, western <span class="hlt">Antarctic</span> Peninsula for environmental or trophic impediments to shoreward expansion. The population density averaged ∼4.5 individuals × 1,000 m−2 within a depth range of 1,100‒1,500 m (overall observed depth range 841–2,266 m). Images of juveniles, discarded molts, and precopulatory behavior, as well as gravid females in a trapping study, suggested a reproductively viable population on the slope. At the time of the survey, there was no thermal barrier to prevent the lithodids from expanding upward and emerging on the outer <span class="hlt">shelf</span> (400- to 550-m depth); however, near-surface temperatures remained too cold for them to survive in inner-<span class="hlt">shelf</span> and coastal environments (<200 m). Ambient salinity, composition of the substrate, and the depth distribution of potential predators likewise indicated no barriers to expansion of lithodids onto the outer <span class="hlt">shelf</span>. Primary food resources for lithodids—echinoderms and mollusks—were abundant on the upper slope (550–800 m) and outer <span class="hlt">shelf</span>. As sea temperatures continue to rise, lithodids will likely play an increasingly important role in the trophic structure of subtidal communities closer to shore. PMID:26417090</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018ISPAr42.3.1597S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018ISPAr42.3.1597S"><span>The Research on Elevation Change of <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet Based on CRYOSAT-2 Alimeter</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sun, Q.; Wan, J.; Liu, S.; Li, Y.</p> <p>2018-04-01</p> <p>In this paper, the Cryosat-2 altimeter data distributed by the ESA, and these data are processed to extract the information of the elevation change of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet from 2010 to 2017. Firstly, the main pretreatment preprocessing for Cryosat-2 altimetry data is crossover adjustment and elimination of rough difference. Then the grid DEM of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet was constructed by using the kriging interpolation method,and analyzed the spatial characteristic time characteristics of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet. The latitude-weighted elevation can be obtained by using the elevation data of each cycle, and then the general trend of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet elevation variation can be seen roughly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70018390','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70018390"><span>Active volcanism beneath the West <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet and implications for <span class="hlt">ice</span>-sheet stability</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Blankenship, D.D.; Bell, R.E.; Hodge, S.M.; Brozena, J.M.; Behrendt, John C.; Finn, C.A.</p> <p>1993-01-01</p> <p>IT is widely understood that the collapse of the West <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet (WAIS) would cause a global sea level rise of 6 m, yet there continues to be considerable debate about the detailed response of this <span class="hlt">ice</span> sheet to climate change1-3. Because its bed is grounded well below sea level, the stability of the WAIS may depend on geologically controlled conditions at the base which are independent of climate. In particular, heat supplied to the base of the <span class="hlt">ice</span> sheet could increase basal melting and thereby trigger <span class="hlt">ice</span> streaming, by providing the water for a lubricating basal layer of till on which <span class="hlt">ice</span> streams are thought to slide4,5. <span class="hlt">Ice</span> streams act to protect the reservoir of slowly moving inland <span class="hlt">ice</span> from exposure to oceanic degradation, thus enhancing <span class="hlt">ice</span>-sheet stability. Here we present aerogeophysical evidence for active volcanism and associated elevated heat flow beneath the WAIS near the critical region where <span class="hlt">ice</span> streaming begins. If this heat flow is indeed controlling <span class="hlt">ice</span>-stream formation, then penetration of ocean waters inland of the thin hot crust of the active portion of the West <span class="hlt">Antarctic</span> rift system could lead to the disappearance of <span class="hlt">ice</span> streams, and possibly trigger a collapse of the inland <span class="hlt">ice</span> reservoir.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013TCD.....7.4177B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013TCD.....7.4177B"><span>Seabed topography beneath Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span> from seismic soundings</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brisbourne, A. M.; Smith, A. M.; King, E. C.; Nicholls, K. W.; Holland, P. R.; Makinson, K.</p> <p>2013-08-01</p> <p>Seismic reflection soundings of <span class="hlt">ice</span> thickness and seabed depth were acquired on the Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in order to test a sub-<span class="hlt">shelf</span> bathymetry model derived from the inversion of <span class="hlt">Ice</span>Bridge gravity data. A series of lines were collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the <span class="hlt">ice</span> front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-<span class="hlt">shelf</span> oceanic circulation may be affected by <span class="hlt">ice</span> draft and sub-<span class="hlt">shelf</span> cavity thickness. The seismic velocity profile in the upper 100 m of firn and <span class="hlt">ice</span> was derived from shallow refraction surveys at a number of locations. Measured temperatures within the <span class="hlt">ice</span> column and at the <span class="hlt">ice</span> base were used to define the velocity profile through the remainder of the <span class="hlt">ice</span> column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in <span class="hlt">ice</span> and water cavity thickness are in general <10 m. Compared with the seismic measurements, the root-mean-square error in the gravimetrically derived bathymetry at the seismic sites is 162 m. The seismic profiles prove the non-existence of several bathymetric features that are indicated in the gravity inversion model, significantly modifying the expected oceanic circulation beneath the <span class="hlt">ice</span> <span class="hlt">shelf</span>. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of <span class="hlt">Ice</span>Bridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-<span class="hlt">shelf</span> ocean circulation models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C51F..03A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C51F..03A"><span>Sedimentological fingerprint of modern and ancient meltwater outbursts across <span class="hlt">Antarctic</span> continental shelves and slopes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anderson, J. B.; Simkins, L. M.; Prothro, L. O.</p> <p>2016-12-01</p> <p>On formerly glaciated <span class="hlt">Antarctic</span> continental shelves, the crystalline inner <span class="hlt">shelf</span> is commonly dissected by linked subglacial lake and channel systems; however, signatures of meltwater are rare within subglacial and glacial-marine deposits on the middle to outer continental <span class="hlt">shelf</span>. Recent observations of <span class="hlt">ice</span>-marginal landforms incised by meltwater channels in the western Ross Sea indicate pulses of meltwater outbursts at marine-based grounding lines during deglaciation of the continental <span class="hlt">shelf</span>. Here we present sedimentological evidence of meltwater outbursts and associated plumes from new and legacy cores collected on the continental <span class="hlt">shelf</span> and slope within the Ross Sea, Amundsen Sea, and Marguerite Bay. Discrete fine-grained silt deposits are found overlying till and within proximal grounding line deposits and open-marine diatomaceous sediments. The deposits are massive to laminated, contain little to no coarser material, moderately sorted and dominated by a 10 μm grain-size mode. Grain-size measurements show no indication of winnowing; therefore, we interpret these deposits as meltwater deposits, transported by subglacial meltwater drainage systems to the grounding line and dispersed further seaward by meltwater plumes. The similarity of the deposits down-core and between <span class="hlt">shelf</span> and slope sites within the Ross Sea, Amundsen Sea, and Marguerite Bay indicate that sorting and/or production of the fine silts occurs due to subglacial hydrodynamic processes. These distinctive meltwater deposits within the stratigraphic record provide an accessible proxy for identifying meltwater discharge from the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet and potentially be used to correlate cores on and off the continental <span class="hlt">shelf</span>. Dating events on the continental <span class="hlt">shelf</span> is notoriously difficult; therefore, deeper ocean records offer an easier means of bracketing the timing of meltwater discharge events. Longer records of <span class="hlt">ice</span> dynamics from off the continental <span class="hlt">shelf</span> are commonly used to reconstruct IRD records</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C33D..01P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C33D..01P"><span>Modeling <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet retreat in warm climates: a historical perspective.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pollard, D.; Deconto, R. M.; Gasson, E.</p> <p>2016-12-01</p> <p>Early modeling of <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet size vs. climate focused on asymmetry between retreat and growth, with much greater warming needed to cause retreat from full <span class="hlt">ice</span> cover, due to Height Mass Balance Feedback and albedo feedback. This led to a long-standing model-data conflict, with models needing 1000 to2000 ppmv atmospheric CO2 to produce retreat from full size, vs. proxy data of large <span class="hlt">ice</span> fluctuations despite much lower CO2 since the Miocene.Subsequent modeling with marine <span class="hlt">ice</span> physics found that the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet could undergo repeated warm-period collapses with realistic past forcing. However, that yields only 3 to 7 m equivalent sea-level rise above modern, compared to 10 to 20 m or more suggested by some geologic data. Large subglacial basins in East Antarctica could be vulnerable to the same processes,but did not retreat in most models due to narrower and shallower sills.After recent modifications, some <span class="hlt">ice</span> sheet models were able to produce warm-period collapse of major East <span class="hlt">Antarctic</span> basins, with sea-level rise of up to 15 m. The modifications are (i) hydrofracturing by surface melt, and structural failure of <span class="hlt">ice</span> cliffs, or (ii) numerical treatment at the grounding line. In these models, large retreat occurs both for past warmintervals, and also for future business-as-usual scenarios.Some interpretations of data in the late Oligocene and Miocene suggest yet larger fluctuations, between 50 to 100% of modern <span class="hlt">Antarctic</span> size. That would require surface-melt driven retreat of some terrestrial East <span class="hlt">Antarctic</span> <span class="hlt">ice</span>, despite the hysteresis issue raised above. A recent study using a coupled climate-<span class="hlt">ice</span> sheet model found that with a finer climate gridand more frequent coupling exchange, substantial retreat of terrestrial Antarctica can occur with 500 to 840 ppmv CO2, much lower than in earlier models. This will allow meaningful interactions between modeling and deeper-time geologic interpretations since the late Oligocene.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1912539S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1912539S"><span>Analysis on variability and trend in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> albedo between 1983 and 2009</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Seo, Minji; Kim, Hyun-cheol; Choi, Sungwon; Lee, Kyeong-sang; Han, Kyung-soo</p> <p>2017-04-01</p> <p>Sea <span class="hlt">ice</span> is key parameter in order to understand the cryosphere climate change. Several studies indicate the different trend of sea <span class="hlt">ice</span> between Antarctica and Arctic. Albedo is important factor for understanding the energy budget and factors for observing of environment changes of Cryosphere such as South Pole, due to it mainly covered by <span class="hlt">ice</span> and snow with high albedo value. In this study, we analyzed variability and trend of long-term sea <span class="hlt">ice</span> albedo data to understand the changes of sea <span class="hlt">ice</span> over Antarctica. In addiction, sea <span class="hlt">ice</span> albedo researched the relationship with <span class="hlt">Antarctic</span> oscillation in order to determine the atmospheric influence. We used the sea <span class="hlt">ice</span> albedo data at The Satellite Application Facility on Climate Monitoring and <span class="hlt">Antarctic</span> Oscillation data at NOAA Climate Prediction Center (CPC). We analyzed the annual trend in albedo using linear regression to understand the spatial and temporal tendency. <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> albedo has two spatial trend. Weddle sea / Ross sea sections represent a positive trend (0.26% ˜ 0.04% yr-1) and Bellingshausen Amundsen sea represents a negative trend (- 0.14 ˜ -0.25%yr-1). Moreover, we performed the correlation analysis between albedo and <span class="hlt">Antarctic</span> oscillation. As a results, negative area indicate correlation coefficient of - 0.3639 and positive area indicates correlation coefficient of - 0.0741. Theses results sea <span class="hlt">ice</span> albedo has regional trend according to ocean. Decreasing sea <span class="hlt">ice</span> trend has negative relationship with <span class="hlt">Antarctic</span> oscillation, its represent a possibility that sea <span class="hlt">ice</span> influence atmospheric factor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C51A0967B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51A0967B"><span>Mapping Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> with ROSETTA-<span class="hlt">Ice</span> airborne laser altimetry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Becker, M. K.; Fricker, H. A.; Padman, L.; Bell, R. E.; Siegfried, M. R.; Dieck, C. C. M.</p> <p>2017-12-01</p> <p>The Ross Ocean and <span class="hlt">ice</span> <span class="hlt">Shelf</span> Environment and Tectonic setting Through Aerogeophysical surveys and modeling (ROSETTA-<span class="hlt">Ice</span>) project combines airborne glaciological, geological, and oceanographic observations to enhance our understanding of the history and dynamics of the large ( 500,000 square km) Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (RIS). Here, we focus on the Light Detection And Ranging (LiDAR) data collected in 2015 and 2016. This data set represents a significant advance in resolution: Whereas the last attempt to systematically map RIS (the surface-based RIGGS program in the 1970s) was at 55 km grid spacing, the ROSETTA-<span class="hlt">Ice</span> grid has 10-20 km line spacing and much higher along-track resolution. We discuss two different strategies for processing the raw LiDAR data: one that requires proprietary software (Riegl's RiPROCESS package), and one that employs open-source programs and libraries. With the processed elevation data, we are able to resolve fine-scale <span class="hlt">ice-shelf</span> features such as the "rampart-moat" <span class="hlt">ice</span>-front morphology, which has previously been observed on and modeled for icebergs. This feature is also visible in the ROSETTA-<span class="hlt">Ice</span> shallow-<span class="hlt">ice</span> radar data; comparing the laser data with radargrams provides insight into the processes leading to their formation. Near-surface firn state and total firn air content can also be investigated through combined analysis of laser altimetry and radar data. By performing similar analyses with data from the radar altimeter aboard CryoSat-2, we demonstrate the utility of the ROSETTA-<span class="hlt">Ice</span> LiDAR data set in satellite validation efforts. The incorporation of the LiDAR data from the third and final field season (December 2017) will allow us to construct a DEM and an <span class="hlt">ice</span> thickness map of RIS for the austral summers of 2015-2017. These products will be used to validate and extend observations of height changes from satellite radar and laser altimetry, as well as to update regional models of ocean circulation and <span class="hlt">ice</span> dynamics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C41B0663K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C41B0663K"><span>Using paleoclimate data to improve models of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>King, M. A.; Phipps, S. J.; Roberts, J. L.; White, D.</p> <p>2016-12-01</p> <p><span class="hlt">Ice</span> sheet models are the most descriptive tools available to simulate the future evolution of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (AIS), including its contribution towards changes in global sea level. However, our knowledge of the dynamics of the coupled <span class="hlt">ice</span>-ocean-lithosphere system is inevitably limited, in part due to a lack of observations. Furthemore, to build computationally efficient models that can be run for multiple millennia, it is necessary to use simplified descriptions of <span class="hlt">ice</span> dynamics. <span class="hlt">Ice</span> sheet modeling is therefore an inherently uncertain exercise. The past evolution of the AIS provides an opportunity to constrain the description of physical processes within <span class="hlt">ice</span> sheet models and, therefore, to constrain our understanding of the role of the AIS in driving changes in global sea level. We use the Parallel <span class="hlt">Ice</span> Sheet Model (PISM) to demonstrate how paleoclimate data can improve our ability to predict the future evolution of the AIS. A large, perturbed-physics ensemble is generated, spanning uncertainty in the parameterizations of four key physical processes within <span class="hlt">ice</span> sheet models: <span class="hlt">ice</span> rheology, <span class="hlt">ice</span> <span class="hlt">shelf</span> calving, and the stress balances within <span class="hlt">ice</span> sheets and <span class="hlt">ice</span> shelves. A Latin hypercube approach is used to optimally sample the range of uncertainty in parameter values. This perturbed-physics ensemble is used to simulate the evolution of the AIS from the Last Glacial Maximum ( 21,000 years ago) to present. Paleoclimate records are then used to determine which ensemble members are the most realistic. This allows us to use data on past climates to directly constrain our understanding of the past contribution of the AIS towards changes in global sea level. Critically, it also allows us to determine which ensemble members are likely to generate the most realistic projections of the future evolution of the AIS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.2210A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.2210A"><span>Circumpolar Deep Water transport and current structure at the Amundsen Sea <span class="hlt">shelf</span> break</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Assmann, Karen M.; Wåhlin, Anna K.; Heywood, Karen J.; Jenkins, Adrian; Kim, Tae Wan; Lee, Sang Hoon</p> <p>2017-04-01</p> <p>The West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet has been losing mass at an increasing rate over the past decades. Ocean heat transport to the <span class="hlt">ice</span>-ocean interface has been identified as an important contributor to this mass loss and the role it plays in <span class="hlt">ice</span> sheet stability makes it crucial to understand its drivers in order to make accurate future projections of global sea level. While processes closer to the <span class="hlt">ice</span>-ocean interface modulate this heat transport, its ultimate source is located in the deep basin off the continental <span class="hlt">shelf</span> as a core of relatively warm, salty water underlying a colder, fresher shallow surface layer. To reach the marine terminating glaciers and the base of floating <span class="hlt">ice</span> shelves, this warm, salty water mass must cross the bathymetric obstacle of the <span class="hlt">shelf</span> break. Glacial troughs that intersect the Amundsen <span class="hlt">shelf</span> break and deepen southwards towards the <span class="hlt">ice</span> <span class="hlt">shelf</span> fronts have been shown to play an important role in transporting warm, salty Circumpolar Deep Water (CDW) towards the <span class="hlt">ice</span> shelves. North of the <span class="hlt">shelf</span> break, circulation in the Amundsen Sea occupies an intermediate regime between the eastward <span class="hlt">Antarctic</span> Circumpolar Current that impinges on the <span class="hlt">shelf</span> break in the Bellingshausen Sea and the westward southern limb of the Ross Gyre that follows the <span class="hlt">shelf</span> break in the Ross Sea. Hydrographic and mooring observations and numerical model results at the mouth of the central <span class="hlt">shelf</span> break trough leading to Pine Island and Thwaites Glaciers show a westward wind-driven <span class="hlt">shelf</span> break current overlying an eastward undercurrent that turns onto the <span class="hlt">shelf</span> in the trough. It is thought that the existence of the latter feature facilitates the on-<span class="hlt">shelf</span> transport of CDW. A less clearly defined <span class="hlt">shelf</span> break depression further west acts as the main pathway for CDW to Dotson and eastern Getz <span class="hlt">Ice</span> shelves. Model results indicate that a similar eastward undercurrent exists here driving the on-<span class="hlt">shelf</span> transport of CDW. Two moorings on the upper slope east of the trough entrance show a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20020048255&hterms=enrichment&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Denrichment','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20020048255&hterms=enrichment&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Denrichment"><span>Sublimation: A Mechanism for the Enrichment of Organics in <span class="hlt">Antarctic</span> <span class="hlt">Ice</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Becker, Luann; McDonald, Gene D.; Glavin, Daniel P.; Bada, Jeffrey L.; Bunch, Theodore E.; Chang, Sherwood (Technical Monitor)</p> <p>1997-01-01</p> <p>Recent analyses of the carbonate globules present in the Martian meteorite ALH84001 have detected polycyclic aromatic hydrocarbons (PAHs) at the ppm level. The distribution of PAHs observed in ALH84001 was interpreted as being inconsistent with a terrestrial origin and were claimed to be indigenous to the meteorite, perhaps derived from an ancient Martian biota. However, Becker et al., have examined PAHs in the Martian meteorite EETA79001, in several <span class="hlt">Antarctic</span> carbonaceous chondrites and <span class="hlt">Antarctic</span> Allan Hills <span class="hlt">Ice</span> and detected many of the same PAHs found in ALH84001. The reported presence of L-amino acids of apparent terrestrial origin in the EETA79001 druse material, suggests that this meteorite is contaminated with terrestrial/extraterrestrial organics probably derived from <span class="hlt">Antarctic</span> <span class="hlt">ice</span> meltwater that had percolated through the meteorite. The detection of PAHs and L-amino acids in these Martian meteorites suggests that despite storage in the <span class="hlt">Antarctic</span> <span class="hlt">ice</span>, selective changes of certain chemical and mineralogical phases has occurred.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C54A..05H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C54A..05H"><span>Snow, Firn and <span class="hlt">Ice</span> Heterogeneity within Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Revealed by Borehole Optical-televiewing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hubbard, B. P.; Ashmore, D.; Luckman, A. J.; Kulessa, B.; Bevan, S. L.; Booth, A.; Kuipers Munneke, P.; O'Leary, M.; Sevestre, H.</p> <p>2016-12-01</p> <p>The north-western sector of Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (LCIS), Antarctica, hosts intermittent surface ponds resulting from intense melting, largely driven by warm föhn winds. The fate of such surface melt water is largely controlled by the <span class="hlt">shelf</span>'s firn structure, which also dictates <span class="hlt">shelf</span> density (widely used to reconstruct <span class="hlt">ice</span> <span class="hlt">shelf</span> thickness from altimetric data) and preconditioning to hydrofracture. Here, we report a suite of five 90 m long optical-televiewer (OPTV) borehole logs from the northern and central regions of LCIS recorded in spring 2014 and 2015. For each OPTV log we reconstruct vertical variations in material density via an empirical OPTV log-<span class="hlt">ice</span> core calibration, and apply a thresholding technique to estimate refrozen <span class="hlt">ice</span> content within the firn column. These data are combined to define five material facies present within this sector of LCIS. The firn/<span class="hlt">ice</span> column is anomalously dense at all five sites, having an overall mean depth-averaged density of 873 +/-32 kg m-3. In terms of spatial variability, our findings generally support previous estimates of firn air content fields and implied infiltration <span class="hlt">ice</span> content. However, they also highlight finer-resolution complexity of <span class="hlt">ice</span> <span class="hlt">shelf</span> structure. For example, the most dense <span class="hlt">ice</span>, with the lowest equivalent firn air content, is not located within the most westerly inlets, where firn-driven melting and ponding are most active, but some tens of km down-flow of these areas. We interpret this effect in terms of the inheritance nearer the grounding line of relatively low-density glacial <span class="hlt">ice</span> (e.g., 52 m thick with a density of 852 +/-21 kg m-3 in northernmost Cabinet Inlet) advected from inland. This inherited <span class="hlt">ice</span> forms one of five facies identified across the study region. These are, extending broadly downwards into the <span class="hlt">shelf</span>, and with different representation at each site: local accumulation (F1); local accumulation hosting substantial infiltration <span class="hlt">ice</span>, i.e. influenced by intense melt but insufficient to form</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010GeoRL..3721601P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010GeoRL..3721601P"><span>Seals map bathymetry of the <span class="hlt">Antarctic</span> continental <span class="hlt">shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Padman, Laurie; Costa, Daniel P.; Bolmer, S. Thompson; Goebel, Michael E.; Huckstadt, Luis A.; Jenkins, Adrian; McDonald, Birgitte I.; Shoosmith, Deborah R.</p> <p>2010-11-01</p> <p>We demonstrate the first use of marine mammal dive-depth data to improve maps of bathymetry in poorly sampled regions of the continental <span class="hlt">shelf</span>. A group of 57 instrumented elephant seals made on the order of 2 × 105 dives over and near the continental <span class="hlt">shelf</span> on the western side of the <span class="hlt">Antarctic</span> Peninsula during five seasons, 2005-2009. Maximum dive depth exceeded 2000 m. For dives made near existing ship tracks with measured water depths H<700 m, ˜30% of dive depths were to the seabed, consistent with expected benthic foraging behavior. By identifying the deepest of multiple dives within small areas as a dive to the seabed, we have developed a map of seal-derived bathymetry. Our map fills in several regions for which trackline data are sparse, significantly improving delineation of troughs crossing the continental <span class="hlt">shelf</span> of the southern Bellingshausen Sea.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ACPD...14.5771G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ACPD...14.5771G"><span>Downslope föhn winds over the <span class="hlt">Antarctic</span> Peninsula and their effect on the Larsen <span class="hlt">Ice</span> Shelves</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grosvenor, D. P.; King, J. C.; Choularton, T. W.; Lachlan-Cope, T.</p> <p>2014-03-01</p> <p>Mesoscale model simulations are presented of a westerly föhn event over the <span class="hlt">Antarctic</span> Peninsula mountain ridge and onto the Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, just south of the recently collapsed Larsen B <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. Aircraft observations showed the presence of föhn jets descending near to the <span class="hlt">ice</span> <span class="hlt">shelf</span> surface with maximum wind speeds at 250-350 m in height. Surface flux measurements suggested that melting was occurring. Simulated profiles of wind speed, temperature and wind direction were very similar to the observations. However, the good match only occurred at a model time corresponding to ˜9 h before the aircraft observations were made since the model föhn jets died down after this. Through comparison to an Automatic Weather Station (AWS) on the <span class="hlt">ice</span> <span class="hlt">shelf</span> surface (east side of the ridge) this was attributed to problems with the time evolution of the large scale meteorology of the analysis used to nudge the upper levels of the model. Timing issues aside, the otherwise good comparison between the model and observations gave confidence that the model flow structure was similar to that in reality. Details of the model jet structure are explored and discussed and are found to have ramifications for the placement of AWS stations on the <span class="hlt">ice</span> <span class="hlt">shelf</span> in order to detect föhn flow. Cross sections of the flow are also examined and were found to compare well to the aircraft measurements. Gravity wave breaking above the mountain crest likely created a situation similar to hydraulic flow and allowed föhn flow and <span class="hlt">ice</span> <span class="hlt">shelf</span> surface warming to occur despite strong upwind blocking, which in previous studies of this region has generally not been considered. The surface energy budget of the model during the melting periods showed that the net downwelling shortwave surface flux was the largest contributor to the melting energy, indicating that the cloud clearing effect of föhn events is likely to be the most important factor for increased melting relative to non-föhn days. The results also</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011MsT.........18M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011MsT.........18M"><span>Quantification of Changes for the Milne <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Nunavut, Canada, 1950 -- 2009</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mortimer, Colleen Adel</p> <p></p> <p>This study presents a comprehensive overview of the current state of the Milne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and how it has changed over the last 59 years. The 205 +/-1 km2 <span class="hlt">ice</span> <span class="hlt">shelf</span> experienced a 28% (82 +/-0.8 km 2) reduction in area between 1950 -- 2009, and a 20% (2.5 +/-0.9km 3 water equivalent (w.e.)) reduction in volume between 1981 -- 2008/2009, suggesting a long-term state of negative mass balance. Comparison of mean annual specific mass balances (up to -0.34 m w.e. yr-1) with surface mass balance measurements for the nearby Ward Hunt <span class="hlt">Ice</span> <span class="hlt">Shelf</span> suggest that basal melt is a key contributor to total <span class="hlt">ice</span> <span class="hlt">shelf</span> thinning. The development and expansion of new and existing surface cracks, as well as <span class="hlt">ice</span>-marginal and epishelf lake development, indicate significant <span class="hlt">ice</span> <span class="hlt">shelf</span> weakening. Over the next few decades it is likely that the Milne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> will continue to deteriorate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2007/1047/kp/kp07/of2007-1047kp07.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2007/1047/kp/kp07/of2007-1047kp07.pdf"><span>Late Cenozoic Climate History of the Ross Embayment from the AND-1B Drill Hole: Culmination of Three Decades of <span class="hlt">Antarctic</span> Margin Drilling</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Naish, T.R.; Powell, R.D.; Barrett, P.J.; Levy, R.H.; Henrys, S.; Wilson, G.S.; Krissek, L.A.; Niessen, F.; Pompilio, M.; Ross, J.; Scherer, R.; Talarico, F.; Pyne, A.; ,</p> <p>2007-01-01</p> <p>Because of the paucity of exposed rock, the direct physical record of <span class="hlt">Antarctic</span> Cenozoic glacial history has become known only recently and then largely from offshore <span class="hlt">shelf</span> basins through seismic surveys and drilling. The number of holes on the continental <span class="hlt">shelf</span> has been small and largely confined to three areas (McMurdo Sound, Prydz Bay, and <span class="hlt">Antarctic</span> Peninsula), but even in McMurdo Sound, where Oligocene and early Miocene strata are well cored, the late Cenozoic is poorly known and dated. The latest <span class="hlt">Antarctic</span> geological drilling program, ANDRILL, successfully cored a 1285-m-long record of climate history spanning the last 13 m.y. from subsea-floor sediment beneath the McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (MIS), using drilling systems specially developed for operating through <span class="hlt">ice</span> shelves. The cores provide the most complete <span class="hlt">Antarctic</span> record to date of <span class="hlt">ice</span>-sheet and climate fluctuations for this period of Earth’s history. The >60 cycles of advance and retreat of the grounded <span class="hlt">ice</span> margin preserved in the AND-1B record the evolution of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet since a profound global cooling step in deep-sea oxygen isotope records ~14 m.y.a. A feature of particular interest is a ~90-m-thick interval of diatomite deposited during the warm Pliocene and representing an extended period (~200,000 years) of locally open water, high phytoplankton productivity, and retreat of the glaciers on land.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSME12B..03L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSME12B..03L"><span>Under the Sea <span class="hlt">Ice</span>: Exploration of the Relationships Between Sea <span class="hlt">Ice</span> Patterns and Foraging Movements of a Marine Predator in East Antarctica.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Labrousse, S.; Sallee, J. B.; Fraser, A. D.; Massom, R. A.; Reid, P.; Sumner, M.; Guinet, C.; Harcourt, R.; Bailleul, F.; Hindell, M.; Charrassin, J. B.</p> <p>2016-02-01</p> <p>Investigating ecological relationships between top predators and their environment is essential to understand the response of marine ecosystems to climate variability. Specifically, variability and changes in sea <span class="hlt">ice</span>, which is known as an important habitat for marine ecosystems, presents complex patterns in East <span class="hlt">Antarctic</span>. The impact for ecosystems of such changes of their habitat is however still unknown. Acting as an ecological double-edged sword, sea <span class="hlt">ice</span> can impede access to marine resources while harboring a rich ecosystem during winter. Here, we investigated which type of sea <span class="hlt">ice</span> habitat is used by male and female southern elephant seals during winter and examine if and how the spatio-temporal variability of sea <span class="hlt">ice</span> concentration (SIC) influence their foraging strategies. We also examined over a 10 years time-series the impact of SIC and sea <span class="hlt">ice</span> advance anomaly on foraging activity. To do this, we studied 46 individuals equipped with Satellite linked data recorders between 2004 and 2014, undertaking post-moult trips in winter from Kerguelen to the peri-<span class="hlt">Antarctic</span> <span class="hlt">shelf</span>. The general patterns of sea <span class="hlt">ice</span> use by males and females are clearly distinct; while females tended to follow the sea <span class="hlt">ice</span> edge as it extended northward, males remained on the continental <span class="hlt">shelf</span>. Female foraging activity was higher in late autumn in the outer part of the pack <span class="hlt">ice</span> in concentrated SIC and spatially stable. They remained in areas of variable SIC over time and low persistence. The seal hunting time, a proxy of foraging activity inferred from the diving behaviour, was much higher during earlier advance of sea <span class="hlt">ice</span> over female time-series. The females were possibly taking advantage of the <span class="hlt">ice</span> algal autumn bloom sustaining krill and an under <span class="hlt">ice</span> ecosystem without being trapped in sea <span class="hlt">ice</span>. Males foraging activity increased when they remained deep inside sea <span class="hlt">ice</span> over the <span class="hlt">shelf</span> using variable SIC in time and space, presumably in polynyas or flaw leads between fast and pack <span class="hlt">ice</span>. This strategy</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.G43A1033W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.G43A1033W"><span>Combustion of available fossil-fuel resources sufficient to eliminate the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Winkelmann, R.; Levermann, A.; Ridgwell, A.; Caldeira, K.</p> <p>2015-12-01</p> <p>The <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet stores water equivalent to 58 meters in global sea-level rise. Here we show in simulations with the Parallel <span class="hlt">Ice</span> Sheet Model that burning the currently attainable fossil-fuel resources is sufficient to eliminate the <span class="hlt">ice</span> sheet. With cumulative fossil-fuel emissions of 10 000 GtC, Antarctica is projected to become almost <span class="hlt">ice</span>-free with an average contribution to sea-level rise exceeding 3 meters per century during the first millennium. Consistent with recent observations and simulations, the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of <span class="hlt">ice</span> basins in both West- and East Antarctica results in a threshold-increase in global sea level. Unabated carbon emissions thus threaten the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Natur.526..421G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Natur.526..421G"><span>The multi-millennial <span class="hlt">Antarctic</span> commitment to future sea-level rise</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Golledge, N. R.; Kowalewski, D. E.; Naish, T. R.; Levy, R. H.; Fogwill, C. J.; Gasson, E. G. W.</p> <p>2015-10-01</p> <p>Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above pre-industrial values by the end of this century. If anthropogenic emissions continue unchecked, the warming increase may reach 8-10 degrees Celsius by 2300 (ref. 2). The contribution that large <span class="hlt">ice</span> sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of <span class="hlt">ice</span> sheets is longer than those of the atmosphere or ocean. Here we use a coupled <span class="hlt">ice-sheet/ice-shelf</span> model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major <span class="hlt">Antarctic</span> <span class="hlt">ice</span> shelves triggers a centennial- to millennial-scale response of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day <span class="hlt">Antarctic</span> <span class="hlt">ice</span>-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We find that substantial <span class="hlt">Antarctic</span> <span class="hlt">ice</span> loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to <span class="hlt">ice</span> loss from <span class="hlt">Antarctic</span> that will raise sea level by 0.6-3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet to global sea level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.1406G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.1406G"><span>The multi-millennial <span class="hlt">Antarctic</span> commitment to future sea-level rise</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Golledge, Nicholas R.; Kowalewski, Douglas E.; Naish, Timothy R.; Levy, Richard H.; Fogwill, Christopher J.; Gasson, Edward G. W.</p> <p>2016-04-01</p> <p>Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above present values by the end of this century (Collins et al., 2013). If anthropogenic emissions continue unchecked, the warming increase may reach 8-10 degrees Celsius by 2300 (Rogelj et al., 2012). The contribution that large <span class="hlt">ice</span> sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of <span class="hlt">ice</span> sheets is longer than those of the atmosphere or ocean. Here we use a coupled <span class="hlt">ice-sheet/ice-shelf</span> model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major <span class="hlt">Antarctic</span> <span class="hlt">ice</span> shelves triggers a centennial- to millennial-scale response of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day <span class="hlt">Antarctic</span> <span class="hlt">ice</span>-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Collins et al., 2013). We find that substantial <span class="hlt">Antarctic</span> <span class="hlt">ice</span> loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to <span class="hlt">ice</span> loss from <span class="hlt">Antarctic</span> that will raise sea level by 0.6-3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet to global sea level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26469052','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26469052"><span>The multi-millennial <span class="hlt">Antarctic</span> commitment to future sea-level rise.