Sample records for ice shelf antarctica

  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. 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.

  3. 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.

  4. 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

  5. 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

  6. 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.

  7. 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.

  8. 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.

  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. 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.

  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. 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.

  13. 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

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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

  17. 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

  18. 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

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  1. 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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-12-01

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

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2018-05-01

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

  16. 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.

  17. 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.

  18. 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

  19. 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).

  20. 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

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

    NASA Astrophysics Data System (ADS)

    McGrath, Daniel J.

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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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).

  8. 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.

  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. 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.

  11. 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.

  12. 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

  13. Antarctica and Its Ice Sheet: Knowledge Gained During the IGY/IGC

    NASA Astrophysics Data System (ADS)

    Bentley, C. R.

    2006-12-01

    At the end of World War II, the interior of Antarctica, with the exception of the mountains south of the Ross Ice Shelf, was still terra incognita. It was described simply as a nearly continuous high plateau. Even less was known about the ice thickness; the eminent glacial geologist, Richard Foster Flint, believed it "unlikely that the ice thickness exceeds 2000 feet except very locally; probably its average thickness is considerably less." Then in the late 1940's and early 1950's, seismic sounding in Greenland by the Expéditions Polaires Françaises and in Queen Maud Land by the Norwegian-British-Swedish Antarctic Expedition, 1949-52, revealed that, inland of the coastal mountains, the beds in both regions lie close to sea level. This led to a reappraisal of the Antarctic ice sheet, such that the prescient glaciologist, Robert P. Sharp, could predict, on the eve of the IGY, that "between 3000 and 4000 meters of ice will be found" in East Antarctica and that "work during IGY will establish an average thickness for Antarctic inland ice in excess of 1600 m." Seismic and gravity soundings on oversnow traverses conducted by eight countries during the IGY and the succeeding IGC showed Sharp to be basically correct, but there were major surprises, such as the vast Gamburtsev Subglacial Mountains, completely hidden by the ice in central East Antarctica, and the equally vast Byrd Subglacial Basin beneath much of the West Antarctic ice sheet, so deep that roughly half the ice in the region lies below sea level. There were major discoveries on and above the surface too, such as the huge size of the Filchner/Ronne Ice Shelf, and the very existence of the Ellsworth and Pensacola Mountains, the former including the highest peak on the continent. Further, the fundamental difference between the crustal structures of East and West Antarctica became clear. A summary paper published in 1960, looking primarily at West Antarctica where the main U.S. activity lay, could conclude that

  14. 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

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-10-01

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

  17. Modelling the influence of tides on ice-shelf melt rates in the Amundsen Sea, Antarctica.

    NASA Astrophysics Data System (ADS)

    Jourdain, Nicolas C.; Molines, Jean-Marc; Le Sommer, Julien; Mathiot, Pierre; Chanut, Jérome; Madec, Gurvan

    2017-04-01

    Variations in melt beneath ice- shelves may trigger ice-sheet instabilities, in particular in West Antarctica. Therefore, improving the understanding and modelling of ice-shelf 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 ice-shelf 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 ice 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.

  18. Nitrate flux on the Ross Ice Shelf, Antarctica and its relation to solar cosmic rays

    NASA Astrophysics Data System (ADS)

    Zeller, Edward J.; Dreschhoff, Gisela A. M.; Laird, Claude M.

    1986-11-01

    Nitrate flux has been determined in the snow sequence deposited at Windless Bight on the Ross Ice Shelf (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.

  19. 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.

  20. 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.

  1. 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.

  2. Crevasse detection with GPR across the Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Delaney, A.; Arcone, S.

    2005-12-01

    We have used 400-MHz ground penetrating radar (GPR) to detect crevasses within a shear zone on the Ross Ice Shelf, 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 ice 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 ice 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 ice extension. Our experiments demonstrate capability of high-frequency GPR in a cold-snow environment for both defining snow layers and locating voids.

  3. 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

  4. 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

  5. Insights into Spatial Sensitivities of Ice Mass Response to Environmental Change from the SeaRISE Ice Sheet Modeling Project I: Antarctica

    NASA Technical Reports Server (NTRS)

    Nowicki, Sophie; Bindschadler, Robert A.; Abe-Ouchi, Ayako; Aschwanden, Andy; Bueler, Ed; Choi, Hyengu; Fastook, Jim; Granzow, Glen; Greve, Ralf; Gutowski, Gail; hide

    2013-01-01

    Atmospheric, oceanic, and subglacial forcing scenarios from the Sea-level Response to Ice Sheet Evolution (SeaRISE) project are applied to six three-dimensional thermomechanical ice-sheet models to assess Antarctic ice 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 ice); and (iii) mass loss with enhanced ice shelf melting (with changes in West Antarctica dominating the signal due to its marine setting and extensive ice shelves; cf. minimal impact in the Terre Adelie, George V, Oates, and Victoria Land region of East Antarctica). Ice loss due to dynamic changes associated with enhanced sliding and/or sub-shelf melting exceeds the gain due to increased precipitation. Furthermore, differences in results between and within basins as well as the controlling impact of sub-shelf melting on ice dynamics highlight the need for improved understanding of basal conditions, grounding-zone processes, ocean-ice interactions, and the numerical representation of all three.

  6. 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.

  7. 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.

  8. Balloons on Ice: Launch # 2 takes flight in Antarctica

    NASA Image and Video Library

    2017-12-08

    The second of three missions as part of NASA’s Antarctica Long Duration Balloon Flight Campaign was successfully launched at 8:10 a.m. EDT, Dec. 2. The Antarctic Impulsive Transient Antenna (ANITA) from the University of Hawaii at Manoa was launched from Antarctica’s Ross Ice Shelf near McMurdo Station with support from the National Science Foundation’s United States Antarctic Program. Scientists will use ANITA’s instruments to study the reactions in the core of stars and as they explode via the release of neutrinos that travel to Earth and interact with the Antarctica ice. More: go.nasa.gov/2ghR6Le

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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

  15. Note On The Ross Sea Shelf Water Downflow Processes (antarctica)

    NASA Astrophysics Data System (ADS)

    Bergamasco, A.; Defendi, V.; Spezie, G.; Budillon, G.; Carniel, S.

    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 shelf 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 Shelf 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 Ice Shelf Water (ISW, originated below the Ross Ice Shelf and outflowing northward). Both bottom waters spill over the shelf 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 shelf break, nevertheless distribution captures the evidence of a downslope flow process.

  16. 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.

  17. 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.

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

    USGS Publications Warehouse

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

    2005-01-01

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

  19. 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

  20. The Larsen Ice Shelf in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign

    NASA Image and Video Library

    2004-03-16

    The Larsen Ice Shelf 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 ice shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia ice fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with the Airborne Synthetic Aperture Radar developed by scientists from NASA’s Jet Propulsion Laboratory. AirSAR will provide a baseline model and unprecedented mapping of the region. This data will make it possible to determine whether the warming trend is slowing, continuing or accelerating. AirSAR will also provide reliable information on ice shelf thickness to measure the contribution of the glaciers to sea level.

  1. The Larsen Ice Shelf in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign

    NASA Image and Video Library

    2004-03-13

    The Larsen Ice Shelf 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 ice shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia ice fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with the Airborne Synthetic Aperture Radar developed by scientists from NASA’s Jet Propulsion Laboratory. AirSAR will provide a baseline model and unprecedented mapping of the region. This data will make it possible to determine whether the warming trend is slowing, continuing or accelerating. AirSAR will also provide reliable information on ice shelf thickness to measure the contribution of the glaciers to sea level.

  2. The Larsen Ice Shelf in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign

    NASA Image and Video Library

    2004-03-16

    The Larsen Ice Shelf 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 ice shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia ice fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with 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 ice shelf thickness to measure the contribution of the glaciers to sea level.

  3. 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

  4. Tidal influences on a future evolution of the Filchner-Ronne Ice Shelf cavity in the Weddell Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Mueller, Rachael D.; Hattermann, Tore; Howard, Susan L.; Padman, Laurie

    2018-02-01

    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 Ice Shelf (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS ice 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 ice shelf 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 ice 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 ice sheet as individual ice-stream grounding zones experience different responses to warming of the ocean inflow.

  5. DEM generation and tidal deformation detection for sulzberger ice shelf, West Antarctica using SAR interferometry

    USGS Publications Warehouse

    Baek, S.; Kwoun, Oh-Ig; Bassler, M.; Lu, Z.; Shum, C.K.; Dietrich, R.

    2004-01-01

    In this study we generated a relative Digital Elevation Model (DEM) over the Sulzberger Ice Shelf, 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.

  6. 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

  7. 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

  8. Surface winds over West Antarctica

    NASA Astrophysics Data System (ADS)

    Bromwich, David

    1993-07-01

    Five winter months (April-August 1988) of thermal infrared satellite images were examined to investigate the occurrence of dark (warm) signatures across the Ross Ice Shelf in the Antarctic continent. These features are inferred to be generated by katabatic winds that descend from southern Marie Byrd Land and then blow horizontally across the ice shelf. Significant mass is added to this airstream by katabatic winds blowing from the major glaciers that flow through the Transantarctic Mountains from East Antarctica. These negatively buoyant katabatic winds can reach the northwestern edge of the shelf - a horizontal propagation distance of up to 1,000 km - 14 percent of the time. Where the airstream crosses from the ice shelf to the ice-covered Ross Sea, a prominent coastal polynya is formed. Because the downslope buoyancy force is near zero over the Ross Ice Shelf, the northwestward propagation of the katabatic air mass requires pressure gradient support. The study shows that the extended horizontal propagation of this atmospheric density current occurred in conjunction with the passage of synoptic cyclones over the southern Amundsen Sea. These cyclones can strengthen the pressure gradient in the interior of West Antarctica and make the pressure field favorable for northwestward movement of the katabatic winds from West Antarctica across the ice shelf in a geostrophic direction. The glacier winds from East Antarctica are further accelerated by the synoptic pressure gradient, usually undergo abrupt adjustment beyond the exit to the glacier valley, and merge into the mountain-parallel katabatic air mass.

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

    USGS Publications Warehouse

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

    2007-01-01

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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Late Summer Frazil Ice-Associated Algal Blooms around Antarctica

    NASA Astrophysics Data System (ADS)

    DeJong, Hans B.; Dunbar, Robert B.; Lyons, Evan A.

    2018-01-01

    Antarctic continental shelf waters are the most biologically productive in the Southern Ocean. Although satellite-derived algorithms report peak productivity during the austral spring/early summer, recent studies provide evidence for substantial late summer productivity that is associated with green colored frazil ice. Here we analyze daily Moderate Resolution Imaging Spectroradiometer satellite images for February and March from 2003 to 2017 to identify green colored frazil ice hot spots. Green frazil ice is concentrated in 11 of the 13 major sea ice production polynyas, with the greenest frazil ice in the Terra Nova Bay and Cape Darnley polynyas. While there is substantial interannual variability, green frazil ice is present over greater than 300,000 km2 during March. Late summer frazil ice-associated algal productivity may be a major phenomenon around Antarctica that is not considered in regional carbon and ecosystem models.

  16. Climatological aspects of mesoscale cyclogenesis over the Ross Sea and Ross Ice shelf regions of Antarctica

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

    Carrasco, J.F.; Bromwich, D.H.

    1994-11-01

    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 Ice Shelf. 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 Ice Shelf, 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 Ice Shelf 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

  17. 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.

  18. Downslope flow across the Ross Sea shelf break (Antarctica)

    NASA Astrophysics Data System (ADS)

    Bergamasco, A.; Budillon, G.; Carniel, S.; Defendi, V.; Meloni, R.; Paschini, E.; Sclavo, M.; Spezie, G.

    2003-12-01

    The analysis of some high-resolution hydrological data sets acquired during the 1997, 1998, 2001 and 2003 austral summers across the Ross Sea continental shelf 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 shelf break, ventilate the deep ocean. Two Antarctic continental shelf 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 Shelf Water (HSSW). The HSSW formation is linked to the rejection of salt into the water column as sea ice freezes, especially during winter, in the polynya areas, where the ice is continuously pushed offshore by the strong katabatic winds. The latter one is responsible of the formation of a supercold water mass, the Ice Shelf Water (ISW). The salt supplied by the HSSW recirculated below the Ross Ice Shelf, the latent heat of melting and the heat sink provided by the Ross Ice Shelf give rise to plumes of ISW, characterized by temperatures below the sea-surface freezing point. The dense shelf waters migrate to the continental shelf-break, spill over the shelf edge and descend the continental slope as a shelf-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

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. 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.

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

    PubMed

    Rignot, Eric

    2006-07-15

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

  10. 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

  11. 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.

  12. 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.

  13. Coastal-Change and Glaciological Map of the Larsen Ice Shelf Area, Antarctica, 1940-2005

    USGS Publications Warehouse

    Ferrigno, Jane G.; Cook, Alison J.; Mathie, Amy M.; Williams, Richard S.; Swithinbank, Charles; Foley, Kevin M.; Fox, Adrian J.; Thomson, Janet W.; Sievers, Jorn

    2008-01-01

    Changes in the area and volume of polar ice sheets are intricately linked to changes in global climate, and the resulting changes in sea level could severely impact the densely populated coastal regions on Earth. Antarctica is Earth's largest reservoir of glacial ice. Melting of the West Antarctic part alone of the Antarctic ice sheet would cause a sea-level rise of approximately 6 meters (m), and the potential sea-level rise after melting of the entire Antarctic ice sheet is estimated to be 65 m (Lythe and others, 2001) to 73 m (Williams and Hall, 1993). The mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is highly complex, responding differently to different climatic and other conditions in each region (Vaughan, 2005). In a review paper, Rignot and Thomas (2002) concluded that the West Antarctic ice sheet is probably becoming thinner overall; although it is known to be thickening in the west, it is thinning in the north. The mass balance of the East Antarctic ice sheet is thought by Davis and others (2005) to be positive on the basis of the change in satellite-altimetry measurements made between 1992 and 2003. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), in subsequent recommendations by the Scientific Committee on Antarctic Research (SCAR) (1989, 1993), and by the National Science Foundation's (1990) Division of Polar Programs. On the basis of these recommendations, the U.S. Geological Survey (USGS) decided that the archive of early 1970s Landsat 1, 2, and 3 Multispectral Scanner (MSS) images of Antarctica and the subsequent repeat coverage made possible with Landsat and other satellite images provided an excellent means of documenting changes in the cryospheric coastline of Antarctica (Ferrigno and Gould, 1987). The availability of this information provided the impetus for carrying out a

  14. 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

  15. 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).

  16. Coupled ice sheet-ocean modelling to investigate ocean driven melting of marine ice sheets in Antarctica

    NASA Astrophysics Data System (ADS)

    Jong, Lenneke; Gladstone, Rupert; Galton-Fenzi, Ben

    2017-04-01

    Ocean induced melting below the ice shelves of marine ice sheets is a major source of uncertainty for predictions of ice mass loss and Antarctica's resultant contribution to future sea level rise. The floating ice shelves provide a buttressing force against the flow of ice across the grounding line into the ocean. Thinning of these ice shelves due to an increase in melting reduces this force and can lead to an increase in the discharge of grounded ice. Fully coupled modelling of ice sheet-ocean interactions is key to improving understanding the influence of the Southern ocean on the evolution of the Antarctic ice sheet, and to predicting its future behaviour under changing climate conditions. Coupling of ocean and ice sheet models is needed to provide more realistic melt rates at the base of ice shelves and hence make better predictions of the behaviour of the grounding line and the shape of the ice-shelf cavity as the ice sheet evolves. The Framework for Ice Sheet - Ocean Coupling (FISOC) has been developed to provide a flexible platform for performing coupled ice sheet - ocean modelling experiments. We present preliminary results using FISOC to couple the Regional Ocean Modelling System (ROMS) with Elmer/Ice in idealised experiments Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP). These experiments use an idealised geometry motivated by that of Pine Island glacier and the adjacent Amundsen Sea in West Antarctica, a region which has shown shown signs of thinning ice and grounding line retreat.

  17. 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

  18. Antarctica

    Atmospheric Science Data Center

    2013-04-16

    article title:  Twilight in Antarctica     View larger JPEG ... SpectroRadiometer (MISR) instrument on board Terra. The Ross Ice Shelf and Transantarctic Mountains are illuminated by low Sun. MISR was ...

  19. 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.

  20. 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.

  1. Earth - Ross Ice Shelf, Antarctica

    NASA Image and Video Library

    1996-02-09

    This color picture of Antarctica is one part of a mosaic of pictures covering the entire Antarctic continent taken during the hours following NASA's Galileo historic first encounter with its home planet. http://photojournal.jpl.nasa.gov/catalog/PIA00117

  2. Increased future ice discharge from Antarctica owing to higher snowfall

    NASA Astrophysics Data System (ADS)

    Winkelmann, Ricarda; Levermann, Anders; Martin, Maria A.; Frieler, Katja

    2013-04-01

    Anthropogenic climate change is likely to cause continuing global sea-level rise, but some processes within the Earth system may mitigate the magnitude of the projected effect. Regional and global climate models simulate enhanced snowfall over Antarctica, which would provide a direct offset of the future contribution to global sea level rise from cryospheric mass loss and ocean expansion. Uncertainties exist in modelled snowfall, but even larger uncertainties exist in the potential changes of dynamic ice discharge from Antarctica. Here we show that snowfall and discharge are not independent, but that future ice discharge will increase by up to three times as a result of additional snowfall under global warming. Our results, based on an ice-sheet model forced by climate simulations through to the end of 2500, show that the enhanced discharge effect exceeds the effect of surface warming as well as that of basal ice-shelf melting, and is due to the difference in surface elevation change caused by snowfall on grounded versus floating ice. Although different underlying forcings drive ice loss from basal melting versus increased snowfall, similar ice dynamical processes are nonetheless at work in both; therefore results are relatively independent of the specific representation of the transition zone. In an ensemble of simulations designed to capture ice-physics uncertainty, the additional dynamic ice loss along the coastline compensates between 30 and 65 per cent of the ice gain due to enhanced snowfall over the entire continent. This results in a dynamic ice loss of up to 1.25 metres in the year 2500 for the strongest warming scenario.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. Top predators in relation to bathymetry, ice and krill during austral winter in Marguerite Bay, Antarctica

    USGS Publications Warehouse

    Ribic, C.A.; Chapman, E.; Fraser, William R.; Lawson, G.L.; Wiebe, P.H.

    2008-01-01

    A key hypothesis guiding the US Southern Ocean Global Ocean Ecosystems Dynamics (US SO GLOBEC) program is that deep across-shelf troughs facilitate the transport of warm and nutrient-rich waters onto the continental shelf of the Western Antarctic Peninsula, resulting in enhanced winter production and prey availability to top predators. We tested aspects of this hypothesis during austral winter by assessing the distribution of the resident pack-ice top predators in relation to these deep across-shelf troughs and by investigating associations between top predators and their prey. Surveys were conducted July-August 2001 and August-September 2002 in Marguerite Bay, Antarctica, with a focus on the main across-shelf trough in the bay, Marguerite Trough. The common pack-ice seabird species were snow petrel (Pagodroma nivea, 1.2 individuals km-2), Antarctic petrel (Thalassoica antarctica, 0.3 individuals km-2), and Ade??lie penguin (Pygoscelis adeliae, 0.5 individuals km-2). The most common pack-ice pinniped was crabeater seal (Lobodon carcinophagus). During both winters, snow and Antarctic petrels were associated with low sea-ice concentrations independent of Marguerite Trough, while Ade??lie penguins occurred in association with this trough. Krill concentrations, both shallow and deep, also were associated with Ade??lie penguin and snow petrel distributions. During both winters, crabeater seal occurrence was associated with deep krill concentrations and with regions of lower chlorophyll concentration. The area of lower chlorophyll concentrations occurred in an area with complex bathymetry close to land and heavy ice concentrations. Complex or unusual bathymetry via its influence on physical and biological processes appears to be one of the keys to understanding how top predators survive during the winter in this Antarctic region. ?? 2007 Elsevier Ltd. All rights reserved.

