Sample records for ice shelf calving

  1. 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.

  2. 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.

  3. 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.

  4. Towards a Universal Calving Law: Modeling Ice Shelves Using Damage Mechanics

    NASA Astrophysics Data System (ADS)

    Whitcomb, M.; Bassis, J. N.; Price, S. F.; Lipscomb, W. H.

    2017-12-01

    Modeling iceberg calving from ice shelves and ice tongues is a particularly difficult problem in glaciology because of the wide range of observed calving rates. Ice shelves naturally calve large tabular icebergs at infrequent intervals, but may instead calve smaller bergs regularly or disintegrate due to hydrofracturing in warmer conditions. Any complete theory of iceberg calving in ice shelves must be able to generate realistic calving rate values depending on the magnitudes of the external forcings. Here we show that a simple damage evolution law, which represents crevasse distributions as a continuum field, produces reasonable estimates of ice shelf calving rates when added to the Community Ice Sheet Model (CISM). Our damage formulation is based on a linear stability analysis and depends upon the bulk stress and strain rate in the ice shelf, as well as the surface and basal melt rates. The basal melt parameter in our model enhances crevasse growth near the ice shelf terminus, leading to an increased iceberg production rate. This implies that increasing ocean temperatures underneath ice shelves will drive ice shelf retreat, as has been observed in the Amundsen and Bellingshausen Seas. We show that our model predicts broadly correct calving rates for ice tongues ranging in length from 10 km (Erebus) to over 100 km (Drygalski), by matching the computed steady state lengths to observations. In addition, we apply the model to idealized Antarctic ice shelves and show that we can also predict realistic ice shelf extents. Our damage mechanics model provides a promising, computationally efficient way to compute calving fluxes and links ice shelf stability to climate forcing.

  5. 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

  6. 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.

  7. 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).

  8. 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.

  9. 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

  10. 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).

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. Accelerated ice shelf rifting and retreat at Pine Island Glacier, West Antarctica

    NASA Astrophysics Data System (ADS)

    Jeong, Seongsu; Howat, Ian M.; Bassis, Jeremy N.

    2016-11-01

    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 ice shelf. This type of calving is common on polar ice shelves, with no clear connection to ocean-ice dynamic forcing. In contrast, we report on the recent development of multiple rifts initiating from basal crevasses in the center of the ice shelf, resulted in calving further upglacier than previously observed. Coincident with rift formation was the sudden disintegration of the ice mélange that filled the northern shear margin, resulting in ice sheet detachment from this margin. Examination of ice velocity suggests that this internal rifting resulted from the combination of a change in ice shelf stress regime caused by disintegration of the mélange and intensified melting within basal crevasses, both of which may be linked to ocean forcing.

  16. 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

  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. 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.

  19. 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.

  20. 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.

    , which likely has limited lateral variation in its mechanical properties, accounts for ~60% of the total ice thickness near the calving front. This suggests that the material heterogeneities present in the lower ~40% of the ice column are responsible for resisting fracture propagation and thereby delaying tabular calving events. This represents a highly sensitive aspect of ice-shelf stability, as changes in the oceanic forcing may lead to the loss of this heterogeneity.

  1. 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.

  2. 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

  3. 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.

  4. 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

  5. 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

  6. The structure and effect of suture zones in the Larsen C Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    McGrath, Daniel; Steffen, Konrad; Holland, Paul R.; Scambos, Ted; Rajaram, Harihar; Abdalati, Waleed; Rignot, Eric

    2014-03-01

    Ice shelf fractures frequently terminate where they encounter suture zones, regions of material heterogeneity that form between meteoric inflows in ice shelves. This heterogeneity can consist of marine ice, meteoric ice with modified rheological properties, or the presence of fractures. Here, we use radar observations on the Larsen C Ice Shelf, Antarctica, to investigate (i) the termination of a 25 km long rift in the Churchill Peninsula suture zone, which was found to contain 60 m of accreted marine ice, and (ii) the along-flow evolution of a suture zone originating at Cole Peninsula. We determine a steady state field of basal melting/freezing rates and apply it to a flowline model to delineate the along-flow evolution of layers within the ice shelf. The thickening surface wedge of locally accumulated meteoric ice, which likely has limited lateral variation in its mechanical properties, accounts for 60% of the total ice thickness near the calving front. Thus, we infer that the lower 40% of the ice column and the material heterogeneities present there are responsible for resisting fracture propagation and thereby delaying tabular calving events, as demonstrated in the >40 year time series leading up to the 2004/2005 calving event for Larsen C. This likely represents a highly sensitive aspect of ice shelf stability, as changes in the oceanic forcing may lead to the loss of this heterogeneity.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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

  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. 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. 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.

  15. The evolving instability of the remnant Larsen B Ice Shelf and its tributary glaciers

    NASA Astrophysics Data System (ADS)

    Khazendar, Ala; Borstad, Christopher P.; Scheuchl, Bernd; Rignot, Eric; Seroussi, Helene

    2015-06-01

    Following the 2002 disintegration of the northern and central parts of the Larsen B Ice Shelf, the tributary glaciers of the southern surviving part initially appeared relatively unchanged and hence assumed to be buttressed sufficiently by the remnant ice shelf. Here, we modify this perception with observations from IceBridge altimetry and InSAR-inferred ice 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 ice shelf 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 ice shelf, a weakening of the shear zones between its flow units and an increase in its fracture. The fast flowing northwestern part of the remnant ice shelf 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 ice shelf, defining the likely front of the next large calving event. We propose that the flow acceleration, ice front retreat and enhanced fracture of the remnant Larsen B Ice Shelf presage its approaching demise.

  16. 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.

  17. 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.

  18. Ice Island calves off Petermann Glacier

    NASA Image and Video Library

    2010-08-09

    NASA image acquired August 5, 2010 On August 5, 2010, an enormous chunk of ice, roughly 97 square miles (251 square kilometers) in size, broke off the Petermann Glacier, along the northwestern coast of Greenland. The Canadian Ice Service detected the remote event within hours in near real-time data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite. The Peterman Glacier lost about one-quarter of its 70-kilometer (40-mile) long floating ice shelf, said researchers who analyzed the satellite data at the University of Delaware. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured these natural-color images of Petermann Glacier 18:05 UTC on August 5, 2010 (top), and 17:15 UTC on July 28, 2010 (bottom). The Terra image of the Petermann Glacier on August 5 was acquired almost 10 hours after the Aqua observation that first recorded the event. By the time Terra took this image, skies were less cloudy than they had been earlier in the day, and the oblong iceberg had broken free of the glacier and moved a short distance down the fjord. Icebergs calving off the Petermann Glacier are not unusual. Petermann Glacier’s floating ice tongue is the Northern Hemisphere’s largest, and it has occasionally calved large icebergs. The recently calved iceberg is the largest to form in the Arctic since 1962, said the University of Delaware. To read more and or to download the high res go here: www.nasa.gov/topics/earth/features/petermann-calve.html or Click here to see more images from NASA Goddard’s Earth Observatory NASA Earth Observatory image created by Jesse Allen and Robert Simmon, using data obtained from the Goddard Level 1 and Atmospheric Archive and Distribution System (LAADS). Caption by Holli Riebeek and Michon Scott. Instrument: Terra - MODIS NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft

  19. 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.

  20. Simulating Ice Shelf Response to Potential Triggers of Collapse Using the Material Point Method

    NASA Astrophysics Data System (ADS)

    Huth, A.; Smith, B. E.

    2017-12-01

    Weakening or collapse of an ice shelf can reduce the buttressing effect of the shelf on its upstream tributaries, resulting in sea level rise as the flux of grounded ice into the ocean increases. Here we aim to improve sea level rise projections by developing a prognostic 2D plan-view model that simulates the response of an ice sheet/ice shelf system to potential triggers of ice shelf weakening or collapse, such as calving events, thinning, and meltwater ponding. We present initial results for Larsen C. Changes in local ice shelf stresses can affect flow throughout the entire domain, so we place emphasis on calibrating our model to high-resolution data and precisely evolving fracture-weakening and ice geometry throughout the simulations. We primarily derive our initial ice geometry from CryoSat-2 data, and initialize the model by conducting a dual inversion for the ice viscosity parameter and basal friction coefficient that minimizes mismatch between modeled velocities and velocities derived from Landsat data. During simulations, we implement damage mechanics to represent fracture-weakening, and track ice thickness evolution, grounding line position, and ice front position. Since these processes are poorly represented by the Finite Element Method (FEM) due to mesh resolution issues and numerical diffusion, we instead implement the Material Point Method (MPM) for our simulations. In MPM, the ice domain is discretized into a finite set of Lagrangian material points that carry all variables and are tracked throughout the simulation. Each time step, information from the material points is projected to a Eulerian grid where the momentum balance equation (shallow shelf approximation) is solved similarly to FEM, but essentially treating the material points as integration points. The grid solution is then used to determine the new positions of the material points and update variables such as thickness and damage in a diffusion-free Lagrangian frame. The grid does not store

  1. 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

  2. Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

    NASA Astrophysics Data System (ADS)

    De Rydt, Jan; Hilmar Gudmundsson, G.; Nagler, Thomas; Wuite, Jan; King, Edward C.

    2018-02-01

    We report on the recent reactivation of a large rift in the Brunt Ice Shelf, 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 ice shelf. A numerical ice flow model and a simple propagation algorithm based on the stress distribution in the ice shelf were successfully used to hindcast the observed trajectories and to simulate future rift progression under different assumptions. Results show a high likelihood of ice loss at the McDonald Ice Rumples, the only pinning point of the ice shelf. The nascent iceberg calving and associated reduction in pinning of the Brunt Ice Shelf may provide a uniquely monitored natural experiment of ice shelf variability and provoke a deeper understanding of similar processes elsewhere in Antarctica.

  3. Breaking Ice 2: A rift system on the Ross Ice Shelf as an analog for tidal tectonics on icy moons

    NASA Astrophysics Data System (ADS)

    Brunt, K. M.; Hurford, T., Jr.; Schmerr, N. C.; Sauber, J. M.; MacAyeal, D. R.

    2016-12-01

    Ice shelves are the floating regions of the polar ice 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 ice shelves, including: the tidal influence on the ice-shelf surface height, which changes by as much as 6 to 7 m on the southern extreme of the Ronne-Filchner Ice Shelf; the tidal modulation of the ice-shelf horizontal flow velocities, which changes the mean ice-flow rate by as much as two fold on the Ross Ice Shelf; 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 Ice Shelf. 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 Ice Shelf rift system, we can investigate the geological processes observed on icy satellites and advance modeling efforts of their tidal-tectonic evolution.

  4. Gradual slowdown and thickening of Fimbulisen ice shelf, East Antarctica, over the past decade

    NASA Astrophysics Data System (ADS)

    van Oostveen, Jelte; Moholdt, Geir; Kääb, Andreas; Matsuoka, Kenichi

    2017-04-01

    Fimbulisen is a fast-flowing (up to 780±10 ma-1) ice shelf in the Dronning Maud Land region of East Antarctica. Fed by one of the few major outlet glaciers along that coast, Jutulstraumen, the ice shelf has the potential to affect the stability of a considerable part of the inland ice sheet. Here we present evidence of a slowdown and thickening of Fimbulisen over the last decade. We derive ice shelf 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 ice shelf 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 ice 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 ice shelf. In support of this theory we have found several uncharted ice rumples and stationary icebergs near the eastern front of the ice shelf, indicating the presence of shallow bathymetry that might affect the ice shelf dynamics considerably in the event of ice shelf grounding or ungrounding.

  5. 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.

  6. Iceberg Ploughmarks Indicate Past Rapid Iceberg Calving and Retreat of Pine Island-Thwaites Ice Stream due to Marine Ice-Cliff Instability Processes

    NASA Astrophysics Data System (ADS)

    Wise, M.; Dowdeswell, J. A.; Larter, R. D.; Jakobsson, M.

    2016-12-01

    Seafloor ploughmarks provide evidence of past and present iceberg dimensions and drift direction. Today, Pine Island and Thwaites glaciers, which account for 35% of mass loss from the West Antarctic Ice Sheet (WAIS), calve mainly large, tabular icebergs, which, when grounded, produce `toothcomb-like' multi-keeled ploughmarks. High-resolution multi-beam swath bathymetry of the mid-shelf Pine Island Trough and adjacent banks, reveals many linear-curvilinear depressions interpreted as iceberg-keel ploughmarks, the majority of which are single-keeled in form. From measurements of ploughmark planform and cross-sections, we find iceberg calving from the palaeo-Pine Island-Thwaites Ice Stream was not characterised by small numbers of large, tabular icebergs, but instead, by a large number of `smaller' icebergs with v-shaped keels. Geological evidence of ploughmark form and water-depth distribution indicates calving-margin thicknesses ( 950 m) and subaerial ice-cliff elevations ( 100 m) equivalent to the theoretical threshold recently predicted to trigger ice-cliff structural collapse through Marine Ice Cliff Instability (MICI) processes. Significantly, our proposed period of iceberg ploughing predates the early Holocene climate optimum, and likely occurred in an absence of widespread surface melt. We therefore provide the first observational evidence of rapid retreat of the Palaeo-Pine Island-Thwaites ice stream from the crest of a large, mid-shelf sedimentary depocentre or grounding-zone wedge, to a restabilising position 112 km offshore of the December 2013 calving line, driven by MICI processes commencing 12.3 cal. ka BP. We emphasise the effective operation of MICI processes without extensive surface melt and induced hydrofracture, and conclude that such processes are unlikely to be confined to the past, given the steep, retrograde bed-slope which the modern grounding lines of Pine Island and Thwaites Glaciers are approaching, and the absence of any discernible

  7. 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

  8. Boundary layer models for calving marine outlet glaciers

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

    Schoof, Christian; Davis, Andrew D.; Popa, Tiberiu V.

    We consider the flow of marine-terminating outlet glaciers that are laterally confined in a channel of prescribed width. In that case, the drag exerted by the channel side walls on a floating ice shelf can reduce extensional stress at the grounding line. If ice flux through the grounding line increases with both ice thickness and extensional stress, then a longer shelf can reduce ice flux by decreasing extensional stress. Consequently, calving has an effect on flux through the grounding line by regulating the length of the shelf. In the absence of a shelf, it plays a similar role by controllingmore » the above-flotation height of the calving cliff. Using two calving laws, one due to Nick et al. (2010) based on a model for crevasse propagation due to hydrofracture and the other simply asserting that calving occurs where the glacier ice becomes afloat, we pose and analyse a flowline model for a marine-terminating glacier by two methods: direct numerical solution and matched asymptotic expansions. The latter leads to a boundary layer formulation that predicts flux through the grounding line as a function of depth to bedrock, channel width, basal drag coefficient, and a calving parameter. By contrast with unbuttressed marine ice sheets, we find that flux can decrease with increasing depth to bedrock at the grounding line, reversing the usual stability criterion for steady grounding line location. Stable steady states can then have grounding lines located on retrograde slopes. We show how this anomalous behaviour relates to the strength of lateral versus basal drag on the grounded portion of the glacier and to the specifics of the calving law used.« less

  9. Boundary layer models for calving marine outlet glaciers

    DOE PAGES

    Schoof, Christian; Davis, Andrew D.; Popa, Tiberiu V.

    2017-10-05

    We consider the flow of marine-terminating outlet glaciers that are laterally confined in a channel of prescribed width. In that case, the drag exerted by the channel side walls on a floating ice shelf can reduce extensional stress at the grounding line. If ice flux through the grounding line increases with both ice thickness and extensional stress, then a longer shelf can reduce ice flux by decreasing extensional stress. Consequently, calving has an effect on flux through the grounding line by regulating the length of the shelf. In the absence of a shelf, it plays a similar role by controllingmore » the above-flotation height of the calving cliff. Using two calving laws, one due to Nick et al. (2010) based on a model for crevasse propagation due to hydrofracture and the other simply asserting that calving occurs where the glacier ice becomes afloat, we pose and analyse a flowline model for a marine-terminating glacier by two methods: direct numerical solution and matched asymptotic expansions. The latter leads to a boundary layer formulation that predicts flux through the grounding line as a function of depth to bedrock, channel width, basal drag coefficient, and a calving parameter. By contrast with unbuttressed marine ice sheets, we find that flux can decrease with increasing depth to bedrock at the grounding line, reversing the usual stability criterion for steady grounding line location. Stable steady states can then have grounding lines located on retrograde slopes. We show how this anomalous behaviour relates to the strength of lateral versus basal drag on the grounded portion of the glacier and to the specifics of the calving law used.« less

  10. An East Siberian ice shelf during the Late Pleistocene glaciations: Numerical reconstructions

    NASA Astrophysics Data System (ADS)

    Colleoni, Florence; Kirchner, Nina; Niessen, Frank; Quiquet, Aurélien; Liakka, Johan

    2016-09-01

    A recent data campaign in the East Siberian Sea has revealed evidence of grounded and floating ice 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 ice cap developed over Beringia and expanded over the East Siberian continental margin during some of the Late Pleistocene glaciations. Other similar evidence of ice 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 ice 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 ice cap and ice shelf. Results show that the ice cap developing over Beringia connects to the Eurasian ice sheet in all simulations and that its volume ranges between 6 and 14 m SLE, depending on the climate forcing. This ice cap generates an ice shelf of dimensions comparable with or larger than the present-day Ross ice shelf in West Antarctica. Although the ice shelf extent strongly depends on the ice 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 ice cap with the Eurasian ice sheet affects the expansion of the ice shelf only in the simulations where the ice cap fluxes are not large enough to compensate for the fluxes coming from the Eurasian ice sheet.

  11. 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

  12. Thurston Island Calving

    NASA Image and Video Library

    2014-11-10

    A sea of icebergs float near the Thurston Island calving front off of western Antarctica as seen on the IceBridge flight on Nov. 5, 2014. Image Credit: NASA/Jim Yungel NASA’s Operation IceBridge collected some rare images on a flight out of Punta Arenas, Chile on Nov. 5, 2014, on a science flight over western Antarctica dubbed Ferrigno-Alison-Abbott 01. The crew snapped a few shots of a calving front of the Antarctic ice sheet. This particular flight plan was designed to collect data on changes in ice elevation along the coast near the Ferrigno and Alison ice streams, on the Abbot Ice Shelf, and grounded ice along the Eights Coast.

  13. 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.

  14. Ocean wave generation by collapsing ice shelves

    NASA Astrophysics Data System (ADS)

    Macayeal, D. R.; Bassis, J. N.; Okal, E. A.; Aster, R. C.; Cathles, L. M.

    2008-12-01

    The 28-29 February, 2008, break-up of the Wilkins Ice Shelf, Antarctica, exemplifies the now-familiar, yet largely unexplained pattern of explosive ice-shelf break-up. While environmental warming is a likely ultimate cause of explosive break-up, several key aspects of their short-term behavior need to be explained: (1) The abrupt, near-simultaneous onset of iceberg calving across long spans of the ice front margin; (2) High outward drift velocity (about 0.3 m/s) of a leading phalanx of tabular icebergs that originate from the seaward edge of the intact ice shelf prior to break-up; (3) Rapid coverage of the ocean surface in the wake of this leading phalanx by small, capsized and dismembered tabular icebergs; (4) Extremely large gravitational potential energy release rates, e.g., up to 3 × 1010 W; (5) Lack of proximal iceberg-calving triggers that control the timing of break-up onset and that maintain the high break-up calving rates through to the conclusion of the event. Motivated by seismic records obtained from icebergs and the Ross Ice Shelf that show hundreds of micro- tsunamis emanating from near the ice shelf front, we re-examine the basic dynamic features of ice- shelf/ocean-wave interaction and, in particular, examine the possibility that collapsing ice shelves themselves are a source of waves that stimulate the disintegration process. We propose that ice-shelf generated surface-gravity waves associated with initial calving at an arbitrary seed location produce stress perturbations capable of triggering the onset of calving on the entire ice front. Waves generated by parting detachment rifts, iceberg capsize and break-up act next to stimulate an inverted submarine landslide (ice- slide) process, where gravitational potential energy released by upward movement of buoyant ice is radiated as surface gravity waves in the wake of the advancing phalanx of tabular icebergs. We conclude by describing how field research and remote sensing can be used to test the

  15. Automatic, Satellite-Linked "Webcams" as a Tool in Ice-Shelf and Iceberg Research.

    NASA Astrophysics Data System (ADS)

    Ross, R.; Okal, M. H.; Thom, J. E.; Macayeal, D. R.

    2004-12-01

    Important dynamic events governing the behavior of ice shelves and icebergs are episodic in time and small in scale, making them difficult to observe. Traditional satellite imagery is acquired on a rigid schedule with coarse spatial resolution and this means that collisions between icebergs or the processes which create ice "mélange" that fills detachment rifts leading to ice-shelf calving, to give examples, cannot be readily observed. To overcome the temporal and spatial gaps in traditional remote sensing, we have deployed cameras at locations in Antarctica where research is conducted on the calving and subsequent evolution of icebergs. One camera is located at the edge of iceberg C16 in the Ross Sea, and is positioned to capture visual imagery of collisions between C16 and neighboring B15A. The second camera is located within the anticipated detachment rift of a "nascent" iceberg on the Ross Ice Shelf. The second camera is positioned to capture visual imagery of the rift's propagation and the in-fill of ice mélange, which constrains the mechanical influence of such rifts on the surrounding ice shelf. Both cameras are designed for connection to the internet (hence are referred to as "webcams") and possess variable image qualities and image-control technology. The cameras are also connected to data servers via the Iridium satellite telephone network and produce a daily image that is transmitted to the internet through the Iridium connection. Results of the initial trial deployments will be presented as a means of assessing both the techniques involved and the value of the scientific information acquired by these webcams. In the case of the iceberg webcam, several collisions between B15A and C16 were monitored over the period between January, 2003 and December, 2004. The time-lapse imagery obtained through this period showed giant "push mounds" of damaged firn on the edge and surface of the icebergs within the zones of contact as a consequence of the collisions

  16. Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics

    NASA Astrophysics Data System (ADS)

    Yu, Hongju; Rignot, Eric; Morlighem, Mathieu; Seroussi, Helene

    2017-05-01

    Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that are consistent with the distribution of depth and width of surface and bottom crevasses observed by NASA's Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate crevasses that are consistent with observations. We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of calving events. It is more prominent for glaciers with rapid calving rates than for glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining crevasse formation and iceberg calving.

  17. Remote Characterization of Ice Shelf Surface and Basal Processes: Examples from East Antarctica

    NASA Astrophysics Data System (ADS)

    Greenbaum, J. S.; Blankenship, D. D.; Grima, C.; Schroeder, D. M.; Soderlund, K. M.; Young, D. A.; Kempf, S. D.; Siegert, M. J.; Roberts, J. L.; Warner, R. C.; van Ommen, T. D.

    2017-12-01

    The ability to remotely characterize surface and basal processes of ice shelves has important implications for conducting systematic, repeatable, and safe evaluations of their stability in the context of atmospheric and oceanic forcing. Additionally, techniques developed for terrestrial ice shelves can be adapted to orbital radar sounding datasets planned for forthcoming investigations of icy moons. This has been made possible through recent advances in radar signal processing that enable these data to be used to test hypotheses derived from conceptual and numerical models of ice shelf- and ice shell-ocean interactions. Here, we present several examples of radar sounding-derived characterizations of surface and basal processes underway on ice shelves in East Antarctica. These include percolation of near-surface meltwater in warm austral summers, brine infiltration along ice shelf calving fronts, basal melt rate and distribution, and basal freeze distribution. On Europa, near-surface brines and their migration may impact local geological variability, while basal processes likely control the distribution of melt and freeze. Terrestrially, we emphasize radar-sounding records of the Totten Glacier Ice Shelf which hosts each of these processes as well as the highest known density of basal melt channels of any terrestrial ice shelf. Further, with a maximum floating ice thickness of over 2.5 km, the pressure at Totten's basal interface may be similar to that at Europa's ice-ocean interface; therefore, evaluating surface and basal processes of Totten Glacier and other ice shelves could serve as analogs for understanding melting processes of Europa's ice shell.

  18. Oceanographic Controls on the Variability of Ice-Shelf Basal Melting and Circulation of Glacial Meltwater in the Amundsen Sea Embayment, Antarctica

    NASA Astrophysics Data System (ADS)

    Kimura, Satoshi; Jenkins, Adrian; Regan, Heather; Holland, Paul R.; Assmann, Karen M.; Whitt, Daniel B.; Van Wessem, Melchoir; van de Berg, Willem Jan; Reijmer, Carleen H.; Dutrieux, Pierre

    2017-12-01

    Ice shelves in the Amundsen Sea Embayment have thinned, accelerating the seaward flow of ice sheets upstream over recent decades. This imbalance is caused by an increase in the ocean-driven melting of the ice shelves. Observations and models show that the ocean heat content reaching the ice shelves is sensitive to the depth of thermocline, which separates the cool, fresh surface waters from warm, salty waters. Yet the processes controlling the variability of thermocline depth remain poorly constrained. Here we quantify the oceanic conditions and ocean-driven melting of Cosgrove, Pine Island Glacier (PIG), Thwaites, Crosson, and Dotson ice shelves in the Amundsen Sea Embayment from 1991 to 2014 using a general circulation model. Ice-shelf melting is coupled to variability in the wind field and the sea-ice motions over the continental shelf break and associated onshore advection of warm waters in deep troughs. The layer of warm, salty waters at the calving front of PIG and Thwaites is thicker in austral spring (June-October) than in austral summer (December-March), whereas the seasonal cycle at the calving front of Dotson is reversed. Furthermore, the ocean-driven melting in PIG is enhanced by an asymmetric response to changes in ocean heat transport anomalies at the continental shelf break: melting responds more rapidly to increases in ocean heat transport than to decreases. This asymmetry is caused by the inland deepening of bathymetry and the glacial meltwater circulation around the ice shelf.

  19. 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

  20. Investigating the response of Crane Glacier, Antarctic Peninsula to the disintegration of the Larsen B ice shelf using a 2-D flowline model

    NASA Astrophysics Data System (ADS)

    Campbell, A. J.; Hulbe, C. L.; Sergienko, O.

    2009-12-01

    Many of the glaciers flowing into the Larsen B ice shelf 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 ice shelf 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 ice shelf 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 ice shelf 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 ice sheet outlet glaciers and modeling their future behavior. Correct representation of iceberg calving is also important.

  1. 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.

  2. 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

  3. 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

  4. Understanding calving dynamics of Greenland outlet glaciers by comparing calving laws in a 3D ice sheet model

    NASA Astrophysics Data System (ADS)

    Choi, Y.; Morlighem, M.; Wood, M.; Bondzio, J. H.; Mouginot, J.

    2017-12-01

    Mass loss from marine terminating glaciers along coastal Greenland is a significant contributor to global sea-level rise. Calving is one of the important processes that control the dynamics, and therefore the discharge, of these glaciers. As glacier termini are exposed to warmer ocean currents, ocean-induced melt at the calving front increases, which may lead to glacier retreat and ice flow acceleration. It is therefore important to accurately parameterize calving in ice sheet models in order to improve the projections of ice sheet change. Several calving laws have been proposed, but most of them have been applied only to a specific region and have not been tested on other glaciers, while some others have only been implemented in one-dimensional flowline or vertical flowband models. Here, we test and compare several calving laws recently proposed in the literature using a 3D ice sheet model. Namely: the height-above-buoyancy criterion (Vieli et al., 2002), the crevasse-depth calving law (Benn et al., 2007), the eigencalving law (Levermann et al., 2012) and von Mises tensile stress calving law (Morlighem et al., 2016). We test these calving laws on Zachariae Isstrøm (Northeast), Upernavik (Central West) and Helheim (East) glaciers of Greenland. We compare the modeled ice front evolution to the observed retreat from Landsat data, and assess which calving law has the best predictive skills for each glacier. Overall, von Mises tensile stress calving laws is more satisfactory than others for most regions. This study shows that calving dynamics needs to be 3D in ice sheet models to account for the complex geometry and narrow fjords along the coast of Greenland. Comparing calving laws in a 3D model makes it possible to find missing mechanisms in each criterion and to improve existing calving laws in numerical ice sheet models, which could reduce uncertainties in future sea level rise projections.

  5. 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 ...

  6. Regional Changes in Icescape Impact Shelf Circulation and Basal Melting

    NASA Astrophysics Data System (ADS)

    Cougnon, E. A.; Galton-Fenzi, B. K.; Rintoul, S. R.; Legrésy, B.; Williams, G. D.; Fraser, A. D.; Hunter, J. R.

    2017-11-01

    Ice shelf basal melt is the dominant contribution to mass loss from Antarctic ice shelves. However, the sensitivity of basal melt to changes in icescape (grounded icebergs, ice shelves, and sea ice) 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 ice and icebergs on the basal melt rate of the local ice shelves. We find that the position of the grounded tabular iceberg B9B controls the water masses that reach the nearby ice shelf 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 shelf driving a 57% increase of the deep MGT basal melting. Major changes in icescape influence the oceanic heat flux responsible for basal ice shelf melting.

  7. 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.

  8. Ocean-driven thinning enhances iceberg calving and retreat of Antarctic ice shelves

    PubMed Central

    Liu, Yan; Moore, John C.; Cheng, Xiao; Gladstone, Rupert M.; Bassis, Jeremy N.; Liu, Hongxing; Wen, Jiahong; Hui, Fengming

    2015-01-01

    Iceberg calving from all Antarctic ice shelves has never been directly measured, despite playing a crucial role in ice sheet mass balance. Rapid changes to iceberg calving naturally arise from the sporadic detachment of large tabular bergs but can also be triggered by climate forcing. Here we provide a direct empirical estimate of mass loss due to iceberg calving and melting from Antarctic ice shelves. We find that between 2005 and 2011, the total mass loss due to iceberg calving of 755 ± 24 gigatonnes per year (Gt/y) is only half the total loss due to basal melt of 1516 ± 106 Gt/y. However, we observe widespread retreat of ice shelves that are currently thinning. Net mass loss due to iceberg calving for these ice shelves (302 ± 27 Gt/y) is comparable in magnitude to net mass loss due to basal melt (312 ± 14 Gt/y). Moreover, we find that iceberg calving from these decaying ice shelves is dominated by frequent calving events, which are distinct from the less frequent detachment of isolated tabular icebergs associated with ice shelves in neutral or positive mass balance regimes. Our results suggest that thinning associated with ocean-driven increased basal melt can trigger increased iceberg calving, implying that iceberg calving may play an overlooked role in the demise of shrinking ice shelves, and is more sensitive to ocean forcing than expected from steady state calving estimates. PMID:25733856

  9. 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.

  10. Motion of Major Ice Shelf Fronts in Antarctica from Slant Range Analysis of Radar Altimeter Data, 1978 - 1998

    NASA Technical Reports Server (NTRS)

    Zwally, H. J.; Beckley, M. A.; Brenner, A. C.; Giovinetto, M. B.; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    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 Antarctic ice shelves. The barrier locations, which are the seaward edges or fronts of floating ice shelves, advance with time as the ice flows from the grounded ice 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 ice shelf 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 ice shelves that lie in large embayments (the Filchner-Ronne, Amery, and Ross), and marginal ice 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 ice shelves). All the ice shelves included in the study account for approximately three-fourths of the total ice shelf area of Antarctica, and discharge approximately two-thirds of the total grounded ice area.

  11. 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.

  12. 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.

  13. Petermann Glacier, North Greenland: massive calving in 2010 and the past half century

    NASA Astrophysics Data System (ADS)

    Johannessen, O. M.; Babiker, M.; Miles, M. W.

    2011-01-01

    Greenland's marine-terminating glaciers drain large amounts of solid ice through calving of icebergs, as well as melting of floating glacial ice. Petermann Glacier, North Greenland, has the Northern Hemisphere's long floating ice shelf. A massive (~270 km2) calving event was observed from satellite sensors in August 2010. In order to understand this in perspective, here we perform a comprehensive retrospective data analysis of Petermann Glacier calving-front variability spanning half a century. Here we establish that there have been at least four massive (100+ km2) calving events over the past 50 years: (1) 1959-1961 (~153 km2), (2) 1991 (~168 km2), (3) 2001 (~71 km2) and (4) 2010 (~270 km2), as well as ~31 km2 calved in 2008. The terminus position in 2010 has retreated ~15 km beyond the envelope of previous observations. Whether the massive calving in 2010 represents natural episodic variability or a response to global and/or ocean warming in the fjord remains speculative, although this event supports the contention that the ice shelf recently has become vulnerable due to extensive fracturing and channelized basal melting.

  14. 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.

  15. 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

  16. The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

    NASA Astrophysics Data System (ADS)

    Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

    2011-09-01

    We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf 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 ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf 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 ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. Icequake Tremors During Glacier Calving (Invited)

    NASA Astrophysics Data System (ADS)

    Walter, F.; O'Neel, S.; Bassis, J. N.; Fricker, H. A.; Pfeffer, W. T.

    2009-12-01

    ice shelf calving in Antarctica. The similarities and differences in seismic signatures of these different calving settings provide valuable insights and will be helpful in the theoretical treatment of glacier calving.

  3. 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

  4. 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

  5. The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

    NASA Astrophysics Data System (ADS)

    Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

    2010-08-01

    We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and 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 dynamic calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf 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 ice. This approach also leads to a natural emergence of streams in this new 3-D marine ice sheet model.

  6. 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.

  7. The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 1: Model description

    NASA Astrophysics Data System (ADS)

    Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

    2011-09-01

    We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011) and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP). A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011).

  8. 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.

  9. 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.

  10. 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.

  11. Channelized bottom melting and stability of floating ice shelves

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Steffen, K.

    2008-01-01

    The floating ice shelf in front of Petermann Glacier, in northwest Greenland, experiences massive bottom melting that removes 80% of its ice before calving into the Arctic Ocean. Detailed surveys of the ice shelf reveal the presence of 1-2 km wide, 200-400 m deep, sub-ice shelf channels, aligned with the flow direction and spaced by 5 km. We attribute their formation to the bottom melting of ice from warm ocean waters underneath. Drilling at the center of one of channel, only 8 m above sea level, confirms the presence of ice-shelf melt water in the channel. These deep incisions in ice-shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously.

  12. 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.

  13. 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 ...

  14. The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 1: Model description

    NASA Astrophysics Data System (ADS)

    Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

    2010-08-01

    We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams naturally emerge through this approach and can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid scale representation of calving front motion (Albrecht et al., 2010) and a physically motivated dynamic calving law based on horizontal spreading rates. The model is validated within the Marine Ice Sheet Model Intercomparison Project (MISMIP) and is used for a dynamic equilibrium simulation of Antarctica under present-day conditions in the second part of this paper (Martin et al., 2010).

  15. 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

  16. 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.

  17. Investigating role of ice-ocean interaction on glacier dynamic: Results from numerical modeling applied to Petermann Glacier

    NASA Astrophysics Data System (ADS)

    Nick, F. M.; van der Veen, C. J.; Vieli, A.; Pattyn, F.; Hubbard, A.; Box, J. E.

    2010-12-01

    Calving of icebergs and bottom melting from ice shelves accounts for roughly half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. Petermann Glacier (north Greenland) with its ~17 km wide and ~ 60 km long floating ice-shelf is experiencing high rates of bottom melting. The recent partial disintegration of its shelf (in August 2010) presents a natural experiment to investigate the dynamic response of the ice sheet to its shelf retreat. We apply a numerical ice flow model using a physically-based calving criterion based on crevasse depth to investigate the contribution of processes such as shelf disintegration, bottom melting, sea ice or sikkusak disintegration and surface run off to the mass balance of Petermann Glacier and assess its stability. Our modeling study provides insights into the role of ice-ocean interaction, and on response of Petermann Glacier to its recent massive ice loss.

  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. A laboratory scale model of abrupt ice-shelf disintegration

    NASA Astrophysics Data System (ADS)

    Macayeal, D. R.; Boghosian, A.; Styron, D. D.; Burton, J. C.; Amundson, J. M.; Cathles, L. M.; Abbot, D. S.

    2010-12-01

    An important mode of Earth’s disappearing cryosphere is the abrupt disintegration of ice shelves along the Peninsula of Antarctica. This disintegration process may be triggered by climate change, however the work needed to produce the spectacular, explosive results witnessed with the Larsen B and Wilkins ice-shelf events of the last decade comes from the large potential energy release associated with iceberg capsize and fragmentation. To gain further insight into the underlying exchanges of energy involved in massed iceberg movements, we have constructed a laboratory-scale model designed to explore the physical and hydrodynamic interactions between icebergs in a confined channel of water. The experimental apparatus consists of a 2-meter water tank that is 30 cm wide. Within the tank, we introduce fresh water and approximately 20-100 rectangular plastic ‘icebergs’ having the appropriate density contrast with water to mimic ice. The blocks are initially deployed in a tight pack, with all blocks arranged in a manner to represent the initial state of an integrated ice shelf or ice tongue. The system is allowed to evolve through time under the driving forces associated with iceberg hydrodynamics. Digitized videography is used to quantify how the system of plastic icebergs evolves between states of quiescence to states of mobilization. Initial experiments show that, after a single ‘agitator’ iceberg begins to capsize, an ‘avalanche’ of capsizing icebergs ensues which drives horizontal expansion of the massed icebergs across the water surface, and which stimulates other icebergs to capsize. A surprise initially evident in the experiments is the fact that the kinetic energy of the expanding mass of icebergs is only a small fraction of the net potential energy released by the rearrangement of mass via capsize. Approximately 85 - 90 % of the energy released by the system goes into water motion modes, including a pervasive, easily observed seich mode of the tank

  20. 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.

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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).

  6. 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

  7. 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

  8. Airborne thickness and freeboard measurements over the McMurdo Ice Shelf, Antarctica, and implications for ice density

    NASA Astrophysics Data System (ADS)

    Rack, Wolfgang; Haas, Christian; Langhorne, Pat J.

    2013-11-01

    We present airborne measurements to investigate the thickness of the western McMurdo Ice Shelf in the western Ross Sea, Antarctica. Because of basal accretion of marine ice and brine intrusions conventional radar systems are limited in detecting the ice 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 ice shelf. The maximum electromagnetically detectable ice thickness was about 55 m. Assuming hydrostatic equilibrium, the simultaneous measurement of ice freeboard and thickness was used to derive bulk ice densities ranging from 800 to 975 kg m-3. Densities higher than those of pure ice can be largely explained by the abundance of sediments accumulated at the surface and present within the ice shelf, and are likely to a smaller extent related to the overestimation of ice 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 ice shelf, similar to what is observed in front of the ice shelf below the sea ice, is likely to exist in areas of highest thickness. The thickness and density distribution reflects a picture of areas of basal freezing and supercooled Ice Shelf Water emerging from below the central ice shelf cavity into McMurdo Sound.

  9. Chilean Tsunami Rocks the Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    The response of the Ross Ice Shelf (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 shelf 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 ice edge (https://scripps.ucsd.edu/centers/iceshelfvibes/). Signals generated by both the tsunami and IG waves were recorded at all stations on floating ice, with little ocean wave-induced energy reaching stations on grounded ice. 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-ice flexural-gravity waves propagating through the ice shelf 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 shelf, and water layer and ice shelf thickness and properties.

  10. 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

  11. SPH non-Newtonian Model for Ice Sheet and Ice Shelf Dynamics

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

    Tartakovsky, Alexandre M.; Pan, Wenxiao; Monaghan, Joseph J.

    2012-07-07

    We propose a new three-dimensional smoothed particle hydrodynamics (SPH) non-Newtonian model to study coupled ice sheet and ice shelf dynamics. Most existing ice sheet numerical models use a grid-based Eulerian approach, and are usually restricted to shallow ice sheet and ice shelf 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 ice along a horizontal surface. Next, the SPH model is used to investigate the grounding line dynamics of ice sheet/shelf. 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, ice-to-fluid density ratios, and flux. We examine the effect of non-Newtonian behavior of ice on the grounding line dynamics. The non-Newtonian constitutive model is based on Glen's law for a creeping flow of a polycrystalline ice. Finally, we investigate the effect of a bedrock geometry on a steady-state position of the grounding line.« less

  12. 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.

  13. Ice-Shelf Flexure and Tidal Forcing of Bindschadler Ice Stream, West Antarctica

    NASA Technical Reports Server (NTRS)

    Walker, Ryan T.; Parizek, Bryron R.; Alley, Richard B.; Brunt, Kelly M.; Anandakrishnan, Sridhar

    2014-01-01

    Viscoelastic models of ice-shelf flexure and ice-stream velocity perturbations are combined into a single efficient flowline model to study tidal forcing of grounded ice. 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 Ice Stream (formerly Ice Stream D) on semidiurnal time scales; however, other forcings such as tidally driven ice-shelf slope transverse to the flowline and flexurally driven till deformation must also be considered if diurnal motion is to be matched

  14. 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.

  15. Calving Geometry of Thwaites Glacier Linked to Semi-brittle Ice Dynamics

    NASA Astrophysics Data System (ADS)

    Logan, L. C.; Lavier, L.; Choi, E.; Tan, E.; Catania, G. A.; Holt, J.

    2016-12-01

    In the coming decades the linkage between ice dynamics, basal melt, and calving will play a central role in the flow of Thwaites Glacier, which has undergone vast and recent retreat. We explore this connection using a 3D, transient, thermomechanical ice flow model under different basal melt scenarios. Our use of a semi-brittle ice rheology enables the time-dependent development and tracking of surface and basal crevasses that determine the calving rate at this location. With the use of adaptive re-meshing, we are able to simulate the glacier's retreat response to different boundary forcings. We show that the resulting characteristic pinch-and-swell model geometries in the floating tongue compare well with airborne radar data acquired across the grounding line and floating tongue of Thwaites Glacier. These geometric features may be reproduced using this semi-brittle rheology, and further, are linked directly to the calving rate of Thwaites Glacier (and others). The use of semi-brittle rheology on decadal time scales may help provide constraints on the near-term future behavior of glaciers vulnerable to ocean-induced retreat, as this rheology targets the complex interaction of ice failure, basal melt, and flow.

  16. Simulating Ice-Flow and Calving on Store Glacier, West Greenland, with a 3D Full Stokes Model

    NASA Astrophysics Data System (ADS)

    Todd, J.; Christoffersen, P.; Zwinger, T.; Luckman, A. J.; Benn, D.

    2015-12-01

    The mass balance and long-term stability of the ice sheets in Greenland and Antarctica depend heavily on the dynamics of their ice-ocean margins. Iceberg calving accounts for the majority of the net annual loss of ice in Antarctica and around half of that from Greenland. Furthermore, climate driven changes to dynamics at these calving margins can be transmitted far inland. Thus, predicting future sea level contribution from the cryosphere requires an improved understanding of calving, and the processes which link it to climate and ice-sheet flow. We present results from a new 3D calving model coupled to a full-Stokes, time evolving glacier dynamic model, implemented for Store Glacier, a 5-km-wide calving glacier in the Uummannaq region of West Greenland, which flows at a rate of 20 m/day at its terminus. The model is developed using the open source finite element package Elmer/Ice, with the criterion that calving occurs when surface and basal crevasses meet. Crevasses open in response to tensile stresses near the terminus and water pressure at the bed. When the model was applied in 2D for the central flowline of Store Glacier, we found that basal topography exerts overarching control on the long term position of the calving front, while ice mélange buttressing allows the seasonal extension of a floating tongue, which collapses in early summer. New results emerging from implementation of calving in a 3D model indicate significant spatial heterogeneity in calving dynamics because the northern half of the terminus is grounded whereas the southern half is floating. This contrasting setting affects calving dynamics, further underlining the importance of geometry and basal topography, and suggesting that lower dimensional calving models may miss important aspects of calving dynamics. Our results also suggest that implementing grounding line dynamics is important for modelling calving, even for glaciers which are, for the most part, firmly grounded.

  17. Geometric controls of the flexural gravity waves on the Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

    Sergienko, O. V.

    2017-12-01

    Long-period ocean waves, formed locally or at distant sources, can reach sub-ice-shelf cavities and excite coupled motion in the cavity and the ice shelf - flexural gravity waves. Three-dimensional numerical simulations of the flexural gravity waves on the Ross Ice Shelf show that propagation of these waves is strongly controlled by the geometry of the system - the cavity shape, its water-column thickness and the ice-shelf 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 ice-shelf front. As a result, depending on the beams orientation, parts of the Ross Ice Shelf 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 ice-shelf front exciting flexural stresses in the vicinity of the grounding line.

  18. 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

  19. Seismic Excitation of the Ross Ice Shelf by Whillans Ice Stream Stick-Slip Events

    NASA Astrophysics Data System (ADS)

    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.

    2015-12-01

    Rapid variations in the flow rate of upstream glaciers and ice streams may cause significant deformation of ice shelves. The Whillans Ice 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 Ice Shelf (RIS) detected by broadband seismographs deployed on the ice shelf. 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 ice shelf are significantly slower than the P wave velocity in ice, as the long period displacement pulse is also sensitive to velocities of the water and sediments beneath the ice shelf. 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 ice velocity, thickness, and the thickness of water and sediment beneath. Study of this phenomenon should lead to greater understanding of how the ice shelf responds to sudden forcing around the periphery.

  20. Change in Dense Shelf Water and Adélie Land Bottom Water Precipitated by Iceberg Calving

    NASA Astrophysics Data System (ADS)

    Snow, K.; Rintoul, S. R.; Sloyan, B. M.; Hogg, A. McC.

    2018-03-01

    Antarctic Bottom Water supplies the deep limb of the global overturning circulation and ventilates the abyssal ocean. Antarctic Bottom Water has warmed, freshened, and contracted in recent decades, but the causes remain poorly understood. We use unique multiyear observations from the continental shelf and deep ocean near the Mertz Polynya to examine the sensitivity of this bottom water formation region to changes on the continental shelf, including the calving of a large iceberg. Postcalving, the seasonal cycle of Dense Shelf Water (DSW) density almost halved in amplitude and the volume of DSW available for export reduced. In the deep ocean, the density and volume of Adélie Land Bottom Water decreased sharply after calving, while oxygen concentrations remained high, indicating continued ventilation by DSW. This natural experiment illustrates how local changes in forcing over the Antarctic continental shelf can drive large and rapid changes in the abyssal ocean.

  1. 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.

  2. Seabed topography beneath Larsen C Ice Shelf from seismic soundings

    NASA Astrophysics Data System (ADS)

    Brisbourne, A. M.; Smith, A. M.; King, E. C.; Nicholls, K. W.; Holland, P. R.; Makinson, K.

    2013-08-01

    Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-shelf bathymetry model derived from the inversion of IceBridge 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 ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-shelf oceanic circulation may be affected by ice draft and sub-shelf cavity thickness. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Measured temperatures within the ice column and at the ice base were used to define the velocity profile through the remainder of the ice column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice 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 ice shelf. 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 IceBridge 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-shelf ocean circulation models.

  3. Mapping Ross Ice Shelf with ROSETTA-Ice airborne laser altimetry

    NASA Astrophysics Data System (ADS)

    Becker, M. K.; Fricker, H. A.; Padman, L.; Bell, R. E.; Siegfried, M. R.; Dieck, C. C. M.

    2017-12-01

    The Ross Ocean and ice Shelf Environment and Tectonic setting Through Aerogeophysical surveys and modeling (ROSETTA-Ice) 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 Ice Shelf (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-Ice 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 ice-shelf features such as the "rampart-moat" ice-front morphology, which has previously been observed on and modeled for icebergs. This feature is also visible in the ROSETTA-Ice shallow-ice 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-Ice 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 ice 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 ice dynamics.

  4. Damage Mechanics in the Community Ice Sheet Model

    NASA Astrophysics Data System (ADS)

    Whitcomb, R.; Cathles, L. M. M., IV; Bassis, J. N.; Lipscomb, W. H.; Price, S. F.

    2016-12-01

    Half of the mass that floating ice shelves lose to the ocean comes from iceberg calving, which is a difficult process to simulate accurately. This is especially true in the large-scale ice dynamics models that couple changes in the cryosphere to climate projections. Damage mechanics provide a powerful technique with the potential to overcome this obstacle by describing how fractures in ice evolve over time. Here, we demonstrate the application of a damage model to ice shelves that predicts realistic geometries. We incorporated this solver into the Community Ice Sheet Model, a three dimensional ice sheet model developed at Los Alamos National Laboratory. The damage mechanics formulation that we use comes from a first principles-based evolution law for the depth of basal and surface crevasses and depends on the large scale strain rate, stress state, and basal melt. We show that under idealized conditions it produces ice tongue lengths that match well with observations for a selection of natural ice tongues, including Erebus, Drygalski, and Pine Island in Antarctica, as well as Petermann in Greenland. We also apply the model to more generalized ideal ice shelf geometries and show that it produces realistic calving front positions. Although our results are preliminary, the damage mechanics model that we developed provides a promising first principles method for predicting ice shelf extent and how the calving margins of ice shelves respond to climate change.

  5. 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

  6. Snow, Firn and Ice Heterogeneity within Larsen C Ice Shelf Revealed by Borehole Optical-televiewing

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    The north-western sector of Larsen C Ice Shelf (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 shelf's firn structure, which also dictates shelf density (widely used to reconstruct ice shelf 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-ice core calibration, and apply a thresholding technique to estimate refrozen ice content within the firn column. These data are combined to define five material facies present within this sector of LCIS. The firn/ice 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 ice content. However, they also highlight finer-resolution complexity of ice shelf structure. For example, the most dense ice, 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 ice (e.g., 52 m thick with a density of 852 +/-21 kg m-3 in northernmost Cabinet Inlet) advected from inland. This inherited ice forms one of five facies identified across the study region. These are, extending broadly downwards into the shelf, and with different representation at each site: local accumulation (F1); local accumulation hosting substantial infiltration ice, i.e. influenced by intense melt but insufficient to form

  7. Quantification of Changes for the Milne Ice Shelf, Nunavut, Canada, 1950 -- 2009

    NASA Astrophysics Data System (ADS)

    Mortimer, Colleen Adel

    This study presents a comprehensive overview of the current state of the Milne Ice Shelf and how it has changed over the last 59 years. The 205 +/-1 km2 ice shelf 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 Ice Shelf suggest that basal melt is a key contributor to total ice shelf thinning. The development and expansion of new and existing surface cracks, as well as ice-marginal and epishelf lake development, indicate significant ice shelf weakening. Over the next few decades it is likely that the Milne Ice Shelf will continue to deteriorate.

  8. 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.

  9. Iceberg calving during transition from grounded to floating ice: Columbia Glacier, Alaska

    USGS Publications Warehouse

    Walter, Fabian; O'Neel, Shad; McNamara, Daniel; Pfeffer, W.T.; Bassis, Jeremy N.; Fricker, Helen Amanda

    2010-01-01

    The terminus of Columbia Glacier, Alaska, unexpectedly became ungrounded in 2007 during its prolonged retreat. Visual observations showed that calving changed from a steady release of low-volume bergs, to episodic flow-perpendicular rifting, propagation, and release of very large icebergs - a style reminiscent of calving from ice shelves. Here, we compare passive seismic and photographic observations through this transition to examine changes in calving. Mechanical changes accompany the visible changes in calving style post flotation: generation of seismic energy during calving is substantially reduced. We propose this is partly due to changes in source processes.

  10. 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.

  11. Role of ice-ocean interaction on glacier instability: Results from numerical modelling applied to Petermann Glacier

    NASA Astrophysics Data System (ADS)

    Nick, Faezeh M.; Hubbard, Alun; van der Veen, Kees; Vieli, Andreas

    2010-05-01

    Calving of icebergs and bottom melting from ice shelves accounts for roughly half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. Petermann Glacier (north Greenland) with its 16 km wide and 80 km long floating tongue, experiences massive bottom melting. We apply a numerical ice flow model using a physically-based calving criterion based on crevasse depth to investigate the contribution of processes such as bottom melting, sea ice or sikkusak disintegration, surface run off and iceberg calving to the mass balance and instability of Petermann Glacier and its ice shelf. Our modelling study provides insights into the role of ice-ocean interaction, and on how to incorporate calving in ice sheet models, improving our ability to predict future ice sheet change.

  12. NASA-ISRO synthetic aperture radar (NISAR) for temporal tracking of iceberg calving events in the Antarctica

    NASA Astrophysics Data System (ADS)

    Jawak, S. D.; Luis, A. J.

    2017-12-01

    Estimating mass loss of the Antarctic ice sheet caused by iceberg calving is a challenging job. Antarctica is surrounded by a variety of large, medium and small sized ice shelves, glacier tongues and coastal areas without offshore floating ice masses. It is possible to monitor surface structures on the continental ice and the ice shelves as well as calved icebergs using NASA-ISRO synthetic aperture radar (NISAR) satellite images in future. The NISAR, which is planned to be launched in 2020, can be used as an all-weather and all-season system to classify the coastline of Antarctica to map patterns of surface structures close to the calving front. Additionally, classifying patterns and density of surface structures distributed over the ice shelves and ice tongues can be a challenging research where NISAR can be of a great advantage. So this work explores use of NISAR to map surface structures visible on ice shelves which can provide advisories to field teams. The ice shelf fronts has been categorized into various classes based on surface structures relative to the calving front within a 30 km-wide seaward strip. The resulting map of the classified calving fronts around Antarctica and their description would provide a detailed representation of crevasse formation and dominant iceberg in the southern ocean which pose a threat to navigation of Antarctic bound ships.

  13. The far reach of ice-shelf thinning in Antarctica

    NASA Astrophysics Data System (ADS)

    Reese, R.; Gudmundsson, G. H.; Levermann, A.; Winkelmann, R.

    2018-01-01

    Floating ice shelves, which fringe most of Antarctica's coastline, regulate ice flow into the Southern Ocean1-3. Their thinning4-7 or disintegration8,9 can cause upstream acceleration of grounded ice 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 ice-shelf mass loss. We show that highly localized ice-shelf thinning can reach across the entire shelf and accelerate ice flow in regions far from the initial perturbation. As an example, this `tele-buttressing' enhances outflow from Bindschadler Ice 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 ice streams and ice rises, but also by thinning, for instance, well-within the Filchner-Ronne and Ross Ice Shelves. The most critical regions in all major ice 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.

  14. Ocean interactions with the base of Amery Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    Hellmer, Hartmut H.; Jacobs, Stanley S.

    1992-01-01

    Using a two-dimensional ocean themohaline circulation model, we varied the cavity shape beneath Amery Ice Shelf in an attempt to reproduce the 150-m-thick marine ice layer observed at the 'G1' ice core site. Most simulations caused melting rates which decrease the ice thickness by as much as 400 m between grounding line and G1, but produce only minor accumulation at the ice core site and closer to the ice front. Changes in the sea floor and ice 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 ice thickness. Model results showed temperature/salinity gradients similar to observations from beneath other ice shelves where ice is melting into seawater. Modeled outflow characteristics at the ice 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 ice. This ice is formed from water cooled by ocean/ice shelf interactions along the interior ice shelf base.

  15. Surface and basal ice shelf mass balance processes of the Southern McMurdo Ice Shelf determined through radar statistical reconnaissance

    NASA Astrophysics Data System (ADS)

    Grima, C.; Koch, I.; Greenbaum, J. S.; Soderlund, K. M.; Blankenship, D. D.; Young, D. A.; Fitzsimons, S.

    2017-12-01

    The McMurdo ice shelves (northern and southern MIS), adjacent to the eponymous station and the Ross Ice Shelf, Antarctica, are known for large gradients in surface snow accumulation and snow/ice impurities. Marine ice 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 ice once accreted at the ice shelf 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 ice-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 ice shelf surface accumulation rates. We also compare the composition of SMIS ice surface samples to test the ability of RSR to discriminate ices with varying dielectric properties (e.g., marine versus meteoric ice) and hypothesize relationships between the RSR-derived basal reflectance/scattered coefficients and accretion or melting at the ice-ocean interface. This improved knowledge of air-ice and ice-ocean boundaries provides a new perspective on the processes governing SMIS surface and basal mass balance.

  16. Modelling tidewater glacier calving: from detailed process models to simple calving laws

    NASA Astrophysics Data System (ADS)

    Benn, Doug; Åström, Jan; Zwinger, Thomas; Todd, Joe; Nick, Faezeh

    2017-04-01

    The simple calving laws currently used in ice sheet models do not adequately reflect the complexity and diversity of calving processes. To be effective, calving laws must be grounded in a sound understanding of how calving actually works. We have developed a new approach to formulating calving laws, using a) the Helsinki Discrete Element Model (HiDEM) to explicitly model fracture and calving processes, and b) the full-Stokes continuum model Elmer/Ice to identify critical stress states associated with HiDEM calving events. A range of observed calving processes emerges spontaneously from HiDEM in response to variations in ice-front buoyancy and the size of subaqueous undercuts, and we show that HiDEM calving events are associated with characteristic stress patterns simulated in Elmer/Ice. Our results open the way to developing calving laws that properly reflect the diversity of calving processes, and provide a framework for a unified theory of the calving process continuum.

  17. Role of ice-ocean interaction on glacier instability: Results from numerical modeling applied to Petermann Glacier (Invited)

    NASA Astrophysics Data System (ADS)

    Nick, F.; Hubbard, A.; Vieli, A.; van der Veen, C. J.; Box, J. E.; Bates, R.; Luckman, A. J.

    2009-12-01

    Calving of icebergs and bottom melting from ice shelves accounts for roughly half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. Petermann Glacier (north Greenland) with its 16 km wide and 80 km long floating tongue, experiences massive bottom melting. We apply a numerical ice flow model using a physically-based calving criterion based on crevasse depth to investigate the contribution of processes such as bottom melting, sea ice or sikkusak disintegration, surface run off and iceberg calving to the mass balance and instability of Petermann Glacier and its ice shelf. Our modeling study provides insights into the role of ice-ocean interaction, and on how to incorporate calving in ice sheet models, improving our ability to predict future ice sheet change.

  18. 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

  19. 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.

  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. Ocean mixing beneath Pine Island Glacier ice shelf, West Antarctica

    NASA Astrophysics Data System (ADS)

    Kimura, Satoshi; Jenkins, Adrian; Dutrieux, Pierre; Forryan, Alexander; Naveira Garabato, Alberto C.; Firing, Yvonne

    2016-12-01

    Ice 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 ice-shelf cavities. We present measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate, and thermal variance dissipation rate beneath Pine Island Glacier ice shelf, 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 ice-shelf base, with a maximum value found ˜0.5 m away from the ice. The measurements of turbulent kinetic energy dissipation rate near the ice are used to estimate basal melting of the ice shelf. 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.