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Golledge, N R; Kowalewski, D E; Naish, T R; Levy, R H; Fogwill, C J; Gasson, E G W</p> <p>2015-10-15</p> <p>Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above pre-industrial values by the end of this century. If anthropogenic emissions continue unchecked, the warming increase may reach 8-10 degrees Celsius by 2300 (ref. 2). The contribution that large <span class="hlt">ice</span> sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of <span class="hlt">ice</span> sheets is longer than those of the atmosphere or ocean. Here we use a coupled <span class="hlt">ice-sheet/ice-shelf</span> model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major <span class="hlt">Antarctic</span> <span class="hlt">ice</span> shelves triggers a centennial- to millennial-scale response of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day <span class="hlt">Antarctic</span> <span class="hlt">ice</span>-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We find that substantial <span class="hlt">Antarctic</span> <span class="hlt">ice</span> loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to <span class="hlt">ice</span> loss from <span class="hlt">Antarctic</span> that will raise sea level by 0.6-3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet to global sea level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016TCry...10.2721E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016TCry...10.2721E"><span>Estimating the extent of <span class="hlt">Antarctic</span> summer sea <span class="hlt">ice</span> during the Heroic Age of <span class="hlt">Antarctic</span> Exploration</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Edinburgh, Tom; Day, Jonathan J.</p> <p>2016-11-01</p> <p>In stark contrast to the sharp decline in Arctic sea <span class="hlt">ice</span>, there has been a steady increase in <span class="hlt">ice</span> extent around Antarctica during the last three decades, especially in the Weddell and Ross seas. In general, climate models do not to capture this trend and a lack of information about sea <span class="hlt">ice</span> coverage in the pre-satellite period limits our ability to quantify the sensitivity of sea <span class="hlt">ice</span> to climate change and robustly validate climate models. However, evidence of the presence and nature of sea <span class="hlt">ice</span> was often recorded during early <span class="hlt">Antarctic</span> exploration, though these sources have not previously been explored or exploited until now. We have analysed observations of the summer sea <span class="hlt">ice</span> edge from the ship logbooks of explorers such as Robert Falcon Scott, Ernest Shackleton and their contemporaries during the Heroic Age of <span class="hlt">Antarctic</span> Exploration (1897-1917), and in this study we compare these to satellite observations from the period 1989-2014, offering insight into the <span class="hlt">ice</span> conditions of this period, from direct observations, for the first time. This comparison shows that the summer sea <span class="hlt">ice</span> edge was between 1.0 and 1.7° further north in the Weddell Sea during this period but that <span class="hlt">ice</span> conditions were surprisingly comparable to the present day in other sectors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20010097733','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20010097733"><span>Motion of Major <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Fronts in Antarctica from Slant Range Analysis of Radar Altimeter Data, 1978 - 1998</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zwally, H. J.; Beckley, M. A.; Brenner, A. C.; Giovinetto, M. B.; Koblinsky, Chester J. (Technical Monitor)</p> <p>2001-01-01</p> <p>Slant range analysis of radar altimeter data from the Seasat, Geosat, ERS-1 and ERS-2 databases are used to determine barrier location at particular times, and estimate barrier motion (km/yr) for major <span class="hlt">Antarctic</span> <span class="hlt">ice</span> shelves. The barrier locations, which are the seaward edges or fronts of floating <span class="hlt">ice</span> shelves, advance with time as the <span class="hlt">ice</span> flows from the grounded <span class="hlt">ice</span> sheets and retreat whenever icebergs calve from the fronts. The analysis covers various multiyear intervals from 1978 to 1998, supplemented by barrier location maps produced elsewhere for 1977 and 1986. Barrier motion is estimated as the ratio between mean annual <span class="hlt">ice</span> <span class="hlt">shelf</span> area change for a particular interval, and the length of the discharge periphery. This value is positive if the barrier location progresses seaward, or negative if the barrier location regresses (break-back). Either positive or negative values are lower limit estimates because the method does not detect relatively small area changes due to calving or surge events. The findings are discussed in the context of the three <span class="hlt">ice</span> shelves that lie in large embayments (the Filchner-Ronne, Amery, and Ross), and marginal <span class="hlt">ice</span> shelves characterized by relatively short distances between main segments of grounding line and barrier (those in the Queen Maud Land sector between 10.1 deg. W and 32.5 deg. E, and the West and Shackleton <span class="hlt">ice</span> shelves). All the <span class="hlt">ice</span> shelves included in the study account for approximately three-fourths of the total <span class="hlt">ice</span> <span class="hlt">shelf</span> area of Antarctica, and discharge approximately two-thirds of the total grounded <span class="hlt">ice</span> area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1986GeoRL..13.1264Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1986GeoRL..13.1264Z"><span>Nitrate flux on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica and its relation to solar cosmic rays</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zeller, Edward J.; Dreschhoff, Gisela A. M.; Laird, Claude M.</p> <p>1986-11-01</p> <p>Nitrate flux has been determined in the snow sequence deposited at Windless Bight on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (Antarctica). The data were obtained from on-site analysis of nitrate concentrations from a glaciological pit and a firn core spanning the time interval from midwinter 1971 to January 1986. The high resolution data can be combined with precipitation records collected from adjacent areas to provide a record of nitrate flow. The resulting time series contains a signal which corresponds to the two major solar events of 1972 and 1984. The concentration and flux profiles may be useful in studies of <span class="hlt">Antarctic</span> ozone depletion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21637255','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21637255"><span>A dynamic early East <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet suggested by <span class="hlt">ice</span>-covered fjord landscapes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Young, Duncan A; Wright, Andrew P; Roberts, Jason L; Warner, Roland C; Young, Neal W; Greenbaum, Jamin S; Schroeder, Dustin M; Holt, John W; Sugden, David E; Blankenship, Donald D; van Ommen, Tas D; Siegert, Martin J</p> <p>2011-06-02</p> <p>The first Cenozoic <span class="hlt">ice</span> sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling ∼34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving <span class="hlt">Antarctic</span> circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of <span class="hlt">ice</span>-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. <span class="hlt">Ice</span>-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of <span class="hlt">Antarctic</span> topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5 km of <span class="hlt">ice</span>, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from <span class="hlt">ice</span>-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of <span class="hlt">ice</span>-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C51A0963P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51A0963P"><span>Improving Altimetry Height-change Retrieval on the Fringes of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paolo, F. S.; Nilsson, J.; Gardner, A. S.</p> <p>2017-12-01</p> <p>Projections of sea-level change over the next century are highly uncertain, in part, due to insufficient understanding of <span class="hlt">ice</span>-sheet sensitivity to changes in oceanic and atmospheric circulation. This limitation is, to a large degree, related to the lack of long and continuous observational records covering critical regions along the <span class="hlt">ice</span>-sheet margins where the <span class="hlt">ice</span> interacts with the ocean. Of particular importance are accurate records of changes in <span class="hlt">ice</span> thickness that provide information on how mass fluctuates on the floating extensions of <span class="hlt">ice</span> streams and glaciers through which the <span class="hlt">ice</span>-sheet drains. These changes can modify the stability of the grounded <span class="hlt">ice</span> sheet through changing back-stress, for example, through loss of <span class="hlt">ice-shelf</span> buttressing. Here, we synthetize 25+ years of satellite altimetry observations to extend the time span and improve the resolution and accuracy of the existing record of <span class="hlt">Antarctic</span> floating <span class="hlt">ice</span> thickness. We incorporate data from ESA's ERS-1, ERS-2, Envisat and Cryosat-2 radar altimeters (1992-present) and NASA's ICESat laser altimeter (2003-2009) and Operation <span class="hlt">Ice</span>Bridge surveys (2009-present); with plans to include ICESat-2 data soon after its launch in September 2018. Towards this effort, we revisit some of the main corrections applied to altimeter data, such as minimization of the difference between measurements from radar and laser systems; and we improve the approach for the synthesis of heterogeneous measurements of <span class="hlt">ice</span>-surface topography and uncertainty estimation. We report on our progress in constructing this long-term and homogeneous record, with a particular focus on the floating <span class="hlt">ice</span> shelves.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSHE44B1501M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSHE44B1501M"><span>Glider observations of the Dotson <span class="hlt">Ice</span> <span class="hlt">Shelf</span> outflow and its connection to the Amundsen Sea Polynya</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miles, T. N.; Schofield, O.; Lee, S. H.; Yager, P. L.; Ha, H. K.</p> <p>2016-02-01</p> <p>The Amundsen Sea is one of the most productive polynyas in the <span class="hlt">Antarctic</span> per unit area and is undergoing rapid changes including a reduction in sea <span class="hlt">ice</span> duration, thinning <span class="hlt">ice</span> sheets, retreat of glaciers and the potential collapse of the Thwaites Glacier in Pine Island Bay. A growing body of research has indicated that these changes are altering the water mass properties and associated biogeochemistry within the polynya. Unfortunately difficulties in accessing the remote location have greatly limited the amount of in situ data that has been collected. In this study data from a Teledyne-Web Slocum glider was used to supplement ship-based sampling along the Dotson <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (DIS). This autonomous underwater vehicle revealed a detailed view of a meltwater laden outflow from below the western flank of the DIS. Circumpolar Deep Water intruding onto the <span class="hlt">shelf</span> drives glacial melt and the supply of macronutrients that, along with ample light, supports the large phytoplankton blooms in the Amundsen Sea Polynya. Less well understood is the source of micronutrients, such as iron, necessary to support this bloom to the central polynya where chlorophyll concentrations are highest. This outflow region showed decreasing optical backscatter with proximity to the bed indicating that particulate matter was sourced from the overlying glacier rather than resuspended sediment. This result suggests that particulate iron, and potentially phytoplankton primary productivity, is intrinsically linked to the magnitude and duration of sub-glacial melt from Circumpolar Deep Water intrusions onto the <span class="hlt">shelf</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017ERL....12h4010L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017ERL....12h4010L"><span>Improved simulation of <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> due to the radiative effects of falling snow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, J.-L. F.; Richardson, Mark; Hong, Yulan; Lee, Wei-Liang; Wang, Yi-Hui; Yu, Jia-Yuh; Fetzer, Eric; Stephens, Graeme; Liu, Yinghui</p> <p>2017-08-01</p> <p>Southern Ocean sea-<span class="hlt">ice</span> cover exerts critical control on local albedo and <span class="hlt">Antarctic</span> precipitation, but simulated <span class="hlt">Antarctic</span> sea-<span class="hlt">ice</span> concentration commonly disagrees with observations. Here we show that the radiative effects of precipitating <span class="hlt">ice</span> (falling snow) contribute substantially to this discrepancy. Many models exclude these radiative effects, so they underestimate both shortwave albedo and downward longwave radiation. Using two simulations with the climate model CESM1, we show that including falling-snow radiative effects improves the simulations relative to cloud properties from CloudSat-CALIPSO, radiation from CERES-EBAF and sea-<span class="hlt">ice</span> concentration from passive microwave sensors. From 50-70°S, the simulated sea-<span class="hlt">ice</span>-area bias is reduced by 2.12 × 106 km2 (55%) in winter and by 1.17 × 106 km2 (39%) in summer, mainly because increased wintertime longwave heating restricts sea-<span class="hlt">ice</span> growth and so reduces summer albedo. Improved <span class="hlt">Antarctic</span> sea-<span class="hlt">ice</span> simulations will increase confidence in projected <span class="hlt">Antarctic</span> sea level contributions and changes in global warming driven by long-term changes in Southern Ocean feedbacks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20170005812&hterms=sea&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dsea','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20170005812&hterms=sea&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dsea"><span>Bellingshausen Sea <span class="hlt">Ice</span> Extent Recorded in an <span class="hlt">Antarctic</span> Peninsula <span class="hlt">Ice</span> Core</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Porter, Stacy E.; Parkinson, Claire L.; Mosley-Thompson, Ellen</p> <p>2016-01-01</p> <p>Annual net accumulation (A(sub n)) from the Bruce Plateau (BP) <span class="hlt">ice</span> core retrieved from the <span class="hlt">Antarctic</span> Peninsula exhibits a notable relationship with sea <span class="hlt">ice</span> extent (SIE) in the Bellingshausen Sea. Over the satellite era, both BP A(sub n) and Bellingshausen SIE are influenced by large-scale climatic factors such as the Amundsen Sea Low, Southern Annular Mode, and Southern Oscillation. In addition to the direct response of BP A(sub n) to Bellingshausen SIE (e.g., more open water as a moisture source), these large-scale climate phenomena also link the BP and the Bellingshausen Sea indirectly such that they exhibit similar responses (e.g., northerly wind anomalies advect warm, moist air to the <span class="hlt">Antarctic</span> Peninsula and neighboring Bellingshausen Sea, which reduces SIE and increases A(sub n)). Comparison with a time series of fast <span class="hlt">ice</span> at South Orkney Islands reveals a relationship between BP A(sub n) and sea <span class="hlt">ice</span> in the northern Weddell Sea that is relatively consistent over the twentieth century, except when it is modulated by atmospheric wave patterns described by the Trans-Polar Index. The trend of increasing accumulation on the Bruce Plateau since approximately 1970 agrees with other climate records and reconstructions in the region and suggests that the current rate of sea <span class="hlt">ice</span> loss in the Bellingshausen Sea is unrivaled in the twentieth century.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JGRF..117.2037G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JGRF..117.2037G"><span>Investigation of land <span class="hlt">ice</span>-ocean interaction with a fully coupled <span class="hlt">ice</span>-ocean model: 1. Model description and behavior</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.; Hallberg, R.; Oppenheimer, M.</p> <p>2012-06-01</p> <p><span class="hlt">Antarctic</span> <span class="hlt">ice</span> shelves interact closely with the ocean cavities beneath them, with <span class="hlt">ice</span> <span class="hlt">shelf</span> geometry influencing ocean cavity circulation, and heat from the ocean driving changes in the <span class="hlt">ice</span> shelves, as well as the grounded <span class="hlt">ice</span> streams that feed them. We present a new coupled model of an <span class="hlt">ice</span> stream-<span class="hlt">ice</span> <span class="hlt">shelf</span>-ocean system that is used to study this interaction. The model is capable of representing a moving grounding line and dynamically responding ocean circulation within the <span class="hlt">ice</span> <span class="hlt">shelf</span> cavity. Idealized experiments designed to investigate the response of the coupled system to instantaneous increases in ocean temperature show <span class="hlt">ice</span>-ocean system responses on multiple timescales. Melt rates and <span class="hlt">ice</span> <span class="hlt">shelf</span> basal slopes near the grounding line adjust in 1-2 years, and downstream advection of the resulting <span class="hlt">ice</span> <span class="hlt">shelf</span> thinning takes place on decadal timescales. Retreat of the grounding line and adjustment of grounded <span class="hlt">ice</span> takes place on a much longer timescale, and the system takes several centuries to reach a new steady state. During this slow retreat, and in the absence of either an upward-or downward-sloping bed or long-term trends in ocean heat content, the <span class="hlt">ice</span> <span class="hlt">shelf</span> and melt rates maintain a characteristic pattern relative to the grounding line.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4643791','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4643791"><span>Combustion of available fossil fuel resources sufficient to eliminate the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Winkelmann, Ricarda; Levermann, Anders; Ridgwell, Andy; Caldeira, Ken</p> <p>2015-01-01</p> <p>The <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel <span class="hlt">Ice</span> Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the <span class="hlt">ice</span> sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost <span class="hlt">ice</span>-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of <span class="hlt">ice</span> basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources. PMID:26601273</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26601273','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26601273"><span>Combustion of available fossil fuel resources sufficient to eliminate the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Winkelmann, Ricarda; Levermann, Anders; Ridgwell, Andy; Caldeira, Ken</p> <p>2015-09-01</p> <p>The <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel <span class="hlt">Ice</span> Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the <span class="hlt">ice</span> sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost <span class="hlt">ice</span>-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of <span class="hlt">ice</span> basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018NatCC...8...53R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018NatCC...8...53R"><span>The far reach of <span class="hlt">ice-shelf</span> thinning in Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reese, R.; Gudmundsson, G. H.; Levermann, A.; Winkelmann, R.</p> <p>2018-01-01</p> <p>Floating <span class="hlt">ice</span> shelves, which fringe most of Antarctica's coastline, regulate <span class="hlt">ice</span> flow into the Southern Ocean1-3. Their thinning4-7 or disintegration8,9 can cause upstream acceleration of grounded <span class="hlt">ice</span> and raise global sea levels. So far the effect has not been quantified in a comprehensive and spatially explicit manner. Here, using a finite-element model, we diagnose the immediate, continent-wide flux response to different spatial patterns of <span class="hlt">ice-shelf</span> mass loss. We show that highly localized <span class="hlt">ice-shelf</span> thinning can reach across the entire <span class="hlt">shelf</span> and accelerate <span class="hlt">ice</span> flow in regions far from the initial perturbation. As an example, this `tele-buttressing' enhances outflow from Bindschadler <span class="hlt">Ice</span> Stream in response to thinning near Ross Island more than 900 km away. We further find that the integrated flux response across all grounding lines is highly dependent on the location of imposed changes: the strongest response is caused not only near <span class="hlt">ice</span> streams and <span class="hlt">ice</span> rises, but also by thinning, for instance, well-within the Filchner-Ronne and Ross <span class="hlt">Ice</span> Shelves. The most critical regions in all major <span class="hlt">ice</span> shelves are often located in regions easily accessible to the intrusion of warm ocean waters10-12, stressing Antarctica's vulnerability to changes in its surrounding ocean.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C33B1190R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C33B1190R"><span>Atmospheric Influences on the Anomalous 2016 <span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span> Decay</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Raphael, M. N.; Schlosser, E.; Haumann, A.</p> <p>2017-12-01</p> <p>Over the past three decades, a small but significant increase in sea <span class="hlt">ice</span> extent (SIE) has been observed in the <span class="hlt">Antarctic</span>. However, in 2016 there was a surprisingly early onset of the melt season. The maximum <span class="hlt">Antarctic</span> SIE was reached in August rather than end of September, and was followed by a rapid decrease. The decline of the sea <span class="hlt">ice</span> area (SIA) started even earlier, in July. The retreat of the <span class="hlt">ice</span> was particularly large in November where <span class="hlt">Antarctic</span> SIE exhibited a negative anomaly (compared to the 1981-2010 average) of almost 2 Mio. km2, which, combined with reduced Arctic SIE, led to a distinct minimum in global SIE. And, satellite observations show that from November 2016 to February 2017, the daily <span class="hlt">Antarctic</span> SIE has been at record low levels. We use sea level pressure and geopotential height data from the ECMWF- Interim reanalysis, in conjunction with sea <span class="hlt">ice</span> data obtained from the National Snow and <span class="hlt">Ice</span> Data Centre (NSIDC), to investigate possible atmospheric influences on the observed phenomena. Indications are that both the onset of the melt in July and the rapid decrease in SIA and SIE in November were triggered by atmospheric flow patterns related to a positive Zonal Wave 3 index, i.e. synoptic situations leading to strong meridional flow. Additionally the Southern Annular Mode (SAM) index reached its second lowest November value since the beginning of the satellite observations. It is likely that the SIE decrease was preconditioned by SIA decrease. Positive feedback effects led to accelerated melt and consequently to the extraordinary low November SIE.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930037350&hterms=rate+sensitivity+ice&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Drate%2Bsensitivity%2Bice','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930037350&hterms=rate+sensitivity+ice&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Drate%2Bsensitivity%2Bice"><span>Ocean interactions with the base of Amery <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hellmer, Hartmut H.; Jacobs, Stanley S.</p> <p>1992-01-01</p> <p>Using a two-dimensional ocean themohaline circulation model, we varied the cavity shape beneath Amery <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in an attempt to reproduce the 150-m-thick marine <span class="hlt">ice</span> layer observed at the 'G1' <span class="hlt">ice</span> core site. Most simulations caused melting rates which decrease the <span class="hlt">ice</span> thickness by as much as 400 m between grounding line and G1, but produce only minor accumulation at the <span class="hlt">ice</span> core site and closer to the <span class="hlt">ice</span> front. Changes in the sea floor and <span class="hlt">ice</span> topographies revealed a high sensitivity of the basal mass balance to water column thickness near the grounding line, to submarine sills, and to discontinuities in <span class="hlt">ice</span> thickness. Model results showed temperature/salinity gradients similar to observations from beneath other <span class="hlt">ice</span> shelves where <span class="hlt">ice</span> is melting into seawater. Modeled outflow characteristics at the <span class="hlt">ice</span> front are in general agreement with oceanographic data from Prydz Bay. We concur with Morgan's inference that the G1 core may have been taken in a basal crevasse filled with marine <span class="hlt">ice</span>. This <span class="hlt">ice</span> is formed from water cooled by ocean/<span class="hlt">ice</span> <span class="hlt">shelf</span> interactions along the interior <span class="hlt">ice</span> <span class="hlt">shelf</span> base.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C51B0977G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51B0977G"><span>Surface and basal <span class="hlt">ice</span> <span class="hlt">shelf</span> mass balance processes of the Southern McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> determined through radar statistical reconnaissance</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grima, C.; Koch, I.; Greenbaum, J. S.; Soderlund, K. M.; Blankenship, D. D.; Young, D. A.; Fitzsimons, S.</p> <p>2017-12-01</p> <p>The McMurdo <span class="hlt">ice</span> shelves (northern and southern MIS), adjacent to the eponymous station and the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica, are known for large gradients in surface snow accumulation and snow/<span class="hlt">ice</span> impurities. Marine <span class="hlt">ice</span> accretion and melting are important contributors to MIS's mass balance. Due to erosive winds, the southern MIS (SMIS) shows a locally negative surface mass balance. Thus, marine <span class="hlt">ice</span> once accreted at the <span class="hlt">ice</span> <span class="hlt">shelf</span> base crops out at the surface. However, the exact processes that exert primary control on SMIS mass balance have remained elusive. Radar statistical reconnaissance (RSR) is a recent technique that has been used to characterize the surface properties of the Earth's cryosphere, Mars, and Titan from the stochastic character of energy scattered by the surface. Here, we apply RSR to map the surface density and roughness of the SMIS and extend the technique to derive the basal reflectance and scattering coefficients of the <span class="hlt">ice</span>-ocean interface. We use an airborne radar survey grid acquired over the SMIS in the 2014-2015 austral summer by the University of Texas Institute for Geophysics with the High Capability Radar Sounder (HiCARS2; 60-MHz center frequency and 15-MHz bandwidth). The RSR-derived snow density values and patterns agree with directly -measured <span class="hlt">ice</span> <span class="hlt">shelf</span> surface accumulation rates. We also compare the composition of SMIS <span class="hlt">ice</span> surface samples to test the ability of RSR to discriminate <span class="hlt">ices</span> with varying dielectric properties (e.g., marine versus meteoric <span class="hlt">ice</span>) and hypothesize relationships between the RSR-derived basal reflectance/scattered coefficients and accretion or melting at the <span class="hlt">ice</span>-ocean interface. This improved knowledge of air-<span class="hlt">ice</span> and <span class="hlt">ice</span>-ocean boundaries provides a new perspective on the processes governing SMIS surface and basal mass balance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140017824','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140017824"><span>Changes in Arctic and <span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span> as a Microcosm of Global Climate Change</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Parkinson, Claire L.</p> <p>2014-01-01</p> <p>Polar sea <span class="hlt">ice</span> is a key element of the climate system and has now been monitored through satellite observations for over three and a half decades. The satellite observations reveal considerable information about polar <span class="hlt">ice</span> and its changes since the late 1970s, including a prominent downward trend in Arctic sea <span class="hlt">ice</span> coverage and a much lesser upward trend in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> coverage, illustrative of the important fact that climate change entails spatial contrasts. The decreasing <span class="hlt">ice</span> coverage in the Arctic corresponds well with contemporaneous Arctic warming and exhibits particularly large decreases in the summers of 2007 and 2012, influenced by both preconditioning and atmospheric conditions. The increasing <span class="hlt">ice</span> coverage in the <span class="hlt">Antarctic</span> is not as readily explained, but spatial differences in the <span class="hlt">Antarctic</span> trends suggest a possible connection with atmospheric circulation changes that have perhaps been influenced by the <span class="hlt">Antarctic</span> ozone hole. The changes in the polar <span class="hlt">ice</span> covers and the issues surrounding those changes have many commonalities with broader climate changes and their surrounding issues, allowing the sea <span class="hlt">ice</span> changes to be viewed in some important ways as a microcosm of global climate change.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C54A..08S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C54A..08S"><span>Tropical pacing of <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> increase</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schneider, D. P.</p> <p>2015-12-01</p> <p>One reason why coupled climate model simulations generally do not reproduce the observed increase in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> extent may be that their internally generated climate variability does not sync with the observed phases of phenomena like the Pacific Decadal Oscillation (PDO) and ENSO. For example, it is unlikely for a free-running coupled model simulation to capture the shift of the PDO from its positive to negative phase during 1998, and the subsequent ~15 year duration of the negative PDO phase. In previously presented work based on atmospheric models forced by observed tropical SSTs and stratospheric ozone, we demonstrated that tropical variability is key to explaining the wind trends over the Southern Ocean during the past ~35 years, particularly in the Ross, Amundsen and Bellingshausen Seas, the regions of the largest trends in sea <span class="hlt">ice</span> extent and <span class="hlt">ice</span> season duration. Here, we extend this idea to coupled model simulations with the Community Earth System Model (CESM) in which the evolution of SST anomalies in the central and eastern tropical Pacific is constrained to match the observations. This ensemble of 10 "tropical pacemaker" simulations shows a more realistic evolution of <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> anomalies than does its unconstrained counterpart, the CESM Large Ensemble (both sets of runs include stratospheric ozone depletion and other time-dependent radiative forcings). In particular, the pacemaker runs show that increased sea <span class="hlt">ice</span> in the eastern Ross Sea is associated with a deeper Amundsen Sea Low (ASL) and stronger westerlies over the south Pacific. These circulation patterns in turn are linked with the negative phase of the PDO, characterized by negative SST anomalies in the central and eastern Pacific. The timing of tropical decadal variability with respect to ozone depletion further suggests a strong role for tropical variability in the recent acceleration of the <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> trend, as ozone depletion stabilized by late 1990s, prior to the most</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016OcMod.104...99M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016OcMod.104...99M"><span><span class="hlt">Antarctic</span> icebergs melt over the Southern Ocean : Climatology and impact on sea <span class="hlt">ice</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Merino, Nacho; Le Sommer, Julien; Durand, Gael; Jourdain, Nicolas C.; Madec, Gurvan; Mathiot, Pierre; Tournadre, Jean</p> <p>2016-08-01</p> <p>Recent increase in <span class="hlt">Antarctic</span> freshwater release to the Southern Ocean is suggested to contribute to change in water masses and sea <span class="hlt">ice</span>. However, climate models differ in their representation of the freshwater sources. Recent improvements in altimetry-based detection of small icebergs and in estimates of the mass loss of Antarctica may help better constrain the values of <span class="hlt">Antarctic</span> freshwater releases. We propose a model-based seasonal climatology of iceberg melt over the Southern Ocean using state-of-the-art observed glaciological estimates of the <span class="hlt">Antarctic</span> mass loss. An improved version of a Lagrangian iceberg model is coupled with a global, eddy-permitting ocean/sea <span class="hlt">ice</span> model and compared to small icebergs observations. Iceberg melt increases sea <span class="hlt">ice</span> cover, about 10% in annual mean sea <span class="hlt">ice</span> volume, and decreases sea surface temperature over most of the Southern Ocean, but with distinctive regional patterns. Our results underline the importance of improving the representation of <span class="hlt">Antarctic</span> freshwater sources. This can be achieved by forcing ocean/sea <span class="hlt">ice</span> models with a climatological iceberg fresh-water flux.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.C31C0414B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.C31C0414B"><span>Downslope flow across the Ross Sea <span class="hlt">shelf</span> break (Antarctica)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bergamasco, A.; Budillon, G.; Carniel, S.; Defendi, V.; Meloni, R.; Paschini, E.; Sclavo, M.; Spezie, G.</p> <p>2003-12-01</p> <p>The analysis of some high-resolution hydrological data sets acquired during the 1997, 1998, 2001 and 2003 austral summers across the Ross Sea continental <span class="hlt">shelf</span> break are here presented. The main focus of these cruises carried out in the framework of the Italian National <span class="hlt">Antarctic</span> Program was the investigation of the downslope flow of the dense waters originated inside the Ross Sea. Such dense waters, flow near the bottom and, reaching the continental <span class="hlt">shelf</span> break, ventilate the deep ocean. Two <span class="hlt">Antarctic</span> continental <span class="hlt">shelf</span> mechanisms can originate dense and deep waters. The former mechanism involves the formation, along the Victoria Land coasts, of a dense and saline water mass, the High Salinity <span class="hlt">Shelf</span> Water (HSSW). The HSSW formation is linked to the rejection of salt into the water column as sea <span class="hlt">ice</span> freezes, especially during winter, in the polynya areas, where the <span class="hlt">ice</span> is continuously pushed offshore by the strong katabatic winds. The latter one is responsible of the formation of a supercold water mass, the <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Water (ISW). The salt supplied by the HSSW recirculated below the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, the latent heat of melting and the heat sink provided by the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> give rise to plumes of ISW, characterized by temperatures below the sea-surface freezing point. The dense <span class="hlt">shelf</span> waters migrate to the continental <span class="hlt">shelf</span>-break, spill over the <span class="hlt">shelf</span> edge and descend the continental slope as a <span class="hlt">shelf</span>-break gravity current, subject to friction and possibly enhanced by topographic channelling. Friction, in particular, breaks the constraint of potential vorticity conservation, counteracting the geostrophic tendency for along slope flow. The density-driven downslope motion or cascading entrains ambient water, namely the lower layer of the CDW, reaches a depth where density is the same and spreads off-slope. In fact, the cascading event is inhibited by friction without entrainment. The downslope processes are important for the ocean and climate system because they play a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMGC32B..02P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMGC32B..02P"><span>Contrasting Trends in Arctic and <span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span> Coverage Since the Late 1970s</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Parkinson, C. L.</p> <p>2016-12-01</p> <p>Satellite observations have allowed a near-continuous record of Arctic and <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> coverage since late 1978. This record has revealed considerable interannual variability in both polar regions but also significant long-term trends, with the Arctic losing, the <span class="hlt">Antarctic</span> gaining, and the Earth as a whole losing sea <span class="hlt">ice</span> coverage. Over the period 1979-2015, the trend in yearly average sea <span class="hlt">ice</span> extents in the Arctic is -53,100 km2/yr (-4.3 %/decade) and in the <span class="hlt">Antarctic</span> is 23,800 km2/yr (2.1 %/decade). For all 12 months, trends are negative in the Arctic and positive in the <span class="hlt">Antarctic</span>, with the highest magnitude monthly trend being for September in the Arctic, at -85,300 km2/yr (-10.9 %/decade). The decreases in Arctic sea <span class="hlt">ice</span> extents have been so dominant that not a single month since 1986 registered a new monthly record high, whereas 75 months registered new monthly record lows between 1987 and 2015 and several additional record lows were registered in 2016. The <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> record highs and lows are also out of balance, in the opposite direction, although not in such dramatic fashion. Geographic details on the changing <span class="hlt">ice</span> covers, down to the level of individual pixels, can be seen by examining changes in the length of the sea <span class="hlt">ice</span> season. Results reveal (and quantify) shortening <span class="hlt">ice</span> seasons throughout the bulk of the Arctic marginal <span class="hlt">ice</span> zone, the main exception being within the Bering Sea, and lengthening sea <span class="hlt">ice</span> seasons through much of the Southern Ocean but shortening seasons in the Bellingshausen Sea, southern Amundsen Sea, and northwestern Weddell Sea. The decreasing Arctic sea <span class="hlt">ice</span> coverage was widely anticipated and fits well with a large array of environmental changes in the Arctic, whereas the increasing <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> coverage was not widely anticipated and explaining it remains an area of active research by many scientists exploring a variety of potential explanations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRC..121.8496K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRC..121.8496K"><span>Ocean mixing beneath Pine Island Glacier <span class="hlt">ice</span> <span class="hlt">shelf</span>, West Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kimura, Satoshi; Jenkins, Adrian; Dutrieux, Pierre; Forryan, Alexander; Naveira Garabato, Alberto C.; Firing, Yvonne</p> <p>2016-12-01</p> <p><span class="hlt">Ice</span> shelves around Antarctica are vulnerable to an increase in ocean-driven melting, with the melt rate depending on ocean temperature and the strength of flow inside the <span class="hlt">ice-shelf</span> cavities. We present measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate, and thermal variance dissipation rate beneath Pine Island Glacier <span class="hlt">ice</span> <span class="hlt">shelf</span>, West Antarctica. These measurements were obtained by CTD, ADCP, and turbulence sensors mounted on an Autonomous Underwater Vehicle (AUV). The highest turbulent kinetic energy dissipation rate is found near the grounding line. The thermal variance dissipation rate increases closer to the <span class="hlt">ice-shelf</span> base, with a maximum value found ˜0.5 m away from the <span class="hlt">ice</span>. The measurements of turbulent kinetic energy dissipation rate near the <span class="hlt">ice</span> are used to estimate basal melting of the <span class="hlt">ice</span> <span class="hlt">shelf</span>. The dissipation-rate-based melt rate estimates is sensitive to the stability correction parameter in the linear approximation of universal function of the Monin-Obukhov similarity theory for stratified boundary layers. We argue that our estimates of basal melting from dissipation rates are within a range of previous estimates of basal melting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140009626','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140009626"><span><span class="hlt">Ice-Shelf</span> Tidal Flexure and Subglacial Pressure Variations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Walker, Ryan T.; Parizek, Byron R.; Alley, Richard B.; Anandakrishnan, Sridhar; Riverman, Kiya L.; Christianson, Knut</p> <p>2013-01-01</p> <p>We develop a model of an <span class="hlt">ice</span> <span class="hlt">shelf-ice</span> stream system as a viscoelastic beam partially supported by an elastic foundation. When bed rock near the grounding line acts as a fulcrum, leverage from the <span class="hlt">ice</span> <span class="hlt">shelf</span> dropping at low tide can cause significant (approx 1 cm) uplift in the first few kilometers of grounded <span class="hlt">ice</span>.This uplift and the corresponding depression at high tide lead to basal pressure variations of sufficient magnitude to influence subglacial hydrology.Tidal flexure may thus affect basal lubrication, sediment flow, and till strength, all of which are significant factors in <span class="hlt">ice</span>-stream dynamics and grounding-line stability. Under certain circumstances, our results suggest the possibility of seawater being drawn into the subglacial water system. The presence of sea water beneath grounded <span class="hlt">ice</span> would significantly change the radar reflectivity of the grounding zone and complicate the interpretation of grounded versus floating <span class="hlt">ice</span> based on <span class="hlt">ice</span>-penetrating radar observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ISPAr41B8..481B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ISPAr41B8..481B"><span>Mass Balance Changes and <span class="hlt">Ice</span> Dynamics of Greenland and <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheets from Laser Altimetry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Babonis, G. S.; Csatho, B.; Schenk, T.