  9. Increased future ice discharge from Antarctica owing to higher snowfall.

    PubMed

    Winkelmann, R; Levermann, A; Martin, M A; Frieler, K

    2012-12-13

    Anthropogenic climate change is likely to cause continuing global sea level rise, but some processes within the Earth system may mitigate the magnitude of the projected effect. Regional and global climate models simulate enhanced snowfall over Antarctica, which would provide a direct offset of the future contribution to global sea level rise from cryospheric mass loss and ocean expansion. Uncertainties exist in modelled snowfall, but even larger uncertainties exist in the potential changes of dynamic ice discharge from Antarctica and thus in the ultimate fate of the precipitation-deposited ice mass. Here we show that snowfall and discharge are not independent, but that future ice discharge will increase by up to three times as a result of additional snowfall under global warming. Our results, based on an ice-sheet model forced by climate simulations through to the end of 2500 (ref. 8), show that the enhanced discharge effect exceeds the effect of surface warming as well as that of basal ice-shelf melting, and is due to the difference in surface elevation change caused by snowfall on grounded versus floating ice. Although different underlying forcings drive ice loss from basal melting versus increased snowfall, similar ice dynamical processes are nonetheless at work in both; therefore results are relatively independent of the specific representation of the transition zone. In an ensemble of simulations designed to capture ice-physics uncertainty, the additional dynamic ice loss along the coastline compensates between 30 and 65 per cent of the ice gain due to enhanced snowfall over the entire continent. This results in a dynamic ice loss of up to 1.25 metres in the year 2500 for the strongest warming scenario. The reported effect thus strongly counters a potential negative contribution to global sea level by the Antarctic Ice Sheet.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    Bell, R. E.

    2015-12-01

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

  12. Cryoconite and Ice-bubble Microbial Ecosystems in Antarctica

    NASA Technical Reports Server (NTRS)

    Hoover, Richard B.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    During the Antarctica 2000 Expedition samples of rocks and ice bubbles entrained in ice were collected from the blue ice fields near the Moulton Escarpment of the Thiel Mountains (85S, 94W) and the Morris Moraine of the Patriot Hills (80S, 8 1 W) Ellsworth Mountains of Antarctica. Investigation of the microbiota of these cryoconite and ice bubble ecosystems are now being conducted to help refine chemical and morphological biomarkers of potential significance to Astrobiology. The Antarctica 2000 Expedition will be discussed and the preliminary results of the studies of the ice bubble and cryoconite microbial ecosystems discussed. Recent ESEM images of the Antarctic microbiota will be presented a the relevance of ice ecosystems to Astrobiology will be discussed.

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

    NASA Astrophysics Data System (ADS)

    Chuter, Stephen; Bamber, Jonathan

    2016-04-01

    .3% and 4.7% across the whole shelf and within 10 km of the grounding line, respectively. These represent a two to three fold improvement in accuracy when compared to the previous data product. The impact of these improvements on Input-Output estimates of mass balance is illustrated for the Abbot Ice Shelf. Our new product shows a mean reduction of 29% in thickness at the grounding line when compared to the previous dataset as well as the elimination of non-physical 'data spikes' that were prevalent in the previous product in areas of complex terrain. The reduction in grounding line thickness equates to a change in mass balance for the areas from -14±9 GTyr-1to -4±9 GTyr-1. We show examples from other sectors including the Getz and George VI ice shelves. The updated estimate is more consistent with the positive surface elevation rate in this region obtained from satellite altimetry. The new thickness dataset will greatly reduce the uncertainty in Input-Output estimates of mass balance for the ˜30% of the grounding line of Antarctica where direct ice thickness measurements do not exist.

  14. 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

  15. 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 ...

  16. Regional ice-mass changes and glacial-isostatic adjustment in Antarctica from GRACE

    NASA Astrophysics Data System (ADS)

    Sasgen, Ingo; Martinec, Zdeněk; Fleming, Kevin

    2007-12-01

    We infer regional mass changes in Antarctica using ca. 4 years of Gravity Recovery and Climate Experiment (GRACE) level 2 data. We decompose the time series of the Stokes coefficients into their linear as well as annual and semi-annual components by a least-squares adjustment and apply a statistical reliability test to the Stokes potential-coefficients' linear temporal trends. Mass changes in three regions of Antarctica that display prominent geoid-height change are determined by adjusting predictions of glacier melting at the tip of the Antarctic Peninsula and in the Amundsen Sea Sector, and of the glacial-isostatic adjustment (GIA) over the Ronne Ice Shelf. We use the GFZ RL04, CNES RL01C, JPL RL04 and CSR RL04 potential-coefficient releases, and show that, although all data sets consistently reflect the prominent mass changes, differences in the mass-change estimates are considerably larger than the uncertainties estimated by the propagation of the GRACE errors. We then use the bootstrapping method based on the four releases and six time intervals, each with 3.5 years of data, to quantify the variability of the mean mass-change estimates. We find 95% of our estimates to lie within 0.08 and 0.09 mm/a equivalent sea-level (ESL) change for the Antarctic Peninsula and within 0.18 and 0.20 mm/a ESL for the Amundsen Sea Sector. Forward modelling of the GIA over the Ronne Ice Shelf region suggests that the Antarctic continent was covered by 8.4 to 9.4 m ESL of additional ice during the Last-Glacial Maximum (ca. 22 to 15 ka BP). With regards to the mantle-viscosity values and the glacial history used, this value is considered as a minimum estimate. The mass-change estimates derived from all GRACE releases and time intervals lie within ca. 20% (Amundsen Sea Sector), 30% (Antarctic Peninsula) and 50% (Ronne Ice Shelf region) of the bootstrap-estimated mean, demonstrating the reliability of results obtained using GRACE observations.

  17. Environmental and ice volume changes based on seismic stratigraphy in Sabrina Coast, East Antarctica: Preliminary results from NBP1402

    NASA Astrophysics Data System (ADS)

    Gulick, S. P. S.; Fernandez-Vasquez, R. A.; Frederick, B.; Saustrup, S., Sr.; Domack, E. W.; Lavoie, C.; Shevenell, A.; Blankenship, D. D.; Leventer, A.

    2014-12-01

    In 2014, the R/V Nathaniel B. Palmer (NBP1402) sailed to a virtually unexplored continental shelf along the Sabrina Coast, East Antarctica. The shelf contains the sedimentary record of environmental and ice volume changes within the Aurora Subglacial Basin (ASB), which is presently occupied by ~7 m sea level-rise equivalent of ice. We acquired 750 km of high-resolution seismic data proximal to the Reynolds Trough and Moscow University Ice Shelf glacial systems west of the Dalton Ice Tongue using dual 45/45 cu. in. G.I. guns and a 24 ch. streamer with 3.125 m groups providing a vertical resolution of ~3 m simultaneously with CHIRP data. These are the first images of this margin acquired and show a remarkable set of sequence stratigraphic transitions. Crystalline basement is at the seafloor landward and buried seaward with a transition to smoother reflection interface. Reflective sedimentary strata overlie the basement, dip seaward, and are capped by a landward-dipping regional angular unconformity. Above this are a series of transparent seismic facies that, along with the middle to outer shelf seafloor, dip landward towards a shelf-oblique glacial trough. The older, seaward-dipping strata include a deeper series of units that display at least three stratal architectures interpreted to be shelf deltas implying a pre-glacial, fluvial environment within the drainage basin. Above these sequences, the seismic facies transition to surfaces exhibiting significant erosion, small u-shaped valleys, and channel fill sequences, all of which are reminiscent of temperate glacial features. We interpret these sequences as including sub-ice tunnel valleys and grounding zone wedges with interspersed non-glacial to pro-glacial deposits. Increasing glaciogenic facies upsection suggests a gradual fluvial to glacial transition and increasing glacial extent with time. The subsequent transition to ice sheets is marked by erosion to basement landward and the angular unconformity seaward

  18. 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

  19. 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.

  20. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2017-01-01

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

  2. 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

  3. 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.

  4. Calcareous nannofossil evidence for Marine Isotope Stage 31 (1 Ma) in the AND-1B Core, ANDRILL McMurdo Ice Shelf Project (Antarctica).

    NASA Astrophysics Data System (ADS)

    Villa, G.; Persico, D.; Wise, S. W.; Gadaleta, A.

    2009-04-01

    During the austral summer 2006 the ANDRILL Program recovered a 1285 m-long succession of cyclic glacimarine sediments from the McMurdo Ice Shelf (MIS). The aim of the MIS Project was to obtain continuous Neogene (c. 0-10 Ma) glacial, glacimarine, volcanic, and biogenic sediments that have accumulated in the region of the McMurdo Ice Shelf (Ross Sea) nourished by ice flowing from East Antarctic Ice Sheet (EAIS) outlet glaciers in the Transantarctic Mountains (TAM). The MIS AND-1B drill core represents the longest and most complete (98% recovery) geological record from the Antarctic continental margin to date, and will provide a key reference record of climate and ice-sheet variability through the Late Neogene; detailed investigations of this record will contribute for improving our knowledge of Antarctica's influence on global climate. Preliminary on-ice analysis of the smear slides of the Andrill core revealed calcareous microfossils (dinoflagellates, calciosponge spicula and small foraminifera) occurring with variable concentrations. The presence of thoracosphaerid fragments in the smear slides of the first 600 mbsf (Quaternary), probably belong to the species Thoracosphaera saxea (Stradner 1961), and Thoracosphaera heimi (Kamptner, 1941) and other, potentially undescribed species (Villa & Wise 1998), suggests either a peculiar adaptation to this environment, due to their ability to develop cysts or warmer conditions at the time of their deposition, or a combination of both. However, they represent an additional element to use with the other proxies for inferring palaeoenvironmental conditions of the core. Subsequent shore-based analyses of 100 samples from 86-96 mbsf revealed for the first time the presence of Pleistocene coccolithophorids at these high southern latitudes (77° S), including: Coccolithus pelagicus, small Gephyrocapsa, Reticulofenestra asanoi, Pseudoemiliania lacunosa, Dictyoccocites productus, Reticulofenestra sp., Reticulofenestra minutula

  5. The Antarctica component of postglacial rebound model ICE-6G_C (VM5a) based on GPS positioning, exposure age dating of ice thicknesses, and relative sea level histories

    NASA Astrophysics Data System (ADS)

    Argus, Donald F.; Peltier, W. R.; Drummond, R.; Moore, Angelyn W.

    2014-07-01

    A new model of the deglaciation history of Antarctica over the past 25 kyr has been developed, which we refer to herein as ICE-6G_C (VM5a). This revision of its predecessor ICE-5G (VM2) has been constrained to fit all available geological and geodetic observations, consisting of: (1) the present day uplift rates at 42 sites estimated from GPS measurements, (2) ice thickness change at 62 locations estimated from exposure-age dating, (3) Holocene relative sea level histories from 12 locations estimated on the basis of radiocarbon dating and (4) age of the onset of marine sedimentation at nine locations along the Antarctic shelf also estimated on the basis of 14C dating. Our new model fits the totality of these data well. An additional nine GPS-determined site velocities are also estimated for locations known to be influenced by modern ice loss from the Pine Island Bay and Northern Antarctic Peninsula regions. At the 42 locations not influenced by modern ice loss, the quality of the fit of postglacial rebound model ICE-6G_C (VM5A) is characterized by a weighted root mean square residual of 0.9 mm yr-1. The Southern Antarctic Peninsula is inferred to be rising at 2 mm yr-1, requiring there to be less Holocene ice loss there than in the prior model ICE-5G (VM2). The East Antarctica coast is rising at approximately 1 mm yr-1, requiring ice loss from this region to have been small since Last Glacial Maximum. The Ellsworth Mountains, at the base of the Antarctic Peninsula, are inferred to be rising at 5-8 mm yr-1, indicating large ice loss from this area during deglaciation that is poorly sampled by geological data. Horizontal deformation of the Antarctic Plate is minor with two exceptions. First, O'Higgins, at the tip of the Antarctic Peninsula, is moving southeast at a significant 2 mm yr-1 relative to the Antarctic Plate. Secondly, the margins of the Ronne and Ross Ice Shelves are moving horizontally away from the shelf centres at an approximate rate of 0.8 mm yr-1, in

  6. 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.

  7. 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.

  8. 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.

  9. Constraining ice sheet history in the Weddell Sea, West Antarctica, using ice fabric at Korff Ice Rise

    NASA Astrophysics Data System (ADS)

    Brisbourne, A.; Smith, A.; Kendall, J. M.; Baird, A. F.; Martin, C.; Kingslake, J.

    2017-12-01

    The grounding history of ice rises (grounded area of independent flow regime within a floating ice shelf) can be used to constrain large scale ice sheet history: ice fabric, resulting from the preferred orientation of ice crystals due to the stress regime, can be used to infer this grounding history. With the aim of measuring the present day ice fabric at Korff Ice Rise, West Antarctica, a multi-azimuth wide-angle seismic experiment was undertaken. Three wide-angle common-midpoint gathers were acquired centred on the apex of the ice rise, at azimuths of 60 degrees to one another, to measure variation in seismic properties with offset and azimuth. Both vertical and horizontal receivers were used to record P and S arrivals including converted phases. Measurements of the variation with offset and azimuth of seismic traveltimes, seismic attenuation and shear wave splitting have been used to quantify seismic anisotropy in the ice column. The observations cannot be reproduced using an isotropic ice column model. Anisotropic ray tracing has been used to test likely models of ice fabric by comparison with the data. A model with a weak girdle fabric overlying a strong cluster fabric provides the best fit to the observations. Fabric of this nature is consistent with Korff Ice Rise having been stable for the order of 10,000 years without any ungrounding or significant change in the ice flow configuration across the ice rise for this period. This observation has significant implications for the ice sheet history of the Weddell Sea sector.

  10. Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations

    NASA Astrophysics Data System (ADS)

    Minchew, B. M.; Simons, M.; Riel, B.; Milillo, P.

    2017-01-01

    To better understand the influence of stress changes over floating ice shelves on grounded ice streams, we develop a Bayesian method for inferring time-dependent 3-D surface velocity fields from synthetic aperture radar (SAR) and optical remote sensing data. Our specific goal is to observe ocean tide-induced variability in vertical ice shelf position and horizontal ice stream flow. Thus, we consider the special case where observed surface displacement at a given location can be defined by a 3-D secular velocity vector, a family of 3-D sinusoidal functions, and a correction to the digital elevation model used to process the SAR data. Using nearly 9 months of SAR data collected from multiple satellite viewing geometries with the COSMO-SkyMed 4-satellite constellation, we infer the spatiotemporal response of Rutford Ice Stream, West Antarctica, to ocean tidal forcing. Consistent with expected tidal uplift, inferred vertical motion over the ice shelf is dominated by semidiurnal and diurnal tidal constituents. Horizontal ice flow variability, on the other hand, occurs primarily at the fortnightly spring-neap tidal period (Msf). We propose that periodic grounding of the ice shelf is the primary mechanism for translating vertical tidal motion into horizontal flow variability, causing ice flow to accelerate first and most strongly over the ice shelf. Flow variations then propagate through the grounded ice stream at a mean rate of ˜29 km/d and decay quasi-linearly with distance over ˜85 km upstream of the grounding zone.

  11. 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.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  14. RICE ice core: Black Carbon reflects climate variability at Roosevelt Island, West Antarctica

    NASA Astrophysics Data System (ADS)

    Ellis, Aja; Edwards, Ross; Bertler, Nancy; Winton, Holly; Goodwin, Ian; Neff, Peter; Tuohy, Andrea; Proemse, Bernadette; Hogan, Chad; Feiteng, Wang

    2015-04-01

    The Roosevelt Island Climate Evolution (RICE) project successfully drilled a deep ice core from Roosevelt Island during the 2011/2012 and 2012/2013 seasons. Located in the Ross Ice Shelf in West Antarctica, the site is an ideal location for investigating climate variability and the past stability of the Ross Ice Shelf. Black carbon (BC) aerosols are emitted by both biomass burning and fossil fuels, and BC particles emitted in the southern hemisphere are transported in the atmosphere and preserved in Antarctic ice. The past record of BC is expected to be sensitive to climate variability, as it is modulated by both emissions and transport. To investigate BC variability over the past 200 years, we developed a BC record from two overlapping ice cores (~1850-2012) and a high-resolution snow pit spanning 2010-2012 (cal. yr). Consistent results are found between the snow pit profiles and ice core records. Distinct decadal trends are found with respect to BC particle size, and the record indicates a steady rise in BC particle size over the last 100 years. Differences in emission sources and conditions may be a possible explanation for changes in BC size. These records also show a significant increase in BC concentration over the past decade with concentrations rising over 1.5 ppb (1.5*10^-9 ng/g), suggesting a fundamental shift in BC deposition to the site.

  15. Byrd Glacier, Antarctica

    NASA Image and Video Library

    2008-11-17

    Byrd Glacier is a major glacier in Antarctica; it drains an extensive area of the polar plateau and flows eastward between the Britannia Range and the Churchill Mountains to discharge into the Ross Ice Shelf. This image is from NASA Terra satellite.

  16. Relative sea-level rise around East Antarctica during Oligocene glaciation

    NASA Astrophysics Data System (ADS)

    Stocchi, Paolo; Escutia, Carlota; Houben, Alexander J. P.; Vermeersen, Bert L. A.; Bijl, Peter K.; Brinkhuis, Henk; Deconto, Robert M.; Galeotti, Simone; Passchier, Sandra; Pollard, David; Brinkhuis, Henk; Escutia, Carlota; Klaus, Adam; Fehr, Annick; Williams, Trevor; Bendle, James A. P.; Bijl, Peter K.; Bohaty, Steven M.; Carr, Stephanie A.; Dunbar, Robert B.; Flores, Jose Abel; Gonzàlez, Jhon J.; Hayden, Travis G.; Iwai, Masao; Jimenez-Espejo, Francisco J.; Katsuki, Kota; Kong, Gee Soo; McKay, Robert M.; Nakai, Mutsumi; Olney, Matthew P.; Passchier, Sandra; Pekar, Stephen F.; Pross, Jörg; Riesselman, Christina; Röhl, Ursula; Sakai, Toyosaburo; Shrivastava, Prakash Kumar; Stickley, Catherine E.; Sugisaki, Saiko; Tauxe, Lisa; Tuo, Shouting; van de Flierdt, Tina; Welsh, Kevin; Yamane, Masako

    2013-05-01

    During the middle and late Eocene (~ 48-34Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarctica induced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rose despite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an ice-sheet grounding line.

  17. Accuracy Assessment of Recent Global Ocean Tide Models around Antarctica

    NASA Astrophysics Data System (ADS)

    Lei, J.; Li, F.; Zhang, S.; Ke, H.; Zhang, Q.; Li, W.

    2017-09-01

    Due to the coverage limitation of T/P-series altimeters, the lack of bathymetric data under large ice shelves, and the inaccurate definitions of coastlines and grounding lines, the accuracy of ocean tide models around Antarctica is poorer than those in deep oceans. Using tidal measurements from tide gauges, gravimetric data and GPS records, the accuracy of seven state-of-the-art global ocean tide models (DTU10, EOT11a, GOT4.8, FES2012, FES2014, HAMTIDE12, TPXO8) is assessed, as well as the most widely-used conventional model FES2004. Four regions (Antarctic Peninsula region, Amery ice shelf region, Filchner-Ronne ice shelf region and Ross ice shelf region) are separately reported. The standard deviations of eight main constituents between the selected models are large in polar regions, especially under the big ice shelves, suggesting that the uncertainty in these regions remain large. Comparisons with in situ tidal measurements show that the most accurate model is TPXO8, and all models show worst performance in Weddell sea and Filchner-Ronne ice shelf regions. The accuracy of tidal predictions around Antarctica is gradually improving.