  3. 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.

  4. Ice-Shelf Tidal Flexure and Subglacial Pressure Variations

    NASA Technical Reports Server (NTRS)

    Walker, Ryan T.; Parizek, Byron R.; Alley, Richard B.; Anandakrishnan, Sridhar; Riverman, Kiya L.; Christianson, Knut

    2013-01-01

    We develop a model of an ice shelf-ice 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 ice shelf dropping at low tide can cause significant (approx 1 cm) uplift in the first few kilometers of grounded ice.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 ice-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 ice would significantly change the radar reflectivity of the grounding zone and complicate the interpretation of grounded versus floating ice based on ice-penetrating radar observations.

  5. Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation

    USGS Publications Warehouse

    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

    2016-01-01

    The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (~140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

  6. Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation

    PubMed Central

    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

    2016-01-01

    The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (∼140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening. PMID:26778247

  7. Seabed topography beneath Larsen C Ice Shelf from seismic soundings

    NASA Astrophysics Data System (ADS)

    Brisbourne, A. M.; Smith, A. M.; King, E. C.; Nicholls, K. W.; Holland, P. R.; Makinson, K.

    2014-01-01

    Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-ice shelf bathymetry model derived from the inversion of IceBridge 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 ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-ice shelf oceanic circulation may be affected by ice draft and seabed depth. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Measured temperatures within the ice column and at the ice base were used to define the velocity profile through the remainder of the ice column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice 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 ice shelf. 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 IceBridge 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-ice shelf ocean circulation models.

  8. On the impact of ice-ocean interaction on Greenland glaciers versus calving speed.

    NASA Astrophysics Data System (ADS)

    Rignot, E. J.; Menemenlis, D.; Morlighem, M.; Wood, M.; Millan, R.; Mouginot, J.; An, L.

    2016-12-01

    Glacier retreat from frontal ablation is a delicate balance between subaqueous melt, calving processes and bed geometry. Here, we model subaqueous melt from a large number of Greenland tidewater glaciers using generalized 3D, high resolution simulations of ice melt from the MITgcm ocean model constrained by subglacial melt from RACMO2.3 and ISSM, ocean temperature from ECCO2-4km Arctic, and bed topography from OMG and MC for 1992-2015. The results are analyzed in combination with ice-front retreat and glacier speed from Landsat and imaging radar data since the 1990s. We find that subaqueous melt is 2-3 times greater in summer than in winter and doubled in magnitude since the 1990s because of enhanced ice sheet runoff and warmer ocean temperature. Glaciers that retreated rapidly are characterized by subaqueous melt rates comparable to their calving speed and favorable bed geometry. Glaciers dominated by calving processes are in contrast more resilient to thermal forcing from the ocean, especially in the presence of stabilizing geometry. The study highlights the fundamental importance of calving processes in controlling glacier retreat in Greenland.

  9. 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.

  10. 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.

  11. 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

  12. Flexural-gravity Wave Attenuation in a Thick Ice Shelf

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    A thirty-four station broadband seismic array was deployed on the Ross Ice Shelf, 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 shelf 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 ice shelf are 50 dB higher than those on grounded ice. 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 shelf 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 ice shelves and potentially trigger disintegration events. These measurements indicate that the propensity for shelf weakening and disintegration decays exponentially with distance from the ice front for gravity waves in the 0.003 to 0.02Hz band.

  13. 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.

  14. 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.

  15. Hydroelastic analysis of ice shelves under long wave excitation

    NASA Astrophysics Data System (ADS)

    Papathanasiou, T. K.; Karperaki, A. E.; Theotokoglou, E. E.; Belibassakis, K. A.

    2015-05-01

    The transient hydroelastic response of an ice shelf under long wave excitation is analysed by means of the finite element method. The simple model, presented in this work, is used for the simulation of the generated kinematic and stress fields in an ice shelf, when the latter interacts with a tsunami wave. The ice shelf, being of large length compared to its thickness, is modelled as an elastic Euler-Bernoulli beam, constrained at the grounding line. The hydrodynamic field is represented by the linearised shallow water equations. The numerical solution is based on the development of a special hydroelastic finite element for the system of governing of equations. Motivated by the 2011 Sulzberger Ice Shelf (SIS) calving event and its correlation with the Honshu Tsunami, the SIS stable configuration is studied. The extreme values of the bending moment distribution in both space and time are examined. Finally, the location of these extrema is investigated for different values of ice shelf thickness and tsunami wave length.

  16. Hydroelastic analysis of ice shelves under long wave excitation

    NASA Astrophysics Data System (ADS)

    Papathanasiou, T. K.; Karperaki, A. E.; Theotokoglou, E. E.; Belibassakis, K. A.

    2015-08-01

    The transient hydroelastic response of an ice shelf under long wave excitation is analysed by means of the finite element method. The simple model, presented in this work, is used for the simulation of the generated kinematic and stress fields in an ice shelf, when the latter interacts with a tsunami wave. The ice shelf, being of large length compared to its thickness, is modelled as an elastic Euler-Bernoulli beam, constrained at the grounding line. The hydrodynamic field is represented by the linearised shallow water equations. The numerical solution is based on the development of a special hydroelastic finite element for the system of governing of equations. Motivated by the 2011 Sulzberger Ice Shelf (SIS) calving event and its correlation with the Honshu Tsunami, the SIS stable configuration is studied. The extreme values of the bending moment distribution in both space and time are examined. Finally, the location of these extrema is investigated for different values of ice shelf thickness and tsunami wave length.

  17. 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.

  18. A Mathematical Model of Melt Lake Development on an Ice Shelf

    NASA Astrophysics Data System (ADS)

    Buzzard, S. C.; Feltham, D. L.; Flocco, D.

    2018-02-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. Melt lakes have been implicated in ice shelf collapse; Antarctica's Larsen B Ice Shelf 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 ice shelf. The model incorporates a calculation of the ice shelf surface energy balance, heat transfer through the firn, the production and percolation of meltwater into the firn, the formation of ice lenses, and the development and refreezing of surface melt lakes. The model is applied to the Larsen C Ice Shelf, 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 ice shelf evolution within climate models, of which our model could form the basis for the thermodynamic component.

  19. 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

  20. Ice Island Calves off Petermann Glacier

    NASA Image and Video Library

    2017-12-08

    NASA image acquired August 11, 2010. After breaking off the Petermann Glacier on August 5, 2010, a massive ice island floated slowly down the fjord toward the Nares Strait. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite captured this false-color image of the ice island on August 11, 2010. In this image, ice is light blue, water is nearly black, and clouds are nearly white. Although a bank of thin clouds hovers over the fjord, the southernmost margin of the ice island is still visible. Toward the north, the leading edge of the ice island retains the same shape it had days earlier, at the time of the initial calving. NASA Earth Observatory image created by Jesse Allen, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. Caption by Michon Scott. Instrument: Terra - ASTER To see more images from of the glacier go to: earthobservatory.nasa.gov/NaturalHazards/event.php?id=45116 NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe. Follow us on Twitter Join us on Facebook

  1. 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

  2. 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.

  3. Results from ISOMIP+ and MISOMIP1, two interrelated marine ice sheet and ocean model intercomparison projects

    NASA Astrophysics Data System (ADS)

    Asay-Davis, X.; Galton-Fenzi, B.; Gwyther, D.; Jourdain, N.; Martin, D. F.; Nakayama, Y.; Seroussi, H. L.

    2016-12-01

    MISMIP+ (the third Marine Ice Sheet MIP), ISOMIP+ (the second Ice Shelf-Ocean MIP) and MISOMIP1 (the first Marine Ice Sheet-Ocean MIP) prescribe a set of idealized experiments for marine ice-sheet models, ocean models with ice-shelf cavities, and coupled ice sheet-ocean models, respectively. Here, we present results from ISOMIP+ and MISOMIP1 experiments using several ocean-only and coupled ice sheet-ocean models. Among the ocean models, we show that differences in model behavior are significant enough that similar results can only be achieved by tuning model parameters (the heat- and salt-transfer coefficients across the sub-ice-shelf boundary layer) for each model. This tuning is constrained by a desired mean melt rate in quasi-steady state under specified forcing conditions, akin to tuning the models to match observed melt rates. We compare the evolution of ocean temperature transects, melt rate, friction velocity and thermal driving between ocean models for the five ISOMIP+ experiments (Ocean0-4), which have prescribed ice-shelf topography. We find that melt patterns differ between models based on the relative importance of overturning strength and vertical mixing of temperature even when the models have been tuned to achieve similar melt rates near the grounding line. For the two MISOMIP1 experiments (IceOcean1 without dynamic calving and IceOcean2 with a simple calving parameterization), we compare temperature transects, melt rate, ice-shelf topography and grounded area across models and for several model configurations. Consistent with preliminary results from MISMIP+, we find that for a given coupled model, the use of a Coulomb-limited basal friction parameterization below grounded ice and the application of dynamic calving both significantly increase the rate of grounding-line retreat, whereas the rate of retreat appears to be less sensitive to the ice stress approximation (shallow-shelf approximation, higher-order, etc.). We show that models with similar

  4. Variability of Basal Melt Beneath the Pine Island Glacier Ice Shelf, West Antarctica

    NASA Technical Reports Server (NTRS)

    Bindschadler, Robert; Vaughan, David G.; Vornberger, Patricia

    2011-01-01

    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 ice shelf, West Antarctica, by ocean waters. Satellite imagery shows surface features that suggest ice-shelf-wide changes to the ocean s influence on the ice shelf as the grounding line retreated. Longitudinal profiles of ice 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-ice-shelf melting. Ice surface troughs are hydrostatically compensated by ice-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 ice shelf of 22%. Residual warm water is believed to cause three persistent polynyas at the ice-shelf front seen in Landsat imagery. Landsat thermal imagery confirms the occurrence of warm water at the same locations.

  5. 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.

  6. Basal melt rates of Filchner Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Humbert, A.; Nicholls, K. W.; Corr, H. F. J.; Steinhage, D.; Stewart, C.; Zeising, O.

    2017-12-01

    Thinning of ice 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-ice shelf 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 ice 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 Ice Shelf, 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 Ice Shelf, 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.

  7. Ocean forcing of Ice Sheet retreat in central west Greenland from LGM to the early Holocene

    NASA Astrophysics Data System (ADS)

    Jennings, Anne E.; Andrews, John T.; Ó Cofaigh, Colm; Onge, Guillaume St.; Sheldon, Christina; Belt, Simon T.; Cabedo-Sanz, Patricia; Hillaire-Marcel, Claude

    2017-08-01

    Three radiocarbon dated sediment cores from trough mouth fans on the central west Greenland continental slope were studied to determine the timing and processes of Greenland Ice Sheet (GIS) retreat from the shelf edge during the last deglaciation and to test the role of ocean forcing (i.e. warm ocean water) thereon. Analyses of lithofacies, quantitative x-ray diffraction mineralogy, benthic foraminiferal assemblages, the sea-ice biomarker IP25, and δ18 O of the planktonic foraminifera Neogloboquadrina pachyderma sinistral from sediments in the interval from 17.5-10.8 cal ka BP provide consistent evidence for ocean and ice sheet interactions during central west Greenland (CWG) deglaciation. The Disko and Uummannaq ice streams both retreated from the shelf edge after the last glacial maximum (LGM) under the influence of subsurface, warm Atlantic Water. The warm subsurface water was limited to depths below the ice stream grounding lines during the LGM, when the GIS terminated as a floating ice shelf in a sea-ice covered Baffin Bay. The deeper Uummannaq ice stream retreated first (ca. 17.1 cal ka BP), while the shallower Disko ice stream retreated at ca. 16.2 cal ka BP. The grounding lines were protected from accelerating mass loss (calving) by a buttressing ice shelf and by landward shallowing bathymetry on the outer shelf. Calving retreat was delayed until ca. 15.3 cal ka BP in the Uummannaq Trough and until 15.1 cal ka BP in the Disko Trough, during another interval of ocean warming. Instabilities in the Laurentide, Innuitian and Greenland ice sheets with outlets draining into northern Baffin Bay periodically released cold, fresh water that enhanced sea ice formation and slowed GIS melt. During the Younger Dryas, the CWG records document strong cooling, lack of GIS meltwater, and an increase in iceberg rafted material from northern Baffin Bay. The ice sheet remained in the cross-shelf troughs until the early Holocene, when it retreated rapidly by calving and strong

  8. 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.

  9. 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.

  10. Sea-level response to ice sheet evolution: An ocean perspective

    NASA Technical Reports Server (NTRS)

    Jacobs, Stanley S.

    1991-01-01

    The ocean's influence upon and response to Antarctic ice sheet changes is considered in relation to sea level rise over recent and future decades. Assuming present day ice fronts are in approximate equilibrium, a preliminary budget for the ice sheet is estimated from accumulation vs. iceberg calving and the basal melting that occurs beneath floating ice shelves. Iceberg calving is derived from the volume of large bergs identified and tracked by the Navy/NOAA Joint Ice Center and from shipboard observations. Basal melting exceeds 600 cu km/yr and is concentrated near the ice fronts and ice shelf grounding lines. An apparent negative mass balance for the Antarctic ice sheet may result from an anomalous calving rate during the past decade, but there are large uncertainties associated with all components of the ice 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 Antarctic Ice Sheet Initiative.

  11. 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.

  12. 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.

  13. Simultaneous observations of ice motion, calving and seismicity on the Yahtse Glacier, Alaska. (Invited)

    NASA Astrophysics Data System (ADS)

    Larsen, C. F.; Bartholomaus, T. C.; O'Neel, S.; West, M. E.

    2010-12-01

    We observe ice motion, calving and seismicity simultaneously and with high-resolution on an advancing tidewater glacier in Icy Bay, Alaska. Icy Bay’s tidewater glaciers dominate regional glacier-generated seismicity in Alaska. Yahtse emanates from the St. Elias Range near the Bering-Bagley-Seward-Malaspina Icefield system, the most extensive glacier cover outside the polar regions. Rapid rates of change and fast flow (>16 m/d near the terminus) at Yahtse Glacier provide a direct analog to the disintegrating outlet systems in Greenland. Our field experiment co-locates GPS and seismometers on the surface of the glacier, with a greater network of bedrock seismometers surrounding the glacier. Time-lapse photogrammetry, fjord wave height sensors, and optical survey methods monitor iceberg calving and ice velocity near the terminus. This suite of geophysical instrumentation enables us to characterize glacier motion and geometry changes while concurrently listening for seismic energy release. We are performing a close examination of calving as a seismic source, and the associated mechanisms of energy transfer to seismic waves. Detailed observations of ice motion (GPS and optical surveying), glacier geometry and iceberg calving (direct observations and timelapse photogrammetry) have been made in concert with a passive seismic network. Combined, the observations form the basis of a rigorous analysis exploring the relationship between glacier-generated seismic events and motion, glacier-fiord interactions, calving and hydraulics. Our work is designed to demonstrate the applicability and utility of seismology to study the impact of climate forcing on calving glaciers.

  14. Ocean stratification reduces melt rates at the grounding zone of the Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

    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.

    2017-12-01

    Ocean-driven melting of ice shelves is often invoked as the primary mechanism for triggering ice loss from Antarctica. However, due to the difficulty in accessing the sub-ice-shelf ocean cavity, the relationship between ice-shelf melt rates and ocean conditions is poorly understood, particularly near the transition from grounded to floating ice, known as the grounding zone. Here we present the first borehole oceanographic observations from the grounding zone of Antarctica's largest ice shelf. Contrary to predictions that tidal currents near grounding zones should mix the water column, driving high ice-shelf melt rates, we find a stratified sub-ice-shelf 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 ice-shelf 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.

  15. Long-term observing system for the oceanic regime of Filchner-Ronne Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Østerhus, Svein; Schröder, Michael; Hellmer, Hartmunt; Darelius, Elin; Nicholls, Keith; Makinson, Keith

    2014-05-01

    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 Shelf Water (HSSW) on the continental shelf north of Ronne Ice Front, the transformation to Ice Shelf Water (ISW) beneath the floating Filchner-Ronne ice shelf, and the flux of ISW overflowing the shelf break to the deep Weddell Sea. Equally important is the return flow of warm water toward the Filchner-Ronne Ice Shelf 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-ice shelf 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 Ice 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 ice shelf. In 1999 we established Site 5 on Ronne Ice Shelf using a hot-water drill to access

  16. 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.

  17. 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.

  18. Ice-ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers

    NASA Astrophysics Data System (ADS)

    Chauché, N.; Hubbard, A.; Gascard, J.-C.; Box, J. E.; Bates, R.; Koppes, M.; Sole, A.; Christoffersen, P.; Patton, H.

    2014-08-01

    Warm, subtropical-originating Atlantic water (AW) has been identified as a primary driver of mass loss across the marine sectors of the Greenland Ice Sheet (GrIS), yet the specific processes by which this water mass interacts with and erodes the calving front of tidewater glaciers is frequently modelled and much speculated upon but remains largely unobserved. We present a suite of fjord salinity, temperature, turbidity versus depth casts along with glacial runoff estimation from Rink and Store glaciers, two major marine outlets draining the western sector of the GrIS during 2009 and 2010. We characterise the main water bodies present and interpret their interaction with their respective calving fronts. We identify two distinct processes of ice-ocean interaction which have distinct spatial and temporal footprints: (1) homogenous free convective melting which occurs across the calving front where AW is in direct contact with the ice mass, and (2) localised upwelling-driven melt by turbulent subglacial runoff mixing with fjord water which occurs at distinct injection points across the calving front. Throughout the study, AW at 2.8 ± 0.2 °C was consistently observed in contact with both glaciers below 450 m depth, yielding homogenous, free convective submarine melting up to ~200 m depth. Above this bottom layer, multiple interactions are identified, primarily controlled by the rate of subglacial fresh-water discharge which results in localised and discrete upwelling plumes. In the record melt year of 2010, the Store Glacier calving face was dominated by these runoff-driven plumes which led to a highly crenulated frontal geometry characterised by large embayments at the subglacial portals separated by headlands which are dominated by calving. Rink Glacier, which is significantly deeper than Store has a larger proportion of its submerged calving face exposed to AW, which results in a uniform, relatively flat overall frontal geometry.

  19. 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.

  20. 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.

  1. 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

  2. Sediment features at the grounding zone and beneath Ekström Ice Shelf, East Antarctica, imaged using on-ice vibroseis.

    NASA Astrophysics Data System (ADS)

    Smith, Emma C.; Eisen, Olaf; Hofstede, Coen; Lambrecht, Astrid; Mayer, Christoph

    2017-04-01

    The grounding zone, where an ice sheet becomes a floating ice shelf, is known to be a key threshold region for ice flow and stability. A better understanding of ice dynamics and sediment transport across such zones will improve knowledge about contemporary and palaeo ice flow, as well as past ice extent. Here we present a set of seismic reflection profiles crossing the grounding zone and continuing to the shelf edge of Ekström Ice Shelf, East Antarctica. Using an on-ice vibroseis source combined with a snowstreamer we have imaged a range of sub-glacial and sub-shelf 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 ice dynamics to quantify past and present interactions between ice and the solid Earth in East Antarctica; leading to a better understanding of future contributions of this region to sea-level rise.

  3. Can Thermal Bending Fracture Ice Shelves?

    NASA Astrophysics Data System (ADS)

    MacAyeal, D. R.; Sergienko, O. V.; Banwell, A. F.; Willis, I.; Macdonald, G. J.; Lin, J.

    2017-12-01

    Visco-elastic plates will bend if the temperature on one side is cooled. If the plate is constrained to float, as for sea ice floes, this bending will lead to tensile stresses that can fracture the ice. The hydroacoustic regime below sea ice displays increased fracture-sourced noise when air temperatures above the ice cools with the diurnal cycle. The McMurdo Ice Shelf, Antarctica, also displays a massive increase in seismicity during the cooling phase of the diurnal cycle, and this motivates the question: Can surface cooling (or other forcing with thermal consequences) drive through-thickness fracture leading to iceberg calving? Past study of this question for sea ice gives an upper limit of ice-plate thickness (order meters) for which diurnal-scale thermal bending fracture can occur; but could cooling with longer time scales induce fracture of thicker ice plates? Given the seismic evidence of thermal bending fracture on the McMurdo Ice Shelf, the authors examine this question further.

  4. Growing Crack in Antarctica Larsen C Ice Shelf Spotted by NASA MISR

    NASA Image and Video Library

    2016-08-31

    Project MIDAS, a United Kingdom-based group that studies the Larsen Ice Shelf in Antarctica, reported Aug. 18, 2016, that a large crack in the Larsen C shelf 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 ice shelf 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 ice shelf to collapse, resulting in the loss of 2,300 square miles (6,000 square kilometers) of ice -- more than the area of Delaware. This follows the collapse of the Larsen B shelf in 2002 and the Larsen A shelf in 1995, which removed about 1,255 square miles (3,250 square kilometers) and 580 square miles (1,500 square kilometers) of ice, 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 shelf 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 shelf is on the left, while thinner sea ice is present on the right. A variety of cracks are visible in the Larsen C shelf, 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

  5. Does Arctic sea ice reduction foster shelf-basin exchange?

    PubMed

    Ivanov, Vladimir; Watanabe, Eiji

    2013-12-01

    The recent shift in Arctic ice conditions from prevailing multi-year ice to first-year ice will presumably intensify fall-winter sea ice 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 ice, 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 ice production influences shelf-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 ice formation was calculated as part of a 30-year experiment of the pan-Arctic coupled ice-ocean general circulation model (GCM). The GCM results indicate that mechanical sea ice divergence associated with lateral advection accounts for a significant part of the interannual variations in sea ice 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 ice formation depend on geographical location and shelf-basin bathymetry. In the Pacific sector, strong density stratification in slope waters impedes noticeable deepening of shelf-origin water, even for the strongest forcing applied. In the Atlantic sector, a 1.5x increase of

  6. 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.

  7. Boundary condition of grounding lines prior to collapse, Larsen-B Ice Shelf, Antarctica.

    PubMed

    Rebesco, M; Domack, E; Zgur, F; Lavoie, C; Leventer, A; Brachfeld, S; Willmott, V; Halverson, G; Truffer, M; Scambos, T; Smith, J; Pettit, E

    2014-09-12

    Grounding zones, where ice sheets transition between resting on bedrock to full floatation, help regulate ice flow. Exposure of the sea floor by the 2002 Larsen-B Ice Shelf 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 ice 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 ice shelf collapse. This implies that the 2002 Larsen-B Ice Shelf 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 Ice Shelf. Copyright © 2014, American Association for the Advancement of Science.

  8. 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. 

  9. 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

    Totten Glacier drains at least 3.5 meters of eustatic sea level potential from marine-based ice in the Aurora Subglacial Basin (ASB) in East Antarctica, more than the combined total of all glaciers in West Antarctica. Totten Glacier has been the most rapidly thinning glacier in East Antarctica since satellite altimetry time series began and the nature of the thinning suggests that it is driven by enhanced basal melting due to ocean processes. While grounded ice thinning rates have been steady, recent work has shown that Totten's floating ice shelf may not have the same thinning behavior; as a result, it is critical to observe ice shelf and cavity boundary conditions and basal processes to understand this apparent discrepancy. Warm Modified Circumpolar Deep Water (MCDW), which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby Sabrina Coast continental shelf and deep depressions in the seafloor provide access for MCDW to reach the ice shelf cavity. Given its northern latitude, numerical ice sheet modeling indicates that Totten Glacier may be prone to retreat caused by hydrofracture in a warming climate, so it is important to understand how intruding MCDW is affecting thinning of Totten Glacier's ice shelf. Here we use post-processed, focused airborne radar observations of the Totten Glacier Ice Shelf to delineate multi-km wide basal channels and flat basal terraces associated with high basal reflectivity and specularity (flatness) anomalies and correspondingly large ice surface depressions that indicate active basal melting. Using a simple temperature-attenuation model, and basal roughness corrections, we present basal melt rates associated with the radar reflection and specularity anomalies and compare them to those derived from numerical ocean circulation modeling and an ice flow divergence calculation. Sub-ice shelf ocean circulation modeling and under-ice robotic observations of Pine Island Glacier Ice

  10. 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.

  11. A calving law for ice sheet models; Investigating the role of surface melt on dynamics of Greenland outlet glaciers

    NASA Astrophysics Data System (ADS)

    Nick, F. M.; van der Veen, C. J.; Vieli, A.

    2008-12-01

    alving of icebergs accounts for perhaps as much as half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. We have formulated a calving model that can be readily incorporated into time-evolving numerical ice-flow models. Our model is based on downward penetration of water-filled surface crevasses and upward propagation of basal crevasses. A calving event occurs when the depth of the surface crevasse (which increases as melting progresses through the summer) reaches the height of the basal crevasse. Our numerical ice sheet model is able to reproduce observed seasonal changes of Greenland outlet glaciers, such as fluctuations in flow speed and terminus positions. We have applied the model to Helheim Glacier on the east coast, and Petermann Glacier in the northwest. Our model suggests that rapid retreat of the claving front is highly affected by the amplified calving rate due to increasing water level in surface crevasses during warmer summers. Our results show little response to seasonally enhanced basal lubrication from surface melt. This modeling study provides insights into the role of surface and basal hydrology to ice sheet dynamics and on how to incorporate calving in ice sheet models and therefore advances our ability to predict future ice sheet change.

  12. Sulzberger Ice Shelf Tidal Signal Reconstruction Using InSAR

    NASA Astrophysics Data System (ADS)

    Baek, S.; Shum, C.; Yi, Y.; Kwoun, O.; Lu, Z.; Braun, A.

    2005-12-01

    Synthetic Aperture Radar Interferometry (InSAR) and Differential InSAR (DInSAR) have been demonstrated as useful techniques to detect surface deformation over ice sheet and ice 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 ice shelf. 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 Ice Shelf, West Antarctica. Tidal differences measured by InSAR are obtained by the phase difference between a point on the grounded ice and a point on ice shelf. 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.

  13. Arctic continental shelf morphology related to sea-ice zonation, Beaufort Sea, Alaska

    USGS Publications Warehouse

    Reimnitz, E.; Toimil, L.; Barnes, P.

    1978-01-01

    Landsat-1 and NOAA satellite imagery for the winter 1972-1973, and a variety of ice and sea-floor data were used to study sea-ice zonation and dynamics and their relation to bottom morphology and geology on the Beaufort Sea continental shelf of arctic Alaska. In early winter the location of the boundary between undeformed fast ice and westward-drifting pack ice 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-ice drift and slippage is continuous along the shelf edge, at average rates of 3-10 km/day. Whether slippage occurs along the stamukhi zone or along the shelf edge, it is restricted to a zone several hundred meters wide, and ice seaward of the slip face moves at uniform rates without discernible drag effects. A causal relationship is seen between the spatial distribution of major ice-ridge systems and offshore shoals downdrift of major coastal promontories. The shoals appear to have migrated shoreward under the influence of ice up to 400 m in the last 25 years. The sea floor seaward of these shoals within the stamukhi zone shows high ice-gouge density, large incision depths, and a high degree of disruption of internal sedimentary structures. The concentration of large ice ridges and our sea floor data in the stamukhi zone indicate that much of the available marine energy is expended here, while the inner shelf and coast, where the relatively undeformed fast ice grows, are sheltered. There is evidence that anomalies in the overall arctic shelf profile are related to sea-ice zonation, ice dynamics, and bottom

  14. 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.

  15. Ice stream reorganization and glacial retreat on the northwest Greenland shelf

    NASA Astrophysics Data System (ADS)

    Newton, A. M. W.; Knutz, P. C.; Huuse, M.; Gannon, P.; Brocklehurst, S. H.; Clausen, O. R.; Gong, Y.

    2017-08-01

    Understanding conditions at the grounding-line of marine-based ice sheets is essential for understanding ice sheet evolution. Offshore northwest Greenland, knowledge of the Last Glacial Maximum (LGM) ice 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 ice sheet reached the shelf edge before undergoing flow reorganization. After retreat of 80 km across the outer shelf, the margin stabilized in a mid-shelf position, possibly during the Younger Dryas (12.9-11.7 ka). The ice 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.

  16. 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.

  17. 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.

  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. 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

    Theory, modeling, and observations indicate that marine ice sheets on a retrograde bed, including Thwaites Glacier, Antarctica, are only conditionally stable. Previous modeling studies have shown that rapid, unstable retreat can occur when steady ice-shelf basal melting causes the grounding line to retreat past restraining bedrock bumps. Here we explore the initiation and evolution of unstable retreat of Thwaites Glacier when the ice-shelf basal melt forcing includes temporal variability mimicking realistic climate variability. We use the three-dimensional, higher-order Model for Prediction Across Scales-Land Ice (MPASLI) model forced with an ice shelf basal melt parameterization derived from previous coupled ice sheet/ocean simulations. We add sinusoidal temporal variability to the melt parameterization that represents shoaling and deepening of Circumpolar Deep Water. We perform an ensemble of 250 year duration simulations with different values for the amplitude, period, and phase of the variability. Preliminary results suggest that, overall, variability leads to slower grounding line retreat and less mass loss than steady simulations. Short period (2 yr) variability leads to similar results as steady forcing, whereas decadal variability can result in up to one-third less mass loss. Differences in phase lead to a large range in mass loss/grounding line retreat, but it is always less than the steady forcing. The timing of ungrounding from each restraining bedrock bump, which is strongly affected by the melt variability, is the rate limiting factor, and variability-driven delays in ungrounding at each bump accumulate. Grounding line retreat in the regions between bedrock bumps is relatively unaffected by ice shelf melt variability. While the results are sensitive to the form of the melt parameterization and its variability, we conclude that decadal period ice shelf melt variability could potentially delay marine ice sheet instability by up to many decades. However

  20. 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.

  1. 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

  2. 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.

  3. 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

  4. 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

  5. Ice-shelf collapse from subsurface warming as a trigger for Heinrich events

    PubMed Central

    Marcott, Shaun A.; Clark, Peter U.; Padman, Laurie; Klinkhammer, Gary P.; Springer, Scott R.; Liu, Zhengyu; Otto-Bliesner, Bette L.; Carlson, Anders E.; Ungerer, Andy; Padman, June; He, Feng; Cheng, Jun; Schmittner, Andreas

    2011-01-01

    Episodic iceberg-discharge events from the Hudson Strait Ice Stream (HSIS) of the Laurentide Ice Sheet, referred to as Heinrich events, are commonly attributed to internal ice-sheet instabilities, but their systematic occurrence at the culmination of a large reduction in the Atlantic meridional overturning circulation (AMOC) indicates a climate control. We report Mg/Ca data on benthic foraminifera from an intermediate-depth site in the northwest Atlantic and results from a climate-model simulation that reveal basin-wide subsurface warming at the same time as large reductions in the AMOC, with temperature increasing by approximately 2 °C over a 1–2 kyr interval prior to a Heinrich event. In simulations with an ocean model coupled to a thermodynamically active ice shelf, the increase in subsurface temperature increases basal melt rate under an ice shelf fronting the HSIS by a factor of approximately 6. By analogy with recent observations in Antarctica, the resulting ice-shelf loss and attendant HSIS acceleration would produce a Heinrich event. PMID:21808034

  6. 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

  7. Frazil-ice growth rate and dynamics in mixed layers and sub-ice-shelf plumes

    NASA Astrophysics Data System (ADS)

    Rees Jones, David W.; Wells, Andrew J.

    2018-01-01

    The growth of frazil or granular ice is an important mode of ice formation in the cryosphere. Recent advances have improved our understanding of the microphysical processes that control the rate of ice-crystal growth when water is cooled beneath its freezing temperature. These advances suggest that crystals grow much faster than previously thought. In this paper, we consider models of a population of ice crystals with different sizes to provide insight into the treatment of frazil ice in large-scale models. We consider the role of crystal growth alongside the other physical processes that determine the dynamics of frazil ice. We apply our model to a simple mixed layer (such as at the surface of the ocean) and to a buoyant plume under a floating ice shelf. We provide numerical calculations and scaling arguments to predict the occurrence of frazil-ice explosions, which we show are controlled by crystal growth, nucleation, and gravitational removal. Faster crystal growth, higher secondary nucleation, and slower gravitational removal make frazil-ice explosions more likely. We identify steady-state crystal size distributions, which are largely insensitive to crystal growth rate but are affected by the relative importance of secondary nucleation to gravitational removal. Finally, we show that the fate of plumes underneath ice shelves is dramatically affected by frazil-ice dynamics. Differences in the parameterization of crystal growth and nucleation give rise to radically different predictions of basal accretion and plume dynamics, and can even impact whether a plume reaches the end of the ice shelf or intrudes at depth.

  8. Field Investigation of Surface-Lake Processes on Ice Shelves: Results of the 2015/16 Field Campaign on McMurdo Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    MacAyeal, Doug; Banwell, Alison; Willis, Ian; Macdonald, Grant

    2016-04-01

    Ice-shelf instability and breakup of the style exhibited by Larsen B Ice Shelf in 2002 remains the most difficult glaciological process of consequence to observe in detail. 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 been proposed, including the ability of surface lakes to introduce ice-shelf fractures when they fill and drain, thereby changing the surface loads the ice-shelf must adjust to. Our model suggest that these fractures resulted in a chain-reaction style drainage of >2750 surface lakes on the Larsen B in the days prior to its demise. To validate this and other models, we began a field project on the McMurdo Ice Shelf (MIS) during the 2015/16 austral summer. Advantages of the MIS study site are: there is considerable surface melting during 3-6 weeks of the summer season, the ice is sufficiently thin (< 30 m in places) to allow observable viscoelastic responses to relatively small loads, and it is close to a center of logistical support (McMurdo Station). Here we show initial results from the field campaign, including GPS and water-depth observations of a lake that has filled and drained over multiple week timescales in previous austral summers. We also report on the analysis of high-resolution WorldView satellite imagery from several summers that reveals the complexity of surface meltwater movement in channels and subsurface void spaces. Initial reconnaissance of the largest surface-lake features reveal that they have a central circular depression surrounded by an uplifted ring, which supports one of the central tenets of our ice-shelf flexure theory. A second field season is anticipated for the 2016/17 austral summer.

  9. 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

  10. The kinematic response of Petermann Glacier, Greenland to ice shelf perturbation

    NASA Astrophysics Data System (ADS)

    Hubbard, A.; Box, J. E.; Bates, R.; Nick, F.; Luckman, A. J.; van de Wal, R.; Doyle, S. H.

    2010-12-01

    The acceleration and dynamic thinning of interior zones of the polar ice sheets due to outlet/ice shelf retreat has been identified as a factor hastening their demise and contribution to global sea-level rise. The detachment of a 275 square km area of the Petermann Glacier ice shelf in August, 2010 presents a natural experiment to investigate the timing, mechanisms and efficacy of upstream dynamic feedbacks resulting from a singular but potentially significant frontal perturbation. In 2009, a permanent geodetic/differential GPS strain network logging every 10 seconds was deployed along a 200 km longitudinal profile from the ice front across the grounding line extending into the interior of Petermann Glacier to characterize the system’s state before, during and after any such event. We present an overview of the geophysical measurements conducted and analyze the kinematics of the shelf detachment in relation to local environmental forcing. Finally, we discuss the postulated instantaneous and ongoing evolution in force-balance and concomitant dynamic response resulting from the perturbation along with its implications for Petermann's ongoing stability. Petermann Glacier GNSS base & telemetric GPS facility: community AA & rehab meet point. On ice geodetic-GPS station flat out & reading 0 Volts

  11. Observed vulnerability of Filchner-Ronne Ice Shelf to wind-driven inflow of warm deep water.

    PubMed

    Darelius, E; Fer, I; Nicholls, K W

    2016-08-02

    The average rate of melting at the base of the large Filchner-Ronne Ice Shelf in the southern Weddell Sea is currently low, but projected to increase dramatically within the next century. In a model study, melt rates increase as changing ice conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner Ice Shelf cavity. Here we present observations from near Filchner Ice Shelf and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the ice front. This southward heat transport follows the eastern flank of the Filchner Depression and is found to be directly linked to the strength of a wind-driven coastal current. Our observations emphasize the potential sensitivity of Filchner-Ronne Ice Shelf melt rates to changes in wind forcing.

  12. Observed vulnerability of Filchner-Ronne Ice Shelf to wind-driven inflow of warm deep water

    PubMed Central

    Darelius, E.; Fer, I.; Nicholls, K. W.

    2016-01-01

    The average rate of melting at the base of the large Filchner-Ronne Ice Shelf in the southern Weddell Sea is currently low, but projected to increase dramatically within the next century. In a model study, melt rates increase as changing ice conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner Ice Shelf cavity. Here we present observations from near Filchner Ice Shelf and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the ice front. This southward heat transport follows the eastern flank of the Filchner Depression and is found to be directly linked to the strength of a wind-driven coastal current. Our observations emphasize the potential sensitivity of Filchner-Ronne Ice Shelf melt rates to changes in wind forcing. PMID:27481659

  13. 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.

  14. Characteristics and processing of seismic data collected on thick, floating ice: Results from the Ross Ice Shelf, Antarctica

    USGS Publications Warehouse

    Beaudoin, Bruce C.; ten Brink, Uri S.; Stern, Tim A.

    1992-01-01

    Coincident reflection and refraction data, collected in the austral summer of 1988/89 by Stanford University and the Geophysical Division of the Department of Scientific and Industrial Research, New Zealand, imaged the crust beneath the Ross Ice Shelf, Antarctica. The Ross Ice Shelf is a unique acquisition environment for seismic reflection profiling because of its thick, floating ice cover. The ice shelf velocity structure is multilayered with a high velocity‐gradient firn layer constituting the upper 50 to 100 m. This near surface firn layer influences the data character by amplifying and frequency modulating the incoming wavefield. In addition, the ice‐water column introduces pervasive, high energy seafloor, intra‐ice, and intra‐water multiples that have moveout velocities similar to the expected subseafloor primary velocities. Successful removal of these high energy multiples relies on predictive deconvolution, inverse velocity stack filtering, and frequency filtering. Removal of the multiples reveals a faulted, sedimentary wedge which is truncated at or near the seafloor. Beneath this wedge the reflection character is diffractive to a two‐way traveltime of ∼7.2 s. At this time, a prominent reflection is evident on the southeast end of the reflection profile. This reflection is interpreted as Moho indicating that the crust is ∼21-km thick beneath the profile. These results provide seismic evidence that the extensional features observed in the Ross Sea region of the Ross Embayment extend beneath the Ross Ice Shelf.

  15. Antarctic ice sheet mass loss estimates using Modified Antarctic Mapping Mission surface flow observations

    NASA Astrophysics Data System (ADS)

    Ren, Diandong; Leslie, Lance M.; Lynch, Mervyn J.

    2013-03-01

    The long residence time of ice and the relatively gentle slopes of the Antarctica Ice Sheet make basal sliding a unique positive feedback mechanism in enhancing ice discharge along preferred routes. The highly organized ice 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 ice flow. In this study, constraining the model-simulated year 2000 ice flow fields with surface velocities obtained from InSAR measurements permits retrieval of the basal sliding parameters. Forward integrations of the ice model driven by atmospheric and oceanic parameters from coupled general circulation models under different emission scenarios provide a range of estimates of total ice 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 Ice Sheet in a warming climate is due primarily to a dynamic response in the form of an increase in ice flow speed. Ice shelves contribute to this feedback through a reduced buttressing effect due to more frequent systematic, tabular calving events. For example, by 2100 the Ross Ice Shelf is projected to shed 40 km3 during each systematic tabular calving. After the frontal section's attrition, the remaining shelf 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 ice shelves, oceanic effects likely will play a very important role in the future mass balance of the Antarctica Ice Sheet, under a possible future warming climate.

  16. 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.

  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. Fives decades of strong temporal variability in the flow of the Brunt Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    De Rydt, Jan; Gudmundsson, Hilmar; Nagler, Thomas

    2017-04-01

    The Brunt Ice Shelf, East Antarctica, is a complex conglomerate of meteoric and marine ice, weakly connected to the much larger and faster-flowing Stancomb Wills Glacier Tongue to the east, and pinned down to the seabed in a small area around the McDonalds Ice Rumples in the north. The ice shelf is home to the UK research station Halley, from which changes to the ice shelf have been monitored closely since the 1960s. A unique 50-year record of the flow speed and an intense surveying programme over the past 10 years, have revealed a strong temporal variability in the flow. In particular, the speed of the ice shelf has increased by 10% each year over the past few years. In order to understand these rapid changes, we use a state-of-the-art flow model in combination with a range of satellite, ground-based and airborne radar data, to accurately simulate the historical flow and recent changes. In particular, we model the effects of a recently formed rift that is propagating at a speed of up to 600m/day and threatens to dislodge the ice shelf from its pinning point at the McDonalds Ice Rumples. We also report on the recent reactivation of a large chasm which has prompted the relocation of the station during the 2016/17 austral summer.

  19. Evolution of Meltwater on the McMurdo Ice Shelf, Antarctica During Two Summer Melt Seasons

    NASA Astrophysics Data System (ADS)

    Macdonald, G. J.; Banwell, A. F.; Willis, I.; Mayer, D. P.; Hansen, E. K.; MacAyeal, D. R.

    2017-12-01

    Ice shelves surround > 50% of Antarctica's coast and their response to climate change is key to the ice sheet's future and global sea-level rise. Observations of the development and drainage of 2750 lakes prior to the collapse of the Larsen B Ice Shelf, combined with our understanding of ice-shelf flexure/fracture, suggest that surface meltwater plays a key role in ice-shelf stability, although the present state of knowledge remains limited. Here, we report results of an investigation into the seasonal evolution of meltwater on the McMurdo Ice Shelf (MIS) during the 2015/16 and 2016/17 austral summers using satellite remote sensing, complemented by ground survey. Although the MIS is relatively far south (78° S), it experiences relatively high ablation rates in the west due to adiabatically warmed winds, making it a useful example of how meltwater could evolve on more southerly ice shelves in a warming climate. We calculate the areas and depths of ponded surface meltwater on the ice shelf at different stages of the two melt seasons using a modified NDWI approach and water-depth algorithm applied to both Landsat 8 and Worldview imagery. Data from two automatic weather stations on the ice shelf are used to drive a positive degree-day model to compare our observations of surface water volumes with modelled meltwater production. Results suggest that the spatial and temporal variations in surface meltwater coverage on the ice shelf vary not only with climatic conditions but also in response to other important processes. First, a rift that widens and propagates between the two melt seasons intercepts meltwater streams, redirecting flow and facilitating ponding elsewhere. Second, some lakes from previous years remain frozen over and become pedestalled, causing streams to divert around their perimeter. Third, surface debris conditions also cause large-scale spatial variation in melt rates and the flow and storage of water.

  20. 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

  1. 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.

  2. 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.

  3. The Beauty and Complexity of the Brunt Ice Shelf from MOA and ICESat

    NASA Technical Reports Server (NTRS)

    Humbert, Angelika; Shuman, Christopher A.

    2005-01-01

    Beginning in February 2003, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) has determined surface elevations from approx. 86degN to 86degS latitude. To date, altimetry data have been acquired in a series of observation periods in repeated track patterns using all three Geoscience Laser Altimeter System (GLAS) lasers. This paper will focus on ice shelf elevation data that were obtained in 2003 across the Brunt Ice Shelf and the Stancomb-Wills Ice Tongue. Integrating the altimetry with the recently available MODIS Mosaic of Antarctica (MOA), quantifies the relative accuracy and precision of the resulting ice shelf elevations. Furthermore, the elevation data was processed onto an elevation grid, by regional interpolation across the area s complex glacial features only. Ice thickness estimation from the altimetry of the floating ice is discussed. ICESat operates at 40Hz and its elevation data is obtained every 172m along track. These elevations have a relative accuracy of about 14cm based on the standard deviation of low-slope crossover differences and a precision of close to 2cm for the Laser 2a, Release 21, GLA12 data used here.

  4. A Simple Diagnostic Model of the Circulation Beneath an Ice Shelf

    NASA Astrophysics Data System (ADS)

    Jenkins, Adrian; Nøst, Ole Anders

    2017-04-01

    The ocean circulation beneath ice shelves supplies the heat required to melt ice and exports the resulting freshwater. It therefore plays a key role in determining the mass balance and geometry of the ice shelves and hence the restraint they impose on the outflow of grounded ice from the interior of the ice sheet. Despite this critical role in regulating the ice sheet's contribution to eustatic sea level, an understanding of some of the most basic features of the circulation is lacking. The conventional paradigm is one of a buoyancy-forced overturning circulation, with inflow of warm, salty water along the seabed and outflow of cooled and freshened waters along the ice base. However, most sub-ice-shelf cavities are broad relative to the internal Rossby radius, so a horizontal circulation accompanies the overturning. Primitive equation ocean models applied to idealised geometries produce cyclonic gyres of comparable magnitude, but in the absence of a theoretical understanding of what controls the gyre strength, those solutions can only be validated against each other. Furthermore, we have no understanding of how the gyre circulation should change given more complex geometries. To begin to address this gap in our theoretical understanding we present a simple, linear, steady-state model for the circulation beneath an ice shelf. Our approach in analogous to that of Stommel's classic analysis of the wind-driven gyres, but is complicated by the fact that his most basic assumption of homogeneity is inappropriate. The only forcing on the flow beneath an ice shelf arises because of the horizontal density gradients set up by melting. We thus arrive at a diagnostic model which gives us the depth-dependent horizontal circulation that results from an imposed geometry and density distribution. We describe the development of the model and present some preliminary solutions for the simplest cavity geometries.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Evolution of ocean-induced ice melt beneath Zachariæ Isstrøm, Northeast Greenland combining observations and an ocean general circulation model from 1978 to present

    NASA Astrophysics Data System (ADS)

    Cai, C.; Rignot, E. J.; Menemenlis, D.; Millan, R.; Bjørk, A. A.; Khan, S. A.; Charolais, A.

    2017-12-01

    Zachariæ Isstrøm, a major ice stream in northeast Greenland, lost a large fraction of its ice shelf during the last decade. We study the evolution of subaqueous melting of its floating section from 1978 to present. The ice shelf melt rate depends on thermal forcing from warm, salty, subsurface ocean waters of Atlantic origin (AW), the mixing of AW with fresh, buoyant subglacial discharge at the calving margin, and the shape of the sub-ice-shelf cavity. Subglacial discharge doubled as a result of enhanced ice sheet runoff caused by warmer air temperatures. Ocean thermal forcing has increased due to enhanced advection of AW. Using an Eulerian method, MEaSUREs ice velocity, Operation IceBridge (OIB) ice thickness, and RACMO2.3 surface balance data, we evaluate the ice shelf melt rate in 1978, 1999 and 2010. The melt rate doubled from 1999 to 2010. Using a Lagrangian method with World View imagery, we map the melt rate in detail from 2011 to 2016. We compare the results with 2D simulations from the Massachusetts Institute of Technology general circulation model (MITgcm), at a high spatial resolution (20-m horizontal and 40-m vertical grid spacing), using OIB ice thickness and sub-ice-shelf cavity for years 1978, 1996, 2010 and 2011, combined with in-situ ocean temperature/salinity data from Ocean Melting Greenland (OMG) 2017. We find that winter melt rates are 2 3 times smaller than summer rates and melt rates increase by one order magnitude during the transition from ice shelf termination to near-vertical calving wall termination. As the last remaining bits of floating ice shelf disappear, ice-ocean interaction will therefore play an increasing role in driving the glacier retreat into its marine-based basin. This work was performed under a contract with NASA Cryosphere Program at UC Irvine and Caltech's Jet Propulsion Laboratory.

  10. 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

  11. 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

  12. Ice Shelf Microbial Ecosystems in the High Arctic and Implications for Life on Snowball Earth

    NASA Astrophysics Data System (ADS)

    Vincent, W. F.; Gibson, J. A. E.; Pienitz, R.; Villeneuve, V.; Broady, P. A.; Hamilton, P. B.; Howard-Williams, C.

    The Ward Hunt Ice Shelf (83°N, 74°W) is the largest remaining section of thick (>10m) landfast sea ice along the northern coastline of Ellesmere Island, Canada. Extensive meltwater lakes and streams occur on the surface of the ice and are colonized by photosynthetic microbial mat communities. This High Arctic cryo-ecosystem is similar in several of its physical, biological and geochemical features to the McMurdo Ice Shelf in Antarctica. The ice-mats in both polar regions are dominated by filamentous cyanobacteria but also contain diatoms, chlorophytes, flagellates, ciliates, nematodes, tardigrades and rotifers. The luxuriant Ward Hunt consortia also contain high concentrations (107-108cm-2) of viruses and heterotrophic bacteria. During periods of extensive ice cover, such as glaciations during the Proterozoic, cryotolerant mats of the type now found in these polar ice shelf ecosystems would have provided refugia for the survival, growth and evolution of a variety of organisms, including multicellular eukaryotes.

  13. Microseismicity along major Ross Ice Shelf rift resulting from thermal contraction of the near-surface firn layer

    NASA Astrophysics Data System (ADS)

    Olinger, S.; Wiens, D.; Aster, R. C.; Bromirski, P. D.; Gerstoft, P.; Nyblade, A.; Stephen, R. A.

    2017-12-01

    Seismicity within ice shelves arises from a variety of sources, including calving, rifting, and movement along internal discontinuities. In this study, we identify and locate cryoseisms in the Ross Ice Shelf (RIS) to better understand ice shelf internal stress and deformation. We use data from a two-year 34-station deployment of broadband seismographs operational from December 2014 - November 2016. Two lines of seismographs intersect near 79Sº, 180º close to a large rift, and cryoseisms were recorded by up to 10 seismographs within 40 km of the rift tip. We identified 3600 events from 2015 and grouped them by quality based on the number of stations recording and signal-to-noise ratio. The events show a long-period character compared to similar magnitude tectonic earthquakes, with peak amplitudes at 1-4 Hz and P, S, longitudinal, and surface wave arrivals. Cross correlation analysis shows that the events cannot be divided into a small number of repeating event clusters with identical waveforms. 262 A-quality events were located with a least-squares algorithm using P and S arrivals, and the resulting locations show strong spatial correlation with the rift, with events distributed along the rift rather than concentrated at the tip or any other specific feature. The events do not show teleseismic triggering, and did not occur with increased frequency following the Illapel earthquake (8.3 Mw) or subsequent tsunami. Instead, we note a concentration of activity during the winter months, with several days exhibiting particularly high seismicity rates. We compare the full catalog of events with temperature data from the Antarctic Weather Stations (Lazzara et al, 2012) and find that the largest swarms occur during the most rapid periods of seasonal temperature decline. Internal stress in ice floes and shelves is known to vary with air temperature; as temperature drops, the upper layer of ice thermally contracts, causing near-surface extensional stress to accumulate. We

  14. Modeling of cryoseismicity observed at the Fimbulisen Ice Shelf, East Antarctica

    NASA Astrophysics Data System (ADS)

    Hainzl, S.; Pirli, M.; Dahm, T.; Schweitzer, J.; Köhler, A.

    2017-12-01

    A source region of repetitive cryoseismic activity has been identified at the Fimbulisen ice shelf, in Dronning Maud Land, East Antarctica. The specific area is located at the outlet of the Jutulstraumen glacier, near the Kupol Moskovskij ice rise. A unique event catalog extending over 13 years, from 2003 to 2016 has been built based on waveform cross-correlation detectors and Hidden Markov Model classifiers. Phases of low seismicity rates are alternating with intense activity intervals that exhibit a strong tidal modulation. We performed a detailed analysis and modeling of the more than 2000 events recorded between July and October 2013. The observations are characterized by a number of very clear signals: (i) the event rate follows both the neap-spring and the semi-diurnal ocean-tide cycle; (ii) recurrences have a characteristic time of approximately 8 minutes; (iii) magnitudes vary systematically both on short and long time scales; and (iv) the events migrate within short-time clusters. We use these observations to constrain the dynamic processes at work at this particular region of the Fimbulisen ice shelf. Our model assumes a local grounding of the ice shelf, where stick-slip motion occurs. We show that the observations can be reproduced considering the modulation of the Coulomb-Failure stress by ocean tides.

  15. Chemotrophic Ecosystem Beneath the Larsen Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Leventer, A.; Domack, E.; Ishman, S.; Sylva, S.; Willmott, V.; Huber, B.; Padman, L.

    2005-12-01

    The first living chemotrophic ecosystem in the Southern Ocean was discovered in a region of the seafloor previously occupied by the Larsen-B Ice Shelf. A towed video survey documents an ecosystem characterized by a bottom-draping white mat that appears similar to mats of Begiattoa, hydrogen sulfide oxidizing bacteria, and bivalves, 20-30 cm large, similar to vesicomyid clams commonly found at cold seeps. The carbon source is unknown; three potential sources are hypothesized. First, thermogenically-produced methane may occur as the marine shales of this region are similar to hydrocarbon-bearing rocks to the north in Patagonia. The site occurs in an 850 m deep glacially eroded trough located along the contact between Mesozoic-Tertiary crystalline basement and Cretaceous-Tertiary marine rocks; decreased overburden could have induced upward fluid flow. Also possible is the dissociation of methane hydrates, a process that might have occurred as a result of warming oceanic bottom waters. This possibility will be discussed in light of the distribution of early diagenetic ikaite in the region. Third, the possibility of a biogenic methane source will be discussed. A microstratigraphic model for the features observed at the vent sites will be presented; the system is comprised of mud mounds with central vents and surrounding mud flow channels. A series of still image mosaics record the dynamic behavior of the system, which appears to demonstrate episodic venting. These images show the spatial relationship between more and less active sites, as reflected in the superposition of several episodes of mud flow activity and the formation of mud channels. In addition, detailed microscale features of the bathymetry of the site will be presented, placing the community within the context of glacial geomorphologic features. The Larsen-B Ice Shelf persisted through the entire Holocene, limiting carbon influx from a photosynthetic source. Tidal modeling of both pre and post breakup

  16. 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.

  17. McMurdo Ice Shelf Sounding and Radar Statistical Reconnaissance at 60-MHz: Brine Infiltration Extent and Surface Properties

    NASA Astrophysics Data System (ADS)

    Grima, C.; Rosales, A.; Blankenship, D. D.; Young, D. A.

    2014-12-01

    McMurdo Ice Shelf, Antarctica, is characterized by two particular geophysical processes. (1) Marine ice accretion supplies most of the ice shelf material rather than meteoric ice from glacier outflow and snow-falls. (2) A brine layer infiltrates the ice shelf laterally up to 20-km inward. The infiltration mainly initiates at the ice-front from sea water percolation when the firn/snow transition is below sea-level. A better characterization of the McMurdo ice shelf could constrain our knowledges of these mechanisms and assess the stability of the region that hosts numerous human activities from the close McMurdo station (USA) and Scott base (New-Zealand). McMurdo ice shelf is also an analog for the Jovian icy moon Europa where brine pockets are supposed to reside in the ice crust and accretion to occur at the 10-30-km deep ice-ocean interface.The University of Texas Institute for Geophysics (UTIG) acquired two radar survey grids over the McMurdo Ice Shelf during southern summers 2011-2012 and 2012-2013 with the High Capability Radar Sounder (HiCARS) on-board a Basler DC-3 aircraft. HiCARS transmits a chirped signal at 60-MHz central frequency and 15-MHz bandwidth. The corresponding vertical resolution in ice is 5-10 m. An important design goal of the radar was to maintain sufficient dynamic range to correctly measure echo intensities.Here we present the brine infiltration extent and bathymetry derived from its dielectric horizon well distinguishable on the HiCARS radargram. We complement the ice-shelf characterization by classifying its surface thanks to the novel Radar Statistical Reconnaissance (RSR) methodology. The RSR observable is the statistical distribution of the surface echo amplitudes from successive areas defined along-track. The distributions are best-fitted with a theoretical stochastic envelop parameterized with the signal reflectance and scattering. Once those two components are deduced from the fit, they are used in a backscattering model to invert

  18. 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.

  19. Modeling modified Circumpolar Deep Water intrusions onto the Prydz Bay continental shelf, East Antarctica

    NASA Astrophysics Data System (ADS)

    Liu, Chengyan; Wang, Zhaomin; Cheng, Chen; Xia, Ruibin; Li, Bingrui; Xie, Zelin

    2017-07-01

    An eddy-resolving coupled regional ocean-sea ice-ice shelf model is employed to locate the hot spots where modified Circumpolar Deep Water (mCDW) intrudes onto the continental shelf within Prydz Bay, and locate the paths through which mCDW is transported to the Amery Ice Shelf (AIS) calving front. Evaluation of the model output is with satellite, hydrographic and borehole data. Two critical windows responsible for mCDW intrusions are identified. The first is the eastern branch of the cyclonic Prydz Bay gyre (PBG) that carries mCDW to the ice front line, accounting for an annual mean heat transport of ˜8.7 ×1011 J s-1. The second is located to the east of the Four Ladies Bank (FLB) where mCDW is channeled through submarine troughs, accounting for an annual mean heat transport of ˜16.2 ×1011 J s-1. The eddy-induced heat transport accounts for ˜23% in the path of the PBG and ˜52% in the path of the eastern coastal current, with respect to their total onshore heat transport. The seasonal pulsing of mCDW intrusions is greatly dependent on the seasonal cycle of the Antarctic Slope Current (ASC) that peaks with a maximum of ˜29.3 Sv at 75°E in June. In austral winter, mCDW is allowed to access the eastern flank of the AIS calving front with potential consequences for the basal mass balance of the AIS. The dynamic effects of small-scale troughs on the longshore ASC play an important role in the onshore mCDW transport.

  20. Terrestrial lidar measurement of an ongoing calving event on Lange Glacier.

    NASA Astrophysics Data System (ADS)

    Pętlicki, Michał

    2017-04-01

    Increased tourist and scientific marine traffic along the fronts of tidewater glaciers face a security risk due to possible calving-related hazards. A series of serious accidents involving the falling ice block, calving-generated tsunami wave and the ice projectile impacts were reported. Despite the large interest in calving mechanics, still little is known about the impact range of calving events. Three ongoing calving events on Lange Glacier, King George Island, South Shetland Islands were measured with a terrestrial lidar, giving an insight to the mechanics of the calving processes including the subsequent splash of sea water and the range of ice projectiles released from the front. During the acquisition of the point cloud of the ice front, three calving events of different size occurred. The volume of the calved ice, its potential energy and free-fall velocity was computed and compared with the range of the water splash and ice projectiles. Such measurements can be used in future to mitigate the risk of calving-related marine accidents.

  1. Conditions for a steady ice sheet ice shelf junction

    NASA Astrophysics Data System (ADS)

    Nowicki, S. M. J.; Wingham, D. J.