</p> <p>2016-06-01</p> <p>During the past few decades the Greenland and <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets have lost <span class="hlt">ice</span> at accelerating rates, caused by increasing surface temperature. The melting of the two big <span class="hlt">ice</span> sheets has a big impact on global sea level rise. If the <span class="hlt">ice</span> sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser altimetry data, acquired by NASA's <span class="hlt">Ice</span>, Cloud and land Elevation Satellite mission (ICESat) and airborne laser campaigns, such as Airborne Topographic Mapper (ATM) and Land, Vegetation and <span class="hlt">Ice</span> Sensor (LVIS). For detecting changes in <span class="hlt">ice</span> sheet elevations we have developed the Surface Elevation Reconstruction And Change detection (SERAC) method. It computes elevation changes of small surface patches by keeping the surface shape constant and considering the absolute values as surface elevations. We report about important upgrades of earlier results, for example the inclusion of local <span class="hlt">ice</span> caps and the temporal extension from 1993 to 2014 for the Greenland <span class="hlt">Ice</span> Sheet and for a comprehensive reconstruction of <span class="hlt">ice</span> thickness and mass changes for the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70021530','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70021530"><span><span class="hlt">Antarctic</span> glacial history from numerical models and continental margin sediments</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Barker, P.F.; Barrett, P.J.; Cooper, A. K.; Huybrechts, P.</p> <p>1999-01-01</p> <p>The climate record of glacially transported sediments in prograded wedges around the <span class="hlt">Antarctic</span> outer continental <span class="hlt">shelf</span>, and their derivatives in continental rise drifts, may be combined to produce an <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet history, using numerical models of <span class="hlt">ice</span> sheet response to temperature and sea-level change. Examination of published models suggests several preliminary conclusions about <span class="hlt">ice</span> sheet history. The <span class="hlt">ice</span> sheet's present high sensitivity to sea-level change at short (orbital) periods was developed gradually as its size increased, replacing a declining sensitivity to temperature. Models suggest that the <span class="hlt">ice</span> sheet grew abruptly to 40% (or possibly more) of its present size at the Eocene-Oligocene boundary, mainly as a result of its own temperature sensitivity. A large but more gradual middle Miocene change was externally driven, probably by development of the <span class="hlt">Antarctic</span> Circumpolar Current (ACC) and Polar Front, provided that a few million years' delay can be explained. The Oligocene <span class="hlt">ice</span> sheet varied considerably in size and areal extent, but the late Miocene <span class="hlt">ice</span> sheet was more stable, though significantly warmer than today's. This difference probably relates to the confining effect of the <span class="hlt">Antarctic</span> continental margin. Present-day numerical models of <span class="hlt">ice</span> sheet development are sufficient to guide current sampling plans, but sea-<span class="hlt">ice</span> formation, polar wander, basal topography and <span class="hlt">ice</span> streaming can be identified as factors meriting additional modelling effort in the future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70168450','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70168450"><span>Evidence for an <span class="hlt">ice</span> <span class="hlt">shelf</span> covering the central Arctic Ocean during the penultimate glaciation</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Jakobsson, Martin; Nilsson, Johan; Anderson, Leif G.; Backman, Jan; Bjork, Goran; Cronin, Thomas M.; Kirchner, Nina; Koshurnikov, Andrey; Mayer, Larry; Noormets, Riko; O'Regan, Matthew; Stranne, Christian; Ananiev, Roman; Macho, Natalia Barrientos; Cherniykh, Dennis; Coxall, Helen; Eriksson, Bjorn; Floden, Tom; Gemery, Laura; Gustafsson, Orjan; Jerram, Kevin; Johansson, Carina; Khortov, Alexey; Mohammad, Rezwan; Semiletov, Igor</p> <p>2016-01-01</p> <p>The hypothesis of a km-thick <span class="hlt">ice</span> <span class="hlt">shelf</span> covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating <span class="hlt">ice</span> shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of <span class="hlt">ice</span> shelves should, however, exist where <span class="hlt">ice</span> grounded along their flow paths. Here we present new evidence of <span class="hlt">ice-shelf</span> groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an <span class="hlt">ice</span> <span class="hlt">shelf</span> extending over the entire central Arctic Ocean during at least one previous <span class="hlt">ice</span> age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean <span class="hlt">ice</span> <span class="hlt">shelf</span> dated to marine isotope stage 6 (~140 ka). Bathymetric highs were likely critical in the <span class="hlt">ice-shelf</span> development by acting as pinning points where stabilizing <span class="hlt">ice</span> rises formed, thereby providing sufficient back stress to allow <span class="hlt">ice</span> <span class="hlt">shelf</span> thickening.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4735638','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4735638"><span>Evidence for an <span class="hlt">ice</span> <span class="hlt">shelf</span> covering the central Arctic Ocean during the penultimate glaciation</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Jakobsson, Martin; Nilsson, Johan; Anderson, Leif; Backman, Jan; Björk, Göran; Cronin, Thomas M.; Kirchner, Nina; Koshurnikov, Andrey; Mayer, Larry; Noormets, Riko; O'Regan, Matthew; Stranne, Christian; Ananiev, Roman; Barrientos Macho, Natalia; Cherniykh, Denis; Coxall, Helen; Eriksson, Björn; Flodén, Tom; Gemery, Laura; Gustafsson, Örjan; Jerram, Kevin; Johansson, Carina; Khortov, Alexey; Mohammad, Rezwan; Semiletov, Igor</p> <p>2016-01-01</p> <p>The hypothesis of a km-thick <span class="hlt">ice</span> <span class="hlt">shelf</span> covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating <span class="hlt">ice</span> shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of <span class="hlt">ice</span> shelves should, however, exist where <span class="hlt">ice</span> grounded along their flow paths. Here we present new evidence of <span class="hlt">ice-shelf</span> groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an <span class="hlt">ice</span> <span class="hlt">shelf</span> extending over the entire central Arctic Ocean during at least one previous <span class="hlt">ice</span> age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean <span class="hlt">ice</span> <span class="hlt">shelf</span> dated to marine isotope stage 6 (∼140 ka). Bathymetric highs were likely critical in the <span class="hlt">ice-shelf</span> development by acting as pinning points where stabilizing <span class="hlt">ice</span> rises formed, thereby providing sufficient back stress to allow <span class="hlt">ice</span> <span class="hlt">shelf</span> thickening. PMID:26778247</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20160013301&hterms=sea&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dsea','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20160013301&hterms=sea&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dsea"><span>Assessment of Arctic and <span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span> Predictability in CMIP5 Decadal Hindcasts</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Yang, Chao-Yuan; Liu, Jiping (Inventor); Hu, Yongyun; Horton, Radley M.; Chen, Liqi; Cheng, Xiao</p> <p>2016-01-01</p> <p>This paper examines the ability of coupled global climate models to predict decadal variability of Arctic and <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span>. We analyze decadal hindcasts/predictions of 11 Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Decadal hindcasts exhibit a large multimodel spread in the simulated sea <span class="hlt">ice</span> extent, with some models deviating significantly from the observations as the predicted <span class="hlt">ice</span> extent quickly drifts away from the initial constraint. The anomaly correlation analysis between the decadal hindcast and observed sea <span class="hlt">ice</span> suggests that in the Arctic, for most models, the areas showing significant predictive skill become broader associated with increasing lead times. This area expansion is largely because nearly all the models are capable of predicting the observed decreasing Arctic sea <span class="hlt">ice</span> cover. Sea <span class="hlt">ice</span> extent in the North Pacific has better predictive skill than that in the North Atlantic (particularly at a lead time of 3-7 years), but there is a reemerging predictive skill in the North Atlantic at a lead time of 6-8 years. In contrast to the Arctic, <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> decadal hindcasts do not show broad predictive skill at any timescales, and there is no obvious improvement linking the areal extent of significant predictive skill to lead time increase. This might be because nearly all the models predict a retreating <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> cover, opposite to the observations. For the Arctic, the predictive skill of the multi-model ensemble mean outperforms most models and the persistence prediction at longer timescales, which is not the case for the <span class="hlt">Antarctic</span>. Overall, for the Arctic, initialized decadal hindcasts show improved predictive skill compared to uninitialized simulations, although this improvement is not present in the <span class="hlt">Antarctic</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014TCry....8....1B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014TCry....8....1B"><span>Seabed topography beneath Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span> from seismic soundings</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brisbourne, A. M.; Smith, A. M.; King, E. C.; Nicholls, K. W.; Holland, P. R.; Makinson, K.</p> <p>2014-01-01</p> <p>Seismic reflection soundings of <span class="hlt">ice</span> thickness and seabed depth were acquired on the Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in order to test a sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> bathymetry model derived from the inversion of <span class="hlt">Ice</span>Bridge gravity data. A series of lines was collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the <span class="hlt">ice</span> front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> oceanic circulation may be affected by <span class="hlt">ice</span> draft and seabed depth. The seismic velocity profile in the upper 100 m of firn and <span class="hlt">ice</span> was derived from shallow refraction surveys at a number of locations. Measured temperatures within the <span class="hlt">ice</span> column and at the <span class="hlt">ice</span> base were used to define the velocity profile through the remainder of the <span class="hlt">ice</span> column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in <span class="hlt">ice</span> and water cavity thickness are in general < 10 m. Compared with the seismic measurements, the root-mean-square error in the gravimetrically derived bathymetry at the seismic sites is 162 m. The seismic profiles prove the non-existence of several bathymetric features that are indicated in the gravity inversion model, significantly modifying the expected oceanic circulation beneath the <span class="hlt">ice</span> <span class="hlt">shelf</span>. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of <span class="hlt">Ice</span>Bridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> ocean circulation models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16905428','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16905428"><span>Crustacea in Arctic and <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span>: distribution, diet and life history strategies.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Arndt, Carolin E; Swadling, Kerrie M</p> <p>2006-01-01</p> <p>This review concerns crustaceans that associate with sea <span class="hlt">ice</span>. Particular emphasis is placed on comparing and contrasting the Arctic and <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> habitats, and the subsequent influence of these environments on the life history strategies of the crustacean fauna. Sea <span class="hlt">ice</span> is the dominant feature of both polar marine ecosystems, playing a central role in physical processes and providing an essential habitat for organisms ranging in size from viruses to whales. Similarities between the Arctic and <span class="hlt">Antarctic</span> marine ecosystems include variable cover of sea <span class="hlt">ice</span> over an annual cycle, a light regimen that can extend from months of total darkness to months of continuous light and a pronounced seasonality in primary production. Although there are many similarities, there are also major differences between the two regions: The <span class="hlt">Antarctic</span> experiences greater seasonal change in its sea <span class="hlt">ice</span> extent, much of the <span class="hlt">ice</span> is over very deep water and more than 80% breaks out each year. In contrast, Arctic sea <span class="hlt">ice</span> often covers comparatively shallow water, doubles in its extent on an annual cycle and the <span class="hlt">ice</span> may persist for several decades. Crustaceans, particularly copepods and amphipods, are abundant in the sea <span class="hlt">ice</span> zone at both poles, either living within the brine channel system of the <span class="hlt">ice</span>-crystal matrix or inhabiting the <span class="hlt">ice</span>-water interface. Many species associate with <span class="hlt">ice</span> for only a part of their life cycle, while others appear entirely dependent upon it for reproduction and development. Although similarities exist between the two faunas, many differences are emerging. Most notable are the much higher abundance and biomass of <span class="hlt">Antarctic</span> copepods, the dominance of the <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> copepod fauna by calanoids, the high euphausiid biomass in Southern Ocean waters and the lack of any species that appear fully dependent on the <span class="hlt">ice</span>. In the Arctic, the <span class="hlt">ice</span>-associated fauna is dominated by amphipods. Calanoid copepods are not tightly associated with the <span class="hlt">ice</span>, while harpacticoids and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70021553','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70021553"><span>Crustal and lithospheric structure of the west <span class="hlt">Antarctic</span> Rift System from geophysical investigations: A review</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Behrendt, John C.</p> <p>1999-01-01</p> <p>The active West <span class="hlt">Antarctic</span> Rift System, which extends from the continental <span class="hlt">shelf</span> of the Ross Sea, beneath the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet, is comparable in size to the Basin and Range in North America, or the East African rift systems. Geophysical surveys (primarily marine seismic and aeromagnetic combined with radar <span class="hlt">ice</span> sounding) have extended the information provided by sparse geologic exposures and a few drill holes over the <span class="hlt">ice</span> and sea covered area. Rift basins developed in the early Cretaceous accompanied by the major extension of the region. Tectonic activity has continued episodically in the Cenozoic to the present, including major uplift of the Transantarctic Mountains. The West <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet, and the late Cenozoic volcanic activity in the West <span class="hlt">Antarctic</span> Rift System, through which it flows, have been coeval since at least Miocene time. The rift is characterized by sparse exposures of late Cenozoic alkaline volcanic rocks extending from northern Victoria Land throughout Marie Byrd Land. The aeromagnetic interpretations indicate the presence of > 5 x 105 km2 (> 106 km3) of probable late Cenozoic volcanic rocks (and associated subvolcanic intrusions) in the West <span class="hlt">Antarctic</span> rift. This great volume with such limited exposures is explained by glacial removal of the associated late Cenozoic volcanic edifices (probably hyaloclastite debris) concomitantly with their subglacial eruption. Large offset seismic investigations in the Ross Sea and on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> indicate a ~ 17-24-km-thick, extended continental crust. Gravity data suggest that this extended crust of similar thickness probably underlies the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and Byrd Subglacial Basin. Various authors have estimated maximum late Cretaceous-present crustal extension in the West <span class="hlt">Antarctic</span> rift area from 255-350 km based on balancing crustal thickness. Plate reconstruction allowed < 50 km of Tertiary extension. However, paleomagnetic measurements suggested about 1000 km of post</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4060491','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4060491"><span>Cyclone-induced rapid creation of extreme <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> conditions</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wang, Zhaomin; Turner, John; Sun, Bo; Li, Bingrui; Liu, Chengyan</p> <p>2014-01-01</p> <p>Two polar vessels, Akademik Shokalskiy and Xuelong, were trapped by thick sea <span class="hlt">ice</span> in the <span class="hlt">Antarctic</span> coastal region just to the west of 144°E and between 66.5°S and 67°S in late December 2013. This event demonstrated the rapid establishment of extreme <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> conditions on synoptic time scales. The event was associated with cyclones that developed at lower latitudes. Near the event site, cyclone-enhanced strong southeasterly katabatic winds drove large westward drifts of <span class="hlt">ice</span> floes. In addition, the cyclones also gave southward <span class="hlt">ice</span> drift. The arrival and grounding of Iceberg B9B in Commonwealth Bay in March 2011 led to the growth of fast <span class="hlt">ice</span> around it, forming a northward protruding barrier. This barrier blocked the westward <span class="hlt">ice</span> drift and hence aided sea <span class="hlt">ice</span> consolidation on its eastern side. Similar cyclone-induced events have occurred at this site in the past after the grounding of Iceberg B9B. Future events may be predictable on synoptic time scales, if cyclone-induced strong wind events can be predicted. PMID:24937550</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17..233W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17..233W"><span>The <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet during the last Interglaciation: Insights from my Thesis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Whipple, Matthew; Lunt, Dan; Singarayer, Joy; Bradley, Sarah; Milne, Glenn; Wolff, Eric; Siddall, Mark</p> <p>2015-04-01</p> <p>The last interglaciation represents a period of warmer climates and higher sea levels, and a useful analogue to future climate. While many studies have focussed on the response of the Greenland <span class="hlt">Ice</span> sheet, far less is known about the response of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet. Here, I present the summarised results of my PhD thesis "Constraints on the minimum extent of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet during the last interglaciation". Firstly, I cover the timings of interglaciation in Antarctica, and their differences with respect to the Northern Hemisphere timings, based on paleo sea level indicators, and oceanic temperature records. I move on to cover climate forcings, and how they influence the <span class="hlt">ice</span> sheet, relative to present, and early Holocene. Secondly, I present thesis results, from looking at <span class="hlt">ice</span> core stable water isotopes. These are compared with Isostatic and Climatic modelling results, for various different <span class="hlt">Ice</span> sheet scenarios, as to the resulting Climate, from changes in Elevation, Temperature, Precipitation, and Sublimation, all contributing to the recorded stable water isotope record. Thirdly, I move on to looking at the mid-field relative sea level records, from Australia and Argentina. Using isostatic modelling, these are used to assess the relative contribution of the Eastern and Western <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> sheets. Although data uncertainties result in us being to identify the contribution from West Antarctica. Overall, using model-data comparison, we find a lack of evidence for a substantial retreat of the Wilkes Subglacial basin. No data location is close enough to determine the existence of the marine based West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> sheet. Model uncertainty is unable to constrain evidence of variations in <span class="hlt">ice</span> thickness in East Antarctica.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28008213','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28008213"><span>The surface climatology of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Antarctica.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Costanza, Carol A; Lazzara, Matthew A; Keller, Linda M; Cassano, John J</p> <p>2016-12-01</p> <p>The University of Wisconsin-Madison <span class="hlt">Antarctic</span> Automatic Weather Station (AWS) project has been making meteorological surface observations on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (RIS) for approximately 30 years. This network offers the most continuous set of routine measurements of surface meteorological variables in this region. The Ross Island area is excluded from this study. The surface climate of the RIS is described using the AWS measurements. Temperature, pressure, and wind data are analysed on daily, monthly, seasonal, and annual time periods for 13 AWS across the RIS. The AWS are separated into three representative regions - central, coastal, and the area along the Transantarctic Mountains - in order to describe specific characteristics of sections of the RIS. The climatology describes general characteristics of the region and significant changes over time. The central AWS experiences the coldest mean temperature, and the lowest resultant wind speed. These AWSs also experience the coldest potential temperatures with a minimum of 209.3 K at Gill AWS. The AWS along the Transantarctic Mountains experiences the warmest mean temperature, the highest mean sea-level pressure, and the highest mean resultant wind speed. Finally, the coastal AWS experiences the lowest mean pressure. Climate indices (MEI, SAM, and SAO) are compared to temperature and pressure data of four of the AWS with the longest observation periods, and significant correlation is found for most AWS in sea-level pressure and temperature. This climatology study highlights characteristics that influence the climate of the RIS, and the challenges of maintaining a long-term <span class="hlt">Antarctic</span> AWS network. Results from this effort are essential for the broader <span class="hlt">Antarctic</span> meteorology community for future research.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5137343','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5137343"><span>The surface climatology of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Antarctica</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lazzara, Matthew A.; Keller, Linda M.; Cassano, John J.</p> <p>2016-01-01</p> <p>ABSTRACT The University of Wisconsin‐Madison <span class="hlt">Antarctic</span> Automatic Weather Station (AWS) project has been making meteorological surface observations on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (RIS) for approximately 30 years. This network offers the most continuous set of routine measurements of surface meteorological variables in this region. The Ross Island area is excluded from this study. The surface climate of the RIS is described using the AWS measurements. Temperature, pressure, and wind data are analysed on daily, monthly, seasonal, and annual time periods for 13 AWS across the RIS. The AWS are separated into three representative regions – central, coastal, and the area along the Transantarctic Mountains – in order to describe specific characteristics of sections of the RIS. The climatology describes general characteristics of the region and significant changes over time. The central AWS experiences the coldest mean temperature, and the lowest resultant wind speed. These AWSs also experience the coldest potential temperatures with a minimum of 209.3 K at Gill AWS. The AWS along the Transantarctic Mountains experiences the warmest mean temperature, the highest mean sea‐level pressure, and the highest mean resultant wind speed. Finally, the coastal AWS experiences the lowest mean pressure. Climate indices (MEI, SAM, and SAO) are compared to temperature and pressure data of four of the AWS with the longest observation periods, and significant correlation is found for most AWS in sea‐level pressure and temperature. This climatology study highlights characteristics that influence the climate of the RIS, and the challenges of maintaining a long‐term <span class="hlt">Antarctic</span> AWS network. Results from this effort are essential for the broader <span class="hlt">Antarctic</span> meteorology community for future research. PMID:28008213</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20070016598&hterms=sea+ice+albedo&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dsea%2Bice%2Balbedo','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20070016598&hterms=sea+ice+albedo&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dsea%2Bice%2Balbedo"><span>Observational Evidence of a Hemispheric-wide <span class="hlt">Ice</span>-ocean Albedo Feedback Effect on <span class="hlt">Antarctic</span> Sea-<span class="hlt">ice</span> Decay</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nihashi, Sohey; Cavalieri, Donald J.</p> <p>2007-01-01</p> <p>The effect of <span class="hlt">ice</span>-ocean albedo feedback (a kind of <span class="hlt">ice</span>-albedo feedback) on sea-<span class="hlt">ice</span> decay is demonstrated over the <span class="hlt">Antarctic</span> sea-<span class="hlt">ice</span> zone from an analysis of satellite-derived hemispheric sea <span class="hlt">ice</span> concentration and European Centre for Medium-Range Weather Forecasts (ERA-40) atmospheric data for the period 1979-2001. Sea <span class="hlt">ice</span> concentration in December (time of most active melt) correlates better with the meridional component of the wind-forced <span class="hlt">ice</span> drift (MID) in November (beginning of the melt season) than the MID in December. This 1 month lagged correlation is observed in most of the <span class="hlt">Antarctic</span> sea-<span class="hlt">ice</span> covered ocean. Daily time series of <span class="hlt">ice</span> , concentration show that the <span class="hlt">ice</span> concentration anomaly increases toward the time of maximum sea-<span class="hlt">ice</span> melt. These findings can be explained by the following positive feedback effect: once <span class="hlt">ice</span> concentration decreases (increases) at the beginning of the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in <span class="hlt">ice</span> concentration by the oceanic heat. Results obtained fi-om a simple <span class="hlt">ice</span>-ocean coupled model also support our interpretation of the observational results. This positive feedback mechanism explains in part the large interannual variability of the sea-<span class="hlt">ice</span> cover in summer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.G52B..03B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.G52B..03B"><span>The East <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet and the Gamburtsev Subglacial Mountains (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bell, R. E.; Studinger, M.; Ferraccioli, F.; Damaske, D.; Finn, C.; Braaten, D. A.; Fahnestock, M. A.; Jordan, T. A.; Corr, H.; Elieff, S.; Frearson, N.; Block, A. E.; Rose, K.</p> <p>2009-12-01</p> <p>Models of the onset of glaciation in Antarctica routinely document the early growth of the <span class="hlt">ice</span> sheet on the summit of the Gamburtsev Subglacial Mountains in the center of the East <span class="hlt">Antarctic</span> Craton. While <span class="hlt">ice</span> sheet models replicate the formation of the East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet 35 million years ago, the age, evolution and structure of the Gamburtsev Mountains remain completely unresolved. During the International Polar Year scientists from seven nations have launched a major collaborative program (AGAP) to explore the Gamburtsev Subglacial Mountains buried by the East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet and bounded by numerous subglacial lakes. The AGAP umbrella is a multi-national, multi-disciplinary effort and includes aerogeophysics, passive seismology, traverse programs and will be complimented by future <span class="hlt">ice</span> core and bedrock drilling. A major new airborne data set including gravity; magnetics; <span class="hlt">ice</span> thickness; SAR images of the <span class="hlt">ice</span>-bed interface; near-surface and deep internal layers; and <span class="hlt">ice</span> surface elevation is providing insights into a more dynamic East Antarctica. More than 120,000 km of aerogeophysical data have been acquired from two remote field camps during the 2008/09 field season. AGAP effort was designed to address several fundamental questions including: 1) What role does topography play in the nucleation of continental <span class="hlt">ice</span> sheets? 2) How do tectonic processes control the formation, distribution, and stability of subglacial lakes? The preliminary analysis of this major new data set indicated these 3000m high mountains are deeply dissected by a dendritic system. The northern margin of the mountain range terminates against the inland extent of the Lambert Graben. Evidence of the onset of glaciation is preserved as cirques and U shaped valleys along the axis of the uplifted massifs. The geomorphology reflects the interaction between the <span class="hlt">ice</span> sheet and the Gamburtsev Mountains. Bright reflectors in the radar data in the deep valleys indicate the presence of water that has</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.P52A..05D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.P52A..05D"><span>Environmentally Non-Disturbing Under-<span class="hlt">ice</span> Robotic <span class="hlt">ANtarctiC</span> Explorer (ENDURANCE)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Doran, P. T.; Stone, W.; Priscu, J.; McKay, C.; Johnson, A.; Chen, B.</p> <p>2007-12-01</p> <p>Permanently <span class="hlt">ice</span>-covered liquid water environments are among the leading candidate sites for finding evidence of extant life elsewhere in our solar system (e.g. on Europa and other Galiean satellites, and possibly in subglacial lakes on Mars). In order to have the proper tools and strategies for exploring the extant <span class="hlt">ice</span>-covered planetary environments, we are developing an autonomous underwater vehicle (AUV) capable of generating for the first time 3-D biogeochemical datasets in the extreme environment of perennially <span class="hlt">ice</span>-covered <span class="hlt">Antarctic</span> dry valley lakes. The ENDURANCE (Environmentally Non-Disturbing Under-<span class="hlt">ice</span> Robotic <span class="hlt">ANtarctic</span> Explorer) will map the under-<span class="hlt">ice</span> lake dimensions of West Lake Bonney in the McMurdo Dry Valleys, and be equipped to measure a comprehensive suite of physical and biogeochemical indices in the water column, as well as Raman Spectrometry of the water column and benthos. The AUV is being specifically designed to minimize impact on the environment it is working in. This is primarily to meet strict <span class="hlt">Antarctic</span> environmental protocols, but will also be useful for planetary protection and improved science in the future. We will carry out two <span class="hlt">Antarctic</span> field seasons (in concert with our NSF-funded Long Term Ecological Research) and test two central hypotheses: H1: The low kinetic energy of the system (diffusion dominates the spatial transport of constituents) produces an ecosystem and ecosystem limits that vary significantly in three dimensions. H2: The whole-lake physical and biogeochemical structure remains static from year to year The talk will provide an overview of the ENDURANCE project and an update on the AUV development at the time of presentation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030056665&hterms=Parkinsons&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DParkinsons','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030056665&hterms=Parkinsons&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DParkinsons"><span>30-Year Satellite Record Reveals Accelerated Arctic Sea <span class="hlt">Ice</span> Loss, <span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span> Trend Reversal</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cavalieri, Donald J.; Parkinson, C. L.; Vinnikov, K. Y.</p> <p>2003-01-01</p> <p>Arctic sea <span class="hlt">ice</span> extent decreased by 0.30 plus or minus 0.03 x 10(exp 6) square kilometers per decade from 1972 through 2002, but decreased by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per decade from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast to the Arctic, the <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> extent decreased dramatically over the period 1973-1977, then gradually increased, with an overall 30-year trend of -0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10yr. The trend reversal is attributed to a large positive anomaly in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> extent observed in the early 1970's.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008DSRII..55.2404S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008DSRII..55.2404S"><span>The FOODBANCS project: Introduction and sinking fluxes of organic carbon, chlorophyll- a and phytodetritus on the western <span class="hlt">Antarctic</span> Peninsula continental <span class="hlt">shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, Craig R.; Mincks, Sarah; DeMaster, David J.</p> <p>2008-11-01</p> <p>The impact of the highly seasonal <span class="hlt">Antarctic</span> primary production cycle on <span class="hlt">shelf</span> benthic ecosystems remains poorly evaluated. Here we describe a times-series research project on the West <span class="hlt">Antarctic</span> Peninsula (WAP) <span class="hlt">shelf</span> designed to evaluate the seafloor deposition, and subsequent ecological and biogeochemical impacts, of the summer phytoplankton bloom along a transect crossing the <span class="hlt">Antarctic</span> <span class="hlt">shelf</span> near Anvers Island. During this project, entitled Food for Benthos on the <span class="hlt">Antarctic</span> Continental <span class="hlt">Shelf</span> (FOODBANCS), we deployed replicate sediment traps 150-170 m above the seafloor (total water-column depth of 590 m) on the central <span class="hlt">shelf</span> from December 1999 to March 2001, recovering trap samples every 3-4 months. In addition, we used a seafloor time-lapse camera system, as well as video surveys conducted at 3-4 months intervals, to monitor the presence and accumulation of phytodetritus at the sediment-water interface. The fluxes of particulate organic carbon and chlorophyll- a into sediment traps (binned over 3-4 month intervals) showed patterns consistent with seasonal variability, with average summer fluxes during the first year exceeding winter fluxes by a factor of ˜2-3. However, inter-annual variability in summer fluxes was even greater than seasonal variability, with 4-10-fold differences in the flux of organic carbon and chlorophyll- a between the summer seasons of 1999-2000 and 2000-2001. Phytodetrital accumulation at the <span class="hlt">shelf</span> floor also exhibited intense inter-annual variability, with no visible phytodetritus from essentially December 1999 to November 2000, followed by pulsed accumulation of 1-2 cm of phytodetritus over a ˜30,000 km 2 <span class="hlt">shelf</span> area by March 2001. Comparisons with other studies suggest that the levels of inter-annual variability we observed are typical of the <span class="hlt">Antarctic</span> <span class="hlt">shelf</span> over decadal time scales. We conclude that fluxes of particulate organic carbon, chlorophyll- a and phytodetritus to WAP-<span class="hlt">shelf</span> sediments vary intensely on seasonal to inter</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C33C0833S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C33C0833S"><span>Flexural-gravity Wave Attenuation in a Thick <span class="hlt">Ice</span> <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stephen, R. A.; Bromirski, P. D.; Gerstoft, P.; Chen, Z.; Wiens, D.; Aster, R. C.; Nyblade, A.</p> <p>2016-12-01</p> <p>A thirty-four station broadband seismic array was deployed on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica from November 2014 to November 2017. Analyses indicate that phase speeds of infra-gravity wave and tsunami excitation in the 0.003 to 0.02 Hz band are 70 m/s, corresponding to the low frequency limit of flexural-gravity waves. Median spectral amplitudes in this band decay exponentially with distance from the <span class="hlt">shelf</span> edge in a manner consistent with intrinsic attenuation. Seismic Q is typically 7-9, with an RMS amplitude decay of 0.04-0.05dB/km and an e-folding distance of 175-220 km. Amplitudes do not appear to drop crossing crevasse fields. Vertical and horizontal acceleration levels at stations on the floating <span class="hlt">ice</span> <span class="hlt">shelf</span> are 50 dB higher than those on grounded <span class="hlt">ice</span>. Horizontal accelerations are about 15 dB higher than vertical accelerations. Median spectral levels at 0.003 Hz are within 6 dB for stations from 2 to 430 km from the <span class="hlt">shelf</span> edge. In contrast, the levels drop by 90 dB at 0.02 Hz. Ocean gravity wave excitation has been proposed as a mechanism that can weaken <span class="hlt">ice</span> shelves and potentially trigger disintegration events. These measurements indicate that the propensity for <span class="hlt">shelf</span> weakening and disintegration decays exponentially with distance from the <span class="hlt">ice</span> front for gravity waves in the 0.003 to 0.02Hz band.