  18. Galileo spacecraft solid-state imaging system view of Antarctica

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Galileo spacecraft solid-state imaging system view of Antarctica was taken during its first encounter with the Earth. This color picture of Antarctica is part of a mosaic of pictures covering the entire polar continent showing the Ross Ice Shelf and its border with the sea and mountains poking through the ice near the McMurdo Station. From top to bottom, the frame looks across about half of Antarctica. View provided by the Jet Propulsion Laboratory (JPL) with alternate number P-37297.

  19. 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.

  20. 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

  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. 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.

  3. Glaciers of Antarctica

    USGS Publications Warehouse

    Williams, Richard S.; Ferrigno, Jane G.

    1988-01-01

    have been included. Again, these represent only a small fraction of the large number of aerial photographs now available in various national collections. The chapter is divided into five geographic sections. The first is the Transantarctic Mountains in the Ross Sea area. Some very large outlet glaciers flow from the East Antarctic ice sheet through the Transantarctic Mountains to the Ross Ice Shelf. Byrd Glacier, one of the largest in the world, drains an area of more than 1,000,000 km2. Next, images from the Indian Ocean sector are discussed. These include the Lambert Glacier- Amery Ice Shelf system, so large that about 25 images must be mosaicked to cover its complex system of tributary glaciers. Shirase Glacier, a tidal outlet glacier in the sector, flows at a speed of 2.5 km a-l. About 200 km inland and 200 km west of Shirase Glacier lie the Queen Fabiola (?Yamato?) Mountains, whose extensive exposures of `blue ice? lay claim to being the world?s most important meteorite-collecting locality, with more than 4,700 meteorite fragments discovered since 1969. The Atlantic Ocean sector is fringed by ice shelves into which flow large ice streams like Jutulstraumen, Stancomb-Wills, Slessor, and Recovery Glaciers. Filchner and Ronne Ice Shelves together cover an area two-thirds the size of Texas. From the western margin of the Ronne Ice Shelf, the north-trending arc of the Antarctic Peninsula, with its fjord and alpine landscape and fringing ice shelves, stretches towards South America. The Pacific Ocean sector begins with the Ellsworth Mountains, which include the highest peaks (Vinson Massif at 4,897 m) in Antarctica. The area between the Ellsworth Mountains and the eastern margin of the Ross Ice Shelf is fringed with small ice shelves and some major outlet glaciers. One of these, Pine Island Glacier, was found from comparing 1973 and 1975 images to have an average ice-front velocity of 2.4 km a-l. This part of Antarctica

  4. Extensive massive basal-ice structures in West Antarctica relate to ice-sheet anisotropy and ice-flow

    NASA Astrophysics Data System (ADS)

    Ross, N.; Bingham, R. G.; Corr, H. F. J.; Siegert, M. J.

    2016-12-01

    Complex structures identified within both the East Antarctic and Greenland ice sheets are thought to be generated by the action of basal water freezing to the ice-sheet base, evolving under ice flow. Here, we use ice-penetrating radar to image an extensive series of similarly complex basal ice facies in West Antarctica, revealing a thick (>500 m) tectonised unit in an area of cold-based and relatively slow-flowing ice. We show that major folding and overturning of the unit perpendicular to ice flow elevates deep, warm ice into the mid ice-sheet column. Fold axes align with present ice flow, and axis amplitudes increase down-ice, suggesting long-term consistency in the direction and convergence of flow. In the absence of basal water, and the draping of the tectonised unit over major subglacial mountain ranges, the formation of the unit must be solely through the deformation of meteoric ice. Internal layer radar reflectivity is consistently greater parallel to flow compared with the perpendicular direction, revealing ice-sheet crystal anisotropy is associated with the folding. By linking layers to the Byrd ice-core site, we show the basal ice dates to at least the last glacial cycle and may be as old as the last interglacial. Deformation of deep-ice in this sector of WAIS, and potentially elsewhere in Antarctica, may be caused by differential shearing at interglacial-glacial boundaries, in a process analogous to that proposed for interior Greenland. The scale and heterogeneity of the englacial structures, and their subsequent impact on ice sheet rheology, means that the nature of ice flow across the bulk of West Antarctica must be far more complex that is currently accounted for by any numerical ice sheet model.

  5. 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.

  6. Increased Ocean Access to Totten Glacier, East Antarctica

    NASA Astrophysics Data System (ADS)

    Blankenship, D. D.; Greenbaum, J. S.; Young, D. A.; Richter, T. G.; Roberts, J. L.; Aitken, A.; Legresy, B.; Warner, R. C.; van Ommen, T. D.; Siegert, M. J.

    2015-12-01

    The Totten Glacier is the largest ice sheet outlet in East Antarctica, draining 3.5 meters of eustatic sea level potential from the Aurora Subglacial Basin (ASB) into the Sabrina Coast. Recent work has shown that the ASB has drained and filled many times since largescale glaciation began including evidence that it collapsed during the Pliocene. Steady thinning rates observed near Totten Glacier's grounding line since the beginning of the satellite altimetry record are the largest in East Antarctica and the nature of the thinning suggests that it is driven by enhanced basal melting due to ocean processes. 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 Sabrina Coast continental shelf in the 400-500 m depth range. Using airborne geophysical data acquired over multiple years we delineate seafloor valleys connecting the inner continental shelf to the cavity beneath Totten Glacier that cut through a large sill centered along the ice shelf calving front. The sill shallows to depths of about 300 mbsl and was likely a grounding line pinning point during Holocene retreat, however, the two largest seafloor valleys are deeper than the observed range of thermocline depths. The deeper of the two valleys, a 4 km-wide trough, connects to the ice shelf cavity through an area of the coastline that was previously believed to be grounded but that our analysis demonstrates is floating, revealing a second, deeper entryway to ice shelf cavity. The previous coastline was charted using satellite-based mapping techniques that infer subglacial properties based on surface expression and behavior; the new geophysical analysis techniques we use enable inferences of subglacial characteristics using direct observations of the ice-water interface. The results indicate that Totten Glacier and, by extension, the Aurora Subglacial Basin are vulnerable to MCDW that has been observed on the nearby

  7. Widespread surface meltwater drainage in Antarctica

    NASA Astrophysics Data System (ADS)

    Kingslake, J.; Ely, J.; Das, I.; Bell, R. E.

    2016-12-01

    Surface meltwater is thought to cause ice-shelf disintegration, which accelerates the contribution of ice sheets to sea-level rise. Antarctic surface melting is predicted to increase and trigger further ice-shelf disintegration during this century. These climate-change impacts could be modulated by an active hydrological network analogous to the one in operation in Greenland. Despite some observations of Antarctic surface and sub-surface hydrological systems, large-scale active surface drainage in Antarctica has rarely been studied. We use satellite imagery and aerial photography to reveal widespread active hydrology on the surface of the Antarctic Ice Sheet as far south as 85o and as high as 1800 m a.s.l., often near mountain peaks that protrude through the ice (nunataks) and relatively low-albedo `blue-ice areas'. Despite predominantly sub-zero regional air temperatures, as simulated by a regional climate model, Antarctic active drainage has persisted for decades, transporting water through surface streams and feeding vast melt ponds up to 80 km long. Drainage networks (the largest are over 100 km in length) form on flat ice shelves, steep outlet glaciers and ice-sheet flanks across the West and East Antarctica Ice Sheets. Motivated by the proximity of many drainage systems to low-albedo rock and blue-ice areas, we hypothesize a positive feedback between exposed-rock extent, BIA formation, melting and ice-sheet thinning. This feedback relies on drainage moving water long distances from areas near exposed rock, across the grounding line onto and across ice shelves - a process we observe, but had previously thought to be unlikely in Antarctica. This work highlights previously-overlooked processes, not captured by current regional-scale models, which may accelerate the retreat of the Antarctic Ice Sheet.

  8. 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.

  9. 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.

  10. Landscape evolution of Antarctica

    USGS Publications Warehouse

    Jamieson, S.S.R.; Sugden, D.E.

    2007-01-01

    shelf before retreating to its present dimensions at ~13.5 Ma. Subsequent changes in ice extent have been forced mainly by sea-level change. Weathering rates of exposed bedrock have been remarkably slow at high elevations around the margin of East Antarctica under the hyperarid polar climate of the last ~13.5 Ma, offering potential for a long quantitative record of ice-sheet evolution with techniques such as cosmogenic isotope analysis

  11. 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.

  12. Past ice-sheet behaviour: retreat scenarios and changing controls in the Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Halberstadt, Anna Ruth W.; Simkins, Lauren M.; Greenwood, Sarah L.; Anderson, John B.

    2016-05-01

    Studying the history of ice-sheet behaviour in the Ross Sea, Antarctica's largest drainage basin can improve our understanding of patterns and controls on marine-based ice-sheet dynamics and provide constraints for numerical ice-sheet models. Newly collected high-resolution multibeam bathymetry data, combined with two decades of legacy multibeam and seismic data, are used to map glacial landforms and reconstruct palaeo ice-sheet drainage. During the Last Glacial Maximum, grounded ice reached the continental shelf edge in the eastern but not western Ross Sea. Recessional geomorphic features in the western Ross Sea indicate virtually continuous back-stepping of the ice-sheet grounding line. In the eastern Ross Sea, well-preserved linear features and a lack of small-scale recessional landforms signify rapid lift-off of grounded ice from the bed. Physiography exerted a first-order control on regional ice behaviour, while sea floor geology played an important subsidiary role. Previously published deglacial scenarios for Ross Sea are based on low-spatial-resolution marine data or terrestrial observations; however, this study uses high-resolution basin-wide geomorphology to constrain grounding-line retreat on the continental shelf. Our analysis of retreat patterns suggests that (1) retreat from the western Ross Sea was complex due to strong physiographic controls on ice-sheet drainage; (2) retreat was asynchronous across the Ross Sea and between troughs; (3) the eastern Ross Sea largely deglaciated prior to the western Ross Sea following the formation of a large grounding-line embayment over Whales Deep; and (4) our glacial geomorphic reconstruction converges with recent numerical models that call for significant and complex East Antarctic ice sheet and West Antarctic ice sheet contributions to the ice flow in the Ross Sea.

  13. Topographic Steering of Enhanced Ice Flow at the Bottleneck Between East and West Antarctica

    NASA Astrophysics Data System (ADS)

    Winter, Kate; Ross, Neil; Ferraccioli, Fausto; Jordan, Tom A.; Corr, Hugh F. J.; Forsberg, René; Matsuoka, Kenichi; Olesen, Arne V.; Casal, Tania G.

    2018-05-01

    Hypothesized drawdown of the East Antarctic Ice Sheet through the "bottleneck" zone between East and West Antarctica would have significant impacts for a large proportion of the Antarctic Ice Sheet. Earth observation satellite orbits and a sparseness of radio echo sounding data have restricted investigations of basal boundary controls on ice flow in this region until now. New airborne radio echo sounding surveys reveal complex topography of high relief beneath the southernmost Weddell/Ross ice divide, with three subglacial troughs connecting interior Antarctica to the Foundation and Patuxent Ice Streams and Siple Coast ice streams. These troughs route enhanced ice flow through the interior of Antarctica but limit potential drawdown of the East Antarctic Ice Sheet through the bottleneck zone. In a thinning or retreating scenario, these topographically controlled corridors of enhanced flow could however drive ice divide migration and increase mass discharge from interior West Antarctica to the Southern Ocean.

  14. Under the sea ice: Exploring the relationship between sea ice and the foraging behaviour of southern elephant seals in East Antarctica

    NASA Astrophysics Data System (ADS)

    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

    2017-08-01

    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 ice (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 ice both supports a rich (under-ice) 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 ice 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 shelf between 2004 and 2014. These data indicate distinct general patterns of sea ice usage: while females tended to follow the sea ice edge as it extended northward, the males remained on the continental shelf despite increasing sea ice. 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 ice, ∼150-370 km south of the ice edge. Within persistent regions of compact sea ice, females had a longer foraging activity (i) in the highest sea ice concentration at their position, but (ii) their foraging activity was longer when there were more patches of low concentration sea ice around their position (either in time or in space; 30 days & 50 km). The high spatio-temporal variability of sea ice 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 ice-water interface or within the water column (from

  15. 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.

  16. 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.

  17. Deciphering tectonic phases of the Amundsen Sea Embayment shelf, West Antarctica, from a magnetic anomaly grid

    NASA Astrophysics Data System (ADS)

    Gohl, Karsten; Denk, Astrid; Eagles, Graeme; Wobbe, Florian

    2013-02-01

    The Amundsen Sea Embayment (ASE), with Pine Island Bay (PIB) in the eastern embayment, is a key location to understanding tectonic processes of the Pacific margin of West Antarctica. PIB has for a long time been suggested to contain the crustal boundary between the Thurston Island block and the Marie Byrd Land block. Plate tectonic reconstructions have shown that the initial rifting and breakup of New Zealand from West Antarctica occurred between Chatham Rise and the eastern Marie Byrd Land at the ASE. Recent concepts have discussed the possibility of PIB being the site of one of the eastern branches of the West Antarctic Rift System (WARS). About 30,000 km of aeromagnetic data - collected opportunistically by ship-based helicopter flights - and tracks of ship-borne magnetics were recorded over the ASE shelf during two RV Polarstern expeditions in 2006 and 2010. Grid processing, Euler deconvolution and 2D modelling were applied for the analysis of magnetic anomaly patterns, identification of structural lineaments and characterisation of magnetic source bodies. The grid clearly outlines the boundary zone between the inner shelf with outcropping basement rocks and the sedimentary basins of the middle to outer shelf. Distinct zones of anomaly patterns and lineaments can be associated with at least three tectonic phases from (1) magmatic emplacement zones of Cretaceous rifting and breakup (100-85 Ma), to (2) a southern distributed plate boundary zone of the Bellingshausen Plate (80-61 Ma) and (3) activities of the WARS indicated by NNE-SSW trending lineaments (55-30 Ma?). The analysis and interpretation are also used for constraining the directions of some of the flow paths of past grounded ice streams across the shelf.

  18. 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 ...

  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. 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.

  1. GPS-derived estimates of surface mass balance and ocean-induced basal melt for Pine Island Glacier ice shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    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.

    2017-11-01

    In the last 2 decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to marine ice-sheet instability and ice-shelf 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 shelf 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 ice-bottom acoustic ranging, phase-sensitive ice-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 ice-shelf mass balance studies, with implications for the sensitivity of ice-ocean interaction at PIG.

  2. Observations of the Summertime Boundary Layer over the Ross Ice Shelf, Antarctica Using SUMO UAVs

    NASA Astrophysics Data System (ADS)

    Nigro, M. A.; Cassano, J. J.; Jolly, B.; McDonald, A.

    2014-12-01

    During January 2014 Small Unmanned Meteorological Observer (SUMO) unmanned aerial vehicles (UAVs) were used to observe the boundary layer over the Ross Ice Shelf, Antarctica. A total of 41 SUMO flights were completed during a 9-day period with a maximum of 11 flights during a single day. Flights occurred as frequently as every 1.5 hours so that the time evolution of the boundary layer could be documented. On almost all of the flights the boundary layer was well mixed from the surface to a depth of less than 50 m to over 350 m. The depth of the well-mixed layer was observed to both increase and decrease over the course of an individual day suggesting that processes other than entrainment were altering the boundary layer depth. The well-mixed layer was observed to both warm and cool during the field campaign indicating that advective processes as well as surface fluxes were acting to control the temporal evolution of the boundary layer temperature. Only a small number of weakly stably stratified boundary layers were observed. Strong, shallow inversions, of up to 6 K, were observed above the top of the boundary layer. Observations from a 30 m automatic weather station and two temporary automatic weather stations 10 km south and west of the main field campaign location provide additional data for understanding the boundary layer evolution observed by the SUMO UAVs during this 9-day period. This presentation will discuss the observed evolution of the summertime boundary layer as well as comment on lessons learned operating the SUMO UAVs at a remote Antarctic field camp.

  3. Bacterial abundance and composition in marine sediments beneath the Ross Ice Shelf, Antarctica.

    PubMed

    Carr, S A; Vogel, S W; Dunbar, R B; Brandes, J; Spear, J R; Levy, R; Naish, T R; Powell, R D; Wakeham, S G; Mandernack, K W

    2013-07-01

    Marine sediments of the Ross Sea, Antarctica, harbor microbial communities that play a significant role in the decomposition, mineralization, and recycling of organic carbon (OC). In this study, the cell densities within a 153-cm sediment core from the Ross Sea were estimated based on microbial phospholipid fatty acid (PLFA) concentrations and acridine orange direct cell counts. The resulting densities were as high as 1.7 × 10⁷ cells mL⁻¹ in the top ten centimeters of sediments. These densities are lower than those calculated for most near-shore sites but consistent with deep-sea locations with comparable sedimentation rates. The δ¹³C measurements of PLFAs and sedimentary and dissolved carbon sources, in combination with ribosomal RNA (SSU rRNA) gene pyrosequencing, were used to infer microbial metabolic pathways. The δ¹³C values of dissolved inorganic carbon (DIC) in porewaters ranged downcore from -2.5‰ to -3.7‰, while δ¹³C values for the corresponding sedimentary particulate OC (POC) varied from -26.2‰ to -23.1‰. The δ¹³C values of PLFAs ranged between -29‰ and -35‰ throughout the sediment core, consistent with a microbial community dominated by heterotrophs. The SSU rRNA gene pyrosequencing revealed that members of this microbial community were dominated by β-, δ-, and γ-Proteobacteria, Actinobacteria, Chloroflexi and Bacteroidetes. Among the sequenced organisms, many appear to be related to known heterotrophs that utilize OC sources such as amino acids, oligosaccharides, and lactose, consistent with our interpretation from δ¹³CPLFA analysis. Integrating phospholipids analyses with porewater chemistry, δ¹³CDIC and δ¹³CPOC values and SSU rRNA gene sequences provides a more comprehensive understanding of microbial communities and carbon cycling in marine sediments, including those of this unique ice shelf environment. © 2013 John Wiley & Sons Ltd.

  4. 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

  5. Geoengineering Marine Ice Sheets

    NASA Astrophysics Data System (ADS)

    Wolovick, M.

    2017-12-01

    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 ice shelf 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 ice sheet may even enter a runaway collapse via the marine ice sheet instability. The warm water that triggers this process resides offshore at depth and accesses the grounding line through deep troughs in the continental shelf. 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 ice 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-ice cavity causes ice shelf thickening, increased buttressing, and grounding line readvance. The increase in buttressing is greatly magnified if the thickened ice shelf 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 ice sheet collapse. If the ice shelf regrounds on the artificial sill itself, erosion of the sill beneath the grounded ice 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

  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. 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.

  8. Seismic stratigraphy and tomography in the outer shelf and slope of the Central Basin, Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Kim, Sookwan; De Santis, Laura; Böhm, Gualtiero; Kuk Hong, Jong; Jin, Young Keun; Geletti, Riccardo; Wardell, Nigel; Petronio, Lorenzo; Colizza, Ester

    2014-05-01

    The Ross Sea, located between Victoria Land and Marie Byrd Land in Antarctica, is one of the main drainage of the Antarctic Ice Sheet (AIS). Reflection seismic data acquired by many countries during several decades have provided insights into the history of the Ross Sea and the AIS evolution. However the majority of the existing seismic data are concentrated in the shelf area, where hiatus formed by grounding ice sheet erosion multiple events prevent to reconstruct the entire sedimentary sequences depositional evolution. On the outer shelf and upper slope, the sedimentary sequences are relatively well preserved. The main purpose of this study is the investigation of the Cenozoic Antarctic Ice Sheet evolution through the seismic sequence analysis of the outer shelf and slope of the Central Basin, in the Ross Sea. The data used are the new multi-channel seismic data, KSL12, were acquired on the outer shelf and upper slope of the Central Bain in February 2013 by Korea Polar Research Institute. The reflection seismic data, previously collected by the Italian Antarctic Program (PNRA) and other data available from the Seismic Data Library System (SDLS) are also used for velocity tomography and seismic sequence mapping. The seismic data were processed by a conventional processing flow to produce the seismic profiles. Preliminary results show well-developed prograding wedges at the mouth of glacial troughs, eroded by a major glacial unconformity, the Ross Sea Unconformity 4 (RSU-4), correlated to a main event between early- and mid-Miocene. The velocity anomalies shown along KSL12-1 can be interpreted as showing the occurrence of gas and fluids, diagenetic horizons and sediment compactions. The isopach maps of each sequence show the variation of thickness of the sediments depocenter shift. The seismic sequence stratigraphy and acoustic facies analysis provide information about different phases of ice sheet's advance and retreat related to the AIS Cenozoic dynamics.