    2008-01-01

    This paper investigates the conditions under which a marine ice sheet may adopt a steady profile. The ice is treated as a linear viscous fluid caused to flow from a rigid base to and over water, treated as a denser but inviscid fluid. The solutions in the region around the point of flotation, or 'transition' zone, are calculated numerically. In-flow and out-flow conditions appropriate to ice sheet and ice shelf flow are applied at the ends of the transition zone and the rigid base is specified; the flow and steady free surfaces are determined as part of the solutions. The basal stress upstream, and the basal deflection downstream, of the flotation point are examined to determine which of these steady solutions satisfy 'contact' conditions that would prevent (i) the steady downstream basal deflection contacting the downstream base, and (ii) the upstream ice commencing to float in the event it was melted at the base. In the case that the upstream bed is allowed to slide, we find only one mass flux that satisfies the contact conditions. When no sliding is allowed at the bed, however, we find a range of mass fluxes satisfy the contact conditions. The effect of 'backpressure' on the solutions is investigated, and is found to have no affect on the qualitative behaviour of the junctions. To the extent that the numerical, linearly viscous treatment may be applied to the case of ice flowing out over the ocean, we conclude that when sliding is present, Weertman's 'instability' hypothesis holds.

  2. Geoengineering Outlet Glaciers and Ice Streams

    NASA Astrophysics Data System (ADS)

    Wolovick, Michael

    2017-04-01

    Mass loss from Greenland and Antarctica is highly sensitive to the presence of warm ocean water that drives melting of ice shelves and marine terminated glaciers. This warm water resides offshore at depth and accesses the grounding line through deep but narrow troughs and fjords. Here, we investigate the possibility of blocking warm water transport through these choke points with an artificial sill. Using a simple width-averaged model of ice stream flow coupled to a buoyant-plume model of submarine melt, we find that grounding line retreat and sea level rise can be delayed or reversed for hundreds of years if warm water is prevented from accessing outlet glaciers and ice-shelf cavities. Glaciers with a floating shelf exhibit a strong response to the presence of the artificial sill regardless of our choice of calving law, while tidewater glaciers require a strong linkage between submarine melt and iceberg calving for the artificial sill to have an effect. As a result of this difference and as a result of differing degrees of overdeepening in the basal topography, Antarctica and Greenland present very different societal cost-benefit analyses. Intervention in Greenland would be low-cost and low-reward: the volume of the artificial sill is comparable to existing large public works projects such as the Dubai Islands or the Suez Canal, but the magnitude of averted sea-level rise is small, the success of the intervention depends on the choice of calving law, and the glaciers return to their non-geoengineered trajectories within one to two centuries. Intervention in Antarctica, on the other hand, would be high-cost and high-reward: the volume of the artificial sill is one to two orders of magnitude greater, but the averted sea level rise is much larger, the intervention is successful regardless of the choice of calving law, and the ice streams remain far from their non-geoengineered trajectories throughout the 1000 year duration of our model runs. In both cases, an

  3. The Effects of Conductivity on High-Resolution Impulse Radar Sounding, Ross Ice Shelf, Antarctica,

    DTIC Science & Technology

    1982-12-01

    OFSTNDRS96- - . -t - . J’-t -. -t-t ---- . f- t..- -.f ~ *~~ "EPORDT82-42 US Army CorpsREPORT 82of Engineers Cold Regions Research &Engineering...bottom of the Ross Ice Shelf at Site J-9, 2) detecting the preferred horizontal c-axis azi- muthal’direction of the sea ice crystals, using the...which drilling revealed to be 416 m below the snow surface. The radar system was used to profile the McMurdo Ice Shelf both from the snow surface and

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. Anomalously-dense firn in an ice-shelf channel revealed by wide-angle radar

    NASA Astrophysics Data System (ADS)

    Drews, R.; Brown, J.; Matsuoka, K.; Witrant, E.; Philippe, M.; Hubbard, B.; Pattyn, F.

    2015-10-01

    The thickness of ice shelves, a basic parameter for mass balance estimates, is typically inferred using hydrostatic equilibrium for which knowledge of the depth-averaged density is essential. The densification from snow to ice depends on a number of local factors (e.g. temperature and surface mass balance) causing spatial and temporal variations in density-depth profiles. However, direct measurements of firn density are sparse, requiring substantial logistical effort. Here, we infer density from radio-wave propagation speed using ground-based wide-angle radar datasets (10 MHz) collected at five sites on Roi Baudouin Ice Shelf (RBIS), Dronning Maud Land, Antarctica. Using a novel algorithm including traveltime inversion and raytracing with a prescribed shape of the depth-density relationship, we show that the depth to internal reflectors, the local ice thickness and depth-averaged densities can reliably be reconstructed. For the particular case of an ice-shelf channel, where ice thickness and surface slope change substantially over a few kilometers, the radar data suggests that firn inside the channel is about 5 % denser than outside the channel. Although this density difference is at the detection limit of the radar, it is consistent with a similar density anomaly reconstructed from optical televiewing, which reveals 10 % denser firn inside compared to outside the channel. The denser firn in the ice-shelf channel should be accounted for when using the hydrostatic ice thickness for determining basal melt rates. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.

  10. Can we use ice calving on glacier fronts as a proxy for rock slope failures?

    NASA Astrophysics Data System (ADS)

    Abellan, Antonio; Penna, Ivanna; Daicz, Sergio; Carrea, Dario; Derron, Marc-Henri; Jaboyedoff, Michel; Riquelme, Adrian; Tomas, Roberto

    2015-04-01

    Ice failures on glacier terminus show very similar fingerprints to rock-slope failure (RSF) processes, nevertheless, the investigation of gravity-driven instabilities that shape rock cliffs and glacier's fronts are currently dissociated research topics. Since both materials (ice and rocks) have very different rheological properties, the development of a progressive failure on mountain cliffs occurs at a much slower rate than that observed on glacier fronts, which leads the latter a good proxy for investigating RSF. We utilized a terrestrial Laser Scanner (Ilris-LR system from Optech) for acquiring successive 3D point clouds of one of the most impressive calving glacier fronts, the Perito Moreno glacier located in the Southern Patagonian Ice Fields (Argentina). We scanned the glacier terminus during five days (from 10th to 14th of March 2014) with very high accuracy (0.7cm standard deviation of the error at 100m) and a high density of information (200 points per square meter). Each data series was acquired at a mean interval of 20 minutes. The maximum attainable range for the utilized wavelength of the Ilris-LR system (1064 nm) was around 500 meters over massive ice (showing no-significant loss of information), being this distance considerably reduced on crystalline or wet ice short after the occurrence of calving events. As for the data treatment, we have adapted our innovative algorithms originally developed for the investigation of both precursory deformation and rockfalls to study calving events. By comparing successive three-dimensional datasets, we have investigated not only the magnitude and frequency of several ice failures at the glacier's terminus (ranging from one to thousands of cubic meters), but also the characteristic geometrical features of each failure. In addition, we were able to quantify a growing strain rate on several areas of the glacier's terminus shortly after their final collapse. For instance, we investigated the spatial extent of the

  11. 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

  12. Ross Ice Shelf, Antarctica: Bathymetry, Structural Geology and Ocean Circulation from New IcePod Airborne Geophysical Data

    NASA Astrophysics Data System (ADS)

    Siddoway, C. S.; Tinto, K. J.; Bell, R. E.; Padman, L.; Fricker, H. A.; Springer, S. R.

    2016-12-01

    Rock exposures in the Ford Ranges, Marie Byrd Land (MBL), on the eastern margin of the Ross Embayment, contain direct evidence of the geological processes that led to formation of West Antarctica's continental lithosphere. Processes include wide regional extension, volcanism, and thermal reequilibration, with creation of crustal structures that are prone to reactivation today. Marie Byrd Land is tectonically active, as is evident from Late Pleistocene to Holocene eruptive centers, englacial volcanic tephra as young as 2200 years, a site of magma propagation inferred from POLEnet seismic records, and the occurrence of a 2012 earthquake cluster of magnitude M4.4 to M5.5 north of Edward VII Peninsula. However, the lithosphere underlying the Ross Ice Shelf (RIS) is poorly known due to the thick cover of shelf ice floating on the ocean, difficult to penetrate by satellite remote sensing or other methods. Airborne geophysical data for the Ford Ranges and the Ross Ice Shelf (RIS) suggest that the rock formations and structures that underlie MBL continue beneath the RIS. Notable features known in outcrop and detected/inferred from potential fields data are Pleistocene or younger mafic volcanic centers and Cretaceous core complexes, both likely associated with wrench faults. The Ford Ranges legacy dataset that now provides a fundamental basis for sub-RIS geological interpretation is a product of research in coastal MBL led by B.P. Luyendyk from 1989 - 2006. To improve our knowledge of lithospheric evolution, identify active faults and prospective zones of volcanism/heat flow, and to determine the sub-RIS bathymetry, the RIS sector is being explored via new Icepod aerogeophysics acquisition during the ROSETTA-Ice project (Ross Ocean and ice Shelf Environment, and Tectonic setting Through Aerogeophysical surveys and modeling), now underway over this vast under-explored sector of the Ross Embayment. ROSETTA-Ice collects and employs new gravity data with magnetics to delineate

  13. Mapping the grounding zone of Ross Ice Shelf using ICESat laser altimetry

    USGS Publications Warehouse

    Brunt, Kelly M.; Fricker, Helen A.; Padman, Laurie; Scambos, Ted A.; O'Neel, Shad

    2010-01-01

    We use laser altimetry from the Ice, Cloud, and land Elevation Satellite (ICESat) to map the grounding zone (GZ) of the Ross Ice Shelf, Antarctica, at 491 locations where ICESat tracks cross the grounding line (GL). Ice flexure in the GZ occurs as the ice shelf responds to short-term sea-level changes due primarily to tides. ICESat repeat-track analysis can be used to detect this region of flexure since each repeated pass is acquired at a different tidal phase; the technique provides estimates for both the landward limit of flexure and the point where the ice becomes hydrostatically balanced. We find that the ICESat-derived landward limits of tidal flexure are, in many places, offset by several km (and up to ∼60 km) from the GL mapped previously using other satellite methods. We discuss the reasons why different mapping methods lead to different GL estimates, including: instrument limitations; variability in the surface topographic structure of the GZ; and the presence of ice plains. We conclude that reliable and accurate mapping of the GL is most likely to be achieved when based on synthesis of several satellite datasets

  14. Using aerogravity and seismic data to model the bathymetry and upper crustal structure beneath the Pine Island Glacier ice shelf, West Antarctica

    NASA Astrophysics Data System (ADS)

    Muto, A.; Peters, L. E.; Anandakrishnan, S.; Alley, R. B.; Riverman, K. L.

    2013-12-01

    Recent estimates indicate that ice shelves along the Amundsen Sea coast in West Antarctica are losing substantial mass through sub-ice-shelf melting and contributing to the accelerating mass loss of the grounded ice buttressed by them. For Pine Island Glacier (PIG), relatively warm Circumpolar Deep Water has been identified as the key driver of the sub-ice-shelf melting although poor constraints on PIG sub-ice shelf have restricted thorough understanding of these ice-ocean interactions. Aerogravity data from NASA's Operation IceBridge (OIB) have been useful in identifying large-scale (on the order of ten kilometers) features but the results have relatively large uncertainties due to the inherent non-uniqueness of the gravity inversion. Seismic methods offer the most direct means of providing water thickness and upper crustal geological constraints, but availability of such data sets over the PIG ice shelf has been limited due to logistical constraints. Here we present a comparative analysis of the bathymetry and upper crustal structure beneath the ice shelf of PIG through joint inversion of OIB aerogravity data and in situ active-source seismic measurements collected in the 2012-13 austral summer. Preliminary results indicate improved resolution of the ocean cavity, particularly in the interior and sides of the PIG ice shelf, and sedimentary drape across the region. Seismically derived variations in ice and ocean water densities are also applied to the gravity inversion to produce a more robust model of PIG sub-ice shelf structure, as opposed to commonly used single ice and water densities across the entire study region. Misfits between the seismically-constrained gravity inversion and that estimated previously from aerogravity alone provide insights on the sensitivity of gravity measurements to model perturbations and highlight the limitations of employing gravity data to model ice shelf environments when no other sub-ice constraints are available.

  15. Constraints on ice volume changes of the WAIS and Ross Ice Shelf since the LGM based on cosmogenic exposure ages in the Darwin-Hatherton glacial system of the Transantarctic Mountains

    NASA Astrophysics Data System (ADS)

    Fink, David; Storey, Bryan; Hood, David; Joy, Kurt; Shulmeister, James

    2010-05-01

    Quantitative assessment of the spatial and temporal scale of ice volume change of the West Antarctic ice sheet (WAIS) and Ross Ice Shelf since the last glacial maximum (LGM) ~20 ka is essential to accurately predict ice sheet response to current and future climate change. Although global sea level rose by approximately 120 metres since the LGM, the contribution of polar ice 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 ice 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 ice free mountains which archive limits of former ice 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 ice 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 Ice Shelf 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 ice-sheet regions due to the prevalence of cold-based ice over-riding events and absence of outwash processes which removes

  16. Modern shelf ice, equatorial Aeolis Quadrangle, Mars

    NASA Technical Reports Server (NTRS)

    Brakenridge, G. R.

    1993-01-01

    As part of a detailed study of the geological and geomorphological evolution of Aeolis Quadrangle, I have encountered evidence suggesting that near surface ice exists at low latitudes and was formed by partial or complete freezing of an inland sea. The area of interest is centered at approximately -2 deg, 196 deg. As seen in a suite of Viking Orbiter frames obtained at a range of approximately 600 km, the plains surface at this location is very lightly cratered or uncratered, and it is thus of late Amazonian age. Extant topographic data indicate that the Amazonian plains at this location occupy a trough whose surface lies at least 1000 m below the Mars datum. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. In either case, the thin (a few meters at most) high albedo, low thermal inertia cover of aeolian materials was instrumental in allowing ice preservation, and at least the lower portions of this dust cover may be cemented by water ice. Detailed mapping using Viking stereopairs and quantitative comparisons to terrestrial shelf ice geometries are underway.

  17. 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.

  18. Potential population-level effects of increased haulout-related mortality of Pacific walrus calves

    USGS Publications Warehouse

    Udevitz, Mark S.; Taylor, Rebecca L.; Garlich-Miller, Joel L.; Quakenbush, Lori T.; Snyder, Jonathan A.

    2013-01-01

    Availability of summer sea ice has been decreasing in the Chukchi Sea during recent decades, and increasing numbers of Pacific walruses have begun using coastal haulouts in late summer during years when sea ice retreats beyond the continental shelf. Calves and yearlings are particularly susceptible to being crushed during disturbance events that cause the herd to panic and stampede at these large haulouts, but the potential population-level effects of this mortality are unknown. We used recent harvest data, along with previous assumptions about demographic parameters for this population, to estimate female population size and structure in 2009 and project these numbers forward using a range of assumptions about future harvests and haulout-related mortality that might result from increased use of coastal haulouts during late summer. We found that if demographic parameters were held constant, the levels of harvest that occurred during 1990–2008 would have allowed the population to grow during that period. Our projections indicate, however, that an increase in haulout-related mortality affecting only calves has a greater effect on the population than an equivalent increase in harvest-related mortality distributed among all age classes. Therefore, disturbance-related mortality of calves at coastal haulouts may have relatively important population consequences.

  19. Contrasts in Arctic shelf sea-ice regimes and some implications: Beaufort Sea versus Laptev Sea

    USGS Publications Warehouse

    Reimnitz, E.; Dethleff, D.; Nurnberg, D.

    1994-01-01

    The winter ice-regime of the 500 km) from the mainland than in the Beaufort Sea. As a result, the annual freeze-up does not incorporate old, deep-draft ice, and with a lack of compression, such deep-draft ice is not generated in situ, as on the Beaufort Sea shelf. The Laptev Sea has as much as 1000 km of fetch at the end of summer, when freezing storms move in and large (6 m) waves can form. Also, for the first three winter months, the polynya lies inshore at a water depth of only 10 m. Turbulence and freezing are excellent conditions for sediment entrainment by frazil and anchor ice, when compared to conditions in the short-fetched Beaufort Sea. We expect entrainment to occur yearly. Different from the intensely ice-gouged Beaufort Sea shelf, hydraulic bedforms probably dominate in the Laptev Sea. Corresponding with the large volume of ice produced, more dense water is generated in the Laptev Sea, possibly accompanied by downslope sediment transport. Thermohaline convection at the midshelf polynya, together with the reduced rate of bottom disruption by ice keels, may enhance benthic productivity and permit establishment of open-shelf benthic communities which in the Beaufort Sea can thrive only in the protection of barrier islands. Indirect evidence for high benthic productivity is found in the presence of walrus, who also require year-round open water. By contrast, lack of a suitable environment restricts walrus from the Beaufort Sea, although over 700 km farther to the south. We could speculate on other consequences of the different ice regimes in the Beaufort and Laptev Seas, but these few examples serve to point out the dangers of exptrapolating from knowledge gained in the North American Arctic to other shallow Arctic shelf settings. ?? 1994.

  20. Biomarker-based reconstruction of late Holocene sea-ice variability: East versus West Greenland continental shelf.

    NASA Astrophysics Data System (ADS)

    Kolling, H. M.; Stein, R. H.; Fahl, K.

    2016-12-01

    Sea is a critical component of the climate system and its role is not yet fully understood e.g. the recent rapid decrease in sea ice is not clearly reflected in climate models. This illustrates the need for high-resolution proxy-based sea-ice reconstructions going beyond the time scale of direct measurements in order to understand the processes controlling present and past natural variability of sea ice on short time scales. Here we present the first comparison of two high-resolution biomarker records from the East and West Greenland Shelf for the late Holocene. Both areas are highly sensitive to sea-ice changes as they are influenced by the East Greenland Current, the main exporter of Arctic freshwater and sea ice. On the East Greenland Shelf, we do not find any clear evidence for a long-term increase of sea ice during the late Holocene Neoglacial. This sea-ice record seems to be more sensitive to short-term climate events, such as the Roman Warm Period, the Dark Ages, the Medieval Warm Period and the Little Ice Age. In contrary, the West Greenland Shelf record shows a strong and gradual increase in sea ice concentration and a reduction in marine productivity markers starting near 1.6 ka. In general, the increase in sea ice seems to follow the decreasing solar insolation trend. Short-term events are not as clearly pronounced as on the East Greenland Shelf. A comparison to recently published foraminiferal records from the same cores (Perner et al., 2011, 2015) illuminates the differences of biomarker and micropaleontoligical proxies. It seems that the general trend is reflected in both proxies but the signal of small-scale events is preserved rather differently, pointing towards different environmental requirements of the species behind both proxies. References: Perner, K., et al., 2011. Quat. Sci. Revs. 30, 2815-2826 Perner, K., et al., 2015. Quat. Sci. Revs. 129, 296-307

  1. Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting

    NASA Astrophysics Data System (ADS)

    Gladstone, Rupert Michael; Warner, Roland Charles; Galton-Fenzi, Benjamin Keith; Gagliardini, Olivier; Zwinger, Thomas; Greve, Ralf

    2017-01-01

    Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flow-line model accounting for all stress components and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting.Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction in resolution dependence.A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line.Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), impact on capability to simulate marine ice sheets. If there exists an abrupt change across the grounding line in either basal drag or basal melting, then high resolution will be required to solve the problem. However, the plausible combination of a physical dependency of basal drag on effective pressure, and the possibility of low ice shelf basal melt rates next to the grounding line, may mean that some marine ice sheet systems can be reliably simulated at

  2. Detailed Ar-Ar Geochronology of Volcanism at Minna Bluff, Antarctica: Two-Phased Growth and Influence on Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

    Ross, J. I.; McIntosh, W. C.; Wilch, T. I.

    2012-12-01

    Minna Bluff has been a significant topographic barrier to the flow of the Ross Ice Shelf since the mid-Miocene. Detailed Ar-Ar analyses of kaersutite and sanidine phenocrysts, and groundmass concentrates from volcanic units indicate an overall west to east progression of volcanic activity. Eruptions of basaltic to intermediate lavas, domes, and scoria cones started at ~12 Ma in at what is now the eastern most point of Minna Bluff, "Minna Hook." Activity was centered in this area for ~4 Ma, constructing a pre-Minna Bluff island. Multiple glacial unconformities found at Minna Hook suggest repeated interaction with large warm-based, erosive ice sheets. Activity migrated westward from Minna Bluff Island at 7-8 Ma closing the gap created by the island and the mainland. Significant edifice construction continued until 4-5 Ma with sporadic and parasitic scoria cone eruptions, possibly associated with Mt. Discovery activity, continuing until 2 Ma. The orientations of Minna Bluff's two major axes are strongly controlled by regional tectonic features. Minna Bluff's E-W axis, McIntosh Cliffs, is sub-parallel to the Radial Lineament and the N-S axis, Minna Hook, appears as extension of faulting bounding the Terror Rift. The constructional evolution of the 70km long volcanic complex has an important role in interpreting the climate signals recovered by the ANDRILL Project. Minna Bluff influenced the material delivered to the AND-1B drill site (ANDRILL MIS 2006-2007) in three critical ways: 1) Minna Bluff diverted upstream material, 2) provided a pinning and stabilizing point for the Ross Ice Shelf, possible controlling the calving line prior to the emergence of Ross Island, and 3) was a significant source of fresh volcanic material throughout much of the period recovered by ANDRILL MIS. For example, a kaersutite-bearing clast recovered from 822.78 mbsf in AND-1B yielded an age of 8.53±0.51 Ma, and was likely derived from Minna Bluff. The results from this study can be

  3. Grounding Zone and Tidal Response of the Amery Ice Shelf, East Antarctica

    NASA Technical Reports Server (NTRS)

    Fricker, Helen A.; Sandwell, David; Coleman, Richard; Minster, Bernard

    2005-01-01

    This report summarizes the main findings of the research project. Unfortunately, it turned out that there was not a great deal of SAR data over the Amery Ice Shelf that we were able to work with on the project; nevertheless, we did make considerable progress on this project, with both the existing SAR data and new field measurements that were collected under this grant. In total we had constructed two SAR interferograms (SSIs), and four SSIs. The latter were combined them to construct two differential SAR interferograms (DSIs;). DSIs are useful because the contribution to the SAR phase from horizontal ice motion is eliminated, since the time difference between the first and second pass within both image pairs used to make the DSI is the same for each pair. The SSIs and DSIs have revealed several interesting glaciological features, and have added to our knowledge of the Amery Ice Shelf (AIS).

  4. New insights into 3D calving investigations: use of Terrestrial LiDAR for monitoring the Perito Moreno glacier front (Southern Patagonian Ice Fields, Argentina)

    NASA Astrophysics Data System (ADS)

    Abellan, Antonio; Penna, Ivanna; Daicz, Sergio; Carrea, Dario; Derron, Marc-Henri; Guerin, Antoine; Jaboyedoff, Michel

    2015-04-01

    There exists a great incertitude concerning the processes that control and lead to glaciers' fronts disintegration, including the laws and the processes governing ice calving phenomena. The record of surface processes occurring at glacier's front has proven problematic due to the highly dynamic nature of the calving phenomenon, creating a great uncertainty concerning the processes and forms controlling and leading to the occurrence of discrete calving events. For instance, some common observational errors for quantifying the sudden occurrence of the calving phenomena include the insufficient spatial and/or temporal resolution of the conventional photogrammetric techniques and satellites missions. Furthermore, a lack of high quality four dimensional data of failures is currently affecting our ability to straightforward analyse and predict the glaciers' dynamics. In order to overcome these limitations, we used a terrestrial LiDAR sensor (Optech Ilris 3D-LR) for intensively monitoring the changes occurred at one of the most impressive calving glacier fronts: the Perito Moreno glacier, located in the Southern Patagonian Ice Fields (Argentina). Using this system, we were able to capture at an unprecedented level of detail the three-dimensional geometry of the glacier's front during five days (from 10th to 14th of March 2014). Each data collection, which was acquired at a mean interval of 20 minutes each, consisted in the automatic acquisition of several million points at a mean density between 100-200 points per square meter. The maximum attainable range for the utilized wavelength of the Ilris-LR system (1064 nm) was around 500 meters over massive ice (showing no-significant loss of information), being this distance considerably reduced on crystalline or wet ice short after the occurrence of calving events. By comparing successive three-dimensional datasets, we have investigated not only the magnitude and frequency of several ice failures at the glacier's terminus, but

  5. Processes influencing formation of low-salinity high-biomass lenses near the edge of the Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

    Li, Yizhen; McGillicuddy, Dennis J.; Dinniman, Michael S.; Klinck, John M.

    2017-02-01

    Both remotely sensed and in situ observations in austral summer of early 2012 in the Ross Sea suggest the presence of cold, low-salinity, and high-biomass eddies along the edge of the Ross Ice Shelf (RIS). Satellite measurements include sea surface temperature and ocean color, and shipboard data sets include hydrographic profiles, towed instrumentation, and underway acoustic Doppler current profilers. Idealized model simulations are utilized to examine the processes responsible for ice shelf eddy formation. 3-D model simulations produce similar cold and fresh eddies, although the simulated vertical lenses are quantitatively thinner than observed. Model sensitivity tests show that both basal melting underneath the ice shelf and irregularity of the ice shelf edge facilitate generation of cold and fresh eddies. 2-D model simulations further suggest that both basal melting and downwelling-favorable winds play crucial roles in forming a thick layer of low-salinity water observed along the edge of the RIS. These properties may have been entrained into the observed eddies, whereas that entrainment process was not captured in the specific eddy formation events studied in our 3-D model-which may explain the discrepancy between the simulated and observed eddies, at least in part. Additional sensitivity experiments imply that uncertainties associated with background stratification and wind stress may also explain why the model underestimates the thickness of the low-salinity lens in the eddy interiors. Our study highlights the importance of incorporating accurate wind forcing, basal melting, and ice shelf irregularity for simulating eddy formation near the RIS edge. The processes responsible for generating the high phytoplankton biomass inside these eddies remain to be elucidated. Appendix B. Details for the basal melting and mechanical forcing by the ice shelf edge.

  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. 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

  8. Climate Process Team "Representing calving and iceberg dynamics in global climate models"

    NASA Astrophysics Data System (ADS)

    Sergienko, O. V.; Adcroft, A.; Amundson, J. M.; Bassis, J. N.; Hallberg, R.; Pollard, D.; Stearns, L. A.; Stern, A. A.

    2016-12-01

    Iceberg calving accounts for approximately 50% of the ice mass loss from the Greenland and Antarctic ice sheets. By changing a glacier's geometry, calving can also significantly perturb the glacier's stress-regime far upstream of the grounding line. This process can enhance discharge of ice across the grounding line. Once calved, icebergs drift into the open ocean where they melt, injecting freshwater to the ocean and affecting the large-scale ocean circulation. The spatial redistribution of the freshwater flux have strong impact on sea-ice formation and its spatial variability. A Climate Process Team "Representing calving and iceberg dynamics in global climate models" was established in the fall 2014. The major objectives of the CPT are: (1) develop parameterizations of calving processes that are suitable for continental-scale ice-sheet models that simulate the evolution of the Antarctic and Greenland ice sheets; (2) compile the data sets of the glaciological and oceanographic observations that are necessary to test, validate and constrain the developed parameterizations and models; (3) develop a physically based iceberg component for inclusion in the large-scale ocean circulation model. Several calving parameterizations based suitable for various glaciological settings have been developed and implemented in a continental-scale ice sheet model. Simulations of the present-day Antarctic and Greenland ice sheets show that the ice-sheet geometric configurations (thickness and extent) are sensitive to the calving process. In order to guide the development as well as to test calving parameterizations, available observations (of various kinds) have been compiled and organized into a database. Monthly estimates of iceberg distribution around the coast of Greenland have been produced with a goal of constructing iceberg size distribution and probability functions for iceberg occurrence in particular regions. A physically based iceberg model component was used in a GFDL

  9. Exploration of the Climate Change Frontier in Polar Regions at the Land Ice-Ocean Boundary.

    NASA Astrophysics Data System (ADS)

    Rignot, E. J.

    2014-12-01

    Ice sheets are the largest contributors to sea level rise at present, and responsible for the largest uncertainty in sea level projections. Ice sheets raised sea level 5 m per century 13.5 kyr ago during one period of rapid change. Leading regions for future rapid changes include the marine-based, retrograde bed parts of Greenland (north center and east), West Antarctica (Amundsen Sea), and East Antarctica (Filchner basin and Wilkes Land). Fast changes require an increase in ice melt from a warmer ocean and an increase in iceberg calving. Our understanding of both processes remains limited due to a lack of basic observations. Understanding ocean forcing requires observations on the continental shelf, along bays and glacial fjords and at ice-ocean boundaries, beneath kilometers of ice (Antarctica) or at near-vertical calving cliffs (Greenland), of ocean temperature and sea floor bathymetry. Where such observations exist, the sea floor is much deeper than anticipated because of the carving of deep channels by multiple glacier advances. Warm subsurface waters penetrate throughout the Amundsen Sea Embayment of West Antarctica, the southeast and probably the entire west coasts of Greenland. In Greenland, discharge of subglacial water from surface runoff at the glacier grounding line increases ice melting by the ocean even if the ocean temperature remains the same. Near ice-ocean boundaries, satellite observations are challenged, airborne observations and field surveys are limited, so advanced robotic techniques for cold, deep, remote environments are ultimately required in combination with advanced numerical modeling techniques. Until such technological advances take place and advanced networks are put in place, it is critical to conduct boat surveys, install moorings, and conduct extensive airborne campaigns (for instance, gravity-derived bathymetry and air-dropped CTDs), some of which is already taking place. In the meantime, projections of ice sheet evolution in a

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. Changing pattern of ice flow and mass balance for glaciers discharging into the Larsen A and B embayments, Antarctic Peninsula, 2011 to 2016

    NASA Astrophysics Data System (ADS)

    Rott, Helmut; Abdel Jaber, Wael; Wuite, Jan; Scheiblauer, Stefan; Floricioiu, Dana; Melchior van Wessem, Jan; Nagler, Thomas; Miranda, Nuno; van den Broeke, Michiel R.

    2018-04-01

    We analysed volume change and mass balance of outlet glaciers on the northern Antarctic Peninsula over the periods 2011 to 2013 and 2013 to 2016, using high-resolution topographic data from the bistatic interferometric radar satellite mission TanDEM-X. Complementary to the geodetic method that applies DEM differencing, we computed the net mass balance of the main outlet glaciers using the mass budget method, accounting for the difference between the surface mass balance (SMB) and the discharge of ice into an ocean or ice shelf. The SMB values are based on output of the regional climate model RACMO version 2.3p2. To study glacier flow and retrieve ice discharge we generated time series of ice velocity from data from different satellite radar sensors, with radar images of the satellites TerraSAR-X and TanDEM-X as the main source. The study area comprises tributaries to the Larsen A, Larsen Inlet and Prince Gustav Channel embayments (region A), the glaciers calving into the Larsen B embayment (region B) and the glaciers draining into the remnant part of the Larsen B ice shelf in Scar Inlet (region C). The glaciers of region A, where the buttressing ice shelf disintegrated in 1995, and of region B (ice shelf break-up in 2002) show continuing losses in ice mass, with significant reduction of losses after 2013. The mass balance numbers for the grounded glacier area of region A are -3.98 ± 0.33 Gt a-1 from 2011 to 2013 and -2.38 ± 0.18 Gt a-1 from 2013 to 2016. The corresponding numbers for region B are -5.75 ± 0.45 and -2.32 ± 0.25 Gt a-1. The mass balance in region C during the two periods was slightly negative, at -0.54 ± 0.38 Gt a-1 and -0.58 ± 0.25 Gt a-1. The main share in the overall mass losses of the region was contributed by two glaciers: Drygalski Glacier contributing 61 % to the mass deficit of region A, and Hektoria and Green glaciers accounting for 67 % to the mass deficit of region B. Hektoria and Green glaciers accelerated significantly in 2010

  16. 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.

  17. Ocean Observations Below Petermann Gletscher Ice Shelf, Greenland From a Cabled Observatory

    NASA Astrophysics Data System (ADS)

    Muenchow, A.; Nicholls, K. W.; Padman, L.; Washam, P.

    2016-12-01

    Petermann Gletscher in North Greenland features the second largest floating ice shelf by area in the northern hemisphere. In August of 2015 we drilled three holes through the ice shelf and deployed ocean sensors between 5 and 700 m below the glacier-ocean interface. The sensors are controlled by data loggers at the surface that also support a weather station and GPS. All data are transmitted near real-time via a satellite communication link that allowed data downloads and software uploads until February 2016. The system provided gap-free hourly data through the polar night with air temperatures dropping below -48 °C. Mean glacier speeds in winter (Nov.-Feb) were 1180±18 m/year; these values are 12±5% larger than previously reported winter speeds at this location. Hourly ocean observations revealed large bi-monthly pulses within 30 m of the glacier-ocean interface and amplitudes that exceed 1 °C in temperature and 1 psu in salinity. We posit that episodic discharge of glacial meltwater, modulated by the spring-neap tidal cycle thickens the boundary layer under the ice shelf at the location of our measurements. All data are posted at http://ows.udel.edu . A site visit is planned for August 2016 to fix communication failures, retrieve locally stored data, add sensors, and evaluate sustainability of this first cabled observatory on a floating and rapidly melting Greenland glacier.

  18. A century of variation in the dependence of Greenland iceberg calving on ice sheet surface mass balance and regional climate change.

    PubMed

    Bigg, G R; Wei, H L; Wilton, D J; Zhao, Y; Billings, S A; Hanna, E; Kadirkamanathan, V

    2014-06-08

    Iceberg calving is a major component of the total mass balance of the Greenland ice sheet (GrIS). A century-long record of Greenland icebergs comes from the International Ice Patrol's record of icebergs (I48N) passing latitude 48° N, off Newfoundland. I48N exhibits strong interannual variability, with a significant increase in amplitude over recent decades. In this study, we show, through a combination of nonlinear system identification and coupled ocean-iceberg modelling, that I48N's variability is predominantly caused by fluctuation in GrIS calving discharge rather than open ocean iceberg melting. We also demonstrate that the episodic variation in iceberg discharge is strongly linked to a nonlinear combination of recent changes in the surface mass balance (SMB) of the GrIS and regional atmospheric and oceanic climate variability, on the scale of the previous 1-3 years, with the dominant causal mechanism shifting between glaciological (SMB) and climatic (ocean temperature) over time. We suggest that this is a change in whether glacial run-off or under-ice melting is dominant, respectively. We also suggest that GrIS calving discharge is episodic on at least a regional scale and has recently been increasing significantly, largely as a result of west Greenland sources.

  19. Late Weichselian ice-sheet dynamics and deglaciation history of the northern Svalbard margin

    NASA Astrophysics Data System (ADS)

    Fransner, O.; Noormets, R. R. N. N.; Flink, A.; Hogan, K.; Dowdeswell, J. A.; O'Regan, M.; Jakobsson, M.

    2016-12-01

    The glacial evolution of the northern Svalbard margin is poorly known compared with the western margin. Gravity cores, swath bathymetric, sub-bottom acoustic and 2D airgun data are used to investigate the Late Weichselian Svalbard-Barents Ice Sheet history on the northern Svalbard margin. Prograding sequences in Kvitøya and Albertini trough mouths (TMs) indicate ice streaming to the shelf edge multiple times during the Quaternary. While Kvitøya Trough has an associated trough-mouth fan (TMF), Albertini TM is cut back into the shelf edge. Down-faulted bedrock below Albertini TM suggests larger sediment accommodation space there, explaining the absence of a TMF. The bathymetry indicates that ice flow in Albertini Trough was sourced from Duvefjorden and Albertinibukta. Exposed crystalline bedrock likely kept the two ice flows separated before merging north of Karl XII-Øya. Subglacial landforms in Rijpfjorden and Duvefjorden indicate that both fjords accommodated northward-flowing ice streams during the LGM. The deeper fjord basin and higher elongation ratios of landforms in Duvefjorden suggest a more focused and/or larger ice flow there. Easily erodible sedimentary rocks are common in Duvefjorden, which may explain different ice flow dynamics in these fjords. Kvitøya TMF is flanked by gullies, probably formed through erosive downslope gravity flows triggered by sediment-laden meltwater during early deglaciation. Glacial landforms in Albertini Trough comprise retreat-related landforms indicating slow deglaciation. Iceberg scours in Albertini Trough suggest the importance of calving for mass-loss. Sets of De Geer moraines in Rijpfjorden imply that slow, grounded retreat continued in <210 m water depth. Lack of retreat-related landforms in deeper areas of Rijpfjorden and in Duvefjorden indicates floating glacier fronts influenced by calving. 14C ages suggest that deglaciation of inner Rijpfjorden and central Duvefjorden were complete before 10,434 cal a BP and 10

  20. Understanding ice sheet evolution to avoid massive sea level rise instead of experiencing it (Louis Agassiz Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Rignot, Eric

    2017-04-01

    With unabated climate warming, massive sea level rise from the melting of ice sheets in Greenland and Antarctica looms at the horizon. This is unfortunately an experiment that we can afford to run only once. Satellite and airborne sensors have significantly helped reveal the magnitude of the mass balance of the ice sheets, where the changes take place, when they started, how they change with time and the nature of the physical processes controlling them. These observations have constrained the maturation of numerical modeling techniques for projecting changes in these ice sheets, including the coupling of ocean and ice sheet models, yet significant uncertainties remain to make these projections directly policy relevant and many challenges remain. I will review the state of balance of the ice sheets as we know it today and the fundamental processes that will drive fast ice sheet retreat and sea level change: ice-ocean interaction and iceberg calving. Ice-ocean interaction are dominated by the wind-forced intrusion of warm, salty, subsurface waters toward the ice sheet periphery to melt ice from below at rates orders of magnitude greater than at the surface. In Greenland, these rates are difficult to observe, but model simulations indicate rates of ice melt along vertical calving faces of meters per day, along with undercutting of the ice faces. Constraining the temperature of the ocean waters from high resolution models and observations, however, remains a significant challenge. I will describe the progress we have made in addressing one major issue which is the mapping of fjord bathymetry around Greenland to define the pathways for warm waters. In Antarctica, the rates of melt are measured from remote sensing data but averaged over long periods, so that we are dependent on in-situ observations to understand the interaction of ocean waters with ice within the sub-ice-shelf cavities. I will describe progress made in mapping the bathymetry of the ice shelves and how

  1. Modeling the fracture of ice sheets on parallel computers.

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

    Waisman, Haim; Bell, Robin; Keyes, David

    2010-03-01

    The objective of this project is to investigate the complex fracture of ice and understand its role within larger ice sheet simulations and global climate change. At the present time, ice fracture is not explicitly considered within ice sheet models due in part to large computational costs associated with the accurate modeling of this complex phenomena. However, fracture not only plays an extremely important role in regional behavior but also influences ice dynamics over much larger zones in ways that are currently not well understood. Dramatic illustrations of fracture-induced phenomena most notably include the recent collapse of ice shelves inmore » Antarctica (e.g. partial collapse of the Wilkins shelf in March of 2008 and the diminishing extent of the Larsen B shelf from 1998 to 2002). Other fracture examples include ice calving (fracture of icebergs) which is presently approximated in simplistic ways within ice sheet models, and the draining of supraglacial lakes through a complex network of cracks, a so called ice sheet plumbing system, that is believed to cause accelerated ice sheet flows due essentially to lubrication of the contact surface with the ground. These dramatic changes are emblematic of the ongoing change in the Earth's polar regions and highlight the important role of fracturing ice. To model ice fracture, a simulation capability will be designed centered around extended finite elements and solved by specialized multigrid methods on parallel computers. In addition, appropriate dynamic load balancing techniques will be employed to ensure an approximate equal amount of work for each processor.« less

  2. 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.

  3. 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

  4. Near-surface elastic changes in the Ross Ice Shelf arising from transient storm and melt forcing observed with high-frequency ambient seismic noise

    NASA Astrophysics Data System (ADS)

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

    2017-12-01

    Ice shelf collapse can herald subsequent grounded ice instability. However, robust understanding of external mechanisms capable of triggering rapid changes remains elusive. Improved understanding therefore requires improved remote and in-situ measurements of ice shelf properties. Using nearly three years of continuous data from a recently deployed 34-station broadband seismic array on the Ross Ice Shelf, we analyze persistent temporally varying, anisotropic near-surface resonant wave modes at frequencies above 1 Hz that are highly sensitive to small changes in elastic shelf properties to depths of tens of m. We further find that these modes exhibit both progressive (on the scale of months) and rapid (on the scale of hours) changes in frequency content. The largest and most rapid excursions are associated with forcing from local storms, and with a large regional ice shelf melt event in January 2016. We hypothesize that temporally variable behavior of the resonance features arises from wind slab formation during storms and/or to porosity changes, and to the formation of percolation-related refrozen layers and thinning in the case of surface melting. These resonance variations can be reproduced and inverted for structural changes using numerical wave propagation models, and thus present an opportunity for 4-D structural monitoring of shallow ice shelf elasticity and structure using long-duration seismic recordings.

  5. 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.

  6. 22-year surface salinity changes in the Seasonal Ice Zone near 140°E off Antarctica

    NASA Astrophysics Data System (ADS)

    Morrow, Rosemary; Kestenare, Elodie

    2017-11-01

    Seasonal and interannual variations in sea surface salinity (SSS) are analyzed in the Sea Ice Zone south of 60°S, from a 22-year time series of observations near 140°E. In the northern sea-ice zone during the warming, melting cycle from October to March, waters warm by an average of 3.5 °C and become fresher by 0.1 to 0.25. In the southern sea-ice zone, the surface temperatures vary from - 1 to 1 °C over summer, and the maximal SSS range occurs in December, with a minimum SSS of 33.65 near the Southern Boundary of the ACC, reaching 34.4 in the shelf waters close to the coast. The main fronts, normally defined at subsurface, are shown to have more distinct seasonal characteristics in SSS than in SST. The interannual variations in SSS are more closely linked to variations in upstream sea-ice cover than surface forcing. SSS and sea-ice variations show distinct phases, with large biannual variations in the early 1990s, weaker variations in the 2000s and larger variations again from 2009 onwards. The calving of the Mertz Glacier Tongue in February 2010 leads to increased sea-ice cover and widespread freshening of the surface layers from 2011 onwards. Summer freshening in the northern sea-ice zone is 0.05-0.07 per decade, increasing to 0.08 per decade in the southern sea-ice zone, largely influenced by the Mertz Glacier calving event at the end of our time series. The summer time series of SSS on the shelf at 140°E is in phase but less variable than the SSS observed upstream in the Adélie Depression, and thus represents a spatially integrated index of the wider SSS variations.

  7. The dynamics of climate-induced deglacial ice stream acceleration

    NASA Astrophysics Data System (ADS)

    Robel, A.; Tziperman, E.

    2015-12-01

    Geological observations indicate that ice streams were a significant contributor to ice flow in the Laurentide Ice Sheet during the Last Glacial Maximum. Conceptual and simple model studies have also argued that the gradual development of ice streams increases the sensitivity of large ice sheets to weak climate forcing. In this study, we use an idealized configuration of the Parallel Ice Sheet Model to explore the role of ice streams in rapid deglaciation. In a growing ice sheet, ice streams develop gradually as the bed warms and the margin expands outward onto the continental shelf. Then, a weak change in equilibrium line altitude commensurate with Milankovitch forcing results in a rapid deglacial response, as ice stream acceleration leads to enhanced calving and surface melting at low elevations. We explain the dynamical mechanism that drives this ice stream acceleration and its broader applicability as a feedback for enhancing ice sheet decay in response to climate forcing. We show how our idealized ice sheet simulations match geomorphological observations of deglacial ice stream variability and previous model-data analyses. We conclude with observations on the potential for interaction between ice streams and other feedback mechanisms within the earth system.

  8. A 3D Full-Stokes Calving Model Applied to a West Greenland Outlet Glacier

    NASA Astrophysics Data System (ADS)

    Todd, Joe; Christoffersen, Poul; Zwinger, Thomas; Råback, Peter; Chauché, Nolwenn; Hubbard, Alun; Toberg, Nick; Luckman, Adrian; Benn, Doug; Slater, Donald; Cowton, Tom

    2017-04-01

    Iceberg calving from outlet glaciers accounts for around half of all mass loss from both the Greenland and Antarctic ice sheets. The diverse nature of calving and its complex links to both internal dynamics and external climate make it challenging to incorporate into models of glaciers and ice sheets. Consequently, calving represents one of the most significant uncertainties in predictions of future sea level rise. Here, we present results from a new 3D full-Stokes calving model developed in Elmer/Ice and applied to Store Glacier, the second largest outlet glacier in West Greenland. The calving model implements the crevasse depth criterion, which states that calving occurs when surface and basal crevasses penetrate the full thickness of the glacier. The model also implements a new 3D rediscretization approach and a time-evolution scheme which allow the calving front to evolve realistically through time. We use the model to test Store's sensitivity to two seasonal environmental processes believed to significantly influence calving: submarine melt undercutting and ice mélange buttressing. Store Glacier discharges 13.9 km3 of ice annually, and this calving rate shows a strong seasonal trend. We aim to reproduce this seasonal trend by forcing the model with present day levels of submarine melting and ice mélange buttressing. Sensitivity to changes in these frontal processes was also investigated, by forcing the model with a) increased submarine melt rates acting over longer periods of time and b) decreased mélange buttressing force acting over a reduced period. The model displays a range of observed calving behaviour and provides a good match to the observed seasonal evolution of the Store's terminus. The results indicate that ice mélange is the primary driver of the observed seasonal advance of the terminus and the associated seasonal variation in calving rate. The model also demonstrates a significant influence from submarine melting on calving rate. The results

  9. The direct mechanical influence of sea ice state on ice sheet mass loss via iceberg mélange

    NASA Astrophysics Data System (ADS)

    Robel, A.

    2017-12-01

    The interaction between sea ice and land ice has typically been considered as a large-scale exchange of moisture, heat and salinity through the ocean and atmosphere. However, recent observations from marine-terminating glaciers in Greenland indicate that the long-term decline of local sea ice cover has been accompanied by an increase in nearby iceberg calving and associated ice sheet mass loss. Near glacier calving fronts, sea ice binds icebergs together into an aggregate granular material known as iceberg mélange. Studies have hypothesized that mélange may suppress calving by exerting a mechanical buttressing force directly on the glacier terminus. Here, we show explicitly how sea ice thickness and concentration play a critical role in setting the material strength of mélange. To do so, we adapt a discrete element model to simulate mélange as a cohesive granular material. In these simulations, mélange laden with thick, dense, landfast sea ice can produce enough resistance to shut down calving at the terminus. When sea ice thins, mélange weakens, reducing the mechanical force of mélange on the glacier terminus, and increasing the likelihood of calving. We discuss whether longer periods of sea-ice-free conditions in winter may lead to a transition from currently slow calving, predominantly occurring in the summer, to rapid calving, occurring throughout the year. We also discuss the potential role of freshwater discharge in promoting sea ice formation in fjords, potentially strengthening mélange.

  10. Calving of Talyor Glacier, Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Carmichael, J. D.; Pettit, E. C.; Creager, K. C.; Hallet, B.

    2007-12-01

    Calving of tide-water glaciers has received considerable attention, with seismic arrays in Alaska, Greenland, and Antarctica devoted to their observation. In these environments, ice cliffs are directly coupled to oceanic temperatures. The land-based polar glaciers of the McMurdo Dry Valleys in Antarctica represent a simpler environment unaffected directly by water contact where other factors can be isolated. In particular, summer calving events of Taylor Glacier are observed to consist of precursory activity including crack growth, cliff overhang, and active seismicity at least 1 hour before collapse. We propose that collapse occurs only after a stress threshold has been crossed, evident from 'pre-calving' of ice from the cliff base 1-3 days prior to the major event. We provide photographic, seismic, and temperature data to illustrate the thermal and stress landscape for land-based calving of polar glaciers.

  11. Upper ocean stratification and sea ice growth rates during the summer-fall transition, as revealed by Elephant seal foraging in the Adélie Depression, East Antarctica

    NASA Astrophysics Data System (ADS)

    Williams, G. D.; Hindell, M.; Houssais, M.-N.; Tamura, T.; Field, I. C.

    2010-11-01

    Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140-148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine-rejection in the local coastal polynyas. In 2005 two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for nearly two weeks at the onset of sea ice growth. One of the seals migrated north thereafter and the other headed west, possibly utilising the Antarctic Slope Front current near the continental shelf break. In 2010, after that years calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and occupied the Commonwealth Bay polynya from March through April. Here we present unique observations of the regional oceanography during the summer-fall transition, in particular (a) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (b) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (c) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth (7.5-12.5 cm s-1). Heat and freshwater budgets to 200-300 m are used to estimate the ocean heat content, heat flux and sea ice growth rates. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer-fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep seasonal mixed layer and chlorophyll maximum that is a reported feature of this location.

  12. Sedimentology and chronology of the advance and retreat of the last British-Irish Ice Sheet on the continental shelf west of Ireland

    NASA Astrophysics Data System (ADS)

    Peters, Jared L.; Benetti, Sara; Dunlop, Paul; Ó Cofaigh, Colm; Moreton, Steven G.; Wheeler, Andrew J.; Clark, Christopher D.

    2016-05-01

    The last British-Irish Ice Sheet (BIIS) had extensive marine-terminating margins and was drained by multiple large ice streams and is thus a useful analogue for marine-based areas of modern ice sheets. However, despite recent advances from investigating the offshore record of the BIIS, the dynamic history of its marine margins, which would have been sensitive to external forcing(s), remain inadequately understood. This study is the first reconstruction of the retreat dynamics and chronology of the western, marine-terminating, margin of the last (Late Midlandian) BIIS. Analyses of shelf geomorphology and core sedimentology and chronology enable a reconstruction of the Late Midlandian history of the BIIS west of Ireland, from initial advance to final retreat onshore. Five AMS radiocarbon dates from marine cores constrain the timing of retreat and associated readvances during deglaciation. The BIIS advanced without streaming or surging, depositing a bed of highly consolidated subglacial traction till, and reached to within ∼20 km of the shelf break by ∼24,000 Cal BP. Ice margin retreat was likely preceded by thinning, grounding zone retreat and ice shelf formation on the outer shelf by ∼22,000 Cal BP. This ice shelf persisted for ≤2500 years, while retreating at a minimum rate of ∼24 m/yr and buttressing a >150-km long, 20-km wide, bathymetrically-controlled grounding zone. A large (∼150 km long), arcuate, flat-topped grounding-zone wedge, termed here the Galway Lobe Grounding-Zone Wedge (GLGZW), was deposited below this ice shelf and records a significant stillstand in BIIS retreat. Geomorphic relationships indicate that the BIIS experienced continued thinning during its retreat across the shelf, which led to increased topographic influence on its flow dynamics following ice shelf break up and grounding zone retreat past the GLGZW. At this stage of retreat the western BIIS was comprised of several discrete, asynchronous lobes that underwent several

  13. Theory of buttressed marine ice sheet dynamics and its application to the assessment of tipping-point conditions

    NASA Astrophysics Data System (ADS)

    Pegler, S.

    2017-12-01

    Understanding the fate of the West Antarctic Ice Sheet is constrained by difficulties of resolving the buttressing effect of ice shelves and its dynamic response to grounding-line migration. This effect may be responsible for protecting a large majority of outlet glaciers in Antarctica against surging into the ocean. I present a theoretical methodology for assessing the positions and stability of grounding lines that incorporates closed-form, dynamic descriptions of ice-shelf buttressing and extensional (stretching) viscous stresses. The method is applied to assess the conditions for grounding-line tipping points. Such points are shown to produce abrupt `cliff-edge' transitions to runaway retreat, representing the so-called marine ice sheet instability. Depending on the bed profile, melt and calving rates, a tipping point can either lie very near to a local maximum in the bed topography or potentially far upstream of it, along a reverse bed. The model predictions for both wide and narrow embayments are validated by numerical simulations and laboratory experiments. A case study of Pine Island Glacier indicates the possibility for long-term stabilisation, with the analytical method affording an extensive exploration of scenarios. The theory also elucidates a mode of grounding-line migration controlled entirely by the determinants of the ice-shelf buttressing force, with a loss of sensitivity to basal conditions, contrasting with the conclusion from one-dimensional theory that the ice shelf is irrelevant. The results provide an interpretive framework for understanding grounding-line dynamics, its coupling with ice-shelf dynamics, an efficient exploration of parameter variation, and a complement to large-scale simulation.

  14. Coupling of a continuum ice sheet model and a discrete element calving model using a scientific workflow system

    NASA Astrophysics Data System (ADS)

    Memon, Shahbaz; Vallot, Dorothée; Zwinger, Thomas; Neukirchen, Helmut

    2017-04-01

    Scientific communities generate complex simulations through orchestration of semi-structured analysis pipelines which involves execution of large workflows on multiple, distributed and heterogeneous computing and data resources. Modeling ice dynamics of glaciers requires workflows consisting of many non-trivial, computationally expensive processing tasks which are coupled to each other. From this domain, we present an e-Science use case, a workflow, which requires the execution of a continuum ice flow model and a discrete element based calving model in an iterative manner. Apart from the execution, this workflow also contains data format conversion tasks that support the execution of ice flow and calving by means of transition through sequential, nested and iterative steps. Thus, the management and monitoring of all the processing tasks including data management and transfer of the workflow model becomes more complex. From the implementation perspective, this workflow model was initially developed on a set of scripts using static data input and output references. In the course of application usage when more scripts or modifications introduced as per user requirements, the debugging and validation of results were more cumbersome to achieve. To address these problems, we identified a need to have a high-level scientific workflow tool through which all the above mentioned processes can be achieved in an efficient and usable manner. We decided to make use of the e-Science middleware UNICORE (Uniform Interface to Computing Resources) that allows seamless and automated access to different heterogenous and distributed resources which is supported by a scientific workflow engine. Based on this, we developed a high-level scientific workflow model for coupling of massively parallel High-Performance Computing (HPC) jobs: a continuum ice sheet model (Elmer/Ice) and a discrete element calving and crevassing model (HiDEM). In our talk we present how the use of a high

  15. Towards Quantification of Glacier Dynamic Ice Loss through Passive Seismic Monitoring

    NASA Astrophysics Data System (ADS)

    Köhler, A.; Nuth, C.; Weidle, C.; Schweitzer, J.; Kohler, J.; Buscaino, G.

    2015-12-01

    Global glaciers and ice caps loose mass through calving, while existing models are currently not equipped to realistically predict dynamic ice loss. This is mainly because long-term continuous calving records, that would help to better understand fine scale processes and key climatic-dynamic feedbacks between calving, climate, terminus evolution and marine conditions, do not exist. Combined passive seismic/acoustic strategies are the only technique able to capture rapid calving events continuously, independent of daylight or meteorological conditions. We have produced such a continuous calving record for Kronebreen, a tidewater glacier in Svalbard, using data from permanent seismic stations between 2001 and 2014. However, currently no method has been established in cryo-seismology to quantify the calving ice loss directly from seismic data. Independent calibration data is required to derive 1) a realistic estimation of the dynamic ice loss unobserved due to seismic noise and 2) a robust scaling of seismic calving signals to ice volumes. Here, we analyze the seismic calving record at Kronebreen and independent calving data in a first attempt to quantify ice loss directly from seismic records. We make use of a) calving flux data with weekly to monthly resolution obtained from satellite remote sensing and GPS data between 2007 and 2013, and b) direct, visual calving observations in two weeks in 2009 and 2010. Furthermore, the magnitude-scaling property of seismic calving events is analyzed. We derive and discuss an empirical relation between seismic calving events and calving flux which for the first time allows to estimate a time series of calving volumes more than one decade back in time. Improving our model requires to incorporate more precise, high-resolution calibration data. A new field campaign will combine innovative, multi-disciplinary monitoring techniques to measure calving ice volumes and dynamic ice-ocean interactions simultaneously with terrestrial laser

  16. 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.

  17. 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

  18. Ice shelf breaking and increase velocity of glacier: the view from analogue experiment

    NASA Astrophysics Data System (ADS)

    Corti, Giacomo; Iandelli, Irene

    2013-04-01

    Collapse of the Larsen II platform during the late 90s has generated an increase in velocity if ice sheet discharge, highlighting that these processes may strongly destabilize large ice masses speeding up the plateau discharge toward the sea. Parameters such as ice thickness, valley width and slope, ice pack dimensions may contribute to modulate the effect of increase in ice flow velocity following the removal of ice. We analyze this process through scale analogue models, aimed at reproducing the flow of ice from a plateau into the sea through a narrow valley. The ice is reproduced with a transparent silicone (Polydimethisiloxane), flowing at velocities of a few centimeters per hour and simulating natural velocities in the range of a few meters per year. Having almost the same density of the ice, PDMS floats on water and simulate the ice-shelf formation. Results of preliminary experimental series support that this methodology is able to reasonably reproduce the process and support a significant increase in velocity discharge following the removal of ice pack. Additional tests are designed to verify the influence of the above-mentioned parameters on the increase in ice velocity.

  19. Upper ocean stratification and sea ice growth rates during the summer-fall transition, as revealed by Elephant seal foraging in the Adélie Depression, East Antarctica

    NASA Astrophysics Data System (ADS)

    Williams, G. D.; Hindell, M.; Houssais, M.-N.; Tamura, T.; Field, I. C.

    2011-03-01

    Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140-148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine rejection in the local coastal polynyas. In 2005, two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for several weeks from the end of February. One of the seals migrated west to the Dibble Ice Tongue, apparently utilising the Antarctic Slope Front current near the continental shelf break. In 2010, immediately after that year's calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and sampled the Commonwealth Bay polynya from March through April. Here we present observations of the regional oceanography during the summer-fall transition, in particular (i) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (ii) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (iii) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth. Heat and freshwater budgets to 200-300 m are used to estimate the ocean heat content (400→50 MJ m-2), flux (50-200 W m-2 loss) and sea ice growth rates (maximum of 7.5-12.5 cm day-1). Mean seal-derived sea ice growth rates were within the range of satellite-derived estimates from 1992-2007 using ERA-Interim data. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer/fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep

  20. 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.

  1. 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.

  2. Marine geological and geophysical records of the last British-Irish Ice Sheet on the continental shelf west of Ireland

    NASA Astrophysics Data System (ADS)

    O'Cofaigh, Colm; Callard, S. Louise; Benetti, Sara; Chiverell, Richard C.; Saher, Margot; van Landeghem, Katrien; Livingstone, Stephen J.; Scourse, James; Clark, Chris D.