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JAMES..10..262B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JAMES..10..262B"><span>A Mathematical Model of Melt Lake Development on an <span class="hlt">Ice</span> <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Buzzard, S. C.; Feltham, D. L.; Flocco, D.</p> <p>2018-02-01</p> <p>The accumulation of surface meltwater on <span class="hlt">ice</span> shelves can lead to the formation of melt lakes. Melt lakes have been implicated in <span class="hlt">ice</span> <span class="hlt">shelf</span> collapse; Antarctica's Larsen B <span class="hlt">Ice</span> <span class="hlt">Shelf</span> was observed to have a large amount of surface melt lakes present preceding its collapse in 2002. Such collapse can affect ocean circulation and temperature, cause habitat loss and contribute to sea level rise through the acceleration of tributary glaciers. We present a mathematical model of a surface melt lake on an idealized <span class="hlt">ice</span> <span class="hlt">shelf</span>. The model incorporates a calculation of the <span class="hlt">ice</span> <span class="hlt">shelf</span> surface energy balance, heat transfer through the firn, the production and percolation of meltwater into the firn, the formation of <span class="hlt">ice</span> lenses, and the development and refreezing of surface melt lakes. The model is applied to the Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, where melt lakes have been observed. This region has warmed several times the global average over the last century and the Larsen C firn layer could become saturated with meltwater by the end of the century. When forced with weather station data, our model produces surface melting, meltwater accumulation, and melt lake development consistent with observations. We examine the sensitivity of lake formation to uncertain parameters and provide evidence of the importance of processes such as lateral meltwater transport. We conclude that melt lakes impact surface melt and firn density and warrant inclusion in dynamic-thermodynamic models of <span class="hlt">ice</span> <span class="hlt">shelf</span> evolution within climate models, of which our model could form the basis for the thermodynamic component.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.7564M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.7564M"><span>A Tale of Two Forcings: Present-Day Coupled <span class="hlt">Antarctic</span> <span class="hlt">Ice</span>-sheet/Southern Ocean dynamics using the POPSICLES model.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin, Daniel; Asay-Davis, Xylar; Cornford, Stephen; Price, Stephen; Ng, Esmond; Collins, William</p> <p>2015-04-01</p> <p>We present POPSICLES simulation results covering the full <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet and the Southern Ocean spanning the period 1990 to 2010 resulting from two different choices of climate forcing: a 'normal-year' climatology and the CORE v. 2 interannual forcing data (Large and Yeager 2008). Simulations are performed at 0.1o (~5 km) ocean resolution and adaptive <span class="hlt">ice</span> sheet resolution as fine as 500 m. We compare time-averaged melt rates below a number of major <span class="hlt">ice</span> shelves with those reported by Rignot et al. (2013) as well as other recent studies. We also present seasonal variability and decadal melting trends from several <span class="hlt">Antarctic</span> regions, along with the response of the <span class="hlt">ice</span> shelves and consequent dynamics of the grounded <span class="hlt">ice</span> sheet. POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES <span class="hlt">ice</span>-sheet model (Cornford et al., 2012). POP2x includes sub-<span class="hlt">ice-shelf</span> circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard <span class="hlt">ice</span>-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh (2009) to accurately model regions of dynamic complexity, such as <span class="hlt">ice</span> streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d; Pattyn et al., 2013) and realistic configurations (Favier et al. 2014).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980021232','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980021232"><span>Sea <span class="hlt">Ice</span> on the Southern Ocean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jacobs, Stanley S.</p> <p>1998-01-01</p> <p>Year-round satellite records of sea <span class="hlt">ice</span> distribution now extend over more than two decades, providing a valuable tool to investigate related characteristics and circulations in the Southern Ocean. We have studied a variety of features indicative of oceanic and atmospheric interactions with <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span>. In the Amundsen & Bellingshausen Seas, sea <span class="hlt">ice</span> extent was found to have decreased by approximately 20% from 1973 through the early 1990's. This change coincided with and probably contributed to recently warmer surface conditions on the west side of the <span class="hlt">Antarctic</span> Peninsula, where air temperatures have increased by approximately 0.5 C/decade since the mid-1940's. The sea <span class="hlt">ice</span> decline included multiyear cycles of several years in length superimposed on high interannual variability. The retreat was strongest in summer, and would have lowered the regional mean <span class="hlt">ice</span> thickness, with attendant impacts upon vertical heat flux and the formation of snow <span class="hlt">ice</span> and brine. The cause of the regional warming and loss of sea <span class="hlt">ice</span> is believed to be linked to large-scale circulation changes in the atmosphere and ocean. At the eastern end of the Weddell Gyre, the Cosmonaut Polyna revealed greater activity since 1986, a recurrence pattern during recent winters and two possible modes of formation. Persistence in polynya location was noted off Cape Ann, where the coastal current can interact more strongly with the <span class="hlt">Antarctic</span> Circumpolar Current. As a result of vorticity conservation, locally enhanced upwelling brings warmer deep water into the mixed layer, causing divergence and melting. In the Ross Sea, <span class="hlt">ice</span> extent fluctuates over periods of several years, with summer minima and winter maxima roughly in phase. This leads to large interannual cycles of sea <span class="hlt">ice</span> range, which correlate positively with meridinal winds, regional air temperatures and subsequent <span class="hlt">shelf</span> water salinities. Deep <span class="hlt">shelf</span> waters display considerable interannual variability, but have freshened by approximately 0.03/decade</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.P54A..01S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.P54A..01S"><span>Seismometers on Europa: Insights from Modeling and <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Analogs (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmerr, N. C.; Brunt, K. M.; Cammarano, F.; Hurford, T. A.; Lekic, V.; Panning, M. P.; Rhoden, A.; Sauber, J. M.</p> <p>2013-12-01</p> <p> the depth of an ocean layer. Likewise, evaluation of arrival times of reflected wave multiples observed at a single seismic station would record properties of the mantle and core of Europa. Cluster analysis of waveforms from various seismic source mechanisms could be used to classify different types of seismicity originating from the <span class="hlt">ice</span> and rocky parts of the moon. We examine examples of single station results for analogous seismic experiments on Earth, e.g., where broadband, 3-component seismometers have been placed upon the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> of Antarctica. Ultimately this work reveals that seismometer deployments will be essential for understanding the internal dynamics, habitability, and surface evolution of Europa, and that seismic instruments need to be a key component of future missions to surface of Europa and outer satellites.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/9974394','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/9974394"><span>Hunting behavior of a marine mammal beneath the <span class="hlt">antarctic</span> fast <span class="hlt">Ice</span></span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Davis; Fuiman; Williams; Collier; Hagey; Kanatous; Kohin; Horning</p> <p>1999-02-12</p> <p>The hunting behavior of a marine mammal was studied beneath the <span class="hlt">Antarctic</span> fast <span class="hlt">ice</span> with an animal-borne video system and data recorder. Weddell seals stalked large <span class="hlt">Antarctic</span> cod and the smaller subice fish Pagothenia borchgrevinki, often with the under-<span class="hlt">ice</span> surface for backlighting, which implies that vision is important for hunting. They approached to within centimeters of cod without startling the fish. Seals flushed P. borchgrevinki by blowing air into subice crevices or pursued them into the platelet <span class="hlt">ice</span>. These observations highlight the broad range of insights that are possible with simultaneous recordings of video, audio, three-dimensional dive paths, and locomotor effort.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030102176','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030102176"><span>30-Year Satellite Record Reveals Contrasting Arctic and <span class="hlt">Antarctic</span> Decadal Sea <span class="hlt">Ice</span> Variability</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cavalieri, D. J.; Parkinson, C. L.; Vinnikov, K. Y.</p> <p>2003-01-01</p> <p>A 30-year satellite record of sea <span class="hlt">ice</span> extents derived mostly from satellite microwave radiometer observations reveals that the Arctic sea <span class="hlt">ice</span> extent decreased by 0.30+0.03 x 10(exp 6) square kilometers per 10 yr from 1972 through 2002, but by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per 10yr from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast, the <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> extent decreased dramatically over the period 1973-1977, then gradually increased. Over the full 30-year period, the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> extent decreased by 0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10 yr. The trend reversal is attributed to a large positive anomaly in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> extent in the early 1970's, an anomaly that apparently began in the late 1960's, as observed in early visible and infrared satellite images.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..1112497V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..1112497V"><span>Calcareous nannofossil evidence for Marine Isotope Stage 31 (1 Ma) in the AND-1B Core, ANDRILL McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Project (Antarctica).</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Villa, G.; Persico, D.; Wise, S. W.; Gadaleta, A.</p> <p>2009-04-01</p> <p>During the austral summer 2006 the ANDRILL Program recovered a 1285 m-long succession of cyclic glacimarine sediments from the McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (MIS). The aim of the MIS Project was to obtain continuous Neogene (c. 0-10 Ma) glacial, glacimarine, volcanic, and biogenic sediments that have accumulated in the region of the McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (Ross Sea) nourished by <span class="hlt">ice</span> flowing from East <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (EAIS) outlet glaciers in the Transantarctic Mountains (TAM). The MIS AND-1B drill core represents the longest and most complete (98% recovery) geological record from the <span class="hlt">Antarctic</span> continental margin to date, and will provide a key reference record of climate and <span class="hlt">ice</span>-sheet variability through the Late Neogene; detailed investigations of this record will contribute for improving our knowledge of Antarctica's influence on global climate. Preliminary on-<span class="hlt">ice</span> analysis of the smear slides of the Andrill core revealed calcareous microfossils (dinoflagellates, calciosponge spicula and small foraminifera) occurring with variable concentrations. The presence of thoracosphaerid fragments in the smear slides of the first 600 mbsf (Quaternary), probably belong to the species Thoracosphaera saxea (Stradner 1961), and Thoracosphaera heimi (Kamptner, 1941) and other, potentially undescribed species (Villa & Wise 1998), suggests either a peculiar adaptation to this environment, due to their ability to develop cysts or warmer conditions at the time of their deposition, or a combination of both. However, they represent an additional element to use with the other proxies for inferring palaeoenvironmental conditions of the core. Subsequent shore-based analyses of 100 samples from 86-96 mbsf revealed for the first time the presence of Pleistocene coccolithophorids at these high southern latitudes (77° S), including: Coccolithus pelagicus, small Gephyrocapsa, Reticulofenestra asanoi, Pseudoemiliania lacunosa, Dictyoccocites productus, Reticulofenestra sp., Reticulofenestra minutula</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020004188','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020004188"><span>Modeling South Pacific <span class="hlt">Ice</span>-Ocean Interactions in the Global Climate System</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Holland, David M.; Jenkins, Adrian; Jacobs, Stanley S.</p> <p>2001-01-01</p> <p>The objective of this project has been to improve the modeling of interactions between large <span class="hlt">Antarctic</span> <span class="hlt">ice</span> shelves and adjacent regions of the Southern Ocean. Our larger goal is to gain a better understanding of the extent to which the ocean controls <span class="hlt">ice</span> <span class="hlt">shelf</span> attrition, thereby influencing the size and dynamics of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet. Melting and freezing under <span class="hlt">ice</span> shelves also impacts seawater properties, regional upwelling and sinking and the larger-scale ocean circulation. Modifying an isopycnal coordinate general circulation model for use in sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> cavities, we found that the abrupt change in water column thickness at an <span class="hlt">ice</span> <span class="hlt">shelf</span> front does not form a strong barrier to buoyancy-driven circulation across the front. Outflow along the <span class="hlt">ice</span> <span class="hlt">shelf</span> base, driven by melting of the thickest <span class="hlt">ice</span>, is balanced by deep inflow. Substantial effort was focused on the Filchner-Ronne cavity, where other models have been applied and time-series records are available from instruments suspended beneath the <span class="hlt">ice</span>. A model comparison indicated that observed changes in the production of High Salinity <span class="hlt">Shelf</span> Water could have a major impact on circulation within the cavity. This water propagates into the cavity with an asymmetric seasonal signal that has similar phasing and shape in the model and observations, and can be related to winter production at the sea surface. Even remote parts of the sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> cavity are impacted by external forcing on sub-annual time scales. This shows that cavity circulations and products, and therefore cavity shape, will respond to interannual variability in sea <span class="hlt">ice</span> production and longer-term climate change. The isopycnal model gives generally lower net melt rates than have been obtained from other models and oceanographic data, perhaps due to its boundary layer formulation, or the lack of tidal forcing. Work continues on a manuscript describing the Ross cavity results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120010371','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120010371"><span>Variability of Basal Melt Beneath the Pine Island Glacier <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, West Antarctica</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bindschadler, Robert; Vaughan, David G.; Vornberger, Patricia</p> <p>2011-01-01</p> <p>Observations from satellite and airborne platforms are combined with model calculations to infer the nature and efficiency of basal melting of the Pine Island Glacier <span class="hlt">ice</span> <span class="hlt">shelf</span>, West Antarctica, by ocean waters. Satellite imagery shows surface features that suggest <span class="hlt">ice-shelf</span>-wide changes to the ocean s influence on the <span class="hlt">ice</span> <span class="hlt">shelf</span> as the grounding line retreated. Longitudinal profiles of <span class="hlt">ice</span> surface and bottom elevations are analyzed to reveal a spatially dependent pattern of basal melt with an annual melt flux of 40.5 Gt/a. One profile captures a persistent set of surface waves that correlates with quasi-annual variations of atmospheric forcing of Amundsen Sea circulation patterns, establishing a direct connection between atmospheric variability and sub-<span class="hlt">ice-shelf</span> melting. <span class="hlt">Ice</span> surface troughs are hydrostatically compensated by <span class="hlt">ice</span>-bottom voids up to 150m deep. Voids form dynamically at the grounding line, triggered by enhanced melting when warmer-than-average water arrives. Subsequent enlargement of the voids is thermally inefficient (4% or less) compared with an overall melting efficiency beneath the <span class="hlt">ice</span> <span class="hlt">shelf</span> of 22%. Residual warm water is believed to cause three persistent polynyas at the <span class="hlt">ice-shelf</span> front seen in Landsat imagery. Landsat thermal imagery confirms the occurrence of warm water at the same locations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12.1103S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12.1103S"><span>Atmospheric influences on the anomalous 2016 <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> decay</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schlosser, Elisabeth; Haumann, F. Alexander; Raphael, Marilyn N.</p> <p>2018-03-01</p> <p>In contrast to the Arctic, where total sea <span class="hlt">ice</span> extent (SIE) has been decreasing for the last three decades, <span class="hlt">Antarctic</span> SIE has shown a small, but significant, increase during the same time period. However, in 2016, an unusually early onset of the melt season was observed; the maximum <span class="hlt">Antarctic</span> SIE was already reached as early as August rather than the end of September, and was followed by a rapid decrease. The decay was particularly strong in November, when <span class="hlt">Antarctic</span> SIE exhibited a negative anomaly (compared to the 1979-2015 average) of approximately 2 million km2. ECMWF Interim reanalysis data showed that the early onset of the melt and the rapid decrease in sea <span class="hlt">ice</span> area (SIA) and SIE were associated with atmospheric flow patterns related to a positive zonal wave number three (ZW3) index, i.e., synoptic situations leading to strong meridional flow and anomalously strong southward heat advection in the regions of strongest sea <span class="hlt">ice</span> decline. A persistently positive ZW3 index from May to August suggests that SIE decrease was preconditioned by SIA decrease. In particular, in the first third of November northerly flow conditions in the Weddell Sea and the Western Pacific triggered accelerated sea <span class="hlt">ice</span> decay, which was continued in the following weeks due to positive feedback effects, leading to the unusually low November SIE. In 2016, the monthly mean Southern Annular Mode (SAM) index reached its second lowest November value since the beginning of the satellite observations. A better spatial and temporal coverage of reliable <span class="hlt">ice</span> thickness data is needed to assess the change in <span class="hlt">ice</span> mass rather than <span class="hlt">ice</span> area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C41E..03H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C41E..03H"><span>Basal melt rates of Filchner <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Humbert, A.; Nicholls, K. W.; Corr, H. F. J.; Steinhage, D.; Stewart, C.; Zeising, O.</p> <p>2017-12-01</p> <p>Thinning of <span class="hlt">ice</span> shelves around Antarctica has been found to be partly driven by an increase in basal melt as a result of warmer waters entering the sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> cavity. In-situ observations of basal melt rate are, however, sparse. A new robust and efficient phase sensitive radio echo sounder (pRES) allows to measure change in <span class="hlt">ice</span> thickness and vertical strain at high accuracy, so that the contribution of basal melt to the change in thickness can be estimated. As modeling studies suggest that the cavity beneath Filchner <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica, might be prone to intrusion of warm water pulses within this century, we wished to derive a baseline dataset and an understanding of its present day spatial variability. Here we present results from pRES measurements over two field seasons, 2015/16-16/17, comprising 86 datasets over the southern Filchner <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, covering an area of about 6500km2. The maximum melt rate is only slightly more than 1m/a, but the spatial distribution exhibits a complex pattern. For the purpose of testing variability of basal melt rates on small spatial scales, we performed 26 measurements over distances of about 1km, and show that the melt rates do not vary by more than 0.25m/a.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ACP....16.2185H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ACP....16.2185H"><span>Unexpectedly high ultrafine aerosol concentrations above East <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Humphries, R. S.; Klekociuk, A. R.; Schofield, R.; Keywood, M.; Ward, J.; Wilson, S. R.</p> <p>2016-02-01</p> <p>Better characterisation of aerosol processes in pristine, natural environments, such as Antarctica, have recently been shown to lead to the largest reduction in uncertainties in our understanding of radiative forcing. Our understanding of aerosols in the <span class="hlt">Antarctic</span> region is currently based on measurements that are often limited to boundary layer air masses at spatially sparse coastal and continental research stations, with only a handful of studies in the vast sea-<span class="hlt">ice</span> region. In this paper, the first observational study of sub-micron aerosols in the East <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> region is presented. Measurements were conducted aboard the icebreaker Aurora Australis in spring 2012 and found that boundary layer condensation nuclei (CN3) concentrations exhibited a five-fold increase moving across the polar front, with mean polar cell concentrations of 1130 cm-3 - higher than any observed elsewhere in the <span class="hlt">Antarctic</span> and Southern Ocean region. The absence of evidence for aerosol growth suggested that nucleation was unlikely to be local. Air parcel trajectories indicated significant influence from the free troposphere above the <span class="hlt">Antarctic</span> continent, implicating this as the likely nucleation region for surface aerosol, a similar conclusion to previous <span class="hlt">Antarctic</span> aerosol studies. The highest aerosol concentrations were found to correlate with low-pressure systems, suggesting that the passage of cyclones provided an accelerated pathway, delivering air masses quickly from the free troposphere to the surface. After descent from the <span class="hlt">Antarctic</span> free troposphere, trajectories suggest that sea-<span class="hlt">ice</span> boundary layer air masses travelled equatorward into the low-albedo Southern Ocean region, transporting with them emissions and these aerosol nuclei which, after growth, may potentially impact on the region's radiative balance. The high aerosol concentrations and their transport pathways described here, could help reduce the discrepancy currently present between simulations and observations of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017DPS....4911301O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017DPS....4911301O"><span>Modeling the Thermal Interactions of Meteorites Below the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Oldroyd, William Jared; Radebaugh, Jani; Stephens, Denise C.; Lorenz, Ralph; Harvey, Ralph; Karner, James</p> <p>2017-10-01</p> <p>Meteorites with high specific gravities, such as irons, appear to be underrepresented in <span class="hlt">Antarctic</span> collections over the last 40 years. This underrepresentation is in comparison with observed meteorite falls, which are believed to represent the actual population of meteorites striking Earth. Meteorites on the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet absorb solar flux, possibly leading to downward tunneling into the <span class="hlt">ice</span>, though observations of this in action are very limited. This descent is counteracted by <span class="hlt">ice</span> sheet flow supporting the meteorites coupled with ablation near mountain margins, which helps to force meteorites towards the surface. Meteorites that both absorb adequate thermal energy and are sufficiently dense may instead reach a shallow equilibrium depth as downward melting overcomes upward forces during the <span class="hlt">Antarctic</span> summer. Using a pyronometer, we have measured the incoming solar flux at multiple depths in two deep field sites in Antarctica, the Miller Range and Elephant Moraine. We compare these data with laboratory analogues and model the thermal and physical interactions between a variety of meteorites and their surroundings. Our Matlab code model will account for a wide range of parameters used to characterize meteorites in an <span class="hlt">Antarctic</span> environment. We will present the results of our model along with depth estimates for several types of meteorites. The recovery of an additional population of heavy meteorites would increase our knowledge of the formation and composition of the solar system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20060042623&hterms=stress+relationship&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dstress%2Brelationship','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20060042623&hterms=stress+relationship&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dstress%2Brelationship"><span>Glacial isostatic stress shadowing by the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ivins, E. R.; James, T. S.; Klemann, V.</p> <p>2005-01-01</p> <p>Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to those resulting from a Coulomb analysis. The approach utilizes gravitational viscoelastodynamic theory and explores the relationships between <span class="hlt">ice</span> mass history and regional seismicity and faulting in a segment of East Antarctica containing the great <span class="hlt">Antarctic</span> Plate (Balleny Island) earthquake of 25 March 1998 (Mw 8.1). Predictions of the failure stress fields within the seismogenic crust are generated for differing assumptions about background stress orientation, mantle viscosity, lithospheric thickness, and possible late Holocene deglaciation for the D91 <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet history. Similar stress fracture fields are predicted by Mogi-von Mises and Coulomb theory, thus validating previous rebound Coulomb analysis. A thick lithosphere, of the order of 150-240 km, augments stress shadowing by a late melting (middle-late Holocene) coastal East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> complex and could cause present-day earthquakes many hundreds of kilometers seaward of the former Last Glacial Maximum grounding line.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.C21A0973B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.C21A0973B"><span>Investigating the crustal elements of the central <span class="hlt">Antarctic</span> Plate (ICECAP): How long-range aerogeophysics is critical to understanding the evolution of the East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blankenship, D. D.; Brozena, J. M.; Siegert, M. J.; Morse, D. L.; Dalziel, I. W.; Lawver, L. A.; Holt, J. W.; Childers, V. A.; Bamber, J. L.; Payne, A. J.</p> <p>2004-12-01</p> <p>The highlands of the central <span class="hlt">Antarctic</span> Plate have been the nursery for East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets since at least the early Oligocene separation of Antarctica and Australia. Significant strides have been made in deciphering the marine geological, geophysical, and geochemical record of the deposits left by these sheets and the Pleistocene paleoclimate record from <span class="hlt">ice</span> cores taken from the central reaches of the contemporary <span class="hlt">ice</span> sheet. Most recently, the scientific community has realized the importance of the isolated biome represented by the subglacial lakes that characterize the domes of the central East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet and evolve in concert with them. Understanding the evolution of the East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet and its sub-glacial environment would be a major contribution to the IPY 2007-2008 international effort. Critical to understanding offshore and <span class="hlt">ice</span> core records of paleoclimate, as well as the distribution/isolation of any subglacial lake systems, is developing a comprehensive understanding of the crustal elements of the central <span class="hlt">Antarctic</span> Plate. A complete understanding of the evolution of East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets throughout the Cenozoic requires knowledge of the boundaries, elevation and paleolatitude of these crustal elements through time as well as evidence of their morphological, sedimentological and tectono-thermal history. The basic impediments to gaining this understanding are the subcontinental scale of the central <span class="hlt">Antarctic</span> Plate and the one to four kilometers of <span class="hlt">ice</span> cover that inhibits direct access. It is possible however to provide a substantial framework for understanding these crustal elements through a comprehensive program of long-range airborne geophysical observations. We have proposed a plan to measure gravity, magnetics, <span class="hlt">ice</span>-penetrating radar, and laser/radar altimetry over the Gamburtsev, Vostok and Belgica subglacial highlands beneath Domes A - C of the contemporary East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet using a Navy P-3 aircraft based in Mc</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSHE44B1511L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSHE44B1511L"><span>Contribution of Increasing Glacial Freshwater Fluxes to Observed Trends in <span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Le Sommer, J.; Merino, N.; Durand, G.; Jourdain, N.; Goosse, H.; Mathiot, P.; Gurvan, M.</p> <p>2016-02-01</p> <p>Southern Ocean sea-<span class="hlt">ice</span> extent has experienced an overall positive trend over recent decades. While the amplitude of this trend is open to debate, the geographical pattern of regional changes has been clearly identified by observations. Mechanisms driving changes in the <span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span> Extent (SIE) are not fully understood and climate models fail to simulate these trends. Changes in different atmospheric features such as SAM or ENSO seem to explain the observed trend of Antartic sea <span class="hlt">ice</span>, but only partly, since they can not account for the actual amplitude of the observed signal. The increasing injection of freshwater due to the accelerating <span class="hlt">ice</span> discharge from Antarctica <span class="hlt">Ice</span> Sheet (AIS) during the last two decades has been proposed as another candidate to contribute to SIE trend. However, the quantity and the distribution of the extra freshwater injection were not properly constrained. Recent glaciological estimations may improve the way the glacial freshwater is injected in the model. Here, we study the role of the glacial freshwater into the observed SIE trend, using the state-of-the-art <span class="hlt">Antarctic</span> mass loss estimations. Ocean/sea-<span class="hlt">ice</span> model simulations have been carried out with two different <span class="hlt">Antarctic</span> freshwater scenarios corresponding to 20-years of <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet evolution. The combination of an improved iceberg model with the most recent glaciological estimations has been applied to account for the most realistic possible <span class="hlt">Antarctic</span> freshwater evolution scenarios. Results suggest that Antarctica has contributed to almost a 30% of the observed trend in regions of the South Pacific and South East Indian sectors, but has little impact in the South Atlantic sector. We conclude that the observed SIE trend over the last decades is due to a combination of both an atmospheric forcing and the extra freshwater injection. Our results advocates that the evolution of glacial freshwater needs to be correctly represented in climate models.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.1690J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.1690J"><span><span class="hlt">Antarctic</span> Climate Variability: Covariance of Ozone and Sea <span class="hlt">Ice</span> in Atmosphere - Ocean Coupled Model Simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jrrar, Amna; Abraham, N. Luke; Pyle, John A.; Holland, David</p> <p>2014-05-01</p> <p>Changes in sea <span class="hlt">ice</span> significantly modulate climate change because of its high reflective and insulating nature. While Arctic Sea <span class="hlt">Ice</span> Extent (SIE) shows a negative trend. <span class="hlt">Antarctic</span> SIE shows a weak but positive trend, estimated at 0.127 x 106 km2 per decade. The trend results from large regional cancellations, more <span class="hlt">ice</span> in the Weddell and the Ross seas, and less <span class="hlt">ice</span> in the Amundsen - Bellingshausen seas. A number of studies had demonstrated that stratospheric ozone depletion has had a major impact on the atmospheric circulation, causing a positive trend in the Southern Annular Mode (SAM), which has been linked to the observed positive trend in autumn sea <span class="hlt">ice</span> in the Ross Sea. However, other modelling studies show that models forced with prescribed ozone hole simulate decreased sea <span class="hlt">ice</span> in all regions comparative to a control run. A recent study has also shown that stratospheric ozone recovery will mitigate <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> loss. To verify this assumed relationship, it is important first to investigate the covariance between ozone's natural (dynamical) variability and <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> distribution in pre-industrial climate, to estimate the trend due to natural variability. We investigate the relationship between anomalous <span class="hlt">Antarctic</span> ozone years and the subsequent changes in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> distribution in a multidecadal control simulation using the AO-UMUKCA model. The model has a horizontal resolution of 3.75 X 2.5 degrees in longitude and latitude; and 60 hybrid height levels in the vertical, from the surface up to a height of 84 km. The ocean component is the NEMO ocean model on the ORCA2 tripolar grid, and the sea <span class="hlt">ice</span> model is CICE. We evaluate the model's performance in terms of sea <span class="hlt">ice</span> distribution, and we calculate sea <span class="hlt">ice</span> extent trends for composites of anomalously low versus anomalously high SH polar ozone column. We apply EOF analysis to the seasonal anomalies of sea <span class="hlt">ice</span> concentration, MSLP, and Z 500, and identify the leading climate modes controlling the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016QSRv..147..148C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016QSRv..147..148C"><span>An East Siberian <span class="hlt">ice</span> <span class="hlt">shelf</span> during the Late Pleistocene glaciations: Numerical reconstructions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Colleoni, Florence; Kirchner, Nina; Niessen, Frank; Quiquet, Aurélien; Liakka, Johan</p> <p>2016-09-01</p> <p>A recent data campaign in the East Siberian Sea has revealed evidence of grounded and floating <span class="hlt">ice</span> dynamics in regions of up to 1000 m water depth, and which are attributed to glaciations older than the Last Glacial Maximum (21 kyrs BP). The main hypothesis based on this evidence is that a small <span class="hlt">ice</span> cap developed over Beringia and expanded over the East Siberian continental margin during some of the Late Pleistocene glaciations. Other similar evidence of <span class="hlt">ice</span> dynamics that have been previously collected on the shallow continental shelves of the Arctic Ocean have been attributed to the penultimate glaciation, i.e. Marine Isotopes Stage 6 (≈140 kyrs BP). We use an <span class="hlt">ice</span> sheet model, forced by two previously simulated MIS 6 glacial maximum climates, to carry out a series of sensitivity experiments testing the impact of dynamics and mass-balance related parameters on the geometry of the East Siberian <span class="hlt">ice</span> cap and <span class="hlt">ice</span> <span class="hlt">shelf</span>. Results show that the <span class="hlt">ice</span> cap developing over Beringia connects to the Eurasian <span class="hlt">ice</span> sheet in all simulations and that its volume ranges between 6 and 14 m SLE, depending on the climate forcing. This <span class="hlt">ice</span> cap generates an <span class="hlt">ice</span> <span class="hlt">shelf</span> of dimensions comparable with or larger than the present-day Ross <span class="hlt">ice</span> <span class="hlt">shelf</span> in West Antarctica. Although the <span class="hlt">ice</span> <span class="hlt">shelf</span> extent strongly depends on the <span class="hlt">ice</span> flux through the grounding line, it is particularly sensitive to the choice of the calving and basal melting parameters. Finally, inhibiting a merging of the Beringia <span class="hlt">ice</span> cap with the Eurasian <span class="hlt">ice</span> sheet affects the expansion of the <span class="hlt">ice</span> <span class="hlt">shelf</span> only in the simulations where the <span class="hlt">ice</span> cap fluxes are not large enough to compensate for the fluxes coming from the Eurasian <span class="hlt">ice</span> sheet.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.C53B0313F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.C53B0313F"><span>Geological Influences on Bedrock Topography and East <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet Dynamics in the Wilkes Subglacial Basin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ferraccioli, F.; Armadillo, E.; Young, D. A.; Blankenship, D. D.; Jordan, T. A.; Balbi, P.; Bozzo, E.; Siegert, M. J.</p> <p>2014-12-01</p> <p>The Wilkes Subglacial Basin (WSB) extends for 1,400 km from George V Land into the interior of East Antarctica and hosts several major glaciers that drain a large sector of the East <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (EAIS). This region is of key significance for the long-term stability of the <span class="hlt">ice</span> sheet in East Antarctica, as it lies well below sea level and its bedrock deepens inland, making it potentially prone to marine <span class="hlt">ice</span> sheet instability, much like areas of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (WAIS) that are presently experiencing significant mass loss. We present new enhanced potential field images of the WSB combined with existing radar imaging to study geological controls on bedrock topography and <span class="hlt">ice</span> flow regimes in this key sector of the <span class="hlt">ice</span> sheet. These images reveal mayor Precambrian and Paleozoic basement faults that exert tectonic controls both on the margins of the basin and its sub-basins. Several major sub-basins can be recognised: the Eastern Basin, the Central Basins and the Western Basins. Using ICECAP aerogeophysical data we show that these tectonically controlled interior basins connect to newly identified basins underlying the Cook <span class="hlt">Ice</span> <span class="hlt">Shelf</span> region. This connection implies that any ocean-induced changes at the margin of the EAIS could potentially propagate rapidly further into the interior. With the aid of simple magnetic and gravity models we show that the WSB does not presently include major post Jurassic sedimentary infill. Its bedrock geology is highly variable and includes Proterozoic basement, Neoproterozoic and Cambrian sediments, intruded by Cambrian arc rocks, and cover rocks formed by Beacon sediments intruded by Jurassic Ferrar sills. Enhanced <span class="hlt">ice</span> flow in this part of the EAIS occurs therefore in a area of mixed and spatially variable bedrock geology. This contrasts with some regions of the WAIS where more extensive sedimentary basins may represent a geological template for the onset and maintenance of fast glacial flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910017259','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910017259"><span>West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet Initiative. Volume 2: Discipline Reviews</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bindschadler, Robert A. (Editor)</p> <p>1991-01-01</p> <p>Seven discipline review papers are presented on the state of the knowledge of West Antarctica and opinions on how that knowledge must be increased to predict the future behavior of this <span class="hlt">ice</span> sheet and to assess its potential to collapse, rapidly raising the global sea level. These are the goals of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet Initiative (WAIS).