  9. High-resolution sub-ice-shelf seafloor records of twentieth century ungrounding and retreat of Pine Island Glacier, West Antarctica

    NASA Astrophysics Data System (ADS)

    Davies, D.; Bingham, R. G.; Graham, A. G. C.; Spagnolo, M.; Dutrieux, P.; Vaughan, D. G.; Jenkins, A.; Nitsche, F. O.

    2017-09-01

    Pine Island Glacier Ice Shelf (PIGIS) has been thinning rapidly over recent decades, resulting in a progressive drawdown of the inland ice and an upstream migration of the grounding line. The resultant ice loss from Pine Island Glacier (PIG) and its neighboring ice streams presently contributes an estimated ˜10% to global sea level rise, motivating efforts to constrain better the rate of future ice 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 ice flow, proglacial and subglacial sediment transport, overprinting of lightly grounded ice-shelf 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.

  10. Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

    DOE PAGES

    Favier, Lionel; Pattyn, Frank; Berger, Sophie; ...

    2016-11-09

    The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouinmore » ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10%, while omitting the same pinning point in data assimilation decreases it by 10%, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. As a result, pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.« less

  11. Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

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

    Favier, Lionel; Pattyn, Frank; Berger, Sophie

    The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouinmore » ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10%, while omitting the same pinning point in data assimilation decreases it by 10%, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. As a result, pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.« less

  12. 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.

  13. 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

  14. Balloons on Ice: NASA Launches Antarctica Scientific Balloon Campaign

    NASA Image and Video Library

    2017-12-08

    Cosmic rays and the chemicals and atoms that make up the interstellar space between stars are the focus of this year’s NASA Antarctica Long Duration Balloon Flight Campaign, which kicked into high gear with the launch of the Boron And Carbon Cosmic rays in the Upper Stratosphere (BACCUS) payload Nov. 28. The University of Maryland’s BACCUS mission is the first of three payloads taking flight from a balloon launch site on Antarctica’s Ross Ice Shelf near McMurdo Station with support from the National Science Foundation’s United States Antarctic Program. Read more: go.nasa.gov/2gCMtyP 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

  15. 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.

  16. Modelling the bathymetry of the Antarctic continental shelf

    USGS Publications Warehouse

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

    1992-01-01

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

  17. Construction, maintenance, and operation of a glacial runway : McMurdo Station, Antarctica

    DOT National Transportation Integrated Search

    1998-03-01

    On February 7, 1994, a C-141 departed Christchurch, New Zealand, and landed on the 3050-m (10,000-ft) Pegasus glacial ice runway, located on the Ross Ice Shelf 13 km (8 mi) south of McMurdo, Antarctica. This event marked the final test for a five-yea...

  18. 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.

  19. The geomorphic signature of present ice-sheet flow in the radar-sounded subglacial record: Pine Island Glacier, West Antarctica

    NASA Astrophysics Data System (ADS)

    Bingham, R. G.; Davies, D.; King, E. C.; Vaughan, D. G.; Cornford, S. L.; Brisbourne, A.; Smith, A.; De Rydt, J.; Graham, A. G. C.; Spagnolo, M.

    2016-12-01

    Deglaciated landscapes and landforms are much used in the quest to reconstruct past ice-sheet behaviour, on the principle that aspects of landform shapes, sizes and relative associations "fossilise" palaeo-ice-sheet processes. Such techniques have been widely used around the margin of the marine West Antarctic Ice Sheet, taking advantage of bathymetric surveying techniques which have exposed a rich suite of landform assemblages across West Antarctica's continental shelf. Though these geomorphological interpretations are solidly grounded in glacial geological theory, there has, until now, been little ability to compare these deglaciated, and potentially postglacially-modified, landforms offshore with landforms currently situated (and potentially still evolving) beneath the contemporary ice sheet. This paper presents a widespread view of glacial landforms presently situated beneath 1-2 km of ice in multi-square-km "windows to the bed" distributed throughout the catchment of Pine Island Glacier, West Antarctica. Imaged over three field seasons between 2007 and 2013 by dedicated radar surveys designed specifically to capture landforms analogous to those surveyed offshore by bathymetric surveying, the results provide significant insights for the interpretation of palaeo-ice-stream landforms, and their use in modelling ice-ocean interactions around the fringes of marine ice sheets. We show that landform sizes, shapes and associations vary significantly around Pine Island Glacier's catchment. The key controls appear to be substrate composition, pre-existing tectonic structure, and longstanding spatial stability of the ice-stream's flow distribution. The findings offer crucial information for modelling ice coupling to the bed, which should feed through to wider efforts to reconstruct the past behaviour of this significant marine ice sheet using its palaeoglacial landforms.

  20. Geoologic controls on the architecture of the Antarctic Ice Sheet's basal interface: New results from West and East Antarctica from long range geophysics (Invited)

    NASA Astrophysics Data System (ADS)

    Young, D. A.; Blankenship, D. D.; Greenbaum, J. S.; Richter, T.; Aitken, A.; Siegert, M. J.; Roberts, J. L.

    2013-12-01

    The ice-rock interface underlying the Antarctic Ice Sheet was shaped by interactions between underlying gondwanan geology and the overlying ice sheet. The ice sheet now preserves from sedimentary infill an incredibly rugged terrain which now plays a critical role in shaping subglacial hydrology, and thus shape ice sheet behavior. This terrain can by imaged through aerogeophysical means, in particular through ice penetrating radar, while airborne potential fields measurements provide insight into the geological framework that controlled erosion. Over the post IPY era, the density of airborne coverage is only now reaching the point where small scale structure can be identified and placed in context. Of particular importance is understanding the formation of focused erosional valleys, 30-50 km wide, representing now buried subglacial fjords. After initial data from the GIMBLE project in West Antarctica, and five years of sustained long range ICECAP surveys over East Antarctica , we now have a better view of the diversity of these features. The local erosion of these valleys, often cutting through significant topographic barriers, irregularly samples the underlying geology, provided a complex story in the sediment to the Antarctic margin. These valleys now provide the subglacial conduits for significant ice sheet catchments, in particular for subglacial water, including the inland catchments of DeVicq, Thwaites, and Pine Island Glaciers in West Antarctica, and Denman Glacier, Totten Glacier, Byrd Glacier and Cook Ice Shelf in East Antarctica. We find that these features, now sometimes hundreds of kilometers inland of the modern grounding line, often nucleate on or are aligned with structure inherited from the assembly of the Antarctic continent. While many of these features currently host active outlet glaciers or their tributaries, some do not, implying avenues for ice sheet change. In West Antarctica, we find a new deep connection between the coast and interior basin

  1. Sensitivity analysis of sea level rise contribution depending on external forcing: A case study of Victoria Land, East Antarctica.

    NASA Astrophysics Data System (ADS)

    Park, I. W.; Lee, S. H.; Lee, W. S.; Lee, C. K.; Lee, K. K.

    2017-12-01

    As global mean temperature increases, it affects increase in polar glacier melt and thermal expansion of sea, which contributed to global sea level rise. Unlike large sea level rise contributors in Western Antarctica (e. g. Pine island glacier, Thwaites glacier), glaciers in East Antarctica shows relatively stable and slow ice velocity. However, recent calving events related to increase of supraglacier lake in Nansen ice shelf arouse the questions in regards to future evolution of ice dynamics at Victoria Land, East Antarctica. Here, using Ice Sheet System Model (ISSM), a series of numerical simulations were carried out to investigate ice dynamics evolution (grounding line migration, ice velocity) and sea level rise contribution in response to external forcing conditions (surface mass balance, floating ice melting rate, and ice front retreat). In this study, we used control method to set ice dynamic properties (ice rigidity and friction coefficient) with shallow shelf approximation model and check each external forcing conditions contributing to sea level change. Before 50-year transient simulations were conducted based on changing surface mass balance, floating ice melting rate, and ice front retreat of Drygalski ice tongue and Nansen ice shelf, relaxation was performed for 10 years to reduce non-physical undulation and it was used as initial condition. The simulation results showed that sea level rise contribution were expected to be much less compared to other fast glaciers. Floating ice melting rate was most sensitive parameter to sea level rise, while ice front retreat of Drygalski tongue was negligible. The regional model will be further updated utilizing ice radar topography and measured floating ice melting rate.

  2. Data report for the Siple Coast (Antarctica) project

    NASA Technical Reports Server (NTRS)

    Bindschadler, R. A.; Stephenson, S. N.; Roberts, E. P.; Macayeal, D. R.; Lindstrom, D. R.

    1988-01-01

    This report presents data collected during three field seasons of glaciological studies in the Antarctica and describes the methods employed. The region investigated covers the mouths of Ice Streams B and C (the Siple Coast) and Crary Ice Rise on the Ross Ice Shelf. Measurements included in the report are as follows: surface velocity and deformation from repeated satellite geoceiver positions; surface topography from optical levelling; radar sounding of ice thickness; accumulation rates; near-surface densities and temperature profiles; and mapping from aerial photography.

  3. 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.

  4. 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

  5. Basal channels on ice shelves

    NASA Astrophysics Data System (ADS)

    Sergienko, O. V.

    2013-09-01

    Recent surveys of floating ice 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-ice-shelf cavity. The formation of the channels, their evolution over time, and their impact on ice-shelf flow are investigated using a fully-coupled ice-shelf/sub-ice-shelf 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 ice-flow variability in ice-shelf 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 ice bottom between the channels. The melt channels develop through melting, deformation, and advection with ice-shelf flow. Simulations suggest that both steady state and cyclic state solutions are possible depending on conditions along the lateral ice-shelf 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 ice-shelf behavior in warm oceanic conditions.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Coastal-change and glaciological map of the Ross Island area, Antarctica

    USGS Publications Warehouse

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

    2010-01-01

    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. The Ross Island area map is bounded by long 141? E. and 175? E. and by lat 76? S. and 81? S. The map covers the part of southern Victoria Land that includes the northwestern Ross Ice Shelf, the McMurdo Ice Shelf, part of the polar plateau and Transantarctic Mountains, the McMurdo Dry Valleys, northernmost Shackleton Coast, Hillary Coast, the southern part of Scott Coast, and Ross Island. Little noticeable change has occurred in the ice fronts on the map, so the focus is on glaciological features. In the western part of the map area, the polar plateau of East Antarctica, once thought to be a featureless region, has subtle wavelike surface forms (megadunes) and flow traces of glaciers that originate far inland and extend to the coast or into the Ross Ice Shelf. There are numerous outlet glaciers. Glaciers drain into the McMurdo Dry Valleys, through the Transantarctic Mountains into the Ross Sea, or into the Ross Ice Shelf. Byrd Glacier is the largest. West of the Transantarctic Mountains are areas of blue ice, readily identifiable on Landsat images, that have been determined to be prime areas for finding meteorites. Three subglacial lakes have been identified in the map area. Because McMurdo Station, the main U.S. scientific research station in Antarctica, is located on Ross Island in the map area, many of these and other features in the area have been studied extensively. The paper version of this map is

  11. Formation of melt channels on ice shelves

    NASA Astrophysics Data System (ADS)

    Sergienko, Olga

    2013-04-01

    Melt channels have been observed on ice shelves experiencing strong melting in both Greenland (Petermann Glacier) and Antarctica (Pine Island Glacier). Using a fully-couple ice-shelf/sub-ice-shelf-ocean flow model, it is demonstrated that these channels can form spontaneously in laterally confined ice 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 ice bottom. In circumstances where an ice shelf has no-slip conditions at its lateral boundaries, the ice-shelf/sub-ice-shelf-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 ice-shelf thickness are caused by internal dynamics of the melt channels, and, in contrast to traditional interpretation, can be independent of the oceanic forcings.

  12. 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.

  13. 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.

  14. Glacio-isostasy and Glacial Ice Load at Law Dome, Wilkes Land, East Antarctica

    NASA Astrophysics Data System (ADS)

    Goodwin, Ian D.; Zweck, Christopher

    2000-05-01

    The Holocene sea-level high stand or "marine limit" in Wilkes Land, East Antarctica, reached ˜30 m above present sea level at a few dispersed sites. The most detailed marine limit data have been recorded for the Windmill Islands and Budd Coast at the margin of the Law Dome ice cap, a dome of the East Antarctic Ice Sheet (EAIS). Relative sea-level lowering of 30 m and the associated emergence of the Windmill Islands have occurred since 6900 14C (corr.) yr B.P. Numerical modeling of the Earth's rheology is used to determine the glacio-isostatic component of the observed relative sea-level lowering. Glaciological evidence suggests that most of EAIS thickening occurred around its margin, with expansion onto the continental shelf. Consequently, a regional ice history for the last glacial maximum (LGM) was applied in the glacio-isostatic modeling to test whether the observed relative sea-level lowering was primarily produced by regional ice-sheet changes. The results of the modeling indicate that the postglacial (13,000 to 8000 14C yr B.P) removal of an ice load of between 770 and 1000 m from around the margin of the Law Dome and adjacent EAIS have produced the observed relative sea-level lowering. Such an additional ice load would have been associated with a 40- to 65-km expansion of the Law Dome to near the continental shelf break, together with a few hundred meters of ice thickening on the adjoining coastal slope of the EAIS up to 2000 m elevation. Whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes, the glacio-isostatic response at the Windmill Islands results from a combination of regional and, to a lesser extent, Antarctic-wide effects. The correspondence between the Holocene relative sea-level lowering interpreted at the margin of the Law Dome and the lowering interpreted along the remainder of the Wilkes Land and Oates Land coasts (105°-160° E) suggests that a similar ice load of up to 1000 m

  15. Detection and Analysis of Complex Patterns of Ice Dynamics in Antarctica from ICESat Laser Altimetry

    NASA Astrophysics Data System (ADS)

    Babonis, Gregory Scott

    There remains much uncertainty in estimating the amount of Antarctic ice mass change, its dynamic component, and its spatial and temporal patterns. This work remedies the limitations of previous studies by generating the first detailed reconstruction of total and dynamic ice thickness and mass changes across Antarctica, from ICESat satellite altimetry observations in 2003-2009 using the Surface Elevation Reconstruction and Change Detection (SERAC) method. Ice sheet thickness changes are calculated with quantified error estimates for each time when ICESat flew over a ground-track crossover region, at approximately 110,000 locations across the Antarctic Ice Sheet. The time series are partitioned into changes due to surficial processes and ice dynamics. The new results markedly improve the spatial and temporal resolution of surface elevation, volume, and mass change rates for the AIS, and can be sampled at annual temporal resolutions. The results indicate a complex spatiotemporal pattern of dynamic mass loss in Antarctica, especially along individual outlet glaciers, and allow for the quantification of the annual contribution of Antarctic ice loss to sea level rise. Over 5000 individual locations exhibit either strong dynamic ice thickness change patterns, accounting for approximately 500 unique spatial clusters that identify regions likely influenced by subglacial hydrology. The spatial distribution and temporal behavior of these regions reveal the complexity and short-time scale variability in the subglacial hydrological system. From the 500 unique spatial clusters, over 370 represent newly identified, and not previously published, potential subglacial water bodies indicating an active subglacial hydrological system over a much larger region than previously observed. These numerous new observations of dynamic changes provide more than simply a larger set of data. Examination of both regional and local scale dynamic change patterns across Antarctica shows newly

  16. 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

  17. Life on ice, Antarctica and Mars

    NASA Technical Reports Server (NTRS)

    Anderson, D. T.; Mckay, C. P.; Wharton, Robert A., Jr.; Sagan, C.; Squyres, S. W.; Simmons, G. M.

    1991-01-01

    The study of the origin of life and the prospects for human exploration of Mars are two themes developed in a new 57-minute film, Life on Ice, Antarctica, and Mars, produced by the InnerSpace Foundation and WHRO Television for broadcast by the Public Broadcasting System (PBS). A brief explanation of the film and how it relates to the future human exploration of space is presented.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. Natural constraints on exploring Antarctica's continental margin, existing geophysical and geological data basis, and proposed drilling program

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

    Anderson, J.B.

    1987-05-01

    There have been a number of multichannel seismic reflection and seismic refraction surveys of the Antarctic continental shelf. While glacial erosion has left acoustic basement exposed on portions of the inner shelf, thick sedimentary sequences occur on the passive margin of east Antarctica. The thickness and age of these strata vary due to different breakup histories of the margin. Several sedimentary basins have been identified. Most are rift basins formed during the early stages of Antarctica's separation from other Gondwana continents and plateaus. The west Antarctic continental shelf is extensive, being approximately twice the size of the Gulf of Mexicomore » shelf. It has been poorly surveyed to date, owing mainly to its perennial sea ice cover. Gradual subduction of the spreading center from south to north along the margin resulted in old active margin sequences being buried beneath passive margin sequences. The latter should increase in thickness from north to south along the margin although no data bear this out. Hydrocarbon potential on the northern portion of the west Antarctic margin is considered low due to a probable lack of reservoir rocks. Establishment of ice sheets on Antarctica caused destruction of land vegetation and greatly restricted siliciclastic sand-producing environments. So only sedimentary basins which contain pre-early Miocene deposits have good hydrocarbon prospectivity. The Antarctic continental shelf is the deepest in the world, averaging 500 m and in places being more than a kilometer deep. The shelf has been left rugged by glacial erosion and is therefore prone to sediment mass movement. Widespread sediment gravity flow deposits attest to this. The shelf is covered with sea ice most of the year and in a few areas throughout the year. Icebergs, drift freely in the deep waters of the shelf; drift speeds of 1 to 2.5 km/year are not uncommon.« less

  3. Ice shelf melt rates in Greenland and Antarctica using time-tagged digital imagery from World View and TanDEM-X

    NASA Astrophysics Data System (ADS)

    Charolais, A.; Rignot, E. J.; Milillo, P.; Scheuchl, B.; Mouginot, J.

    2017-12-01

    The floating extensions of glaciers, or ice 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/ice mixture and 2) subglacial water injects fresh, buoyant, cold melt water to fuel stronger ice-ocean interactions. Melt also forms along preferential channels, which are not stationary, and create lines of weakness in the shelf. Ice shelf melt rates have been successfully measured from space over the entire Antarctic continent and on the ice shelves in Greenland using an Eulerian approach that combines ice thickness, ice velocity vectors, surface mass balance data, and measurements of ice 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 ice sheet modeling. This work is funded by a grant from NASA Cryosphere Program.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  5. 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

  6. In-situ GPS records of surface mass balance, firn compaction rates, and ice-shelf basal melt rates for Pine Island Glacier, Antarctica

    NASA Astrophysics Data System (ADS)

    Shean, D. E.; Christianson, K.; Larson, K. M.; Ligtenberg, S.; Joughin, I. R.; Smith, B.; Stevens, C.