    2015-04-01

    The record of glaciation on the continental shelf west of Ireland has, until recently, been relatively poorly studied. The UK NERC funded project BRITICE-CHRONO collected marine geophysical data in the form of multibeam swath bathymetry and sub-bottom profiles supplemented by over 50 vibro- and piston cores across the continental shelf west of Ireland during cruise JC106 of the RRS James Cook in 2014. Across the western Irish shelf, offshore of counties Galway and Clare, a series of large arcuate moraines record the former presence of a grounded ice sheet on the shelf. However, geophysical data from further to the west across the Porcupine Bank show a series of ridges and wedge-shaped sedimentary features whose form is consistent with an origin as moraines and/or grounding-zone wedges. Sediment cores from several of these landforms recovered stiff, massive diamictons containing reworked shells that are interpreted as subglacial tills. Cores from the eastern Porcupine Bank recovered laminated muds with cold-water glacimarine foraminifera, in some cases overlying till. Collectively the geophysical and sedimentary data imply the presence of grounded ice across the northern Porcupine Bank and thus much further west on the Irish margin than has previously been considered. This ice underwent retreat in a glacimarine setting. The large 'Olex Moraine' on the western Irish shelf is thus interpreted as recessional feature. Work is currently underway to dates these features and to obtain a retreat chronology for this sector of the last British-Irish Ice Sheet.

  3. Glacier Acceleration and Thinning after Ice Shelf Collapse in the Larsen B Embayment, Antarctica

    NASA Technical Reports Server (NTRS)

    Scambos, T. A.; Bohlander, J. A.; Shuman, C. A.; Skvarca, P.

    2004-01-01

    Ice velocities derived from five Landsat 7 images acquired between January 2000 and February 2003 show a two- to six-fold increase in centerline speed of four glaciers flowing into the now-collapsed section of the Larsen B Ice Shelf. Satellite laser altimetry from ICEsat indicates the surface of Hektoria Glacier lowered by up to 38 +/- 6 m a six-month period beginning one year after the break-up in March 2002. Smaller elevation losses are observed for Crane and Jorum glaciers over a later 5-month period. Two glaciers south of the collapse area, Flask and Leppard, show little change in speed or elevation. Seasonal variations in speed preceding the large post-collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics.

  4. What happened to Larsen C?

    NASA Astrophysics Data System (ADS)

    Rignot, E. J.; Larour, E. Y.; Scheuchl, B.; Khazendar, A.; Bamber, J. L.; Mouginot, J.

    2017-12-01

    In 2017, Larsen C experienced one of the largest calving events in the past century, retreating the ice front by 40 km. The rift that led to this calving event originated decades ago along the flank of Hollick-Kenyon Peninsula and stopped along a suture zone, but started progressing again in 2011 and especially 2014-2015, to eventually lead to the calving of A68. The retreat changed the ice front shape between Bawden Ice Rise and Gibbs Ice Rise from convex to concave, similar to what happened to Larsen B in the late 1990s and Larsen A in the 1980s. Following that retreat, Larsen B eventually collapsed in 2002. The calving is not driven by the traditional processes of viscous bending, hydrofracture, calving cliff failure, longitudinal stress stretching, necking of bottom crevasses joining with surface crevasses, but instead by fracture mechanics. Fracture would be facilitated by the melting of the ice mélange filling the rift, a thinning of the ice shelf, a melting of the heterogeneous marine ice column, or changes in the firn/ice column associated with warming. The ice shelf thinned from the top and below over the last decades; altimetry data from 1994 to 2014 suggesting a decrease in ice shelf thickness of 40-50 m near the zone of rupture. Changes in ocean temperature are relatively undocumented in this part of Antarctica. Air temperature has warmed by 2.4 degrees C over the last 3 decades with a return to colder conditions in recent years yet still much warmer than 30 years ago. We detect no significant change in ice shelf velocity from 2006 to 2017, including after the calving event. The calving front has now retreated within 20-30 km of the compressive arch. We analyze the ice mélange in between the rift with Operation IceBridge laser data from 2009 to 2016 and radio echo sounding data from OIB CreSIS sounder since 2009 to detect changes in ice mélange and marine ice composition. We conclude on how the loss of structural rigidity has lead - or not - to the

  5. Ground-penetrating radar evidence of refrozen meltwater in the firn column of Larsen C Ice Shelf

    NASA Astrophysics Data System (ADS)

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

    2017-12-01

    Firn densification, which has been strongly implicated in ice shelf collapse, can occur rapidly by the percolation and refreezing of surface meltwater. This process reduces the permeability of the firn column, potentially establishing a positive feedback between densification and the occurrence of surface meltwater ponds, and may ultimately facilitate fracturing associated with shelf collapse. Meltwater ponds on Larsen C's Cabinet (CI) and Whirlwind (WI) inlets form where foehn winds reach and influence the shelf surface. While associated zones of refrozen meltwater are strongly evidenced in borehole optical televiewing (OPTV) and seismic refraction data, the sparsity of these observations limits insight into the dimensions of these zones. Here, we present highlights from an 800-km archive of ground-penetrating radar (GPR) profiles acquired by the MIDAS project on CI and WI during November-December 2015. In the upstream reaches of CI and WI, stratified firn layers are abruptly truncated by zones of diminished GPR reflectivity. These initiate 5 m beneath the surface and extend to a depth of 30 m. Volumes appear to exceed 6 km3 (CI) and 1 km3 (WI); these are underestimates, established only where there is GPR control. The horizontal distribution of these zones correlates with the pattern of reduced backscatter in SAR images, supporting their association with meltwater ponds. GPR reflectivity models, derived from OPTV density trends, suggest reduced GPR wavespeeds (as do GPR velocity analyses) and dielectric contrasts consistent with homogenised and densified firn. A firn density model supports the ability of meltwater ponds to form periodically in Cabinet Inlet and subsequently homogenise the density of the firn column. Our observations suggest that ice shelves affected by surface melt and ponding can contain spatially extensive bodies of ice that are warmer and denser than assumed so far, with significant implications for ice shelf flow and fracturing.

  6. Late Spring Nitrate Distributions Beneath the Ice-Covered Northeastern Chukchi Shelf

    NASA Astrophysics Data System (ADS)

    Arrigo, Kevin R.; Mills, Matthew M.; van Dijken, Gert L.; Lowry, Kate E.; Pickart, Robert S.; Schlitzer, Reiner

    2017-09-01

    Measurements of late springtime nutrient concentrations in Arctic waters are relatively rare due to the extensive sea ice cover that makes sampling difficult. During the SUBICE (Study of Under-ice Blooms In the Chukchi Ecosystem) cruise in May-June 2014, an extensive survey of hydrography and prebloom concentrations of inorganic macronutrients, oxygen, particulate organic carbon and nitrogen, and chlorophyll a was conducted in the northeastern Chukchi Sea. Cold (<-1.5°C) winter water was prevalent throughout the study area, and the water column was weakly stratified. Nitrate (NO3-) concentration averaged 12.6 ± 1.92 μM in surface waters and 14.0 ± 1.91 μM near the bottom and was significantly correlated with salinity. The highest NO3- concentrations were associated with winter water within the Central Channel flow path. NO3- concentrations were much reduced near the northern shelf break within the upper halocline waters of the Canada Basin and along the eastern side of the shelf near the Alaskan coast. Net community production (NCP), estimated as the difference in depth-integrated NO3- content between spring (this study) and summer (historical), varied from 28 to 38 g C m-2 a-1. This is much lower than previous NCP estimates that used NO3- concentrations from the southeastern Bering Sea as a baseline. These results demonstrate the importance of using profiles of NO3- measured as close to the beginning of the spring bloom as possible when estimating local NCP. They also show that once the snow melts in spring, increased light transmission through the sea ice to the waters below the ice could fuel large phytoplankton blooms over a much wider area than previously known.

  7. How to choose a calving law

    NASA Astrophysics Data System (ADS)

    O'Leary, M.

    2014-12-01

    Any model of an ocean-terminating ice mass requires a frontal boundary condition, often referred to as a "calving law". The choice of this boundary condition can have complex and poorly-understood effects on the behaviour of the system. Despite this, calving laws are often chosen based on numerical convenience or fashions in the literature. This can often lead to predictions which have "hidden dependencies" on the particular choice of calving law. As an attempt to alleviate this problem, I will show results from a wide variety of calving laws, applied to tidewater glacier scenarios. I will demonstrate how the decadal-scale stability of a tidewater system can put constraints on possible calving laws, and how certain observational phenomena, such as the presence of "pinning points" are largely independent of the choice of calving law. These results can be used by practitioners to decide on appropriate calving laws for the specific problems at hand. They should also be useful to help direct research into new calving laws, and to guide our conception of what an ideal calving law should look like.

  8. Changes in water properties and flow regime on the continental shelf off the Adélie/George V Land coast, East Antarctica, after glacier tongue calving

    NASA Astrophysics Data System (ADS)

    Aoki, S.; Kobayashi, R.; Rintoul, S. R.; Tamura, T.; Kusahara, K.