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1815826M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1815826M"><span>Evaluating <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> predictability at seasonal to interannual timescales in global climate models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marchi, Sylvain; Fichefet, Thierry; Goosse, Hugues; Zunz, Violette; Tietsche, Steffen; Day, Jonny; Hawkins, Ed</p> <p>2016-04-01</p> <p>Unlike the rapid sea <span class="hlt">ice</span> losses reported in the Arctic, satellite observations show an overall increase in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> extent over recent decades. Although many processes have already been suggested to explain this positive trend, it remains the subject of current investigations. Understanding the evolution of the <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> turns out to be more complicated than for the Arctic for two reasons: the lack of observations and the well-known biases of climate models in the Southern Ocean. Irrespective of those issues, another one is to determine whether the positive trend in sea <span class="hlt">ice</span> extent would have been predictable if adequate observations and models were available some decades ago. This study of <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> predictability is carried out using 6 global climate models (HadGEM1.2, MPI-ESM-LR, GFDL CM3, EC-Earth V2, MIROC 5.2 and ECHAM 6-FESOM) which are all part of the APPOSITE project. These models are used to perform hindcast simulations in a perfect model approach. The predictive skill is estimated thanks to the PPP (Potential Prognostic Predictability) and the ACC (Anomaly Correlation Coefficient). The former is a measure of the uncertainty of the ensemble while the latter assesses the accuracy of the prediction. These two indicators are applied to different variables related to sea <span class="hlt">ice</span>, in particular the total sea <span class="hlt">ice</span> extent and the <span class="hlt">ice</span> edge location. This first model intercomparison study about sea <span class="hlt">ice</span> predictability in the Southern Ocean aims at giving a general overview of <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> predictability in current global climate models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29760112','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29760112"><span>Macronutrient and carbon supply, uptake and cycling across the <span class="hlt">Antarctic</span> Peninsula <span class="hlt">shelf</span> during summer.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Henley, Sian F; Jones, Elizabeth M; Venables, Hugh J; Meredith, Michael P; Firing, Yvonne L; Dittrich, Ribanna; Heiser, Sabrina; Stefels, Jacqueline; Dougans, Julie</p> <p>2018-06-28</p> <p>The West <span class="hlt">Antarctic</span> Peninsula <span class="hlt">shelf</span> is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-<span class="hlt">shelf</span> modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the <span class="hlt">shelf</span>, contrary to cross-<span class="hlt">shelf</span> reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially <span class="hlt">shelf</span> sediment porewaters, as the primary drivers of cross-<span class="hlt">shelf</span> enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment.This article is part of the theme issue 'The marine system of the West <span class="hlt">Antarctic</span> Peninsula: status and strategy for progress in a region of rapid change'. © 2018 The Authors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5954468','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5954468"><span>Macronutrient and carbon supply, uptake and cycling across the <span class="hlt">Antarctic</span> Peninsula <span class="hlt">shelf</span> during summer</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Jones, Elizabeth M.; Venables, Hugh J.; Firing, Yvonne L.; Dittrich, Ribanna; Heiser, Sabrina; Dougans, Julie</p> <p>2018-01-01</p> <p>The West <span class="hlt">Antarctic</span> Peninsula <span class="hlt">shelf</span> is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-<span class="hlt">shelf</span> modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the <span class="hlt">shelf</span>, contrary to cross-<span class="hlt">shelf</span> reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially <span class="hlt">shelf</span> sediment porewaters, as the primary drivers of cross-<span class="hlt">shelf</span> enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment. This article is part of the theme issue ‘The marine system of the West <span class="hlt">Antarctic</span> Peninsula: status and strategy for progress in a region of rapid change’. PMID:29760112</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.C21D0463C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.C21D0463C"><span>Investigating the response of Crane Glacier, <span class="hlt">Antarctic</span> Peninsula to the disintegration of the Larsen B <span class="hlt">ice</span> <span class="hlt">shelf</span> using a 2-D flowline model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Campbell, A. J.; Hulbe, C. L.; Sergienko, O.</p> <p>2009-12-01</p> <p>Many of the glaciers flowing into the Larsen B <span class="hlt">ice</span> <span class="hlt">shelf</span> sped up and experienced front retreat following its March 2002 disintegration. Crane Glacier stands out among the fast responding glaciers for its dramatic increase in speed, from ~500 m/a to ~1500 m/a in its downstream reach, large surface lowering, and front retreat. Between march 2002 and early 2005, the glacier's calving front retreated by about 11.5 km to a location at which it has remained since that time. In order to investigate the physical processes that control the reaction of Crane Glacier to <span class="hlt">ice</span> <span class="hlt">shelf</span> disintegration, a flowline model has been developed. The model solves for the full momentum balance along the flowline using the finite element method and allows for basal sliding using a Budd type sliding relation. Model parameters are tuned to reproduce observation of surface velocity prior to <span class="hlt">ice</span> <span class="hlt">shelf</span> disintegration. Model can be applied diagnostically to examine instantaneous changes in boundary conditions or prognostically to evolve surface elevation over time. The instantaneous model response of the glacier to <span class="hlt">ice</span> <span class="hlt">shelf</span> removal produces surface velocities and thinning rates that agree well with observations. When the front position is modified to represent the steady position reached in 2005, the model again produces velocities similar to those observed on the glacier. A typical tidewater calving criterion can be used to predict the steady position toward which the front retreated. We conclude that the post-collapse speed up is facilitated by rapid basal sliding, which allows a small perturbation in vertical shearing to be amplified into a large velocity response. The pattern of glacier front retreat can be explained by a tidewater calving instability. These conclusions underscore the importance of basal sliding parametrizations in understanding observed changes in <span class="hlt">ice</span> sheet outlet glaciers and modeling their future behavior. Correct representation of iceberg calving is also important.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1915507V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1915507V"><span>Gradual slowdown and thickening of Fimbulisen <span class="hlt">ice</span> <span class="hlt">shelf</span>, East Antarctica, over the past decade</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van Oostveen, Jelte; Moholdt, Geir; Kääb, Andreas; Matsuoka, Kenichi</p> <p>2017-04-01</p> <p>Fimbulisen is a fast-flowing (up to 780±10 ma-1) <span class="hlt">ice</span> <span class="hlt">shelf</span> in the Dronning Maud Land region of East Antarctica. Fed by one of the few major outlet glaciers along that coast, Jutulstraumen, the <span class="hlt">ice</span> <span class="hlt">shelf</span> has the potential to affect the stability of a considerable part of the inland <span class="hlt">ice</span> sheet. Here we present evidence of a slowdown and thickening of Fimbulisen over the last decade. We derive <span class="hlt">ice</span> <span class="hlt">shelf</span> velocities using synthetic aperture radar (SAR) data from Envisat in 2008 and Radarsat-2 in 2015. We find that the speeds of Fimbulisen have decreased by 10±2 ma-1 over the last 7 years, which is confirmed with repeated GPS stake readings from 2010-2011. The slow-down of Fimbulisen coincides with a gradual <span class="hlt">ice</span> <span class="hlt">shelf</span> thickening that we infer from ICESat (2003-2009) and CryoSat-2 (2010-2016) altimetry. Available surface mass balance data from Fimbulisen show no clear trends over the past decades, suggesting that <span class="hlt">ice</span> dynamics is the main explanation for the observed thickening. Considering that Fimbulisen is in a long-term phase of advance after its main tongue calved off in 1967, it is plausible that the slowdown is cyclic and related to the longitudinal expansion of the <span class="hlt">ice</span> <span class="hlt">shelf</span>. In support of this theory we have found several uncharted <span class="hlt">ice</span> rumples and stationary icebergs near the eastern front of the <span class="hlt">ice</span> <span class="hlt">shelf</span>, indicating the presence of shallow bathymetry that might affect the <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics considerably in the event of <span class="hlt">ice</span> <span class="hlt">shelf</span> grounding or ungrounding.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMPP43C2290K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMPP43C2290K"><span>Late Oligocene glacimarine sedimentation of the central Ross Sea and implications for the evolution of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kraus, C.; Mckay, R. M.; Naish, T.; Levy, R. H.; Kulhanek, D. K.</p> <p>2015-12-01</p> <p>Today the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (WAIS) is grounded mostly below sea level, making it sensitive to oceanic temperature and circulation changes. However, recent reconstructions of the Cenozoic bedrock topographic evolution of West Antarctica have suggested that the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (WAIS) may have first formed as a terrestrial <span class="hlt">ice</span> sheet at the Eocene-Oligocene boundary (33 Ma), when there was up to 20% more land area in West Antarctica. At some point during the Oligocene or Miocene (23 - 5 Ma) vast areas of West Antarctica became an over-deepened marine-based continental <span class="hlt">shelf</span>, as is observed today. The evolution of the WAIS through this transition is largely unconstrained, but as atmospheric CO2 fluctuated between 600 and 200 ppm over the past 34 Ma, determining the development of a marine-based WAIS is critical in the context of understanding the sensitivity of <span class="hlt">ice</span> sheet systems to environmental change. Our research re-examines the sediment cores recovered from the central Ross Sea, a principal drainage area of the WAIS, at Deep Sea Drilling Project Site 270 (77°26.48'S, 178°30.19'W). These cores contain a glacimarine sequence of late Oligocene age (28 - 23.1 Ma). Sedimentological (visual core description, facies, grain size analysis), geochemical (x-ray fluorescence), geophysical (seismic) techniques, and physical properties (magnetic susceptibility) are used to construct a sedimentation model of this sequence, in order to track the late Oligocene evolution of the WAIS. The late Oligocene warming (25 - 23 Ma) is examined in detail because proximal <span class="hlt">Antarctic</span> geological records of <span class="hlt">ice</span> sheet extent, proxy environmental data, and atmospheric CO2 appear to be at odds with the composite δ18O record of global temperature and <span class="hlt">ice</span> volume at this time. Moreover, our research provides insights into the sensitivity of marine-based <span class="hlt">ice</span> sheets, and supports the hypothesis that they are unstable above a CO2 threshold of 400 ppm. Our preliminary results also</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24031016','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24031016"><span>Channelized <span class="hlt">ice</span> melting in the ocean boundary layer beneath Pine Island Glacier, Antarctica.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stanton, T P; Shaw, W J; Truffer, M; Corr, H F J; Peters, L E; Riverman, K L; Bindschadler, R; Holland, D M; Anandakrishnan, S</p> <p>2013-09-13</p> <p><span class="hlt">Ice</span> shelves play a key role in the mass balance of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets by buttressing their seaward-flowing outlet glaciers; however, they are exposed to the underlying ocean and may weaken if ocean thermal forcing increases. An expedition to the <span class="hlt">ice</span> <span class="hlt">shelf</span> of the remote Pine Island Glacier, a major outlet of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet that has rapidly thinned and accelerated in recent decades, has been completed. Observations from geophysical surveys and long-term oceanographic instruments deployed down bore holes into the ocean cavity reveal a buoyancy-driven boundary layer within a basal channel that melts the channel apex by 0.06 meter per day, with near-zero melt rates along the flanks of the channel. A complex pattern of such channels is visible throughout the Pine Island Glacier <span class="hlt">shelf</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C51B0969B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51B0969B"><span>Ocean stratification reduces melt rates at the grounding zone of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Begeman, C. B.; Tulaczyk, S. M.; Marsh, O.; Mikucki, J.; Stanton, T. P.; Hodson, T. O.; Siegfried, M. R.; Powell, R. D.; Christianson, K. A.; King, M. A.</p> <p>2017-12-01</p> <p>Ocean-driven melting of <span class="hlt">ice</span> shelves is often invoked as the primary mechanism for triggering <span class="hlt">ice</span> loss from Antarctica. However, due to the difficulty in accessing the sub-<span class="hlt">ice-shelf</span> ocean cavity, the relationship between <span class="hlt">ice-shelf</span> melt rates and ocean conditions is poorly understood, particularly near the transition from grounded to floating <span class="hlt">ice</span>, known as the grounding zone. Here we present the first borehole oceanographic observations from the grounding zone of Antarctica's largest <span class="hlt">ice</span> <span class="hlt">shelf</span>. Contrary to predictions that tidal currents near grounding zones should mix the water column, driving high <span class="hlt">ice-shelf</span> melt rates, we find a stratified sub-<span class="hlt">ice-shelf</span> water column. The vertical salinity gradient dominates stratification over a weakly unstable vertical temperature gradient; thus, stratification takes the form of a double-diffusive staircase. These conditions limit vertical heat fluxes and lead to low melt rates in the <span class="hlt">ice-shelf</span> grounding zone. While modern grounding zone melt rates may presently be overestimated in models that assume efficient tidal mixing, the high sensitivity of double-diffusive staircases to ocean freshening and warming suggests future melt rates may be underestimated, biasing projections of global sea-level rise.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1614550O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1614550O"><span>Long-term observing system for the oceanic regime of Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Østerhus, Svein; Schröder, Michael; Hellmer, Hartmunt; Darelius, Elin; Nicholls, Keith; Makinson, Keith</p> <p>2014-05-01</p> <p>Long term observations of the flow of dense waters from their area of formation to the abyss of the World Ocean, and the return flow of warm waters, are central to climate research. For the Weddell Sea an important component of such a system entails monitoring the formation of High Salinity <span class="hlt">Shelf</span> Water (HSSW) on the continental <span class="hlt">shelf</span> north of Ronne <span class="hlt">Ice</span> Front, the transformation to <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Water (ISW) beneath the floating Filchner-Ronne <span class="hlt">ice</span> <span class="hlt">shelf</span>, and the flux of ISW overflowing the <span class="hlt">shelf</span> break to the deep Weddell Sea. Equally important is the return flow of warm water toward the Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> system. AWI, BAS and UNI/UIB operate a number of monitoring stations in the southern Weddell Sea. The systems build upon techniques and methods developed over several decades and have a proven record of high data return. Here we present plans for extending, integrating and operating the existing long term observatories to increase our knowledge of the natural variability of the ocean-<span class="hlt">ice</span> <span class="hlt">shelf</span> system, and to allow early identification of possible changes of regional or global importance. The S2 observatory at the Filchner sill was established in 1977 and continues to deliver the longest existing marine time series from Antarctica. As a key site for monitoring the ISW overflow S2 is a part of the global net of monitoring sites under CLIVAR Southern Ocean Observing System (SOOS) and OceanSITES. The existing S2 observatory consists of a sub-surface mooring carrying sensors for current velocity, temperature, salinity and dissolved oxygen measurements. Observations at the Filchner sill also show a seasonal inflow of relatively warm water that is able to reach Filchner <span class="hlt">Ice</span> Front. New model results indicate that this flow of water might increase in the future and we have deployed a number of instrumented moorings in the Filchner Depression to estimate the heat flux towards the <span class="hlt">ice</span> <span class="hlt">shelf</span>. In 1999 we established Site 5 on Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> using a hot-water drill to access</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.C53A0279G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.C53A0279G"><span>Rapid Access <span class="hlt">Ice</span> Drill: A New Tool for Exploration of the Deep <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheets and Subglacial Geology</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Goodge, J. W.; Severinghaus, J. P.</p> <p>2014-12-01</p> <p>The Rapid Access <span class="hlt">Ice</span> Drill (RAID) will penetrate the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets in order to core through deep <span class="hlt">ice</span>, the glacial bed, and into bedrock below. This new technology will provide a critical first look at the interface between major <span class="hlt">ice</span> caps and their subglacial geology. Currently in construction, RAID is a mobile drilling system capable of making several long boreholes in a single field season in Antarctica. RAID is interdisciplinary and will allow access to polar paleoclimate records in <span class="hlt">ice</span> >1 Ma, direct observation at the base of the <span class="hlt">ice</span> sheets, and recovery of rock cores from the <span class="hlt">ice</span>-covered East <span class="hlt">Antarctic</span> craton. RAID uses a diamond rock-coring system as in mineral exploration. Threaded drill-pipe with hardened metal bits will cut through <span class="hlt">ice</span> using reverse circulation of Estisol for pressure-compensation, maintenance of temperature, and removal of <span class="hlt">ice</span> cuttings. Near the bottom of the <span class="hlt">ice</span> sheet, a wireline bottom-hole assembly will enable diamond coring of <span class="hlt">ice</span>, the glacial bed, and bedrock below. Once complete, boreholes will be kept open with fluid, capped, and made available for future down-hole measurement of thermal gradient, heat flow, <span class="hlt">ice</span> chronology, and <span class="hlt">ice</span> deformation. RAID will also sample for extremophile microorganisms. RAID is designed to penetrate up to 3,300 meters of <span class="hlt">ice</span> and take sample cores in less than 200 hours. This rapid performance will allow completion of a borehole in about 10 days before moving to the next drilling site. RAID is unique because it can provide fast borehole access through thick <span class="hlt">ice</span>; take short <span class="hlt">ice</span> cores for paleoclimate study; sample the glacial bed to determine <span class="hlt">ice</span>-flow conditions; take cores of subglacial bedrock for age dating and crustal history; and create boreholes for use as an observatory in the <span class="hlt">ice</span> sheets. Together, the rapid drilling capability and mobility of the drilling system, along with <span class="hlt">ice</span>-penetrating imaging methods, will provide a unique 3D picture of the interior <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-ED04-0056-132.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-ED04-0056-132.html"><span>The Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2004-03-16</p> <p>The Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign. AirSAR 2004 is a three-week expedition in Central and South America by an international team of scientists that is using an all-weather imaging tool, called the Airborne Synthetic Aperture Radar (AirSAR), located onboard NASA's DC-8 airborne laboratory. Scientists from many parts of the world are combining ground research with NASA's AirSAR technology to improve and expand on the quality of research they are able to conduct. These photos are from the DC-8 aircraft while flying an AirSAR mission over Antarctica. The <span class="hlt">Antarctic</span> Peninsula is more similar to Alaska and Patagonia than to the rest of the <span class="hlt">Antarctic</span> continent. It is drained by fast glaciers, receives abundant precipitation, and melts significantly in the summer months. In recent decades, the Peninsula has experienced significant atmospheric warming (about 2 degrees C since 1950), which has triggered a vast and spectacular retreat of its floating <span class="hlt">ice</span> shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia <span class="hlt">ice</span> fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with the Airborne Synthetic Aperture Radar developed by scientists from NASA’s Jet Propulsion Laboratory. AirSAR will provide a baseline model and unprecedented mapping of the region. This data will make it possible to determine whether the warming trend is slowing, continuing or accelerating. AirSAR will also provide reliable information on <span class="hlt">ice</span> <span class="hlt">shelf</span> thickness to measure the contribution of the glaciers to sea level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-ED04-0056-114.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-ED04-0056-114.html"><span>The Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2004-03-13</p> <p>The Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign. AirSAR 2004 is a three-week expedition in Central and South America by an international team of scientists that is using an all-weather imaging tool, called the Airborne Synthetic Aperture Radar (AirSAR), located onboard NASA's DC-8 airborne laboratory. Scientists from many parts of the world are combining ground research with NASA's AirSAR technology to improve and expand on the quality of research they are able to conduct. These photos are from the DC-8 aircraft while flying an AirSAR mission over Antarctica. The <span class="hlt">Antarctic</span> Peninsula is more similar to Alaska and Patagonia than to the rest of the <span class="hlt">Antarctic</span> continent. It is drained by fast glaciers, receives abundant precipitation, and melts significantly in the summer months. In recent decades, the Peninsula has experienced significant atmospheric warming (about 2 degrees C since 1950), which has triggered a vast and spectacular retreat of its floating <span class="hlt">ice</span> shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia <span class="hlt">ice</span> fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with the Airborne Synthetic Aperture Radar developed by scientists from NASA’s Jet Propulsion Laboratory. AirSAR will provide a baseline model and unprecedented mapping of the region. This data will make it possible to determine whether the warming trend is slowing, continuing or accelerating. AirSAR will also provide reliable information on <span class="hlt">ice</span> <span class="hlt">shelf</span> thickness to measure the contribution of the glaciers to sea level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-ED04-0056-138.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-ED04-0056-138.html"><span>The Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2004-03-16</p> <p>The Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign. AirSAR 2004 is a three-week expedition in Central and South America by an international team of scientists that is using an all-weather imaging tool, called the Airborne Synthetic Aperture Radar (AirSAR), located onboard NASA's DC-8 airborne laboratory. Scientists from many parts of the world are combining ground research with NASA's AirSAR technology to improve and expand on the quality of research they are able to conduct. These photos are from the DC-8 aircraft while flying an AirSAR mission over Antarctica. The <span class="hlt">Antarctic</span> Peninsula is more similar to Alaska and Patagonia than to the rest of the <span class="hlt">Antarctic</span> continent. It is drained by fast glaciers, receives abundant precipitation, and melts significantly in the summer months. In recent decades, the Peninsula has experienced significant atmospheric warming (about 2 degrees C since 1950), which has triggered a vast and spectacular retreat of its floating <span class="hlt">ice</span> shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia <span class="hlt">ice</span> fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with an Airborne Synthetic Aperture Radar (AirSAR) developed by scientists from NASA’s Jet Propulsion Laboratory. AirSAR will provide a baseline model and unprecedented mapping of the region. This data will make it possible to determine whether the warming trend is slowing, continuing or accelerating. AirSAR will also provide reliable information on <span class="hlt">ice</span> <span class="hlt">shelf</span> thickness to measure the contribution of the glaciers to sea level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSMG44B2001H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSMG44B2001H"><span>Reliable radiocarbon evidence for the maximum extent of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet in the easternmost Amundsen Sea Embayment during the Last Glacial Maximum</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hillenbrand, C. D.; Klages, J. P.; Kuhn, G.; Smith, J.; Graham, A. G. C.; Gohl, K.; Wacker, L.</p> <p>2016-02-01</p> <p> sheet reconstructions and to quantify precisely the volume of LGM <span class="hlt">ice</span>-sheet build-up in Antarctica. Our study also alludes to the possibility that refugia for <span class="hlt">Antarctic</span> <span class="hlt">shelf</span> benthos may have existed in the ASE during the last glacial period.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ACPD...1529125H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ACPD...1529125H"><span>Unexpectedly high ultrafine aerosol concentrations above East <span class="hlt">Antarctic</span> sea-<span class="hlt">ice</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Humphries, R. S.; Klekociuk, A. R.; Schofield, R.; Keywood, M.; Ward, J.; Wilson, S. R.</p> <p>2015-10-01</p> <p>The effect of aerosols on clouds and their radiative properties is one of the largest uncertainties in our understanding of radiative forcing. A recent study has concluded that better characterisation of pristine, natural aerosol processes leads to the largest reduction in these uncertainties. Antarctica, being far from anthropogenic activities, is an ideal location for the study of natural aerosol processes. Aerosol measurements in Antarctica are often limited to boundary layer air-masses at spatially sparse coastal and continental research stations, with only a handful of studies in the sea <span class="hlt">ice</span> region. In this paper, the first observational study of sub-micron aerosols in the East <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> region is presented. Measurements were conducted aboard the <span class="hlt">ice</span>-breaker Aurora Australis in spring 2012 and found that boundary layer condensation nuclei (CN3) concentrations exhibited a five-fold increase moving across the Polar Front, with mean Polar Cell concentrations of 1130 cm-3 - higher than any observed elsewhere in the <span class="hlt">Antarctic</span> and Southern Ocean region. The absence of evidence for aerosol growth suggested that nucleation was unlikely to be local. Air parcel trajectories indicated significant influence from the free troposphere above the <span class="hlt">Antarctic</span> continent, implicating this as the likely nucleation region for surface aerosol, a similar conclusion to previous <span class="hlt">Antarctic</span> aerosol studies. The highest aerosol concentrations were found to correlate with low pressure systems, suggesting that the passage of cyclones provided an accelerated pathway, delivering air-masses quickly from the free-troposphere to the surface. After descent from the <span class="hlt">Antarctic</span> free troposphere, trajectories suggest that sea <span class="hlt">ice</span> boundary layer air-masses travelled equator-ward into the low albedo Southern Ocean region, transporting with them emissions and these aerosol nuclei where, after growth, may potentially impact on the region's radiative balance. The high aerosol concentrations and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24451542','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24451542"><span>Impacts of the north and tropical Atlantic Ocean on the <span class="hlt">Antarctic</span> Peninsula and sea <span class="hlt">ice</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, Xichen; Holland, David M; Gerber, Edwin P; Yoo, Changhyun</p> <p>2014-01-23</p> <p>In recent decades, Antarctica has experienced pronounced climate changes. The <span class="hlt">Antarctic</span> Peninsula exhibited the strongest warming of any region on the planet, causing rapid changes in land <span class="hlt">ice</span>. Additionally, in contrast to the sea-<span class="hlt">ice</span> decline over the Arctic, <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> has not declined, but has instead undergone a perplexing redistribution. <span class="hlt">Antarctic</span> climate is influenced by, among other factors, changes in radiative forcing and remote Pacific climate variability, but none explains the observed <span class="hlt">Antarctic</span> Peninsula warming or the sea-<span class="hlt">ice</span> redistribution in austral winter. However, in the north and tropical Atlantic Ocean, the Atlantic Multidecadal Oscillation (a leading mode of sea surface temperature variability) has been overlooked in this context. Here we show that sea surface warming related to the Atlantic Multidecadal Oscillation reduces the surface pressure in the Amundsen Sea and contributes to the observed dipole-like sea-<span class="hlt">ice</span> redistribution between the Ross and Amundsen-Bellingshausen-Weddell seas and to the <span class="hlt">Antarctic</span> Peninsula warming. Support for these findings comes from analysis of observational and reanalysis data, and independently from both comprehensive and idealized atmospheric model simulations. We suggest that the north and tropical Atlantic is important for projections of future climate change in Antarctica, and has the potential to affect the global thermohaline circulation and sea-level change.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24891389','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24891389"><span>Ocean processes at the <span class="hlt">Antarctic</span> continental slope.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Heywood, Karen J; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D; Queste, Bastien Y; Stevens, David P; Wadley, Martin; Thompson, Andrew F; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K; Smith, Walker</p> <p>2014-07-13</p> <p>The <span class="hlt">Antarctic</span> continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea <span class="hlt">ice</span> formation/melting and ocean-atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath <span class="hlt">ice</span> shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental <span class="hlt">shelf</span> into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental <span class="hlt">shelf</span> break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the <span class="hlt">Antarctic</span> Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the <span class="hlt">shelf</span>-break front (the <span class="hlt">Antarctic</span> Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4032510','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4032510"><span>Ocean processes at the <span class="hlt">Antarctic</span> continental slope</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Heywood, Karen J.; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D.; Queste, Bastien Y.; Stevens, David P.; Wadley, Martin; Thompson, Andrew F.; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K.; Smith, Walker</p> <p>2014-01-01</p> <p>The <span class="hlt">Antarctic</span> continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea <span class="hlt">ice</span> formation/melting and ocean–atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath <span class="hlt">ice</span> shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental <span class="hlt">shelf</span> into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental <span class="hlt">shelf</span> break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the <span class="hlt">Antarctic</span> Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the <span class="hlt">shelf</span>-break front (the <span class="hlt">Antarctic</span> Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system. PMID:24891389</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMPP12A..03S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMPP12A..03S"><span>The circum-<span class="hlt">Antarctic</span> sedimentary record; a dowsing rod for <span class="hlt">Antarctic</span> <span class="hlt">ice</span> in the Eocene</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scher, H.</p> <p>2012-12-01</p> <p>Arguments for short-lived <span class="hlt">Antarctic</span> glacial events during the Eocene (55-34 Ma) are compelling, however the paleoceanographic proxy records upon which these arguments are based (e.g., benthic δ18O, eustatic sea level, deep sea carbonate deposition) are global signals in which the role of <span class="hlt">Antarctic</span> <span class="hlt">ice</span> volume variability is ambiguous. That is to say, the proxy response to <span class="hlt">ice</span> volume may be masked other processes. As a result broad correlations between proxies for <span class="hlt">ice</span> volume are lacking during suspected Eocene glacial events. I will present a more direct approach for detecting <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets in the Eocene; utilizing provenance information derived from the radiogenic isotopic composition of the terrigenous component of marine sediments near Antarctica. The method relies on knowledge that marine sediments represent a mixture derived from different basement terrains with different isotopic fingerprints. A key issue when using sedimentary deposits to characterize continental sediment sources is to deconvolve different sources from the mixed signal of the bulk sample. The pioneering work of Roy et al. (2007) and van de Flierdt et al. (2007) represents a major advance in <span class="hlt">Antarctic</span> provenance studies. It is now known that the isotopic composition of neodymium (Nd) and hafnium (Hf) in modern circum-<span class="hlt">Antarctic</span> sediments are distributed in a pattern that mimics the basement age of sediment sources around Antarctica. For this study I selected two Ocean Drilling Program (ODP) sites on southern Kerguelen Plateau (ODP Sites 738 and 748) because of their proximity to Prydz Bay, where Precambrian sediment sources contribute to extremely nonradiogenic isotopic signatures in modern sediments in the Prydz Bay region. New detrital Nd isotope records from these sediment cores reveal an Nd isotope excursion at the Bartonian/Priabonian boundary (ca. 37 Ma) that coincides with a 0.5 ‰ increase in benthic foram δ18O values. Detrital sediment ɛNd values are around -12 in intervals</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.P34A..06B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.P34A..06B"><span>Breaking <span class="hlt">Ice</span> 2: A rift system on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> as an analog for tidal tectonics on icy moons</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brunt, K. M.; Hurford, T., Jr.; Schmerr, N. C.; Sauber, J. M.; MacAyeal, D. R.</p> <p>2016-12-01</p> <p><span class="hlt">Ice</span> shelves are the floating regions of the polar <span class="hlt">ice</span> sheets. Outside of the influence of the narrow region of their grounding zone, they are fully hydrostatic and strongly influenced by the ocean tides. Recent observational and modeling studies have assessed the effect of tides on <span class="hlt">ice</span> shelves, including: the tidal influence on the <span class="hlt">ice-shelf</span> surface height, which changes by as much as 6 to 7 m on the southern extreme of the Ronne-Filchner <span class="hlt">Ice</span> <span class="hlt">Shelf</span>; the tidal modulation of the <span class="hlt">ice-shelf</span> horizontal flow velocities, which changes the mean <span class="hlt">ice</span>-flow rate by as much as two fold on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>; and the tidal contribution to fracture and rift propagation, which eventually leads to iceberg calving. Here, we present the analysis of 16 days of continuous GPS data from a rift system near the front of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. While the GPS sites were installed for a different scientific investigation, and not optimized to assess tidal rifting mechanics, they provide a first-order sense of the tidal evolution of the rift system. These analyses can be used as a terrestrial analog for tidal activity on icy satellites, such as Europa and Enceladus, moons of Jupiter and Saturn, respectively. Using remote sensing and modeling of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> rift system, we can investigate the geological processes observed on icy satellites and advance modeling efforts of their tidal-tectonic evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1912967S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1912967S"><span>Sediment features at the grounding zone and beneath Ekström <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, East Antarctica, imaged using on-<span class="hlt">ice</span> vibroseis.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, Emma C.; Eisen, Olaf; Hofstede, Coen; Lambrecht, Astrid; Mayer, Christoph</p> <p>2017-04-01</p> <p>The grounding zone, where an <span class="hlt">ice</span> sheet becomes a floating <span class="hlt">ice</span> <span class="hlt">shelf</span>, is known to be a key threshold region for <span class="hlt">ice</span> flow and stability. A better understanding of <span class="hlt">ice</span> dynamics and sediment transport across such zones will improve knowledge about contemporary and palaeo <span class="hlt">ice</span> flow, as well as past <span class="hlt">ice</span> extent. Here we present a set of seismic reflection profiles crossing the grounding zone and continuing to the <span class="hlt">shelf</span> edge of Ekström <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, East Antarctica. Using an on-<span class="hlt">ice</span> vibroseis source combined with a snowstreamer we have imaged a range of sub-glacial and sub-<span class="hlt">shelf</span> sedimentary and geomorphological features; from layered sediment deposits to elongated flow features. The acoustic properties of the features as well as their morphology allow us to draw conclusions as to their material properties and origin. These results will eventually be integrated with numerical models of <span class="hlt">ice</span> dynamics to quantify past and present interactions between <span class="hlt">ice</span> and the solid Earth in East Antarctica; leading to a better understanding of future contributions of this region to sea-level rise.