    2016-12-01

    In recent decades, Pine Island Glacier (PIG) has experienced marked retreat, speedup and thinning due to ice-shelf basal melt, internal ice-stream instability and feedbacks between these processes. In an effort to constrain recent ice-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 shelf 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 shelf and 4 m/yr for the South shelf. These melt rates are similar to those derived from ice-bottom acoustic ranging, phase-sensitive ice-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-shelf melt rates are less sensitive to

  7. Antarctica: Is It More Than Just Ice?

    ERIC Educational Resources Information Center

    Johnson, Cheryl; Gutierrez, Melida

    2009-01-01

    The authors introduced polar science in a fourth-grade classroom by means of 3 hands-on activities that addressed (1) the melting of glaciers and ice, (2) the differences between the North and the South Pole, and (3) the geography and landforms of Antarctica. An assessment 4 months after the original activity showed that students remembered the…

  8. Clouds and Ice of the Lambert-Amery System, East Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These views from the Multi-angle Imaging SpectroRadiometer (MISR) illustrate ice surface textures and cloud-top heights over the Amery Ice Shelf/Lambert Glacier system in East Antarctica on October 25, 2002.

    The left-hand panel is a natural-color view from MISR's downward-looking (nadir) camera. The center panel is a multi-angular composite from three MISR cameras, in which color acts as a proxy for angular reflectance variations related to texture. Here, data from the red-band of MISR's 60o forward-viewing, nadir and 60o backward-viewing cameras are displayed as red, green and blue, respectively. With this display technique, surfaces which predominantly exhibit backward-scattering (generally rough surfaces) appear red/orange, while surfaces which predominantly exhibit forward-scattering (generally smooth surfaces) appear blue. Textural variation for both the grounded and sea ice are apparent. The red/orange pixels in the lower portion of the image correspond with a rough and crevassed region near the grounding zone, that is, the area where the Lambert and four other smaller glaciers merge and the ice starts to float as it forms the Amery Ice Shelf. In the natural-color view, this rough ice is spectrally blue in color.

    Clouds exhibit both forward and backward-scattering properties in the middle panel and thus appear purple, in distinct contrast with the underlying ice and snow. An additional multi-angular technique for differentiating clouds from ice is shown in the right-hand panel, which is a stereoscopically derived height field retrieved using automated pattern recognition involving data from multiple MISR cameras. Areas exhibiting insufficient spatial contrast for stereoscopic retrieval are shown in dark gray. Clouds are apparent as a result of their heights above the surface terrain. Polar clouds are an important factor in weather and climate. Inadequate characterization of cloud properties is currently responsible for large uncertainties in climate

  9. 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.

  10. Under Sea Ice phytoplankton bloom detection and contamination in Antarctica

    NASA Astrophysics Data System (ADS)

    Zeng, C.; Zeng, T.; Xu, H.

    2017-12-01

    Previous researches reported compelling sea ice phytoplankton bloom in Arctic, while seldom reports studied about Antarctic. Here, lab experiment showed sea ice increased the visible light albedo of the water leaving radiance. Even a new formed sea ice of 10cm thickness increased water leaving radiance up to 4 times of its original bare water. Given that phytoplankton preferred growing and accumulating under the sea ice with thickness of 10cm-1m, our results showed that the changing rate of OC4 estimated [Chl-a] varied from 0.01-0.5mg/m3 to 0.2-0.3mg/m3, if the water covered by 10cm sea ice. Going further, varying thickness of sea ice modulated the changing rate of estimating [Chl-a] non-linearly, thus current routine OC4 model cannot estimate under sea ice [Chl-a] appropriately. Besides, marginal sea ice zone has a large amount of mixture regions containing sea ice, water and snow, where is favorable for phytoplankton. We applied 6S model to estimate the sea ice/snow contamination on sub-pixel water leaving radiance of 4.25km spatial resolution ocean color products. Results showed that sea ice/snow scale effectiveness overestimated [Chl-a] concentration based on routine band ratio OC4 model, which contamination increased with the rising fraction of sea ice/snow within one pixel. Finally, we analyzed the under sea ice bloom in Antarctica based on the [Chl-a] concentration trends during 21 days after sea ice retreating. Regardless of those overestimation caused by sea ice/snow sub scale contamination, we still did not see significant under sea ice blooms in Antarctica in 2012-2017 compared with Arctic. This research found that Southern Ocean is not favorable for under sea ice blooms and the phytoplankton bloom preferred to occur in at least 3 weeks after sea ice retreating.

  11. 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.

  12. 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.

  13. Perennially ice-covered Lake Hoare, Antarctica: physical environment, biology and sedimentation

    NASA Technical Reports Server (NTRS)

    Wharton, R. A. Jr; Simmons, G. M. Jr; McKay, C. P.; Wharton RA, J. r. (Principal Investigator)

    1989-01-01

    Lake Hoare (77 degrees 38' S, 162 degrees 53' E) is a perennially ice-covered lake at the eastern end of Taylor Valley in southern Victoria Land, Antarctica. The environment of this lake is controlled by the relatively thick ice cover (3-5 m) which eliminates wind generated currents, restricts gas exchange and sediment deposition, and reduces light penetration. The ice cover is in turn largely controlled by the extreme seasonality of Antarctica and local climate. Lake Hoare and other dry valley lakes may be sensitive indicators of short term (< 100 yr) climatic and/or anthropogenic changes in the dry valleys since the onset of intensive exploration over 30 years ago. The time constants for turnover of the water column and lake ice are 50 and 10 years, respectively. The turnover time for atmospheric gases in the lake is 30-60 years. Therefore, the lake environment responds to changes on a 10-100 year timescale. Because the ice cover has a controlling influence on the lake (e.g. light penetration, gas content of water, and sediment deposition), it is probable that small changes in ice ablation, sediment loading on the ice cover, or glacial meltwater (or groundwater) inflow will affect ice cover dynamics and will have a major impact on the lake environment and biota.

  14. New constraints on the structure and dynamics of the East Antarctic Ice Sheet from the joint IPY/Ice Bridge ICECAP aerogeophysical project

    NASA Astrophysics Data System (ADS)

    Blankenship, D. D.; Young, D. A.; Siegert, M. J.; van Ommen, T. D.; Roberts, J. L.; Wright, A.; Warner, R. C.; Holt, J. W.; Young, N. W.; Le Meur, E.; Legresy, B.; Cavitte, M.; Icecap Team

    2010-12-01

    Ice within marine basins of East Antarctica, and their outlets, represent the ultimate limit on sea level change. The region of East Antarctica between the Ross Sea and Wilkes Land hosts a number of major basin, but has been poorly understood. Long range aerogeophysics from US, Australian and French stations, with significant British and IceBridge support, has, under the banner of the ICECAP project, greatly improved our knowledge of ice thickness, surface elevation, and crustal structure of the Wilkes and Aurora Subglacial Basins, as well as the Totten Glacier, Cook Ice Shelf, and Byrd Glacier. We will discuss the evolution of the Wilkes and Aurora Subglacial Basins, new constraints on the geometry of the major outlet glaciers, as well as our results from surface elevation change measurements over dynamic regions of the ice sheet. We will discuss the implications of our data for the presence of mid Pleistocene ice in central East Antarctica. Future directions for ICECAP will be discussed.

  15. The surface climatology of the Ross Ice Shelf Antarctica.

    PubMed

    Costanza, Carol A; Lazzara, Matthew A; Keller, Linda M; Cassano, John J

    2016-12-01

    The University of Wisconsin-Madison Antarctic Automatic Weather Station (AWS) project has been making meteorological surface observations on the Ross Ice Shelf (RIS) for approximately 30 years. This network offers the most continuous set of routine measurements of surface meteorological variables in this region. The Ross Island area is excluded from this study. The surface climate of the RIS is described using the AWS measurements. Temperature, pressure, and wind data are analysed on daily, monthly, seasonal, and annual time periods for 13 AWS across the RIS. The AWS are separated into three representative regions - central, coastal, and the area along the Transantarctic Mountains - in order to describe specific characteristics of sections of the RIS. The climatology describes general characteristics of the region and significant changes over time. The central AWS experiences the coldest mean temperature, and the lowest resultant wind speed. These AWSs also experience the coldest potential temperatures with a minimum of 209.3 K at Gill AWS. The AWS along the Transantarctic Mountains experiences the warmest mean temperature, the highest mean sea-level pressure, and the highest mean resultant wind speed. Finally, the coastal AWS experiences the lowest mean pressure. Climate indices (MEI, SAM, and SAO) are compared to temperature and pressure data of four of the AWS with the longest observation periods, and significant correlation is found for most AWS in sea-level pressure and temperature. This climatology study highlights characteristics that influence the climate of the RIS, and the challenges of maintaining a long-term Antarctic AWS network. Results from this effort are essential for the broader Antarctic meteorology community for future research.

  16. The surface climatology of the Ross Ice Shelf Antarctica

    PubMed Central

    Lazzara, Matthew A.; Keller, Linda M.; Cassano, John J.

    2016-01-01

    ABSTRACT The University of Wisconsin‐Madison Antarctic Automatic Weather Station (AWS) project has been making meteorological surface observations on the Ross Ice Shelf (RIS) for approximately 30 years. This network offers the most continuous set of routine measurements of surface meteorological variables in this region. The Ross Island area is excluded from this study. The surface climate of the RIS is described using the AWS measurements. Temperature, pressure, and wind data are analysed on daily, monthly, seasonal, and annual time periods for 13 AWS across the RIS. The AWS are separated into three representative regions – central, coastal, and the area along the Transantarctic Mountains – in order to describe specific characteristics of sections of the RIS. The climatology describes general characteristics of the region and significant changes over time. The central AWS experiences the coldest mean temperature, and the lowest resultant wind speed. These AWSs also experience the coldest potential temperatures with a minimum of 209.3 K at Gill AWS. The AWS along the Transantarctic Mountains experiences the warmest mean temperature, the highest mean sea‐level pressure, and the highest mean resultant wind speed. Finally, the coastal AWS experiences the lowest mean pressure. Climate indices (MEI, SAM, and SAO) are compared to temperature and pressure data of four of the AWS with the longest observation periods, and significant correlation is found for most AWS in sea‐level pressure and temperature. This climatology study highlights characteristics that influence the climate of the RIS, and the challenges of maintaining a long‐term Antarctic AWS network. Results from this effort are essential for the broader Antarctic meteorology community for future research. PMID:28008213

  17. Ice crystal precipitation at Dome C site (East Antarctica)

    NASA Astrophysics Data System (ADS)

    Santachiara, G.; Belosi, F.; Prodi, F.

    2016-01-01

    For the first time, falling ice crystals were collected on glass slides covered with a thin layer of 2% formvar in chloroform at the Dome Concordia site (Dome C), Antarctica. Samplings were performed in the framework of the 27th Italian Antarctica expedition of the Italian National Program for Research in Antarctica in the period 21 February-6 August 2012. Events of clear-sky precipitations and precipitations from clouds were considered and the replicas obtained were examined under Scanning Electron Microscope (SEM). Several shapes of ice crystals were identified, including ;diamond dust; (plates, pyramids, hollow and solid columns), and crystal aggregates varying in complexity. Single events often contained both small (10 μm to 50 μm) and large (hundreds of microns) crystals, suggesting that crystals can form simultaneously near the ground (height of a few hundred metres) and at higher layers (height of thousands of metres). Images of sampled crystal replicas showed that single bullets are not produced separately, but by the disintegration of combinations of bullets. Rimed ice crystals were absent in the Dome C samples, i.e. the only mode of crystal growth was water vapour diffusion. On considering the aerosol in the sampled crystals, we reached the conclusion that inertial impaction, interception and Brownian motion were insufficient to explain the scavenged aerosol. We therefore presume that phoretic forces play a role in scavenging during the crystal growth process.

  18. 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.

  19. Combined Gravimetric-Seismic Crustal Model for Antarctica

    NASA Astrophysics Data System (ADS)

    Baranov, Alexey; Tenzer, Robert; Bagherbandi, Mohammad

    2018-01-01

    The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz's inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48-50 km) and the Kottas Mountains (48-50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34-38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24

  20. Ice recrystallization inhibition proteins (IRIPs) and freeze tolerance in the cryophilic Antarctic hair grass Deschampsia antarctica E. Desv.

    PubMed

    John, Ulrik P; Polotnianka, Renatam M; Sivakumaran, Kailayapillai A; Chew, Orinda; Mackin, Leanne; Kuiper, Micheal J; Talbot, Jonathan P; Nugent, Gregory D; Mautord, Julie; Schrauf, Gustavo E; Spangenberg, German C

    2009-04-01

    Antarctic hair grass (Deschampsia antarctica E. Desv.), the only grass indigenous to Antarctica, has well-developed freezing tolerance, strongly induced by cold acclimation. Here, we show that in response to low temperatures, D. antarctica expresses potent recrystallization inhibition (RI) activity that, inhibits the growth of small ice crystals into potentially damaging large ones, is proteinaceous and localized to the apoplasm. A gene family from D. antarctica encoding putative homologs of an ice recrystallization inhibition protein (IRIP) has been isolated and characterized. IRIPs are apoplastically targeted proteins with two potential ice-binding motifs: 1-9 leucine-rich repeats (LRRs) and c. 16 'IRIP' repeats. IRIP genes appear to be confined to the grass subfamily Pooideae and their products, exhibit sequence similarity to phytosulphokine receptors and are predicted to adopt conformations with two ice-binding surfaces. D. antarctica IRIP (DaIRIP) transcript levels are greatly enhanced in leaf tissue following cold acclimation. Transgenic Arabidopsis thaliana expressing a DaIRIP has novel RI activity, and purified DaIRIP, when added back to extracts of leaves from non-acclimated D. antarctica, can reconstitute the activity found in acclimated plants. We propose that IRIP-mediated RI activity may contribute to the cryotolerance of D. antarctica, and thus to its unique ability to have colonized Antarctica.

  1. 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.

  2. Meteorites and Microbes: Meteorite Collection and Ice Sampling at Patriot Hills, Thiel Mountains, and South Pole, Antarctica

    NASA Technical Reports Server (NTRS)

    Sipiera, Paul P.; Hoover, Richard B.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    During the Antarctica 2000 Expedition, sponsored by the Planetary Studies Foundation, meteorites and ice microbiota were collected from the Patriot Hills, and Thiel Mountains of Antarctica and snow samples were at the South Pole. Psychrophilic and psychrotrophic microbiota were obtained from blue ice, cryoconite and ice-bubble systems. Twenty frozen meteorites were collected using aseptic techniques from the blue ice fields near the Moulton Escarpment of the Thiel Mountains (85 S, 94 W) and from the Morris Moraine of the Patriot Hills (80 S, 81 W) Ellsworth Mountains. These ice and meteorite samples are of potential significance to Astrobiology. They may help refine chemical and morphological biomarkers and refine characteristics of microbial life in one of the harshest environments on Earth. We discuss the Antarctica 2000 Expedition and provide preliminary results of the investigation of the meteorites and ice microbiota recovered.

  3. 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

  4. Examination Of A Strong Downslope Warming Wind Event Over The Larsen Ice Shelf In Antarctica Through Modeling And Aircraft Observations

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    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 ice 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 ice shelf in 2002. In January 2006 the British Antarctic Survey performed an aircraft flight over the Larsen C ice shelf on the east side of the AP, which sampled a strong downslope wind event. Surface flux measurements over the ice shelf suggest that the sensible heat provided by the warm jets would be likely to be negated by latent heat losses from ice ablation. The main cause of any ice 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 ice shelf 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

  5. 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.

  6. Interplay of grounding-line dynamics and sub-shelf melting during retreat of the Bjørnøyrenna Ice Stream.

    PubMed

    Petrini, Michele; Colleoni, Florence; Kirchner, Nina; Hughes, Anna L C; Camerlenghi, Angelo; Rebesco, Michele; Lucchi, Renata G; Forte, Emanuele; Colucci, Renato R; Noormets, Riko

    2018-05-08

    The Barents Sea Ice Sheet was a marine-based ice sheet, i.e., it rested on the Barents Sea floor during the Last Glacial Maximum (21 ky BP). The Bjørnøyrenna Ice Stream was the largest ice stream draining the Barents Sea Ice Sheet and is regarded as an analogue for contemporary ice streams in West Antarctica. Here, the retreat of the Bjørnøyrenna Ice Stream is simulated by means of two numerical ice sheet models and results assessed against geological data. We investigate the sensitivity of the ice stream to changes in ocean temperature and the impact of grounding-line physics on ice stream retreat. Our results suggest that the role played by sub-shelf melting depends on how the grounding-line physics is represented in the models. When an analytic constraint on the ice flux across the grounding line is applied, the retreat of Bjørnøyrenna Ice Stream is primarily driven by internal ice 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 ice sheets and individual ice streams to ongoing and future ocean warming.

  7. Mezozooplankton Beneath the Summer Sea Ice in McMurdo Sound, Antarctica: Abundance, Species Composition, and DMSP content

    EPA Science Inventory

    The Ross Sea Phaeocystis antarctica bloom contributes to a summer increase in under-ice planton biomass in McMurdo Sound, Antarctica. Due to difficulties of under-ice sampling, information on the mesozooplankton in McMurdo Sound is limited. We measured the abundance of mesooopl...

  8. 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.

  9. 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

  10. Roosevelt Island Climate Evolution Project (RICE): A 65 Kyr ice core record of black carbon aerosol deposition to the Ross Ice Shelf, West Antarctica.

    NASA Astrophysics Data System (ADS)

    Edwards, Ross; Bertler, Nancy; Tuohy, Andrea; Neff, Peter; Proemse, Bernedette; Feiteng, Wang; Goodwin, Ian; Hogan, Chad

    2015-04-01

    Emitted by fires, black carbon aerosols (rBC) perturb the atmosphere's physical and chemical properties and are climatically active. Sedimentary charcoal and other paleo-fire records suggest that rBC emissions have varied significantly in the past due to human activity and climate variability. However, few paleo rBC records exist to constrain reconstructions of the past rBC atmospheric distribution and its climate interaction. As part of the international Roosevelt Island Climate Evolution (RICE) project, we have developed an Antarctic rBC ice core record spanning the past ~65 Kyr. The RICE deep ice core was drilled from the Roosevelt Island ice dome in West Antarctica from 2011 to 2013. The high depth resolution (~ 1 cm) record was developed using a single particle intracavity laser-induced incandescence soot photometer (SP2) coupled to an ice core melter system. The rBC record displays sub-annual variability consistent with both austral dry-season and summer biomass burning. The record exhibits significant decadal to millennial-scale variability consistent with known changes in climate. Glacial rBC concentrations were much lower than Holocene concentrations with the exception of several periods of abrupt increases in rBC. The transition from glacial to interglacial rBC concentrations occurred over a much longer time relative to other ice core climate proxies such as water isotopes and suggests . The protracted increase in rBC during the transition may reflected Southern hemisphere ecosystem / fire regime changes in response to hydroclimate and human activity.

  11. 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

  12. Recent Climate and Ice-Sheet Changes in West Antarctica Compared with the Past 2,000 Years

    NASA Technical Reports Server (NTRS)

    Steig, Eric J.; Ding, Qinghua; White, James W.; Kuttel, Marcel; Rupper, Summer B.; Neumann, Thomas Allen; Neff, Peter D.; Gallant, Ailie J. E.; Mayewski, Paul A.; Taylor, Kendrick C.; hide

    2013-01-01

    Changes in atmospheric circulation over the past five decades have enhanced the wind-driven inflow of warm ocean water onto the Antarctic continental shelf, where it melts ice shelves from below1-3. Atmospheric circulation changes have also caused rapid warming4 over the West Antarctic Ice Sheet, and contributed to declining sea-ice cover in the adjacent Amundsen-Bellingshausen seas5. It is unknown whether these changes are part of a longer-term trend. Here, we use waterisotope (Delta O-18) data from an array of ice-core records to place recent West Antarctic climate changes in the context of the past two millennia. We find that the d18O of West Antarctic precipitation has increased significantly in the past 50 years, in parallel with the trend in temperature, and was probably more elevated during the 1990s than at any other time during the past 200 years. However, Delta O-18 anomalies comparable to those of recent decades occur about 1% of the time over the past 2,000 years. General circulation model simulations suggest that recent trends in Delta O-18 and climate in West Antarctica cannot be distinguished from decadal variability that originates in the tropics. We conclude that the uncertain trajectory of tropical climate variability represents a significant source of uncertainty in projections of West Antarctic climate and ice-sheet change.