    2017-08-01

    Oceanic changes before and after the relocation of iceberg B9B and calving of the Mertz Glacier Tongue (MGT) in February 2010 are examined on the continental shelf off the Adélie Land/George V Land coast, East Antarctica. Summer hydrographic observations, including stable oxygen isotope ratio (δ18O), in 2001/2008 and 2011/2015 and results of a numerical model are used. Along the western flank of the MGT, temperature decreased between 2001 and 2015 for most of the water column in the Adélie Depression. δ18O generally decreased, especially at the MGT draft depths on the northern side. West of the MGT, temperature, salinity, and δ18O decreased in the intermediate layer. East of the MGT, in contrast, temperature increased between 2001 and 2011 at intermediate depths, salinity increased in the intermediate and deep layers, and δ18O slightly decreased in the deep layer but did not change much around 300 dbar. The numerical experiment exhibits a change in ocean circulation, revealing an increase in modified Circumpolar Deep Water (mCDW) inflow in the east and a decrease in the west. The contrasting changes in mCDW intrusion are consistent between the observations and numerical model, and are indicative of the effect of removal of the ice barriers. The contrast is overlain by overall decreases in salinity and δ18O, which suggests an increase in the continental meltwater fraction of 5-20% and might reveal a wide-ranging influence from West Antarctica. The oxygen isotope ratio is, hence, effective in monitoring the increase in continental melt over the Antarctic shelf.Plain Language SummaryAntarctic glaciers, icebergs, and <span class="hlt">ice</span> sheet have significant impact on the surrounding ocean, and, in turn, are affected by the ocean. The Mertz Glacier, East Antarctica, had been melted from below by the oceanic heat. The seaward extension of the glacier of about 500 m tall obstructed sea <span class="hlt">ice</span> drift from the east and enabled a large</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GeoRL..45.4124D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GeoRL..45.4124D"><span>Summer Drivers of Atmospheric Variability Affecting <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Thinning in the Amundsen Sea Embayment, 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>Deb, Pranab; Orr, Andrew; Bromwich, David H.; Nicolas, Julien P.; Turner, John; Hosking, J. Scott</p> <p>2018-05-01</p> <p>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 <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic <span class="hlt">ice</span> shelves.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C23B1220S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C23B1220S"><span>Thermal Imagery Details Larsen C Iceberg <span class="hlt">Calving</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shuman, C. A.; Scambos, T. A.; Schmaltz, J. E.; Melocik, K. A.; Klinger, M. J.</p> <p>2017-12-01</p> <p>The final <span class="hlt">calving</span> of the 5800 km2 iceberg, initially named A-68, from the Larsen C <span class="hlt">ice</span> <span class="hlt">shelf</span> took place in darkness during Antarctica's austral winter. Landsat 8 special acquisitions by the Thermal Infrared Sensor (TIRS) on June 19th and July 21st showed the near-final extent of the rift as well as the iceberg after it had released. Such thermal imagery was a critical tool for seeing changes during this period of winter darkness. The completion of the rift across the Larsen C was first announced by Project MIDAS on 12 July based on thermal imagery from Aqua's Moderate Resolution Imaging Spectroradiometer (MODIS). The thermal contrast between the ocean and <span class="hlt">ice</span> surfaces made it clear that the iceberg had released before Sentinel-1's radar and Landsat 8's thermal data confirmed that later on the same day. In addition to TIRS on Landsat 8 (Band 10) and the MODIS sensors on the Terra and Aqua satellites (Bands 31/32), the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite also acquires thermal imagery at a similar wavelength ( 11.5 microns) with its I5 Band. The advantage to these data relative to MODIS is that they are at a higher resolution, 375 m vs 1 km. This, along with multiple passes per day has enabled a detailed temporal study of the early drift movement of A68, followed by visible-band tracking and structural analysis using MODIS band 1 (Aqua and Terra; 250 m resolution) and Landsat 8 panchromatic band (15 m). Along with constraining the timing of the rift's breakthrough to a small time window on July 11th, these data allow tracking of the major pieces of A-68 as they formed, and of the intact area behind the deep embayment in the Larsen C's <span class="hlt">ice</span> front. Further, we will track the movement of these large <span class="hlt">ice</span> masses, and monitor summer melt and effects of further <span class="hlt">calving</span> and thinning as they move northward in the circulation of the Weddell Gyre.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T53C4697C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T53C4697C"><span>Abbot <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, the Amundsen Sea Continental Margin and the Southern Boundary of the Bellingshausen Plate Seaward of 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>Cochran, J. R.; Tinto, K. J.; Bell, R. E.</p> <p>2014-12-01</p> <p>The Abbot <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">Ice</span>Bridge airborne gravity data for sub-<span class="hlt">ice</span> bathymetry shows that the western part of the <span class="hlt">ice</span> <span class="hlt">shelf</span>, as well as Cosgrove <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">shelf</span> to the west, also formed by Antarctica-Zealandia rifting. The <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental <span class="hlt">shelf</span> has been tectonically quiescent and has primarily been shaped though subsidence, sedimentation and the passage of the West Antarctic <span class="hlt">Ice</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C51B0988S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51B0988S"><span><span class="hlt">Ice</span> velocity and SAR backscatter record for the Antarctic Peninsula</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scheuchl, B.; Mouginot, J.; Rignot, E. J.; Small, D.; Khazendar, A.; Seroussi, H. L.; Kellndorfer, J. M.</p> <p>2017-12-01</p> <p>The Antarctic Peninsula has undergone some dramatic changes in the last three decades. The latest high-profile change was the <span class="hlt">calving</span> of iceberg A68 off the Larsen-C <span class="hlt">ice</span> <span class="hlt">shelf</span>, which resulted in the <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19990071136&hterms=balance+sheet&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dbalance%2Bsheet','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19990071136&hterms=balance+sheet&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dbalance%2Bsheet"><span>Large <span class="hlt">Ice</span> Discharge From the Greenland <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>Rignot, Eric</p> <p>1999-01-01</p> <p>The objectives of this work are to measure the <span class="hlt">ice</span> discharge of the Greenland <span class="hlt">Ice</span> Sheet close to the grounding line and/or <span class="hlt">calving</span> front, and compare the results with mass accumulation and ablation in the interior to estimate the <span class="hlt">ice</span> sheet mass balance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C41B1212K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C41B1212K"><span>Impact of <span class="hlt">calving</span> and ocean regime on the speed of Kangilerngata Sermia, Greenland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kane, E.; Rignot, E. J.; Mouginot, J.; Fahnestock, M. A.</p> <p>2017-12-01</p> <p>Iceberg <span class="hlt">calving</span> from Greenland glaciers is an important process of mass ablation that is poorly understood at present, mostly due to a lack of detailed observations. Realistic projections of sea level rise however hinge on precise parameterization of iceberg <span class="hlt">calving</span>. In this work, we utilize ground portable radar interferometry (GPRI) to collect the high temporal and spatial resolution observations of a <span class="hlt">calving</span> front to analyze changes preceding, surrounding and following <span class="hlt">calving</span> events. A 3-week field campaign took place at Kangilerngata Sermia, Greenland, a marine-terminating glacier that has undergone rapid retreat in 2002-2010. The GPRI was deployed at 100 m elevation, 3 km from the <span class="hlt">ice</span> front, to scan the glacier every 3 minutes. <span class="hlt">Calving</span> events include simple shedding of <span class="hlt">ice</span> along the <span class="hlt">ice</span> face and larger events that detach a large piece of <span class="hlt">ice</span> from the glacier. Two such large events were observed, one in a section of the glacier that is nearly afloat and with large subglacial discharge; another over the grounded part of the glacier. We find that the <span class="hlt">calving</span> in the floating part of the glacier generated no disturbance on the <span class="hlt">ice</span> flow, whereas the other event generated an immediate speed increase of 35% that lasted 5 hours and extended 0.55 km upstream of the <span class="hlt">calving</span> event. The section of <span class="hlt">ice</span> removed was 120 m in length and 800 m in width. We posit that the removal of basal drag from that detached piece of grounded <span class="hlt">ice</span> was responsible for the acceleration, whereas in the case of the floating extension, there was no change in force balance of the glacier. In conjunction with these measurements, we analyzed time series of CTD data taken in front of the glacier from 2008 to 2016, in addition to output products from the JPL/ECCO project to document the impact of <span class="hlt">ice</span> ocean interaction, especially glacial undercutting, in triggering the retreat of the glacier in deeper waters. We also analyze how the glacier may evolve in the future based on the BedMachine topography</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140010286','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140010286"><span>Efficient Flowline Simulations of <span class="hlt">Ice</span> <span class="hlt">Shelf</span>-Ocean Interactions: Sensitivity Studies with a Fully Coupled Model</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Walker, Ryan Thomas; Holland, David; Parizek, Byron R.; Alley, Richard B.; Nowicki, Sophie M. J.; Jenkins, Adrian</p> <p>2013-01-01</p> <p>Thermodynamic flowline and plume models for the <span class="hlt">ice</span> <span class="hlt">shelf</span>-ocean system simplify the <span class="hlt">ice</span> and ocean dynamics sufficiently to allow extensive exploration of parameters affecting <span class="hlt">ice</span>-sheet stability while including key physical processes. Comparison between geophysically and laboratory-based treatments of <span class="hlt">ice</span>-ocean interface thermodynamics shows reasonable agreement between calculated melt rates, except where steep basal slopes and relatively high ocean temperatures are present. Results are especially sensitive to the poorly known drag coefficient, highlighting the need for additional field experiments to constrain its value. These experiments also suggest that if the <span class="hlt">ice</span>-ocean interface near the grounding line is steeper than some threshold, further steepening of the slope may drive higher entrainment that limits buoyancy, slowing the plume and reducing melting; if confirmed, this will provide a stabilizing feedback on <span class="hlt">ice</span> sheets under some circumstances.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70044028','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70044028"><span>Minimum distribution of subsea <span class="hlt">ice</span>-bearing permafrost on the US Beaufort Sea continental <span class="hlt">shelf</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Brothers, Laura L.; Hart, Patrick E.; Ruppel, Carolyn D.</p> <p>2012-01-01</p> <p>Starting in Late Pleistocene time (~19 ka), sea level rise inundated coastal zones worldwide. On some parts of the present-day circum-Arctic continental <span class="hlt">shelf</span>, this led to flooding and thawing of formerly subaerial permafrost and probable dissociation of associated gas hydrates. Relict permafrost has never been systematically mapped along the 700-km-long U.S. Beaufort Sea continental <span class="hlt">shelf</span> and is often assumed to extend to ~120 m water depth, the approximate amount of sea level rise since the Late Pleistocene. Here, 5,000 km of multichannel seismic (MCS) data acquired between 1977 and 1992 were examined for high-velocity (>2.3 km s−1) refractions consistent with <span class="hlt">ice</span>-bearing, coarse-grained sediments. Permafrost refractions were identified along <5% of the tracklines at depths of ~5 to 470 m below the seafloor. The resulting map reveals the minimum extent of subsea <span class="hlt">ice</span>-bearing permafrost, which does not extend seaward of 30 km offshore or beyond the 20 m isobath.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016QSRv..150...55P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016QSRv..150...55P"><span>Long-term record of Barents Sea <span class="hlt">Ice</span> Sheet advance to the <span class="hlt">shelf</span> edge from a 140,000 year record</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pope, Ed L.; Talling, Peter J.; Hunt, James E.; Dowdeswell, Julian A.; Allin, Joshua R.; Cartigny, Matthieu J. B.; Long, David; Mozzato, Alessandro; Stanford, Jennifer D.; Tappin, David R.; Watts, Millie</p> <p>2016-10-01</p> <p>The full-glacial extent and deglacial behaviour of marine-based <span class="hlt">ice</span> sheets, such as the Barents Sea <span class="hlt">Ice</span> Sheet, is well documented since the Last Glacial Maximum about 20,000 years ago. However, reworking of older sea-floor sediments and landforms during repeated Quaternary advances across the <span class="hlt">shelf</span> typically obscures their longer-term behaviour, which hampers our understanding. Here, we provide the first detailed long-term record of Barents Sea <span class="hlt">Ice</span> Sheet advances, using the timing of debris-flows on the Bear Island Trough-Mouth Fan. <span class="hlt">Ice</span> advanced to the <span class="hlt">shelf</span> edge during four distinct periods over the last 140,000 years. By far the largest sediment volumes were delivered during the oldest advance more than 128,000 years ago. Later advances occurred from 68,000 to 60,000, 39,400 to 36,000 and 26,000 to 20,900 years before present. The debris-flows indicate that the dynamics of the Saalian and the Weichselian Barents Sea <span class="hlt">Ice</span> Sheet were very different. The repeated <span class="hlt">ice</span> advance and retreat cycles during the Weichselian were shorter lived than those seen in the Saalian. Sediment composition shows the configuration of the <span class="hlt">ice</span> sheet was also different between the two glacial periods, implying that the <span class="hlt">ice</span> feeding the Bear Island <span class="hlt">Ice</span> stream came predominantly from Scandinavia during the Saalian, whilst it drained more <span class="hlt">ice</span> from east of Svalbard during the Weichselian.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.4784J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.4784J"><span>Modelling the influence of tides on <span class="hlt">ice-shelf</span> melt rates in the Amundsen Sea, Antarctica.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jourdain, Nicolas C.; Molines, Jean-Marc; Le Sommer, Julien; Mathiot, Pierre; Chanut, Jérome; Madec, Gurvan</p> <p>2017-04-01</p> <p>Variations in melt beneath <span class="hlt">ice</span>- shelves may trigger <span class="hlt">ice</span>-sheet instabilities, in particular in West Antarctica. Therefore, improving the understanding and modelling of <span class="hlt">ice-shelf</span> basal melt rates has been a major focus over the last decades. In this presentation, we provide further insight into the role of tides on basal melt rates, and we assess several methods to account for tides in models that do not include an explicit representation of tides. First, we use an explicit representation of tides in a regional configuration of the NEMO-3.6 model deployed over the Amundsen Sea. We show that most of the tidal influence on <span class="hlt">ice-shelf</span> melt is explained by four tidal constituents. Tides enhance melt by more than 30% in some cavities like Abbot, Cosgrove and Dotson, but by less than 10% in others like Thwaites and Pine Island. Over the entire Amundsen Sea sector, tides enhance melt by 92 Gt/yr, which is mostly induced by tidal velocities along <span class="hlt">ice</span> drafts (+148 Gt/yr), partly compensated by tide-induced change in thermal forcing (-31 Gt/yr) and co-variations between tidal velocities and thermal forcing (-26 Gt/yr). In the second part of this presentation, we show that using uniform tidal velocities to account for tides effects in ocean models with no explicit tides produces large biases in melt rates. By contrast, prescribing non-uniform tidal velocities allows an accurate representation of the dynamical effects of tides on melt rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.3772A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.3772A"><span><span class="hlt">Ice</span> streaming in western Scotland and the deglaciation of the Hebrides <span class="hlt">Shelf</span> and Firth of Lorn</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arosio, Riccardo; Howe, John; O'Cofaigh, Colm; Crocket, Kirsty</p> <p>2014-05-01</p> <p>Previously, numerous studies have been undertaken both onshore and offshore to decipher the morphological and sedimentological record in order to better constrain the limits and duration of the British-Irish <span class="hlt">Ice</span> Sheet (BIIS) (Ballantyne et al. 2009, Bradwell et al. 2008b, Clark et al. 2011, Dunlop et al. 2010, Howe et al. 2012, O'Cofaigh et al., 2012). Late glacial <span class="hlt">ice</span> sheet dynamics have been revealed to be far more rapid and responsive to climatic amelioration than had previously been considered. Notable in this debate has been the evidence that has been obtained in the inshore and, to a lesser extent, offshore on the UK continental <span class="hlt">shelf</span>. Here new geomorphological data, principally multibeam echo sounder (MBES) data has provided imagery of previously unseen features interpreted as being glacial in origin. In the wake of these new discoveries this projects aims to investigate the extent, timing, growth and final disintegration of the BIIS across Western Scotland. This area of particular interest for the development of the glaciated North Atlantic margin has been generally neglected in past studies, especially across the mid-outer <span class="hlt">shelf</span>, which constitutes a missing part in the jigsaw of the reconstructed BIIS during the last ~20.000yrs. We aim to mainly focus on geomorphological analyses of MBES data collected in the Firth of Lorn and Sea of Hebrides; a study of features as moraines, glacial lineations and drumlins will provide important clues on the dynamics and maximum extension of the sheet. Subsequently we will examine the geometry and composition of the <span class="hlt">shelf</span> sediment infill, aiming to constrain the influence of <span class="hlt">ice</span> retreat on depositional environments using multi-element geochemical (Pb-isotopes ratios, 14C and OSL dating) and sedimentological techniques. Such an investigation will also give retrospective information on the sources for these sediments, hence more indications on <span class="hlt">ice</span> configuration. Ultimately we aim to provide a model of deglaciation for the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020082883','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020082883"><span><span class="hlt">Ice</span> Shelves and Landfast <span class="hlt">Ice</span> on the Antarctic Perimeter: Revised Scope of Work</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Scambos, Ted</p> <p>2002-01-01</p> <p><span class="hlt">Ice</span> 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 <span class="hlt">ice</span> shelves in the Antarctic Peninsula region (the Larsen 'A', 'B' and Wilkins <span class="hlt">Ice</span> shelves) by the results of a previous grant under ADRO-1. Modeling of <span class="hlt">ice</span> flow and the effects of meltwater indicated that melt pending accelerates <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> shelves of the Antarctic and incorporate an examination of the climate-related characteristics of landfast <span class="hlt">ice</span>. The study now considers just a few <span class="hlt">shelf</span> and fast <span class="hlt">ice</span> areas for study, and is funded for two years. The study regions are the northeastern Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, the Larsen 'B' and 'C' shelves, fast <span class="hlt">ice</span> and floating <span class="hlt">shelf</span> <span class="hlt">ice</span> in the Pine Island Glacier area, and fast <span class="hlt">ice</span> along the Wilkes Land coast. Further, rather than investigating a host of <span class="hlt">shelf</span> and fast <span class="hlt">ice</span> processes, we will home in on developing a series of characteristics associated with climate change over <span class="hlt">shelf</span> and fast <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> surface. Fast <span class="hlt">ice</span> may show some of these same processes on a seasonal timescale, providing insight into <span class="hlt">shelf</span> evolution.</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://adsabs.harvard.edu/abs/2014AGUFM.C31A0270L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.C31A0270L"><span>High Resolution Photogrammetric Digital Elevation Models Across <span class="hlt">Calving</span> Fronts and Meltwater Channels in Greenland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Le Bel, D. A.; Brown, S.; Zappa, C. J.; Bell, R. E.; Frearson, N.; Tinto, K. J.</p> <p>2014-12-01</p> <p>Photogrammetric digital elevation models (DEMs) are a powerful approach for understanding elevation change and dynamics along the margins of the large <span class="hlt">ice</span> sheets. The <span class="hlt">Ice</span>Pod system, mounted on a New York Air National Guard LC-130, can measure high-resolution surface elevations with a Riegl VQ580 scanning laser altimeter and Imperx Bobcat IGV-B6620 color visible-wavelength camera (6600x4400 resolution); the surface temperature with a Sofradir IRE-640L infrared camera (spectral response 7.7-9.5 μm, 640x512 resolution); and the structure of snow and <span class="hlt">ice</span> with two radar systems. We show the use of <span class="hlt">Ice</span>Pod imagery to develop DEMs across <span class="hlt">calving</span> fronts and meltwater channels in Greenland. Multiple over-flights of the Kangerlussaq Airport ramp have provided a test of the technique at a location with accurate, independently-determined elevation. Here the photogrammetric DEM of the airport, constrained by ground control measurements, is compared with the Lidar results. In July 2014 the <span class="hlt">Ice</span>Pod <span class="hlt">ice</span>-ocean imaging system surveyed the <span class="hlt">calving</span> fronts of five outlet glaciers north of Jakobshavn Isbrae. We used Agisoft PhotoScan to develop a DEM of each <span class="hlt">calving</span> front using imagery captured by the <span class="hlt">Ice</span>Pod systems. Adjacent to the <span class="hlt">ice</span> sheet, meltwater plumes foster mixing in the fjord, moving warm ocean water into contact with the front of the <span class="hlt">ice</span> sheet where it can undercut the <span class="hlt">ice</span> front and trigger <span class="hlt">calving</span>. The five glaciers provide an opportunity to examine the <span class="hlt">calving</span> front structure in relation to ocean temperature, fjord circulation, and spatial scale of the meltwater plumes. The combination of the accurate DEM of the <span class="hlt">calving</span> front and the thermal imagery used to constrain the temperature and dynamics of the adjacent plume provides new insights into the <span class="hlt">ice</span>-ocean interactions. <span class="hlt">Ice</span> sheet margins provide insights into the connections between the surface meltwater and the fate of the water at the <span class="hlt">ice</span> sheet base. Surface meltwater channels are visualized here for the first time using</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C23A1203B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C23A1203B"><span>Reconstruction of Jakobshavn Isbrae's <span class="hlt">calving</span> dynamics from 1985 to 2017 and sensitivity to future ocean forcing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bondzio, J. H.; Morlighem, M.; Seroussi, H. L.</p> <p>2017-12-01</p> <p>Oceanic forcing is likely to have triggered the breakup of Jakobshavn Isbræ's floating <span class="hlt">ice</span> tongue in the late 1990s, which led to ongoing dynamic changes such as widespread flow acceleration and mass loss. Our understanding of the link between <span class="hlt">ice</span> dynamics, oceanic forcing, and <span class="hlt">calving</span> is limited, yet crucial for prognostic simulations of Jakobshavn Isbræ. Here, we first reconstruct Jakobshavn's <span class="hlt">calving</span> dynamics from 1985 to 2017, by relying on the model from Bondzio et al. 2017, but with a freely evolving <span class="hlt">ice</span> front. We test different <span class="hlt">calving</span> rate parameterizations implemented in the <span class="hlt">Ice</span> Sheet System Model (ISSM) and determine the best law by comparing the modeled retreat to observations. We then identify the controls on <span class="hlt">calving</span> rate and <span class="hlt">ice</span> front retreat by varying the submarine melting rate and frontal melt rates as a function of subglacial water discharge and ocean thermal forcing. This sensitivity analysis is an important step toward performing prognostic simulations of JI and provides pathways for future data acquisition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.C23A..01M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.C23A..01M"><span>The Joy of <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>MacAyeal, D. R.</p> <p>2013-12-01</p> <p>The effectiveness of cryospheric science in addressing its main purpose (predicting and assessing response to climate change) is powerfully, but intangibly enhanced by the mysterious nature and the remote locations of <span class="hlt">ice</span> and snow phenomena. Study of the cryosphere, in essence, depends as much on the universal human desire to satisfy curiosity as it does on the fact that cryospheric science informs humanity about the consequences of the environmental changes now clearly visible in all realms of the cryosphere. In my presentation, I shall consider the study of <span class="hlt">ice-shelf</span> dynamics and stability, and shall draw on the perspective of my 37 years of involvement in this small, but important corner of glaciology, to show where curiosity has, and continues to be, a major driver of understanding. Joyful moments within the development of <span class="hlt">ice-shelf</span> glaciology include examples where complete misunderstandings and blind alleys have ironically led to unexpected insight into how related phenomena operate, including: the flow of <span class="hlt">ice</span> streams, the role of sticky spots, styles and drivers of iceberg <span class="hlt">calving</span>, tidewater glacier terminus behavior, the source mechanisms and interpretations of cryospheric related seismic signals, and the dynamics of iceberg-drift-steering ocean circulation in basins separated by mid-ocean ridges. The familiar joke, "Why did the man who lost his keys on a dark night only search underneath the streetlamp?", is apt for cryospheric science--but with a perverse twist: We cryospheric scientists are more akin to the man who is driven to also grope for the key in the darkness because of the chance that in addition to the key, the car that the key will start might also be found somewhere beyond the glow of the streetlamp.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017TCry...11.1913F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017TCry...11.1913F"><span>From cyclic <span class="hlt">ice</span> streaming to Heinrich-like events: the grow-and-surge instability in the Parallel <span class="hlt">Ice</span> Sheet Model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Feldmann, Johannes; Levermann, Anders</p> <p>2017-08-01</p> <p>Here we report on a cyclic, physical <span class="hlt">ice</span>-discharge instability in the Parallel <span class="hlt">Ice</span> Sheet Model, simulating the flow of a three-dimensional, inherently buttressed <span class="hlt">ice-sheet-shelf</span> system which periodically surges on a millennial timescale. The thermomechanically coupled model on 1 km horizontal resolution includes an enthalpy-based formulation of the thermodynamics, a nonlinear stress-balance-based sliding law and a very simple subglacial hydrology. The simulated unforced surging is characterized by rapid <span class="hlt">ice</span> streaming through a bed trough, resulting in abrupt discharge of <span class="hlt">ice</span> across the grounding line which is eventually <span class="hlt">calved</span> into the ocean. We visualize the central feedbacks that dominate the subsequent phases of <span class="hlt">ice</span> buildup, surge and stabilization which emerge from the interaction between <span class="hlt">ice</span> dynamics, thermodynamics and the subglacial till layer. Results from the variation of surface mass balance and basal roughness suggest that <span class="hlt">ice</span> sheets of medium thickness may be more susceptible to surging than relatively thin or thick ones for which the surge feedback loop is damped. We also investigate the influence of different basal sliding laws (ranging from purely plastic to nonlinear to linear) on possible surging. The presented mechanisms underlying our simulations of self-maintained, periodic <span class="hlt">ice</span> growth and destabilization may play a role in large-scale <span class="hlt">ice</span>-sheet surging, such as the surging of the Laurentide <span class="hlt">Ice</span> Sheet, which is associated with Heinrich events, and <span class="hlt">ice</span>-stream shutdown and reactivation, such as observed in the Siple Coast region of West Antarctica.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRC..121.5773S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRC..121.5773S"><span>The effects of Antarctic iceberg <span class="hlt">calving</span>-size distribution in a global climate model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stern, A. A.; Adcroft, A.; Sergienko, O.</p> <p>2016-08-01</p> <p>Icebergs <span class="hlt">calved</span> from the Antarctic continent act as moving sources of freshwater while drifting in the Southern Ocean. The lifespan of these icebergs strongly depends on their original size during <span class="hlt">calving</span>. In order to investigate the effects (if any) of the <span class="hlt">calving</span> size of icebergs on the Southern Ocean, we use a coupled general circulation model with an iceberg component. Iceberg <span class="hlt">calving</span> length is varied from 62 m up to 2.3 km, which is the typical range used in climate models. Results show that increasing the size of <span class="hlt">calving</span> icebergs leads to an increase in the westward iceberg freshwater transport around Antarctica. In simulations using larger icebergs, the reduced availability of meltwater in the Amundsen and Bellingshausen Seas suppresses the sea-<span class="hlt">ice</span> growth in the region. In contrast, the increased iceberg freshwater transport leads to increased sea-<span class="hlt">ice</span> growth around much of the East Antarctic coastline. These results suggest that the absence of large tabular icebergs with horizontal extent of tens of kilometers in climate models may introduces systematic biases in sea-<span class="hlt">ice</span> formation, ocean temperatures, and salinities around Antarctica.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140006603','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140006603"><span>Rift in Antarctic Glacier: a Unique Chance to Study <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Retreat</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Howat, Ian M.; Jezek, Ken; Studinger, Michael; Macgregor, Joseph A.; Paden, John; Floricioiu, Dana; Russell, Rob; Linkswiler, Matt; Dominguez, Roseanne T.</p> <p>2012-01-01</p> <p>It happened again, but this time it was caught in the act. During the last week of September 2011 a large transverse rift developed across thefloating terminus of West Antarcticas PineIsland Glacier, less than 5 years after its lastlarge <span class="hlt">calving</span> event, in 2007 (Figure 1). PineIsland Glaciers retreat has accelerated substantiallyin the past 2 decades, and it is nowlosing 50 gigatons of <span class="hlt">ice</span> per year, or roughly 25 of Antarcticas total annual contributionto sea level rise [Rignot et al., 2008]. The glaciers recent accelerated retreat is likely triggered by ocean warming and increased submarine melting. As such, it is of significant interest to glaciologists and of heightened societal relevance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JGRF..118.1342S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JGRF..118.1342S"><span>Basal channels on <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>Sergienko, O. V.</p> <p>2013-09-01</p> <p>Recent surveys of floating <span class="hlt">ice</span> shelves associated with Pine Island Glacier (Antarctica) and Petermann Glacier (Greenland) indicate that there are channels incised upward into their bottoms that may serve as the conduits of meltwater outflow from the sub-<span class="hlt">ice-shelf</span> cavity. The formation of the channels, their evolution over time, and their impact on <span class="hlt">ice-shelf</span> flow are investigated using a fully-coupled <span class="hlt">ice-shelf/sub-ice-shelf</span> ocean model. The model simulations suggest that channels may form spontaneously in response to meltwater plume flow initiated at the grounding line if there are relatively high melt rates and if there is transverse to <span class="hlt">ice</span>-flow variability in <span class="hlt">ice-shelf</span> thickness. Typical channels formed in the simulations have a width of about 1-3 km and a vertical relief of about 100-200 m. Melt rates and sea-water transport in the channels are significantly higher than on the smooth flat <span class="hlt">ice</span> bottom between the channels. The melt channels develop through melting, deformation, and advection with <span class="hlt">ice-shelf</span> flow. Simulations suggest that both steady state and cyclic state solutions are possible depending on conditions along the lateral <span class="hlt">ice-shelf</span> boundaries. This peculiar dynamics of the system has strong implications on the interpretation of observations. The richness of channel morphology and evolution seen in this study suggests that further observations and theoretical analysis are imperative for understanding <span class="hlt">ice-shelf</span> behavior in warm oceanic conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/638181','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/638181"><span>Glacier <span class="hlt">calving</span>, dynamics, and sea-level rise. Final report</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>Meier, M.F.; Pfeffer, W.T.; Amadei, B.</p> <p>1998-08-01</p> <p>The present-day <span class="hlt">calving</span> flux from Greenland and Antarctica is poorly known, and this accounts for a significant portion of the uncertainty in the current mass balance of these <span class="hlt">ice</span> sheets. Similarly, the lack of knowledge about the role of <span class="hlt">calving</span> in glacier dynamics constitutes a major uncertainty in predicting the response of glaciers and <span class="hlt">ice</span> sheets to changes in climate and thus sea level. Another fundamental problem has to do with incomplete knowledge of glacier areas and volumes, needed for analyses of sea-level change due to changing climate. The authors proposed to develop an improved ability to predict the futuremore » contributions of glaciers to sea level by combining work from four research areas: remote sensing observations of <span class="hlt">calving</span> activity and iceberg flux, numerical modeling of glacier dynamics, theoretical analysis of the <span class="hlt">calving</span> process, and numerical techniques for modeling flow with large deformations and fracture. These four areas have never been combined into a single research effort on this subject; in particular, <span class="hlt">calving</span> dynamics have never before been included explicitly in a model of glacier dynamics. A crucial issue that they proposed to address was the general question of how <span class="hlt">calving</span> dynamics and glacier flow dynamics interact.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20170003150','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20170003150"><span>An Intensive Observation of <span class="hlt">Calving</span> at Helheim Glacier, East Greenland</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.; Voytenko, Denis; Christianson, Knut; Dixon, Timothy H.; Mei, M. Jeffrey; Parizek, Byron R.; Vankova, Irena; Walker, Ryan T.; Walter, Jacob I.; Nicholls, Keith; <a style="text-decoration: none; " href="javascript:void(0); " onClick="displayelement('author_20170003150'); toggleEditAbsImage('author_20170003150_show'); toggleEditAbsImage('author_20170003150_hide'); "> <img style="display:inline; width:12px; height:12px; " src="images/arrow-up.gif" width="12" height="12" border="0" alt="hide" id="author_20170003150_show"> <img style="width:12px; height:12px; display:none; " src="images/arrow-down.gif" width="12" height="12" border="0" alt="hide" id="author_20170003150_hide"></p> <p>2016-01-01</p> <p><span class="hlt">Calving</span> of glacial <span class="hlt">ice</span> into the ocean from the Greenland <span class="hlt">Ice</span> Sheet is an important component of global sea-level rise. The <span class="hlt">calving</span> process itself is relatively poorly observed, understood, and modeled; as such, it represents a bottleneck in improving future global sea-level estimates in climate models. We organized a pilot project to observe the <span class="hlt">calving</span> process at Helheim Glacier in east Greenland in an effort to better understand it. During an intensive one-week survey, we deployed a suite of instrumentation, including a terrestrial radar interferometer, global positioning system (GPS) receivers, seismometers, tsunameters, and an automated weather station. We were fortunate to capture a <span class="hlt">calving</span> process and to measure various glaciological, oceanographic, and atmospheric parameters before, during, and after the event. One outcome of our observations is evidence that the <span class="hlt">calving</span> process actually consists of a number of discrete events, spread out over time, in this instance over at least two days. This time span has implications for models of the process. Realistic projections of future global sea level will depend on an accurate parametrization of <span class="hlt">calving</span>, and we argue that more sustained observations will be required to reach this objective.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.476..100W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.476..100W"><span>Rapid drawdown of Antarctica's Wordie <span class="hlt">Ice</span> <span class="hlt">Shelf</span> glaciers in response to ENSO/Southern Annular Mode-driven warming 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>Walker, C. C.; Gardner, A. S.</p> <p>2017-10-01</p> <p>Here we investigate the largest acceleration in <span class="hlt">ice</span> flow across all of Antarctica between ∼2008 InSAR and 2014 Landsat velocity mappings. This occurred in glaciers that used to feed into the Wordie <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span>-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 <span class="hlt">ice</span> to atmospheric-driven ocean warming.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.6407B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.6407B"><span>New surface-based observations of the environment beneath Pine Island Glacier <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>Bindschadler, Robert; Truffer, Martin; Stanton, Tim; Peters, Leo; Shortt, Mike; Pomraning, Dale; Stockel, Jim; Shaw, Bill; Steinarson, Einar; Anandakrishnan, Sridhar; Wilson, Kiya; Holland, David; Bushuk, Mitch; Behar, Alberto; Cocaud, Cedric; Stam, Christina</p> <p>2013-04-01</p> <p>Extensive surface, sub-<span class="hlt">shelf</span> cavity and seabed observations of the Pine Island Glacier (PIG) <span class="hlt">ice</span> <span class="hlt">shelf</span> environment were collected by a surface field team during the 2012-13 austral summer. Three sites aligned along a central, flow-aligned surface valley were occupied for about one week each during which two hot-water holes were drilled at each site. In one hole, a mast-mounted set of oceanographic sensors recorded water temperature, current and salinity in the few meters immediately below the <span class="hlt">ice-shelf</span> bottom. In the other hole, a similarly instrumented profiler was deployed to make quasi-daily vertical transects of the sub-<span class="hlt">shelf</span> cavity by rising and sinking along a cable suspended in the cavity. These instruments are already returning data that provide direct rates of heat and momentum transfer in the boundary layer, basal melt rates and the temporal variation of water movements on daily and longer time scales. Shallow cores of the sea bed and a photographic record of the drill holes, ocean cavity and sea bed were also collected at two of the drill sites. The geophysics program was spatially much broader and consisted of phase-sensitive radars to measure basal melt rates and active seismic instrumentation to explore the character of the sea bed. Continuous profiling between the drill sites established the previously discovered ("Autosub") sea bed ridge is asymmetric with a steeper downstream face. Spot measurements upstream of the drill sites were reached by helicopter and refined the shape of the ocean cavity where extensive melt rates were measured. The field work is concluding as this abstract is being submitted, so most results are not yet available, but will be included in the presentation as first results emerge.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017TCry...11.2655S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017TCry...11.2655S"><span>GPS-derived estimates of surface mass balance and ocean-induced basal melt for Pine Island Glacier <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>Shean, David E.; Christianson, Knut; Larson, Kristine M.; Ligtenberg, Stefan R. M.; Joughin, Ian R.; Smith, Ben E.; Stevens, C. Max; Bushuk, Mitchell; Holland, David M.</p> <p>2017-11-01</p> <p>In the last 2 decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to marine <span class="hlt">ice</span>-sheet instability and <span class="hlt">ice-shelf</span> basal melt. To better understand these processes, we combined 2008-2010 and 2012-2014 GPS records with dynamic firn model output to constrain local surface and basal mass balance for PIG. We used GPS interferometric reflectometry to precisely measure absolute surface elevation (zsurf) and Lagrangian surface elevation change (Dzsurf/ Dt). Observed surface elevation relative to a firn layer tracer for the initial surface (zsurf - zsurf0') is consistent with model estimates of surface mass balance (SMB, primarily snow accumulation). A relatively abrupt ˜ 0.2-0.3 m surface elevation decrease, likely due to surface melt and increased compaction rates, is observed during a period of warm atmospheric temperatures from December 2012 to January 2013. Observed Dzsurf/ Dt trends (-1 to -4 m yr-1) for the PIG <span class="hlt">shelf</span> sites are all highly linear. Corresponding basal melt rate estimates range from ˜ 10 to 40 m yr-1, in good agreement with those derived from <span class="hlt">ice</span>-bottom acoustic ranging, phase-sensitive <span class="hlt">ice</span>-penetrating radar, and high-resolution stereo digital elevation model (DEM) records. The GPS and DEM records document higher melt rates within and near features associated with longitudinal extension (i.e., transverse surface depressions, rifts). Basal melt rates for the 2012-2014 period show limited temporal variability despite large changes in ocean temperature recorded by moorings in Pine Island Bay. Our results demonstrate the value of long-term GPS records for <span class="hlt">ice-shelf</span> mass balance studies, with implications for the sensitivity of <span class="hlt">ice</span>-ocean interaction at PIG.</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 Antarctic 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/2017AGUFM.T22D..06T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T22D..06T"><span>New Crustal Boundary Revealed Beneath the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica, through ROSETTA-<span class="hlt">Ice</span> Integrated Aerogeophysics, Geology, and Ocean Research</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tinto, K. J.; Siddoway, C. S.; Bell, R. E.; Lockett, A.; Wilner, J.</p> <p>2017-12-01</p> <p>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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (RIS), Antarctica, is the focus of ROSETTA-<span class="hlt">ICE</span>, 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-<span class="hlt">ICE</span> 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 <span class="hlt">Ice</span> Sheet requires a revision of the existing tectonic framework. The sub-RIS narrow rift basins and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.1126N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.1126N"><span>Seafloor glacial geomorphology in a cross <span class="hlt">shelf</span> trough: insights into the deglaciation of the Melville Bay <span class="hlt">Ice</span> Stream</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Newton, Andrew; Huuse, Mads</p> <p>2016-04-01</p> <p>Compared to other glaciated margins such as offshore mid-Norway and Svalbard, the Greenland continental <span class="hlt">shelf</span> has, until recently, been the subject of only a limited amount of academic and industry research. This has been mainly due to the difficulty and expense of obtaining data in such harsh and operationally complex settings. Climate amelioration and technological advance has, particularly in recent years, allowed both academics and industry to substantially increase data collection across the many glaciated continental shelves in the Northern Hemisphere. Baffin Bay has been one of the primary regions of interest for the hydrocarbon industry which has sought to operate in the frontier basins offshore Greenland. As a result of these industry operations, a large database of geophysical and geological data has been collected. Some of this data has been made available to glacial scientists and provides a unique opportunity to investigate the seafloor geomorphology for regions where the majority of previous work has been hypothetical rather than grounded in geological evidence. In the work presented here we present a landform record offshore NW Greenland in the Melville Bay cross-<span class="hlt">shelf</span> trough. This is one of the largest troughs on the entire Greenland <span class="hlt">shelf</span> and measures up to 140 km in width. Shallow-marine cores collected in the coastal part of the trough show bedrock of Miocene age and indicate that a significant cover has likely been removed from the <span class="hlt">shelf</span> by <span class="hlt">ice</span> streams operating through the Late Cenozoic. This material has then been deposited at the <span class="hlt">shelf</span> edge as a trough mouth fan. Using multibeam and seismic reflection data a large number of glacial landforms are observed and mapped in the trough. These include mega-scale glacial lineations, grounding-zone wedges, iceberg scours, and iceberg grounding pits. These landforms are used to reconstruct the <span class="hlt">ice</span> dynamics of the Melville Bugt <span class="hlt">Ice</span> Stream at the last glacial maximum and during its deglaciation. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2007/1047/srp/srp043/of2007-1047srp043.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2007/1047/srp/srp043/of2007-1047srp043.pdf"><span>East Antarctic <span class="hlt">ice</span>-sheet dynamics between 5.2 and 0 Ma from a high-resolution terrigenous particle size record, ODP Site 1165, Prydz Bay-Cooperation Sea</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Passchier, S.</p> <p>2007-01-01</p> <p>This paper discusses a 5.2-0 Ma high-resolution terrigenous particle size record recovered from a sediment drift off East Antarctica. The particle size properties of Hole 1165B are interpreted in the context of previously acquired data on a continental <span class="hlt">shelf</span> to slope transect drilled by ODP Leg 188 in Prydz Bay and the Cooperation Sea. The new data indicate that the Lambert <span class="hlt">ice</span> stream stayed predominantly landward of the <span class="hlt">shelf</span> break in the early Pliocene (5.2-3.5 Ma) with periods of <span class="hlt">ice</span> sheet recession on land. The middle Pliocene (3.5-3.1 Ma) is characterized as major <span class="hlt">ice</span> expansion during glacials with deposition of laminated clays from meltwater plumes on the continental rise, alternating with periods of <span class="hlt">ice</span> recession. A change in sedimentary facies and a decrease in sedimentation rates occurred at ~3.1 Ma indicating a more retreated Lambert Glacier. Between 2.5 and 1 Ma the <span class="hlt">ice</span> stream was generally stable and had become cold-based with <span class="hlt">ice</span> flow in a glacial trough extending to the <span class="hlt">shelf</span> break. Three-four large pulses of coarse-grained glacigenic debris mark the record at ~1 Ma. These are interpreted as extensive <span class="hlt">calving</span> due to decoupling of the marine terminus from its bed in response to Northern Hemisphere deglaciations and associated sea level rises.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12..721M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12..721M"><span><span class="hlt">Calving</span> relation for tidewater glaciers based on detailed stress field analysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mercenier, Rémy; Lüthi, Martin P.; Vieli, Andreas</p> <p>2018-02-01</p> <p>Ocean-terminating glaciers in Arctic regions have undergone rapid dynamic changes in recent years, which have been related to a dramatic increase in <span class="hlt">calving</span> rates. Iceberg <span class="hlt">calving</span> is a dynamical process strongly influenced by the geometry at the terminus of tidewater glaciers. We investigate the effect of varying water level, <span class="hlt">calving</span> front slope and basal sliding on the state of stress and flow regime for an idealized grounded ocean-terminating glacier and scale these results with <span class="hlt">ice</span> thickness and velocity. Results show that water depth and <span class="hlt">calving</span> front slope strongly affect the stress state while the effect from spatially uniform variations in basal sliding is much smaller. An increased relative water level or a reclining <span class="hlt">calving</span> front slope strongly decrease the stresses and velocities in the vicinity of the terminus and hence have a stabilizing effect on the <span class="hlt">calving</span> front. We find that surface stress magnitude and distribution for simple geometries are determined solely by the water depth relative to <span class="hlt">ice</span> thickness. Based on this scaled relationship for the stress peak at the surface, and assuming a critical stress for damage initiation, we propose a simple and new parametrization for <span class="hlt">calving</span> rates for grounded tidewater glaciers that is calibrated with observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRF..122.1698D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRF..122.1698D"><span>High-resolution sub-<span class="hlt">ice-shelf</span> seafloor records of twentieth century ungrounding and retreat of 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>Davies, D.; Bingham, R. G.; Graham, A. G. C.; Spagnolo, M.; Dutrieux, P.; Vaughan, D. G.; Jenkins, A.; Nitsche, F. O.</p> <p>2017-09-01</p> <p>Pine Island Glacier <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (PIGIS) has been thinning rapidly over recent decades, resulting in a progressive drawdown of the inland <span class="hlt">ice</span> and an upstream migration of the grounding line. The resultant <span class="hlt">ice</span> loss from Pine Island Glacier (PIG) and its neighboring <span class="hlt">ice</span> streams presently contributes an estimated ˜10% to global sea level rise, motivating efforts to constrain better the rate of future <span class="hlt">ice</span> retreat. One route toward gaining a better understanding of the processes required to underpin physically based projections is provided by examining assemblages of landforms and sediment exposed over recent decades by the ongoing ungrounding of PIG. Here we present high-resolution bathymetry and sub-bottom-profiler data acquired by autonomous underwater vehicle (AUV) surveys beneath PIGIS in 2009 and 2014, respectively. We identify landforms and sediments associated with grounded <span class="hlt">ice</span> flow, proglacial and subglacial sediment transport, overprinting of lightly grounded <span class="hlt">ice-shelf</span> keels, and stepwise grounding line retreat. The location of a submarine ridge (Jenkins Ridge) coincides with a transition from exposed crystalline bedrock to abundant sediment cover potentially linked to a thick sedimentary basin extending upstream of the modern grounding line. The capability of acquiring high-resolution data from AUV platforms enables observations of landforms and understanding of processes on a scale that is not possible in standard offshore geophysical surveys.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C53C0754M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C53C0754M"><span>Quaternary evolution of the Fennoscandian <span class="hlt">Ice</span> Sheet from 3D seismic data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Montelli, A.; Dowdeswell, J. A.; Ottesen, D.; Johansen, S. E.</p> <p>2016-12-01</p> <p>The Quaternary seismic stratigraphy and architecture of the mid-Norwegian continental <span class="hlt">shelf</span> and slope are investigated using extensive grids of marine 2D and 3D seismic reflection data that cover more than 100,000 km2 of the continental margin. At least 26 distinct regional palaeo-surfaces have been interpreted within the stratigraphy of the Quaternary Naust Formation on the mid-Norwegian margin. Multiple assemblages of buried glacigenic landforms are preserved within the Naust Formation across most of the study area, facilitating detailed palaeo-glaciological reconstructions. We document a marine-terminating, <span class="hlt">calving</span> Fennoscandian <span class="hlt">Ice</span> Sheet (FIS) margin present periodically on the Norwegian <span class="hlt">shelf</span> since at least the beginning of the Quaternary. Elongate, streamlined landforms interpreted as mega-scale glacial lineations (MSGLs) have been found within the upper part of the Naust sequence N ( 1.9-1.6 Ma), sugesting the development of fast-flowing <span class="hlt">ice</span> streams since that time. Shifts in the location of depocentres and direction of features indicative of fast <span class="hlt">ice</span>-flow suggest that several reorganisations in the FIS drainage have occurred since 1.5 Ma. Subglacial landforms reveal a complex and dynamic <span class="hlt">ice</span> sheet, with converging palaeo-<span class="hlt">ice</span> streams and several flow-switching events that may reflect major changes in topography and internal <span class="hlt">ice</span>-sheet structure. Lack of subglacial meltwater channels suggests a largely distributed, low-volume meltwater system that drained the FIS through permeable subglacial till without leaving much erosional evidence. This regional palaeo-environmental examination of the FIS provides a useful framework for <span class="hlt">ice</span>-sheet modelling and shows that fragmentary preservation of buried surfaces and variability of <span class="hlt">ice</span>-sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C41C1228M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C41C1228M"><span>Using Continuum Damage Mechanics to Simulate Iceberg <span class="hlt">Calving</span> from Tidewater Outlet Glaciers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mercenier, R.; Lüthi, M.; Vieli, A.</p> <p>2017-12-01</p> <p>Many ocean terminating glaciers in the Arctic are currently undergoingrapid retreat, thinning and strong accelerations in flow. The processof iceberg <span class="hlt">calving</span> plays a crucial role for the related dynamical masslosses and occurs when the stresses at the <span class="hlt">calving</span> front exceed thefracture strength of <span class="hlt">ice</span>, driving the propagation of cracks andeventually leading to the detachment of <span class="hlt">ice</span> blocks from the glacierfront. However, the understanding of the processes involved in icebergcalving as well as the capability of flow models to represent thecalving mechanism remain limited.Here, we use a time-dependent two-dimensional finite-element flowmodel coupled to a damage model to simulate the break-off of <span class="hlt">ice</span> atthe front of idealized tidewater outlet glaciers. The flow modelcomputes flow velocities and the resulting stresses, which are in turnused to calculate the evolution of the glacier geometry anddamage. Damage is defined as a change of rheological properties, e.g.viscosity, due to increasing material degradation. Elements of <span class="hlt">ice</span> areremoved when the damage variable reaches a critical threshold. Theeffects of material properties and of geometrical parameters such aswater depth, <span class="hlt">ice</span> thickness and submarine frontal melting on thesimulated <span class="hlt">calving</span> rates are explored through systematic sensitivityanalyses.The coupled <span class="hlt">ice</span> flow/damage model allows for successful reproductionof <span class="hlt">calving</span> front geometries typically observed for different waterdepths. We further use detailed observations from real glaciergeometries to better constrain the model parameters. Theproposed model approach should be applicable to simulate icebergcalving on arbitrary glaciers, and thus be used to analyse theevolution of tidewater glacier variations from the past to the future.</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('https://www.ncbi.nlm.nih.gov/pubmed/21799799','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21799799"><span>Characterisation of the nematode community of a low-activity cold seep in the recently <span class="hlt">ice-shelf</span> free Larsen B area, Eastern Antarctic Peninsula.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hauquier, Freija; Ingels, Jeroen; Gutt, Julian; Raes, Maarten; Vanreusel, Ann</p> <p>2011-01-01</p> <p>Recent climate-induced <span class="hlt">ice-shelf</span> disintegration in the Larsen A (1995) and B (2002) areas along the Eastern Antarctic Peninsula formed a unique opportunity to assess sub-<span class="hlt">ice-shelf</span> benthic community structure and led to the discovery of unexplored habitats, including a low-activity methane seep beneath the former Larsen B <span class="hlt">ice</span> <span class="hlt">shelf</span>. Since both limited particle sedimentation under previously permanent <span class="hlt">ice</span> 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 <span class="hlt">ice</span>-free, Larsen A and B stations and other Antarctic <span class="hlt">shelf</span> 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 <span class="hlt">ice-shelf</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1614162B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1614162B"><span>The role of <span class="hlt">ice</span> shelves in the Holocene evolution of the Antarctic <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>Bernales, Jorge; Rogozhina, Irina; Thomas, Maik</p> <p>2014-05-01</p> <p>Using the continental-scale <span class="hlt">ice</span> sheet-<span class="hlt">shelf</span> model SICOPOLIS (Greve, 1997 [1]; Sato and Greve, 2012 [2]), we assess the influence of <span class="hlt">ice</span> shelves on the Holocene evolution and present-day geometry of the Antarctic <span class="hlt">ice</span> 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 <span class="hlt">ice</span> core with precipitation pattern using an empirical relation of Dahl-Jensen et al., (1998) [3]. Our numerical experiments show that the geometry of <span class="hlt">ice</span> 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 <span class="hlt">ice</span> shelves at the Last Glacial Maximum (LGM, about 21 kyr before present) has a significant effect on the modelled Early Holocene volume of <span class="hlt">ice</span> shelves (up to 20%) that gradually diminishes to a negligible level for the present-day <span class="hlt">ice</span> <span class="hlt">shelf</span> configuration. Thus, the present-day geometry of the Antarctic <span class="hlt">ice</span> shelves can be attained even if an <span class="hlt">ice-shelf</span>-free initial condition is chosen at the LGM. However, the grounded <span class="hlt">ice</span> volume, thickness and dynamic states are found to be sensitive to the <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics over a longer history spanning several tens of thousands of years. A presence of extensive marine <span class="hlt">ice</span> at the LGM, supported by sediment core reconstructions (e.g. Naish et al., 2009 [4]), has a clear buttressing effect on the grounded <span class="hlt">ice</span> that remains significant over a period of 30 to 50 kyr. If <span class="hlt">ice-shelf</span>-free conditions are prescribed at the LGM, the modelled Early Holocene and present-day grounded <span class="hlt">ice</span> volumes are underestimated by up to 10%, as opposed to simulations incorporating <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics over longer periods. The use of <span class="hlt">ice-shelf</span>-free LGM conditions thus results in 50 to over 200 meters thinner <span class="hlt">ice</span> sheet across much of East Antarctica. References [1] Greve, R. (1997). Application of a polythermal three-dimensional <span class="hlt">ice</span> sheet model to the Greenland <span class="hlt">ice</span> sheet: response to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.C12B..04B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.C12B..04B"><span>Constraining <span class="hlt">calving</span> front processes on W Greenland outlet glaciers using inertial-corrected laser scanning & swath-bathymetry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bates, R.; Hubbard, A.; Neale, M.; Woodward, J.; Box, J. E.; Nick, F.</p> <p>2010-12-01</p> <p><span class="hlt">Calving</span> and submarine melt account for the majority of loss from the Antarctic and over 50% of that from the Greenland <span class="hlt">Ice</span> Sheet. These <span class="hlt">ice</span>-ocean processes are highly efficient mass-loss mechanisms, providing a rapid link between terrestrial <span class="hlt">ice</span> (storage) and the oceanic sink (sea level/freshwater flux) which renders the ocean-outlet-<span class="hlt">ice</span> sheet system potentially highly non-linear. Despite this, the controls on tidewater processes are poorly understood and a process based description of them is lacking from the present generation of coupled <span class="hlt">ice</span> sheet models. We present details from an innovative study where two survey techniques are integrated to enable the construction of accurate, ~m resolution 3d digital terrain models (DTMs) of the aerial and submarine <span class="hlt">ice</span> front of <span class="hlt">calving</span> outlet glaciers. A 2km range terrestrial laser scanner was combined with a 416KHz swath-interferometric system and corrected via an inertial motion unit stabilized by RTK GPS and gyro-compass data. The system was mounted aboard a heavy displacement (20,000kg) yacht in addition to a light displacement (100kg) semi-autonomous boat and used to image the aerial and submarine <span class="hlt">calving</span> fronts of two large outlet glaciers in W Greenland. Six daily surveys, each 2.5km long were repeated across Lille Glacier during which significant <span class="hlt">ice</span> flow, melt and <span class="hlt">calving</span> events were observed and captured from on-<span class="hlt">ice</span> GPS stations and time-lapse sequences. A curtain of CTD and velocity casts were also conducted to constrain the fresh and oceanic mass and energy fluxes within the fjord. The residual of successive DTMs yield the spatial pattern of frontal change enabling the processes of aerial and submarine <span class="hlt">calving</span> and melt to be quantified and constrained in unprecedented detail. These observed frontal changes are tentatively related to local dynamic, atmospheric and oceanographic processes that drive them. A partial survey of Store Glacier (~7km <span class="hlt">calving</span> front & W Greenland 2nd largest outlet after Jakobshavn Isbrae</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C43B0803C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C43B0803C"><span>Laboratory investigations of seismicity caused by iceberg <span class="hlt">calving</span> and capsize</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cathles, L. M. M., IV; Kaluzienski, L. M.; Burton, J. C.</p> <p>2015-12-01</p> <p>The <span class="hlt">calving</span> and capsize of cubic kilometer-sized icebergs in both Greenland and Antarctica are known to be the source of long-period seismic events classified as glacial earthquakes. The ability to monitor both <span class="hlt">calving</span> events and the mass of <span class="hlt">ice</span> <span class="hlt">calved</span> using the Global Seismographic Network is quite attractive, however, the basic physics of these large <span class="hlt">calving</span> events must be understood to develop a robust relationship between seismic magnitude and mass of <span class="hlt">ice</span> <span class="hlt">calved</span>. The amplitude and duration of the seismic signal is expected to be related to the mass of the <span class="hlt">calved</span> iceberg and the magnitude of the acceleration of the iceberg's center of mass, yet a simple relationship between these quantities has proved difficult to develop from in situ observations or numerical models. To address this, we developed and carried out a set of experiments on a laboratory scale model of iceberg <span class="hlt">calving</span>. These experiments were designed to measure several aspects of the post-fracture <span class="hlt">calving</span> process. Our results show that a combination of mechanical contact forces and hydrodynamic pressure forces are generated by the capsize of an iceberg adjacent to a glacier's terminus. These forces combine to produce the net horizontal centroid single force (CSF) which is often used to model glacial earthquake sources. We find that although the amplitude and duration of the force applied to the terminus generally increases with the iceberg mass, the details depend on the geometry of the iceberg and the depth of the water. The resulting seismic signal is thus crucially dependent on hydrodynamics of the capsize process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUSM.C21B..04B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUSM.C21B..04B"><span>Ongoing <span class="hlt">calving</span>-frontal dynamics of glaciers in the Northern Patagonia Icefield, Chile</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bown, F.; Rivera, A.; Burger, F.; Carrión, D.; Cisternas, S.; Gacitúa, G.; Pena, M.; Oberreuter, J.; Silva, R.; Uribe, J. A.; Wendt, A.; Zamora, R.</p> <p>2013-05-01</p> <p>Patagonian glaciers are increasingly contributing to the global-sea level rise due to negative mass balances in recent decades, in spite of moderated temperature and precipitation changes taking place in the region. The Austral Chilean glaciers retreat and thinning are strongly influenced by local topography and frontal characteristics, both playing a key role in disrupting glacier responses. One of the main <span class="hlt">ice</span> bodies in this region is the Northern Patagonian Icefield ( NPI, 46S/73W, 3953 km2), a plateau from where tens of outlet glaciers have been inventoried. Many of these glaciers are ending at sea or freshwater lakes where they are <span class="hlt">calving</span>. This <span class="hlt">calving</span> feature is typically associated to non-climatic fluctuations characterized by abnormally-high and sudden retreat and other exacerbated behaviors such as <span class="hlt">ice</span> flow acceleration and dynamical thinning. The main aim of this work is the study of recent <span class="hlt">calving</span> dynamics of three glaciers of the NPI, in order to analyze similarities versus differences associated to their location, topographical constraints and bathymetry, among other features. With this aim, airborne LIDAR and radar surveys, as well as field trips were conducted to the area in year 2012 where several instruments and sensors were installed. The selected study sites were the NPI eastern side freshwater <span class="hlt">calving</span> glaciers Colonia (47.19S/73.29W) and Nef (47.03S/73.27W), and the NPI western margin tidewater <span class="hlt">calving</span> San Rafael glacier (46.70S/73.76W). With all the collected data, <span class="hlt">calving</span> fluxes of 0.03 km3 a-1 and 0.08 km3 a-1 were detected at Glaciares Colonia and Nef respectively. At San Rafael, the <span class="hlt">calving</span> flux was much higher (0.94 km3 a-1) mainly due to a deeper bathymetry near the glacier front, and very high velocities (10m d-1) compared to the eastern side glaciers. At Glaciar San Rafael the <span class="hlt">calving</span> flux is very likely modulated by tidal components and local buoyancy conditions, while at the eastern glaciers, <span class="hlt">calving</span> is a near marginal feature</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>Antarctic <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('http://adsabs.harvard.edu/abs/2003EAEJA....10580S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA....10580S"><span>Dry <span class="hlt">calving</span> processes at the <span class="hlt">ice</span> cliff of an antarctic local glacier: the study case of Strandline Glacier (Northern Victoria Land, Antarctica)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smiraglia, C.; Motta, M.; Vassena, G.; Diolaiuti, G.</p> <p>2003-04-01</p> <p>In Antartic coastal area, where the <span class="hlt">ice</span> sheet and the large outlet glaciers do not reach the sea and where some rugged mountain chains are often present, many small glaciers can be found. They are the so called local or alpine type glaciers, which have their terminus ground-based such as the real alpine glaciers and rarely reach the main valley floors. They are practically isolated and independent from the supply flowing down from the plateau and their mass balance is mainly controlled by sublimation and aeolic erosion and accumulation. The glaciers closer to the coast are submitted to the melting as well, and when the terminus is cliff-shaped they are also affected by dry <span class="hlt">calving</span>. The most known and studied Antarctic local glaciers are placed in the Dry Valleys region (Chinn, 1985), but this kind of glaciers is also diffused all along the Northern Victoria Land coastal region (Chinn and others, 1989). Since the first Italian Antarctic expedition (1985), many studies have been carried out on this type of glaciers, which can be usefull for detailed mass balance evaluations and for obtaining information about the effects of the present climatic dynamics on the Antarctic coastal environment (Baroni and Orombelli, 1987; Baroni and others, 1995; Meneghel, 1999; Vassena and others., 2001). The Strandline Glacier (74 41 S; 164 07 E), in particular is a small alpine glacier (0,79 kmq) on the coast of Terra Nova Bay, Northern Victoria Land; it is a cold glacier where accumulation and ablation basins are mainly controlled by wind processes. Its terminus forms in the central part a grounded <span class="hlt">ice</span> cliff about 30 m high, about 130 m far from the sea. On that glacier mass balance, surface velocity and <span class="hlt">calving</span> rate were measured. During the southern summer season 2000-2001 many topographycal profiles of the <span class="hlt">ice</span> cliff were surveyed by using both classical topographical and glaciological methods (total station and stakes) and GPS technique. It was so possible to detect the short term</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.C21D0471B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.C21D0471B"><span>Petermann Glacier, North Greenland: Large <span class="hlt">Ice</span>-Discharge Episodes from 20 Years of Satellite Observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Babiker, M.; Johannessen, O. M.; Miles, M. W.; Miles, V. V.</p> <p>2009-12-01</p> <p>The major marine-terminating outlet glaciers of Greenland can undergo large mass losses through <span class="hlt">calving</span> of icebergs and bottom melting from floating <span class="hlt">ice</span> tongues. Recent observations of outlet glaiers around Greenland have shown that large and rapid changes in solid-<span class="hlt">ice</span> fluxes are possible. The Petermann glacier in remote northern Greenland is the region’s largest floating-tongue glacier (~70 km by 10 km). In summer 2008 a large <span class="hlt">calving</span> event was observed, as well as large cracks upstream of the remaining <span class="hlt">calving</span> front, portending a more massive near-term loss. These observations may herald extraordinary and unprecedented change. However, the long-term variability of <span class="hlt">calving</span> events and <span class="hlt">ice</span> velocities are poorly known. Our research goal here is to identify the temporal variability and possible trends in solid-<span class="hlt">ice</span> flux indicators - variability of the <span class="hlt">calving</span> front and <span class="hlt">ice</span> velocity - for Petermann glacier. The methodological approach is observational, based primarily on analysis of 20 years of repetitive satellite data over a period starting from 1990, together with sporadic earlier observations. The multisensor data range from high-resolution optical images from Landsat, SPOT and Terra ASTER and high-resolution synthetic aperture radar (SAR) images from ERS and ENVISAT. These disparate data have been imported, geo-registered and analysed within a Geographic Information System. The following measurements are made: (1) delineating changes in the <span class="hlt">calving</span> front, (2) estimating the area of glacial <span class="hlt">ice</span> loss during <span class="hlt">calving</span> events, and (3) estimating the <span class="hlt">ice</span>-surface velocity using sequential satellite images. We find evidence of a number of previous <span class="hlt">calving</span> episodes of similar magnitude to the summer 2008. The <span class="hlt">ice</span>-velocity estimates compare well with other estimates for particular years, and moreover are relatively consistent during the 20-year period. These findings suggest business-as-usual for Petermann glacier; however, a near-term <span class="hlt">calving</span> event exceeding those observed</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12..453M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12..453M"><span>Tidal influences on a future evolution of the Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> cavity in the Weddell Sea, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mueller, Rachael D.; Hattermann, Tore; Howard, Susan L.; Padman, Laurie</p> <p>2018-02-01</p> <p>Recent modeling studies of ocean circulation in the southern Weddell Sea, Antarctica, project an increase over this century of ocean heat into the cavity beneath Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS <span class="hlt">ice</span> draft. The corresponding change in cavity shape will affect advective pathways and the spatial distribution of tidal currents, which play important roles in basal melting under FRIS. These feedbacks between heat flux, basal melting, and tides will affect the evolution of FRIS under the influence of a changing climate. We explore these feedbacks with a three-dimensional ocean model of the southern Weddell Sea that is forced by thermodynamic exchange beneath the <span class="hlt">ice</span> <span class="hlt">shelf</span> and tides along the open boundaries. Our results show regionally dependent feedbacks that, in some areas, substantially modify the melt rates near the grounding lines of buttressed <span class="hlt">ice</span> streams that flow into FRIS. These feedbacks are introduced by variations in meltwater production as well as the circulation of this meltwater within the FRIS cavity; they are influenced locally by sensitivity of tidal currents to water column thickness (wct) and non-locally by changes in circulation pathways that transport an integrated history of mixing and meltwater entrainment along flow paths. Our results highlight the importance of including explicit tidal forcing in models of future mass loss from FRIS and from the adjacent grounded <span class="hlt">ice</span> sheet as individual <span class="hlt">ice</span>-stream grounding zones experience different responses to warming of the ocean inflow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12.1699R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12.1699R"><span>Tidal bending of <span class="hlt">ice</span> shelves as a mechanism for large-scale temporal variations in <span class="hlt">ice</span> flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rosier, Sebastian H. R.; Hilmar Gudmundsson, G.</p> <p>2018-05-01</p> <p>GPS measurements reveal strong modulation of horizontal <span class="hlt">ice</span> <span class="hlt">shelf</span> and <span class="hlt">ice</span> stream flow at a variety of tidal frequencies, most notably a fortnightly (Msf) frequency not present in the vertical tides themselves. Current theories largely fail to explain the strength and prevalence of this signal over floating <span class="hlt">ice</span> shelves. We show how well-known non-linear aspects of <span class="hlt">ice</span> rheology can give rise to widespread, long-periodic tidal modulation in <span class="hlt">ice</span> <span class="hlt">shelf</span> flow, generated within <span class="hlt">ice</span> shelves themselves through tidal flexure acting at diurnal and semidiurnal frequencies. Using full-Stokes viscoelastic modelling, we show that inclusion of tidal bending within the model accounts for much of the observed tidal modulation of <span class="hlt">ice</span> <span class="hlt">shelf</span> flow. Furthermore, our model shows that, in the absence of vertical tidal forcing, the mean flow of the <span class="hlt">ice</span> <span class="hlt">shelf</span> is reduced by almost 30 % for the geometry that we consider.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.C32A..02D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.C32A..02D"><span>Uncovering the glacial history of the Irish continental <span class="hlt">shelf</span> (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dunlop, P.; Benetti, S.; OCofaigh, C.</p> <p>2013-12-01</p> <p>In 1999 the Irish Government initiated a €32 million survey of its territorial waters known as the Irish National Seabed Survey (INSS). The INSS is amongst the largest marine mapping programmes ever undertaken anywhere in the world and provides high-resolution multibeam, backscatter and seismic data of the seabed around Ireland. These data have been used to provide the first clear evidence for extensive glaciation of the continental <span class="hlt">shelf</span> west and northwest of Ireland. Streamlined drumlins on the mid to outer <span class="hlt">shelf</span> record former offshore-directed <span class="hlt">ice</span> flow towards the <span class="hlt">shelf</span> edge and show that the <span class="hlt">ice</span> sheet was grounded in a zone of confluence where <span class="hlt">ice</span> flowing onto the <span class="hlt">shelf</span> from northwest Ireland merged with <span class="hlt">ice</span> flowing across the Malin <span class="hlt">Shelf</span> from southwest Scotland. The major glacial features on the <span class="hlt">shelf</span> are well developed nested arcuate moraine systems that mark the position of the <span class="hlt">ice</span> sheet margin and confirm that the former British Irish <span class="hlt">Ice</span> Sheet was grounded as far as the <span class="hlt">shelf</span> edge around 100 km offshore of west Donegal at the last glacial maximum. Distal to the moraines, on the outermost <span class="hlt">shelf</span>, prominent zones of iceberg plough marks give way to the Barra/Donegal fan and a well developed system of gullies and canyons which incise the continental slope. Since 2008 several scientific cruises have retrieved cores from the <span class="hlt">shelf</span> and slope to help build a more detailed understanding of glacial events in this region. This presentation will provide an overview of the glacial history of the Irish <span class="hlt">shelf</span> and will discuss ongoing research programmes that are building on the initial research findings to produce a better understanding of the nature and timing of <span class="hlt">ice</span> sheet events in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMOS11A1637B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMOS11A1637B"><span>Recent <span class="hlt">calving</span> dynamics of Glaciar Jorge Montt (Southern Patagonia Icefield) based on feature tracking techniques and oceanographic surveys</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bown, F.; Moffat, C. F.; Rivera, A.; Cisternas, S.; Kohoutek, T.</p> <p>2013-12-01</p> <p>Glaciers in the Southern Patagonia Icefield (SPI) have been retreating, thinning and accelerating in recent decades. Most of the SPI is comprised of temperate <span class="hlt">ice</span>, therefore melting is the dominant wasting factor, however, <span class="hlt">calving</span> is also playing a very important role, especially because <span class="hlt">calving</span> is enhancing <span class="hlt">ice</span> dynamic responses, mainly when glaciers <span class="hlt">calve</span> into deep waters. Some of the most exacerbated responses are connected to the well documented and long-term tidewater <span class="hlt">calving</span> cycle (TCC) overlapped by recent climate-related glacier responses. Glaciar Jorge Montt (48S/73W), is a tidewater glacier (~500 km2) which has experienced the maximum frontal retreat of the whole SPI (near 20 km in 112 years) while retreating up to 400 m water depth. Dead trees found in areas recently open by the glacier's retreat prove a date for the previous advancing cycle which took place during the Little <span class="hlt">Ice</span> Age (250-400 years BP). This result indicates that the glacier is experiencing the retreating phase of the TCC in centennial time-scales. However, very little is known if this phase will stop or will continue, or how do climate change dynamcis will affect it. In order to understand the present behaviour of the glacier, several surveys have recently been conducted in the area, including airborne lidar and radar surveys, water depth measurements and <span class="hlt">ice</span> dynamic studies. In order to survey the <span class="hlt">ice</span> dynamic of the glacier front in connection with tides at the inner fjord, a camera pointing to the glacier terminus and collecting up to 8 photographs per day was installed in April 2012. The camera was continuously working for 60 days, allowing to study in detail the <span class="hlt">ice</span> velocities, <span class="hlt">calving</span> fluxes and tides near the <span class="hlt">ice</span>. Thanks to the geo-location of the oblique photographs, feature tracking techniques were applied to the series in order to determine <span class="hlt">ice</span> velocities and frontal retreat during the operational period. The resulting average velocities are lower than 10 m d-1, which are</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.5267S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.5267S"><span>Formation of melt channels on <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>Sergienko, Olga</p> <p>2013-04-01</p> <p>Melt channels have been observed on <span class="hlt">ice</span> shelves experiencing strong melting in both Greenland (Petermann Glacier) and Antarctica (Pine Island Glacier). Using a fully-couple <span class="hlt">ice-shelf/sub-ice-shelf</span>-ocean flow model, it is demonstrated that these channels can form spontaneously in laterally confined <span class="hlt">ice</span> shelves. These channels have transverse extent of a few kilometers and a vertical relief of about a few hundred meters. Meltrates and sea-water transport in the channels are significantly higher than in between the channels on the smooth flat <span class="hlt">ice</span> bottom. In circumstances where an <span class="hlt">ice</span> <span class="hlt">shelf</span> has no-slip conditions at its lateral boundaries, the <span class="hlt">ice-shelf/sub-ice-shelf</span>-cavity system exhibits equilibrium periodic states, where the same configurations repetitively appear with a periodicity of about 30-35 years. This peculiar dynamics of the system has strong implications on the interpretation of the remote and in-situ observations and inferences of the system parameters (e.g., melt rates) based on these observations. For instance, the persistent temporal changes in the <span class="hlt">ice-shelf</span> thickness are caused by internal dynamics of the melt channels, and, in contrast to traditional interpretation, can be independent of the oceanic forcings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12.1387X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12.1387X"><span>Grounding line migration through the <span class="hlt">calving</span> season at Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xie, Surui; Dixon, Timothy H.; Voytenko, Denis; Deng, Fanghui; Holland, David M.