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/imap/2600/B/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/imap/2600/B/"><span>Coastal-Change and Glaciological Map of the Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Area, Antarctica, 1940-2005</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Ferrigno, Jane G.; Cook, Alison J.; Mathie, Amy M.; Williams, Richard S.; Swithinbank, Charles; Foley, Kevin M.; Fox, Adrian J.; Thomson, Janet W.; Sievers, Jorn</p> <p>2008-01-01</p> <p>Changes in the area and volume of polar <span class="hlt">ice</span> sheets are intricately linked to changes in global climate, and the resulting changes in sea level could severely impact the densely populated coastal regions on Earth. Antarctica is Earth's largest reservoir of glacial <span class="hlt">ice</span>. Melting of the West <span class="hlt">Antarctic</span> part alone of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet would cause a sea-level rise of approximately 6 meters (m), and the potential sea-level rise after melting of the entire <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet is estimated to be 65 m (Lythe and others, 2001) to 73 m (Williams and Hall, 1993). The mass balance (the net volumetric gain or loss) of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet is highly complex, responding differently to different climatic and other conditions in each region (Vaughan, 2005). In a review paper, Rignot and Thomas (2002) concluded that the West <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet is probably becoming thinner overall; although it is known to be thickening in the west, it is thinning in the north. The mass balance of the East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet is thought by Davis and others (2005) to be positive on the basis of the change in satellite-altimetry measurements made between 1992 and 2003. Measurement of changes in area and mass balance of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), in subsequent recommendations by the Scientific Committee on <span class="hlt">Antarctic</span> Research (SCAR) (1989, 1993), and by the National Science Foundation's (1990) Division of Polar Programs. On the basis of these recommendations, the U.S. Geological Survey (USGS) decided that the archive of early 1970s Landsat 1, 2, and 3 Multispectral Scanner (MSS) images of Antarctica and the subsequent repeat coverage made possible with Landsat and other satellite images provided an excellent means of documenting changes in the cryospheric coastline of Antarctica (Ferrigno and Gould, 1987). The availability of this information provided the impetus for carrying out a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040027569','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040027569"><span>Modeling and Observational Study of the Global Atmospheric Impacts of <span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span> Anomalies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bromwich, David H.; Hines, Keith M.</p> <p>2004-01-01</p> <p>A combined observational and modeling study considers the linkage between <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> and the climate of non-local latitudes. The observational component is based upon analyses of monthly station observations and the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) Reanalysis (NNR). The modeling component consists of simulations of the NCAR Community Climate Model versions 2 (CCM2) and 3 (CCM3) and the recent Community Atmosphere Model (CAM2). A convenient mechanism for communication between the <span class="hlt">Antarctic</span> region (particularly the Ross Sea area) and the tropics and Northern Hemisphere is examined. The first evidence of this teleconnection came from CCM2 simulations performed during an earlier NASA supported project. Annual-cycle simulations with and without <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> show statistically- significant responses in monsoon precipitation over central and northern China during the month of September. The changes in monsoon precipitation are physically consistent with an intensified southwest Pacific (Northern Hemisphere) subtropical high in response to all <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> being removed and replaced with open water at -1.9"C. The intensified high is the northernmost component of three primary anomalies. The southernmost anomaly includes the Ross Sea area, where sea <span class="hlt">ice</span> has been removed. An earlier study by Peng and Domros had also found a link between <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> and the East Asian monsoon circulation. The current project has helped to understand the teleconnection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.G21B0875K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.G21B0875K"><span>Exploring the effect of East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> mass loss on GIA-induced horizontal bedrock motions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Konfal, S. A.; Whitehouse, P. L.; Hermans, T.; van der Wal, W.; Wilson, T. J.; Bevis, M. G.; Kendrick, E. C.; Dalziel, I.; Smalley, R., Jr.</p> <p>2017-12-01</p> <p><span class="hlt">Ice</span> history inputs used in <span class="hlt">Antarctic</span> models of GIA include major centers of <span class="hlt">ice</span> mass loss in West Antarctica. In the Transantarctic Mountains (TAM) region spanning the boundary between East and West Antarctica, horizontal crustal motions derived from GPS observations from the <span class="hlt">Antarctic</span> Network (ANET) component of the Polar Earth Observing Network (POLENET) are towards these West <span class="hlt">Antarctic</span> <span class="hlt">ice</span> mass centers, opposite to the pattern of radial crustal motion expected in an unloading scenario. We investigate alternative <span class="hlt">ice</span> history and earth structure inputs to GIA models in an attempt to reproduce observed crustal motions in the region. The W12 <span class="hlt">ice</span> history model is altered to create scenarios including <span class="hlt">ice</span> unloading in the Wilkes Subglacial Basin based on available glaciological records. These altered <span class="hlt">ice</span> history models, along with the unmodified W12 <span class="hlt">ice</span> history model, are coupled with 60 radially varying (1D) earth model combinations, including approximations of optimal earth profiles identified in published GIA models. The resulting model-predicted motions utilizing both the modified and unmodified <span class="hlt">ice</span> history models fit ANET GPS-derived crustal motions in the northern TAM region for a suite of earth model combinations. Further south, where the influence of simulated Wilkes unloading is weakest and West <span class="hlt">Antarctic</span> unloading is strongest, observed and predicted motions do not agree. The influence of simulated Wilkes <span class="hlt">ice</span> unloading coupled with laterally heterogeneous earth models is also investigated. The resulting model-predicted motions do not differ significantly between the original W12 and W12 with simulated Wilkes unloading <span class="hlt">ice</span> histories.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA20894.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA20894.html"><span>Growing Crack in Antarctica Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Spotted by NASA MISR</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2016-08-31</p> <p>Project MIDAS, a United Kingdom-based group that studies the Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in Antarctica, reported Aug. 18, 2016, that a large crack in the Larsen C <span class="hlt">shelf</span> has grown by another 13 miles (22 kilometers) in the past six months. The crack is now more than 80 miles (130 kilometers) long. Larsen C is the fourth largest <span class="hlt">ice</span> <span class="hlt">shelf</span> in Antarctica, with an area of about 19,300 square miles (50,000 square kilometers), greater than the size of Maryland. Computer modeling by Project MIDAS predicts that the crack will continue to grow and eventually cause between nine and twelve percent of the <span class="hlt">ice</span> <span class="hlt">shelf</span> to collapse, resulting in the loss of 2,300 square miles (6,000 square kilometers) of <span class="hlt">ice</span> -- more than the area of Delaware. This follows the collapse of the Larsen B <span class="hlt">shelf</span> in 2002 and the Larsen A <span class="hlt">shelf</span> in 1995, which removed about 1,255 square miles (3,250 square kilometers) and 580 square miles (1,500 square kilometers) of <span class="hlt">ice</span>, respectively. The Multiangle Imaging SpectroRadiometer (MISR) instrument aboard NASA's Terra satellite flew over Larsen C on Aug. 22, 2016. The MISR instrument views Earth with nine cameras pointed at different angles, which provides information about the texture of the surface. On the left is a natural-color image of the <span class="hlt">shelf</span> from MISR's vertical-viewing camera. Antarctica is slowly emerging from its polar night, and the low light gives the scene a bluish tint. The Larsen C <span class="hlt">shelf</span> is on the left, while thinner sea <span class="hlt">ice</span> is present on the right. A variety of cracks are visible in the Larsen C <span class="hlt">shelf</span>, all appearing roughly the same. The image is about 130 by 135 miles (210 by 220 kilometers) in size. On the right is a composite image made by combining data from MISR's 46-degree backward-pointing camera (plotted as blue), the vertical-pointing camera (plotted as green), and the 46-degree forward-pointing camera (plotted as red). This has the effect of highlighting surface roughness; smooth surfaces appear as blue-purple, while rough surfaces appear as</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24555308','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24555308"><span>Does Arctic sea <span class="hlt">ice</span> reduction foster <span class="hlt">shelf</span>-basin exchange?</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ivanov, Vladimir; Watanabe, Eiji</p> <p>2013-12-01</p> <p>The recent shift in Arctic <span class="hlt">ice</span> conditions from prevailing multi-year <span class="hlt">ice</span> to first-year <span class="hlt">ice</span> will presumably intensify fall-winter sea <span class="hlt">ice</span> freezing and the associated salt flux to the underlying water column. Here, we conduct a dual modeling study whose results suggest that the predicted catastrophic consequences for the global thermohaline circulation (THC), as a result of the disappearance of Arctic sea <span class="hlt">ice</span>, may not necessarily occur. In a warmer climate, the substantial fraction of dense water feeding the Greenland-Scotland overflow may form on Arctic shelves and cascade to the deep basin, thus replenishing dense water, which currently forms through open ocean convection in the sub-Arctic seas. We have used a simplified model for estimating how increased <span class="hlt">ice</span> production influences <span class="hlt">shelf</span>-basin exchange associated with dense water cascading. We have carried out case studies in two regions of the Arctic Ocean where cascading was observed in the past. The baseline range of buoyancy-forcing derived from the columnar <span class="hlt">ice</span> formation was calculated as part of a 30-year experiment of the pan-Arctic coupled <span class="hlt">ice</span>-ocean general circulation model (GCM). The GCM results indicate that mechanical sea <span class="hlt">ice</span> divergence associated with lateral advection accounts for a significant part of the interannual variations in sea <span class="hlt">ice</span> thermal production in the coastal polynya regions. This forcing was then rectified by taking into account sub-grid processes and used in a regional model with analytically prescribed bottom topography and vertical stratification in order to examine specific cascading conditions in the Pacific and Atlantic sectors of the Arctic Ocean. Our results demonstrate that the consequences of enhanced <span class="hlt">ice</span> formation depend on geographical location and <span class="hlt">shelf</span>-basin bathymetry. In the Pacific sector, strong density stratification in slope waters impedes noticeable deepening of <span class="hlt">shelf</span>-origin water, even for the strongest forcing applied. In the Atlantic sector, a 1.5x increase of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25214629','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25214629"><span>Boundary condition of grounding lines prior to collapse, Larsen-B <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rebesco, M; Domack, E; Zgur, F; Lavoie, C; Leventer, A; Brachfeld, S; Willmott, V; Halverson, G; Truffer, M; Scambos, T; Smith, J; Pettit, E</p> <p>2014-09-12</p> <p>Grounding zones, where <span class="hlt">ice</span> sheets transition between resting on bedrock to full floatation, help regulate <span class="hlt">ice</span> flow. Exposure of the sea floor by the 2002 Larsen-B <span class="hlt">Ice</span> <span class="hlt">Shelf</span> collapse allowed detailed morphologic mapping and sampling of the embayment sea floor. Marine geophysical data collected in 2006 reveal a large, arcuate, complex grounding zone sediment system at the front of Crane Fjord. Radiocarbon-constrained chronologies from marine sediment cores indicate loss of <span class="hlt">ice</span> contact with the bed at this site about 12,000 years ago. Previous studies and morphologic mapping of the fjord suggest that the Crane Glacier grounding zone was well within the fjord before 2002 and did not retreat further until after the <span class="hlt">ice</span> <span class="hlt">shelf</span> collapse. This implies that the 2002 Larsen-B <span class="hlt">Ice</span> <span class="hlt">Shelf</span> collapse likely was a response to surface warming rather than to grounding zone instability, strengthening the idea that surface processes controlled the disintegration of the Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. Copyright © 2014, American Association for the Advancement of Science.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.P34A..05S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.P34A..05S"><span>Breaking <span class="hlt">Ice</span>: Fracture Processes in Floating <span class="hlt">Ice</span> on Earth and Elsewhere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scambos, T. A.</p> <p>2016-12-01</p> <p>Rapid, intense fracturing events in the <span class="hlt">ice</span> shelves of the <span class="hlt">Antarctic</span> Peninsula reveal a set of processes that were not fully appreciated prior to the series of <span class="hlt">ice</span> <span class="hlt">shelf</span> break-ups observed in the late 1990s and early 2000s. A series of studies have uncovered a fascinating array of relationships between climate, ocean, and <span class="hlt">ice</span>: intense widespread hydrofracture; repetitive hydrofracture induced by <span class="hlt">ice</span> plate bending; the ability for sub-surface flooded firn to support hydrofracture; potential triggering by long-period wave action; accelerated fracturing by trapped tsunamic waves; iceberg disintegration, and a remarkable <span class="hlt">ice</span> rebound process from lake drainage that resembles runaway nuclear fission. The events and subsequent studies have shown that rapid regional warming in <span class="hlt">ice</span> <span class="hlt">shelf</span> areas leads to catastrophic changes in a previously stable <span class="hlt">ice</span> mass. More typical fracturing of thick <span class="hlt">ice</span> plates is a natural consequence of <span class="hlt">ice</span> flow in a complex geographic setting, i.e., it is induced by shear and divergence of spreading plate flow around obstacles. While these are not a result of climate or ocean change, weather and ocean processes may impact the exact timing of final separation of an iceberg from a <span class="hlt">shelf</span>. Taking these terrestrial perspectives to other <span class="hlt">ice</span>-covered ocean worlds, cautiously, provides an observational framework for interpreting features on Europa and Enceladus.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoRL..4311720J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoRL..4311720J"><span>Accelerated <span class="hlt">ice</span> <span class="hlt">shelf</span> rifting and retreat at Pine Island Glacier, West Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jeong, Seongsu; Howat, Ian M.; Bassis, Jeremy N.</p> <p>2016-11-01</p> <p>Pine Island Glacier has undergone several major iceberg calving events over the past decades. These typically occurred when a rift at the heavily fractured shear margin propagated across the width of the <span class="hlt">ice</span> <span class="hlt">shelf</span>. This type of calving is common on polar <span class="hlt">ice</span> shelves, with no clear connection to ocean-<span class="hlt">ice</span> dynamic forcing. In contrast, we report on the recent development of multiple rifts initiating from basal crevasses in the center of the <span class="hlt">ice</span> <span class="hlt">shelf</span>, resulted in calving further upglacier than previously observed. Coincident with rift formation was the sudden disintegration of the <span class="hlt">ice</span> mélange that filled the northern shear margin, resulting in <span class="hlt">ice</span> sheet detachment from this margin. Examination of <span class="hlt">ice</span> velocity suggests that this internal rifting resulted from the combination of a change in <span class="hlt">ice</span> <span class="hlt">shelf</span> stress regime caused by disintegration of the mélange and intensified melting within basal crevasses, both of which may be linked to ocean forcing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.3577P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.3577P"><span>Large-Ensemble modeling of past and future variations of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet with a coupled <span class="hlt">ice</span>-Earth-sea level model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pollard, David; DeConto, Robert; Gomez, Natalya</p> <p>2016-04-01</p> <p>To date, most modeling of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet's response to future warming has been calibrated using recent and modern observations. As an alternate approach, we apply a hybrid 3-D <span class="hlt">ice</span> sheet-<span class="hlt">shelf</span> model to the last deglacial retreat of Antarctica, making use of geologic data of the last ~20,000 years to test the model against the large-scale variations during this period. The <span class="hlt">ice</span> model is coupled to a global Earth-sea level model to improve modeling of the bedrock response and to capture ocean-<span class="hlt">ice</span> gravitational interactions. Following several recent <span class="hlt">ice</span>-sheet studies, we use Large Ensemble (LE) statistical methods, performing sets of 625 runs from 30,000 years to present with systematically varying model parameters. Objective scores for each run are calculated using modern data and past reconstructed grounding lines, relative sea level records, cosmogenic elevation-age data and uplift rates. The LE results are analyzed to calibrate 4 particularly uncertain model parameters that concern marginal <span class="hlt">ice</span> processes and interaction with the ocean. LE's are extended into the future with climates following RCP scenarios. An additional scoring criterion tests the model's ability to reproduce estimated sea-level high stands in the warm mid-Pliocene, for which drastic retreat mechanisms of hydrofracturing and <span class="hlt">ice</span>-cliff failure are needed in the model. The LE analysis provides future sea-level-rise envelopes with well-defined parametric uncertainty bounds. Sensitivities of future LE results to Pliocene sea-level estimates, coupling to the Earth-sea level model, and vertical profiles of Earth properties, will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.G42A..08B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.G42A..08B"><span>Sulzberger <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Tidal Signal Reconstruction Using InSAR</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baek, S.; Shum, C.; Yi, Y.; Kwoun, O.; Lu, Z.; Braun, A.</p> <p>2005-12-01</p> <p>Synthetic Aperture Radar Interferometry (InSAR) and Differential InSAR (DInSAR) have been demonstrated as useful techniques to detect surface deformation over <span class="hlt">ice</span> sheet and <span class="hlt">ice</span> shelves over Antarctica. In this study, we use multiple-pass InSAR from the ERS-1 and ERS-2 data to detect ocean tidal deformation with an attempt towards modeling of tides underneath an <span class="hlt">ice</span> <span class="hlt">shelf</span>. High resolution Digital Elevation Model (DEM) from repeat-pass interferometry and ICESat profiles as ground control points is used for topographic correction over the study region in Sulzberger <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, West Antarctica. Tidal differences measured by InSAR are obtained by the phase difference between a point on the grounded <span class="hlt">ice</span> and a point on <span class="hlt">ice</span> <span class="hlt">shelf</span>. Comparison with global or regional tide models (including NAO, TPXO, GOT, and CATS) of a selected point shows that the tidal amplitude is consistent with the values predicted from tide models to within 4 cm RMS. Even though the lack of data hinders the effort to readily develop a tide model using longer term data (time series span over years), we suggest a method to reconstruction selected tidal constituents using both vertical deformation from InSAR and the knowledge on aliased tidal frequencies from ERS satellites. Finally, we report the comparison results of tidal deformation observed by InSAR and ICESat altimetry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11884754','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11884754"><span><span class="hlt">Antarctic</span> krill under sea <span class="hlt">ice</span>: elevated abundance in a narrow band just south of <span class="hlt">ice</span> edge.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Brierley, Andrew S; Fernandes, Paul G; Brandon, Mark A; Armstrong, Frederick; Millard, Nicholas W; McPhail, Steven D; Stevenson, Peter; Pebody, Miles; Perrett, James; Squires, Mark; Bone, Douglas G; Griffiths, Gwyn</p> <p>2002-03-08</p> <p>We surveyed <span class="hlt">Antarctic</span> krill (Euphausia superba) under sea <span class="hlt">ice</span> using the autonomous underwater vehicle Autosub-2. Krill were concentrated within a band under <span class="hlt">ice</span> between 1 and 13 kilometers south of the <span class="hlt">ice</span> edge. Within this band, krill densities were fivefold greater than that of open water. The under-<span class="hlt">ice</span> environment has long been considered an important habitat for krill, but sampling difficulties have previously prevented direct observations under <span class="hlt">ice</span> over the scale necessary for robust krill density estimation. Autosub-2 enabled us to make continuous high-resolution measurements of krill density under <span class="hlt">ice</span> reaching 27 kilometers beyond the <span class="hlt">ice</span> edge.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29904115','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29904115"><span>Toxic anthropogenic signature in <span class="hlt">Antarctic</span> continental <span class="hlt">shelf</span> and deep sea sediments.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Isla, Enrique; Pérez-Albaladejo, Elisabet; Porte, Cinta</p> <p>2018-06-14</p> <p>Industrial activity generates harmful substances which can travel via aerial or water currents thousands of kilometers away from the place they were used impacting the local biota where they deposit. The presence of harmful anthropogenic substances in the <span class="hlt">Antarctic</span> is particularly surprising and striking due to its remoteness and the apparent geophysical isolation developed with the flows of the <span class="hlt">Antarctic</span> Circumpolar current and the ring of westerly winds surrounding the continent. However, long-range atmospheric transport (LRAT) of pollutants has been detected in the <span class="hlt">Antarctic</span> since the 70's along the <span class="hlt">Antarctic</span> trophic food web from phytoplankton to birds. Still, no information exists on the presence of cytotoxic compounds in marine sediments neither at basin scales (thousands of kilometers) nor in water depths (hundreds of meters) beyond shallow coastal areas near research stations. Our results showed for the first time that there is cytotoxic activity in marine sediment extracts from water depths >1000 m and along thousands of kilometers of <span class="hlt">Antarctic</span> continental <span class="hlt">shelf</span>, in some cases comparable to that observed in Mediterranean areas. Ongoing anthropogenic pressure appears as a serious threat to the sessile benthic communities, which have evolved in near isolation for millions of years in these environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatCC...7..595S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatCC...7..595S"><span>Localized rapid warming of West <span class="hlt">Antarctic</span> subsurface waters by remote winds</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spence, Paul; Holmes, Ryan M.; Hogg, Andrew Mcc.; Griffies, Stephen M.; Stewart, Kial D.; England, Matthew H.</p> <p>2017-08-01</p> <p>The highest rates of <span class="hlt">Antarctic</span> glacial <span class="hlt">ice</span> mass loss are occurring to the west of the Antarctica Peninsula in regions where warming of subsurface continental <span class="hlt">shelf</span> waters is also largest. However, the physical mechanisms responsible for this warming remain unknown. Here we show how localized changes in coastal winds off East Antarctica can produce significant subsurface temperature anomalies (>2 °C) around much of the continent. We demonstrate how coastal-trapped barotropic Kelvin waves communicate the wind disturbance around the <span class="hlt">Antarctic</span> coastline. The warming is focused on the western flank of the <span class="hlt">Antarctic</span> Peninsula because the circulation induced by the coastal-trapped waves is intensified by the steep continental slope there, and because of the presence of pre-existing warm subsurface water offshore. The adjustment to the coastal-trapped waves shoals the subsurface isotherms and brings warm deep water upwards onto the continental <span class="hlt">shelf</span> and closer to the coast. This result demonstrates the vulnerability of the West <span class="hlt">Antarctic</span> region to a changing climate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16..297B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16..297B"><span><span class="hlt">Antarctic</span> glaciations under Pliocene climate conditions from numerical modeling and compilation of local field-based reconstructions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bernales, Jorge; Rogozhina, Irina; Greve, Ralf</p> <p>2014-05-01</p> <p>The mid-Pliocene (3.15 to 2.85 million years before present) is the most recent period in Earth's history when temperatures and CO2 concentrations were likely sustainedly higher than pre-industrial values. Furthermore, the positions of the continents and their sea-land distributions had already reached their present configuration, sharing some similarities with today's patterns of ocean circulation and vegetation distributions. Although significant differences exist -such as a peak sea level that could have been 22 ± 10 m higher than it is today and sea surface temperatures particularly warmer at higher latitudes, mid-Pliocene has been identified as an ideal interval for studying the climate system under conditions similar to those projected for the end of this century. Among the sources of uncertainty in the projections, the response of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet (AIS) to warmer-than-today conditions seems to play a central role. Therefore, a better understanding of AIS's behavior during periods like the mid-Pliocene will provide valuable information that could help improve future predictions. For this purpose, we have compiled a wide range of local field-based reconstructions of the <span class="hlt">ice</span>-sheet margin from Pliocene sediments (with the inclusions of organic matters such as, for instance, diatoms or palynoflora, or <span class="hlt">ice</span> rafted debris), geochemical records, volcanic ashes and rocks, and geomorphology, and designed numerical experiments of the AIS dynamics during the mid-Pliocene warm period using the large-scale polythermal <span class="hlt">ice</span> sheet-<span class="hlt">shelf</span> model SICOPOLIS (Greve, 1997 [1]; Sato and Greve, 2012 [2]). The model is run with a horizontal resolution of 40 × 40 km by the climatology obtained from the PlioMIP Atmosphere Ocean Global Circulation Model experiments (Dolan et al., 2012 [3]). Parameters of the AIS model (e.g. <span class="hlt">ice</span> calving, sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> and surface <span class="hlt">ice</span> melt, basal sliding, etc.) have initially been estimated using <span class="hlt">ice</span>-sheet simulations driven by the present</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1714074E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1714074E"><span>Observationally constrained projections of <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet instability</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Edwards, Tamsin; Ritz, Catherine; Durand, Gael; Payne, Anthony; Peyaud, Vincent; Hindmarsh, Richard</p> <p>2015-04-01</p> <p>Large parts of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet lie on bedrock below sea level and may be vulnerable to a positive feedback known as Marine <span class="hlt">Ice</span> Sheet Instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence MISI may be underway throughout the Amundsen Sea Embayment (ASE) of West Antarctica, induced by circulation of warm Circumpolar Deep Water. If this retreat is sustained the region could contribute up to 1-2 m to global mean sea level, and if triggered in other areas the potential contribution to sea level on centennial to millennial timescales could be two to three times greater. However, physically plausible projections of <span class="hlt">Antarctic</span> MISI are challenging: numerical <span class="hlt">ice</span> sheet models are too low in spatial resolution to resolve grounding line processes or else too computationally expensive to assess modelling uncertainties, and no dynamical models exist of the ocean-atmosphere-<span class="hlt">ice</span> sheet system. Furthermore, previous numerical <span class="hlt">ice</span> sheet model projections for Antarctica have not been calibrated with observations, which can reduce uncertainties. Here we estimate the probability of dynamic mass loss in the event of MISI under a medium climate scenario, assessing 16 modelling uncertainties and calibrating the projections with observed mass losses in the ASE from 1992-2011. We project losses of up to 30 cm sea level equivalent (SLE) by 2100 and 72 cm SLE by 2200 (95% credibility interval: CI). Our results are substantially lower than previous estimates. The ASE sustains substantial losses, 83% of the continental total by 2100 and 67% by 2200 (95% CI), but in other regions losses are limited by <span class="hlt">ice</span> dynamical theory, observations, or a lack of projected triggers.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930022712&hterms=geothermal+heating&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dgeothermal%2Bheating','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930022712&hterms=geothermal+heating&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dgeothermal%2Bheating"><span>Effect of subglacial volcanism on changes in the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Behrendt, John C.</p> <p>1993-01-01</p> <p>Rapid changes in the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (WAIS) may affect future global sea-level changes. Alley and Whillans note that 'the water responsible for separating the glacier from its bed is produced by frictional dissipation and geothermal heat,' but assume that changes in geothermal flux would ordinarily be expected to have slower effects than glaciological parameters. I suggest that episodic subglacial volcanism and geothermal heating may have significantly greater effects on the WAIS than is generally appreciated. The WAIS flows through the active, largely asiesmic West <span class="hlt">Antarctic</span> rift system (WS), which defines the sub-sea-level bed of the glacier. Various lines of evidence summarized in Behrendt et al. (1991) indicate high heat flow and shallow asthenosphere beneath the extended, weak lithosphere underlying the WS and the WAIS. Behrendt and Cooper suggest a possible synergistic relation between Cenozoic tectonism, episodic mountain uplift and volcanism in the West <span class="hlt">Antarctic</span> rift system, and the waxing and waning of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet beginning about earliest Oligocene time. A few active volcanoes and late-Cenozoic volcanic rocks are exposed throughout the WS along both flanks, and geophysical data suggest their presence beneath the WAIS. No part of the rift system can be considered inactive. I propose that subglacial volcanic eruptions and <span class="hlt">ice</span> flow across areas of locally (episodically?) high heat flow--including volcanically active areas--should be considered possibly to have a forcing effect on the thermal regime resulting in increased melting at the base of the <span class="hlt">ice</span> streams.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910017261','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910017261"><span>Sea-level response to <span class="hlt">ice</span> sheet evolution: An ocean perspective</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jacobs, Stanley S.</p> <p>1991-01-01</p> <p>The ocean's influence upon and response to <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet changes is considered in relation to sea level rise over recent and future decades. Assuming present day <span class="hlt">ice</span> fronts are in approximate equilibrium, a preliminary budget for the <span class="hlt">ice</span> sheet is estimated from accumulation vs. iceberg calving and the basal melting that occurs beneath floating <span class="hlt">ice</span> shelves. Iceberg calving is derived from the volume of large bergs identified and tracked by the Navy/NOAA Joint <span class="hlt">Ice</span> Center and from shipboard observations. Basal melting exceeds 600 cu km/yr and is concentrated near the <span class="hlt">ice</span> fronts and <span class="hlt">ice</span> <span class="hlt">shelf</span> grounding lines. An apparent negative mass balance for the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet may result from an anomalous calving rate during the past decade, but there are large uncertainties associated with all components of the <span class="hlt">ice</span> budget. The results from general circulation models are noted in the context of projected precipitation increases and ocean temperature changes on and near the continent. An ocean research program that could help refine budget estimates is consistent with goals of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet Initiative.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70012473','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70012473"><span>Arctic continental <span class="hlt">shelf</span> morphology related to sea-<span class="hlt">ice</span> zonation, Beaufort Sea, Alaska</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Reimnitz, E.; Toimil, L.; Barnes, P.</p> <p>1978-01-01</p> <p>Landsat-1 and NOAA satellite imagery for the winter 1972-1973, and a variety of <span class="hlt">ice</span> and sea-floor data were used to study sea-<span class="hlt">ice</span> zonation and dynamics and their relation to bottom morphology and geology on the Beaufort Sea continental <span class="hlt">shelf</span> of arctic Alaska. In early winter the location of the boundary between undeformed fast <span class="hlt">ice</span> and westward-drifting pack <span class="hlt">ice</span> of the Pacific Gyre is controlled by major coastal promontories. Pronounced linear pressure- and shear-ridges, as well as hummock fields, form along this boundary and are stabilized by grounding, generally between the 10- and 20-m isobaths. Slippage along this boundary occurs intermittently at or seaward of the grounded ridges, forming new grounded ridges in a widening zone, the stamukhi zone, which by late winter extends out to the 40-m isobath. Between intermittent events along the stamukhi zone, pack-<span class="hlt">ice</span> drift and slippage is continuous along the <span class="hlt">shelf</span> edge, at average rates of 3-10 km/day. Whether slippage occurs along the stamukhi zone or along the <span class="hlt">shelf</span> edge, it is restricted to a zone several hundred meters wide, and <span class="hlt">ice</span> seaward of the slip face moves at uniform rates without discernible drag effects. A causal relationship is seen between the spatial distribution of major <span class="hlt">ice</span>-ridge systems and offshore shoals downdrift of major coastal promontories. The shoals appear to have migrated shoreward under the influence of <span class="hlt">ice</span> up to 400 m in the last 25 years. The sea floor seaward of these shoals within the stamukhi zone shows high <span class="hlt">ice</span>-gouge density, large incision depths, and a high degree of disruption of internal sedimentary structures. The concentration of large <span class="hlt">ice</span> ridges and our sea floor data in the stamukhi zone indicate that much of the available marine energy is expended here, while the inner <span class="hlt">shelf</span> and coast, where the relatively undeformed fast <span class="hlt">ice</span> grows, are sheltered. There is evidence that anomalies in the overall arctic <span class="hlt">shelf</span> profile are related to sea-<span class="hlt">ice</span> zonation, <span class="hlt">ice</span> dynamics, and bottom</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.6551F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.6551F"><span>Constraints on <span class="hlt">ice</span> volume changes of the WAIS and Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> since the LGM based on cosmogenic exposure ages in the Darwin-Hatherton glacial system of the Transantarctic Mountains</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fink, David; Storey, Bryan; Hood, David; Joy, Kurt; Shulmeister, James</p> <p>2010-05-01</p> <p>Quantitative assessment of the spatial and temporal scale of <span class="hlt">ice</span> volume change of the West <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet (WAIS) and Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> since the last glacial maximum (LGM) ~20 ka is essential to accurately predict <span class="hlt">ice</span> sheet response to current and future climate change. Although global sea level rose by approximately 120 metres since the LGM, the contribution of polar <span class="hlt">ice</span> sheets is uncertain and the timing of any such contribution is controversial. Mackintosh et al (2007) suggest that sectors of the EAIS, similar to those studied at Framnes Mountains where the <span class="hlt">ice</span> sheet slowly calves at coastal margins, have made marginal contributions to global sea-level rise between 13 and 7 ka. In contrast, Stone et al (2003) document continuing WAIS decay during the mid-late Holocene, raising the question of what was the response of the WAIS since LGM and into the Holocene. Terrestrial evidence is restricted to sparse coastal oasis and <span class="hlt">ice</span> free mountains which archive limits of former <span class="hlt">ice</span> advances. Mountain ranges flanking the Darwin-Hatherton glaciers exhibit well-defined moraines, weathering signatures, boulder rich plateaus and glacial tills, which preserve the evidence of advance and retreat of the <span class="hlt">ice</span> sheet during previous glacial cycles. Previous studies suggest a WAIS at the LGM in this location to be at least 1,000 meters thicker than today. As part of the New Zealand Latitudinal Gradient Project along the Transantarctic, we collected samples for cosmogenic exposure dating at a) Lake Wellman area bordering the Hatherton Glacier, (b) Roadend Nunatak at the confluence of the Darwin and Hatherton glaciers and (c) Diamond Hill which is positioned at the intersection of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and Darwin Glacier outlet. While the technique of exposure dating is very successful in mid-latitude alpine glacier systems, it is more challenging in polar <span class="hlt">ice</span>-sheet regions due to the prevalence of cold-based <span class="hlt">ice</span> over-riding events and absence of outwash processes which removes</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016TCry...10.1823S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016TCry...10.1823S"><span>Mapping and assessing variability in the <span class="hlt">Antarctic</span> marginal <span class="hlt">ice</span> zone, pack <span class="hlt">ice</span> and coastal polynyas in two sea <span class="hlt">ice</span> algorithms with implications on breeding success of snow petrels</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stroeve, Julienne C.; Jenouvrier, Stephanie; Campbell, G. Garrett; Barbraud, Christophe; Delord, Karine</p> <p>2016-08-01</p> <p>Sea <span class="hlt">ice</span> variability within the marginal <span class="hlt">ice</span> zone (MIZ) and polynyas plays an important role for phytoplankton productivity and krill abundance. Therefore, mapping their spatial extent as well as seasonal and interannual variability is essential for understanding how current and future changes in these biologically active regions may impact the <span class="hlt">Antarctic</span> marine ecosystem. Knowledge of the distribution of MIZ, consolidated pack <span class="hlt">ice</span> and coastal polynyas in the total <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> cover may also help to shed light on the factors contributing towards recent expansion of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> cover in some regions and contraction in others. The long-term passive microwave satellite data record provides the longest and most consistent record for assessing the proportion of the sea <span class="hlt">ice</span> cover that is covered by each of these <span class="hlt">ice</span> categories. However, estimates of the amount of MIZ, consolidated pack <span class="hlt">ice</span> and polynyas depend strongly on which sea <span class="hlt">ice</span> algorithm is used. This study uses two popular passive microwave sea <span class="hlt">ice</span> algorithms, the NASA Team and Bootstrap, and applies the same thresholds to the sea <span class="hlt">ice</span> concentrations to evaluate the distribution and variability in the MIZ, the consolidated pack <span class="hlt">ice</span> and coastal polynyas. Results reveal that the seasonal cycle in the MIZ and pack <span class="hlt">ice</span> is generally similar between both algorithms, yet the NASA Team algorithm has on average twice the MIZ and half the consolidated pack <span class="hlt">ice</span> area as the Bootstrap algorithm. Trends also differ, with the Bootstrap algorithm suggesting statistically significant trends towards increased pack <span class="hlt">ice</span> area and no statistically significant trends in the MIZ. The NASA Team algorithm on the other hand indicates statistically significant positive trends in the MIZ during spring. Potential coastal polynya area and amount of broken <span class="hlt">ice</span> within the consolidated <span class="hlt">ice</span> pack are also larger in the NASA Team algorithm. The timing of maximum polynya area may differ by as much as 5 months between algorithms. These</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1210736S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1210736S"><span>Neogene sea surface temperature reconstructions from the Southern McMurdo Sound and the McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (ANDRILL Program, Antarctica)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sangiorgi, Francesca; Willmott, Veronica; Kim, Jung-Hyun; Schouten, Stefan; Brinkhuis, Henk; Sinninghe Damsté, Jaap S.; Florindo, Fabio; Harwood, David; Naish, Tim; Powell, Ross</p> <p>2010-05-01</p> <p>During the austral summers 2006 and 2007 the <span class="hlt">ANtarctic</span> DRILLing Program (ANDRILL) drilled two cores, each recovering more than 1000m of sediment from below the McMurdo <span class="hlt">Ice-Shelf</span> (MIS, AND-1B), and sea-<span class="hlt">ice</span> in Southern McMurdo Sound (SMS, AND-2A), respectively, revealing new information about Neogene <span class="hlt">Antarctic</span> cryosphere evolution. Core AND-1B was drilled in a more distal location than core AND-2A. With the aim of obtaining important information for the understanding of the history of <span class="hlt">Antarctic</span> climate and environment during selected interval of the Neogene, we applied novel organic geochemistry proxies such as TEX86 (Tetra Ether IndeX of lipids with 86 carbon atoms) using a new calibration equation specifically developed for polar areas and based on 116 surface sediment samples collected from polar oceans (Kim et al., subm.), and BIT (Branched and Isoprenoid Tetraether), to derive absolute (sea surface) temperature values and to evaluate the relative contribution of soil organic matter versus marine organic matter, respectively. We will present the state-of-the-art of the methodology applied, discussing its advantages and limitations, and the results so far obtained from the analysis of 60 samples from core AND-2A covering the Miocene Climatic Optimum (and the Mid-late Miocene transition) and of 20 pilot samples from core AND-1B covering the late Pliocene.