  13. 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.

  14. 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. 

  15. 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.

  16. 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

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

    PubMed Central

    van Wijk, Esmee

    2018-01-01

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

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

    PubMed

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

    2018-04-01

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

  19. The tephrostratigraphy of Mt. Berlin volcano, Antarctica: Integrating blue ice tephra and ice core tephra records

    NASA Astrophysics Data System (ADS)

    Iverson, N. A.; Dunbar, N. W.; McIntosh, W. C.; Kurbatov, A.

    2016-12-01

    Reconstructing volcanic activity in Antarctica is difficult because of the limited outcrop exposure. However, ice is an excellent medium for sampling tephra, allowing for a more complete eruptive record than can be found in other depositional environments. Furthermore, because of low ambient temperature, glass shards trapped in ice remain unaltered and unhydrated. Mt. Berlin is an ice covered volcano in Marie Byrd Land, Antarctica, and, because of heavy glaciation, eruptive records on the volcano itself are sparse. Here, we present the integration of two different records of Mt. Berlin volcanism: the blue ice record found at Mt. Moulton (Dunbar et al., 2008) and the ice core record from the WAIS Divide ice core. Tephra from Mt. Berlin are also found in other ice and marine core records, and these have been correlated and integrated into the combined volcanic record. The Mt. Moulton blue ice area is located 30 km from Mt. Berlin and hosts a fabulous tephra record spanning the last 500 ka. A total of 36 tephra from Mt. Berlin were sampled in stratigraphic order and nine were directly dated by 40Ar/39Ar dating method. Twenty five tephra from WAIS Divide have been analyzed and are geochemically similar to Mt. Berlin with ice core ages dating back to 70 ka. The two tephra records were integrated using their respective timescales. In locations where the Mt. Moulton record does not have precise chronology, the δ18O records from Mt. Moulton (Popp, 2008) and WAIS (WAIS, 2015) were used to integrate the stratigraphy. In total 61 tephra from both ice sections provide an excellent record of the magmatic evolution of Mt. Berlin over the past 500 ka. EMP analyses on glass shards show a gradual change in Fe and S over time. Most of the other major elements remain relatively unchanged. The trend in Fe and S could be produced by progressive tapping of a single, stratified magma chamber, but the long duration of volcanism makes this unlikely. We instead favor small batches of

  20. 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.

  1. 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

  2. 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.

  3. Airborne geophysical study in the pensacola mountains of antarctica

    USGS Publications Warehouse

    Behrendt, John C.; Meister, L.; Henderson, J.R.

    1966-01-01

    A seismic reflection, gravity, and aeromagnetic reconnaissance was made in the Pensacola Mountains, Antarctica, during the 1965-66 austral summer. Prominent ice streams located between the Neptune and Patuxent Ranges and east of the Forrestal Range overlie channels in the rock surface 2000 meters below sea level which are probably of glacial origin. Seismic reflections show that the Filchner Ice Shelf is 1270 meters thick near its southern margin. Along the boundary between West and East Antarctica, Bouguer anomalies decrease from +60 milligals in West Antarctica to -80 milligals in East Antarctica. An abrupt change in crustal structure across this boundary is required to explain the 2 milligals per kilometer gradient. This may indicate a fault extending through the crust into the mantle. Aeromagnetic profiles delineate anomalies up to 1800 ?? associated with the basic stratiform intrusion which comprises the Dufek and Forrestal ranges. A probable minimum area of 9500 square kilometers is calculated for the intrusive body on the basis of the magnetic anomalies, making it one of the largest bodies of its type. The extension of this magnetic anomaly across a fault forming the north border of the Pensacola Mountains probably precludes transcurrent movement.

  4. Airborne geophysical study in the pensacola mountains of antarctica.

    PubMed

    Behrendt, J C; Meister, L; Henderson, J R

    1966-09-16

    A seismic reflection, gravity, and aeromagnetic reconnaissance was made in the Pensacola Mountains, Antarctica, during the 1965-66 austral summer. Prominent ice streams located between the Neptune and Patuxent Ranges and east of the Forrestal Range overlie channels in the rock surface 2000 meters below sea level which are probably of glacial origin. Seismic reflections show that the Filchner Ice Shelf is 1270 meters thick near its southern margin. Along the boundary between West and East Antarctica, Bouguer anomalies decrease from +60 milligals in West Antarctica to -80 milligals in East Antarctica. An abrupt change in crustal structure across this boundary is required to explainl the 2 milligals per kilometer gradient. This may indicate a fault extending through the crust into the mantle. Aeromagnetic profiles delineate anomalies up to 1800 gamma associated with the basic stratiform intrusion which comprises the Dufek and Forrestal ranges. A probable minimum area of 9500 square kilometers is calculated for the intrusive body on the basis of the magnetic anomalies, making it one of the largest bodies of its type. The extension of this magnetic anominaly across a fault forming the north border of the Pensacola Mountains probably precludes transcurrent movement.

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

    NASA Astrophysics Data System (ADS)

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

    2018-07-01

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

  6. 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.

  7. 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

  8. Northern Victoria Land (western Ross Sea-Antarctica): inner shelf fine sedimentation

    NASA Astrophysics Data System (ADS)

    Colizza, E.; Finocchiaro, F.; Ivaldi, R.; Pittà, A.; Tolotti, R.; Brambati, A.

    2003-04-01

    The Holocene sedimentation conditions are represented, in the western Ross Sea, by diatomaceous ooze in the uppermost part of sedimentary sequences, while diamicton deposited during Last Glacial Maximum are the basal unit of most cores. Thick layer (> 2 m) of diatomaceous ooze were sampled in the northern Joides Basin and into Granite Harbour. In Drygalski Ice Tongue area and along the coasts of northern Victoria Land, prevails coarse sedimentation, due to seaward flowing of large outlet glacier that drain the Transantarctic Mountain. During 1998-99 and 2001-02 PNRA antarctic cruises, favourable sea ice conditions, has allowed to sample inner shelf area, both in Wood Bay and south of Drygalski ice tongue (Nordenskjold basin). In both sites fine laminated diatomaceous mud are present. Preliminary seismostratigraphy and sedimentological data are here reported. This is the first note of new sites of fine sedimentation in the Ross Sea inner shelf.

  9. Ice-Borehole Probe

    NASA Technical Reports Server (NTRS)

    Behar, Alberto; Carsey, Frank; Lane, Arthur; Engelhardt, Herman

    2006-01-01

    An instrumentation system has been developed for studying interactions between a glacier or ice sheet and the underlying rock and/or soil. Prior borehole imaging systems have been used in well-drilling and mineral-exploration applications and for studying relatively thin valley glaciers, but have not been used for studying thick ice sheets like those of Antarctica. The system includes a cylindrical imaging probe that is lowered into a hole that has been bored through the ice to the ice/bedrock interface by use of an established hot-water-jet technique. The images acquired by the cameras yield information on the movement of the ice relative to the bedrock and on visible features of the lower structure of the ice sheet, including ice layers formed at different times, bubbles, and mineralogical inclusions. At the time of reporting the information for this article, the system was just deployed in two boreholes on the Amery ice shelf in East Antarctica and after successful 2000 2001 deployments in 4 boreholes at Ice Stream C, West Antarctica, and in 2002 at Black Rapids Glacier, Alaska. The probe is designed to operate at temperatures from 40 to +40 C and to withstand the cold, wet, high-pressure [130-atm (13.20-MPa)] environment at the bottom of a water-filled borehole in ice as deep as 1.6 km. A current version is being outfitted to service 2.4-km-deep boreholes at the Rutford Ice Stream in West Antarctica. The probe (see figure) contains a sidelooking charge-coupled-device (CCD) camera that generates both a real-time analog video signal and a sequence of still-image data, and contains a digital videotape recorder. The probe also contains a downward-looking CCD analog video camera, plus halogen lamps to illuminate the fields of view of both cameras. The analog video outputs of the cameras are converted to optical signals that are transmitted to a surface station via optical fibers in a cable. Electric power is supplied to the probe through wires in the cable at a

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  11. Multiphase Reactive Transport and Platelet Ice Accretion in the Sea Ice of McMurdo Sound, Antarctica

    NASA Astrophysics Data System (ADS)

    Buffo, J. J.; Schmidt, B. E.; Huber, C.

    2018-01-01

    Sea ice 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, ice shelf processes, and biological communities. Accurate incorporation of sea ice growth and decay, and its associated thermal and physiochemical processes, is underrepresented in large-scale models due to the complex physics that dictate oceanic ice formation and evolution. Two phenomena complicate sea ice 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 ice formed by supercooled ice shelf water onto the basal surface of the overlying ice. Here a one-dimensional finite difference model capable of simulating both processes is developed and tested against ice core data. Temperature, salinity, liquid fraction, fluid velocity, total salt content, and ice structure are computed during model runs. The model results agree well with empirical observations and simulations highlight the effect platelet ice accretion has on overall ice thickness and characteristics. Results from sensitivity studies emphasize the need to further constrain sea ice microstructure and the associated physics, particularly permeability-porosity relationships, if a complete model of sea ice evolution is to be obtained. Additionally, implications for terrestrial ice shelves and icy moons in the solar system are discussed.

  12. 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.

  13. 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.

  14. 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.

  15. Palaeo-ice stream pathways in the easternmost Amundsen Sea Embayment, West Antarctica

    NASA Astrophysics Data System (ADS)

    Klages, Johann P.; Kuhn, Gerhard; Graham, Alastair G. C.; Smith, James A.; Hillenbrand, Claus-Dieter; Nitsche, Frank O.; Larter, Rob D.; Gohl, Karsten

    2015-04-01

    Multibeam swath bathymetry datasets collected over the past two decades have been compiled to identify palaeo-ice stream pathways in the easternmost Amundsen Sea Embayment. We mapped 3010 glacial landforms to reconstruct palaeo-ice flow in the ~250 km-long Abbot Glacial Trough that was occupied by a large palaeo-ice stream, fed by two tributaries (Cosgrove and Abbot) that reached the continental shelf edge during the last maximum ice-sheet advance. The mapping has enabled a clear differentiation between glacial landforms interpreted as indicative of wet- (e.g. mega-scale glacial lineations) and cold-based ice (e.g. hill-hole pairs) during the last glaciation of the continental shelf. Both the regions of fast palaeo-ice flow within the palaeo-ice stream troughs, and the regions of slow palaeo-ice flow on adjacent seafloor highs (referred to as inter-ice stream ridges) additionally record glacial landforms such as grounding-zone wedges and recessional moraines that indicate grounding line stillstands of the ice sheet during the last deglaciation from the shelf. As the palaeo-ice stream flowed along a trough with variable geometry and variable subglacial substrate, it appears that trough sections characterized by constrictions and outcropping hard substrate that changes the bed gradient, led the pace of grounding-line retreat to slow and subsequently pause, resulting in the deposition of grounding-zone wedges. The stepped retreat recorded within the Abbot Glacial Trough corresponds well to post-glacial stepped retreat interpreted for the neighbouring Pine Island-Thwaites Palaeo-Ice Stream trough, thus suggesting a uniform pattern of episodic retreat across the eastern Amundsen Sea Embayment. The correlation of episodic retreat features with geological boundaries further emphasises the significance of subglacial geology in steering ice stream flow. Our new geomorphological map of the easternmost Amundsen Sea Embayment resolves the pathways of palaeo-ice streams that

  16. 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.

  17. Ice sheet margins and ice shelves

    NASA Technical Reports Server (NTRS)

    Thomas, R. H.

    1984-01-01

    The effect of climate warming on the size of ice 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 ice sheets and ice shelves. For sufficiently large warming (5-10C) the delayed effects would include the breakup of the ice shelves by an increase in ice drainage rates, particularly from the ice sheets. On the basis of published data for periodic changes in the thickness and melting rates of the marine ice sheets and fjord glaciers in Greenland and Antarctica, it is shown that the rate of retreat (or advance) of an ice sheet is primarily determined by: bedrock topography; the basal conditions of the grounded ice sheet; and the ice shelf condition downstream of the grounding line. A program of satellite and ground measurements to monitor the state of ice sheet equilibrium is recommended.