</p> <p>2018-04-01</p> <p><span class="hlt">Ice</span> velocity variations near the terminus of Jakobshavn Isbræ, Greenland, were observed with a terrestrial radar interferometer (TRI) during three summer campaigns in 2012, 2015, and 2016. We estimate a ˜ 1 km wide floating zone near the <span class="hlt">calving</span> front in early summer of 2015 and 2016, where <span class="hlt">ice</span> moves in phase with ocean tides. Digital elevation models (DEMs) generated by the TRI show that the glacier front here was much thinner (within 1 km of the glacier front, average <span class="hlt">ice</span> surface is ˜ 100 and ˜ 110 m above local sea level in 2015 and 2016, respectively) than <span class="hlt">ice</span> upstream (average <span class="hlt">ice</span> surface is > 150 m above local sea level at 2-3 km to the glacier front in 2015 and 2016). However, in late summer 2012, there is no evidence of a floating <span class="hlt">ice</span> tongue in the TRI observations. Average <span class="hlt">ice</span> surface elevation near the glacier front was also higher, ˜ 125 m above local sea level within 1 km of the glacier front. We hypothesize that during Jakobshavn Isbræ's recent <span class="hlt">calving</span> seasons the <span class="hlt">ice</span> front advances ˜ 3 km from winter to spring, forming a > 1 km long floating <span class="hlt">ice</span> tongue. During the subsequent <span class="hlt">calving</span> season in mid- and late summer, the glacier retreats by losing its floating portion through a sequence of <span class="hlt">calving</span> events. By late summer, the entire glacier is likely grounded. In addition to <span class="hlt">ice</span> velocity variation driven by tides, we also observed a velocity variation in the mélange and floating <span class="hlt">ice</span> front that is non-parallel to long-term <span class="hlt">ice</span> flow motion. This cross-flow-line signal is in phase with the first time derivative of tidal height and is likely associated with tidal currents or bed topography.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GGG....16.1421C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GGG....16.1421C"><span>Abbot <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of 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>Cochran, James R.; Tinto, Kirsty J.; Bell, Robin E.</p> <p>2015-05-01</p> <p>Inversion of NASA Operation <span class="hlt">Ice</span>Bridge airborne gravity over the Abbot <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> basin. The <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental <span class="hlt">shelf</span> appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic <span class="hlt">Ice</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-GSFC_20171208_Archive_e001754.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-GSFC_20171208_Archive_e001754.html"><span>Jakobshavn <span class="hlt">Calving</span> Front</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-12-08</p> <p>The <span class="hlt">calving</span> front of the Jakobshavn Glacier in western Greenland, as seen from NASA's P-3B aircraft on April 21, 2012. Credit: NASA/GSFC/Jefferson Beck =========== <span class="hlt">Ice</span>Bridge, a six-year NASA mission, is the largest airborne survey of Earth's polar <span class="hlt">ice</span> ever flown. It will yield an unprecedented three-dimensional view of Arctic and Antarctic <span class="hlt">ice</span> sheets, <span class="hlt">ice</span> shelves and sea <span class="hlt">ice</span>. These flights will provide a yearly, multi-instrument look at the behavior of the rapidly changing features of the Greenland and Antarctic <span class="hlt">ice</span>. Data collected during <span class="hlt">Ice</span>Bridge will help scientists bridge the gap in polar observations between NASA's <span class="hlt">Ice</span>, Cloud and Land Elevation Satellite (ICESat) -- in orbit since 2003 -- and ICESat-2, planned for early 2016. ICESat stopped collecting science data in 2009, making <span class="hlt">Ice</span>Bridge critical for ensuring a continuous series of observations. <span class="hlt">Ice</span>Bridge will use airborne instruments to map Arctic and Antarctic areas once a year. <span class="hlt">Ice</span>Bridge flights are conducted in March-May over Greenland and in October-November over Antarctica. Other smaller airborne surveys around the world are also part of the <span class="hlt">Ice</span>Bridge campaign. To read more about <span class="hlt">Ice</span>Bridge - Arctic 2012 go to: www.nasa.gov/mission_pages/icebridge/index.html 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989QuRes..31..119P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989QuRes..31..119P"><span>Modeling the growth and decay of the Antarctic Peninsula <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>Payne, A. J.; Sugden, D. E.; Clapperton, C. M.</p> <p>1989-03-01</p> <p>A model of the growth and decay of the Antarctic Peninsula <span class="hlt">Ice</span> Sheet during the last glacial/interglacial cycle is used to identify the main controls on <span class="hlt">ice</span> 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 <span class="hlt">ice</span> shelves. An <span class="hlt">ice</span> sheet dome over 3.5 km thick grows on the offshore <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> cover is achieved at 6500 yr B.P. <span class="hlt">Ice</span> 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 <span class="hlt">ice</span> sheet behavior is most sensitive to sea-level change, basal marine melting, and accumulation and is less sensitive to isostasy, spatial variation in accumulation, <span class="hlt">calving</span> rates, and <span class="hlt">ice</span> flow parameterization. Tests of the model against field evidence show good agreement in places, as well as discrepancies which require further work.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C12B..07S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C12B..07S"><span>In-situ GPS records of surface mass balance, firn compaction rates, and <span class="hlt">ice-shelf</span> basal melt rates for Pine Island Glacier, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shean, D. E.; Christianson, K.; Larson, K. M.; Ligtenberg, S.; Joughin, I. R.; Smith, B.; Stevens, C.</p> <p>2016-12-01</p> <p>In recent decades, Pine Island Glacier (PIG) has experienced marked retreat, speedup and thinning due to <span class="hlt">ice-shelf</span> basal melt, internal <span class="hlt">ice</span>-stream instability and feedbacks between these processes. In an effort to constrain recent <span class="hlt">ice</span>-stream dynamics and evaluate potential causes of retreat, we analyzed 2008-2010 and 2012-2014 GPS records for PIG. We computed time series of horizontal velocity, strain rate, multipath-based antenna height, surface elevation, and Lagrangian elevation change (Dh/Dt). These data provide validation for complementary high-resolution WorldView stereo digital elevation model (DEM) records, with sampled DEM vertical error of 0.7 m. The GPS antenna height time series document a relative surface elevation increase of 0.7-1.0 m/yr, which is consistent with estimated surface mass balance (SMB) of 0.7-0.9 m.w.e./yr from RACMO2.3 and firn compaction rates from the IMAU-FDM dynamic firn model. An abrupt 0.2-0.3 m surface elevation decrease due to surface melt and/or greater near-surface firn compaction is observed during a period of warm atmospheric temperatures from December 2012 to January 2013. Observed surface Dh/Dt for all PIG <span class="hlt">shelf</span> sites is highly linear with trends of -1 to -4 m/yr and <0.4 m residuals. Similar Dh/Dt estimates with reduced variability are obtained after removing expected downward GPS pole base velocity from observed GPS antenna Dh/Dt. Estimated Dh/Dt basal melt rates are 10 to 40 m/yr for the outer PIG <span class="hlt">shelf</span> and 4 m/yr for the South <span class="hlt">shelf</span>. These melt rates are similar to those derived from <span class="hlt">ice</span>-bottom acoustic ranging, phase-sensitive <span class="hlt">ice</span>-penetrating radar, and high-resolution stereo DEM records. The GPS/DEM records document higher melt rates within and near transverse surface depressions and rifts associated with longitudinal extension. Basal melt rates for the 2012-2014 period show limited temporal variability, despite significant change in ocean heat content. This suggests that sub-<span class="hlt">shelf</span> melt rates are less sensitive to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22538614','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22538614"><span>Antarctic <span class="hlt">ice</span>-sheet loss driven by basal melting of <span class="hlt">ice</span> shelves.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pritchard, H D; Ligtenberg, S R M; Fricker, H A; Vaughan, D G; van den Broeke, M R; Padman, L</p> <p>2012-04-25</p> <p>Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic <span class="hlt">ice</span>-sheet coastal margins. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating <span class="hlt">ice</span> shelves, potentially limiting their ability to buttress the flow of grounded tributary glaciers. Indeed, recent <span class="hlt">ice-shelf</span> collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. But the extent and magnitude of <span class="hlt">ice-shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice-shelf</span> thinning through increased basal melt. We deduce that this increased melt is the primary control of Antarctic <span class="hlt">ice</span>-sheet loss, through a reduction in buttressing of the adjacent <span class="hlt">ice</span> sheet leading to accelerated glacier flow. The highest thinning rates occur where warm water at depth can access thick <span class="hlt">ice</span> shelves via submarine troughs crossing the continental <span class="hlt">shelf</span>. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic <span class="hlt">ice</span> 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 <span class="hlt">ice</span>-sheet mass balance, and hence global sea level, on annual to decadal timescales.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997PhDT........88C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997PhDT........88C"><span>Neoglacial fluctuations of terrestrial, tidewater, and <span class="hlt">calving</span> lacustrine glaciers, Blackstone-Spencer <span class="hlt">Ice</span> Complex, Kenai Mountains, Alaska</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Crossen, Kristine June</p> <p>1997-12-01</p> <p>The glaciers surrounding the Blackstone-Spencer <span class="hlt">Ice</span> Complex display a variety of termini types: Tebenkov, Spencer, Bartlett, Skookum, Trail, Burns, Shakespeare, Marquette, Lawrence, and Ripon glaciers end in terrestrial margins; Blackstone and Beloit glaciers have tidewater termini; and Portage Glacier has a <span class="hlt">calving</span> lacustrine margin. In addition, steep temperature and precipitation gradients exist across the <span class="hlt">ice</span> complex from the maritime environment of Prince William Sound to the colder, drier interior. The Neoglacial history of Tebenkov Glacier, as based on overrun trees near the terminus, shows advances ca. 250- 430 AD (calibrated date), ca. 1215-1275 AD (calibrated date), and ca. 1320-1430 AD (tree ring evidence), all intervals of glacier advance around the Gulf of Alaska. However, two tidewater glaciers in Blackstone Bay retreated from their outermost moraines by 1350 AD, apparently asynchronously with respect to the regional climate signal. The most extensive Kenai Mountain glacier expansions during Neoglaciation occurred in the late Little <span class="hlt">Ice</span> Age. The outermost moraines are adjacent to mature forest stands and bog peats that yield dates as old as 5,600 BP. Prince William Sound glaciers advanced during two Little <span class="hlt">Ice</span> Age cold periods, 1380-1680 and 1830-1900 AD. The terrestrial glaciers around the Blackstone-Spencer <span class="hlt">Ice</span> Complex all built moraines during the 19th century and began retreating between 1875 and 1900 AD. Portage and Burns glaciers began retreating between 1790 and 1810 AD, but their margins remained close to the outermost moraines during the 19th century. Regional glacier fluctuations are broadly synchronous in the Gulf of Alaska region. With the exception of the two tidewater glaciers in Blackstone Bay, all glaciers in the Kenai Mountains, no matter their sizes, altitudes, orientations, or types of margins, retreated at the end of the Little <span class="hlt">Ice</span> Age. The climate signal, especially temperature, appears to be the strongest control on glacier</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('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3860075','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3860075"><span><span class="hlt">Shelf</span> Acetabuloplasty in the Treatment of Severe Legg-<span class="hlt">Calv</span>é-Perthes Disease: Good Outcomes at Midterm Follow-Up</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Grzegorzewski, Andrzej; Synder, Marek; Kmieć, Krysztof; Krajewski, Karol; Polguj, Michał; Sibiński, Marcin</p> <p>2013-01-01</p> <p>The aim of the study was to retrospectively review results of operative treatment for coverage deficit of femoral head in children with severe epiphysis displacement in Legg-<span class="hlt">Calv</span>é-Perthes (LCP) disease. The material included 23 <span class="hlt">shelf</span> acetabuloplasty procedures for LCP disease. The average age at diagnosis was 8.1 years (range 4–12). Mean follow-up was 5.8 years (range from 2.2 to 11.2 years). Mean Reimer's index decreased statistically significantly from a mean of 32% before surgery to 10.0% at the last follow-up (P < 0.00001). The mean Wiberg center-edge angle increased also statistically significantly from a mean of 17.3° before procedure to 32.3° at the last follow-up (P < 0.00001). According to the Stulberg classification, type I was observed in 2, type II in 13, type III in 6, and type IV in 2 hips. There were no differences in the range of motion or leg length discrepancy in preoperative and postoperative standing. Partial, not significant, bone graft resorption was noted in 6 cases in the first 6–9 months after surgery. To conclude, <span class="hlt">shelf</span> acetabuloplasty allows achieving good midterm results in the treatment of severe stages of LCP disease. The procedure improves coverage of femoral head and allows its remodelling. PMID:24377097</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/AD1036407','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/AD1036407"><span>Geophysical Survey of McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> to Determine Infrastructure Stability and for Future Planning</span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>2017-01-01</p> <p>ER D C/ CR RE L TR -1 7- 2 Engineering for Polar Operations, Logistics, and Research (EPOLAR) Geophysical Survey of McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span>...Army Engineer Research and Development Center (ERDC) solves the nation’s toughest engineering and environmental challenges. ERDC develops...ERDC, visit the ERDC online library at http://acwc.sdp.sirsi.net/client/default. Engineering for Polar Operations, Logistics, and Research (EPOLAR</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSHE44B1516R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSHE44B1516R"><span>Turbulent heat exchange between water and <span class="hlt">ice</span> at an evolving <span class="hlt">ice</span>-water interface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ramudu, E.; Hirsh, B.; Olson, P.; Gnanadesikan, A.</p> <p>2016-02-01</p> <p>Experimental results are presented on the time evolution of <span class="hlt">ice</span> subject to a turbulent shear flow in a layer of water of uniform depth. Our study is motivated by observations in the ocean cavity beneath Antarctic <span class="hlt">ice</span> shelves, where shoaling of Circumpolar Deep Water into the cavity has been implicated in the accelerated melting of the <span class="hlt">ice</span> <span class="hlt">shelf</span> base. Measurements of inflow and outflow at the <span class="hlt">ice</span> <span class="hlt">shelf</span> front have shown that not all of the heat entering the cavity is delivered to the <span class="hlt">ice</span> <span class="hlt">shelf</span>, suggesting that turbulent transfer to the <span class="hlt">ice</span> represents an important bottleneck. Given that a range of turbulent transfer coefficients has been used in models it is important to better constrain this parameter. We measure as a function of time in our experiments the thickness of the <span class="hlt">ice</span>, temperatures in the <span class="hlt">ice</span> and water, and fluid velocity in the shear flow, starting from an initial condition in which the water is at rest and the <span class="hlt">ice</span> has grown by conduction above a cold plate. The strength of the applied turbulent shear flow is represented in terms of a Reynolds number Re, which is varied over the range 3.5 × 103 ≤ Re ≤ 1.9 × 104. Transient partial melting of the <span class="hlt">ice</span> occurs at the lower end of this range of Re and complete transient melting of the <span class="hlt">ice</span> occurs at the higher end of the range. Following these melting transients, the <span class="hlt">ice</span> reforms at a rate that is independent of Re. We fit to our experimental measurements of <span class="hlt">ice</span> thickness and temperature a one-dimensional model for the evolution of the <span class="hlt">ice</span> thickness in which the turbulent heat transfer is parameterized in terms of the friction velocity of the shear flow. Comparison with the Pine Island Glacier <span class="hlt">Ice</span> <span class="hlt">Shelf</span> yields qualitative agreement between the transient <span class="hlt">ice</span> melting rates predicted by our model and the <span class="hlt">shelf</span> melting rate inferred from the field observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16782604','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16782604"><span>Changes in <span class="hlt">ice</span> dynamics and mass balance of the Antarctic <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>Rignot, Eric</p> <p>2006-07-15</p> <p>The concept that the Antarctic <span class="hlt">ice</span> sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered <span class="hlt">ice</span> <span class="hlt">shelf</span> collapse, which led to a 10-fold increase in glacier flow and rapid <span class="hlt">ice</span> sheet retreat. This chain of events illustrated the vulnerability of <span class="hlt">ice</span> 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 <span class="hlt">ice</span> into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1m and trigger widespread retreat of <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from <span class="hlt">ice</span> <span class="hlt">shelf</span> melting by an ocean that has recently warmed by 0.3 degrees C. In contrast, glaciers buffered from oceanic change by large <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.C21B1098D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.C21B1098D"><span>Crevasse detection with GPR across the Ross <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>Delaney, A.; Arcone, S.</p> <p>2005-12-01</p> <p>We have used 400-MHz ground penetrating radar (GPR) to detect crevasses within a shear zone on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Antarctica, to support traverse operations. The transducer was attached to a 6.5-m boom and pushed ahead of an enclosed tracked vehicle. Profile speeds of 4.8-11.3 km / hr allowed real-time crevasse image display and a quick, safe stop when required. Thirty-two crevasses were located with radar along the 4.8 km crossing. Generally, crevasse radar images were characterized by dipping reflections above the voids, high-amplitude reflections originating from <span class="hlt">ice</span> layers at the base of the snow-bridges, and slanting, diffracting reflections from near-vertical crevasse walls. New cracks and narrow crevasses (<50 cm width) show no distinct snow bridge structure, few diffractions, and a distinct band where pulse reflections are absent. Wide (0.5-5.0 m), vertical wall crevasses show distinct dipping snow bridge layering and intense diffractions from <span class="hlt">ice</span> layers near the base of the snow bridge. Pulse reflections are absent from voids beneath the snow bridges. Old, wide (3.0-8.0 m) and complexly shaped crevasses show well-developed, broad, dipping snow-bridge layers and a high-amplitude, complex, diffraction pattern. The crevasse mitigation process, which included hot-water drilling, destroying the bridges with dynamite, and back-filling with bulldozed snow, afforded an opportunity to ground-truth GPR interpretations by comparing void size and snow-bridge geometry with the radar images. While second and third season radar profiles collected along the identical flagged route confirmed stability of the filled crevasses, those profiles also identified several new cracks opened by <span class="hlt">ice</span> extension. Our experiments demonstrate capability of high-frequency GPR in a cold-snow environment for both defining snow layers and locating voids.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRC..120..777M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRC..120..777M"><span>Invisible polynyas: Modulation of fast <span class="hlt">ice</span> thickness by ocean heat flux on the Canadian polar <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>Melling, Humfrey; Haas, Christian; Brossier, Eric</p> <p>2015-02-01</p> <p>Although the Canadian polar <span class="hlt">shelf</span> is dominated by thick fast <span class="hlt">ice</span> in winter, areas of young <span class="hlt">ice</span> or open water do recur annually at locations within and adjacent to the fast <span class="hlt">ice</span>. These polynyas are detectable by eye and sustained by wind or tide-driven <span class="hlt">ice</span> divergence and ocean heat flux. Our <span class="hlt">ice</span>-thickness surveys by drilling and towed electromagnetic sounder reveal that visible polynyas comprise only a subset of thin-<span class="hlt">ice</span> coverage. Additional area in the coastal zone, in shallow channels and in fjords is covered by thin <span class="hlt">ice</span> which is too thick to be discerned by eye. Our concurrent surveys by CTD reveal correlation between thin fast <span class="hlt">ice</span> and above-freezing seawater beneath it. We use winter time series of air and ocean temperatures and <span class="hlt">ice</span> and snow thicknesses to calculate the ocean-to-<span class="hlt">ice</span> heat flux as 15 and 22 W/m2 at locations with thin <span class="hlt">ice</span> in Penny Strait and South Cape Fjord, respectively. Near-surface seawater above freezing is not a sufficient condition for ocean heat to reach the <span class="hlt">ice</span>; kinetic energy is needed to overcome density stratification. The ocean's isolation from wind under fast <span class="hlt">ice</span> in winter leaves tides as the only source. Two tidal mechanisms driving ocean heat flux are discussed: diffusion via turbulence generated by shear at the under-<span class="hlt">ice</span> and benthic boundaries, and the internal hydraulics of flow over topography. The former appears dominant in channels and the coastal zone and the latter in some silled fjords where and when the layering of seawater density permits hydraulically critical flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C21E1171K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C21E1171K"><span>New details about the LGM extent and subsequent retreat of the West Antarctic <span class="hlt">Ice</span> Sheet from the easternmost Amundsen Sea Embayment <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>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.</p> <p>2017-12-01</p> <p>In recent years several previously undiscovered grounding-zone wedges (GZWs) have been described within the Abbot-Cosgrove palaeo-<span class="hlt">ice</span> stream trough on the easternmost Amundsen Sea Embayment <span class="hlt">shelf</span>. 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 <span class="hlt">shelf</span> 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-<span class="hlt">ice</span> free outer <span class="hlt">shelf</span> 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 <span class="hlt">Ice</span> Sheet from the Amundsen Sea Embayment <span class="hlt">shelf</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4981079','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4981079"><span>Dynamics of glacier <span class="hlt">calving</span> at the ungrounded margin of Helheim Glacier, southeast Greenland</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Selmes, Nick; James, Timothy D.; Edwards, Stuart; Martin, Ian; O'Farrell, Timothy; Aspey, Robin; Rutt, Ian; Nettles, Meredith; Baugé, Tim</p> <p>2015-01-01</p> <p>Abstract During summer 2013 we installed a network of 19 GPS nodes at the ungrounded margin of Helheim Glacier in southeast Greenland together with three cameras to study iceberg <span class="hlt">calving</span> mechanisms. The network collected data at rates up to every 7 s and was designed to be robust to loss of nodes as the glacier <span class="hlt">calved</span>. Data collection covered 55 days, and many nodes survived in locations right at the glacier front to the time of iceberg <span class="hlt">calving</span>. The observations included a number of significant <span class="hlt">calving</span> events, and as a consequence the glacier retreated ~1.5 km. The data provide real‐time, high‐frequency observations in unprecedented proximity to the <span class="hlt">calving</span> front. The glacier <span class="hlt">calved</span> by a process of buoyancy‐force‐induced crevassing in which the <span class="hlt">ice</span> downglacier of flexion zones rotates upward because it is out of buoyant equilibrium. <span class="hlt">Calving</span> then occurs back to the flexion zone. This <span class="hlt">calving</span> process provides a compelling and complete explanation for the data. Tracking of oblique camera images allows identification and characterisation of the flexion zones and their propagation downglacier. Interpretation of the GPS data and camera data in combination allows us to place constraints on the height of the basal cavity that forms beneath the rotating <span class="hlt">ice</span> downglacier of the flexion zone before <span class="hlt">calving</span>. The flexion zones are probably formed by the exploitation of basal crevasses, and theoretical considerations suggest that their propagation is strongly enhanced when the glacier base is deeper than buoyant equilibrium. Thus, this <span class="hlt">calving</span> mechanism is likely to dominate whenever such geometry occurs and is of increasing importance in Greenland. PMID:27570721</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFMGC51A1050C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFMGC51A1050C"><span>Impacts of Recent Warming on a Floating <span class="hlt">Ice</span> Tongue in Northern Greenland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cullen, N. J.; Huff, R.; Steffen, K.; Rignot, E.</p> <p>2004-12-01</p> <p>The recent collapse of <span class="hlt">ice</span> shelves in West Antarctica and to the Ward Hunt <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Ellesmere Island, Canada, has been interpreted as evidence of accelerated climate change in the high latitudes. To improve our understanding of the stability of glaciers in northern Greenland a combination of field data, remote sensing observations and modeling is used to investigate both bottom and surface melt processes on the Petermann Gletscher (81 N, 60 W). The Petermann Gletscher is similar to other more well-known <span class="hlt">ice</span> shelves because it has a large floating section, or <span class="hlt">ice</span> tongue, that is 20-km wide by 70-km long. This purpose of this work is to describe in detail the surface climate of the Petermann Gletscher from automatic weather station (AWS) data. Emphasis in placed on describing surface energy exchanges that have controlled ablation over the 3 most recent summer seasons (2002-4). Projection of ablation over the entire surface of the <span class="hlt">ice</span> tongue using a degree-day model shows that surface lowering of the <span class="hlt">ice</span> tongue in 2002-3 is 50 percent higher than a 53-year proxy melt record established from AWS measurements at nearby Alert, Ellesmere Island. If this warming trend continues the increased thinning rate is likely to yield enhanced <span class="hlt">calving</span> rates at the <span class="hlt">ice</span> front of the Petermann Gletscher, which could ultimately weaken and fracture the floating <span class="hlt">ice</span> tongue.</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 Antarctic 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/2013AGUSM.C24A..01S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUSM.C24A..01S"><span>Sea <span class="hlt">Ice</span> Formation Rate and Temporal Variation of Temperature and Salinity at the Vicinity of Wilkins <span class="hlt">Ice</span> <span class="hlt">Shelf</span> from Data Collected by Southern Elephant Seals in 2008</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Santini, M. F.; Souza, R.; Wainer, I.; Muelbert, M.; Hindell, M.</p> <p>2013-05-01</p> <p>The use of marine mammals as autonomous platforms for collecting oceanographic data has revolutionized the understanding of physical properties of low or non-sampled regions of the polar oceans. The use of these animals became possible due to advancements in the development of electronic devices, sensors and batteries carried by them. Oceanographic data collected by two southern elephant seals (Mirounga leonina) during the Fall of 2008 were used to infer the sea-<span class="hlt">ice</span> formation rate in the region adjacent to the Wilkins <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, west of the Antarctic Peninsula at that period. The sea-<span class="hlt">ice</span> formation rate was estimated from the salt balance equation for the upper (100 m) ocean at a daily frequency for the period between 13 February and 20 June 2008. The oceanographic data collected by the animals were also used to present the temporal variation of the water temperature and salinity from surface to 300 m depth in the study area. Sea <span class="hlt">ice</span> formation rate ranged between 0,087 m/day in early April and 0,008 m/day in late June. Temperature and salinity ranged from -1.84°C to 1.60°C and 32.85 to 34.85, respectively, for the upper 300 m of the water column in the analyzed period. The sea-<span class="hlt">ice</span> formation rate estimations do not consider water advection, only temporal changes of the vertical profile of salinity. This may cause underestimates of the real sea-<span class="hlt">ice</span> formation rate. The intense reduction of sea <span class="hlt">ice</span> rate formation from April to June 2008 may be related to the intrusion of the Circumpolar Depth Water (CDW) into the study region. As a consequence of that we believe that this process can be partly responsible for the disintegration of the Wilkins <span class="hlt">Ice</span> <span class="hlt">Shelf</span> during the winter of 2008. The data presented here are considered a new frontier in physical and biological oceanography, providing a new approach for monitoring sea <span class="hlt">ice</span> changes and oceanographic conditions in polar oceans. This is especially valid for regions covered by sea <span class="hlt">ice</span> where traditional instruments deployed by</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 Antarctic <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 Antarctic 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('http://adsabs.harvard.edu/abs/2016EGUGA..18.4179K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4179K"><span>Reconstruction of sea-<span class="hlt">ice</span> cover and primary production on the East Greenland <span class="hlt">Shelf</span> (73°N) during the last 5200 years</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kolling, Henriette Marie; Stein, Rüdiger; Fahl, Kirsten; Perner, Kerstin; Moros, Matthias</p> <p>2016-04-01</p> <p>Over the last decades the extent and thickness of Arctic sea <span class="hlt">ice</span> has changed dramatically and much more rapidly than predicted by climate models. Thus, high-resolution sea-<span class="hlt">ice</span> reconstructions from pre-anthropogenic times are useful and needed in order to better understand the processes controlling the natural sea-<span class="hlt">ice</span> variability. Here, we present the first high-resolution biomarker (IP25, sterols) approach over the last 5.2 ka from the East Greenland <span class="hlt">Shelf</span> (for background about the biomarker approach see Belt et al., 2007; Müller et al., 2009, 2011). This area is highly sensitive to sea-<span class="hlt">ice</span> changes, as it underlies the pathway of the East Greenland Current, the main exporter of Arctic freshwater and sea <span class="hlt">ice</span> that affects the environmental conditions on the East Greenland <span class="hlt">Shelf</span> and deep-water formation/ convection in the Northern North Atlantic. After rather stable sea-<span class="hlt">ice</span> conditions in the mid-Holocene we found a strong increase in sea <span class="hlt">ice</span>, cumulating around 1.5 ka and associated with the Neoglacial cooling. The general trend especially during the last 1ka is interrupted by several short-lived events such as the prominent Medieval Warm Period and Little <span class="hlt">Ice</span> Age, characterized by minimum and maximum sea-<span class="hlt">ice</span> extent, respectively. Using a spectral analysis, we could identify several cyclicites, e.g. a 45-year cyclicity for cold events. A comparison to similar records from the eastern Fram Strait revealed a slight time lag in the onset of the Neoglacial, but also suggesting the direct link of the East Greenland <span class="hlt">Shelf</span> area to the Arctic sea-<span class="hlt">ice</span>/freahwater outflow. A comparison of the biomarker data with a new foraminiferal record obtained from the same site (Perner et al., 2015) suggests that IP25 and foraminifera assemblages are probably controlled by rather different processes within the oceanographic systems, such as the sea-<span class="hlt">ice</span> conditions and, for the foraminifera, water-mass changes and nutrient supply. References: Belt. S.T., Massé, G., Rowland, S.J., Poulin, M</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.8570A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.8570A"><span>Design of the MISMIP+, ISOMIP+, and MISOMIP <span class="hlt">ice</span>-sheet, ocean, and coupled <span class="hlt">ice</span> sheet-ocean intercomparison projects</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Asay-Davis, Xylar; Cornford, Stephen; Martin, Daniel; Gudmundsson, Hilmar; Holland, David; Holland, Denise</p> <p>2015-04-01</p> <p>The MISMIP and MISMIP3D marine <span class="hlt">ice</span> sheet model intercomparison exercises have become popular benchmarks, and several modeling groups have used them to show how their models compare to both analytical results and other models. Similarly, the ISOMIP (<span class="hlt">Ice</span> <span class="hlt">Shelf</span>-Ocean Model Intercomparison Project) experiments have acted as a proving ground for ocean models with sub-<span class="hlt">ice-shelf</span> cavities.As coupled <span class="hlt">ice</span> sheet-ocean models become available, an updated set of benchmark experiments is needed. To this end, we propose sequel experiments, MISMIP+ and ISOMIP+, with an end goal of coupling the two in a third intercomparison exercise, MISOMIP (the Marine <span class="hlt">Ice</span> Sheet-Ocean Model Intercomparison Project). Like MISMIP3D, the MISMIP+ experiments take place in an idealized, three-dimensional setting and compare full 3D (Stokes) and reduced, hydrostatic models. Unlike the earlier exercises, the primary focus will be the response of models to sub-<span class="hlt">shelf</span> melting. The chosen configuration features an <span class="hlt">ice</span> <span class="hlt">shelf</span> that experiences substantial lateral shear and buttresses the upstream <span class="hlt">ice</span>, and so is well suited to melting experiments. Differences between the steady states of each model are minor compared to the response to melt-rate perturbations, reflecting typical real-world applications where parameters are chosen so that the initial states of all models tend to match observations. The three ISOMIP+ experiments have been designed to to make use of the same bedrock topography as MISMIP+ and using <span class="hlt">ice-shelf</span> geometries from MISMIP+ results produced by the BISICLES <span class="hlt">ice</span>-sheet model. The first two experiments use static <span class="hlt">ice-shelf</span> geometries to simulate the evolution of ocean dynamics and resulting melt rates to a quasi-steady state when far-field forcing changes in either from cold to warm or from warm to cold states. The third experiment prescribes 200 years of dynamic <span class="hlt">ice-shelf</span> geometry (with both retreating and advancing <span class="hlt">ice</span>) based on a BISICLES simulation along with similar flips between warm and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.6032M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.6032M"><span>Glacigenic landforms and sediments of the Western Irish <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>McCarron, Stephen; Monteys, Xavier; Toms, Lee</p> <p>2013-04-01</p> <p>Vibrocoring of possible glacigenic landforms identified from high resolution bathymetric coverage of the Irish <span class="hlt">Shelf</span> by the Irish National Seabed Survey (INSS) has provided several clusters of short (<3m) cores that, due to a regional post-glacial erosional event, comprise last glacial age stratigraphies. In addition, new shallow seismic data and sedimentological information from across the Western Irish <span class="hlt">Shelf</span> provide new insights into aspects of the nature, timing and pattern of <span class="hlt">shelf</span> occupation by grounded lobate extensions of the last Irish <span class="hlt">Ice</span> Sheet. Restricted chronological control of deglacial sequences in several cores indicates that northern parts of the western mid-<span class="hlt">shelf</span> (south of a prominent outer Donegal Bay ridge) were <span class="hlt">ice</span> free by ~24 ka B.P., and that <span class="hlt">ice</span> had also probably retreated from outer <span class="hlt">shelf</span> positions (as far west as the Porcupine Bank) at or before this time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017ECSS..194..205B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017ECSS..194..205B"><span>Circulation and fjord-<span class="hlt">shelf</span> exchange during the <span class="hlt">ice</span>-covered period in Young Sound-Tyrolerfjord, Northeast Greenland (74°N)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boone, W.; Rysgaard, S.; Kirillov, S.; Dmitrenko, I.; Bendtsen, J.; Mortensen, J.; Meire, L.; Petrusevich, V.; Barber, D. G.</p> <p>2017-07-01</p> <p>Fjords around Greenland connect the Greenland <span class="hlt">Ice</span> Sheet to the ocean and their hydrography and circulation are determined by the interplay between atmospheric forcing, runoff, topography, fjord-<span class="hlt">shelf</span> exchange, tides, waves, and seasonal growth and melt of sea <span class="hlt">ice</span>. Limited knowledge exists on circulation in high-Arctic fjords, particularly those not impacted by tidewater glaciers, and especially during winter, when they are covered with sea-<span class="hlt">ice</span> and freshwater input is low. Here, we present and analyze seasonal observations of circulation, hydrography and cross-sill exchange of the Young Sound-Tyrolerfjord system (74°N) in Northeast Greenland. Distinct seasonal circulation phases are identified and related to polynya activity, meltwater and inflow of coastal water masses. Renewal of basin water in the fjord is a relatively slow process that modifies the fjord water masses on a seasonal timescale. By the end of winter, there is two-layer circulation, with outflow in the upper 45 m and inflow extending down to approximately 150 m. Tidal analysis showed that tidal currents above the sill were almost barotropic and dominated by the M2 tidal constituent (0.26 m s-1), and that residual currents (∼0.02 m s-1) were relatively small during the <span class="hlt">ice</span>-covered period. Tidal pumping, a tidally driven fjord-<span class="hlt">shelf</span> exchange mechanism, drives a salt flux that is estimated to range between 145 kg s-1 and 603 kg s-1. Extrapolation of these values over the <span class="hlt">ice</span>-covered period indicates that tidal pumping is likely a major source of dense water and driver of fjord circulation during the <span class="hlt">ice</span>-covered period.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050041627','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050041627"><span><span class="hlt">Ice</span> Shelves and Landfast <span class="hlt">Ice</span> on the Antarctic Perimeter: Revised Scope of Work</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Abdalati, Waleed (Technical Monitor); Scambos, Ted</p> <p>2004-01-01</p> <p><span class="hlt">Ice</span> 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 <span class="hlt">ice</span> shelves in the Antarctic Peninsula region (the Larsen 'A', B', and Wilkins <span class="hlt">Ice</span> shelves) in the results of a previous grant under ADRO-1. Modeling of <span class="hlt">shelf</span> <span class="hlt">ice</span> flow and the effects of meltwater indicated that melt ponding accelerates <span class="hlt">shelf</span> breakup by increasing fracturing. The ADRO-2 funding (topic of this report) supported further inquiry into the evolution of <span class="hlt">ice</span> shelves under warming conditions, and the post-breakup effects on their feeder glaciers. Also, this grant considered fast <span class="hlt">ice</span> and sea <span class="hlt">ice</span> characteristics, to the extent that they provide information regarding <span class="hlt">shelf</span> stability. A major component of this work was in the form of NSIDC image data support and in situ sea <span class="hlt">ice</span> research on the Aurora Australis 'ARISE' cruise of September 9 2003 through October 28 2003.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-GSFC_20171208_Archive_e000908.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-GSFC_20171208_Archive_e000908.html"><span>Thurston Island</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-12-08</p> <p>The Thurston Island <span class="hlt">calving</span> front off of western Antarctica as seen from the window of NASA's DC-8 on Nov. 5, 2014. Image Credit: NASA/Jim Yungel NASA’s Operation <span class="hlt">Ice</span>Bridge collected some rare images on a flight out of Punta Arenas, Chile on Nov. 5, 2014, on a science flight over western Antarctica dubbed Ferrigno-Alison-Abbott 01. The crew snapped a few shots of a <span class="hlt">calving</span> front of the Antarctic <span class="hlt">ice</span> sheet. This particular flight plan was designed to collect data on changes in <span class="hlt">ice</span> elevation along the coast near the Ferrigno and Alison <span class="hlt">ice</span> streams, on the Abbot <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, and grounded <span class="hlt">ice</span> along the Eights Coast.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12..609V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12..609V"><span>Effects of undercutting and sliding on <span class="hlt">calving</span>: a global approach applied to Kronebreen, Svalbard</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vallot, Dorothée; Åström, Jan; Zwinger, Thomas; Pettersson, Rickard; Everett, Alistair; Benn, Douglas I.; Luckman, Adrian; van Pelt, Ward J. J.; Nick, Faezeh; Kohler, Jack</p> <p>2018-02-01</p> <p>In this paper, we study the effects of basal friction, sub-aqueous undercutting and glacier geometry on the <span class="hlt">calving</span> process by combining six different models in an offline-coupled workflow: a continuum-mechanical <span class="hlt">ice</span> flow model (Elmer/<span class="hlt">Ice</span>), a climatic mass balance model, a simple subglacial hydrology model, a plume model, an undercutting model and a discrete particle model to investigate fracture dynamics (Helsinki Discrete Element Model, HiDEM). We demonstrate the feasibility of reproducing the observed <span class="hlt">calving</span> retreat at the front of Kronebreen, a tidewater glacier in Svalbard, during a melt season by using the output from the first five models as input to HiDEM. Basal sliding and glacier motion are addressed using Elmer/<span class="hlt">Ice</span>, while <span class="hlt">calving</span> is modelled by HiDEM. A hydrology model calculates subglacial drainage paths and indicates two main outlets with different discharges. Depending on the discharge, the plume model computes frontal melt rates, which are iteratively projected to the actual front of the glacier at subglacial discharge locations. This produces undercutting of different sizes, as melt is concentrated close to the surface for high discharge and is more diffuse for low discharge. By testing different configurations, we show that undercutting plays a key role in glacier retreat and is necessary to reproduce observed retreat in the vicinity of the discharge locations during the melting season. <span class="hlt">Calving</span> rates are also influenced by basal friction, through its effects on near-terminus strain rates and <span class="hlt">ice</span> velocity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28239224','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28239224"><span><span class="hlt">Ice</span>-sheet dynamics through the Quaternary on the mid-Norwegian continental margin inferred from 3D seismic data.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Montelli, A; Dowdeswell, J A; Ottesen, D; Johansen, S E</p> <p>2017-02-01</p> <p>Reconstructing the evolution of <span class="hlt">ice</span> sheets is critical to our understanding of the global environmental system, but most detailed palaeo-glaciological reconstructions have hitherto focused on the very recent history of <span class="hlt">ice</span> sheets. Here, we present a three-dimensional (3D) reconstruction of the changing nature of <span class="hlt">ice</span>-sheet derived sedimentary architecture through the Quaternary <span class="hlt">Ice</span> Age of almost 3 Ma. An extensive geophysical record documents a marine-terminating, <span class="hlt">calving</span> Fennoscandian <span class="hlt">Ice</span> Sheet (FIS) margin present periodically on the mid-Norwegian <span class="hlt">shelf</span> since the beginning of the Quaternary. Spatial and temporal variability of the FIS is illustrated by the gradual development of fast-flowing <span class="hlt">ice</span> streams and associated intensification of focused glacial erosion and sedimentation since that time. Buried subglacial landforms reveal a complex and dynamic <span class="hlt">ice</span> sheet, with converging palaeo-<span class="hlt">ice</span> streams and several flow-switching events that may reflect major changes in topography and basal thermal regime. Lack of major subglacial meltwater channels suggests a largely distributed drainage system beneath the marine-terminating part of the FIS. This palaeo-environmental examination of the FIS provides a useful framework for <span class="hlt">ice</span>-sheet modelling and shows that fragmentary preservation of buried surfaces and variability of <span class="hlt">ice</span>-sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets.</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('https://www.osti.gov/biblio/56744-climatological-aspects-mesoscale-cyclogenesis-over-ross-sea-ross-ice-shelf-regions-antarctica','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/56744-climatological-aspects-mesoscale-cyclogenesis-over-ross-sea-ross-ice-shelf-regions-antarctica"><span>Climatological aspects of mesoscale cyclogenesis over the Ross Sea and Ross <span class="hlt">Ice</span> <span class="hlt">shelf</span> regions of 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>Carrasco, J.F.; Bromwich, D.H.</p> <p>1994-11-01</p> <p>A one-year (1988) statistical study of mesoscale cyclogenesis near Terra Nova Bay and Byrd Glacier, Antarctica, was conducted using high-resolution digital satellite imagery and automatic weather station data. Results indicate that on average two (one) mesoscale cyclones form near Terra Nova Bay (Byrd Glacier) each week, confirming these two locations as mesoscale cyclogeneis areas. The maximum (minimum) weekly frequency of mesoscale cyclones occurred during the summer (winter). The satellite survey of mesoscale vortices was extended over the Ross Sea and Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. Results suggest southern Marie Byrd Land as another area of mesoscale cyclone formation. Also, frequent mesoscale cyclonicmore » activity was noted over the Ross Sea and Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, where, on average, six and three mesoscale vortices were observed each week, respectively, with maximum (minimum) frequency during summer (winter) in both regions. The majority (70-80%) of the vortices were of comma-cloud type and were shallow. Only around 10% of the vortices near Terra Nova Bay and Byrd Glacier were classified as deep vortices, while over the Ross Sea and Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> around 20% were found to be deep. The average large-scale pattern associated with cyclogenesis days near Terra Nova Bay suggests a slight decrease in the sea level pressure and 500-hPa geopotential height to the northwest of this area with respect to the annual average. This may be an indication of the average position of synoptic-scale cyclones entering the Ross Sea region. Comparison with a similar study but for 1984-85 shows that the overall mesoscale cyclogenesis activity was similar during the three years, but 1985 was found to be the year with greater occurrence of {open_quotes}significant{close_quotes} mesoscales cyclones. The large-scale pattern indicates that this greater activity is related to a deeper circumpolar trough and 500-hPa polar vortex for 1985 in comparison to 1984 and 1988. 64 refs., 13 figs., 5 tabs.« less</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 Antarctic 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('https://pubs.er.usgs.gov/publication/70045534','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70045534"><span><span class="hlt">Calving</span> seismicity from iceberg-sea surface interactions</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Bartholomaus, T.C.; Larsen, C.F.; O'Neel, S.; West, M.E.</p> <p>2012-01-01</p> <p>Iceberg <span class="hlt">calving</span> is known to release substantial seismic energy, but little is known about the specific mechanisms that produce <span class="hlt">calving</span> icequakes. At Yahtse Glacier, a tidewater glacier on the Gulf of Alaska, we draw upon a local network of seismometers and focus on 80 hours of concurrent, direct observation of the terminus to show that <span class="hlt">calving</span> is the dominant source of seismicity. To elucidate seismogenic mechanisms, we synchronized video and seismograms to reveal that the majority of seismic energy is produced during iceberg interactions with the sea surface. Icequake peak amplitudes coincide with the emergence of high velocity jets of water and <span class="hlt">ice</span> from the fjord after the complete submergence of falling icebergs below sea level. These icequakes have dominant frequencies between 1 and 3 Hz. Detachment of an iceberg from the terminus produces comparatively weak seismic waves at frequencies between 5 and 20 Hz. Our observations allow us to suggest that the most powerful sources of <span class="hlt">calving</span> icequakes at Yahtse Glacier include iceberg-sea surface impact, deceleration under the influence of drag and buoyancy, and cavitation. Numerical simulations of seismogenesis during iceberg-sea surface interactions support our observational evidence. Our new understanding of iceberg-sea surface interactions allows us to reattribute the sources of <span class="hlt">calving</span> seismicity identified in earlier studies and offer guidance for the future use of seismology in monitoring iceberg <span class="hlt">calving</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.C44A..02B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.C44A..02B"><span>connecting the dots between Greenland <span class="hlt">ice</span> sheet surface melting and <span class="hlt">ice</span> flow dynamics (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Box, J. E.; Colgan, W. T.; Fettweis, X.; Phillips, T. P.; Stober, M.</p> <p>2013-12-01</p> <p>. Because water is 'heavier' than <span class="hlt">ice</span>, water-filled cracks have unlimited capacity to hydraulically ';jack' open fractures, penetrating, fracturing and disaggregating a solid <span class="hlt">ice</span> body. This process promotes iceberg <span class="hlt">calving</span> at more than 150, 1km wide marine terminating Greenland glacier fronts. Resulting from a rising trend of surface melting and sea water temperature, meltwater ejection at the underwater front of marine glaciers drives a an increasing turbulent heat exchange between the glacier front and relatively warm sea water melting it faster. Underwater melting promotes an undercutting of the glacier front leading to <span class="hlt">ice</span> berg <span class="hlt">calving</span>. <span class="hlt">Calving</span> through hydrofracture or marine undercutting provide a direct and immediate <span class="hlt">ice</span> flow speed response mechanism for surface meltwater production. <span class="hlt">Ice</span> flow speed reacts because <span class="hlt">calving</span> reduces flow resistance. The above physical processes interact. Cooling shuts these processes down. Negative feedbacks dampen the warming impulse. Live 21 June, 2013 is a new Danish Web site1 that exploits total mass balance rate of decline as a function of albedo to predict GRACE mass rate of change with 80% explained variance. While surface mass balance explains the mass rate of change slightly higher, surface albedo is an observable quantity as is gravity change.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1914880B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1914880B"><span>Uncertainty quantification of Antarctic contribution to sea-level rise using the fast Elementary Thermomechanical <span class="hlt">Ice</span> Sheet (f.ETISh) model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bulthuis, Kevin; Arnst, Maarten; Pattyn, Frank; Favier, Lionel</p> <p>2017-04-01</p> <p>Uncertainties in sea-level rise projections are mostly due to uncertainties in Antarctic <span class="hlt">ice</span>-sheet predictions (IPCC AR5 report, 2013), because key parameters related to the current state of the Antarctic <span class="hlt">ice</span> sheet (e.g. sub-<span class="hlt">ice-shelf</span> melting) and future climate forcing are poorly constrained. Here, we propose to improve the predictions of Antarctic <span class="hlt">ice</span>-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 <span class="hlt">ice</span>-sheet models. This challenge emphasises the importance of developing reliable and computationally efficient <span class="hlt">ice</span>-sheet models such as the f.ETISh <span class="hlt">ice</span>-sheet model (Pattyn, 2015), a new fast thermomechanical coupled <span class="hlt">ice</span> sheet/<span class="hlt">ice</span> <span class="hlt">shelf</span> model capable of handling complex and critical processes such as the marine <span class="hlt">ice</span>-sheet instability mechanism. Here, we apply these methods to investigate the role of uncertainties in sub-<span class="hlt">ice-shelf</span> melting, <span class="hlt">calving</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-GSFC_20171208_Archive_e000910.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-GSFC_20171208_Archive_e000910.html"><span>Thurston Island</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2014-11-10</p> <p>Snow is blown off of the Thurston Island <span class="hlt">calving</span> front off of western Antarctica as seen on the <span class="hlt">Ice</span>Bridge flight on Nov. 5, 2014. Image Credit: NASA/Jim Yungel NASA’s Operation <span class="hlt">Ice</span>Bridge collected some rare images on a flight out of Punta Arenas, Chile on Nov. 5, 2014, on a science flight over western Antarctica dubbed Ferrigno-Alison-Abbott 01. The crew snapped a few shots of a <span class="hlt">calving</span> front of the Antarctic <span class="hlt">ice</span> sheet. This particular flight plan was designed to collect data on changes in <span class="hlt">ice</span> elevation along the coast near the Ferrigno and Alison <span class="hlt">ice</span> streams, on the Abbot <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, and grounded <span class="hlt">ice</span> along the Eights Coast.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.5862P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.5862P"><span>Initial observations from seismometers frozen into a borehole through the McMurdo <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>Prior, David; Eccles, Jennifer; Cooper, Joanna; Craw, Lisa; van Haastrecht, Laurine; Hamish Bowman, M.; Stevens, Craig; Gamble Rosevear, Madi; Hulbe, Christina; Gorman, Andrew; Horgan, Huw; Pyne, Alex</p> <p>2017-04-01</p> <p>A seismometer cable with two, three-component seismometers was frozen into a hot water borehole through the McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> at Windless Bight in late December 2016. The seismometers are at 39m and 189m depth. The upper seismometer lies just below the firn-<span class="hlt">ice</span> transition ( 37m) and very close to sea level ( 38m). The lower seismometer is positioned 30m above the base of the <span class="hlt">ice</span> <span class="hlt">shelf</span> ( 222m). The seismometers froze in within 40 (upper) to 60 (lower) hours of the last reaming operation. The temperature evolution during freezing is complicated, particularly for the lower seismometer. The complications are interpreted as the result of brine expulsion and brine pocket migration. We conducted an active source experiment using the frozen-in seismometers together with a surface seismometer and four lines of geophones radiating from the borehole, at 45-degree angles, to a distance of 240m. Sources included a traditional hammer and surface plate, two types of hammer activated surface shear wave sources (for hard and soft surfaces) and a hammer activated borehole source. The frozen-in seismometers show excellent separation of P - wave and S - wave arrivals for all sources, particularly on the lower seismometer. The surface shear sources give clearer separation of arrivals on the vertical and horizontal components. For some source to receiver geometries the surface shear sources give no P - wave arrival on the horizontal seismometer components and a very strong S - wave arrival that is partitioned between the horizontal components in correspondence with the source orientation. The borehole source (at 3 to 10m in the firn) also gives clearer separation of P - wave and S - wave arrivals compared to a surface hammer and plate. The frozen-in seismometers were also used to listen for natural events in the <span class="hlt">ice</span>. Comparing the same events recorded at the surface and at depth, the latter are much less noisy than the former, leading to more clear interpretation. As in the active</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28501398','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28501398"><span>Machine-learning-based <span class="hlt">calving</span> prediction from activity, lying, and ruminating behaviors in dairy cattle.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Borchers, M R; Chang, Y M; Proudfoot, K L; Wadsworth, B A; Stone, A E; Bewley, J M</p> <p>2017-07-01</p> <p>The objective of this study was to use automated activity, lying, and rumination monitors to characterize prepartum behavior and predict <span class="hlt">calving</span> in dairy cattle. Data were collected from 20 primiparous and 33 multiparous Holstein dairy cattle from September 2011 to May 2013 at the University of Kentucky Coldstream Dairy. The HR Tag (SCR Engineers Ltd., Netanya, Israel) automatically collected neck activity and rumination data in 2-h increments. The <span class="hlt">Ice</span>Qube (<span class="hlt">Ice</span>Robotics Ltd., South Queensferry, United Kingdom) automatically collected number of steps, lying time, standing time, number of transitions from standing to lying (lying bouts), and total motion, summed in 15-min increments. <span class="hlt">Ice</span>Qube data were summed in 2-h increments to match HR Tag data. All behavioral data were collected for 14 d before the predicted <span class="hlt">calving</span> date. Retrospective data analysis was performed using mixed linear models to examine behavioral changes by day in the 14 d before <span class="hlt">calving</span>. Bihourly behavioral differences from baseline values over the 14 d before <span class="hlt">calving</span> were also evaluated using mixed linear models. Changes in daily rumination time, total motion, lying time, and lying bouts occurred in the 14 d before <span class="hlt">calving</span>. In the bihourly analysis, extreme values for all behaviors occurred in the final 24 h, indicating that the monitored behaviors may be useful in <span class="hlt">calving</span> prediction. To determine whether technologies were useful at predicting <span class="hlt">calving</span>, random forest, linear discriminant analysis, and neural network machine-learning techniques were constructed and implemented using R version 3.1.0 (R Foundation for Statistical Computing, Vienna, Austria). These methods were used on variables from each technology and all combined variables from both technologies. A neural network analysis that combined variables from both technologies at the daily level yielded 100.0% sensitivity and 86.8% specificity. A neural network analysis that combined variables from both technologies in bihourly increments was</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29740089','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29740089"><span>Interplay of grounding-line dynamics and sub-<span class="hlt">shelf</span> melting during retreat of the Bjørnøyrenna <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>Petrini, Michele; Colleoni, Florence; Kirchner, Nina; Hughes, Anna L C; Camerlenghi, Angelo; Rebesco, Michele; Lucchi, Renata G; Forte, Emanuele; Colucci, Renato R; Noormets, Riko</p> <p>2018-05-08</p> <p>The Barents Sea <span class="hlt">Ice</span> Sheet was a marine-based <span class="hlt">ice</span> sheet, i.e., it rested on the Barents Sea floor during the Last Glacial Maximum (21 ky BP). The Bjørnøyrenna <span class="hlt">Ice</span> Stream was the largest <span class="hlt">ice</span> stream draining the Barents Sea <span class="hlt">Ice</span> Sheet and is regarded as an analogue for contemporary <span class="hlt">ice</span> streams in West Antarctica. Here, the retreat of the Bjørnøyrenna <span class="hlt">Ice</span> Stream is simulated by means of two numerical <span class="hlt">ice</span> sheet models and results assessed against geological data. We investigate the sensitivity of the <span class="hlt">ice</span> stream to changes in ocean temperature and the impact of grounding-line physics on <span class="hlt">ice</span> stream retreat. Our results suggest that the role played by sub-<span class="hlt">shelf</span> melting depends on how the grounding-line physics is represented in the models. When an analytic constraint on the <span class="hlt">ice</span> flux across the grounding line is applied, the retreat of Bjørnøyrenna <span class="hlt">Ice</span> Stream is primarily driven by internal <span class="hlt">ice</span> dynamics rather than by oceanic forcing. This suggests that implementations of grounding-line physics need to be carefully assessed when evaluating and predicting the response of contemporary marine-based <span class="hlt">ice</span> sheets and individual <span class="hlt">ice</span> streams to ongoing and future ocean warming.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMGC43E1005H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMGC43E1005H"><span>Glacial-marine sediments record <span class="hlt">ice-shelf</span> retreat during the late Holocene in Beascochea Bay on the western margin of the Antarctic Peninsula</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hardin, L. A.; Wellner, J. S.</p> <p>2010-12-01</p> <p>Beascochea Bay has an overall rapid rate of sedimentation due to retreating fast-flowing <span class="hlt">ice</span>, 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 <span class="hlt">Ice</span> Cap since the grounded <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice-shelf</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA21785.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA21785.html"><span>Spawning of Massive Antarctic Iceberg Captured by NASA</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-07-14</p> <p>Between July 10 and 12, 2017, the Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in West Antarctica <span class="hlt">calved</span> one of the largest icebergs in history (named "A-68"), weighing approximately one trillion tons. The rift in the <span class="hlt">ice</span> <span class="hlt">shelf</span> that spawned the iceberg has been present on the <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> (Jansen et al., 2015). Suture zones are wide bands of <span class="hlt">ice</span> that extend from glacier grounding lines (the boundary between a floating <span class="hlt">ice</span> <span class="hlt">shelf</span> and <span class="hlt">ice</span> resting on bedrock) to the sea comprised of a frozen mixture of glacial <span class="hlt">ice</span> and sea water, traditionally considered to be stabilizing features in <span class="hlt">ice</span> 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 <span class="hlt">calved</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.C44B..04T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.C44B..04T"><span>When <span class="hlt">ice</span> meets water: Sub-aqueous melt and its relevance in various settings</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Truffer, M.; Motyka, R. J.</p> <p>2014-12-01</p> <p>The largest glacier changes are primarily observed in settings where <span class="hlt">ice</span> flows into a proglacial water body. However, the responses to this interaction are not uniform. Rapidly retreating glaciers can occur in close vicinity to advancing ones. <span class="hlt">Calving</span> styles and glacier morphologies vary greatly as well. Temperate lake-<span class="hlt">calving</span> glaciers frequently exhibit floating tongues; but this is rarely observed on temperate tidewater glaciers. <span class="hlt">Calving</span> styles range from mostly sub-aerial <span class="hlt">calving</span> to full-thickness <span class="hlt">calving</span> to slow detachment of large <span class="hlt">ice</span> bergs. In addition to the more obvious mechanical <span class="hlt">calving</span>, glaciers lose mass at their termini through sub-aqueous melting. Melt rates of submerged <span class="hlt">ice</span> have been shown to vary over several orders of magnitudes, and can range up to several meters per day. This large range is a consequence of different proglacial water temperatures, and of different modes of water transport. Water convection in proglacial water bodies can be driven by winds and tides, but subglacial water discharge is commonly the strongest and most variable driver. Here we attempt to relate the variability of forcings and melt rates to the various morphologies and <span class="hlt">calving</span> styles of different water-terminating glaciers. The highest melt rates are observed at low-latitude tidewater glaciers, where ocean water can be warm (7 - 10 deg C) and subglacial discharge high. In such settings, sub-aqueous melt can reach the same magnitude as <span class="hlt">ice</span> flux delivered to the terminus and it can control <span class="hlt">ice</span> terminus position. Polar tidewater glaciers, such as those in Greenland, often exhibit floating tongues. Although melt rates are likely much lower, they can have a large effect under a floating tongue because of the much larger exposure of <span class="hlt">ice</span> to water. Changes in melt rates can therefore affect the stability of such floating tongues. Low melt rates occur at some <span class="hlt">ice</span> shelves at high latitudes, where the temperature and freshwater forcings are small. This situation can also occur at</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>, Thoracosphaera spp.. The presence of several Tertiary reworked species and rare Cretaceous reworked taxa are interpreted in terms of provenance. As the lower temperature limit for living calcareous nannoplankton is about 2.5°C, the presence of nannofossils from 86 to 96 mbsf, though rare, is an indication of <span class="hlt">ice</span>-free and sea surface temperatures warmer than today, in the Ross Sea. The presence of numerous volcaniclastic units and biosiliceous sediments from 86.6 to 92.5 mbsf indicate an extended period of open-water conditions with no sea <span class="hlt">ice</span>, beyond the <span class="hlt">calving</span> line. An 40Ar/39Ar age of 1.014 ± 0.004 Ma on pumice at 85.50 mbsf confirms the age assignment given by diatom biostratigraphy (1.07 Ma) for this interval. Accordingly, the short normal magnetozone between 84.97 and 91.13 mbsf is correlated with the Jaramillo Subchron (C1r.1n) (Wilson et al., 2007). The presence of nannofossil in the biogenic interglacial sediments is consistent with warm episode of surface waters and open marine conditions during the Jaramillo subchron, at ~1 Ma, which corresponds with Marine isotope stage (MIS-31) (Naish et al., 2007). The "superinterglacial" associated with MIS 31 was the last significant warm interglacial of the obliquity-dominated world, and may represent a precursor to the high-amplitude eccentricity-dominated cycles that followed the mid-Pleistocene climate shift. Climate proxies from other studies from the Southern Ocean at ODP Site 1165 (Villa et al., 2008), at ODP Site 1094 (Scherer et al., 2008), and from the Antarctic margin in a shelly carbonate sequence at Cape Roberts 1 (Villa and Wise, 1998; Scherer et al., 2008) also support the idea of a warming event during this time, suggesting that it was extended around the Antarctic Continent. This in turn implies a total or partial collapse of McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and a concurrent shift or temporary dissipation of the Polar Front (Antarctic Convergence) and Antarctic Divergence that currently serve as barriers to the influx of</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 Antarctic 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 Antarctic 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/2017AGUFM.C51B0990S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51B0990S"><span>On the Formation of Rifts in <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>Sayag, R.; Worster, G.</p> <p>2017-12-01</p> <p><span class="hlt">Ice</span> <span class="hlt">calving</span> accounts for significant part in the mass loss of present <span class="hlt">ice</span> sheets. Several processes could lead to <span class="hlt">calving</span>, among them is the formation of rifts near the fronts of <span class="hlt">ice</span> shelves. Here we combine laboratory-scale experiments of <span class="hlt">ice</span> sheets together with theoretical modeling to investigate the formation of rifts in <span class="hlt">ice</span> shelves. We model the deformation of <span class="hlt">ice</span> with a thin viscous film that is driven axisymmetrically by buoyancy. When the viscous fluid intrudes a bath of an inviscid fluid that represents the ocean, the circular symmetry of the front breaks up into a set of tongues with a characteristic wavelength that coarsens over time, a pattern that is reminiscent of <span class="hlt">ice</span> rifts. Theoretically, we model the formation of rifts as a hydrodynamic instability of powerlaw fluid. Our model demonstrates the formation of rifts and the coarsening of the characteristic wavelength, and predicts coarsening transition times that are consistent with our experimental measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhDT.........2G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhDT.........2G"><span>Oceanic Controls of North American East Coast Sea Level Rise and Ocean Warming of the Antarctic <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>Goddard, Paul</p> <p></p> <p>, we use a fine-resolution global climate model (GFDL CM2.6) that resolves an eddying ocean. With this state-of-the-art coupled model, we quantify the mechanisms contributing to ocean warming on the Antarctic continental <span class="hlt">shelf</span> in an idealized experiment of doubling of the atmospheric CO2 concentration. The results show that the CO2 forcing leads to the <span class="hlt">shelf</span> region warming both in the upper 100 m ocean and at depths near the sea floor. These warming patterns are controlled by different mechanisms. In the upper 100 m, the heat anomalies are primarily controlled by increased heat transport into the <span class="hlt">shelf</span> region associated with the warmer near-surface waters from lower latitudes. Below 100 m, the heat anomalies develop due to increased onshore intrusions of relatively warm Circumpolar Deep Water and reduced vertical mixing of heat in the water column. A complete heat budget analysis is performed for the Antarctic <span class="hlt">shelf</span> region as well as for six subdomains and three depth ranges (0-100 m, 100-700 m, and 700-1000 m). The results show that certain regions of the Antarctic <span class="hlt">shelf</span> are more susceptible to large CO2-forced warming. These findings have implications for future Antarctic <span class="hlt">Ice</span> Sheet mass loss and SLR, and can provide more detailed and accurate ocean boundary conditions for dynamical <span class="hlt">ice</span> sheet models. In Appendix C, we use CM2.6 to examine the connections among ocean freshening and the magnitude and location of ocean warming on the Antarctic <span class="hlt">shelf</span>. We find that CO2 forcing freshens the Antarctic <span class="hlt">shelf</span> seas via increases in local precipitation, sea <span class="hlt">ice</span> loss, liquid runoff, and iceberg <span class="hlt">calving</span>. The freshening induces three heat budget-relevant responses: (1) reduced vertical mixing; (2) strengthening of the Antarctic Slope Front (ASF); and (3) increased eddy kinetic energy (EKE) near the ASF. First, heat can accumulate at depth (100-1000 m) as freshening increases the vertical stratification on the <span class="hlt">shelf</span> and reduces upward mixing of heat associated with diffusion and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT.......158T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT.......158T"><span>Rapid thinning and collapse of lake <span class="hlt">calving</span> Yakutat Glacier, Southeast Alaska</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Trussel, Barbara Lea</p> <p></p> <p>Glaciers around the globe are experiencing a notable retreat and thinning, triggered by atmospheric warming. Tidewater glaciers in particular have received much attention, because they have been recognized to contribute substantially to global sea level rise. However, lake <span class="hlt">calving</span> glaciers in Alaska show increasingly high thinning and retreat rates and are therefore contributors to sea level rise. The number of such lake <span class="hlt">calving</span> systems is increasing worldwide as land-terminating glaciers retreat into overdeepened basins and form proglacial lakes. Yakutat Glacier in Southeast Alaska is a low elevation lake <span class="hlt">calving</span> glacier with an accumulation to total area ratio of 0.03. It experienced rapid thinning of 4.43 +/- 0.06 m w.e. yr-1 between 2000-2010 and terminus retreat of over 15 km since the beginning of the 20th century. Simultaneously, adjacent Yakutat Icefield land-terminating glaciers thinned at lower but still substantial rates (3.54 +/- 0.06 m w.e. yr -1 for the same time period), indicating lake <span class="hlt">calving</span> dynamics help drive increased mass loss. Yakutat Glacier sustained a ˜3 km long floating tongue for over a decade, which started to disintegrate into large tabular icebergs in 2010. Such floating tongues are rarely seen on temperate tidewater glaciers. The floating <span class="hlt">ice</span> was weakened by surface ablation, which then allowed rifts to form and intersect. <span class="hlt">Ice</span> velocity from GPS measurements showed that the <span class="hlt">ice</span> on the floating tongue was moving substantially faster than grounded <span class="hlt">ice</span>, which was attributed to rift opening between the floating and grounded <span class="hlt">ice</span>. Temporal variations of rift opening were determined from time-lapse imagery, and correlated well with variations in <span class="hlt">ice</span> speeds. Larger rift opening rates occurred during and after precipitation or increased melt episodes. Both of these events increased subglacial discharge and could potentially increase the subaqueous currents towards the open lake and thus increase drag on the <span class="hlt">ice</span> underside. Simultaneously</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C42A..07R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C42A..07R"><span>Bending the law: tidal bending and its effects on <span class="hlt">ice</span> viscosity and flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rosier, S.; Gudmundsson, G. H.</p> <p>2017-12-01</p> <p>Many <span class="hlt">ice</span> shelves are subject to strong ocean tides and, in order to accommodate this vertical motion, the <span class="hlt">ice</span> must bend within the grounding zone. This tidal bending generates large stresses within the <span class="hlt">ice</span>, changing its effective viscosity. For a confined <span class="hlt">ice</span> <span class="hlt">shelf</span>, this is particularly relevant because the tidal bending stresses occur along the sidewalls, which play an important role in the overall flow regime of the <span class="hlt">ice</span> <span class="hlt">shelf</span>. Hence, tidal bending stresses will affect both the mean and time-varying components of <span class="hlt">ice</span> <span class="hlt">shelf</span> flow. GPS measurements reveal strong variations in horizontal <span class="hlt">ice</span> <span class="hlt">shelf</span> velocities at a variety of tidal frequencies. We show, using full-Stokes viscoelastic modelling, that inclusion of tidal bending within the model accounts for much of the observed tidal modulation of horizontal <span class="hlt">ice</span> <span class="hlt">shelf</span> flow. Furthermore, our model shows that in the absence of a vertical tidal forcing, the mean flow of the <span class="hlt">ice</span> <span class="hlt">shelf</span> is reduced considerably.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70015240','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70015240"><span>SEA-<span class="hlt">ICE</span> INFLUENCE ON ARCTIC COASTAL RETREAT.</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, Erk; Barnes, P.W.</p> <p>1987-01-01</p> <p>Recent studies document the effectiveness of sea <span class="hlt">ice</span> in reshaping the seafloor of the inner <span class="hlt">shelf</span> into sharp-relief features, including <span class="hlt">ice</span> gouges with jagged flanking ridges, <span class="hlt">ice</span>-wallow relief, and 2- to 6-m-deep strudel-scour craters. These <span class="hlt">ice</span>-related relief forms are in disequilibrium with classic open-water hydraulic processes and thus are smoothed over by waves and currents in one to two years. Such alternate reworking of the <span class="hlt">shelf</span> by <span class="hlt">ice</span> and currents - two diverse types of processes, which in the case of <span class="hlt">ice</span> wallow act in unison-contributes to sediment mobility and, thus, to sediment loss from the coast and inner <span class="hlt">shelf</span>. The bulldozing action by <span class="hlt">ice</span> results in coast-parallel sediment displacement. Additionally, suspension of sediment by frazil and anchor <span class="hlt">ice</span>, followed by <span class="hlt">ice</span> rafting, can move large amounts of bottom-derived materials. Our understanding of all these processes is insufficient to model Arctic coastal processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70121037','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70121037"><span>Glacial landforms on German Bank, Scotian <span class="hlt">Shelf</span>: evidence for Late Wisconsinan <span class="hlt">ice</span>-sheet dynamics and implications for the formation of De Geer moraines</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Todd, Brian J.; Valentine, Page C.; Longva, Oddvar; Shaw, John</p> <p>2007-01-01</p> <p>The extent and behaviour of the southeast margin of the Laurentide <span class="hlt">Ice</span> Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan <span class="hlt">ice</span> sheet-ocean interactions. Multibeam sonar imagery of subglacial, <span class="hlt">ice</span>-marginal and glaciomarine landforms on German Bank, Scotian <span class="hlt">Shelf</span>, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-<span class="hlt">ice</span> direction and strike southwest-northeast, normal to the direction of <span class="hlt">ice</span> flow. Ubiquitous, overlying De Geer moraines (</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/2008AGUFM.C23A0594C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.C23A0594C"><span>Reconstructing the history of major Greenland glaciers since the Little <span class="hlt">Ice</span> Age</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Csatho, B. M.; Schenk, A. F.; van der Veen, C. J.; Stearns, L.; Babonis, G. S.