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMGC34A..06R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMGC34A..06R"><span>Assessing the Global Climate Response to Freshwater Forcing from the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet Under Future Climate Scenarios</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rogstad, S.; Condron, A.; DeConto, R.; Pollard, D.</p> <p>2017-12-01</p> <p>Observational evidence indicates that the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (WAIS) is losing mass at an accelerating rate. Impacts to global climate resulting from changing ocean circulation patterns due to increased freshwater runoff from Antarctica in the future could have significant implications for global heat transport, but to-date this topic has not been investigated using complex numerical models with realistic freshwater forcing. Here, we present results from a high resolution fully coupled ocean-atmosphere model (CESM 1.2) forced with runoff from Antarctica prescribed from a high resolution regional <span class="hlt">ice</span> sheet-<span class="hlt">ice</span> <span class="hlt">shelf</span> model. Results from the regional simulations indicate a potential freshwater contribution from Antarctica of up to 1 m equivalent sea level rise by the end of the century under RCP 8.5 indicating that a substantial input of freshwater into the Southern Ocean is possible. Our high resolution global simulations were performed under IPCC future climate scenarios RCP 4.5 and 8.5. We will present results showing the impact of WAIS collapse on global ocean circulation, sea <span class="hlt">ice</span>, air temperature, and salinity in order to assess the potential for abrupt climate change triggered by WAIS collapse.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29540750','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29540750"><span>Recent high-resolution <span class="hlt">Antarctic</span> <span class="hlt">ice</span> velocity maps reveal increased mass loss in Wilkes Land, East Antarctica.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Shen, Qiang; Wang, Hansheng; Shum, C K; Jiang, Liming; Hsu, Hou Tse; Dong, Jinglong</p> <p>2018-03-14</p> <p>We constructed <span class="hlt">Antarctic</span> <span class="hlt">ice</span> velocity maps from Landsat 8 images for the years 2014 and 2015 at a high spatial resolution (100 m). These maps were assembled from 10,690 scenes of displacement vectors inferred from more than 10,000 optical images acquired from December 2013 through March 2016. We estimated the mass discharge of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet in 2008, 2014, and 2015 using the Landsat <span class="hlt">ice</span> velocity maps, interferometric synthetic aperture radar (InSAR)-derived <span class="hlt">ice</span> velocity maps (~2008) available from prior studies, and <span class="hlt">ice</span> thickness data. An increased mass discharge (53 ± 14 Gt yr -1 ) was found in the East Indian Ocean sector since 2008 due to unexpected widespread glacial acceleration in Wilkes Land, East Antarctica, while the other five oceanic sectors did not exhibit significant changes. However, present-day increased mass loss was found by previous studies predominantly in west Antarctica and the <span class="hlt">Antarctic</span> Peninsula. The newly discovered increased mass loss in Wilkes Land suggests that the ocean heat flux may already be influencing <span class="hlt">ice</span> dynamics in the marine-based sector of the East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet (EAIS). The marine-based sector could be adversely impacted by ongoing warming in the Southern Ocean, and this process may be conducive to destabilization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.2609S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.2609S"><span>Combined <span class="hlt">ice</span> core and climate-model evidence for the collapse of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet during Marine Isotope Stage 5e.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Steig, Eric J.; Huybers, Kathleen; Singh, Hansi A.; Steiger, Nathan J.; Frierson, Dargan M. W.; Popp, Trevor; White, James W. C.</p> <p>2015-04-01</p> <p>It has been speculated that collapse of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet explains the very high eustatic sea level rise during the last interglacial period, marine isotope stage (MIS) 5e, but the evidence remains equivocal. Changes in atmospheric circulation resulting from a collapse of the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet (WAIS) would have significant regional impacts that should be detectable in <span class="hlt">ice</span> core records. We conducted simulations using general circulation models (GCMs) at varying levels of complexity: a gray-radiation aquaplanet moist GCM (GRaM), the slab ocean version of GFDL-AM2 (also as an aquaplanet), and the fully-coupled version of NCAR's CESM with realistic topography. In all the experiments, decreased elevation from the removal of the WAIS leads to greater cyclonic circulation over the West <span class="hlt">Antarctic</span> region. This creates increased advection of relatively warm marine air from the Amundsen-Bellingshausen Seas towards the South Pole, and increased cold-air advection from the East <span class="hlt">Antarctic</span> plateau towards the Ross Sea and coastal Marie Byrd Land. The result is anomalous warming in some areas of the East <span class="hlt">Antarctic</span> interior, and significant cooling in Marie Byrd Land. Comparison of <span class="hlt">ice</span> core records shows good agreement with the model predictions. In particular, isotope-paleotemperature records from <span class="hlt">ice</span> cores in East Antarctica warmed more between the previous glacial period (MIS 6) and MIS 5e than coastal Marie Byrd Land. These results add substantial support to other evidence for WAIS collapse during the last interglacial period.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeoJI.198..537A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeoJI.198..537A"><span>The Antarctica component of postglacial rebound model <span class="hlt">ICE</span>-6G_C (VM5a) based on GPS positioning, exposure age dating of <span class="hlt">ice</span> thicknesses, and relative sea level histories</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Argus, Donald F.; Peltier, W. R.; Drummond, R.; Moore, Angelyn W.</p> <p>2014-07-01</p> <p>A new model of the deglaciation history of Antarctica over the past 25 kyr has been developed, which we refer to herein as <span class="hlt">ICE</span>-6G_C (VM5a). This revision of its predecessor <span class="hlt">ICE</span>-5G (VM2) has been constrained to fit all available geological and geodetic observations, consisting of: (1) the present day uplift rates at 42 sites estimated from GPS measurements, (2) <span class="hlt">ice</span> thickness change at 62 locations estimated from exposure-age dating, (3) Holocene relative sea level histories from 12 locations estimated on the basis of radiocarbon dating and (4) age of the onset of marine sedimentation at nine locations along the <span class="hlt">Antarctic</span> <span class="hlt">shelf</span> also estimated on the basis of 14C dating. Our new model fits the totality of these data well. An additional nine GPS-determined site velocities are also estimated for locations known to be influenced by modern <span class="hlt">ice</span> loss from the Pine Island Bay and Northern <span class="hlt">Antarctic</span> Peninsula regions. At the 42 locations not influenced by modern <span class="hlt">ice</span> loss, the quality of the fit of postglacial rebound model <span class="hlt">ICE</span>-6G_C (VM5A) is characterized by a weighted root mean square residual of 0.9 mm yr-1. The Southern <span class="hlt">Antarctic</span> Peninsula is inferred to be rising at 2 mm yr-1, requiring there to be less Holocene <span class="hlt">ice</span> loss there than in the prior model <span class="hlt">ICE</span>-5G (VM2). The East Antarctica coast is rising at approximately 1 mm yr-1, requiring <span class="hlt">ice</span> loss from this region to have been small since Last Glacial Maximum. The Ellsworth Mountains, at the base of the <span class="hlt">Antarctic</span> Peninsula, are inferred to be rising at 5-8 mm yr-1, indicating large <span class="hlt">ice</span> loss from this area during deglaciation that is poorly sampled by geological data. Horizontal deformation of the <span class="hlt">Antarctic</span> Plate is minor with two exceptions. First, O'Higgins, at the tip of the <span class="hlt">Antarctic</span> Peninsula, is moving southeast at a significant 2 mm yr-1 relative to the <span class="hlt">Antarctic</span> Plate. Secondly, the margins of the Ronne and Ross <span class="hlt">Ice</span> Shelves are moving horizontally away from the <span class="hlt">shelf</span> centres at an approximate rate of 0.8 mm yr-1, in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoRL..44.7826N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..44.7826N"><span><span class="hlt">Ice</span> stream reorganization and glacial retreat on the northwest Greenland <span class="hlt">shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Newton, A. M. W.; Knutz, P. C.; Huuse, M.; Gannon, P.; Brocklehurst, S. H.; Clausen, O. R.; Gong, Y.</p> <p>2017-08-01</p> <p>Understanding conditions at the grounding-line of marine-based <span class="hlt">ice</span> sheets is essential for understanding <span class="hlt">ice</span> sheet evolution. Offshore northwest Greenland, knowledge of the Last Glacial Maximum (LGM) <span class="hlt">ice</span> sheet extent in Melville Bugt was previously based on sparse geological evidence. This study uses multibeam bathymetry, combined with 2-D and 3-D seismic reflection data, to present a detailed landform record from Melville Bugt. Seabed landforms include mega-scale glacial lineations, grounding-zone wedges, iceberg scours, and a lateral shear margin moraine, formed during the last glacial cycle. The geomorphology indicates that the LGM <span class="hlt">ice</span> sheet reached the <span class="hlt">shelf</span> edge before undergoing flow reorganization. After retreat of 80 km across the outer <span class="hlt">shelf</span>, the margin stabilized in a mid-<span class="hlt">shelf</span> position, possibly during the Younger Dryas (12.9-11.7 ka). The <span class="hlt">ice</span> sheet then decoupled from the seafloor and retreated to a coast-proximal position. This landform record provides an important constraint on deglaciation history offshore northwest Greenland.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.4084H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4084H"><span>A glimpse beneath <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span>: observation of platelet-layer thickness and <span class="hlt">ice</span>-volume fraction with multifrequency EM</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hoppmann, Mario; Hunkeler, Priska A.; Hendricks, Stefan; Kalscheuer, Thomas; Gerdes, Rüdiger</p> <p>2016-04-01</p> <p>In Antarctica, <span class="hlt">ice</span> crystals (platelets) form and grow in supercooled waters below <span class="hlt">ice</span> shelves. These platelets rise, accumulate beneath nearby sea <span class="hlt">ice</span>, and subsequently form a several meter thick, porous sub-<span class="hlt">ice</span> platelet layer. This special <span class="hlt">ice</span> type is a unique habitat, influences sea-<span class="hlt">ice</span> mass and energy balance, and its volume can be interpreted as an indicator of the health of an <span class="hlt">ice</span> <span class="hlt">shelf</span>. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In the present study, we applied a lateral constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the <span class="hlt">ice-shelf</span> influenced fast-<span class="hlt">ice</span> regime of Atka Bay, eastern Weddell Sea. We adapted the inversion algorithm to incorporate a sensor specific signal bias, and confirmed the reliability of the algorithm by performing a sensitivity study using synthetic data. We inverted the field data for sea-<span class="hlt">ice</span> and platelet-layer thickness and electrical conductivity, and calculated <span class="hlt">ice</span>-volume fractions within the platelet layer using Archie's Law. The thickness results agreed well with drillhole validation datasets within the uncertainty range, and the <span class="hlt">ice</span>-volume fraction yielded results comparable to other studies. Both parameters together enable an estimation of the total <span class="hlt">ice</span> volume within the platelet layer, which was found to be comparable to the volume of landfast sea <span class="hlt">ice</span> in this region, and corresponded to more than a quarter of the annual basal melt volume of the nearby Ekström <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. Our findings show that multi-frequency EM induction sounding is a suitable approach to efficiently map sea-<span class="hlt">ice</span> and platelet-layer properties, with important implications for research into ocean/<span class="hlt">ice-shelf/sea-ice</span> interactions. However, a successful application of this</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.9151B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.9151B"><span>A sensitivity analysis for a thermomechanical model of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet and <span class="hlt">ice</span> shelves</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baratelli, F.; Castellani, G.; Vassena, C.; Giudici, M.</p> <p>2012-04-01</p> <p>The outcomes of an <span class="hlt">ice</span> sheet model depend on a number of parameters and physical quantities which are often estimated with large uncertainty, because of lack of sufficient experimental measurements in such remote environments. Therefore, the efforts to improve the accuracy of the predictions of <span class="hlt">ice</span> sheet models by including more physical processes and interactions with atmosphere, hydrosphere and lithosphere can be affected by the inaccuracy of the fundamental input data. A sensitivity analysis can help to understand which are the input data that most affect the different predictions of the model. In this context, a finite difference thermomechanical <span class="hlt">ice</span> sheet model based on the Shallow-<span class="hlt">Ice</span> Approximation (SIA) and on the Shallow-<span class="hlt">Shelf</span> Approximation (SSA) has been developed and applied for the simulation of the evolution of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet and <span class="hlt">ice</span> shelves for the last 200 000 years. The sensitivity analysis of the model outcomes (e.g., the volume of the <span class="hlt">ice</span> sheet and of the <span class="hlt">ice</span> shelves, the basal melt rate of the <span class="hlt">ice</span> sheet, the mean velocity of the Ross and Ronne-Filchner <span class="hlt">ice</span> shelves, the wet area at the base of the <span class="hlt">ice</span> sheet) with respect to the model parameters (e.g., the basal sliding coefficient, the geothermal heat flux, the present-day surface accumulation and temperature, the mean <span class="hlt">ice</span> shelves viscosity, the melt rate at the base of the <span class="hlt">ice</span> shelves) has been performed by computing three synthetic numerical indices: two local sensitivity indices and a global sensitivity index. Local sensitivity indices imply a linearization of the model and neglect both non-linear and joint effects of the parameters. The global variance-based sensitivity index, instead, takes into account the complete variability of the input parameters but is usually conducted with a Monte Carlo approach which is computationally very demanding for non-linear complex models. Therefore, the global sensitivity index has been computed using a development of the model outputs in a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMPP24A..02H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMPP24A..02H"><span>On the Revealing Firsthand Probing of Ocean-<span class="hlt">Ice</span>-Atmosphere Interactions off Sabrina Coast During NBP1402</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huber, B. A.; Orsi, A. H.; Zielinski, N. J.; Durkin, W. J., IV; Clark, P.; Wiederwohl, C. L.; Rosenberg, M. A.; Gwyther, D.; Greenbaum, J. S.; Lavoie, C.; Shevenell, A.; Leventer, A.; Blankenship, D. D.; Gulick, S. P. S.; Domack, E. W.</p> <p>2014-12-01</p> <p>Diverse interactions of winds, currents and <span class="hlt">ice</span> around Antarctica dictate how, where and when the world's densest waters form and massive floating <span class="hlt">ice</span> shelves and glaciers melt, as well as control sea surface gas exchange and primary productivity. Compelled by recent rate estimates of East <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet mass loss, we contrast the paths and mixing histories of oceanic waters reaching the continental <span class="hlt">ice</span> edge off the Sabrina and Adelie coasts relying on the unique set of synoptic shipboard measurements from NBP1402 (swath bathymetry, ADCP, underway CTD). Analysis of historical hydrography and sea <span class="hlt">ice</span> concentration fields within the Mertz Polynya indicates the apparent effect of evolving ocean-<span class="hlt">ice</span>-atmosphere interactions on the characteristics of local <span class="hlt">Shelf</span> Water (SW) sources to current outflow of newly formed <span class="hlt">Antarctic</span> Bottom Water (AABW). A polynya dominated water mass structure similar to that observed off the Adelie Coast before the removal of the Mertz <span class="hlt">Ice</span> Tongue was expected to the west of the Dalton <span class="hlt">Ice</span> Tongue (DIT). However, we found no evidence of dense SW off Sabrina Coast, which may lessen the region's preconceived influence to global meridional overturning. Present sea <span class="hlt">ice</span> production within the eastern Dalton Polynya is overshadowed by freshwater input to relatively stable interior upper waters. The <span class="hlt">Antarctic</span> Coastal Current (ACoC) picks up distinct meltwater contributions along the DIT western flank and in front of the Moscow University <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (MUIS) and Totten Glacier (TG). Unlike over other highly influential margins to global sea level rise, there is no evidence of local cross-<span class="hlt">shelf</span> inflow and mixing of warm Circumpolar Deep Water. Relatively cold thermocline waters from the continental slope enter the eastern trough off Sabrina Coast, and they are swiftly steered poleward by complex underlying topography. Meltwater export from beneath the MUIS and TG is observed at newly discovered trenches that effectively constrain sub-cavity inflow to low</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1352361-present-day-future-antarctic-ice-sheet-climate-surface-mass-balance-community-earth-system-model','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1352361-present-day-future-antarctic-ice-sheet-climate-surface-mass-balance-community-earth-system-model"><span>Present-day and future <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet climate and surface mass balance in the Community Earth System Model</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Lenaerts, Jan T. M.; Vizcaino, Miren; Fyke, Jeremy Garmeson; ...</p> <p>2016-02-01</p> <p>Here, we present climate and surface mass balance (SMB) of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet (AIS) as simulated by the global, coupled ocean–atmosphere–land Community Earth System Model (CESM) with a horizontal resolution of ~1° in the past, present and future (1850–2100). CESM correctly simulates present-day <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> extent, large-scale atmospheric circulation and near-surface climate, but fails to simulate the recent expansion of <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span>. The present-day <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet SMB equals 2280 ± 131Gtyear –1, which concurs with existing independent estimates of AIS SMB. When forced by two CMIP5 climate change scenarios (high mitigation scenario RCP2.6 and high-emission scenariomore » RCP8.5), CESM projects an increase of <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet SMB of about 70 Gtyear –1 per degree warming. This increase is driven by enhanced snowfall, which is partially counteracted by more surface melt and runoff along the <span class="hlt">ice</span> sheet’s edges. This intensifying hydrological cycle is predominantly driven by atmospheric warming, which increases (1) the moisture-carrying capacity of the atmosphere, (2) oceanic source region evaporation, and (3) summer AIS cloud liquid water content.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JGRD..118.2119R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JGRD..118.2119R"><span><span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet mass loss estimates using Modified <span class="hlt">Antarctic</span> Mapping Mission surface flow observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ren, Diandong; Leslie, Lance M.; Lynch, Mervyn J.</p> <p>2013-03-01</p> <p>The long residence time of <span class="hlt">ice</span> and the relatively gentle slopes of the Antarctica <span class="hlt">Ice</span> Sheet make basal sliding a unique positive feedback mechanism in enhancing <span class="hlt">ice</span> discharge along preferred routes. The highly organized <span class="hlt">ice</span> stream channels extending to the interior from the lower reach of the outlets are a manifestation of the role of basal granular material in enhancing the <span class="hlt">ice</span> flow. In this study, constraining the model-simulated year 2000 <span class="hlt">ice</span> flow fields with surface velocities obtained from InSAR measurements permits retrieval of the basal sliding parameters. Forward integrations of the <span class="hlt">ice</span> model driven by atmospheric and oceanic parameters from coupled general circulation models under different emission scenarios provide a range of estimates of total <span class="hlt">ice</span> mass loss during the 21st century. The total mass loss rate has a small intermodel and interscenario spread, rising from approximately -160 km3/yr at present to approximately -220 km3/yr by 2100. The accelerated mass loss rate of the Antarctica <span class="hlt">Ice</span> Sheet in a warming climate is due primarily to a dynamic response in the form of an increase in <span class="hlt">ice</span> flow speed. <span class="hlt">Ice</span> shelves contribute to this feedback through a reduced buttressing effect due to more frequent systematic, tabular calving events. For example, by 2100 the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> is projected to shed 40 km3 during each systematic tabular calving. After the frontal section's attrition, the remaining <span class="hlt">shelf</span> will rebound. Consequently, the submerged cross-sectional area will reduce, as will the buttressing stress. Longitudinal differential warming of ocean temperature contributes to tabular calving. Because of the prevalence of fringe <span class="hlt">ice</span> shelves, oceanic effects likely will play a very important role in the future mass balance of the Antarctica <span class="hlt">Ice</span> Sheet, under a possible future warming climate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20000074257&hterms=Antarctic+icebergs&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DAntarctic%2Bicebergs','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20000074257&hterms=Antarctic+icebergs&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DAntarctic%2Bicebergs"><span>Glacier and <span class="hlt">Ice</span> Shelves Studies Using Satellite SAR Interferometry</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rignot, Eric</p> <p>1999-01-01</p> <p>Satellite radar interferometry is a powerful technique to measure the surface velocity and topography of glacier <span class="hlt">ice</span>. On <span class="hlt">ice</span> shelves, a quadruple difference technique separates tidal motion from the steady creep flow deformation of <span class="hlt">ice</span>. The results provide a wealth of information about glacier grounding lines , mass fluxes, stability, elastic properties of <span class="hlt">ice</span>, and tidal regime. The grounding line, which is where the glacier detaches from its bed and becomes afloat, is detected with a precision of a few tens of meters. Combining this information with satellite radar altimetry makes it possible to measure glacier discharge into the ocean and state of mass balance with greater precision than ever before, and in turn provide a significant revision of past estimates of mass balance of the Greenland and <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheets. Analysis of creep rates on floating <span class="hlt">ice</span> permits an estimation of basal melting at the <span class="hlt">ice</span> <span class="hlt">shelf</span> underside. The results reveal that the action of ocean water in sub-<span class="hlt">ice-shelf</span> cavities has been largely underestimated by oceanographic models and is the dominant mode of mass release to the ocean from an <span class="hlt">ice</span> <span class="hlt">shelf</span>. Precise mapping of grounding line positions also permits the detection of grounding line migration, which is a fine indicator of glacier change, independent of our knowledge of snow accumulation and <span class="hlt">ice</span> melting. This technique has been successfully used to detect the rapid retreat of Pine Island Glacier, the largest <span class="hlt">ice</span> stream in West Antarctica. Finally, tidal motion of <span class="hlt">ice</span> shelves measured interferometrically provides a modern, synoptic view of the physical processes which govern the formation of tabular icebergs in the <span class="hlt">Antarctic</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1375915-dynamic-influence-pinning-points-marine-ice-sheet-stability-numerical-study-dronning-maud-land-east-antarctica','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1375915-dynamic-influence-pinning-points-marine-ice-sheet-stability-numerical-study-dronning-maud-land-east-antarctica"><span>Dynamic influence of pinning points on marine <span class="hlt">ice</span>-sheet stability: a numerical study in Dronning Maud Land, East Antarctica</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Favier, Lionel; Pattyn, Frank; Berger, Sophie; ...</p> <p>2016-11-09</p> <p>The East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet is likely more stable than its West <span class="hlt">Antarctic</span> counterpart because its bed is largely lying above sea level. However, the <span class="hlt">ice</span> sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded <span class="hlt">ice</span> promontories and <span class="hlt">ice</span> rises, pinning and stabilising the <span class="hlt">ice</span> shelves. In this paper, we use the <span class="hlt">ice</span>-sheet model BISICLES to investigate the effect of sub-<span class="hlt">ice-shelf</span> melting, using a series of scenarios compliant with current values, on the <span class="hlt">ice</span>-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouinmore » <span class="hlt">ice</span> shelves over the next millennium. Overall, the sub-<span class="hlt">ice-shelf</span> melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering <span class="hlt">ice</span> promontories into <span class="hlt">ice</span> rises. Furthermore, our analysis demonstrated that the onset of the marine <span class="hlt">ice</span>-sheet retreat and subsequent promontory transition into <span class="hlt">ice</span> rise is controlled by small pinning points, mostly uncharted in pan-<span class="hlt">Antarctic</span> datasets. Pinning points have a twofold impact on marine <span class="hlt">ice</span> sheets. They decrease the <span class="hlt">ice</span> discharge by buttressing effect, and they play a crucial role in initialising marine <span class="hlt">ice</span> sheets through data assimilation, leading to errors in <span class="hlt">ice-shelf</span> rheology when omitted. Our results show that unpinning increases the sea-level rise by 10%, while omitting the same pinning point in data assimilation decreases it by 10%, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. As a result, pinning points exert a subtle influence on <span class="hlt">ice</span> dynamics at the kilometre scale, which calls for a better knowledge of the <span class="hlt">Antarctic</span> margins.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1375915','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1375915"><span>Dynamic influence of pinning points on marine <span class="hlt">ice</span>-sheet stability: a numerical study in Dronning Maud Land, East Antarctica</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Favier, Lionel; Pattyn, Frank; Berger, Sophie</p> <p></p> <p>The East <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet is likely more stable than its West <span class="hlt">Antarctic</span> counterpart because its bed is largely lying above sea level. However, the <span class="hlt">ice</span> sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded <span class="hlt">ice</span> promontories and <span class="hlt">ice</span> rises, pinning and stabilising the <span class="hlt">ice</span> shelves. In this paper, we use the <span class="hlt">ice</span>-sheet model BISICLES to investigate the effect of sub-<span class="hlt">ice-shelf</span> melting, using a series of scenarios compliant with current values, on the <span class="hlt">ice</span>-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouinmore » <span class="hlt">ice</span> shelves over the next millennium. Overall, the sub-<span class="hlt">ice-shelf</span> melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering <span class="hlt">ice</span> promontories into <span class="hlt">ice</span> rises. Furthermore, our analysis demonstrated that the onset of the marine <span class="hlt">ice</span>-sheet retreat and subsequent promontory transition into <span class="hlt">ice</span> rise is controlled by small pinning points, mostly uncharted in pan-<span class="hlt">Antarctic</span> datasets. Pinning points have a twofold impact on marine <span class="hlt">ice</span> sheets. They decrease the <span class="hlt">ice</span> discharge by buttressing effect, and they play a crucial role in initialising marine <span class="hlt">ice</span> sheets through data assimilation, leading to errors in <span class="hlt">ice-shelf</span> rheology when omitted. Our results show that unpinning increases the sea-level rise by 10%, while omitting the same pinning point in data assimilation decreases it by 10%, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. As a result, pinning points exert a subtle influence on <span class="hlt">ice</span> dynamics at the kilometre scale, which calls for a better knowledge of the <span class="hlt">Antarctic</span> margins.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18..693S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18..693S"><span>Development of source specific diatom lipids biomarkers as <span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span> proxies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smik, Lukas; Belt, Simon T.; Brown, Thomas A.; Lieser, Jan L.; Armand, Leanne K.; Leventer, Amy; Allen, Claire S.</p> <p>2016-04-01</p> <p>C25 highly branched isoprenoid (HBI) are lipid biomarkers biosynthesised by a relatively small number of diatom genera, but are, nonetheless, common constituents of global marine sediments. The occurrence and variable abundance of certain C25 highly branched isoprenoid (HBI) biomarkers in <span class="hlt">Antarctic</span> marine sediments has previously been proposed as a proxy measure of paleo sea-<span class="hlt">ice</span> extent in the Southern Ocean and a small number of paleo sea-<span class="hlt">ice</span> reconstructions based on the variable abundances of these HBIs have appeared in recent years. However, the development of HBIs as proxies for <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> is much less advanced than that for IP25 (another HBI) in the Arctic and has been based on relatively small number of analyses in sea <span class="hlt">ice</span>, water column and sediment samples. To provide further insights into the use of these HBIs as proxies for <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span>, we here describe an assessment of their distributions in surface water, surface sediment and sea <span class="hlt">ice</span> samples collected from a number of <span class="hlt">Antarctic</span> locations experiencing contrasting sea <span class="hlt">ice</span> conditions in recent years. Our study shows that distributions of a di-unsaturated HBI (diene II) and tri-unsaturated HBI (triene III) in surface water samples were found to be extremely sensitive to the local sea-<span class="hlt">ice</span> conditions, with diene II detected for sampling sites that experienced seasonal sea <span class="hlt">ice</span> and highest concentrations found in coastal locations with longer-lasting <span class="hlt">ice</span> cover and a recurrent polynya. In contrast, triene III was observed in all of the samples analysed, but with highest concentrations within the region of the retreating sea <span class="hlt">ice</span> edge, an observation consistent with significant environmental control over the biosynthesis of diene II and triene III by sea <span class="hlt">ice</span> diatoms and open water phytoplankton, respectively. However, additional local factors, such as those associated with polynya formation, may also exert some control over the distribution of triene III and the relative concentrations of diene II and</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930055825&hterms=algae&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dalgae','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930055825&hterms=algae&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dalgae"><span>Bromoalkane production by <span class="hlt">Antarctic</span> <span class="hlt">ice</span> algae</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sturges, W. T.; Sullivan, C. W.; Schnell, R. C.; Heidt, L. E.; Pollock, W. H.</p> <p>1993-01-01</p> <p><span class="hlt">Ice</span> microalgae, collected from the underside of annual sea <span class="hlt">ice</span> in McMurdo Sound, Antarctica, were found to contain and release to seawater a number of brominated hydrocarbons. These included bromoform, dibromomethane, mixed bromochloromethanes, and methyl bromide. Atmospheric measurements in the McMurdo Sound vicinity revealed the presence of bromoform and methyl bromide in the lower atmosphere, with lowest concentrations inland, further indicating that biogenic activity in the Sound is a source of organic bromine gases to the <span class="hlt">Antarctic</span> atmosphere. This may have important implications for boundary layer chemistry in Antarctica. In the Arctic, the presence of bromoform has been linked to loss of surface ozone in the spring. We report here preliminary evidence for similar surface ozone loss at McMurdo Station.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70033489','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70033489"><span>Top predators in relation to bathymetry, <span class="hlt">ice</span> and krill during austral winter in Marguerite Bay, Antarctica</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Ribic, C.A.; Chapman, E.; Fraser, William R.; Lawson, G.L.; Wiebe, P.H.</p> <p>2008-01-01</p> <p>A key hypothesis guiding the US Southern Ocean Global Ocean Ecosystems Dynamics (US SO GLOBEC) program is that deep across-<span class="hlt">shelf</span> troughs facilitate the transport of warm and nutrient-rich waters onto the continental <span class="hlt">shelf</span> of the Western <span class="hlt">Antarctic</span> Peninsula, resulting in enhanced winter production and prey availability to top predators. We tested aspects of this hypothesis during austral winter by assessing the distribution of the resident pack-<span class="hlt">ice</span> top predators in relation to these deep across-<span class="hlt">shelf</span> troughs and by investigating associations between top predators and their prey. Surveys were conducted July-August 2001 and August-September 2002 in Marguerite Bay, Antarctica, with a focus on the main across-<span class="hlt">shelf</span> trough in the bay, Marguerite Trough. The common pack-<span class="hlt">ice</span> seabird species were snow petrel (Pagodroma nivea, 1.2 individuals km-2), <span class="hlt">Antarctic</span> petrel (Thalassoica antarctica, 0.3 individuals km-2), and Ade??lie penguin (Pygoscelis adeliae, 0.5 individuals km-2). The most common pack-<span class="hlt">ice</span> pinniped was crabeater seal (Lobodon carcinophagus). During both winters, snow and <span class="hlt">Antarctic</span> petrels were associated with low sea-<span class="hlt">ice</span> concentrations independent of Marguerite Trough, while Ade??lie penguins occurred in association with this trough. Krill concentrations, both shallow and deep, also were associated with Ade??lie penguin and snow petrel distributions. During both winters, crabeater seal occurrence was associated with deep krill concentrations and with regions of lower chlorophyll concentration. The area of lower chlorophyll concentrations occurred in an area with complex bathymetry close to land and heavy <span class="hlt">ice</span> concentrations. Complex or unusual bathymetry via its influence on physical and biological processes appears to be one of the keys to understanding how top predators survive during the winter in this <span class="hlt">Antarctic</span> region. ?? 