  18. 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 <span class="hlt">Antarctica</span>, 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://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, <span class="hlt">Antarctica</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>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/2010EGUGA..12..761D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12..761D"><span>Compression experiments on artificial, alpine and marine <span class="hlt">ice</span>: implications for <span class="hlt">ice-shelf</span>/continental interactions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dierckx, Marie; Goossens, Thomas; Samyn, Denis; Tison, Jean-Louis</p> <p>2010-05-01</p> <p>Antarctic <span class="hlt">ice</span> shelves are important components of continental <span class="hlt">ice</span> dynamics, in that they control grounded <span class="hlt">ice</span> flow towards the ocean. As such, Antarctic <span class="hlt">ice</span> shelves are a key parameter to the stability of the Antarctic <span class="hlt">ice</span> sheet in the context of global change. Marine <span class="hlt">ice</span>, formed by sea water accretion beneath some <span class="hlt">ice</span> shelves, displays distinct physical (grain textures, bubble content, ...) and chemical (salinity, isotopic composition, ...) characteristics as compared to glacier <span class="hlt">ice</span> and sea <span class="hlt">ice</span>. The aim is to refine Glen's flow relation (generally used for <span class="hlt">ice</span> behaviour in deformation) under various parameters (temperature, salinity, debris, grain size ...) to improve deformation laws used in dynamic <span class="hlt">ice</span> <span class="hlt">shelf</span> models, which would then give more accurate and / or realistic predictions on <span class="hlt">ice</span> <span class="hlt">shelf</span> stability. To better understand the mechanical properties of natural <span class="hlt">ice</span>, deformation experiments were performed on <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> and went on with continental <span class="hlt">ice</span> samples from glaciers in the Alps. The first results allowed us to acquire realistic mechanical data for natural <span class="hlt">ice</span>. <span class="hlt">Ice</span> viscosity was calculated for different types of artificial <span class="hlt">ice</span>, using Glen's flow law, and showed the importance of impurities</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_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" 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_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> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <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 <span class="hlt">Antarctica</span>. 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/2012AGUFM.C31A0578R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.C31A0578R"><span>Detailed Ar-Ar Geochronology of Volcanism at Minna Bluff, <span class="hlt">Antarctica</span>: Two-Phased Growth and Influence on Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ross, J. I.; McIntosh, W. C.; Wilch, T. I.</p> <p>2012-12-01</p> <p>Minna Bluff has been a significant topographic barrier to the flow of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1812769C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1812769C"><span>Analogue modelling of the influence of <span class="hlt">ice</span> <span class="hlt">shelf</span> collapse on the flow of <span class="hlt">ice</span> sheets grounded below sea-level</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Corti, Giacomo; Zeoli, Antonio</p> <p>2016-04-01</p> <p>The sudden breakup of <span class="hlt">ice</span> shelves is expected to result in significant acceleration of inland glaciers, a process related to the removal of the buttressing effect exerted by the <span class="hlt">ice</span> <span class="hlt">shelf</span> on the tributary glaciers. This effect has been tested in previous analogue models, which however applied to <span class="hlt">ice</span> sheets grounded above sea level (e.g., East Antarctic <span class="hlt">Ice</span> Sheet; Antarctic Peninsula and the Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span>). In this work we expand these previous results by performing small-scale laboratory models that analyse the influence of <span class="hlt">ice</span> <span class="hlt">shelf</span> collapse on the flow of <span class="hlt">ice</span> streams draining an <span class="hlt">ice</span> sheet grounded below sea level (e.g., the West Antarctic <span class="hlt">Ice</span> 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 <span class="hlt">ice</span>. This transparent, Newtonian silicone has been shown to well approximate the rheology of natural <span class="hlt">ice</span>. The silicone was allowed to flow into a water reservoir simulating natural conditions in which <span class="hlt">ice</span> streams flow into the sea, terminating in extensive <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> breakup, a process similar to what</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12...25R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12...25R"><span>Frazil-<span class="hlt">ice</span> growth rate and dynamics in mixed layers and sub-<span class="hlt">ice-shelf</span> plumes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rees Jones, David W.; Wells, Andrew J.</p> <p>2018-01-01</p> <p>The growth of frazil or granular <span class="hlt">ice</span> is an important mode of <span class="hlt">ice</span> formation in the cryosphere. Recent advances have improved our understanding of the microphysical processes that control the rate of <span class="hlt">ice</span>-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 <span class="hlt">ice</span> crystals with different sizes to provide insight into the treatment of frazil <span class="hlt">ice</span> in large-scale models. We consider the role of crystal growth alongside the other physical processes that determine the dynamics of frazil <span class="hlt">ice</span>. 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 <span class="hlt">ice</span> <span class="hlt">shelf</span>. We provide numerical calculations and scaling arguments to predict the occurrence of frazil-<span class="hlt">ice</span> 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-<span class="hlt">ice</span> 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 <span class="hlt">ice</span> shelves is dramatically affected by frazil-<span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> or intrudes at depth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2007/1047/srp/srp106/of2007-1047srp106.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2007/1047/srp/srp106/of2007-1047srp106.pdf"><span>Records of past <span class="hlt">ice</span> sheet fluctuations in interior East <span class="hlt">Antarctica</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>Liu, Xiaohan; Huang, Feixin; Kong, Ping; Fang, Aimin; Li, Xiaoli</p> <p>2007-01-01</p> <p>The results of a land-based multi-disciplinary study of the past <span class="hlt">ice</span> surface elevation in the Grove Mountains of interior East <span class="hlt">Antarctica</span> support a dynamic evolution of the East Antarctic <span class="hlt">Ice</span> Sheet (EAIS). Moraine boulders of sedimentary rocks and spore pollen assemblage imply a significant shrinkage of the EAIS, with its margin retreating south of the Grove Mountains (~450 km south of recent coast line) before the middle Pliocene. The exposure ages indicate that the <span class="hlt">ice</span> sheet subsequently re-advanced, with the <span class="hlt">ice</span> surface rising locally at least 450 m higher than today. It then went back down constantly from before 2.3 Ma to 1.6 Ma. The glacial topography and existence of soil show that the <span class="hlt">ice</span> surface fluctuation continued since the early Quaternary, but with highest levels never exceeding ~100 m higher than today.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.C23C0631H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.C23C0631H"><span>The kinematic response of Petermann Glacier, Greenland to <span class="hlt">ice</span> <span class="hlt">shelf</span> perturbation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hubbard, A.; Box, J. E.; Bates, R.; Nick, F.; Luckman, A. J.; van de Wal, R.; Doyle, S. H.</p> <p>2010-12-01</p> <p>The acceleration and dynamic thinning of interior zones of the polar <span class="hlt">ice</span> sheets due to outlet/<span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> geodetic-GPS station flat out & reading 0 Volts</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27481659','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27481659"><span>Observed vulnerability of Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> to wind-driven inflow of warm deep water.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Darelius, E; Fer, I; Nicholls, K W</p> <p>2016-08-02</p> <p>The average rate of melting at the base of the large Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">ice</span> conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner <span class="hlt">Ice</span> <span class="hlt">Shelf</span> cavity. Here we present observations from near Filchner <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> melt rates to changes in wind forcing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4974661','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4974661"><span>Observed vulnerability of Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> to wind-driven inflow of warm deep water</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Darelius, E.; Fer, I.; Nicholls, K. W.</p> <p>2016-01-01</p> <p>The average rate of melting at the base of the large Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">ice</span> conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner <span class="hlt">Ice</span> <span class="hlt">Shelf</span> cavity. Here we present observations from near Filchner <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> melt rates to changes in wind forcing. PMID:27481659</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C51B0992H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51B0992H"><span>Simulating <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Response to Potential Triggers of Collapse Using the Material Point Method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huth, A.; Smith, B. E.</p> <p>2017-12-01</p> <p>Weakening or collapse of an <span class="hlt">ice</span> <span class="hlt">shelf</span> can reduce the buttressing effect of the <span class="hlt">shelf</span> on its upstream tributaries, resulting in sea level rise as the flux of grounded <span class="hlt">ice</span> 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 <span class="hlt">ice</span> sheet/<span class="hlt">ice</span> <span class="hlt">shelf</span> system to potential triggers of <span class="hlt">ice</span> <span class="hlt">shelf</span> weakening or collapse, such as calving events, thinning, and meltwater ponding. We present initial results for Larsen C. Changes in local <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> geometry throughout the simulations. We primarily derive our initial <span class="hlt">ice</span> geometry from CryoSat-2 data, and initialize the model by conducting a dual inversion for the <span class="hlt">ice</span> 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 <span class="hlt">ice</span> thickness evolution, grounding line position, and <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4655561','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4655561"><span>Collapse of the West Antarctic <span class="hlt">Ice</span> Sheet after local destabilization of the Amundsen Basin</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Feldmann, Johannes; Levermann, Anders</p> <p>2015-01-01</p> <p>The future evolution of the Antarctic <span class="hlt">Ice</span> Sheet represents the largest uncertainty in sea-level projections of this and upcoming centuries. Recently, satellite observations and high-resolution simulations have suggested the initiation of an <span class="hlt">ice</span>-sheet instability in the Amundsen Sea sector of West <span class="hlt">Antarctica</span>, caused by the last decades’ enhanced basal <span class="hlt">ice-shelf</span> melting. Whether this localized destabilization will yield a full discharge of marine <span class="hlt">ice</span> from West <span class="hlt">Antarctica</span>, associated with a global sea-level rise of more than 3 m, or whether the <span class="hlt">ice</span> loss is limited by <span class="hlt">ice</span> dynamics and topographic features, is unclear. Here we show that in the Parallel <span class="hlt">Ice</span> Sheet Model, a local destabilization causes a complete disintegration of the marine <span class="hlt">ice</span> in West <span class="hlt">Antarctica</span>. In our simulations, at 5-km horizontal resolution, the region disequilibrates after 60 y of currently observed melt rates. Thereafter, the marine <span class="hlt">ice</span>-sheet instability fully unfolds and is not halted by topographic features. In fact, the <span class="hlt">ice</span> loss in Amundsen Sea sector shifts the catchment's <span class="hlt">ice</span> divide toward the Filchner–Ronne and Ross <span class="hlt">ice</span> shelves, which initiates grounding-line retreat there. Our simulations suggest that if a destabilization of Amundsen Sea sector has indeed been initiated, <span class="hlt">Antarctica</span> will irrevocably contribute at least 3 m to global sea-level rise during the coming centuries to millennia. PMID:26578762</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C23B1224J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C23B1224J"><span>NASA-ISRO synthetic aperture radar (NISAR) for temporal tracking of iceberg calving events in the <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jawak, S. D.; Luis, A. J.</p> <p>2017-12-01</p> <p>Estimating mass loss of the Antarctic <span class="hlt">ice</span> sheet caused by iceberg calving is a challenging job. <span class="hlt">Antarctica</span> is surrounded by a variety of large, medium and small sized <span class="hlt">ice</span> shelves, glacier tongues and coastal areas without offshore floating <span class="hlt">ice</span> masses. It is possible to monitor surface structures on the continental <span class="hlt">ice</span> and the <span class="hlt">ice</span> 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 <span class="hlt">Antarctica</span> to map patterns of surface structures close to the calving front. Additionally, classifying patterns and density of surface structures distributed over the <span class="hlt">ice</span> shelves and <span class="hlt">ice</span> 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 <span class="hlt">ice</span> shelves which can provide advisories to field teams. The <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">Antarctica</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.1769C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.1769C"><span><span class="hlt">ICE</span>-VOLC Project: unravelling the dynamics of <span class="hlt">Antarctica</span> volcanoes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cannata, Andrea; Del Carlo, Paola; Giudice, Gaetano; Giuffrida, Giovanni; Larocca, Graziano; Liuzzo, Marco</p> <p>2017-04-01</p> <p>Melbourne and Rittmann volcanoes are located in the Victoria Land. Whilst Rittmann's last eruption dates probably to Pleistocene, Melbourne's most recent eruption between 1862 and 1922, testifying it is still active. At present, both volcanoes display fumarolic activity. Melbourne was discovered in 1841 by James Clark Ross, Rittmann during the 4th Italian Expedition (1988/1989). Our knowledge on both volcanoes is really little. The position of these volcanoes in the Antarctic region (characterised by absence of anthropic noise) and its proximity with the Italian Mario Zucchelli Station makes them ideal sites for studying volcano seismic sources, geothermal emissions, seismo-acoustic signals caused by cryosphere-hydrosphere-atmosphere dynamics, and volcanic gas impact on environment. Hence, the main aim of the <span class="hlt">ICE</span>-VOLC ("multiparametrIC Experiment at <span class="hlt">antarctica</span> VOLCanoes: data from volcano and cryosphere-ocean-atmosphere dynamics") project is the study of Melbourne and Rittmann, by acquisition, analysis and integration of multiparametric geophysical, geochemical and thermal data. Complementary objectives include investigation of the relationship between seismo-acoustic activity recorded in <span class="hlt">Antarctica</span> and cryosphere-hydrosphere-atmosphere dynamics, evaluation of the impact of volcanic gas in atmosphere. This project involves 26 researchers, technologists and technicians from University of Perugia and from Istituto Nazionale di Geofisica e Vulcanologia of Catania, Palermo, Pisa and Rome. In this work, we show the preliminary results obtained after the first expedition in <span class="hlt">Antarctica</span>, aiming to perform geochemical-thermal surveys in the volcano <span class="hlt">ice</span> caves, as well as to collect ash samples and to install temporary seismic stations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017QSRv..177..189D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017QSRv..177..189D"><span><span class="hlt">Ice</span>-dammed lateral lake and epishelf lake insights into Holocene dynamics of Marguerite Trough <span class="hlt">Ice</span> Stream and George VI <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Alexander Island, 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>Davies, Bethan J.; Hambrey, Michael J.; Glasser, Neil F.; Holt, Tom; Rodés, Angél; Smellie, John L.; Carrivick, Jonathan L.; Blockley, Simon P. E.</p> <p>2017-12-01</p> <p>We present new data regarding the past dynamics of Marguerite Trough <span class="hlt">Ice</span> Stream, George VI <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and valley glaciers from Ablation Point Massif on Alexander Island, Antarctic Peninsula. This <span class="hlt">ice</span>-free oasis preserves a geological record of <span class="hlt">ice</span> stream lateral moraines, <span class="hlt">ice</span>-dammed lakes, <span class="hlt">ice-shelf</span> 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 <span class="hlt">Ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> stream, George VI <span class="hlt">Ice</span> <span class="hlt">Shelf</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24037377','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24037377"><span>Calving fluxes and basal melt rates of Antarctic <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>Depoorter, M A; Bamber, J L; Griggs, J A; Lenaerts, J T M; Ligtenberg, S R M; van den Broeke, M R; Moholdt, G</p> <p>2013-10-03</p> <p>Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic <span class="hlt">ice</span> 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 <span class="hlt">ice-shelf</span> base) for the whole of <span class="hlt">Antarctica</span>. 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 <span class="hlt">ice</span> shelves in <span class="hlt">Antarctica</span>, using satellite measurements of calving flux and grounding-line flux, modelled <span class="hlt">ice-shelf</span> 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 <span class="hlt">ice</span>-sheet surface mass gain is lost through oceanic erosion before reaching the <span class="hlt">ice</span> 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 <span class="hlt">ice</span> shelves. We find a significant positive correlation between basal mass loss and surface elevation change for <span class="hlt">ice</span> shelves experiencing surface lowering and enhanced discharge. We suggest that basal mass loss is a valuable metric for predicting future <span class="hlt">ice-shelf</span> vulnerability to oceanic forcing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JGRD..118.2119R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JGRD..118.2119R"><span>Antarctic <span class="hlt">ice</span> sheet mass loss estimates using Modified Antarctic Mapping Mission surface flow observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ren, Diandong; Leslie, Lance M.; Lynch, Mervyn J.</p> <p>2013-03-01</p> <p>The long residence time of <span class="hlt">ice</span> and the relatively gentle slopes of the <span class="hlt">Antarctica</span> <span class="hlt">Ice</span> Sheet make basal sliding a unique positive feedback mechanism in enhancing <span class="hlt">ice</span> discharge along preferred routes. The highly organized <span class="hlt">ice</span> stream channels extending to the interior from the lower reach of the outlets are a manifestation of the role of basal granular material in enhancing the <span class="hlt">ice</span> flow. In this study, constraining the model-simulated year 2000 <span class="hlt">ice</span> flow fields with surface velocities obtained from InSAR measurements permits retrieval of the basal sliding parameters. Forward integrations of the <span class="hlt">ice</span> model driven by atmospheric and oceanic parameters from coupled general circulation models under different emission scenarios provide a range of estimates of total <span class="hlt">ice</span> mass loss during the 21st century. The total mass loss rate has a small intermodel and interscenario spread, rising from approximately -160 km3/yr at present to approximately -220 km3/yr by 2100. The accelerated mass loss rate of the <span class="hlt">Antarctica</span> <span class="hlt">Ice</span> Sheet in a warming climate is due primarily to a dynamic response in the form of an increase in <span class="hlt">ice</span> flow speed. <span class="hlt">Ice</span> shelves contribute to this feedback through a reduced buttressing effect due to more frequent systematic, tabular calving events. For example, by 2100 the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> is projected to shed 40 km3 during each systematic tabular calving. After the frontal section's attrition, the remaining <span class="hlt">shelf</span> will rebound. Consequently, the submerged cross-sectional area will reduce, as will the buttressing stress. Longitudinal differential warming of ocean temperature contributes to tabular calving. Because of the prevalence of fringe <span class="hlt">ice</span> shelves, oceanic effects likely will play a very important role in the future mass balance of the <span class="hlt">Antarctica</span> <span class="hlt">Ice</span> Sheet, under a possible future warming climate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018FrEaS...6...28W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018FrEaS...6...28W"><span>Unravelling InSAR observed Antarctic <span class="hlt">ice-shelf</span> flexure using 2-D elastic and viscoelastic modelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wild, Christian T.; Marsh, Oliver J.; Rack, Wolfgang</p> <p>2018-04-01</p> <p><span class="hlt">Ice-shelf</span> grounding zones link the Antarctic <span class="hlt">ice</span>-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 <span class="hlt">ice</span> thickness, <span class="hlt">ice</span> properties and tidal conditions beneath the <span class="hlt">ice</span> <span class="hlt">shelf</span>. Here, we combine in-situ data with numerical modelling of <span class="hlt">ice-shelf</span> flexure to investigate 2-D controls on the tidal bending pattern on the Southern McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFMPP11B1783E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFMPP11B1783E"><span>An unusual early Holocene diatom event north of the Getz <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (Amundsen Sea): Implications for West Antarctic <span class="hlt">Ice</span> Sheet development</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Esper, O.; Gersonde, R.; Hillenbrand, C.; Kuhn, G.; Smith, J.</p> <p>2011-12-01</p> <p>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 <span class="hlt">Ice</span> 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 <span class="hlt">shelf</span> basin north of Getz <span class="hlt">Ice</span> <span class="hlt">Shelf</span> document a deglacial warming in three phases. Above a glacial diamicton and a sediment package barren of microfossils that document sediment deposition by grounded <span class="hlt">ice</span> and below an <span class="hlt">ice</span> <span class="hlt">shelf</span> or perennial sea <span class="hlt">ice</span> cover (possibly fast <span class="hlt">ice</span>), respectively, a sediment section with diatom assemblages dominated by sea <span class="hlt">ice</span> taxa indicates <span class="hlt">ice</span> <span class="hlt">shelf</span> retreat and seasonal <span class="hlt">ice</span>-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 <span class="hlt">ice</span>. 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 <span class="hlt">shelf</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17092309','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17092309"><span>Microbiota within the perennial <span class="hlt">ice</span> cover of Lake Vida, <span class="hlt">Antarctica</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mosier, Annika C; Murray, Alison E; Fritsen, Christian H</p> <p>2007-02-01</p> <p>Lake Vida, located in the McMurdo Dry Valleys, <span class="hlt">Antarctica</span>, is an '<span class="hlt">ice</span>-sealed' lake with approximately 19 m of <span class="hlt">ice</span> covering a highly saline water column (approximately 245 ppt). The lower portions of the <span class="hlt">ice</span> cover and the lake beneath have been isolated from the atmosphere and land for circa 2800 years. Analysis of microbial assemblages within the perennial <span class="hlt">ice</span> cover of the lake revealed a diverse array of bacteria and eukarya. Bacterial and eukaryal denaturing gradient gel electrophoresis phylotype profile similarities were low (<59%) between all of the depths compared (five depths spanning 11 m of the <span class="hlt">ice</span> cover), with the greatest differences occurring between surface and deep <span class="hlt">ice</span>. The majority of bacterial 16S rRNA gene sequences in the surface <span class="hlt">ice</span> were related to Actinobacteria (42%) while Gammaproteobacteria (52%) dominated the deep <span class="hlt">ice</span> community. Comparisons of assemblage composition suggest differences in <span class="hlt">ice</span> habitability and organismal origin in the upper and lower portions of <span class="hlt">ice</span> cover. Specifically, the upper <span class="hlt">ice</span> cover microbiota likely reflect the modern day transport and colonization of biota from the terrestrial landscape, whereas assemblages in the deeper <span class="hlt">ice</span> are more likely to be persistent remnant biota that originated from the ancient liquid water column of the lake that froze.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920045032&hterms=GMT&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DGMT','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920045032&hterms=GMT&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DGMT"><span>AVHRR imagery reveals Antarctic <span class="hlt">ice</span> dynamics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bindschadler, Robert A.; Vornberger, Patricia L.</p> <p>1990-01-01</p> <p>A portion of AVHRR data taken on December 5, 1987 at 06:15 GMT over a part of <span class="hlt">Antarctica</span> is used here to show that many of the most significant dynamic features of <span class="hlt">ice</span> sheets can be identified by a careful examination of AVHRR imagery. The relatively low resolution of this instrument makes it ideal for obtaining a broad view of the <span class="hlt">ice</span> sheets, while its wide swath allows coverage of areas beyond the reach of high-resolution imagers either currently in orbit or planned. An interpretation is given of the present data, which cover the area of <span class="hlt">ice</span> streams that drain the interior of the West Antarctic <span class="hlt">ice</span> sheet into the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMPP13C..02D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMPP13C..02D"><span>How does <span class="hlt">ice</span> sheet loading affect ocean flow around <span class="hlt">Antarctica</span>?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dijkstra, H. A.; Rugenstein, M. A.; Stocchi, P.; von der Heydt, A. S.