</p> <p>2008-12-01</p> <p>The Greenland <span class="hlt">Ice</span> Sheet may have been responsible for rapid sea level rise during the last interglacial period and recent studies indicate that it is likely to make a faster contribution to sea-level rise than previously believed. Rapid thinning and velocity increase has been observed on most major outlet glaciers with terminus retreat that might lead to increased discharge from the interior and consequent further thinning and retreat. Potentially, such behavior could have serious implications for global sea level. However, the current thinning may simply be a manifestation of longer-term behavior of the <span class="hlt">ice</span> sheet as it responds to the general warming following the Little <span class="hlt">Ice</span> Age (LIA). Although Greenland outlet glaciers have been comprehensively monitored since the 1980s, studies of long-term changes mostly rely on records of the <span class="hlt">calving</span> front position. Such records can be misleading because the glacier terminus, particularly if it is afloat, can either advance or retreat as <span class="hlt">ice</span> further upstream thins and accelerates. To assess whether recent trends deviate from longer-term behavior, we examined three rapidly thinning and retreating outlet glaciers, Jakobshavn Isbrae in west, Kangerdlussuaq Glacier in east and Petermann Glacier in northwest Greenland. Glacier surface and trimline elevations, as well as terminus positions were measured using historical photographs and declassified satellite imagery acquired between the 1940s and 1985. These results were combined with data from historical records, ground surveys, airborne laser altimetry, satellite observations and field mapping of lateral moraines and trimlines, to reconstruct the history of changes since the (LIA) up to the present. We identified several episodes of rapid thinning and <span class="hlt">ice</span> <span class="hlt">shelf</span> break-up, including thinning episodes that occurred when the <span class="hlt">calving</span> front was stationary. Coastal weather station data are used to assess the influence of air temperatures and intensity of surface melting, and to isolate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.G21A0858L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.G21A0858L"><span>Global <span class="hlt">ice</span> sheet/RSL simulations using the higher-order <span class="hlt">Ice</span> Sheet System Model.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Larour, E. Y.; Ivins, E. R.; Adhikari, S.; Schlegel, N.; Seroussi, H. L.; Morlighem, M.</p> <p>2017-12-01</p> <p>Relative sea-level rise is driven by processes that are intimately linked to the evolution ofglacial areas and <span class="hlt">ice</span> sheets in particular. So far, most Earth System models capable of projecting theevolution of RSL on decadal to centennial time scales have relied on offline interactions between RSL andice sheets. In particular, grounding line and <span class="hlt">calving</span> front dynamics have not been modeled in a way that istightly coupled with Elasto-Static Adjustment (ESA) and/or Glacial-Isostatic Adjustment (GIA). Here, we presenta new simulation of the entire Earth System in which both Greenland and Antarctica <span class="hlt">ice</span> sheets are tightly coupledto an RSL model that includes both ESA and GIA at resolutions and time scales compatible with processes suchas grounding line dynamics for Antarctica <span class="hlt">ice</span> shelves and <span class="hlt">calving</span> front dynamics for Greenland marine-terminatingglaciers. The simulations rely on the <span class="hlt">Ice</span> Sheet System Model (ISSM) and show the impact of higher-orderice flow dynamics and coupling feedbacks between <span class="hlt">ice</span> flow and RSL. We quantify the exact impact of ESA andGIA inclusion on grounding line evolution for large <span class="hlt">ice</span> shelves such as the Ronne and Ross <span class="hlt">ice</span> shelves, as well asthe Agasea Embayment <span class="hlt">ice</span> streams, and demonstate how offline vs online RSL simulations diverge in the long run,and the consequences for predictions of sea-level rise.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory undera contract with the National Aeronautics and Space Administration's Cryosphere Science Program.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JGRF..117.2038G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JGRF..117.2038G"><span>Investigation of land <span class="hlt">ice</span>-ocean interaction with a fully coupled <span class="hlt">ice</span>-ocean model: 2. Sensitivity to external forcings</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>A coupled <span class="hlt">ice</span> stream-<span class="hlt">ice</span> <span class="hlt">shelf</span>-ocean cavity model is used to assess the sensitivity of the coupled system to far-field ocean temperatures, varying from 0.0 to 1.8°C, as well as sensitivity to the parameters controlling grounded <span class="hlt">ice</span> flow. A response to warming is seen in grounding line retreat and grounded <span class="hlt">ice</span> loss that cannot be inferred from the response of integrated melt rates alone. This is due to concentrated thinning at the <span class="hlt">ice</span> <span class="hlt">shelf</span> lateral margin, and to processes that contribute to this thinning. Parameters controlling the flow of grounded <span class="hlt">ice</span> have a strong influence on the response to sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> melting, but this influence is not seen until several years after an initial perturbation in temperatures. The simulated melt rates are on the order of that observed for Pine Island Glacier in the 1990s. However, retreat rates are much slower, possibly due to unrepresented bedrock features.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C41B0664M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C41B0664M"><span>Oceanographic Influences on <span class="hlt">Ice</span> Shelves and Drainage in the Amundsen Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Minzoni, R. T.; Anderson, J. B.; Majewski, W.; Yokoyama, Y.; Fernandez, R.; Jakobsson, M.</p> <p>2016-12-01</p> <p>Marine sediment cores collected during the IB OdenSouthern Ocean 2009-2010 cruise are used to reconstruct the Holocene history of the Cosgrove <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in Ferrero Bay, despite regional warming evident from <span class="hlt">ice</span> core data and <span class="hlt">ice</span> <span class="hlt">shelf</span> loss in the Antarctic Peninsula. High productivity and diatom abundance signify opening of Ferrero Bay and recession of the Cosgrove <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> was a mechanism for under-melting the <span class="hlt">ice</span> <span class="hlt">shelf</span> and destabilizing the grounding line. Major <span class="hlt">ice</span> <span class="hlt">shelf</span> recession may also entail continental <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> 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 <span class="hlt">ice</span> shelves and outlet glaciers</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20170008477','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20170008477"><span>Improving Our Understanding of Antarctic Sea <span class="hlt">Ice</span> with NASA's Operation <span class="hlt">Ice</span>Bridge and the Upcoming ICESat-2 Mission</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Petty, Alek A.; Markus, Thorsten; Kurtz, Nathan T.</p> <p>2017-01-01</p> <p>Antarctic sea <span class="hlt">ice</span> is a crucial component of the global climate system. Rapid sea <span class="hlt">ice</span> 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 <span class="hlt">ice</span> drives the upper branch of the overturning circulation through freshwater input (Abernathy et al. 2016). Wind-driven trends in Antarctic sea <span class="hlt">ice</span> (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 <span class="hlt">ice</span> production and the lack of <span class="hlt">shelf</span> water formation over the Amundsen and Bellingshausen <span class="hlt">shelf</span> seas promote intrusion of warm Circumpolar Deep Water onto the continental <span class="hlt">shelf</span> and the ocean-driven melting of several <span class="hlt">ice</span> shelves fringing the West Antarctic <span class="hlt">Ice</span> Sheet (e.g., Jacobs et al. 2011; Pritchard et al. 2012; Dutrieux et al. 2014). Sea <span class="hlt">ice</span> conditions around Antarctica are also increasingly considered an important factor impacting local atmospheric conditions and the surface melting of Antarctic <span class="hlt">ice</span> shelves (e.g., Scambos et al. 2017). Sea <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> seas (e.g., Petty et al. 2012; Petty et al. 2014).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018OcMod.121...76M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018OcMod.121...76M"><span>Impact of increasing antarctic glacial freshwater release on regional sea-<span class="hlt">ice</span> cover 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>Merino, Nacho; Jourdain, Nicolas C.; Le Sommer, Julien; Goosse, Hugues; Mathiot, Pierre; Durand, Gael</p> <p>2018-01-01</p> <p>The sensitivity of Antarctic sea-<span class="hlt">ice</span> to increasing glacial freshwater release into the Southern Ocean is studied in a series of 31-year ocean/sea-<span class="hlt">ice</span>/iceberg model simulations. Glaciological estimates of <span class="hlt">ice-shelf</span> melting and iceberg <span class="hlt">calving</span> 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 <span class="hlt">ice</span> shelves, which is found to be a key component of changes in freshwater release. In addition, glacial freshwater-induced changes in sea <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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-<span class="hlt">ice</span> 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.</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 Antarctic <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 Antarctic <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> <span class="hlt">calving</span>, 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('https://pubs.er.usgs.gov/publication/70025232','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70025232"><span>The slow advance of a <span class="hlt">calving</span> glacier: Hubbard Glacier, Alaska, U.S.A</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Trabant, D.C.; Krimmel, R.M.; Echelmeyer, K.A.; Zirnheld, S.L.; Elsberg, D.H.</p> <p>2003-01-01</p> <p>Hubbard Glacier is the largest tidewater glacier in North America. In contrast to most glaciers in Alaska and northwestern Canada, Hubbard Glacier thickened and advanced during the 20th century. This atypical behavior is an important example of how insensitive to climate a glacier can become during parts of the <span class="hlt">calving</span> glacier cycle. As this glacier continues to advance, it will close the seaward entrance to 50 km long Russell Fjord and create a glacier-dammed, brackish-water lake. This paper describes measured changes in <span class="hlt">ice</span> thickness, <span class="hlt">ice</span> speed, terminus advance and fjord bathymetry of Hubbard Glacier, as determined from airborne laser altimetry, aerial photogrammetry, satellite imagery and bathymetric measurements. The data show that the lower regions of the glacier have thickened by as much as 83 m in the last 41 years, while the entire glacier increased in volume by 14.1 km3. <span class="hlt">Ice</span> speeds are generally decreasing near the <span class="hlt">calving</span> face from a high of 16.5 m d-1 in 1948 to 11.5 m d-1 in 2001. The <span class="hlt">calving</span> terminus advanced at an average rate of about 16 m a-1 between 1895 and 1948 and accelerated to 32 m a-1 since 1948. However, since 1986, the advance of the part of the terminus in Disenchantment Bay has slowed to 28 m a-1. Bathymetric data from the lee slope of the submarine terminal moraine show that between 1978 and 1999 the moraine advanced at an average rate of 32 m a-1, which is the same as that of the <span class="hlt">calving</span> face.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMPP31E..04D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP31E..04D"><span>Glacial changes in warm pool climate dominated by <span class="hlt">shelf</span> exposure and <span class="hlt">ice</span> sheet albedo</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Di Nezio, P. N.; Tierney, J. E.; Otto-Bliesner, B. L.; Timmermann, A.; Bhattacharya, T.; Brady, E. C.; Rosenbloom, N. A.</p> <p>2017-12-01</p> <p>The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool (IPWP) are unclear. We addressed this issue combining model simulations and paleoclimate reconstructions of the Last Glacial Maximum (LGM). Two drivers - the exposure of tropical shelves due to lower sea level and a monsoonal response to <span class="hlt">ice</span> sheet albedo - explain the proxy-inferred patterns of hydroclimate change. <span class="hlt">Shelf</span> exposure influences IPWP climate by weakening the ascending branch of the Walker circulation. This response is amplified by coupled interactions akin to the Bjerknes feedback involving a stronger sea-surface temperature (SST) gradient along the equatorial Indian Ocean (IO). <span class="hlt">Ice</span> sheet albedo enhances the import of cold, dry air into the tropics, weakening the Afro-Asian monsoon system. This "ventilation" mechanism alters temperature contrasts between the Arabian Sea and surrounding land leading to further monsoon weakening. Additional simulations show that the altered SST patterns associated with these responses are essential for explaining the proxy-inferred changes. Together our results show that <span class="hlt">ice</span> sheets are a first order driver of tropical climate on glacial-interglacial timescales. While glacial climates are not a straightforward analogue for the future, our finding of an active Bjerknes feedback deserves further attention in the context of future climate projections.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009QSRv...28.3101G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009QSRv...28.3101G"><span>Reconstructing the last Irish <span class="hlt">Ice</span> Sheet 2: a geomorphologically-driven model of <span class="hlt">ice</span> sheet growth, retreat and dynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greenwood, Sarah L.; Clark, Chris D.</p> <p>2009-12-01</p> <p>The <span class="hlt">ice</span> sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and <span class="hlt">ice</span>-marginal dynamics and chronologies, with less attention paid to an <span class="hlt">ice</span> sheet wide view of the first order properties of the <span class="hlt">ice</span> sheet: centres of mass, <span class="hlt">ice</span> divide structure, <span class="hlt">ice</span> flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an <span class="hlt">ice</span> sheet reconstruction yielding these fundamental <span class="hlt">ice</span> sheet properties. We present a seven stage model of <span class="hlt">ice</span> sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of <span class="hlt">ice</span> from Scotland likely coalesced with local <span class="hlt">ice</span> caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish <span class="hlt">Ice</span> Sheet was then established during <span class="hlt">ice</span> sheet growth, with a branching <span class="hlt">ice</span> divide structure whose main axis migrated up to 140 km from the west coast towards the east. <span class="hlt">Ice</span> stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. <span class="hlt">Ice</span> cover is reconstructed as extending to the continental <span class="hlt">shelf</span> break. The Irish <span class="hlt">Ice</span> Sheet became autonomous (i.e. separate from the British <span class="hlt">Ice</span> Sheet) during deglaciation and fragmented into multiple <span class="hlt">ice</span> masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the <span class="hlt">ice</span> sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the <span class="hlt">ice</span> stream system in the North Channel - Irish Sea Basin in driving such asymmetry, since rapid</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMGC43H1150W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMGC43H1150W"><span>Geoengineering Marine <span class="hlt">Ice</span> Sheets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wolovick, M.</p> <p>2017-12-01</p> <p>Mass loss from Greenland and Antarctica is highly sensitive to the presence of warm ocean water that drives melting at the grounding line. Rapid melting near the grounding line causes <span class="hlt">ice</span> <span class="hlt">shelf</span> thinning, loss of buttressing, flow acceleration, grounding line retreat, and ultimately mass loss and sea-level rise. If the grounding line enters a section of overdeepened bed the <span class="hlt">ice</span> sheet may even enter a runaway collapse via the marine <span class="hlt">ice</span> sheet instability. The warm water that triggers this process resides offshore at depth and accesses the grounding line through deep troughs in the continental <span class="hlt">shelf</span>. In Greenland, warm water transport is further constricted through narrow fjords. Here, I propose blocking warm water transport through these choke points with an artificial sill. Using a simple width- and depth-averaged model of <span class="hlt">ice</span> stream flow coupled to a buoyant-plume model of ocean melting, I find that grounding line retreat and sea level rise can be delayed or reversed for hundreds of years if warm water is prevented from accessing the grounding line at depth. Blocking of warm water from the sub-<span class="hlt">ice</span> cavity causes <span class="hlt">ice</span> <span class="hlt">shelf</span> thickening, increased buttressing, and grounding line readvance. The increase in buttressing is greatly magnified if the thickened <span class="hlt">ice</span> <span class="hlt">shelf</span> regrounds on a bathymetric high or on the artificial sill itself. In some experiments for Thwaites Glacier the grounding line is able to recover from a severely retreated state over 100 km behind its present-day position. Such a dramatic recovery demonstrates that it is possible, at least in principle, to stop and reverse an ongoing marine <span class="hlt">ice</span> sheet collapse. If the <span class="hlt">ice</span> <span class="hlt">shelf</span> regrounds on the artificial sill itself, erosion of the sill beneath the grounded <span class="hlt">ice</span> could reduce the effectiveness of the intervention. However, experiments including sill erosion suggest that even a very weak sill (1 kPa) could delay a collapse for centuries. The scale of the artificial sills in Greenlandic fjords is comparable to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70020335','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70020335"><span>Retreat of northern margins of George VI and Wilkins <span class="hlt">Ice</span> Shelves, Antarctic Peninsula</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lucchitta, B.K.; Rosanova, C.E.</p> <p>1998-01-01</p> <p>The George VI and Wilkins <span class="hlt">Ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> has been observed previously, but the Wilkins <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> lost a total of 906 km2 between 1974 and 1992, and an additional 87 km2 by 1995. The northern margin of the Wilkins <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">shelf</span> in the ERS images. These two <span class="hlt">ice</span> shelves mark the southernmost documented conspicuous retreat of <span class="hlt">ice-shelf</span> margins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C53C0747T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C53C0747T"><span>High-resolution record of the deglaciation of the British-Irish <span class="hlt">Ice</span> Sheet from North Atlantic deep-sea sediments.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tarlati, S.; Benetti, S.; Callard, L.; O'Cofaigh, C.; Dunlop, P.; Chiverrell, R. C.; Fabel, D.; Moreton, S.; Clark, C.</p> <p>2016-12-01</p> <p>During the last glacial maximum the British-Irish <span class="hlt">Ice</span> Sheet (BIIS) covered the majority of Ireland and Britain. Recent studies have described the BIIS as largely marine-based and highly dynamic with several advances and retreats recorded on the continental <span class="hlt">shelf</span>. The focus of this study is the more recent sediment record from the Donegal Barra Fan (DBF), the largest sediment depocentre formed by the <span class="hlt">ice</span> streaming of the western BIIS onto the North Atlantic continental margin. In this project, well-preserved, glacially-derived, deep-water sediments from 3 cores, up to 6.7 m long and retrieved from the DBF, are used to investigate and chronologically constrain the pattern of deglaciation of the BIIS. Deep-water sediments can record continuous sedimentation through time, avoiding hiatuses and erosional surfaces characteristic of a glacial environment and allow a detailed reconstruction of deglacial processes. Five lithofacies have been identified using sedimentology, x-rays, physical properties and grain size analysis. They include bioturbated foraminifera-bearing muds, interpreted as hemipelagic and contouritic deposits from interglacial periods. Chaotic and laminated muds, <span class="hlt">ice</span>-rafted debris (IRD)-rich layers and laminated mud to sand couplets are characteristic of the glacial period including <span class="hlt">ice</span>-sheet maximum extent and the beginning of retreat. These represent downslope mass movements, plumites from meltwater alongside melting icebergs and turbidites. Radiocarbon dates from foraminifera suggest that the deglacial sedimentary sequence is up to 5m thick. The IRD concentration and abundance of the foraminifera Neogloboquadrina pachyderma sinistral indicate a minimum of 3 different <span class="hlt">calving</span> events during deglaciation and a marked Younger Dryas cooling and <span class="hlt">ice</span> <span class="hlt">calving</span> period. Additionally the δ 18O record will be used to investigate the record of climatic changes in the region and x-ray fluorescence will be used to assess sediment provenance during deglaciation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.C34B..01M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.C34B..01M"><span>North Greenland's <span class="hlt">Ice</span> Shelves and Ocean Warming</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muenchow, A.; Schauer, U.; Padman, L.; Melling, H.; Fricker, H. A.</p> <p>2014-12-01</p> <p>Rapid disintegration of <span class="hlt">ice</span> shelves (the floating extensions of marine-terminating glaciers) can lead to increasing <span class="hlt">ice</span> discharge, thinning upstream <span class="hlt">ice</span> sheets, rising sea level. Pine Island Glacier, Antarctica, and Jacobshavn Isbrae, Greenland, provide prominent examples of these processes which evolve at decadal time scales. We here focus on three glacier systems north of 78 N in Greenland, each of which discharges more than 10 Gt per year of <span class="hlt">ice</span> and had an extensive <span class="hlt">ice</span> <span class="hlt">shelf</span> a decade ago; Petermann Gletscher (PG), Niogshalvfjerdsfjorden (79N), and Zachariae Isstrom (ZI). We summarize and discuss direct observations of ocean and glacier properties for these systems as they have evolved in the northwest (PG) and northeast (79N and ZI) of Greenland over the last two decades. We use a combination of modern and historical snapshots of ocean temperature and salinity (PG, 79N, ZI), moored observations in Nares Strait (PG), and snapshots of temperature and velocity fields on the broad continental <span class="hlt">shelf</span> off northeast Greenland (79N, ZI) collected between 1993 and 2014. Ocean warming adjacent to PG has been small relative to the ocean warming adjacent to 79N and ZI; however, ZI lost its entire <span class="hlt">ice</span> <span class="hlt">shelf</span> during the last decade while 79N, less than 70 km to the north of ZI, remained stable. In contrast, PG has thinned by about 10 m/y just prior to shedding two <span class="hlt">ice</span> islands representing almost half its <span class="hlt">ice</span> <span class="hlt">shelf</span> area or a fifth by volume. At PG advective <span class="hlt">ice</span> flux divergence explains about half of the dominantly basal melting while response to non-steady external forcing explains the other half. The observations at PG,79N, and ZI suggest that remotely sensed ambient surface ocean temperatures are poor proxies to explain <span class="hlt">ice</span> <span class="hlt">shelf</span> thinning and retreat. We posit that local dynamics of the subsurface ocean heat flux matters most. Ocean heat must first be delivered over the sill into the fjord and then within the <span class="hlt">ice</span> <span class="hlt">shelf</span> cavity to the base of the <span class="hlt">shelf</span> near the grounding line</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 Antarctic 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 Antarctic 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('https://www.terrapub.co.jp/e-library/aes/','USGSPUBS'); return false;" href="https://www.terrapub.co.jp/e-library/aes/"><span>Modelling the bathymetry of the Antarctic continental <span class="hlt">shelf</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>ten Brink, Uri S.; Rogers, William P.; Kirkham, R.M.</p> <p>1992-01-01</p> <p>Continental shelves are typically covered by relatively shallow waters (<200 m) which deepen gradually from the coast to the <span class="hlt">shelf</span> edge. The continental <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> edge. We examine the cause for the unusual <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> 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-<span class="hlt">shelf</span> sediment loading and inner-<span class="hlt">shelf</span> 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 <span class="hlt">ice</span> sheet advances across the <span class="hlt">shelf</span>, whereby in each cycle a thin (a few tens of meters) uniform layer of sediments is eroded from under the <span class="hlt">ice</span> sheet and is redeposited seaward 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-Antarctic 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 Antarctic 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/2016EGUGA..18.4084H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4084H"><span>A glimpse beneath Antarctic 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/2017AGUFMPP24A..04C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP24A..04C"><span>New marine geophysical and sediment record of the Northeast Greenland <span class="hlt">Ice</span> Stream.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Callard, L.; Roberts, D. H.; O'Cofaigh, C.; Lloyd, J. M.; Smith, J. A.; Dorschel, B.</p> <p>2017-12-01</p> <p>The NE Greenland <span class="hlt">Ice</span> Stream (NEGIS) drains 16% of the Greenland <span class="hlt">Ice</span> Sheet (GrIS) and has a sea-level equivalent of 1.1-1.4 m. Stabilised by two floating <span class="hlt">ice</span> shelves, 79N and Zachariae Isstrom, until recently it has shown little response to increased atmospheric and oceanic warming. However, since 2010 it has experienced an accelerated rate of grounding line retreat ( 4 km) and significant <span class="hlt">ice</span> <span class="hlt">shelf</span> loss that indicates that this sector of the GrIS is now responding to current oceanic and/or climatic change and has the potential to be a major contributor to future global sea-level rise. The project `NEGIS', a collaboration between Durham University and AWI, aims to reconstruct the history of the NE Greenland <span class="hlt">Ice</span> Stream from the Last Glacial Maximum (LGM) to present using both onshore and offshore geological archives to better understand past <span class="hlt">ice</span> stream response to a warming climate. This contribution presents results and interpretations from an offshore dataset collected on the RV Polarstern, cruises PS100 and PS109 in 2016 and 2017. Gravity and box cores, supplemented by swath bathymetric and sub-bottom profiler data, were acquired and initial core analysis including x-radiographs and MSCL data logging has been performed. Data collection focused principally in the Norske Trough and the area directly in front of the 79N <span class="hlt">ice</span> <span class="hlt">shelf</span>, a sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> environment as recently as two years ago. On the outer <span class="hlt">shelf</span> streamlined subglacial bedforms, grounding-zone wedges and moraines as well as overconsolidated subglacial tills, record an extensive <span class="hlt">ice</span> sheet advance to the <span class="hlt">shelf</span> edge. On the inner <span class="hlt">shelf</span> and in front of the 79N <span class="hlt">ice</span> <span class="hlt">shelf</span>, deep, glacially-eroded bedrock basins are infilled with stratified sediment. The stratified muds represent deglacial and Holocene glacimarine sedimentation, and capture the recent transition from sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> to <span class="hlt">shelf</span> free conditions. Multiproxy palaeoenvironmental reconstructions, including foraminifera and diatom analysis, and radiocarbon</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 Antarctic ozone depletion.</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/2017EGUGA..19.5022A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.5022A"><span>The effect of changing wind forcing on Antarctic <span class="hlt">ice</span> <span class="hlt">shelf</span> melting in high-resolution, global sea <span class="hlt">ice</span>-ocean simulations with the Accelerated Climate Model for Energy (ACME)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Asay-Davis, Xylar; Price, Stephen; Petersen, Mark; Wolfe, Jonathan</p> <p>2017-04-01</p> <p>The capability for simulating sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> 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-<span class="hlt">ice</span> <span class="hlt">shelf</span> melt rates with observations, exploring sources of model biases as well as the effects of the two forcing scenarios.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSMG44B2003M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSMG44B2003M"><span>On the pattern of WAIS retreat in eastern Ross Sea based on a regional synthesis of new geophysical and geological data acquired during NBP1502</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McGlannan, A. J.; Bart, P. J.; Anderson, J. B.</p> <p>2016-02-01</p> <p>New multibeam and seismic data acquired during NBP1502 reveal that a series of backstepping grounding zone wedges (GZWs) were constructed on the middle <span class="hlt">shelf</span> as the West Antarctic <span class="hlt">Ice</span> Sheet (WAIS) retreated from the Whales Deep paleo-<span class="hlt">ice</span> stream trough. The geomorphological information provided by these geophysical data were used to acquire a regional grid of jumbo-piston and kasten cores. Here, we present our regional synthesis of the new geophysical and geological data. The distributions of upcore transitions from diamict to sub-<span class="hlt">ice-shelf</span> facies on the outer-most <span class="hlt">shelf</span> demonstrate that as the grounded <span class="hlt">ice</span> retreated in four discrete backsteps, the <span class="hlt">calving</span> front remained in the vicinity of the <span class="hlt">shelf</span> edge, approximately 50 kilometers to the north. In contrast, the upcore transition at the fourth backstep shows GZW diamict directly overlain by open-marine facies. We interpret this to indicate that a major retreat of both grounded and floating <span class="hlt">ice</span> was associated with the termination of the middle-<span class="hlt">shelf</span> grounding event. The minimum retreat distance was greater than 100 kilometers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850017732&hterms=BALANCE+SHEET&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DBALANCE%2BSHEET','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850017732&hterms=BALANCE+SHEET&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DBALANCE%2BSHEET"><span>Greenland <span class="hlt">Ice</span> Sheet Mass Balance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Reeh, N.</p> <p>1984-01-01</p> <p>Mass balance equation for glaciers; areal distribution and <span class="hlt">ice</span> volumes; estimates of actual mass balance; loss by <span class="hlt">calving</span> of icebergs; hydrological budget for Greenland; and temporal variations of Greenland mass balance are examined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.C33A0367L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.C33A0367L"><span>DynEarthSol3D: numerical studies of basal crevasses and <span class="hlt">calving</span> blocks</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Logan, E.; Lavier, L. L.; Choi, E.; Tan, E.; Catania, G. A.</p> <p>2014-12-01</p> <p>DynEarthSol3D (DES) is a thermomechanical model for the simulation of dynamic <span class="hlt">ice</span> flow. We present the application of DES toward two case studies - basal crevasses and <span class="hlt">calving</span> blocks - to illustrate the potential of the model to aid in understanding <span class="hlt">calving</span> processes. Among the advantages of using DES are: its unstructured meshes which adaptively resolve zones of high interest; its use of multiple rheologies to simulate different types of dynamic behavior; and its explicit and parallel numerical core which both make the implementation of different boundary conditions easy and the model highly scalable. We examine the initiation and development of both basal crevasses and <span class="hlt">calving</span> blocks through time using visco-elasto-plastic rheology. Employing a brittle-to-ductile transition zone (BDTZ) based on local strain rate shows that the style and development of brittle features like crevasses differs markedly on the rheological parameters. Brittle and ductile behavior are captured by Mohr-Coulomb elastoplasticity and Maxwell viscoelasticity, respectively. We explore the parameter spaces which define these rheologies (including temperature) as well as the BDTZ threshold (shown in the literature as 10-7 Pa s), using time-to-failure as a metric for accuracy within the model. As the time it takes for a block of <span class="hlt">ice</span> to fail can determine an iceberg's size, this work has implications for <span class="hlt">calving</span> laws.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFMPP51E..06J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFMPP51E..06J"><span>Detrital Carbonate Events on the Labrador <span class="hlt">Shelf</span>, a 13 to 7 kyr Template for Freshwater Forcing From the Laurentide <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>Jennings, A. E.; Andrews, J. T.</p> <p>2008-12-01</p> <p>A complex sequence of abrupt glacial advances and retreats punctuate the late phases of Laurentide <span class="hlt">Ice</span> Sheet deglaciation. These episodes have been reconstructed from interpretation and mapping of glacial deposits on land and in marine basins proximal to the former <span class="hlt">ice</span> margins in Hudson Strait, Hudson Bay, and the SE Baffin Island <span class="hlt">shelf</span>. As these events likely produced pulses of freshwater discharge into the North Altantic, which may be responsible for rapid climate change, their timing and magnitude need to be understood. The timing of these events is well constrained by radiocarbon ages, but the ocean reservoir age in <span class="hlt">ice</span> proximal areas is subject to very large uncertainties, making it difficult to determine calibrated ages for the glacial events so that they can be compared to other climate records. We suggest that the sequence of high detrital carbonate peaks in Holocene and Late Glacial sediments in the Cartwright Saddle of the Labrador <span class="hlt">shelf</span> provides a template of the abrupt glacial events of the NE margin of the Laurentide <span class="hlt">Ice</span> Sheet, particularly events that issued from Hudson Strait and Hudson Bay, but possibly including events in Baffin Bay. Once the Labrador <span class="hlt">Shelf</span> was deglaciated and the local <span class="hlt">ice</span> had retreated inland, the Cartwright Saddle was a distal trap for sediments released from Hudson Strait and other <span class="hlt">ice</span> sheet outlets farther north as their sediments and meltwater were carried southwards by surface currents. Core MD99-2236 contains a sediment record beginning c. 13.9 cal ka. We assume a marine reservoir age for the Cartwright Saddle of 450 yrs, which is reasonable given the <span class="hlt">ice</span> distal and oceanic position of the site. Carbonate was measured on average at a 30 yr time resolution. Carbonate values are elevated between 11.7 and 7 cal kyr BP, with six spikes exceeding 30 percent. Each spike corresponds to a light isotope spike in foraminifers, suggesting that each major spike is associated with a pulse of glacial meltwater. Elevated IRD counts</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70029435','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70029435"><span>Local response of a glacier to annual filling and drainage of an <span class="hlt">ice</span>-marginal lake</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Walder, J.S.; Trabant, D.C.; Cunico, M.; Fountain, A.G.; Anderson, S.P.; Anderson, R. Scott; Malm, A.</p> <p>2006-01-01</p> <p><span class="hlt">Ice</span>-marginal Hidden Creek Lake, Alaska, USA, outbursts annually over the course of 2-3 days. As the lake fills, survey targets on the surface of the '<span class="hlt">ice</span> dam' (the glacier adjacent to the lake) move obliquely to the <span class="hlt">ice</span> margin and rise substantially. As the lake drains, <span class="hlt">ice</span> motion speeds up, becomes nearly perpendicular to the face of the <span class="hlt">ice</span> dam, and the <span class="hlt">ice</span> surface drops. Vertical movement of the <span class="hlt">ice</span> dam probably reflects growth and decay of a wedge of water beneath the <span class="hlt">ice</span> dam, in line with established ideas about jo??kulhlaup mechanics. However, the distribution of vertical <span class="hlt">ice</span> movement, with a narrow (50-100 m wide) zone where the uplift rate decreases by 90%, cannot be explained by invoking flexure of the <span class="hlt">ice</span> dam in a fashion analogous to tidal flexure of a floating glacier tongue or <span class="hlt">ice</span> <span class="hlt">shelf</span>. Rather, the zone of large uplift-rate gradient is a fault zone: <span class="hlt">ice</span>-dam deformation is dominated by movement along high-angle faults that cut the <span class="hlt">ice</span> dam through its entire thickness, with the sense of fault slip reversing as the lake drains. Survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. The horizontal strain rate also undergoes a reversal across this zone, being compressional as the lake fills, but extensional as the lake drains. Frictional resistance to fault-block motion probably accounts for the fact that lake level falls measurably before the onset of accelerated horizontal motion and vertical downdrop. As the overall fault pattern is the same from year to year, even though <span class="hlt">ice</span> is lost by <span class="hlt">calving</span>, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as <span class="hlt">ice</span> is advected toward the lake basin.</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 Antarctic <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://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 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 <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 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 <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 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 <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://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 Antarctic <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 Antarctic <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/2060/20140009622','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140009622"><span>Insights into Spatial Sensitivities of <span class="hlt">Ice</span> Mass Response to Environmental Change from the SeaRISE <span class="hlt">Ice</span> Sheet Modeling Project I: Antarctica</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nowicki, Sophie; Bindschadler, Robert A.; Abe-Ouchi, Ayako; Aschwanden, Andy; Bueler, Ed; Choi, Hyengu; Fastook, Jim; Granzow, Glen; Greve, Ralf; Gutowski, Gail; <a style="text-decoration: none; " href="javascript:void(0); " onClick="displayelement('author_20140009622'); toggleEditAbsImage('author_20140009622_show'); toggleEditAbsImage('author_20140009622_hide'); "> <img style="display:inline; width:12px; height:12px; " src="images/arrow-up.gif" width="12" height="12" border="0" alt="hide" id="author_20140009622_show"> <img style="width:12px; height:12px; display:none; " src="images/arrow-down.gif" width="12" height="12" border="0" alt="hide" id="author_20140009622_hide"></p> <p>2013-01-01</p> <p>Atmospheric, oceanic, and subglacial forcing scenarios from the Sea-level Response to <span class="hlt">Ice</span> Sheet Evolution (SeaRISE) project are applied to six three-dimensional thermomechanical <span class="hlt">ice</span>-sheet models to assess Antarctic <span class="hlt">ice</span> sheet sensitivity over a 500 year timescale and to inform future modeling and field studies. Results indicate (i) growth with warming, except within low-latitude basins (where inland thickening is outpaced by marginal thinning); (ii) mass loss with enhanced sliding (with basins dominated by high driving stresses affected more than basins with low-surface-slope streaming <span class="hlt">ice</span>); and (iii) mass loss with enhanced <span class="hlt">ice</span> <span class="hlt">shelf</span> melting (with changes in West Antarctica dominating the signal due to its marine setting and extensive <span class="hlt">ice</span> shelves; cf. minimal impact in the Terre Adelie, George V, Oates, and Victoria Land region of East Antarctica). <span class="hlt">Ice</span> loss due to dynamic changes associated with enhanced sliding and/or sub-<span class="hlt">shelf</span> melting exceeds the gain due to increased precipitation. Furthermore, differences in results between and within basins as well as the controlling impact of sub-<span class="hlt">shelf</span> melting on <span class="hlt">ice</span> dynamics highlight the need for improved understanding of basal conditions, grounding-zone processes, ocean-<span class="hlt">ice</span> interactions, and the numerical representation of all three.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C41A1164D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C41A1164D"><span>The Effects of Sulfuric Acid on Mechanical Properties of Polycrystalline <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>DeAngelis, M. K.; Lee, M. S.; Huang, K.</p> <p>2017-12-01</p> <p>The rates of flow for <span class="hlt">ice</span> streams and glaciers are an important contributor to models of future sea level rise. Soluble impurities, such as sulfuric acid from acid rain, have been identified in <span class="hlt">ice</span> cores, making it of utmost importance to understand the complete effects of such impurities on the mechanical properties of <span class="hlt">ice</span>. While previous studies have provided insight into how sulfuric acid affects the viscosity in glaciers, the effects of sulfuric acid on elastic stiffness and friction has received less attention. In this study, we measured and compared the Young's Modulus and steady-state friction of 10 ppm sulfuric acid doped water <span class="hlt">ice</span> samples to that of pure water <span class="hlt">ice</span> samples. Microstructure characterization of the sample indicated that, even at such low concentration, the acid was located in small melt pockets at grain triple junctions. With an ultrasonic velocity testing system at -22 °C, primary waves and secondary waves were sent through each sample and wave velocities were recorded. These values and the density of the samples were used to calculate Young's Modulus. The sulfuric acid doped <span class="hlt">ice</span> has an elastic stiffness that is less than that of pure <span class="hlt">ice</span>. Reduced modulus could influence <span class="hlt">calving</span> rates and other <span class="hlt">ice</span> <span class="hlt">shelf</span> processes. Using a custom cryo-biaxial apparatus, the friction of doped <span class="hlt">ice</span> on rock was directly measured at several programmed velocities. The double direct shear configuration was employed, with a normal stress of 100 kPa and a temperature of -5 °C. Compared to previous studies on pure <span class="hlt">ice</span>, the sulfuric acid doped <span class="hlt">ice</span> sample experienced similar steady state friction. However, preliminary results indicate that doped samples exhibited velocity weakening behavior (i.e. as velocity increased, friction decreased) and stick slip events, while pure <span class="hlt">ice</span> maintained a relatively neutral velocity dependence at this temperature. Field observations have reported stick slip motion at Whillans <span class="hlt">Ice</span> Stream in Antarctica, but an explanation is unclear</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 Antarctic <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('http://adsabs.harvard.edu/abs/2011EOSTr..92..117F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011EOSTr..92..117F"><span>Context for the Recent Massive Petermann Glacier <span class="hlt">Calving</span> Event</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Falkner, Kelly K.; Melling, Humfrey; Münchow, Andreas M.; Box, Jason E.; Wohlleben, Trudy; Johnson, Helen L.; Gudmandsen, Preben; Samelson, Roger; Copland, Luke; Steffen, Konrad; Rignot, Eric; Higgins, Anthony K.</p> <p>2011-04-01</p> <p>On 4 August 2010, about one fifth of the floating <span class="hlt">ice</span> tongue of Petermann Glacier (also known as “Petermann Gletscher”) in northwestern Greenland <span class="hlt">calved</span> (Figure 1). The resulting “<span class="hlt">ice</span> island” had an area approximately 4 times that of Manhattan Island (about 253±17 square kilometers). The <span class="hlt">ice</span> island garnered much attention from the media, politicians, and the public, who raised concerns about downstream implications for shipping, offshore oil and gas operations, and possible connections to Arctic and global warming. Does this event signal a change in the glacier's dynamics? Or can it be characterized as part of the glacier's natural variability? Understanding the known historical context of this event allows scientists and the public to judge its significance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C41C1226M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C41C1226M"><span>Improved Discretization of Grounding Lines and <span class="hlt">Calving</span> Fronts using an Embedded-Boundary Approach in BISICLES</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin, D. F.; Cornford, S. L.; Schwartz, P.; Bhalla, A.; Johansen, H.; Ng, E.</p> <p>2017-12-01</p> <p>Correctly representing grounding line and <span class="hlt">calving</span>-front dynamics is of fundamental importance in modeling marine <span class="hlt">ice</span> sheets, since the configuration of these interfaces exerts a controlling influence on the dynamics of the <span class="hlt">ice</span> sheet. Traditional <span class="hlt">ice</span> sheet models have struggled to correctly represent these regions without very high spatial resolution. We have developed a front-tracking discretization for grounding lines and <span class="hlt">calving</span> fronts based on the Chombo embedded-boundary cut-cell framework. This promises better representation of these interfaces vs. a traditional stair-step discretization on Cartesian meshes like those currently used in the block-structured AMR BISICLES code. The dynamic adaptivity of the BISICLES model complements the subgrid-scale discretizations of this scheme, producing a robust approach for tracking the evolution of these interfaces. Also, the fundamental discontinuous nature of flow across grounding lines is respected by mathematically treating it as a material phase change. We present examples of this approach to demonstrate its effectiveness.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016TCry...10.2203M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016TCry...10.2203M"><span>Quantifying <span class="hlt">ice</span> loss in the eastern Himalayas since 1974 using declassified spy satellite imagery</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maurer, Joshua M.; Rupper, Summer B.; Schaefer, Joerg M.</p> <p>2016-09-01</p> <p>Himalayan glaciers are important natural resources and climate indicators for densely populated regions in Asia. Remote sensing methods are vital for evaluating glacier response to changing climate over the vast and rugged Himalayan region, yet many platforms capable of glacier mass balance quantification are somewhat temporally limited due to typical glacier response times. We here rely on declassified spy satellite imagery and ASTER data to quantify surface lowering, <span class="hlt">ice</span> volume change, and geodetic mass balance during 1974-2006 for glaciers in the eastern Himalayas, centered on the Bhutan-China border. The wide range of glacier types allows for the first mass balance comparison between clean, debris, and lake-terminating (<span class="hlt">calving</span>) glaciers in the region. Measured glaciers show significant <span class="hlt">ice</span> loss, with an estimated mean annual geodetic mass balance of -0.13 ± 0.06 m w.e. yr-1 (meters of water equivalent per year) for 10 clean-<span class="hlt">ice</span> glaciers, -0.19 ± 0.11 m w.e. yr-1 for 5 debris-covered glaciers, -0.28 ± 0.10 m w.e. yr-1 for 6 <span class="hlt">calving</span> glaciers, and -0.17 ± 0.05 m w.e. yr-1 for all glaciers combined. Contrasting hypsometries along with melt pond, <span class="hlt">ice</span> cliff, and englacial conduit mechanisms result in statistically similar mass balance values for both clean-<span class="hlt">ice</span> and debris-covered glacier groups. <span class="hlt">Calving</span> glaciers comprise 18 % (66 km2) of the glacierized area yet have contributed 30 % (-0.7 km3) to the total <span class="hlt">ice</span> volume loss, highlighting the growing relevance of proglacial lake formation and associated <span class="hlt">calving</span> for the future <span class="hlt">ice</span> mass budget of the Himalayas as the number and size of glacial lakes increase.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850042373&hterms=glacier+melt&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dglacier%2Bmelt','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850042373&hterms=glacier+melt&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dglacier%2Bmelt"><span><span class="hlt">Ice</span> sheet margins and <span class="hlt">ice</span> shelves</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Thomas, R. H.</p> <p>1984-01-01</p> <p>The effect of climate warming on the size of <span class="hlt">ice</span> sheet margins in polar regions is considered. Particular attention is given to the possibility of a rapid response to warming on the order of tens to hundreds of years. It is found that the early response of the polar regions to climate warming would be an increase in the area of summer melt on the <span class="hlt">ice</span> sheets and <span class="hlt">ice</span> shelves. For sufficiently large warming (5-10C) the delayed effects would include the breakup of the <span class="hlt">ice</span> shelves by an increase in <span class="hlt">ice</span> drainage rates, particularly from the <span class="hlt">ice</span> sheets. On the basis of published data for periodic changes in the thickness and melting rates of the marine <span class="hlt">ice</span> sheets and fjord glaciers in Greenland and Antarctica, it is shown that the rate of retreat (or advance) of an <span class="hlt">ice</span> sheet is primarily determined by: bedrock topography; the basal conditions of the grounded <span class="hlt">ice</span> sheet; and the <span class="hlt">ice</span> <span class="hlt">shelf</span> condition downstream of the grounding line. A program of satellite and ground measurements to monitor the state of <span class="hlt">ice</span> sheet equilibrium is recommended.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C21C0714O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C21C0714O"><span>Global mapping of sea-<span class="hlt">ice</span> production from the satellite microwaves</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ohshima, K. I.; Nihashi, S.; Iwamoto, K.; Tamaru, N.; Nakata, K.; Tamura, T.</p> <p>2016-12-01</p> <p>Global overturning circulation is driven by density differences. Saline water rejected by sea-<span class="hlt">ice</span> production in coastal polynyas is the main source of dense water, and thus sea-<span class="hlt">ice</span> production is a key factor in the overturning circulation. However, until recently sea-<span class="hlt">ice</span> production and its interannual variability have not been well understood due to difficulties of in situ observation. The most effective means of detection of thin-<span class="hlt">ice</span> area and estimation of sea-<span class="hlt">ice</span> production on large scales is satellite remote sensing using passive microwave sensors, specifically the Special Sensor Microwave/Imager and Advanced Microwave Scanning Radiometer. This is based upon their ability to gain complete polar coverage on a daily basis irrespective of clouds and darkness. We have estimated sea-<span class="hlt">ice</span> production globally based on heat flux calculations using the satellite-derived thin <span class="hlt">ice</span> thickness data. The mapping demonstrates that <span class="hlt">ice</span> production rate is high in Antarctic coastal polynyas, in contrast to Arctic coastal polynyas. This is consistent with the formation of Antarctic Bottom Water (AABW). The Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> polynya has by far the highest <span class="hlt">ice</span> production in the Southern Hemisphere. The mapping has revealed that the Cape Darnley polynya is the second highest production area, leading to the discovery of the missing (fourth) source of AABW in this region. In the region off the Mertz Glacier Tongue, sea-<span class="hlt">ice</span> production decreased by as much as 40 %, due to the glacier <span class="hlt">calving</span> in early 2010, resulting in a significant decrease in AABW production. The Okhotsk Northwestern polynya exhibits the highest <span class="hlt">ice</span> production in the Northern Hemisphere, and the resultant dense water formation leads to overturning in the North Pacific. Estimates of its <span class="hlt">ice</span> production show a significant decrease over the past 30-50 years, likely causing the weakening of the North Pacific overturning. The mapping also provides surface boundary conditions and validation data of heat- and salt-flux associated</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.C53B..03M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.C53B..03M"><span><span class="hlt">Ice</span>-Ocean Interactions to the North-West of Greenland: Glaciers, Straits, <span class="hlt">Ice</span> Bridges, and the Rossby Radius (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muenchow, A.; Falkner, K. K.; Melling, H.; Johnson, H. L.; Huntley, H. S.; Ryan, P.; Friends Of Petermann</p> <p>2010-12-01</p> <p>Petermann Glacier at 81 N latitude is a major outlet glacier adjacent to Nares Strait. It terminates in a long (70 km), narrow (16 km) and thin (50 m) floating tongue and has a grounding line more than 500 m below sea level. A <span class="hlt">calving</span> event in 2010 reduced the floating area by 25% and produced a single 240 km2 <span class="hlt">ice</span> island currently moving south in Nares Strait where it will likely interact with island to potentially create a temporary polynya in Nares Strait. The 2010 <span class="hlt">calving</span> from Petermann Glacier contributes <10% to its mass balance as more than 80% is lost due to basal melting by the ocean. Hence the largely unexplored physics at the <span class="hlt">ice</span>-ocean interface determine how a changing climate impacts this outlet glacier. Conducting exploratory surveys inside Petermann Fjord in 2003, 2007, and 2009, we find a 1100 m deep fjord connected to Nares Strait via a sill at 350-450 m depth. The fjord receives about 3 times the amount of heat required for the basal melt rates. Furthermore, limited data and analytical modeling suggests a 3-dimensional circulation over the upper 300-m of the water column with a coastally trapped buoyant outflow. We integrate these findings with more complete oceanic time series data from an array moored in Nares Strait from 2003 through 2009 near 80.5 N. In the past Nares Strait and Petermann Fjord were covered by land fast sea <span class="hlt">ice</span> during the 9-10 month long winter season. Archeological and remotely sensed records indicate that an <span class="hlt">ice</span> bridge formed regularly at the southern end of Nares Strait creating the North-Water polynya near 79 N latitude. Since 2006 this <span class="hlt">ice</span> bridge has largely failed to form, leading, perhaps, to the occasional formation of a secondary <span class="hlt">ice</span> bridge 300 km to the north where Nares Strait connects to the Arctic Ocean. However, this <span class="hlt">ice</span> bridge appears to form for shorter periods only. Consequently Arctic sea <span class="hlt">ice</span> can now exit the Arctic in winter via pathways to the west of Greenland all year. We speculate that this changed ocean</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('http://adsabs.harvard.edu/abs/2017AGUFM.C41C1229S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C41C1229S"><span>Simulating <span class="hlt">Ice</span> Dynamics in the Amundsen Sea Sector</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schwans, E.; Parizek, B. R.; Morlighem, M.; Alley, R. B.; Pollard, D.; Walker, R. T.; Lin, P.; St-Laurent, P.; LaBirt, T.; Seroussi, H. L.</p> <p>2017-12-01</p> <p>Thwaites and Pine Island Glaciers (TG; PIG) exhibit patterns of dynamic retreat forced from their floating margins, and could act as gateways for destabilization of deep marine basins in the West Antarctic <span class="hlt">Ice</span> Sheet (WAIS). Poorly constrained basal conditions can cause model predictions to diverge. Thus, there is a need for efficient simulations that account for shearing within the <span class="hlt">ice</span> column, and include adequate basal sliding and <span class="hlt">ice-shelf</span> melting parameterizations. To this end, UCI/NASA JPL's <span class="hlt">Ice</span> Sheet System Model (ISSM) with coupled SSA/higher-order physics is used in the Amundsen Sea Embayment (ASE) to examine threshold behavior of TG and PIG, highlighting areas particularly vulnerable to retreat from oceanic warming and <span class="hlt">ice-shelf</span> removal. These moving-front experiments will aid in targeting critical areas for additional data collection in ASE as well as for weighting accuracy in further melt parameterization development. Furthermore, a sub-<span class="hlt">shelf</span> melt parameterization, resulting from Regional Ocean Modeling System (ROMS; St-Laurent et al., 2015) and coupled ISSM-Massachusetts Institute of Technology general circulation model (MITgcm; Seroussi et al., 2017) output, is incorporated and initially tested in ISSM. Data-guided experiments include variable basal conditions and <span class="hlt">ice</span> hardness, and are also forced with constant modern climate in ISSM, providing valuable insight into i) effects of different basal friction parameterizations on <span class="hlt">ice</span> dynamics, illustrating the importance of constraining the variable bed character beneath TG and PIG; ii) the impact of including vertical shear in <span class="hlt">ice</span> flow models of outlet glaciers, confirming its role in capturing complex feedbacks proximal to the grounding zone; and iii) ASE's sensitivity to sub-<span class="hlt">shelf</span> melt and <span class="hlt">ice</span>-front retreat, possible thresholds, and how these affect <span class="hlt">ice</span>-flow evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70195489','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70195489"><span>Morphology and stratal geometry of the Antarctic continental <span class="hlt">shelf</span>: Insights from models</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Cooper, Alan K.; Barker, Peter F.; Brancolini, Giuliano</p> <p>1997-01-01</p> <p>Reconstruction of past <span class="hlt">ice</span>-sheet fluctuations from the stratigraphy of glaciated continental shelves requires understanding of the relationships among the stratal geometry, glacial and marine sedimentary processes, and <span class="hlt">ice</span> dynamics. We investigate the formation of the morphology and the broad stratal geometry of topsets on the Antarctic continental <span class="hlt">shelf</span> 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 <span class="hlt">ice</span>. The location of the grounding line varies with time almost randomly across the <span class="hlt">shelf</span>. With these simple assumptions, the models can successfully mimic salient features of the morphology and the stratal geometry. The models suggest that the current <span class="hlt">shelf</span> has gradually evolved to its present geometry by many glacial advances and retreats of the grounding line to different locations across the <span class="hlt">shelf</span>. 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 <span class="hlt">ice</span> 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 <span class="hlt">shelf</span>, and erosion decreases and deposition increases toward the <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span>, 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoRL..4411878S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..4411878S"><span>The Response of <span class="hlt">Ice</span> Sheets to Climate Variability</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Snow, K.; Goldberg, D. N.; Holland, P. R.; Jordan, J. R.; Arthern, R. J.; Jenkins, A.</p> <p>2017-12-01</p> <p>West Antarctic <span class="hlt">Ice</span> Sheet loss is a significant contributor to sea level rise. While the <span class="hlt">ice</span> loss is thought to be triggered by fluctuations in oceanic heat at the <span class="hlt">ice</span> <span class="hlt">shelf</span> bases, <span class="hlt">ice</span> sheet response to ocean variability remains poorly understood. Using a synchronously coupled <span class="hlt">ice</span>-ocean model permitting grounding line migration, this study evaluates the response of an <span class="hlt">ice</span> sheet to periodic variations in ocean forcing. Resulting oscillations in grounded <span class="hlt">ice</span> 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 <span class="hlt">ice</span> sheets. The <span class="hlt">ice</span> <span class="hlt">shelf</span> residence time offers a critical time scale, above which the <span class="hlt">ice</span> response amplitude is a linear function of ocean forcing period and below which it is quadratic. These results highlight the sensitivity of West Antarctic <span class="hlt">ice</span> streams to perturbations in heat fluxes occurring at decadal time scales.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730015654','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730015654"><span>Sea <span class="hlt">ice</span> and surface water circulation, Alaskan Continental <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wright, F. F. (Principal Investigator); Sharma, G. D.; Burn, J. J.</p> <p>1973-01-01</p> <p>The author has identified the following significant results. The boundaries of land-fast <span class="hlt">ice</span>, distribution of pack <span class="hlt">ice</span>, and major polynya were studied in the vicinity of the Bering Strait. Movement of pack <span class="hlt">ice</span> during 24 hours was determined by plotting the distinctly identifiable <span class="hlt">ice</span> floes on ERTS-1 imagery obtained from two consecutive passes. Considerably large shallow area along the western Seward Peninsula just north of the Bering Strait is covered by land fast <span class="hlt">ice</span>. This <span class="hlt">ice</span> hinders the movement of <span class="hlt">ice</span> formed in eastern Chukchi Sea southward through the Bering Strait. The movement of <span class="hlt">ice</span> along the Russian coast is relatively faster. Plotting of some of the <span class="hlt">ice</span> floes indicated movement of <span class="hlt">ice</span> in excess of 30 km in and south of the Bering Strait between 6 and 7 March, 1973. North of the Bering Strait the movement approached 18 km. The movement of <span class="hlt">ice</span> observed during March 6 and 7 considerably altered the distribution and extent of polynya. These features when continually plotted should be of considerable aid in navigation of <span class="hlt">ice</span> breakers. The movement of <span class="hlt">ice</span> will also help delineate the migration and distribution of sea mammals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813991B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813991B"><span>Evolution of a Greenland <span class="hlt">Ice</span> sheet Including Shelves and Regional Sea Level Variations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bradley, Sarah; Reerink, Thomas; van de Wal, Roderik S. W.; Helsen, Michiel; Goelzer, Heiko</p> <p>2016-04-01</p> <p>Observational evidence, including offshore moraines and marine sediment cores infer that at the Last Glacial maximum (LGM) the Greenland <span class="hlt">ice</span> sheet (GIS) grounded out across the Davis Strait into Baffin Bay, with fast flowing <span class="hlt">ice</span> streams extending out to the continental <span class="hlt">shelf</span> break along the NW margin. These observations lead to a number of questions as to weather the GIS and Laurentide <span class="hlt">ice</span> sheet (LIS) coalesced during glacial maximums, and if so, did a significant <span class="hlt">ice</span> <span class="hlt">shelf</span> develop across Baffin Bay and how would such a configuration impact on the relative contribution of these <span class="hlt">ice</span> sheets to eustatic sea level (ESL). Most previous paleo <span class="hlt">ice</span> sheet modelling simulations of the GIS recreated an <span class="hlt">ice</span> sheet that either did not extend out onto the continental <span class="hlt">shelf</span> or utilised a simplified marine <span class="hlt">ice</span> parameterisation to recreate an extended GIS, and therefore did not fully include <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics. In this study we simulate the evolution of the GIS from 220 kyr BP to present day using IMAU-<span class="hlt">ice</span>; a 3D thermodynamical <span class="hlt">ice</span> sheet model which fully accounts for grounded and floating <span class="hlt">ice</span>, calculates grounding line migration and <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics. As there are few observational estimates of the long-term (yrs) sub marine basal melting rates (mbm) for the GIS, we developed a mbm parameterization within IMAU-<span class="hlt">ice</span> controlled primarily by changes in paleo water depth. We also investigate the influence of the LIS on the GIS evolution by including relative sea level forcing's derived from a Glacial Isostatic Adjustment model. We will present results of how changes in the mbm directly impacts on the <span class="hlt">ice</span> sheet dynamics, timing and spatial extent of the GIS at the glacial maximums, but also on the rate of retreat and spatial extent at the Last interglacial (LIG) minimum. Results indicate that with the inclusion of <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics, a larger GIS is generated which is grounded out into Davis strait, up to a water depth of -750 m, but significantly reduces the GIS contribution to Last</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMPP43C2299B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMPP43C2299B"><span>Evolution of a Greenland <span class="hlt">Ice</span> sheet Including Shelves and Regional Sea Level Variations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bradley, S.; Reerink, T.; Vandewal, R.; Helsen, M.</p> <p>2015-12-01</p> <p>Observational evidence, including offshore moraines and marine sediment cores infer that at the Last Glacial maximum (LGM) the Greenland <span class="hlt">ice</span> sheet (GIS) grounded out across the Davis Strait into Baffin Bay, with fast flowing <span class="hlt">ice</span> streams extending out to the continental <span class="hlt">shelf</span> break along the NW margin. These observations lead to a number of questions as to weather the GIS and Laurentide <span class="hlt">ice</span> sheet (LIS) coalesced during glacial maximums, and if so, did a significant <span class="hlt">ice</span> <span class="hlt">shelf</span> develop across Baffin Bay and how would such a configuration impact on the relative contribution of these <span class="hlt">ice</span> sheets to eustatic sea level (ESL). Most previous paleo <span class="hlt">ice</span> sheet modelling simulations of the GIS recreated an <span class="hlt">ice</span> sheet that either did not extend out onto the continental <span class="hlt">shelf</span> or utilised a simplified marine <span class="hlt">ice</span> parameterisation to recreate an extended GIS, and therefore did not fully include <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics. In this study we simulate the evolution of the GIS from 220 kyr BP to present day using IMAU-<span class="hlt">ice</span>; a 3D thermodynamical <span class="hlt">ice</span> sheet model which fully accounts for grounded and floating <span class="hlt">ice</span>, calculates grounding line migration and <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics. There is few observational estimates of long-term (yrs) sub marine basal melting rates (mbm) for the GIS. Therefore we investigate a range of relationships to constrain the spatial and temporal parameterisation of mbm within IMAU-<span class="hlt">ice</span> related to changes in paleo water depth, driven by changes in relative sea level and ocean temperature. We will present results of how changes in the mbm directly impacts on the <span class="hlt">ice</span> sheet dynamics, timing and spatial extent of the GIS at the glacial maximums, but also on the rate of retreat and spatial extent at the Last interglacial (LIG) minimum. Initial results indicate that with the inclusion of <span class="hlt">ice</span> <span class="hlt">shelf</span> dynamics, a larger GIS is generated which is grounded out into Davis strait, up to a water depth of -750 m, but the total contribution to LIG ESL is reduced by up to 0.6 m.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.C13A0732Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.C13A0732Y"><span>Monitoring Antarctic <span class="hlt">ice</span> sheet surface melting with TIMESAT algorithm</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ye, Y.; Cheng, X.; Li, X.; Liang, L.</p> <p>2011-12-01</p> <p>Antarctic <span class="hlt">ice</span> 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. <span class="hlt">Ice</span> sheet melting will cause snow humidity increase, which will accelerate the disintegration and movement of <span class="hlt">ice</span> sheet. As a result, detecting Antarctic <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> region. It is affected by land cover type, surface elevation and geographic location (latitude). In addition, the Antarctic <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and Ronnie <span class="hlt">Ice</span> <span class="hlt">Shelf</span> have the greatest interannual variability in amount of melting, which largely determines the overall interannual variability in Antarctica. Other regions, especially Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and Wilkins <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, which is in the Antarctic Peninsula</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GeoRL..45.4086A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GeoRL..45.4086A"><span>Variable Basal Melt Rates of Antarctic Peninsula <span class="hlt">Ice</span> Shelves, 1994-2016</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Adusumilli, Susheel; Fricker, Helen Amanda; Siegfried, Matthew R.; Padman, Laurie; Paolo, Fernando S.; Ligtenberg, Stefan R. M.</p> <p>2018-05-01</p> <p>We have constructed 23-year (1994-2016) time series of Antarctic Peninsula (AP) <span class="hlt">ice-shelf</span> 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, <span class="hlt">ice</span> dynamics, and basal mass balance. On the Bellingshausen coast of the AP, <span class="hlt">ice</span> shelves lost 84 ± 34 Gt a-1 to basal melting, compared to contributions of 50 ± 7 Gt a-1 from surface mass balance and <span class="hlt">ice</span> dynamics. Net basal melting on the Weddell coast was 51 ± 71 Gt a-1. Recent changes in <span class="hlt">ice-shelf</span> height include increases over major AP <span class="hlt">ice</span> shelves driven by changes in firn state. Basal melt rates near Bawden <span class="hlt">Ice</span> Rise, a major pinning point of Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, showed large increases, potentially leading to substantial loss of buttressing if sustained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013OcMod..67...39K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013OcMod..67...39K"><span>Adaptation of an unstructured-mesh, finite-element ocean model to the simulation of ocean circulation beneath <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>Kimura, Satoshi; Candy, Adam S.; Holland, Paul R.; Piggott, Matthew D.; Jenkins, Adrian</p> <p>2013-07-01</p> <p>Several different classes of ocean model are capable of representing floating glacial <span class="hlt">ice</span> shelves. We describe the incorporation of <span class="hlt">ice</span> shelves into Fluidity-ICOM, a nonhydrostatic finite-element ocean model with the capacity to utilize meshes that are unstructured and adaptive in three dimensions. This geometric flexibility offers several advantages over previous approaches. The model represents melting and freezing on all <span class="hlt">ice-shelf</span> surfaces including vertical faces, treats the <span class="hlt">ice</span> <span class="hlt">shelf</span> topography as continuous rather than stepped, and does not require any smoothing of the <span class="hlt">ice</span> topography or any of the additional parameterisations of the ocean mixed layer used in isopycnal or z-coordinate models. The model can also represent a water column that decreases to zero thickness at the 'grounding line', where the floating <span class="hlt">ice</span> <span class="hlt">shelf</span> is joined to its tributary <span class="hlt">ice</span> streams. The model is applied to idealised <span class="hlt">ice-shelf</span> geometries in order to demonstrate these capabilities. In these simple experiments, arbitrarily coarsening the mesh outside the <span class="hlt">ice-shelf</span> cavity has little effect on the <span class="hlt">ice-shelf</span> melt rate, while the mesh resolution within the cavity is found to be highly influential. Smoothing the vertical <span class="hlt">ice</span> front results in faster flow along the smoothed <span class="hlt">ice</span> front, allowing greater exchange with the ocean than in simulations with a realistic <span class="hlt">ice</span> front. A vanishing water-column thickness at the grounding line has little effect in the simulations studied. We also investigate the response of <span class="hlt">ice</span> <span class="hlt">shelf</span> basal melting to variations in deep water temperature in the presence of salt stratification.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.A33B0131N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.A33B0131N"><span>A Self-Organizing Map Based Evaluation of the Antarctic Mesoscale Prediction System Using Observations from a 30-m Instrumented Tower on the Ross <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>Nigro, M. A.; Cassano, J. J.; Wille, J.; Bromwich, D. H.; Lazzara, M. A.</p> <p>2015-12-01</p> <p>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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> is stable approximately 80% of the time, indicating the influence of the permanent <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C21A0709M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C21A0709M"><span>Is the Wilkins <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miller, J.; Scambos, T.; Forster, R. R.; Long, D. G.; Ligtenberg, S.; van den Broeke, M.; Vaughan, D. G.</p> <p>2015-12-01</p> <p>Near-surface liquid meltwater on <span class="hlt">ice</span> shelves has been inferred to influence <span class="hlt">ice</span> <span class="hlt">shelf</span> stability if it induces hydrofracture and is linked to disintegration events on the Larsen B and the Wilkins <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span>, 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFMOS31D1659S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFMOS31D1659S"><span>Seismic Stratigraphic Evidence From SE Ross Sea for Late Oligocene Glaciers and <span class="hlt">ice</span> Streams Issuing From Marie Byrd Land</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sorlien, C. C.; Luyendyk, B. P.; Wilson, D. S.; Decesari, R. C.; Bartek, L. R.; Diebold, J. B.</p> <p>2006-12-01</p> <p>The extent of the West Antarctic <span class="hlt">ice</span> sheet during mid-Cenozoic time is controversial and important to climate models. High-resolution multichannel seismic reflection data were acquired using the RVIB Palmer along the edge of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> across the Eastern Basin of Ross Sea, in an area where <span class="hlt">calving</span> of the <span class="hlt">ice</span> <span class="hlt">shelf</span> has exposed seafloor that has not been accessible to marine geophysics in several decades. A sub-basin in the far southeast corner of Ross Sea contains a succession of sediment-filled troughs, each capped by an unconformity. These troughs range between 2 and 20 km across, are 100 to 150 m-deep, with the narrower ones bounded by flat-topped ridges interpreted as moraines. We interpret the troughs interval to slightly predate 25 Ma. Reflections just 100 m below the troughs interval can be directly correlated to near DSDP270 where they underlie strata dated at ~25 Ma. A deeper stack of prograding sequences associated with a flat- topped ridge are interpreted as pre-25 Ma, possibly early Oligocene, deltas formed adjacent to the grounding line of a glacier, and the flat-topped ridge to be a moraine. The shallowest of the stack of unconformities capping the broad troughs can be projected across a basement ridge on trend with Roosevelt Island to a regional angular unconformity ("Red"), present across 70 km to deep sedimentary Eastern Basin. This unconformity represents about 1 km of missing stratigraphic section, is smooth and level, and splits into several major sequence boundaries within deep Eastern Basin. The second shallowest of these boundaries is dated about 14 Ma at DSDP-270. We interpret this unconformity to be cut by regional thick, grounded <span class="hlt">ice</span> at depths several hundred meters below sea level. Pre-25 Ma strata show evidence of narrow erosional troughs and reflective mounds or ridges on the west flank of the basement ridge, but such features are not present in southern deep Eastern Basin near the <span class="hlt">ice</span> <span class="hlt">shelf</span> edge. This is evidence that the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23197526','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23197526"><span><span class="hlt">Ice</span>-sheet response to oceanic forcing.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Joughin, Ian; Alley, Richard B; Holland, David M</p> <p>2012-11-30</p> <p>The <span class="hlt">ice</span> sheets of Greenland and Antarctica are losing <span class="hlt">ice</span> at accelerating rates, much of which is a response to oceanic forcing, especially of the floating <span class="hlt">ice</span> shelves. Recent observations establish a clear correspondence between the increased delivery of oceanic heat to the <span class="hlt">ice</span>-sheet margin and increased <span class="hlt">ice</span> loss. In Antarctica, most of these processes are reasonably well understood but have not been rigorously quantified. In Greenland, an understanding of the processes by which warmer ocean temperatures drive the observed retreat remains elusive. Experiments designed to identify the relevant processes are confounded by the logistical difficulties of instrumenting <span class="hlt">ice</span>-choked fjords with actively <span class="hlt">calving</span> glaciers. For both <span class="hlt">ice</span> sheets, multiple challenges remain before the fully coupled <span class="hlt">ice</span>-ocean-atmosphere models needed for rigorous sea-level projection are available.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMPP21A2268T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMPP21A2268T"><span>Upper Ocean Circulation in the Glacial Northeast Atlantic during Heinrich Stadials <span class="hlt">Ice</span>-Sheet Retreat</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Toucanne, S.; Soulet, G.; Bosq, M.; Marjolaine, S.; Zaragosi, S.; Bourillet, J. F.; Bayon, G.</p> <p>2016-12-01</p> <p>Intermediate ocean water variability is involved in climate changes over geological timescales. As a prominent example, changes in North Atlantic subsurface water properties (including warming) during Heinrich Stadials may have triggered the so-called Heinrich events through <span class="hlt">ice-shelf</span> loss and attendant <span class="hlt">ice</span>-stream acceleration. While the origin of Heinrich Stadials and subsequent iceberg <span class="hlt">calving</span> remains controversial, paleoceanographic research efforts mainly focus on the deep Atlantic overturning, leaving the upper ocean largely unexplored. To further evaluate variability in upper ocean circulation and its possible relationship with <span class="hlt">ice</span>-sheet instabilities, a depth-transect of eight cores (BOBGEO and GITAN-TANDEM cruises) from the Northeast Atlantic (down to 2 km water depth) have been used to investigate kinematic and chemical changes in the upper ocean during the last glacial period. Our results reveal that near-bottom flow speeds (reconstructed by using sortable silt mean grain-size and X-ray fluorescence core-scanner Zr/Rb ratio) and water-masses chemistry (carbon and neodymium isotopes performed on foraminifera) substantially changed in phase with the millennial-scale climate changes recognized in the <span class="hlt">ice</span>-core records. Our results are compared with paleoceanographic reconstructions of the 'Western Boundary Undercurrent' in order to discuss regional hydrographic differences at both sides of the North Atlantic, as well as with the fluctuations of both the marine- (through <span class="hlt">ice</span>-rafted debris) and terrestrial-terminating <span class="hlt">ice</span>-streams (through meltwater discharges) of the circum-Atlantic <span class="hlt">ice</span>-sheets. Particular attention will be given to the Heinrich Stadials and concomitant Channel River meltwater discharges into the Northeast Atlantic in response to the melting of the European <span class="hlt">Ice</span>-Sheet. This comparison helps to disentangle the cryosphere-ocean interactions throughout the last <span class="hlt">ice</span> age, and the sequence of events occurring in the course of the Heinrich Stadials.