2007 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.419..199K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.419..199K"><span>The evolving instability of the remnant Larsen B <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and its tributary glaciers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Khazendar, Ala; Borstad, Christopher P.; Scheuchl, Bernd; Rignot, Eric; Seroussi, Helene</p> <p>2015-06-01</p> <p>Following the 2002 disintegration of the northern and central parts of the Larsen B <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, the tributary glaciers of the southern surviving part initially appeared relatively unchanged and hence assumed to be buttressed sufficiently by the remnant <span class="hlt">ice</span> <span class="hlt">shelf</span>. Here, we modify this perception with observations from <span class="hlt">Ice</span>Bridge altimetry and InSAR-inferred <span class="hlt">ice</span> flow speeds. Our analyses show that the surfaces of Leppard and Flask glaciers directly upstream from their grounding lines lowered by 15 to 20 m in the period 2002-2011. The thinning appears to be dynamic as the flow of both glaciers and the remnant <span class="hlt">ice</span> <span class="hlt">shelf</span> accelerated in the same period. Flask Glacier started accelerating even before the 2002 disintegration, increasing its flow speed by ∼55% between 1997 and 2012. Starbuck Glacier meanwhile did not change much. We hypothesize that the different evolutions of the three glaciers are related to their dissimilar bed topographies and degrees of grounding. We apply numerical modeling and data assimilation that show these changes to be accompanied by a reduction in the buttressing afforded by the remnant <span class="hlt">ice</span> <span class="hlt">shelf</span>, a weakening of the shear zones between its flow units and an increase in its fracture. The fast flowing northwestern part of the remnant <span class="hlt">ice</span> <span class="hlt">shelf</span> exhibits increasing fragmentation, while the stagnant southeastern part seems to be prone to the formation of large rifts, some of which we show have delimited successive calving events. A large rift only 12 km downstream from the grounding line is currently traversing the stagnant part of the <span class="hlt">ice</span> <span class="hlt">shelf</span>, defining the likely front of the next large calving event. We propose that the flow acceleration, <span class="hlt">ice</span> front retreat and enhanced fracture of the remnant Larsen B <span class="hlt">Ice</span> <span class="hlt">Shelf</span> presage its approaching demise.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20080045469&hterms=conversion+rate&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dconversion%2Brate%2527','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20080045469&hterms=conversion+rate&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dconversion%2Brate%2527"><span><span class="hlt">Antarctic</span> Sea <span class="hlt">Ice</span> Thickness and Snow-to-<span class="hlt">Ice</span> Conversion from Atmospheric Reanalysis and Passive Microwave Snow Depth</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Markus, Thorsten; Maksym, Ted</p> <p>2007-01-01</p> <p>Passive microwave snow depth, <span class="hlt">ice</span> concentration, and <span class="hlt">ice</span> motion estimates are combined with snowfall from the European Centre for Medium Range Weather Forecasting (ECMWF) reanalysis (ERA-40) from 1979-200 1 to estimate the prevalence of snow-to-<span class="hlt">ice</span> conversion (snow-<span class="hlt">ice</span> formation) on level sea <span class="hlt">ice</span> in the <span class="hlt">Antarctic</span> for April-October. Snow <span class="hlt">ice</span> is ubiquitous in all regions throughout the growth season. Calculated snow- <span class="hlt">ice</span> thicknesses fall within the range of estimates from <span class="hlt">ice</span> core analysis for most regions. However, uncertainties in both this analysis and in situ data limit the usefulness of snow depth and snow-<span class="hlt">ice</span> production to evaluate the accuracy of ERA-40 snowfall. The East <span class="hlt">Antarctic</span> is an exception, where calculated snow-<span class="hlt">ice</span> production exceeds observed <span class="hlt">ice</span> thickness over wide areas, suggesting that ERA-40 precipitation is too high there. Snow-<span class="hlt">ice</span> thickness variability is strongly controlled not just by snow accumulation rates, but also by <span class="hlt">ice</span> divergence. Surprisingly, snow-<span class="hlt">ice</span> production is largely independent of snow depth, indicating that the latter may be a poor indicator of total snow accumulation. Using the presence of snow-<span class="hlt">ice</span> formation as a proxy indicator for near-zero freeboard, we examine the possibility of estimating level <span class="hlt">ice</span> thickness from satellite snow depths. A best estimate for the mean level <span class="hlt">ice</span> thickness in September is 53 cm, comparing well with 51 cm from ship-based observations. The error is estimated to be 10-20 cm, which is similar to the observed interannual and regional variability. Nevertheless, this is comparable to expected errors for <span class="hlt">ice</span> thickness determined by satellite altimeters. Improvement in satellite snow depth retrievals would benefit both of these methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.A13I0402G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.A13I0402G"><span>Examination Of A Strong Downslope Warming Wind Event Over The Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> In Antarctica Through Modeling And Aircraft Observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grosvenor, D. P.; Choularton, T. W.; Gallagher, M. W.; Lachlan-Cope, T. A.; King, J. C.</p> <p>2009-12-01</p> <p>The high mountains of the <span class="hlt">Antarctic</span> Peninsula (AP) provide a climatic barrier between the west and east. The east side is generally blocked from the warmer oceanic air of the west and is consequently usually under the influence of colder continental air. On occasion, however, air from the west can cross the barrier in the form of strong winds travelling down the eastern slopes, which are also very warm and dry due to adiabatic descent. They penetrate onto the Larsen <span class="hlt">ice</span> shelves where they lead to above zero surface temperatures and are therefore likely to encourage surface melting. Crevasse propagation due to the weight of accumulated meltwater is currently thought to have been the major factor in causing the near total disintegration of the Larsen B <span class="hlt">ice</span> <span class="hlt">shelf</span> in 2002. In January 2006 the British <span class="hlt">Antarctic</span> Survey performed an aircraft flight over the Larsen C <span class="hlt">ice</span> <span class="hlt">shelf</span> on the east side of the AP, which sampled a strong downslope wind event. Surface flux measurements over the <span class="hlt">ice</span> <span class="hlt">shelf</span> suggest that the sensible heat provided by the warm jets would be likely to be negated by latent heat losses from <span class="hlt">ice</span> ablation. The main cause of any <span class="hlt">ice</span> melting was likely to be due to shortwave radiation input. However, the warming from the jets is still likely to be important by acting as an on/off control for melting by keeping air temperatures above zero. In addition, the dryness of the winds is likely to prevent cloud cover and thus maximize exposure of the <span class="hlt">ice</span> <span class="hlt">shelf</span> to solar energy input. This case study has been modeled using the WRF mesoscale model. The model reproduces the strong downslope winds seen by the aircraft with good comparisons of wind speed and temperature profiles through the wind jets. Further comparisons to surface station data have allowed progress towards achieving the best set up of the model for this case. The modeling agrees with the results of the aircraft study in suggesting that solar radiation input is likely to provide the largest amount of energy for</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T12A..05Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T12A..05Y"><span>Geoologic controls on the architecture of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet's basal interface: New results from West and East Antarctica from long range geophysics (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Young, D. A.; Blankenship, D. D.; Greenbaum, J. S.; Richter, T.; Aitken, A.; Siegert, M. J.; Roberts, J. L.</p> <p>2013-12-01</p> <p>The <span class="hlt">ice</span>-rock interface underlying the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet was shaped by interactions between underlying gondwanan geology and the overlying <span class="hlt">ice</span> sheet. The <span class="hlt">ice</span> sheet now preserves from sedimentary infill an incredibly rugged terrain which now plays a critical role in shaping subglacial hydrology, and thus shape <span class="hlt">ice</span> sheet behavior. This terrain can by imaged through aerogeophysical means, in particular through <span class="hlt">ice</span> penetrating radar, while airborne potential fields measurements provide insight into the geological framework that controlled erosion. Over the post IPY era, the density of airborne coverage is only now reaching the point where small scale structure can be identified and placed in context. Of particular importance is understanding the formation of focused erosional valleys, 30-50 km wide, representing now buried subglacial fjords. After initial data from the GIMBLE project in West Antarctica, and five years of sustained long range ICECAP surveys over East Antarctica , we now have a better view of the diversity of these features. The local erosion of these valleys, often cutting through significant topographic barriers, irregularly samples the underlying geology, provided a complex story in the sediment to the <span class="hlt">Antarctic</span> margin. These valleys now provide the subglacial conduits for significant <span class="hlt">ice</span> sheet catchments, in particular for subglacial water, including the inland catchments of DeVicq, Thwaites, and Pine Island Glaciers in West Antarctica, and Denman Glacier, Totten Glacier, Byrd Glacier and Cook <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in East Antarctica. We find that these features, now sometimes hundreds of kilometers inland of the modern grounding line, often nucleate on or are aligned with structure inherited from the assembly of the <span class="hlt">Antarctic</span> continent. While many of these features currently host active outlet glaciers or their tributaries, some do not, implying avenues for <span class="hlt">ice</span> sheet change. In West Antarctica, we find a new deep connection between the coast and interior basin</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17843316','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17843316"><span>Physical conditions at the base of a fast moving <span class="hlt">antarctic</span> <span class="hlt">ice</span> stream.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Engelhardt, H; Humphrey, N; Kamb, B; Fahnestock, M</p> <p>1990-04-06</p> <p>Boreholes drilled to the bottom of <span class="hlt">ice</span> stream B in the West <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet reveal that the base of the <span class="hlt">ice</span> stream is at the melting point and the basal water pressure is within about 1.6 bars of the <span class="hlt">ice</span> overburden pressure. These conditions allow the rapid <span class="hlt">ice</span> streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the <span class="hlt">ice</span> in a layer at least 2 meters thick. The mechanics of <span class="hlt">ice</span> streaming plays a role in the response of the <span class="hlt">ice</span> sheet to climatic change.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013DSRII..88...47M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013DSRII..88...47M"><span>Foraging habitats of southern elephant seals, Mirounga leonina, from the Northern <span class="hlt">Antarctic</span> Peninsula</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muelbert, Monica M. C.; de Souza, Ronald B.; Lewis, Mirtha N.; Hindell, Mark A.</p> <p>2013-04-01</p> <p>Elephant Island (EI) is uniquely placed to provide southern elephant seals (SES) breeding there with potential access to foraging grounds in the Weddell Sea, the frontal zones of the South Atlantic Ocean, the Patagonian <span class="hlt">shelf</span> and the Western <span class="hlt">Antarctic</span> Peninsula (WAP). Quantifying where seals from EI forage therefore provides insights into the types of important habitats available, and which are of particular importance to elephant seals. Twenty nine SES (5 sub-adult males—SAM and 24 adult females—AF) were equipped with SMRU CTD-SLDRs during the post-breeding (PB 2008, 2009) and post-moulting (PM 2007, 2008, 2009, 2010) trips to sea. There were striking intra-annual and inter-sex differences in foraging areas, with most of the PB females remaining within 150 km of EI. One PB AF travelled down the WAP as did 16 out of the 20 PM females and foraged near the winter <span class="hlt">ice</span>-edge. Most PM sub-adult males remained close to EI, in areas similar to those used by adult females several months earlier, although one SAM spent the early part of the winter foraging on the Patagonian <span class="hlt">Shelf</span>. The waters of the Northern <span class="hlt">Antarctic</span> Peninsula (NAP) contain abundant resources to support the majority of the Islands' SES for the summer and early winter, such that the animals from this population have shorter migrations than those from most other populations. Sub-adult males and PB females are certainly taking advantage of these resources. However, PM females did not remain there over the winter months, instead they used the same waters at the <span class="hlt">ice</span>-edge in the southern WAP that females from both King George Island and South Georgia used. Females made more benthic dives than sub-adult males—again this contrasts with other sites where SAMs do more benthic diving. Unlike most other populations studied to date EI is a relatively southerly breeding colony located on the <span class="hlt">Antarctic</span> continental <span class="hlt">shelf</span>. EI seals are using <span class="hlt">shelf</span> habitats more than other SES populations but some individuals still</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014E%26PSL.397...32N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014E%26PSL.397...32N"><span>Rapid bedrock uplift in the <span class="hlt">Antarctic</span> Peninsula explained by viscoelastic response to recent <span class="hlt">ice</span> unloading</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nield, Grace A.; Barletta, Valentina R.; Bordoni, Andrea; King, Matt A.; Whitehouse, Pippa L.; Clarke, Peter J.; Domack, Eugene; Scambos, Ted A.; Berthier, Etienne</p> <p>2014-07-01</p> <p>Since 1995 several <span class="hlt">ice</span> shelves in the Northern <span class="hlt">Antarctic</span> Peninsula have collapsed and triggered <span class="hlt">ice</span>-mass unloading, invoking a solid Earth response that has been recorded at continuous GPS (cGPS) stations. A previous attempt to model the observation of rapid uplift following the 2002 breakup of Larsen B <span class="hlt">Ice</span> <span class="hlt">Shelf</span> was limited by incomplete knowledge of the pattern of <span class="hlt">ice</span> unloading and possibly the assumption of an elastic-only mechanism. We make use of a new high resolution dataset of <span class="hlt">ice</span> elevation change that captures <span class="hlt">ice</span>-mass loss north of 66°S to first show that non-linear uplift of the Palmer cGPS station since 2002 cannot be explained by elastic deformation alone. We apply a viscoelastic model with linear Maxwell rheology to predict uplift since 1995 and test the fit to the Palmer cGPS time series, finding a well constrained upper mantle viscosity but less sensitivity to lithospheric thickness. We further constrain the best fitting Earth model by including six cGPS stations deployed after 2009 (the LARISSA network), with vertical velocities in the range 1.7 to 14.9 mm/yr. This results in a best fitting Earth model with lithospheric thickness of 100-140 km and upper mantle viscosity of 6×1017-2×1018 Pa s - much lower than previously suggested for this region. Combining the LARISSA time series with the Palmer cGPS time series offers a rare opportunity to study the time-evolution of the low-viscosity solid Earth response to a well-captured <span class="hlt">ice</span> unloading event.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28708127','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28708127"><span>An active bacterial community linked to high chl-a concentrations in <span class="hlt">Antarctic</span> winter-pack <span class="hlt">ice</span> and evidence for the development of an anaerobic sea-<span class="hlt">ice</span> bacterial community.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Eronen-Rasimus, Eeva; Luhtanen, Anne-Mari; Rintala, Janne-Markus; Delille, Bruno; Dieckmann, Gerhard; Karkman, Antti; Tison, Jean-Louis</p> <p>2017-10-01</p> <p><span class="hlt">Antarctic</span> sea-<span class="hlt">ice</span> bacterial community composition and dynamics in various developmental stages were investigated during the austral winter in 2013. Thick snow cover likely insulated the <span class="hlt">ice</span>, leading to high (<4 μg l -1 ) chlorophyll-a (chl-a) concentrations and consequent bacterial production. Typical sea-<span class="hlt">ice</span> bacterial genera, for example, Octadecabacter, Polaribacter and Glaciecola, often abundant in spring and summer during the sea-<span class="hlt">ice</span> algal bloom, predominated in the communities. The variability in bacterial community composition in the different <span class="hlt">ice</span> types was mainly explained by the chl-a concentrations, suggesting that as in spring and summer sea <span class="hlt">ice</span>, the sea-<span class="hlt">ice</span> bacteria and algae may also be coupled during the <span class="hlt">Antarctic</span> winter. Coupling between the bacterial community and sea-<span class="hlt">ice</span> algae was further supported by significant correlations between bacterial abundance and production with chl-a. In addition, sulphate-reducing bacteria (for example, Desulforhopalus) together with odour of H 2 S were observed in thick, apparently anoxic <span class="hlt">ice</span>, suggesting that the development of the anaerobic bacterial community may occur in sea <span class="hlt">ice</span> under suitable conditions. In all, the results show that bacterial community in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span> can stay active throughout the winter period and thus possible future warming of sea <span class="hlt">ice</span> and consequent increase in bacterial production may lead to changes in bacteria-mediated processes in the <span class="hlt">Antarctic</span> sea-<span class="hlt">ice</span> zone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012TCD.....6..505F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012TCD.....6..505F"><span>Quantification of ikaite in <span class="hlt">Antarctic</span> sea <span class="hlt">ice</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fischer, M.; Thomas, D. N.; Krell, A.; Nehrke, G.; Göttlicher, J.; Norman, L.; Riaux-Gobin, C.; Dieckmann, G. S.</p> <p>2012-02-01</p> <p>Calcium carbonate precipitation in sea <span class="hlt">ice</span> can increase pCO2 during precipitation in winter and decrease pCO2 during dissolution in spring. CaCO3 precipitation in sea <span class="hlt">ice</span> is thought to potentially drive significant CO2 uptake by the ocean. However, little is known about the quantitative spatial and temporal distribution of CaCO3 within sea <span class="hlt">ice</span>. This is the first quantitative study of hydrous calcium carbonate, as ikaite, in sea <span class="hlt">ice</span> and discusses its potential significance for the carbon cycle in polar oceans. <span class="hlt">Ice</span> cores and brine samples were collected from pack and land fast sea <span class="hlt">ice</span> between September and December 2007 during an expedition in the East <span class="hlt">Antarctic</span> and another off Terre Adélie, Antarctica. Samples were analysed for CaCO3, Salinity, DOC, DON, Phosphate, and total alkalinity. A relationship between the measured parameters and CaCO3 precipitation could not be observed. We found calcium carbonate, as ikaite, mostly in the top layer of sea <span class="hlt">ice</span> with values up to 126 mg ikaite per liter melted sea <span class="hlt">ice</span>. This potentially represents a contribution between 0.12 and 9 Tg C to the annual carbon flux in polar oceans. The horizontal distribution of ikaite in sea <span class="hlt">ice</span> was heterogenous. We also found the precipitate in the snow on top of the sea <span class="hlt">ice</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C13D..08T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C13D..08T"><span>Grounding Zones, Subglacial Lakes, and Dynamics of an <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Stream: The WISSARD Glaciological Experiment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tulaczyk, S. M.; Schwartz, S. Y.; Fisher, A. T.; Powell, R. D.; Fricker, H. A.; Anandakrishnan, S.; Horgan, H. J.; Scherer, R. P.; Walter, J. I.; Siegfried, M. R.; Mikucki, J.; Christianson, K.; Beem, L.; Mankoff, K. D.; Carter, S. P.; Hodson, T. O.; Marsh, O.; Barcheck, C. G.; Branecky, C.; Neuhaus, S.; Jacobel, R. W.</p> <p>2015-12-01</p> <p>Interactions of West <span class="hlt">Antarctic</span> <span class="hlt">ice</span> streams with meltwater at their beds, and with seawater at their grounding lines, are widely considered to be the primary drivers of <span class="hlt">ice</span> stream flow variability on different timescales. Understanding of processes controlling <span class="hlt">ice</span> flow variability is needed to build quantitative models of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet that can be used to help predict its future behavior and to reconstruct its past evolution. The <span class="hlt">ice</span> plain of Whillans <span class="hlt">Ice</span> Stream provides a natural glaciological laboratory for investigations of <span class="hlt">Antarctic</span> <span class="hlt">ice</span> flow dynamics because of its highly variable flow rate modulated by tidal processes and fill-drain cycles of subglacial lakes. Moreover, this part of Antarctica has one of the longest time series of glaciological observations, which can be used to put recently acquired datasets in a multi-decadal context. Since 2007 Whillans <span class="hlt">Ice</span> Stream has been the focus of a regional glaciological experiment, which included surface GPS and passive-source seismic sensors, radar and seismic imaging of subglacial properties, as well as deep borehole geophysical sensors. This experiment was possible thanks to the NSF-funded multidisciplinary WISSARD project (Whillans <span class="hlt">Ice</span> Stream Subglacial Access Research Drilling). Here we will review the datasets collected during the WISSARD glaciological experiment and report on selected results pertaining to interactions of this <span class="hlt">ice</span> stream with water at its bed and its grounding line.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12..505D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12..505D"><span>Recent rift formation and impact on the structural integrity of the Brunt <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, East Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>De Rydt, Jan; Hilmar Gudmundsson, G.; Nagler, Thomas; Wuite, Jan; King, Edward C.</p> <p>2018-02-01</p> <p>We report on the recent reactivation of a large rift in the Brunt <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, East Antarctica, in December 2012 and the formation of a 50 km long new rift in October 2016. Observations from a suite of ground-based and remote sensing instruments between January 2000 and July 2017 were used to track progress of both rifts in unprecedented detail. Results reveal a steady accelerating trend in their width, in combination with alternating episodes of fast ( > 600 m day-1) and slow propagation of the rift tip, controlled by the heterogeneous structure of the <span class="hlt">ice</span> <span class="hlt">shelf</span>. A numerical <span class="hlt">ice</span> flow model and a simple propagation algorithm based on the stress distribution in the <span class="hlt">ice</span> <span class="hlt">shelf</span> were successfully used to hindcast the observed trajectories and to simulate future rift progression under different assumptions. Results show a high likelihood of <span class="hlt">ice</span> loss at the McDonald <span class="hlt">Ice</span> Rumples, the only pinning point of the <span class="hlt">ice</span> <span class="hlt">shelf</span>. The nascent iceberg calving and associated reduction in pinning of the Brunt <span class="hlt">Ice</span> <span class="hlt">Shelf</span> may provide a uniquely monitored natural experiment of <span class="hlt">ice</span> <span class="hlt">shelf</span> variability and provoke a deeper understanding of similar processes elsewhere in Antarctica.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011TCry....5..727M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011TCry....5..727M"><span>The Potsdam Parallel <span class="hlt">Ice</span> Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.</p> <p>2011-09-01</p> <p>We present a dynamic equilibrium simulation of the <span class="hlt">ice</span> sheet-<span class="hlt">shelf</span> system on Antarctica with the Potsdam Parallel <span class="hlt">Ice</span> Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and <span class="hlt">ice</span> thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-<span class="hlt">shelf</span> basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and <span class="hlt">ice</span> flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross <span class="hlt">ice</span> <span class="hlt">shelf</span> areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded <span class="hlt">ice</span>. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine <span class="hlt">ice</span> sheet model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C42A..05C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C42A..05C"><span><span class="hlt">Ice</span> <span class="hlt">shelf</span> melt rates in Greenland and Antarctica using time-tagged digital imagery from World View and TanDEM-X</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Charolais, A.; Rignot, E. J.; Milillo, P.; Scheuchl, B.; Mouginot, J.</p> <p>2017-12-01</p> <p>The floating extensions of glaciers, or <span class="hlt">ice</span> shelves, melt vigorously in contact with ocean waters. Melt is non uniform, with the highest melt taking place in the deepest part of the cavity, where thermal forcing is the greatest because of 1) the pressure dependence of the freezing point of the seawater/<span class="hlt">ice</span> mixture and 2) subglacial water injects fresh, buoyant, cold melt water to fuel stronger <span class="hlt">ice</span>-ocean interactions. Melt also forms along preferential channels, which are not stationary, and create lines of weakness in the <span class="hlt">shelf</span>. <span class="hlt">Ice</span> <span class="hlt">shelf</span> melt rates have been successfully measured from space over the entire <span class="hlt">Antarctic</span> continent and on the <span class="hlt">ice</span> shelves in Greenland using an Eulerian approach that combines <span class="hlt">ice</span> thickness, <span class="hlt">ice</span> velocity vectors, surface mass balance data, and measurements of <span class="hlt">ice</span> thinning rates. The Eulerian approach is limited by the precision of the thickness gradients, typically of a few km, and requires significant spatial averaging to remove advection effects. A Lagrangian approach has been shown to be robust to advection effects and provides higher resolution details. We implemented a Lagrangian methodology for time-tagged World View DEMs by the Polar Geoscience Center (PGS) at the University of Minnesota and time-tagged TanDEM-X DEMs separated by one year. We derive melt rates on a 300-m grid with a precision of a few m/yr. Melt is strongest along grounding lines and along preferred channels. Channels are non-stationary because melt is not the same on opposite sides of the channels. Examining time series of data and comparing with the time-dependent grounding line positions inferred from satellite radar interferometry, we evaluate the magnitude of melt near the grounding line and even within the grounding zone. A non-zero melt rate in the grounding zone has vast implications for <span class="hlt">ice</span> sheet modeling. This work is funded by a grant from NASA Cryosphere Program.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010ffcd.confE.150L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010ffcd.confE.150L"><span>Diagnosing <span class="hlt">Antarctic</span> Fog</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lazzara, M. A.</p> <p>2010-07-01</p> <p>Fog affects aviation and other logistical operations in the <span class="hlt">Antarctic</span>; nevertheless limited studies have been conducted to understand fog behavior in this part of the world. A study has been conducted in the Ross Island region of Antarctica, the location of McMurdo Station and Scott Base - the main stations of the United States and New Zealand <span class="hlt">Antarctic</span> programs, respectively. Using tools such as multi-channel satellites observations and supported by in situ radiosonde and ground-based automatic weather station observations, combined with back trajectory and mesoscale numerical models, discover that austral summer fog events are "advective" in temperament. The diagnosis finds a primary source region from the southeast over the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (over 72% of the cases studied) while a minority of cases point toward a secondary fog source region to the north along the Scott Coast of the Ross Sea with influences from the East <span class="hlt">Antarctic</span> Plateau. Part of this examination confirms existing anecdotes from forecasters and weather observers, while refuting others about fog and its behavior in this environment. This effort marks the beginning of our understanding of <span class="hlt">Antarctic</span> fog behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19494912','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19494912"><span>The Gamburtsev mountains and the origin and early evolution of the <span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bo, Sun; Siegert, Martin J; Mudd, Simon M; Sugden, David; Fujita, Shuji; Xiangbin, Cui; Yunyun, Jiang; Xueyuan, Tang; Yuansheng, Li</p> <p>2009-06-04</p> <p><span class="hlt">Ice</span>-sheet development in Antarctica was a result of significant and rapid global climate change about 34 million years ago. <span class="hlt">Ice</span>-sheet and climate modelling suggest reductions in atmospheric carbon dioxide (less than three times the pre-industrial level of 280 parts per million by volume) that, in conjunction with the development of the <span class="hlt">Antarctic</span> Circumpolar Current, led to cooling and glaciation paced by changes in Earth's orbit. Based on the present subglacial topography, numerical models point to <span class="hlt">ice</span>-sheet genesis on mountain massifs of Antarctica, including the Gamburtsev mountains at Dome A, the centre of the present <span class="hlt">ice</span> sheet. Our lack of knowledge of the present-day topography of the Gamburtsev mountains means, however, that the nature of early glaciation and subsequent development of a continental-sized <span class="hlt">ice</span> sheet are uncertain. Here we present radar information about the base of the <span class="hlt">ice</span> at Dome A, revealing classic Alpine topography with pre-existing river valleys overdeepened by valley glaciers formed when the mean summer surface temperature was around 3 degrees C. This landscape is likely to have developed during the initial phases of <span class="hlt">Antarctic</span> glaciation. According to <span class="hlt">Antarctic</span> climate history (estimated from offshore sediment records) the Gamburtsev mountains are probably older than 34 million years and were the main centre for <span class="hlt">ice</span>-sheet growth. Moreover, the landscape has most probably been preserved beneath the present <span class="hlt">ice</span> sheet for around 14 million years.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C34B..08F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C34B..08F"><span><span class="hlt">Antarctic</span> <span class="hlt">Ice</span> Sheet Discharge Driven by Atmosphere-Ocean Feedbacks Across the Last Glacial Termination</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fogwill, C. J.; Turney, C. S.; Golledge, N. R.; Etheridge, D. M.; Rubino, M.; Thornton, D.; Baker, A.; Weber, M. E.; Woodward, J.; van Ommen, T. D.; Moy, A. D.; Davies, S. M.; Bird, M. I.; Winter, K.; Munksgaard, N.; Menviel, L.; Rootes, C.; Vohra, J.; Rivera, A.; Cooper, A.</p> <p>2016-12-01</p> <p>Reconstructing the dynamic response of the <span class="hlt">Antarctic</span> <span class="hlt">ice</span> sheets to warming during the Last Glacial Termination (LGT; 18,000-11,650 yrs ago) allows us to identify <span class="hlt">ice</span>-climate feedbacks that could improve future projections1,2. Whilst the sequence of events during this period are reasonably well-known, relatively poor chronological control has precluded precise alignment of <span class="hlt">ice</span>, atmospheric and marine records2, making it difficult to assess relationships between <span class="hlt">Antarctic</span> <span class="hlt">ice</span>-sheet dynamics, climate change and sea-level rise3-5. Here we present results from a highly-resolved `horizontal <span class="hlt">ice</span> core'6,7 from the Weddell Sea Embayment, which records millennial-scale <span class="hlt">ice</span>-sheet dynamics across this extensive sector of Antarctica. Counterintuitively, we find <span class="hlt">ice</span>-sheet surface drawdown of 600 m across the <span class="hlt">Antarctic</span> Cold Reversal (ACR; 14,600-12,700 yrs ago)5, with stabilisation during the subsequent millennia of atmospheric warming. Earth system and <span class="hlt">ice</span>-sheet modelling highlights that this response was likely sustained by strong ocean-<span class="hlt">ice</span> feedbacks4,8; however, the drivers remain uncertain. Given the coincidence of the <span class="hlt">ice</span>-sheet changes recorded with marked shifts in atmospheric circulation9,10,11we suggest that millennial-scale <span class="hlt">Antarctic</span> <span class="hlt">ice</span>-sheet behaviour was initiated and sustained by global atmospheric teleconnections across the LGT. This has important ramifications <span class="hlt">ice</span>-sheet stability under contemporary climate change, with changing atmospheric and oceanic circulation patterns. 1 Collins, M. et al. in Climate Change 2013: The Physical Science Basis. 2 Weber, M. E. et al. Nature 510, 134-138, (2014). 3 Weaver, A. J., et al., Science 299, 1709-1713, (2003). 4 Golledge, N. R. et al. Nat Commun 5, (2014). 5 Pedro, J. B. et al. Nature Geosci9. 51-55 (2015). 6 Turney, C. S. M. et al. Journal of Quaternary Science 28, 697-704 (2013). 7 Winter, K. et al. Geophys. Res. Lett.43. 5. 2019-2026 (2016). 8 Menviel, L., A. et al., Quaternary Science Reviews 30, 1155-1172 (2011). 9 Hogg</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EaFut...5.1217K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EaFut...5.1217K"><span>Evolving Understanding of <span class="hlt">Antarctic</span> <span class="hlt">Ice</span>-Sheet Physics and Ambiguity in Probabilistic Sea-Level Projections</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kopp, Robert E.; DeConto, Robert M.; Bader, Daniel A.; Hay, Carling C.; Horton, Radley M.; Kulp, Scott; Oppenheimer, Michael; Pollard, David; Strauss, Benjamin H.</p> <p>2017-12-01</p> <p>Mechanisms such as <span class="hlt">ice-shelf</span> hydrofracturing and <span class="hlt">ice</span>-cliff collapse may rapidly increase discharge from marine-based <span class="hlt">ice</span> sheets. Here, we link a probabilistic framework for sea-level projections to a small ensemble of <span class="hlt">Antarctic</span> <span class="hlt">ice</span>-sheet (AIS) simulations incorporating these physical processes to explore their influence on global-mean sea-level (GMSL) and relative sea-level (RSL). We compare the new projections to past results using expert assessment and structured expert elicitation about AIS changes. Under high greenhouse gas emissions (Representative Concentration Pathway [RCP] 8.5), median projected 21st century GMSL rise increases from 79 to 146 cm. Without protective measures, revised median RSL projections would by 2100 submerge land currently home to 153 million people, an increase of 44 million. The use of a physical model, rather than simple parameterizations assuming constant acceleration of <span class="hlt">ice</span> loss, increases forcing sensitivity: overlap between the central 90% of simulations for 2100 for RCP 8.5 (93-243 cm) and RCP 2.6 (26-98 cm) is minimal. By 2300, the gap between median GMSL estimates for RCP 8.5 and RCP 2.6 reaches >10 m, with median RSL projections for RCP 8.5 jeopardizing land now occupied by 950 million people (versus 167 million for RCP 2.6). The minimal correlation between the contribution of AIS to GMSL by 2050 and that in 2100 and beyond implies current sea-level observations cannot exclude future extreme outcomes. The sensitivity of post-2050 projections to deeply uncertain physics highlights the need for robust decision and adaptive management frameworks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20180000708&hterms=physics&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dphysics','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20180000708&hterms=physics&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dphysics"><span>Evolving Understanding of <span class="hlt">Antarctic</span> <span class="hlt">Ice</span>-Sheet Physics and Ambiguity in Probabilistic Sea-Level Projections</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kopp, Robert E.; DeConto, Robert M.; Bader, Daniel A.; Hay, Carling C.; Horton, Radley M.; Kulp, Scott; Oppenheimer, Michael; Pollard, David; Strauss, Benjamin</p> <p>2017-01-01</p> <p>Mechanisms such as <span class="hlt">ice-shelf</span> hydrofracturing and <span class="hlt">ice</span>-cliff collapse may rapidly increase discharge from marine-based <span class="hlt">ice</span> sheets. Here, we link a probabilistic framework for sea-level projections to a small ensemble of <span class="hlt">Antarctic</span> <span class="hlt">ice</span>-sheet (AIS) simulations incorporating these physical processes to explore their influence on global-mean sea-level (GMSL) and relative sea-level (RSL). We compare the new projections to past results using expert assessment and structured expert elicitation about AIS changes. Under high greenhouse gas emissions (Representative Concentration Pathway [RCP] 8.5), median projected 21st century GMSL rise increases from 79 to 146 cm. Without protective measures, revised median RSL projections would by 2100 submerge land currently home to 153 million people, an increase of 44 million. The use of a physical model, rather than simple parameterizations assuming constant acceleration of <span class="hlt">ice</span> loss, increases forcing sensitivity: overlap between the central 90% of simulations for 2100 for RCP 8.5 (93-243 cm) and RCP 2.6 (26-98 cm) is minimal. By 2300, the gap between median GMSL estimates for RCP 8.5 and RCP 2.6 reaches >10 m, with median RSL projections for RCP 8.5 jeopardizing land now occupied by 950 million people (versus 167 million for RCP 2.6). The minimal correlation between the contribution of AIS to GMSL by 2050 and that in 2100 and beyond implies current sea-level observations cannot exclude future extreme outcomes. The sensitivity of post-2050 projections to deeply uncertain physics highlights the need for robust decision and adaptive management frameworks.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <div class="footer-extlink text-muted" style="margin-bottom:1rem; text-align:center;">Some links on this page may take you to non-federal websites. 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