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26347539','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26347539"><span>The East Siberian Arctic <span class="hlt">Shelf</span>: towards further assessment of permafrost-related methane fluxes and role of 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>Shakhova, Natalia; Semiletov, Igor; Sergienko, Valentin; Lobkovsky, Leopold; Yusupov, Vladimir; Salyuk, Anatoly; Salomatin, Alexander; Chernykh, Denis; Kosmach, Denis; Panteleev, Gleb; Nicolsky, Dmitry; Samarkin, Vladimir; Joye, Samantha; Charkin, Alexander; Dudarev, Oleg; Meluzov, Alexander; Gustafsson, Orjan</p> <p>2015-10-13</p> <p>Sustained release of methane (CH(4)) to the atmosphere from thawing Arctic permafrost may be a positive and significant feedback to climate warming. Atmospheric venting of CH(4) from the East Siberian Arctic <span class="hlt">Shelf</span> (ESAS) was recently reported to be on par with flux from the Arctic tundra; however, the future scale of these releases remains unclear. Here, based on results of our latest observations, we show that CH(4) emissions from this <span class="hlt">shelf</span> are likely to be determined by the state of subsea permafrost degradation. We observed CH(4) emissions from two previously understudied areas of the ESAS: the outer <span class="hlt">shelf</span>, where subsea permafrost is predicted to be discontinuous or mostly degraded due to long submergence by seawater, and the near shore area, where deep/open taliks presumably form due to combined heating effects of seawater, river run-off, geothermal flux and pre-existing thermokarst. CH(4) emissions from these areas emerge from largely thawed sediments via strong flare-like ebullition, producing fluxes that are orders of magnitude greater than fluxes observed in background areas underlain by largely frozen sediments. We suggest that progression of subsea permafrost thawing and decrease in <span class="hlt">ice</span> extent could result in a significant increase in CH(4) emissions from the ESAS. © 2015 The Authors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4607703','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4607703"><span>The East Siberian Arctic <span class="hlt">Shelf</span>: towards further assessment of permafrost-related methane fluxes and role of sea <span class="hlt">ice</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>Shakhova, Natalia; Semiletov, Igor; Sergienko, Valentin; Lobkovsky, Leopold; Yusupov, Vladimir; Salyuk, Anatoly; Salomatin, Alexander; Chernykh, Denis; Kosmach, Denis; Panteleev, Gleb; Nicolsky, Dmitry; Samarkin, Vladimir; Joye, Samantha; Charkin, Alexander; Dudarev, Oleg; Meluzov, Alexander; Gustafsson, Orjan</p> <p>2015-01-01</p> <p>Sustained release of methane (CH4) to the atmosphere from thawing Arctic permafrost may be a positive and significant feedback to climate warming. Atmospheric venting of CH4 from the East Siberian Arctic <span class="hlt">Shelf</span> (ESAS) was recently reported to be on par with flux from the Arctic tundra; however, the future scale of these releases remains unclear. Here, based on results of our latest observations, we show that CH4 emissions from this <span class="hlt">shelf</span> are likely to be determined by the state of subsea permafrost degradation. We observed CH4 emissions from two previously understudied areas of the ESAS: the outer <span class="hlt">shelf</span>, where subsea permafrost is predicted to be discontinuous or mostly degraded due to long submergence by seawater, and the near shore area, where deep/open taliks presumably form due to combined heating effects of seawater, river run-off, geothermal flux and pre-existing thermokarst. CH4 emissions from these areas emerge from largely thawed sediments via strong flare-like ebullition, producing fluxes that are orders of magnitude greater than fluxes observed in background areas underlain by largely frozen sediments. We suggest that progression of subsea permafrost thawing and decrease in <span class="hlt">ice</span> extent could result in a significant increase in CH4 emissions from the ESAS. PMID:26347539</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JGRC..123..324B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JGRC..123..324B"><span>Multiphase Reactive Transport and Platelet <span class="hlt">Ice</span> Accretion in the Sea <span class="hlt">Ice</span> of McMurdo Sound, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Buffo, J. J.; Schmidt, B. E.; Huber, C.</p> <p>2018-01-01</p> <p>Sea <span class="hlt">ice</span> seasonally to interannually forms a thermal, chemical, and physical boundary between the atmosphere and hydrosphere over tens of millions of square kilometers of ocean. Its presence affects both local and global climate and ocean dynamics, <span class="hlt">ice</span> <span class="hlt">shelf</span> processes, and biological communities. Accurate incorporation of sea <span class="hlt">ice</span> growth and decay, and its associated thermal and physiochemical processes, is underrepresented in large-scale models due to the complex physics that dictate oceanic <span class="hlt">ice</span> formation and evolution. Two phenomena complicate sea <span class="hlt">ice</span> simulation, particularly in the Antarctic: the multiphase physics of reactive transport brought about by the inhomogeneous solidification of seawater, and the buoyancy driven accretion of platelet <span class="hlt">ice</span> formed by supercooled <span class="hlt">ice</span> <span class="hlt">shelf</span> water onto the basal surface of the overlying <span class="hlt">ice</span>. Here a one-dimensional finite difference model capable of simulating both processes is developed and tested against <span class="hlt">ice</span> core data. Temperature, salinity, liquid fraction, fluid velocity, total salt content, and <span class="hlt">ice</span> structure are computed during model runs. The model results agree well with empirical observations and simulations highlight the effect platelet <span class="hlt">ice</span> accretion has on overall <span class="hlt">ice</span> thickness and characteristics. Results from sensitivity studies emphasize the need to further constrain sea <span class="hlt">ice</span> microstructure and the associated physics, particularly permeability-porosity relationships, if a complete model of sea <span class="hlt">ice</span> evolution is to be obtained. Additionally, implications for terrestrial <span class="hlt">ice</span> shelves and icy moons in the solar system are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..MARF40007Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..MARF40007Z"><span>From Glaciers to Icebergs</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Wendy</p> <p></p> <p>I will describe works from a collaboration between physics and glaciology that grew out of interactions at the Computations in Science seminar Leo Kadanoff organized at the University of Chicago. The first project considers the interaction between ocean waves and Antarctic <span class="hlt">ice</span> shelves, large floating portions of <span class="hlt">ice</span> formed by glacial outflows. Back-of-envelop calculation and seismic sensor data suggest that crevasses may be distributed within an <span class="hlt">ice</span> <span class="hlt">shelf</span> to shield it from wave energy. We also examine numerical scenarios in which changes in environmental forcing causes the <span class="hlt">ice</span> <span class="hlt">shelf</span> to fail catastrophically. The second project investigates the aftermath of iceberg <span class="hlt">calving</span> off glacier terminus in Greenland using data recorded via time-lapse camera and terrestrial radar. Our observations indicate that the mélange of icebergs within the fjord experiences widespread jamming during a <span class="hlt">calving</span> event and therefore is always close to being in a jammed state during periods of terminus quiescence. Joint work with Jason Amundson, Ivo R. Peters, Julian Freed Brown, Nicholas Guttenberg, Justin C Burton, L. Mac Cathles, Ryan Cassotto, Mark Fahnestock, Kristopher Darnell, Martin Truffer, Dorian S. Abbot and Douglas MacAyeal. Kadanoff Session DCMP.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70019727','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70019727"><span><span class="hlt">Ice</span>-front change and iceberg behaviour along Oates and George V Coasts, Antarctica, 1912-96</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Frezzotti, M.; Cimbelli, A.; Ferrigno, J.G.</p> <p>1998-01-01</p> <p><span class="hlt">Ice</span>-front change may well be a sensitive indicator of regional climate change. We have studied the western Oates Coast from Cape Kinsey (158??50'E, 69??19'S) to Cape Hudson (153??45'E, 68??20'S) and the entire George V Coast, from Cape Hudson to Point Alden (142??02'E, 66??48'S). The glaciers here drain part of the Dome Charlie and Talos Dome areas (640 000 km2). A comparison between various documents, dated several years apart, has allowed an estimate of the surficial <span class="hlt">ice</span> discharge, the <span class="hlt">ice</span>-front fluctuation and the iceberg-<span class="hlt">calving</span> flux during the last 50 years. The <span class="hlt">ice</span>-front discharge of the studied coast has been estimated at about 90??12 km3 a-1 in 1989-91, 8.5 km3 a-1 for western Oates Coast and 82 km3 a-1 for George V Coast. From 1962-63 to 1973-74 the floating glaciers underwent a net reduction that continued from 1973-74 to 1989-91. On the other hand, from 1989-91 to 1996 the area of floating glaciers increased. Ninnis Glacier Tongue and the western part of Cook <span class="hlt">Ice</span> <span class="hlt">Shelf</span> underwent a significant retreat after 1980 and 1947, respectively. Satellite-image analysis of large icebergs has provided information about <span class="hlt">ice</span>-ocean interaction and the existence of an 'iceberg trap' along George V Coast. A first estimate of the mass balance of the drainage basin of Mertz and Ninnis Glaciers shows a value close to zero or slightly negative.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110015161','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110015161"><span>Thickening and Thinning of Antarctic <span class="hlt">Ice</span> Shelves and Tongues and Mass Balance Estimates</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; Giovinetto, Mario; Robbins, John; Saba, Jack L.; Yi, Donghui</p> <p>2011-01-01</p> <p>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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, were mostly thinning and losing mass whereas the Ronne <span class="hlt">Ice</span> <span class="hlt">shelf</span> also in WA was mostly thickening. The estimated total mass loss for the floating <span class="hlt">ice</span> shelves and <span class="hlt">ice</span> tongues from <span class="hlt">ice</span> draining WA and the AP was 95 Gt/a. In contrast, the floating <span class="hlt">ice</span> shelves and <span class="hlt">ice</span> tongues from <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> and -42.4 and - 27.2 cm/a on the East Getz <span class="hlt">ice</span> <span class="hlt">shelf</span>, and some values that indicate more thinning in the latter period, including -17.9 and -36.2 cm/a on the Larsen C <span class="hlt">ice</span> <span class="hlt">shelf</span>, -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.</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('http://adsabs.harvard.edu/abs/2018JGRG..123..760L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JGRG..123..760L"><span>Linking the Modern Distribution of Biogenic Proxies in High Arctic Greenland <span class="hlt">Shelf</span> Sediments to Sea <span class="hlt">Ice</span>, Primary Production, and Arctic-Atlantic Inflow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Limoges, Audrey; Ribeiro, Sofia; Weckström, Kaarina; Heikkilä, Maija; Zamelczyk, Katarzyna; Andersen, Thorbjørn J.; Tallberg, Petra; Massé, Guillaume; Rysgaard, Søren; Nørgaard-Pedersen, Niels; Seidenkrantz, Marit-Solveig</p> <p>2018-03-01</p> <p>The eastern north coast of Greenland is considered to be highly sensitive to the ongoing Arctic warming, but there is a general lack of data on modern conditions and in particular on the modern distribution of climate and environmental proxies to provide a baseline and context for studies on past variability. Here we present a detailed investigation of 11 biogenic proxies preserved in surface sediments from the remote High Arctic Wandel Sea <span class="hlt">shelf</span>, the entrance to the Independence, Hagen, and Danmark fjords. The composition of organic matter (organic carbon, C:N ratios, δ13C, δ15N, biogenic silica, and IP25) and microfossil assemblages revealed an overall low primary production dominated by benthic diatoms, especially at the shallow sites. While the benthic and planktic foraminiferal assemblages underline the intrusion of chilled Atlantic waters into the deeper parts of the study area, the distribution of organic-walled dinoflagellate cysts is controlled by the local bathymetry and sea <span class="hlt">ice</span> conditions. The distribution of the dinoflagellate cyst Polarella glacialis matches that of seasonal sea <span class="hlt">ice</span> and the specific biomarker IP25, highlighting the potential of this species for paleo sea <span class="hlt">ice</span> studies. The information inferred from our multiproxy study has important implications for the interpretation of the biogenic-proxy signal preserved in sediments from circum-Arctic fjords and <span class="hlt">shelf</span> regions and can serve as a baseline for future studies. This is the first study of its kind in this area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.P31A2092B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.P31A2092B"><span>Jamming of granular <span class="hlt">ice</span> mélange in tidewater glacial fjords</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burton, J. C.; Cassotto, R.; Amundson, J. M.; Kuo, C. C.; Dennin, M.</p> <p>2016-12-01</p> <p>In tidewater glacial fjords, the open water in front of the glacier terminus is often filled with a collection of <span class="hlt">calved</span> iceberg fragments and sea <span class="hlt">ice</span>. For glaciers with large <span class="hlt">calving</span> rates, this "mélange" of <span class="hlt">ice</span> can be jam-packed, so that the flow is mostly determined by granular interactions, in addition to underlying fjord currents. As the glacier pushes the <span class="hlt">ice</span> mélange through the fjord, the mélange will become jammed and may potentially influence <span class="hlt">calving</span> rates if the back-stress applied to the glacier terminus is large enough. However, the stress applied by a granular <span class="hlt">ice</span> mélange will depend on its rheology, i.e. iceberg-iceberg contact forces, geometry, friction, etc. Here we report 2D, discrete particle simulations to model the granular mechanics of <span class="hlt">ice</span> mélange. A polydisperse collection of particles is packed into a long channel and pushed downfjord at a constant speed, the latter derived from terrestrial radar interferometry (TRI). Each individual particle experiences viscoelastic contact forces and tangential frictional forces upon collision with another particle or channel walls. We find the two most important factors that govern the total force applied to the glacier are the geometry of the channel, and the shape of the particles. In addition, our simulated velocity fields reveal shearing margins near the fjord walls with more uniform flow in the middle of the mélange, consistent with TRI observations. Finally, we find that the magnitude of the back-stress applied to the glacier terminus can influence <span class="hlt">calving</span>, however, the maximum back-stress is limited by the buckling of icebergs into the fjord waters, so that the stress in the quasi-2D mélange is partially determined by the thickness of the mélange layer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/imap/2600/D/i2600d-pamphlet.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/imap/2600/D/i2600d-pamphlet.pdf"><span>Coastal-change and glaciological map of the Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> area, Antarctica, 1974-2002</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.; Foley, K.M.; Swithinbank, C.; Williams, R.S.; Dalide, L.M.</p> <p>2005-01-01</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 may severely impact the densely populated coastal regions on Earth. Melting of the West Antarctic part alone of the Antarctic <span class="hlt">ice</span> sheet could cause a sea-level rise of approximately 6 meters (m). The potential sea-level rise after melting of the entire Antarctic <span class="hlt">ice</span> 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 <span class="hlt">ice</span> sheet is poorly known; it is not known for certain whether the <span class="hlt">ice</span> sheet is growing or shrinking. In a review paper, Rignot and Thomas (2002) concluded that the West Antarctic part of the Antarctic <span class="hlt">ice</span> 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 <span class="hlt">ice</span>-flow velocities derived from synthetic aperture radar, concluded that most of the Ross <span class="hlt">ice</span> streams (<span class="hlt">ice</span> streams on the east side of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>) 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 <span class="hlt">ice</span> sheet is unknown, but thought to be in near equilibrium. Measurement of changes in area and mass balance of the Antarctic <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 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27.6348B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27.6348B"><span>Note On The Ross Sea <span class="hlt">Shelf</span> Water Downflow Processes (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.; Defendi, V.; Spezie, G.; Budillon, G.; Carniel, S.</p> <p></p> <p>In the framework of the CLIMA Project of the Italian National Program for Research in Antarctica, three different experimental data sets were acquired along the continental <span class="hlt">shelf</span> break; two of them (in 1997 and 2001) close to Cape Adare, the 1998 one in the middle of the Ross Sea (i.e. 75 S, 177 W). The investigations were chosen in order to explore the downslope flow of the bottom waters produced in the Ross Sea, namely the High Salinity <span class="hlt">Shelf</span> Water (HSSW, the densest water mass of the southern ocean coming from its formation site in the polynya region in Terra Nova bay), and the <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Water (ISW, originated below the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and outflowing northward). Both bottom waters spill over the <span class="hlt">shelf</span> edge and mix with the Circumpolar Deep Water (CDW) contributing to the formation of the Antarctic Bottom Waters (AABW). Interpreting temperature, salinity and density maps in terms of cascading processes, both HSSW and ISW overflows are evidenced during, respectively, 1997 and 1998. During the 2001 acquisition there is no presence of HSSW along the <span class="hlt">shelf</span> break, nevertheless distribution captures the evidence of a downslope flow process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C13C0835K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C13C0835K"><span>Seasonal variability in <span class="hlt">ice</span>-front position, glacier speed, and surface elevation at Helheim Glacier, SE Greenland, from 2010-2016</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kehrl, L. M.; Joughin, I. R.; Shean, D. E.</p> <p>2016-12-01</p> <p>Marine-terminating glaciers can be very sensitive to changes in <span class="hlt">ice</span>-front position, depending on their geometry. If a nearly grounded glacier retreats into deeper water, the glacier typically must speed up to produce the additional longitudinal and lateral stress gradients necessary to restore force balance. This speedup often causes thinning, which can increase the glacier's susceptibility to further retreat. In this study, we combine satellite observations and numerical modeling (Elmer/<span class="hlt">Ice</span>) to investigate how seasonal changes in <span class="hlt">ice</span>-front position affect glacier speed and surface elevation at Helheim Glacier, SE Greenland, from 2010-2016. Helheim's <span class="hlt">calving</span> front position fluctuated about a mean position from 2010-2016. During 2010/11, 2013/14, and 2015/16, Helheim seasonally retreated and advanced along a reverse bed slope by > 3 km. During these years, the glacier retreated from winter/spring to late summer and then readvanced until winter/spring. During the retreat, Helheim sped up by 20-30% and thinned by 20 m near its <span class="hlt">calving</span> front. This thinning caused the <span class="hlt">calving</span> front to unground, and a floating <span class="hlt">ice</span> tongue was then able to readvance over the following winter with limited iceberg <span class="hlt">calving</span>. The advance, which continued until the glacier reached the top of the bathymetric high, caused the glacier to slow and thicken. During years when Helheim likely did not form a floating <span class="hlt">ice</span> tongue, iceberg <span class="hlt">calving</span> continued throughout the winter. Consequently, the formation of this floating <span class="hlt">ice</span> tongue may have helped stabilize Helheim after periods of rapid retreat and dynamic thinning. Helheim's rapid retreat from 2001-2005 also ended when a floating <span class="hlt">ice</span> tongue formed and readvanced over the 2005/06 winter. These seasonal retreat/advance cycles may therefore be important for understanding Helheim's long-term behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012QSRv...35...63G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012QSRv...35...63G"><span>Palaeoglaciology of the Alexander Island <span class="hlt">ice</span> cap, western Antarctic Peninsula, reconstructed from marine geophysical and core data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Graham, Alastair G. C.; Smith, James A.</p> <p>2012-03-01</p> <p>The glacial history of the continental <span class="hlt">shelf</span> northwest of Alexander Island is not well known, due mainly to a lack of targeted marine data on Antarctica's palaeo-<span class="hlt">ice</span> sheets in their inter-<span class="hlt">ice</span>-stream areas. Recently it has been argued that the region was <span class="hlt">ice</span>-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 <span class="hlt">shelf</span>'s palaeoglaciology. Sea-floor bedforms provide evidence that an independent <span class="hlt">ice</span> cap persisted on Alexander Island through the LGM and deglaciation. We show that this <span class="hlt">ice</span> cap drained via two major, previously-undescribed tidewater outlets (Rothschild and Charcot Glaciers) sourced from an <span class="hlt">ice</span> dome centred over the west of the island and near-shore areas. The glaciers grounded along deep, fjord-like cross-<span class="hlt">shelf</span> troughs to within at least ˜10-20 km of the <span class="hlt">shelf</span> edge, and probably reached the <span class="hlt">shelf</span> break. Only one small outer-<span class="hlt">shelf</span> zone appears to have remained free of <span class="hlt">ice</span> throughout an otherwise extensive LGM. During retreat, grounding-line geomorphology indicates periodic stabilisation of Charcot Glacier on the mid-<span class="hlt">shelf</span> after 13,500 cal yrs BP, while Rothschild Glacier retreated across its mid-<span class="hlt">shelf</span> 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 <span class="hlt">Ice</span> Sheet. The fine details of <span class="hlt">ice</span> flow documented by our new reconstruction highlight the importance of capturing complex <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> at the LGM as indicated by previous biological studies; instead</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMPP21E..08A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP21E..08A"><span><span class="hlt">Ice</span> dynamics of Heinrich events: Insights and implications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alley, R. B.; Parizek, B. R.; Anandakrishnan, S.</p> <p>2017-12-01</p> <p>Physical understanding of <span class="hlt">ice</span> flow provides important constraints on Heinrich (H) events, which in turn provide lessons for <span class="hlt">ice</span> dynamics and future sea-level change. Iceberg-rafted debris (IRD), the defining feature of H events, is a complex indicator; however, in cold climates with extensive marine-ending <span class="hlt">ice</span>, increased IRD flux records <span class="hlt">ice-shelf</span> loss. <span class="hlt">Ice</span> shelves fed primarily by inflow from grounded <span class="hlt">ice</span> experience net basal melting, giving sub-<span class="hlt">ice</span>-sedimentation rather than open-ocean IRD. <span class="hlt">Ice-shelf</span> loss has been observed recently in response to atmospheric warming increasing surface meltwater that wedged open crevasses (Larsen B), but also by break-off following thinning from warming of waters reaching the grounding line (Jakobshavn). The H events consistently occurred during cold times resulting from reduced North Atlantic overturning circulation ("conveyor"), but as argued by Marcott et al. (PNAS 2011), this was accompanied by delayed warming at grounding-line depths of the Hudson Strait <span class="hlt">ice</span> stream, the source of the Heinrich layers, implicating oceanic control. As shown in a rich literature, additional considerations involving thermal state of the <span class="hlt">ice</span>-stream bed, isostasy and probably other processes influenced why some reduced-conveyor events triggered H-events while others did not. <span class="hlt">Ice</span> shelves, including the inferred Hudson Strait <span class="hlt">ice</span> <span class="hlt">shelf</span>, typically exist in high-salinity, cold waters produced by brine rejection from sea-<span class="hlt">ice</span> formation, which are the coldest abundant waters in the world ocean. Thus, almost any change in air or ocean temperature, winds or currents can remove <span class="hlt">ice</span> shelves, because "replacement" water masses are typically warmer. And, because <span class="hlt">ice</span> shelves almost invariably slow flow of non-floating <span class="hlt">ice</span> into the ocean, climatic perturbations to regions with <span class="hlt">ice</span> shelves typically lead to sea-level rise, with important implications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAMES...9.1948S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAMES...9.1948S"><span>Modeling tabular icebergs submerged in the ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stern, A. A.; Adcroft, A.; Sergienko, O.; Marques, G.</p> <p>2017-08-01</p> <p>Large tabular icebergs <span class="hlt">calved</span> from Antarctic <span class="hlt">ice</span> shelves have long lifetimes (due to their large size), during which they drift across large distances, altering ambient ocean circulation, bottom-water formation, sea-<span class="hlt">ice</span> formation, and biological primary productivity in the icebergs' vicinity. However, despite their importance, the current generation of ocean circulation models usually do not represent large tabular icebergs. In this study, we develop a novel framework to model large tabular icebergs submerged in the ocean. In this framework, tabular icebergs are represented by pressure-exerting Lagrangian elements that drift in the ocean. The elements are held together and interact with each other via bonds. A breaking of these bonds allows the model to emulate <span class="hlt">calving</span> events (i.e., detachment of a tabular iceberg from an <span class="hlt">ice</span> <span class="hlt">shelf</span>) and tabular icebergs breaking up into smaller pieces. Idealized simulations of a <span class="hlt">calving</span> tabular iceberg, its drift, and its breakup demonstrate capabilities of the developed framework.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1616930P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1616930P"><span>The extent and timing of the last British-Irish <span class="hlt">Ice</span> Sheet offshore of west Ireland-preliminary findings</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peters, Jared; Benetti, Sara; Dunlop, Paul; Cofaigh, Colm Ó.</p> <p>2014-05-01</p> <p>Recently interpreted marine geophysical data from the western Irish <span class="hlt">shelf</span> has provided the first direct evidence that the last British-Irish <span class="hlt">Ice</span> Sheet (BIIS) extended westwards onto the Irish continental <span class="hlt">shelf</span> as a grounded <span class="hlt">ice</span> mass composed of several lobes with marine-terminating margins. Marine terminating <span class="hlt">ice</span> margins are known to be sensitive to external forcing mechanisms and currently there is concern regarding the future stability of marine based <span class="hlt">ice</span> sheets, such as the West Antarctic <span class="hlt">Ice</span> Sheet, in a warming world. Given its position, the glaciated western Irish continental <span class="hlt">shelf</span> is a prime location to investigate the processes of how marine-based <span class="hlt">ice</span> sheets responded to past climatic and oceanic events, which may in turn help us better predict the future trajectory of the marine sectors of modern <span class="hlt">Ice</span> Sheets. However, despite the potential importance of the former Irish <span class="hlt">ice</span> margin to our understanding of <span class="hlt">ice</span> sheet behaviour, the timing and nature of its advance and retreat is currently poorly understood. This study aims to describe the depositional history of the last BIIS on the continental <span class="hlt">shelf</span> west of Ireland and age-constrain the rate of retreat of two <span class="hlt">ice</span> lobes that extended from Galway Bay and Clew Bay. This is being accomplished through a multifaceted analysis of at least 29 sediment cores gathered across the continental <span class="hlt">shelf</span> offshore of counties Galway and Mayo, Ireland. This poster shows results from initial sedimentological descriptions of cores from the mid to outer <span class="hlt">shelf</span>, which support previous geomorphic interpretations of BIIS history. Preliminary palaeoenvironmental results from ongoing micropaleontological analyses are also discussed and provide new data that verifies sedimentary interpretations on <span class="hlt">ice</span> proximity. Finally, results from several radiocarbon dates are discussed, which limit these deposits to the last glacial maximum and constrain the timings of <span class="hlt">ice</span> advance and retreat on the continental <span class="hlt">shelf</span> west of Ireland.</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 Antarctic 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 Antarctic 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 Antarctic 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/2017EGUGA..1912886L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1912886L"><span><span class="hlt">Calving</span> laws and strain rates: a comparison between modelled relationships and observations from InSAR velocity maps from across Greenland.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lea, James; Nick, Faezeh; Benn, Douglas; Kirchner, Nina</p> <p>2017-04-01</p> <p><span class="hlt">Calving</span> is a major mechanism of cryospheric <span class="hlt">ice</span> mass loss and a significant contributor to global sea level change, though it is currently poorly understood as a process. Longitudinal strain rate is often cited as a first order control on <span class="hlt">calving</span>, however multiple different <span class="hlt">calving</span> laws (not always including the strain rate) have been used to represent this in numerical models of <span class="hlt">ice</span> sheets. This study seeks to investigate how (1) different <span class="hlt">calving</span> laws within a 1D flowline model predict strain rate will evolve within increasing terminus thickness for steady state and transient simulations, and (2) how these relationships compare with observed strains (derived from MEaSUREs Greenland InSAR velocity maps; Joughin et al., 2010 [updated 2016]) and depths (from BedMachine v.2 subglacial topography data; Morlighem et al., 2014). We identify that systematic relationships with terminus thickness exist for height above buoyancy, waterline and full-depth crevasse <span class="hlt">calving</span> laws amongst others for both steady state and transient simulations. However, analysis of observed near-terminus strain rates for multiple Greenlandic glaciers using a variety of metrics (with a range of bed depths predicted by BedMachine) does not reproduce the shape or magnitude of any of these modelled relationships. Relationships between strain rate and depth derived from simple 1D model simulations therefore cannot be realistically compared to current real-world observations. This suggests that the magnitude of observed strain rates at an individual point, or area-averaged conditions near a real-world terminus are not meaningful in determining the potential for <span class="hlt">calving</span> when taken in isolation. To improve understanding of first/second order <span class="hlt">calving</span> processes, future modelling work should therefore look to analyse how/if the distribution of strain across the terminus region impacts <span class="hlt">calving</span> as part of 2D-planform/3D models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C53A0767E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C53A0767E"><span>The North Water Polynya and Velocity, <span class="hlt">Calving</span> Front and Mass Change in Surrounding Glaciers in Greenland and Canada Over the Last 30 Years</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Edwards, L.</p> <p>2015-12-01</p> <p>Major uncertainties surround future estimates of sea level rise attributable to mass loss from Greenland and the surrounding <span class="hlt">ice</span> caps in Canada. Understanding changes across these regions is vital as their glaciers have experienced dramatic changes in recent times. Attention has focused on the periphery of these regions where land <span class="hlt">ice</span> meets the ocean and where <span class="hlt">ice</span> acceleration, thinning and increased <span class="hlt">calving</span> have been observed. Polynyas are areas of open water within sea <span class="hlt">ice</span> which remain unfrozen for much of the year. They vary significantly in size (~3 km2 to > ~85,000 km2 in the Arctic), recurrence rates and duration. Despite their relatively small size, polynyas strongly impact regional oceanography and play a vital role in heat and moisture exchange between the polar oceans and atmosphere. Where polynyas are present adjacent to tidewater glaciers their influence on ocean circulation and water temperatures has the potential to play a major part in controlling subsurface <span class="hlt">ice</span> melt rates by impacting on the water masses reaching the <span class="hlt">calving</span> front. They also have the potential to influence air masses reaching nearby glaciers and <span class="hlt">ice</span> caps by creating a maritime climate which may impact on the glaciers' accumulation and surface melt and hence their thickness and mass balance. Polynya presence and size also have implications for sea <span class="hlt">ice</span> extent and therefore may influence the buttressing effect on neighbouring tidewater glaciers. The work presented uses remote sensing and mass balance model data to study changes in the North Water polynya (extent, <span class="hlt">ice</span> concentration, duration) and neighbouring glaciers and <span class="hlt">ice</span> caps (velocities, <span class="hlt">calving</span> front positions and mass balance) in Canada and Greenland over a period of approximately 30 years from the mid-1980s through to 2015.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-GSFC_20171208_Archive_e001933.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-GSFC_20171208_Archive_e001933.html"><span><span class="hlt">Ice</span> Waves</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-12-08</p> <p><span class="hlt">Ice</span> Waves - May 21st, 2001 Description: Along the southeastern coast of Greenland, an intricate network of fjords funnels glacial <span class="hlt">ice</span> to the Atlantic Ocean. During the summer melting season, newly <span class="hlt">calved</span> icebergs join slabs of sea <span class="hlt">ice</span> and older, weathered bergs in an offshore slurry that the southward-flowing East Greenland Current sometimes swirls into stunning shapes. Exposed rock of mountain peaks, tinted red in this image, hints at a hidden landscape. Credit: USGS/NASA/Landsat 7 To learn more about the Landsat satellite go to: landsat.gsfc.nasa.gov/ 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 Join us on Facebook</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018OcSci..14..293R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018OcSci..14..293R"><span>Short commentary on marine productivity at Arctic <span class="hlt">shelf</span> breaks: upwelling, advection and vertical mixing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Randelhoff, Achim; Sundfjord, Arild</p> <p>2018-04-01</p> <p>The future of Arctic marine ecosystems has received increasing attention in recent years as the extent of the sea <span class="hlt">ice</span> cover is dwindling. Although the Pacific and Atlantic inflows both import huge quantities of nutrients and plankton, they feed into the Arctic Ocean in quite diverse regions. The strongly stratified Pacific sector has a historically heavy <span class="hlt">ice</span> cover, a shallow <span class="hlt">shelf</span> and dominant upwelling-favourable winds, while the Atlantic sector is weakly stratified, with a dynamic <span class="hlt">ice</span> edge and a complex bathymetry. We argue that <span class="hlt">shelf</span> break upwelling is likely not a universal but rather a regional, albeit recurring, feature of <q>the new Arctic</q>. It is the regional oceanography that decides its importance through a range of diverse factors such as stratification, bathymetry and wind forcing. Teasing apart their individual contributions in different regions can only be achieved by spatially resolved time series and dedicated modelling efforts. The Northern Barents Sea <span class="hlt">shelf</span> is an example of a region where <span class="hlt">shelf</span> break upwelling likely does not play a dominant role, in contrast to the shallower shelves north of Alaska where ample evidence for its importance has already accumulated. Still, other factors can contribute to marked future increases in biological productivity along the Arctic <span class="hlt">shelf</span> break. A warming inflow of nutrient-rich Atlantic Water feeds plankton at the same time as it melts the sea <span class="hlt">ice</span>, permitting increased photosynthesis. Concurrent changes in sea <span class="hlt">ice</span> cover and zooplankton communities advected with the boundary currents make for a complex mosaic of regulating factors that do not allow for Arctic-wide generalizations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ESD.....5..271L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ESD.....5..271L"><span>Projecting Antarctic <span class="hlt">ice</span> discharge using response functions from SeaRISE <span class="hlt">ice</span>-sheet models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2014-08-01</p> <p>The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical <span class="hlt">ice</span> discharge from Antarctica. Basal <span class="hlt">ice-shelf</span> melting induced by a warming ocean has been identified as a major cause for additional <span class="hlt">ice</span> flow across the grounding line. Here we attempt to estimate the uncertainty range of future <span class="hlt">ice</span> discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the <span class="hlt">ice</span>-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 <span class="hlt">Ice</span>2Sea. The dynamic <span class="hlt">ice</span>-sheet response is derived from linear response functions for basal <span class="hlt">ice-shelf</span> melting for four different Antarctic drainage regions using experiments from the Sea-level Response to <span class="hlt">Ice</span> Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic <span class="hlt">ice</span>-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 <span class="hlt">ice</span>-sheet models with an explicit representation of <span class="hlt">ice-shelf</span> dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional <span class="hlt">ice</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1511771L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1511771L"><span>The northern Uummannaq <span class="hlt">Ice</span> Stream System, West Greenland: <span class="hlt">ice</span> dynamics and and controls upon deglaciation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lane, Timothy; Roberts, David; Rea, Brice; Cofaigh, Colm Ó.; Vieli, Andreas</p> <p>2013-04-01</p> <p>At the Last Glacial Maximum (LGM), the Uummannaq <span class="hlt">Ice</span> Stream System comprised a series coalescent outlet glaciers which extended along the trough to the <span class="hlt">shelf</span> edge, draining a large proportion of the West Greenland <span class="hlt">Ice</span> Sheet. Geomorphological mapping, terrestrial cosmogenic nuclide (TCN) exposure dating, and radiocarbon dating constrain warm-based <span class="hlt">ice</span> stream activity in the north of the system to 1400 m a.s.l. during the LGM. Intervening plateaux areas (~ 2000 m a.s.l.) either remained <span class="hlt">ice</span> free, or were covered by cold-based icefields, preventing diffluent or confluent flow throughout the inner to outer fjord region. Beyond the fjords, a topographic sill north of Ubekendt Ejland prevented the majority of westward <span class="hlt">ice</span> flow, forcing it south through Igdlorssuit Sund, and into the Uummannaq Trough. Here it coalesced with <span class="hlt">ice</span> from the south, forming the trunk zone of the UISS. Deglaciation of the UISS began at 14.9 cal. ka BP, rapidly retreating through the overdeepened Uummannaq Trough. Once beyond Ubekendt Ejland, the northern UISS retreated northwards, separating from the south. Retreat continued, and <span class="hlt">ice</span> reached the present fjord confines in northern Uummannaq by 11.6 kyr. Both geomorphological (termino-lateral moraines) and geochronological (14C and TCN) data provide evidence for an <span class="hlt">ice</span> marginal stabilisation at within Karrat-Rink Fjord, at Karrat Island, from 11.6-6.9 kyr. The Karrat moraines appear similar in both fjord position and form to 'Fjord Stade' moraines identified throughout West Greenland. Though chronologies constraining moraine formation are overlapping (Fjord Stade moraines - 9.3-8.2 kyr, Karrat moraines - 11.6-6.9 kyr), these moraines have not been correlated. This <span class="hlt">ice</span> margin stabilisation was able to persist during the Holocene Thermal Maximum (~7.2 - 5 kyr). It overrode climatic and oceanic forcings, remaining on Karrat Island throughout peaks of air temperature and relative sea-level, and during the influx of the warm West Greenland Current into</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70026419','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70026419"><span>DEM generation and tidal deformation detection for sulzberger <span class="hlt">ice</span> <span class="hlt">shelf</span>, West Antarctica using SAR interferometry</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Baek, S.; Kwoun, Oh-Ig; Bassler, M.; Lu, Z.; Shum, C.K.; Dietrich, R.</p> <p>2004-01-01</p> <p>In this study we generated a relative Digital Elevation Model (DEM) over the Sulzberger <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, West Antarctica using ERS1/2 synthetic aperture radar (SAR) interferometry data. Four repeat pass differential interferograms are used to find the grounding zone and to classify the study area. An interferometrically derived DEM is compared with laser altimetry profile from ICESat. Standard deviation of the relative height difference is 5.12 m and 1.34 m in total length of the profile and at the center of the profile respectively. The magnitude and the direction of tidal changes estimated from interferogram are compared with those predicted tidal differences from four ocean tide models. Tidal deformation measured in InSAR is -16.7 cm and it agrees well within 3 cm with predicted ones from tide models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.mna.it/english/Publications/TAP/TA_pdfs/Volume_14/TA_14_167_Downhole_Measurements.pdf','USGSPUBS'); return false;" href="http://www.mna.it/english/Publications/TAP/TA_pdfs/Volume_14/TA_14_167_Downhole_Measurements.pdf"><span>Downhole measurements in the AND-1B borehole, ANDRILL McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Project, 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>Morin, R.; Williams, T.; Henrys, S.; Crosby, T.; Hansaraj, D.</p> <p>2007-01-01</p> <p>A comprehensive set of downhole measurements was collected in the AND-1B drillhole as part of the on-<span class="hlt">ice</span> scientific programme defined for the McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (MIS) Project. Geophysical logs were recorded over two operation phases and consisted of calliper, temperature, fluid conductivity, induction resistivity, magnetic susceptibility, natural gamma activity, acoustic televiewer, borehole deviation, and dipmeter. In addition, two standard vertical seismic profiles (VSP) and one walk-away VSP were obtained. Radioactive logs (porosity and density) were not run because of unstable borehole conditions. Although the total depth of the hole is 1285 metres below seafloor (mbsf), the depth range for in situ measurements was limited by the length of the wireline (1018 mbsf) and by the nullification of some geophysical logs due to the presence of steel casing. A depth correction was derived to account for systematic discrepancies in depth between downhole measurements and cores; consequently, log responses can be directly compared to core properties. The resulting data are amenable to studies of cyclicity and climate, heat flux and fluid flow, and stricture and stress. When integrated with physical properties and fractures measured on the core, this information should play a significant role in addressing many of the scientific objectives of the ANDRILL programme.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GSL.....3...13O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GSL.....3...13O"><span>Global view of sea-<span class="hlt">ice</span> production in polynyas and its linkage to dense/bottom water formation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ohshima, Kay I.; Nihashi, Sohey; Iwamoto, Katsushi</p> <p>2016-12-01</p> <p>Global overturning circulation is driven by density differences. Saline water rejected during sea-<span class="hlt">ice</span> formation in polynyas is the main source of dense water, and thus sea-<span class="hlt">ice</span> production is a key factor in the overturning circulation. Due to difficulties associated with in situ observation, sea-<span class="hlt">ice</span> production and its interannual variability have not been well understood until recently. Methods to estimate sea-<span class="hlt">ice</span> production on large scales have been developed using heat flux calculations based on satellite microwave radiometer data. Using these methods, we present the mapping of sea-<span class="hlt">ice</span> production with the same definition and scale globally, and review the polynya <span class="hlt">ice</span> production and its relationship with dense/bottom water. The mapping demonstrates that <span class="hlt">ice</span> production rate is high in Antarctic coastal polynyas, in contrast to Arctic coastal polynyas. This is consistent with the formation of Antarctic Bottom Water (AABW), the densest water mass which occupies the abyssal layer of the global ocean. The Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> polynya has by far the highest <span class="hlt">ice</span> production in the Southern Hemisphere. The Cape Darnley polynya (65°E-69°E) is found to be the second highest production area and recent observations revealed that this is the missing (fourth) source of AABW. In the region off the Mertz Glacier Tongue (MGT), the third source of AABW, sea-<span class="hlt">ice</span> production decreased by as much as 40 %, due to the MGT <span class="hlt">calving</span> in early 2010, resulting in a significant decrease in AABW production. The Okhotsk Northwestern polynya exhibits the highest <span class="hlt">ice</span> production in the Northern Hemisphere, and the resultant dense water formation leads to overturning in the North Pacific, extending to the intermediate layer. Estimates of its <span class="hlt">ice</span> production show a significant decrease over the past 30-50 years, likely causing the weakening of the North Pacific overturning. These regions demonstrate the strong linkage between variabilities of sea-<span class="hlt">ice</span> production and bottom/intermediate water formation. The</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 Antarctic. 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-Antarctic <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_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://www.ncbi.nlm.nih.gov/pubmed/18460132','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18460132"><span>Potential of oregano essential oil and MAP to extend the <span class="hlt">shelf</span> life of fresh swordfish: a comparative study with <span class="hlt">ice</span> storage.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Giatrakou, V; Kykkidou, S; Papavergou, A; Kontominas, M G; Savvaidis, I N</p> <p>2008-05-01</p> <p>The present study evaluated the effect of modified atmosphere packaging (MAP, 5% O(2)/50% CO(2)/45% N(2); treatment M), the addition of oregano oil (0.1%, v/w; treatment AO) as a natural preservative, as well as their combination (treatment MO) on the quality and <span class="hlt">shelf</span> life extension of fresh Mediterranean swordfish fillets during a refrigerated storage (4 degrees C) period of 18 d. Simultaneously, swordfish fillets were stored under aerobic conditions (control treatment A, 4 degrees C) and on <span class="hlt">ice</span> (usual commercial method of preservation, treatment I, 0 degrees C). Among the 5 treatments examined in the present study, the most effective one to inhibit the microbial and sensory spoilage proved to be the MO treatment, achieving a <span class="hlt">shelf</span> life extension of 8 to 9 d. The dominant bacteria in the microflora of swordfish, irrespective of treatment, were the Pseudomonads and the H(2)S-producing bacteria, while both lactic acid bacteria (LAB) and the Enterobacteriaceae produced the lowest populations in swordfish samples kept on <span class="hlt">ice</span>. Among the chemical indices examined, thiobarbituric acid (TBA) values showed no specific trend of lipid oxidation for swordfish, irrespective of treatment. Final trimethylamine nitrogen (TMA-N) and total volatile basic nitrogen (TVB-N) values for treatments, A, AO, M, and MO ranged between 1.33 and 14.29 mg N/100 g and 14.11 to 55.52 mg N/100 g, respectively, whereas for I samples they remained almost unchanged during storage. Sensory analysis (taste attribute) correlated well with microbiological analysis, indicating a <span class="hlt">shelf</span> life of approximately 5 to 6 d for control, 10 to 11 d for AO, 12 d for I, 13 d for M, and 14 d for MO samples.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1615392R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1615392R"><span>Recent <span class="hlt">Ice</span> thickness helicopter borne radar surveys in Patagonia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rivera, Andres; Zamora, Rodrigo; Andres Uribe, Jose; Oberreuter, Jonathan; Gacitua, Guisella; Rignot, Eric</p> <p>2014-05-01</p> <p>The Patagonian icefields are the biggest temperate <span class="hlt">ice</span> bodies in southern hemisphere, which have experienced important areal shrinkage and thinning in recent decades, significantly contributing to sea level rise. The main driving factor behind this retreating condition is recent decade atmospheric warming explaining higher melting rates and equilibrium line altitude upward migration. <span class="hlt">Ice</span> dynamic is also playing an important role especially in glaciers <span class="hlt">calving</span> into deep fjords or lakes, type of glaciers that are predominant in the Patagonian icefields. In order to better understand their <span class="hlt">ice</span> dynamics, several recent works have measured <span class="hlt">ice</span> velocities using feature tracking and other techniques, however, <span class="hlt">ice</span> thickness is still barely known. In spite of several on the ground radar measurements successfully detecting several hundred of m of <span class="hlt">ice</span> thickness at the higher plateaus, this variable remains the great missing part of the equation especially when the thickness is approximately deeper than 600 m or where the glacier surfaces are very crevassed or nearby the Equilibrium line Altitude, where on the ground measurements are logistically constrained. In order to tackle the lack of thickness data, a helicopter borne radar system was used to survey several Patagonian temperate glaciers <span class="hlt">calving</span> into fjords (Glaciares San Rafael and Jorge Montt) or lakes (Nef, Colonia and Steffen). The radar system is comprised by a hanging bow-tie dipole antenna working at a central frequency of 20 MHz. The antenna is an aluminum structure of 7 x 5 x 1.2 m weighting near 350 kg that is hanging at 20 m below a helicopter, and is connected to the helicopter cabin by an optical fiber cable. At the antenna are installed a 3,200 Volts peak transmitter, a two channel radar receiver, and an integrated GPS registering each trace. The helicopter flying speed was kept at near 40 knots and the antenna was normally hanging at 40 m above the <span class="hlt">ice</span>. The surveys took place along predefined tracks</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70018818','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70018818"><span>Glacial morphology and depositional sequences of the Antarctic Continental <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>ten Brink, Uri S.; Schneider, Christopher</p> <p>1995-01-01</p> <p>Proposes a simple model for the unusual depositional sequences and morphology of the Antarctic continental <span class="hlt">shelf</span>. 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 <span class="hlt">ice</span> grounding line. The model offers several guidelines for stratigraphic interpretation of the Antarctic <span class="hlt">shelf</span> and a Northern Hemisphere <span class="hlt">shelf</span>, both of which were subject to many glacial advances and retreats. -Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PrOce.156...17L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PrOce.156...17L"><span>Under the sea <span class="hlt">ice</span>: Exploring the relationship between sea <span class="hlt">ice</span> and the foraging behaviour of southern elephant seals 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, Sara; Sallée, Jean-Baptiste; Fraser, Alexander D.; Massom, Robert A.; Reid, Phillip; Sumner, Michael; Guinet, Christophe; Harcourt, Robert; McMahon, Clive; Bailleul, Frédéric; Hindell, Mark A.; Charrassin, Jean-Benoit</p> <p>2017-08-01</p> <p>Investigating ecological relationships between predators and their environment is essential to understand the response of marine ecosystems to climate variability and change. This is particularly true in polar regions, where sea <span class="hlt">ice</span> (a sensitive climate variable) plays a crucial yet highly dynamic and variable role in how it influences the whole marine ecosystem, from phytoplankton to top predators. For mesopredators such as seals, sea <span class="hlt">ice</span> both supports a rich (under-<span class="hlt">ice</span>) food resource, access to which depends on local to regional coverage and conditions. Here, we investigate sex-specific relationships between the foraging strategies of southern elephant seals (Mirounga leonina) in winter and spatio-temporal variability in sea <span class="hlt">ice</span> concentration (SIC) and coverage in East Antarctica. We satellite-tracked 46 individuals undertaking post-moult trips in winter from Kerguelen Islands to the peri-Antarctic <span class="hlt">shelf</span> between 2004 and 2014. These data indicate distinct general patterns of sea <span class="hlt">ice</span> usage: while females tended to follow the sea <span class="hlt">ice</span> edge as it extended northward, the males remained on the continental <span class="hlt">shelf</span> despite increasing sea <span class="hlt">ice</span>. Seal hunting time, a proxy of foraging activity inferred from the diving behaviour, was longer for females in late autumn in the outer part of the pack <span class="hlt">ice</span>, ∼150-370 km south of the <span class="hlt">ice</span> edge. Within persistent regions of compact sea <span class="hlt">ice</span>, females had a longer foraging activity (i) in the highest sea <span class="hlt">ice</span> concentration at their position, but (ii) their foraging activity was longer when there were more patches of low concentration sea <span class="hlt">ice</span> around their position (either in time or in space; 30 days & 50 km). The high spatio-temporal variability of sea <span class="hlt">ice</span> around female positions is probably a key factor allowing them to exploit these concentrated patches. Despite lack of information on prey availability, females may exploit mesopelagic finfishes and squids that concentrate near the <span class="hlt">ice</span>-water interface or within the water column (from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/imap/i-2600-h/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/imap/i-2600-h/"><span>Coastal-Change and Glaciological Map of the Northern Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Area, Antarctica: 1962-2004</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.; Foley, Kevin M.; Swithinbank, Charles; Williams, Richard S.</p> <p>2007-01-01</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. Melting of the West Antarctic part alone of the Antarctic <span class="hlt">ice</span> sheet would cause a sea-level rise of approximately 6 meters (m). The potential sea-level rise after melting of the entire Antarctic <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 Antarctic <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span>-flow velocities derived from synthetic aperture radar, concluded that most of the Ross <span class="hlt">ice</span> streams (<span class="hlt">ice</span> streams on the east side of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>) 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 <span class="hlt">ice</span> 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 <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 Antarctic Research (SCAR) (1989, 1993), and by the National Science Foundation?s (1990) Division of Polar</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 Antarctic <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 Antarctic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110015207','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110015207"><span>Regional Changes in the Sea <span class="hlt">Ice</span> Cover and <span class="hlt">Ice</span> Production in the Antarctic</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Comiso, Josefino C.</p> <p>2011-01-01</p> <p>Coastal polynyas around the Antarctic continent have been regarded as sea <span class="hlt">ice</span> factories because of high <span class="hlt">ice</span> production rates in these regions. The observation of a positive trend in the extent of Antarctic sea <span class="hlt">ice</span> during the satellite era has been intriguing in light of the observed rapid decline of the <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> cover could be caused primarily by enhanced <span class="hlt">ice</span> production in the Ross Sea that may be associated with more persistent and larger coastal polynyas in the region. 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 km2 per year. For a characteristic <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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-<span class="hlt">ice</span> <span class="hlt">shelf</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140008938','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140008938"><span>The Annual Glaciohydrology Cycle in the Ablation Zone of the Greenland <span class="hlt">Ice</span> Sheet: Part 2. Observed and Modeled <span class="hlt">Ice</span> Flow</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Colgan, William Terence; Rajaram, Harihar; Anderson, Robert S.; Steffen, Konrad; Zwally, H. Jay; Phillips, Thomas; Abdalati, Waleed</p> <p>2012-01-01</p> <p><span class="hlt">Ice</span> velocities observed in 2005/06 at three GPS stations along the Sermeq Avannarleq flowline, West Greenland, are used to characterize an observed annual velocity cycle. We attempt to reproduce this annual <span class="hlt">ice</span> velocity cycle using a 1-D <span class="hlt">ice</span>-flow model with longitudinal stresses coupled to a 1-D hydrology model that governs an empirical basal sliding rule. Seasonal basal sliding velocity is parameterized as a perturbation of prescribed winter sliding velocity that is proportional to the rate of change of glacier water storage. The coupled model reproduces the broad features of the annual basal sliding cycle observed along this flowline, namely a summer speed-up event followed by a fall slowdown event. We also evaluate the hypothesis that the observed annual velocity cycle is due to the annual <span class="hlt">calving</span> cycle at the terminus. We demonstrate that the <span class="hlt">ice</span> acceleration due to a catastrophic <span class="hlt">calving</span> event takes an order of magnitude longer to reach CU/ETH ('Swiss') Camp (46km upstream of the terminus) than is observed. The seasonal acceleration observed at Swiss Camp is therefore unlikely to be the result of velocity perturbations propagated upstream via longitudinal coupling. Instead we interpret this velocity cycle to reflect the local history of glacier water balance.</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 Antarctic 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 Antarctic 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 Antarctic 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/2016AGUFMPP13A2064B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMPP13A2064B"><span>Timing, variability and sediment provenance of the Norwegian Channel <span class="hlt">Ice</span> Stream 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>Becker, L. W. M.; Sejrup, H. P.; Hjelstuen, B. O. B.; Haflidason, H.</p> <p>2016-12-01</p> <p>The extent of the NW European <span class="hlt">ice</span> sheet during the Last Glacial Maximum is fairly well constrained to, at least in periods, the <span class="hlt">shelf</span> edge. However, the exact timing and varying activity of the largest <span class="hlt">ice</span> stream, the Norwegian Channel <span class="hlt">Ice</span> Stream (NCIS), remains uncertain. We here present three sediment records, recovered proximal and distal to the upper NW European continental slope. All age models for the cores are constructed in the same way and based solely on 14C dating of planktonic foraminifera. The sand-sized sediments in the discussed cores is believed to be primarily transported by <span class="hlt">ice</span> rafting. All records suggest <span class="hlt">ice</span> streaming activity between 25.8 and 18.5 ka BP. However, the core proximal to the mouth of the Norwegian Channel (NC) shows distinct periods of activity and periods of very little coarse sediment input. Out of this there appear to be at least three well-defined periods of <span class="hlt">ice</span> streaming activity which lasted each for 1.5 to 2 ka, with "pauses" of several hundred years in between. The same core shows a conspicuous variation in several proxies and sediment colour within the first peak of <span class="hlt">ice</span> stream activity, compared to the second and third peak. The light grey colour of the sediment was earlier attributed to Triassic chalk grains, yet all "chalk" grains are in fact mollusc fragments. The low magnetic susceptibility values, the high Ca, high Sr and low Fe content compared to the other peaks suggests a different provenance for the material of the first peak. We suggest therefore, that the origin of this material is rather the British Irish <span class="hlt">Ice</span> Sheet (BIIS) and not the Fennoscandian <span class="hlt">Ice</span> Sheet (FIS). Earlier studies have shown an extent of the BIIS at least to the NC, whereas <span class="hlt">ice</span> from the FIS likely stayed within the boundaries of the NC. A possible scenario for the different provenance could therefore be the build-up of the BIIS into the NC until it merged with the FIS. At this point the BIIS <span class="hlt">calved</span> off the <span class="hlt">shelf</span> edge southwest of the mouth of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA03700.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA03700.html"><span>Icebergs Adrift in the Amundsen Sea</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2002-03-27</p> <p>The Thwaites <span class="hlt">Ice</span> Tongue is a large sheet of glacial <span class="hlt">ice</span> extending from the West Antarctic mainland into the southern Amundsen Sea. A large crack in the Thwaites Tongue was discovered in imagery from Terra's Moderate Resolution Imaging SpectroRadiometer (MODIS). Subsequent widening of the crack led to the <span class="hlt">calving</span> of a large iceberg. The development of this berg, designated B-22 by the National <span class="hlt">Ice</span> Center, can be observed in these images from the Multi-angle Imaging SpectroRadiometer, also aboard Terra. The two views were acquired by MISR's nadir (vertical-viewing) camera on March 10 and 24, 2002. The B-22 iceberg, located below and to the left of image center, measures approximately 82 kilometers long x 62 kilometers wide. Comparison of the two images shows the berg to have drifted away from the <span class="hlt">ice</span> <span class="hlt">shelf</span> edge. The breakup of <span class="hlt">ice</span> near the <span class="hlt">shelf</span> edge, in the area surrounding B-22, is also visible in the later image. These natural-color images were acquired during Terra orbits 11843 and 12047, respectively. At the right-hand edge is Pine Island Bay, where the <span class="hlt">calving</span> of another large iceberg (B-21) occurred in November 2001. B-21 subsequently split into two smaller bergs, both of which are visible to the right of B-22. http://photojournal.jpl.nasa.gov/catalog/PIA03700</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11458335','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11458335"><span>The <span class="hlt">ice</span> nucleation temperature determines the primary drying rate of lyophilization for samples frozen on a temperature-controlled <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>Searles, J A; Carpenter, J F; Randolph, T W</p> <p>2001-07-01</p> <p>The objective of this study was to determine the influence of <span class="hlt">ice</span> nucleation temperature on the primary drying rate during lyophilization for samples in vials that were frozen on a lyophilizer <span class="hlt">shelf</span>. Aqueous solutions of 10% (w/v) hydroxyethyl starch were frozen in vials with externally mounted thermocouples and then partially lyophilized to determine the primary drying rate. Low- and high-particulate-containing samples, <span class="hlt">ice</span>-nucleating additives silver iodide and Pseudomonas syringae, and other methods were used to obtain a wide range of nucleation temperatures. In cases where the supercooling exceeded 5 degrees C, freezing took place in the following three steps: (1) primary nucleation, (2) secondary nucleation encompassing the entire liquid volume, and (3) final solidification. The primary drying rate was dependent on the <span class="hlt">ice</span> nucleation temperature, which is stochastic in nature but is affected by particulate content and the presence of <span class="hlt">ice</span> nucleators. Sample cooling rates of 0.05 to 1 degrees C/min had no effect on nucleation temperatures and drying rate. We found that the <span class="hlt">ice</span> nucleation temperature is the primary determinant of the primary drying rate. However, the nucleation temperature is not under direct control, and its stochastic nature and sensitivity to difficult-to-control parameters result in drying rate heterogeneity. Nucleation temperature heterogeneity may also result in variation in other morphology-related parameters such as surface area and secondary drying rate. Overall, these results document that factors such as particulate content and vial condition, which influence <span class="hlt">ice</span> nucleation temperature, must be carefully controlled to avoid, for example, lot-to-lot variability during cGMP production. In addition, if these factors are not controlled and/or are inadvertently changed during process development and scaleup, a lyophilization cycle that was successful on the research scale may fail during large-scale production.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011TCry....5..791K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011TCry....5..791K"><span>Deriving mass balance and <span class="hlt">calving</span> variations from reanalysis data and sparse observations, Glaciar San Rafael, northern Patagonia, 1950-2005</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koppes, M.; Conway, H.; Rasmussen, L. A.; Chernos, M.</p> <p>2011-09-01</p> <p>Mass balance variations of Glaciar San Rafael, the northernmost tidewater glacier in the Southern Hemisphere, are reconstructed over the period 1950-2005 using NCEP-NCAR reanalysis climate data together with sparse, local historical observations of air temperature, precipitation, accumulation, ablation, thinning, <span class="hlt">calving</span>, and glacier retreat. The combined observations over the past 50 yr indicate that Glaciar San Rafael has thinned and retreated since 1959, with a total mass loss of ~22 km3 of <span class="hlt">ice</span> eq. Over that period, except for a short period of cooling from 1998-2003, the climate has become progressively warmer and drier, which has resulted primarily in pervasive thinning of the glacier surface and a decrease in <span class="hlt">calving</span> rates, with only minor acceleration in retreat of the terminus. A comparison of <span class="hlt">calving</span> fluxes derived from the mass balance variations and from theoretical <span class="hlt">calving</span> and sliding laws suggests that <span class="hlt">calving</span> rates are inversely correlated with retreat rates, and that terminus geometry is more important than balance fluxes to the terminus in driving <span class="hlt">calving</span> dynamics. For Glaciar San Rafael, regional climate warming has not yet resulted in the significant changes in glacier length seen in other <span class="hlt">calving</span> glaciers in the region, emphasizing the complex dynamics between climate inputs, topographic constraints and glacier response in <span class="hlt">calving</span> glacier systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011TCD.....5.1123K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011TCD.....5.1123K"><span>Deriving mass balance and <span class="hlt">calving</span> variations from reanalysis data and sparse observations, Glaciar San Rafael, northern Patagonia, 1950-2005</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koppes, M.; Conway, H.; Rasmussen, L. A.; Chernos, M.</p> <p>2011-04-01</p> <p>Mass balance variations of Glaciar San Rafael, the most equatorial tidewater glacier in the North Patagonian Icefield, are reconstructed over the period 1950-2005 using NCEP-NCAR reanalysis climate data together with sparse, local historical observations of air temperature, precipitation, accumulation, ablation, thinning, <span class="hlt">calving</span>, and glacier retreat. The combined observations over the past 50 yr indicate that Glaciar San Rafael has thinned and retreated since 1959, with a total mass loss of ~22 km3 of <span class="hlt">ice</span> equivalent. Over that period, except for a short period of cooling from 1998-2003, the climate has become progressively warmer and drier, which has resulted primarily in pervasive thinning of the glacier surface and a decrease in <span class="hlt">calving</span> rates, with only minor acceleration in retreat of the terminus. A comparison of <span class="hlt">calving</span> fluxes derived from the mass balance variations and from theoretical <span class="hlt">calving</span> and sliding laws suggest that <span class="hlt">calving</span> rates are inversely correlated with retreat rates, and that terminus geometry is more important than changes in balance fluxes to the terminus in driving <span class="hlt">calving</span> dynamics. For Glaciar San Rafael, regional climate warming has not yet resulted in the significant changes in glacier length seen in other <span class="hlt">calving</span> glaciers in the region, emphasizing the complex dynamics between climate inputs, topographic constraints and glacier response in <span class="hlt">calving</span> glacier systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.5867S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.5867S"><span>Changes in <span class="hlt">ice</span> dynamics along the northern Antarctic Peninsula</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Seehaus, Thorsten; Marinsek, Sebastian; Cook, Alison; Van Wessem, Jan-Melchior; Braun, Matthias</p> <p>2017-04-01</p> <p>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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> disintegration, as well as to better quantify the <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> thickness reconstructions and modeled climatic mass balance fields regional imbalances were calculated. Variations in <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>) showed a strong deceleration. Nearly all former <span class="hlt">ice</span> <span class="hlt">shelf</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3528R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3528R"><span>New insights into West Greenland <span class="hlt">ice</span> sheet/stream dynamics during the last glacial cycle.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roberts, David; Lane, Tim; Rea, Brice; Cofaigh, Colm O.; Jamieson, Stewart; Vieli, Andreas; Rodes, Angel</p> <p>2015-04-01</p> <p>Onshore and offshore geomorphological mapping and deglacial chronologies from West Greenland constrain the nature and magnitude of <span class="hlt">ice</span> advance and decay of the Greenland <span class="hlt">Ice</span> Sheet (GrIS) during the last glacial cycle. Several <span class="hlt">ice</span> stream troughs are known to have fed <span class="hlt">ice</span> to the <span class="hlt">shelf</span> edge during the last glacial cycle. Their offshore expression suggests that many were coalescent systems fed by smaller outlet glaciers and <span class="hlt">ice</span> streams onshore but their central flow pathways were also controlled by geology and preglacial topography. The bed morphology of these large <span class="hlt">ice</span> streams shows they operated over soft, deforming beds with drumlins, mega-scale glacial lineations and grounding zone wedges marking an offshore transition from predominant areal scour onshore. Records of offshore deglacial chronology remain sparse but the Uummannaq and Disko Bugt <span class="hlt">ice</span> stream corridors are now well constrained. The Uummannaq <span class="hlt">ice</span> stream (UIS) completely deglaciated from the continental <span class="hlt">shelf</span> between 14.8 ka and 11.0 ka in response to rising air temperatures, increasing JJA solar radiation and sea-level rise, but temporary standstills and the asynchronous retreat history of its feeder zones suggest that topography/bathymetry strongly modulated retreat rates as <span class="hlt">ice</span> became 'locked' back into the coastal fjord system. Initial reconstructions of behaviour UIS discounted an oceanic role in early deglaciation and favoured retreat from the mid-<span class="hlt">shelf</span> and inner-<span class="hlt">shelf</span> prior to the Younger Dryas but both these concepts remain under investigation. In Disko Bugt, Jakobshavn Isbrae deglaciated later than the UIS and remained on the outer <span class="hlt">shelf</span> during the Younger Dyras stadial (12.8 - 11.7 cal. kyrs BP) only reaching in the inner coast fjords at approximately 10.0 ka. The later deglaciation of the Disko system (despite similar external forcing mechanisms) was controlled by regional topographic/bathymetric contrasts in their respective trough morphologies. This hypothesis is supported by recent model</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/120940-glacier-fluctuations-kenai-fjords-alaska-evaluation-controls-iceberg-calving-glaciers','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/120940-glacier-fluctuations-kenai-fjords-alaska-evaluation-controls-iceberg-calving-glaciers"><span>Glacier fluctuations in the Kenai Fjords, Alaska, U.S.A.: An evaluation of controls on Iceberg-<span class="hlt">calving</span> glaciers</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>Wiles, G.C.; Calkin, P.E.; Post, A.</p> <p></p> <p>The histories of four iceberg-<span class="hlt">calving</span> outlet-glacier systems in the Kenai Fjords National Park underscore the importance of fiord depth, sediment supply, and fiord geometry on glacier stability. These parameters, in turn, limit the reliability of <span class="hlt">calving</span> glacier chronologies as records of climatic change. Tree-ring analysis together with radiocarbon dating show that the Northwestern and McCarty glaciers, with large drainage basins, were advancing in concert with nearby land-terminating glaciers about A.D. 600. After an interval of retreat and possible nonclimatically induced extension during the Medieval Warm Period, these <span class="hlt">ice</span> margins advanced again through the Little <span class="hlt">Ice</span> Age and then retreated synchronouslymore » with the surrounding land-terminating glaciers about A.D. 1900. In contrast, Holgate and Aialik glaciers, with deeper fiords and smaller basins, retreated about 300 yr earlier. Reconstructions of Little <span class="hlt">Ice</span> Age glaciers suggest that equilibrium-line altitudes of Northwestern and McCarty glaciers were, respectively, 270 and 500 m lower than now. Furthermore, the reconstructions show that these two glaciers were climatically sensitive when at their terminal moranies. However, with <span class="hlt">ice</span> margins at their present recessional positions and accumulation area ratios between 0.8 and 0.9, only McCarty Glacier shows evidence of advance. Aialik and Holgate glaciers were climatically insensitive during the Little <span class="hlt">Ice</span> Age maxima and remain insensitive to climate. 40 refs., 7 figs., 2 tabs.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.C43D0650H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.C43D0650H"><span>Fjord dynamics and glacio-marine interactions on Northern Ellesmere Island, Canada</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hamilton, A.; Mueller, D.; Laval, B.</p> <p>2012-12-01</p> <p> <span class="hlt">ice</span> <span class="hlt">calving</span> events and epishelf lake drainage. Figure 1. Elevation schematic of Milne Fjord, Ellesmere Island showing the <span class="hlt">ice</span> <span class="hlt">shelf</span>-dammed freshwater lake overlying deeper saltwater between the floating <span class="hlt">ice</span> <span class="hlt">shelf</span> and glacier tongue. Processes shown include a hypothesized estuarine-like fjord circulation, supra- and sub-glacial runoff, basal <span class="hlt">ice</span> melting, tides, and sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> freshwater outflow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.C11D0699A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.C11D0699A"><span>Programme for Monitoring of the Greenland <span class="hlt">Ice</span> Sheet - <span class="hlt">Ice</span> Surface Velocities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andersen, S. B.; Ahlstrom, A. P.; Boncori, J. M.; Dall, J.</p> <p>2011-12-01</p> <p>In 2007, the Danish Ministry of Climate and Energy launched the Programme for Monitoring of the Greenland <span class="hlt">Ice</span> Sheet (PROMICE) as an ongoing effort to assess changes in the mass budget of the Greenland <span class="hlt">Ice</span> Sheet. Iceberg <span class="hlt">calving</span> from the outlet glaciers of the Greenland <span class="hlt">Ice</span> Sheet, often termed the <span class="hlt">ice</span>-dynamic mass loss, is responsible for an important part of the mass loss during the last decade. To quantify this part of the mass loss, we combine airborne surveys yielding <span class="hlt">ice</span>-sheet thickness along the entire margin, with surface velocities derived from satellite synthetic-aperture radar (SAR). In order to derive <span class="hlt">ice</span> sheet surface velocities from SAR a processing chain has been developed for GEUS by DTU Space based on a commercial software package distributed by GAMMA Remote Sensing. The processor, named SUSIE (Scripts and Utilities for SAR <span class="hlt">Ice</span>-motion Estimation), can use both differential SAR interferometry and offset-tracking techniques to measure the horizontal velocity components, providing also an estimate of the corresponding measurement error. So far surface velocities have been derived for a number of sites including Nioghalvfjerdsfjord Glacier, the Kangerlussuaq region, the Nuuk region, Helheim Glacier and Daugaard-Jensen Glacier using data from ERS-1/ERS-2, ENVISAT ASAR and ALOS Palsar. Here we will present these first results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C51A0639C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C51A0639C"><span>Subaqueous melting in Zachariae Isstrom, Northeast Greenland combining observations and an ocean general circulation model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cai, C.; Rignot, E. J.; Menemenlis, D.; Nakayama, Y.</p> <p>2016-12-01</p> <p>Zachariae Isstrom, a major <span class="hlt">ice</span> stream in northeast Greenland, has lost its entire <span class="hlt">ice</span> <span class="hlt">shelf</span> in the past decade. Here, we study the evolution of subaqueous melting of its floating section during the transition. Observations show that the rate of <span class="hlt">ice</span> <span class="hlt">shelf</span> melting has doubled during 1999-2010 and is twice higher than that maintaining the <span class="hlt">ice</span> <span class="hlt">shelf</span> in a steady state. The <span class="hlt">ice</span> <span class="hlt">shelf</span> melt rate depends on the thermal forcing from warm, saline, subsurface ocean water of Atlantic origin (AW), and on the mixing of AW with fresh buoyant subglacial discharge. Subglacial discharge has increased as result of enhanced <span class="hlt">ice</span> sheet runoff driven by warmer air temperature; ocean thermal forcing has increased due to enhanced advection of AW. Here, we employ the Massachusetts Institute of Technology general circulation model (MITgcm) at a high spatial resolution to simulate the melting process in 3-D. The model is constrained by <span class="hlt">ice</span> thickness from mass conservation, oceanic bathymetry inverted from gravity data by NASA Operation <span class="hlt">Ice</span>Bridge and NASA Ocean Melting Greenland missions, in-situ ocean temperature/salinity data, ocean tide height and current from the Arctic Ocean Tidal Inverse Model (AOTIM-5) and reconstructed seasonal subglacial discharge from the Regional Atmospheric Climate Model (RACMO2). We compare the results in winter (small runoff but not negligible) with summer (maximum runoff) at two different stages with (prior to 2012) and without the <span class="hlt">ice</span> <span class="hlt">shelf</span> (after 2012) to subaqueous melt rates deduced from remote sensing observations. We show that <span class="hlt">ice</span> melting by the ocean has increased by one order of magnitude as a result of the transition from <span class="hlt">ice</span> <span class="hlt">shelf</span> terminating to near-vertical <span class="hlt">calving</span> front terminating. We also find that subglacial discharge has a significant impact on <span class="hlt">ice</span> <span class="hlt">shelf</span> melt rates in Greenland. We conclude on the impact of ocean warming and air temperature warming on the melting regime of the <span class="hlt">ice</span> margin of Zachariae Isstrom, Greenland. This work was performed</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. Their policies may differ from this site.</div> </div><!-- container --> <footer><a id="backToTop" href="#top"> </a><nav><a id="backToTop" href="#top"> </a><ul class="links"><a id="backToTop" href="#top"> </a><li><a id="backToTop" href="#top"></a><a href="/sitemap.html">Site Map</a></li> <li><a href="/members/index.html">Members Only</a></li> <li><a href="/website-policies.html">Website Policies</a></li> <li><a href="https://doe.responsibledisclosure.com/hc/en-us" target="_blank">Vulnerability Disclosure Program</a></li> <li><a href="/contact.html">Contact Us</a></li> </ul> <div class="small">Science.gov is maintained by the U.S. Department of Energy's <a href="https://www.osti.gov/" target="_blank">Office of Scientific and Technical Information</a>, in partnership with <a href="https://www.cendi.gov/" target="_blank">CENDI</a>.</div> </nav> </footer> <script type="text/javascript"><!-- // var lastDiv = ""; function showDiv(divName) { // hide last div if (lastDiv) { document.getElementById(lastDiv).className = "hiddenDiv"; } //if value of the box is not nothing and an object with that name exists, then change the class if (divName && document.getElementById(divName)) { document.getElementById(divName).className = "visibleDiv"; lastDiv = divName; } } //--> </script> <script> /** * Function that tracks a click on an outbound link in Google Analytics. * This function takes a valid URL string as an argument, and uses that URL string * as the event label. */ var trackOutboundLink = function(url,collectionCode) { try { h = window.open(url); setTimeout(function() { ga('send', 'event', 'topic-page-click-through', collectionCode, url); }, 1000); } catch(err){} }; </script> <!-- Google Analytics --> <script> (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','//www.google-analytics.com/analytics.js','ga'); ga('create', 'UA-1122789-34', 'auto'); ga('send', 'pageview'); </script> <!-- End Google Analytics --> <script> showDiv('page_1') </script> </body> </html>