</p> <p>2012-12-01</p> <p>Interactions and dynamical feedbacks between ocean circulation, heat and atmospheric moisture transport, <span class="hlt">ice</span> sheet evolution, and Glacial Isostatic Adjustment (GIA) are overlooked issues in paleoclimatology. Here we will present first results on how ocean flows were possibly affected by the glaciation of <span class="hlt">Antarctica</span> across the Eocene-Oligocene Transition (~ 34 Ma) through GIA and bathymetry variations. GIA-induced gravitationally self-consistent bathymetry variations are determined by solving the Sea Level Equation (SLE), which describes the time dependent shape of (i) the solid Earth and (ii) the equipotential surface of gravity. Since the ocean circulation equations are defined relative to the equipotential surface of gravity, only bathymetry variations can influence ocean flows, although the sea surface slope will also change through time due to gravitational attraction. We use the Hallberg Isopycnal Model under late Eocene conditions to calculate equilibrium ocean flows in a domain in which the bathymetry evolves under <span class="hlt">ice</span> loading according to the SLE. The bathymetric effects of the glaciation of <span class="hlt">Antarctica</span> lead to substantial spatial changes in ocean flows, and close to the coast, the flow even reverses direction. Volume transports through the Drake Passage and Tasman Seaway adjust to the new bathymetry. The results indicate that GIA-induced ocean flow variations alone may have had an impact on sedimentation and erosion patterns, the repositioning of fronts, ocean heat transport and grounding line and <span class="hlt">ice</span> sheet stability.</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/2013JGRC..118.6951M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JGRC..118.6951M"><span>The effect of basal channels on oceanic <span class="hlt">ice-shelf</span> melting</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Millgate, Thomas; Holland, Paul R.; Jenkins, Adrian; Johnson, Helen L.</p> <p>2013-12-01</p> <p>The presence of <span class="hlt">ice-shelf</span> basal channels has been noted in a number of Antarctic and Greenland <span class="hlt">ice</span> 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 <span class="hlt">ice-shelf</span> basal channels on oceanic melt rate for an idealized <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> shelves.</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 <span class="hlt">Antarctica</span>. 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 <span class="hlt">Antarctica</span> 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/2017EGUGA..1910364J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1910364J"><span>A Simple Diagnostic Model of the Circulation Beneath an <span class="hlt">Ice</span> <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jenkins, Adrian; Nøst, Ole Anders</p> <p>2017-04-01</p> <p>The ocean circulation beneath <span class="hlt">ice</span> shelves supplies the heat required to melt <span class="hlt">ice</span> and exports the resulting freshwater. It therefore plays a key role in determining the mass balance and geometry of the <span class="hlt">ice</span> shelves and hence the restraint they impose on the outflow of grounded <span class="hlt">ice</span> from the interior of the <span class="hlt">ice</span> sheet. Despite this critical role in regulating the <span class="hlt">ice</span> 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 <span class="hlt">ice</span> base. However, most sub-<span class="hlt">ice-shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span>. 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016DSRII.123...16M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016DSRII.123...16M"><span>Glider observations of the Dotson <span class="hlt">Ice</span> <span class="hlt">Shelf</span> outflow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miles, Travis; Lee, Sang Hoon; Wåhlin, Anna; Ha, Ho Kyung; Kim, Tae Wan; Assmann, Karen M.; Schofield, Oscar</p> <p>2016-01-01</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-Webb 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.C32A..05Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C32A..05Y"><span>The subglacial roughness of <span class="hlt">Antarctica</span>: Analogs, interpretation and implications for <span class="hlt">ice</span> thickness uncertainities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Young, D. A.; Grima, C.; Greenbaum, J. S.; Beem, L.; Cavitte, M. G.; Quartini, E.; Kempf, S. D.; Roberts, J. L.; Siegert, M. J.; Ritz, C.; Blankenship, D. D.</p> <p>2017-12-01</p> <p>Over the last twenty five years, extensive <span class="hlt">ice</span> penetrating radar (IPR) coverage of <span class="hlt">Antarctica</span> has been obtained, at lines spacings down to 1 km in some cases. However, many glacial processes occur at finer scales, so infering likely landscape parameters is required for a useful interpolation between lines. Profile roughness is also important for understanding the uncertainties inherent in IPR observations. Subglacial roughness has also been used to infer large scale bed rock properties and history. Similar work has been conducted on a regional basis with complilations of data from the 1970's and more recent local studies. Here we present a compilation of IPR-derived profile roughness data covering three great basins of <span class="hlt">Antarctica</span>: the Byrd Subglacial Basin in West <span class="hlt">Antarctica</span>, and the Wilkes Subglacial Basin and Aurora Subglacial Basins in East <span class="hlt">Antarctica</span>; and treat these data using root mean squared deviation (RMSD). Coverage is provied by a range of IPR systems with varying vintages with differing instrument and processing parameters; we present approaches to account for the differences between these systems. We use RMSD, a tool commonly used in planetary investigations, to investigate the self-affine behaviour of the bed at kilometer scales and extract fractal parameters from the data to predict roughness and uncertainties in <span class="hlt">ice</span> thickness measurement. Lastly, we apply a sensor model to a range of bare-earth terrestrial digital elevation models to futher understand the impact of the sensor model on the inference of subglacial topography and roughness, and to the first order analogies for the lithology of the substrate. This map of roughness, at scales between the pulse limited radar footprint and typical line spacings, provides an understanding of the distribution of Paleogene subglacial sediments, insight in to the distribution of uncertainties and a potential basal properties mask for <span class="hlt">ice</span> sheet models. A particular goal of this map is to provide insight into</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMPP51E..06K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP51E..06K"><span>Estimating Past Temperature Change in <span class="hlt">Antarctica</span> Based on <span class="hlt">Ice</span> Core Stable Water Isotope Diffusion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kahle, E. C.; Markle, B. R.; Holme, C.; Jones, T. R.; Steig, E. J.</p> <p>2017-12-01</p> <p>The magnitude of the last glacial-interglacial transition is a key target for constraining climate sensitivity on long timescales. <span class="hlt">Ice</span> core proxy records and general circulation models (GCMs) both provide insight on the magnitude of climate change through the last glacial-interglacial transition, but appear to provide different answers. In particular, the magnitude of the glacial-interglacial temperature change reconstructed from East Antarctic <span class="hlt">ice</span>-core water-isotope records is greater ( 9 degrees C) than that from most GCM simulations ( 6 degrees C). A possible source of this difference is error in the linear-scaling of water isotopes to temperature. We employ a novel, nonlinear temperature-reconstruction technique using the physics of water-isotope diffusion to infer past temperature. Based on new, <span class="hlt">ice</span>-core data from the South Pole, this diffusion technique suggests East Antarctic temperature change was smaller than previously thought. We are able to confirm this result using a simple, water-isotope fractionation model to nonlinearly reconstruct temperature change at <span class="hlt">ice</span> core locations across <span class="hlt">Antarctica</span> based on combined oxygen and hydrogen isotope ratios. Both methods produce a temperature change of 6 degrees C for South Pole, agreeing with GCM results for East <span class="hlt">Antarctica</span>. Furthermore, both produce much larger changes in West <span class="hlt">Antarctica</span>, also in agreement with GCM results and independent borehole thermometry. These results support the fidelity of GCMs in simulating last glacial maximum climate, and contradict the idea, based on previous work, that the climate sensitivity of current GCMs is too low.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70171513','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70171513"><span>Oceanic and atmospheric forcing of Larsen C <span class="hlt">Ice-Shelf</span> thinning</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Holland, P. R.; Brisbourne, A.; Corr, H. F. J.; Mcgrath, Daniel; Purdon, K.; Paden, J.; Fricker, H. A.; Paolo, F. S.; Fleming, A.H.</p> <p>2015-01-01</p> <p>The catastrophic collapses of Larsen A and B <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (LCIS), the largest <span class="hlt">ice</span> <span class="hlt">shelf</span> on the peninsula, is lowering. This could be caused by unbalanced ocean melting (<span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> loss (0.28 ± 0.18 m yr−1) and firn-air loss (0.037 ± 0.026 m yr−1). The <span class="hlt">ice</span> loss is much larger than the air loss, but both contribute approximately equally to the lowering because the <span class="hlt">ice</span> is floating. The <span class="hlt">ice</span> loss could be explained by high basal melting and/or <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> Rise or <span class="hlt">ice</span>-front retreat past a "compressive arch" in strain rates. Recent evidence suggests that either mechanism could pose an imminent risk.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016DSRI..117...51L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016DSRI..117...51L"><span>Physical-biological coupling in the Amundsen Sea, <span class="hlt">Antarctica</span>: Influence of physical factors on phytoplankton community structure and biomass</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Youngju; Yang, Eun Jin; Park, Jisoo; Jung, Jinyoung; Kim, Tae Wan; Lee, SangHoon</p> <p>2016-11-01</p> <p>To understand the spatial distribution of phytoplankton communities in various habitats in the Amundsen Sea, western <span class="hlt">Antarctica</span>, a field survey was conducted at 15 stations during the austral summer, from December 2013 to January 2014. Water samples were analyzed by microscopy. We found high phytoplankton abundance and biomass in the Amundsen Sea polynya (ASP). Their strong positive correlation with water temperature suggests that phytoplankton biomass accumulated in the surface layer of the stratified polynya. In the ASP, the predominant phytoplankton species was Phaeocystis <span class="hlt">antarctica</span>, while diatoms formed a major group in the sea <span class="hlt">ice</span> zone, especially Fragilariopsis spp., Chaetoceros spp., and Proboscia spp. Although this large diatom abundance sharply decreased just off the marginal sea <span class="hlt">ice</span> zone, weakly silicified diatoms, due to their high buoyancy, were distributed at almost all stations on the continental <span class="hlt">shelf</span>. Dictyocha speculum appeared to favor the area between the marginal sea <span class="hlt">ice</span> zone and the ASP in contrast to cryptophytes and picophytoplankton, whose abundance was higher in the area between the continental <span class="hlt">shelf</span> and the open ocean of Amundsen Sea. Several environmental factors were found to affect the spatial variation of phytoplankton species, but the community structure appeared to be controlled mainly by the seawater density related to sea-<span class="hlt">ice</span> melting and water circulation in the Amundsen Sea.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011TCry....5..715W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011TCry....5..715W"><span>The Potsdam Parallel <span class="hlt">Ice</span> Sheet Model (PISM-PIK) - Part 1: Model description</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.</p> <p>2011-09-01</p> <p>We present the Potsdam Parallel <span class="hlt">Ice</span> Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale <span class="hlt">ice</span> sheet-<span class="hlt">shelf</span> systems. It is derived from the Parallel <span class="hlt">Ice</span> Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire <span class="hlt">ice</span> covered region: the shallow <span class="hlt">ice</span> approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow <span class="hlt">shelf</span> approximation (SSA) dominates the velocity field in <span class="hlt">ice</span> <span class="hlt">shelf</span> regions and serves as a basal sliding velocity in grounded regions. <span class="hlt">Ice</span> 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 <span class="hlt">ice</span> fronts. <span class="hlt">Ice</span> <span class="hlt">shelf</span> margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> Sheet Model Intercomparison Project (MISMIP). A dynamic equilibrium simulation of <span class="hlt">Antarctica</span> under present-day conditions is presented in Martin et al. (2011).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C33D..05V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C33D..05V"><span>Improved estimate of accelerated <span class="hlt">Antarctica</span> <span class="hlt">ice</span> mass loses from GRACE, Altimetry and surface mass balance from regional climate model output</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Velicogna, I.; Sutterley, T. C.; A, G.; van den Broeke, M. R.; Ivins, E. R.</p> <p>2016-12-01</p> <p>We use Gravity Recovery and Climate Experiment (GRACE) monthly gravity fields to determine the regional acceleration in <span class="hlt">ice</span> mass loss in <span class="hlt">Antarctica</span> for 2002-2016. We find that the total mass loss is controlled by only a few regions. In <span class="hlt">Antarctica</span>, the Amundsen Sea (AS) sector and the Antarctic Peninsula account for 65% and 18%, respectively, of the total loss (186 ± 10 Gt/yr) mainly from <span class="hlt">ice</span> dynamics. The AS sector contributes most of the acceleration in loss (9 ± 1 Gt/yr2 ), and Queen Maud Land, East <span class="hlt">Antarctica</span>, is the only sector with a significant mass gain due to a local increase in SMB (57 ± 5 Gt/yr). We compare GRACE regional mass balance estimates with independent estimates from ICESat-1 and Operation <span class="hlt">Ice</span>Bridge laser altimetry, CryoSat-2 radar altimetry, and surface mass balance outputs from RACMO2.3. In the Amundsen Sea Embayment of West <span class="hlt">Antarctica</span>, an area experiencing rapid retreat and mass loss to the sea, we find good agreement between GRACE and altimetry estimates. Comparison of GRACE with these independent techniques in East Antarctic shows that GIA estimates from the new regional <span class="hlt">ice</span> deglaciation models underestimate the GIA correction in the EAIS interior, which implies larger losses of the <span class="hlt">Antarctica</span> <span class="hlt">ice</span> sheet by about 70 Gt/yr. Sectors where we are observing the largest losses are closest to warm circumpolar water, and with polar constriction of the westerlies enhanced by climate warming, we expect these sectors to contribute more and more to sea level as the <span class="hlt">ice</span> shelves that protect these glaciers will melt faster in contact with more heat from the surrounding oc</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AREPS..43..207A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AREPS..43..207A"><span>Oceanic Forcing of <span class="hlt">Ice</span>-Sheet Retreat: West <span class="hlt">Antarctica</span> and More</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alley, Richard B.; Anandakrishnan, Sridhar; Christianson, Knut; Horgan, Huw J.; Muto, Atsu; Parizek, Byron R.; Pollard, David; Walker, Ryan T.</p> <p>2015-05-01</p> <p>Ocean-<span class="hlt">ice</span> interactions have exerted primary control on the Antarctic <span class="hlt">Ice</span> Sheet and parts of the Greenland <span class="hlt">Ice</span> Sheet, and will continue to do so in the near future, especially through melting of <span class="hlt">ice</span> shelves and calving cliffs. Retreat in response to increasing marine melting typically exhibits threshold behavior, with little change for forcing below the threshold but a rapid, possibly delayed shift to a reduced state once the threshold is exceeded. For Thwaites Glacier, West <span class="hlt">Antarctica</span>, the threshold may already have been exceeded, although rapid change may be delayed by centuries, and the reduced state will likely involve loss of most of the West Antarctic <span class="hlt">Ice</span> Sheet, causing >3 m of sea-level rise. Because of shortcomings in physical understanding and available data, uncertainty persists about this threshold and the subsequent rate of change. Although sea-level histories and physical understanding allow the possibility that <span class="hlt">ice</span>-sheet response could be quite fast, no strong constraints are yet available on the worst-case scenario. Recent work also suggests that the Greenland and East Antarctic <span class="hlt">Ice</span> Sheets share some of the same vulnerabilities to shrinkage from marine influence.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C11E..01K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C11E..01K"><span>Extensive Holocene <span class="hlt">ice</span> sheet grounding line retreat and uplift-driven readvance in West <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kingslake, J.; Scherer, R. P.; Albrecht, T.; Coenen, J. J.; Powell, R. D.; Reese, R.; Stansell, N.; Tulaczyk, S. M.; Whitehouse, P. L.</p> <p>2017-12-01</p> <p>The West Antarctic <span class="hlt">Ice</span> Sheet (WAIS) reached its Last Glacial Maximum (LGM) extent 29-14 kyr before present. Numerical models used to project future <span class="hlt">ice</span>-sheet contributions to sea-level rise exploit reconstructions of post-LGM <span class="hlt">ice</span> mass loss to tune model parameterizations. <span class="hlt">Ice</span>-sheet reconstructions are poorly constrained in areas where floating <span class="hlt">ice</span> shelves or a lack of exposed geology obstruct conventional glacial-geological techniques. In the Weddell and Ross Sea sectors, <span class="hlt">ice</span>-sheet reconstructions have traditionally assumed progressive grounding line (GL) retreat throughout the Holocene. Contrasting this view, using three distinct lines of evidence, we show that the GL retreated hundreds of kilometers inland of its present position, before glacial isostatic rebound during the Mid to Late Holocene caused the GL to readvance to its current position. Evidence for retreat and readvance during the last glacial termination includes (1) widespread radiocarbon in sediment cores recovered from beneath <span class="hlt">ice</span> streams along the Siple and Gould Coasts, indicating marine exposure at least 200 km inland of the current GL, (2) <span class="hlt">ice</span>-penetrating radar observations of relic crevasses and other englacial structures preserved in slow-moving grounded <span class="hlt">ice</span>, indicating <span class="hlt">ice-shelf</span> grounding and (3) an ensemble of new <span class="hlt">ice</span>-sheet simulations showing widespread post-LGM retreat of the GL inland of its current location and later readvance. The model indicates that GL readvance across low slope <span class="hlt">ice</span>-stream troughs requires uplift-driven grounding of the <span class="hlt">ice</span> <span class="hlt">shelf</span> on topographic highs (<span class="hlt">ice</span> rises). Our findings highlight <span class="hlt">ice-shelf</span> pinning points and lithospheric response to unloading as drivers of major <span class="hlt">ice</span>-sheet fluctuations. Full WAIS collapse likely requires GL retreat well beyond its current position in the Ronne and Ross Sectors and linkage via Amundsen Sea sector glaciers.</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 <span class="hlt">Antarctica</span>. 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://adsabs.harvard.edu/abs/2012AGUFM.C31A0574J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.C31A0574J"><span>Geological control of flow in the Institute and Möller <span class="hlt">Ice</span> Streams, West <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jordan, T. A.; Ferraccioli, F.; Ross, N.; Corr, H.; Bingham, R. G.; Rippin, D. M.; Le Brocq, A.; Siegert, M. J.</p> <p>2012-12-01</p> <p>The conditions at the base of an <span class="hlt">ice</span> sheet influence its flow, and reflect the ongoing interaction between moving <span class="hlt">ice</span> and the underlying geology. Critical influences on <span class="hlt">ice</span> flow include subglacial topography, bed lithology, and geothermal heat flux. These factors are influenced either directly by local geology, or by the regional tectonic setting. Geophysical methods have been used in many parts of <span class="hlt">Antarctica</span>, such as the Siple Coast, to reveal the role subglacial geology plays in influencing <span class="hlt">ice</span> flow. Until recently, however, the Institute and Möller <span class="hlt">Ice</span> Streams, which drain ~20% of the West Antarctic <span class="hlt">Ice</span> Sheet into the Weddell Sea, were only covered by sparse airborne radar (~50 km line spacing), and reconnaissance aeromagnetic data, limiting our understanding of the geological template for this sector of the West Antarctic <span class="hlt">Ice</span> Sheet. Here we present our geological interpretation of the first integrated aerogeophysical survey over the catchments of the Institute and Möller <span class="hlt">Ice</span> Streams, which collected ~25,000 km of new aerogeophysical data during the 2010/11 field season. These new airborne radar, magnetic and gravity data reveals both the subglacial topography, and the subglacial geology. Our maps show the fastest flowing coastal part of the Institute <span class="hlt">Ice</span> Stream crosses a sedimentary basin underlain by thinned continental crust. Further inland two distinct <span class="hlt">ice</span> flow provinces are recognised: the Pagano <span class="hlt">Ice</span> Flow Province, which follows the newly identified, ~75 km wide, sinistral strike-slip Pagano Fault Zone at the boundary between East and West <span class="hlt">Antarctica</span>; and the Ellsworth <span class="hlt">Ice</span> Flow Province, which is controlled by the Permo-Triassic structural grain of folded Middle Cambrian-Permian meta-sediments, and Jurassic granitic rocks which form significant subglacial highlands. Our new data highlight the importance of understanding subglacial geology when explaining the complex pattern of <span class="hlt">ice</span> flow observed in the <span class="hlt">ice</span> sheet interior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24031016','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24031016"><span>Channelized <span class="hlt">ice</span> melting in the ocean boundary layer beneath Pine Island Glacier, <span class="hlt">Antarctica</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stanton, T P; Shaw, W J; Truffer, M; Corr, H F J; Peters, L E; Riverman, K L; Bindschadler, R; Holland, D M; Anandakrishnan, S</p> <p>2013-09-13</p> <p><span class="hlt">Ice</span> shelves play a key role in the mass balance of the Antarctic <span class="hlt">ice</span> sheets by buttressing their seaward-flowing outlet glaciers; however, they are exposed to the underlying ocean and may weaken if ocean thermal forcing increases. An expedition to the <span class="hlt">ice</span> <span class="hlt">shelf</span> of the remote Pine Island Glacier, a major outlet of the West Antarctic <span class="hlt">Ice</span> Sheet that has rapidly thinned and accelerated in recent decades, has been completed. Observations from geophysical surveys and long-term oceanographic instruments deployed down bore holes into the ocean cavity reveal a buoyancy-driven boundary layer within a basal channel that melts the channel apex by 0.06 meter per day, with near-zero melt rates along the flanks of the channel. A complex pattern of such channels is visible throughout the Pine Island Glacier <span class="hlt">shelf</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010E%26PSL.291..138B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010E%26PSL.291..138B"><span>Multiple sources supply eolian mineral dust to the Atlantic sector of coastal <span class="hlt">Antarctica</span>: Evidence from recent snow layers at the top of Berkner Island <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>Bory, Aloys; Wolff, Eric; Mulvaney, Robert; Jagoutz, Emil; Wegner, Anna; Ruth, Urs; Elderfield, Harry</p> <p>2010-03-01</p> <p>The Sr and Nd isotopic composition of dust extracted from recent snow layers at the top of Berkner Island <span class="hlt">ice</span> sheet (located within the Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> at the southern end of the Weddell Sea) enables us, for the first time, to document dust provenance in <span class="hlt">Antarctica</span> outside the East Antarctic Plateau (EAP) where all previous studies based on isotopic fingerprinting were carried out. Berkner dust displays an overall crust-like isotopic signature, characterized by more radiogenic 87Sr/ 86Sr and much less radiogenic 143Nd/ 144Nd compared to dust deposited on the EAP during glacial periods. Differences with EAP interglacial dust are not as marked but still significant, indicating that present-day Berkner dust provenance is distinct, at least to some extent, from that of the dust reaching the EAP. The fourteen snow-pit sub-seasonal samples that were obtained span a two-year period (2002-2003) and their dust Sr and Nd isotopic composition reveals that multiple sources are at play over a yearly time period. Southern South America, Patagonia in particular, likely accounts for part of the observed spring/summer dust deposition maxima, when isotopic composition is shifted towards "younger" isotopic signatures. In the spring, possible additional inputs from Australian sources would also be supported by the data. Most of the year, however, the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in East <span class="hlt">Antarctica</span>, which carry old-crust-like isotopic fingerprints. Whether the restricted East Antarctic <span class="hlt">ice</span>-free areas produce sufficient eolian material has yet to be substantiated however. The fact that large (> 5 μm) particles represent a significant fraction of the samples throughout the entire time-series supports scenarios that involve contributions from proximal sources, either in Patagonia and/or <span class="hlt">Antarctica</span> (possibly including snow-free areas in the Antarctic Peninsula and other areas as well). This also</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.4564V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.4564V"><span>GIA models with composite rheology and 3D viscosity: effect on GRACE mass balance in <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van der Wal, Wouter; Whitehouse, Pippa; Schrama, Ernst</p> <p>2014-05-01</p> <p>Most Glacial Isostatic Adjustment (GIA) models that have been used to correct GRACE data for the influence of GIA assume a radial stratification of viscosity in the Earth's mantle (1D viscosity). Seismic data in <span class="hlt">Antarctica</span> indicate that there are large viscosity variations in the horizontal direction (3D viscosity). The purpose of this research is to determine the effect of 3D viscosity on GIA model output, and hence mass balance estimates in <span class="hlt">Antarctica</span>. We use a GIA model with 3D viscosity and composite rheology in combination with <span class="hlt">ice</span> loading histories <span class="hlt">ICE</span>-5G and W12a. From comparisons with uplift and sea-level data in Fennoscandia and North America three preferred viscosity models are selected. For two of the 3D viscosity models the maximum gravity rate due to <span class="hlt">ICE</span>-5G forcing is located over the Ronne-Filchner <span class="hlt">ice</span> <span class="hlt">shelf</span>. This is in contrast with the results obtained using a 1D model, in which the maximum gravity rate due to <span class="hlt">ICE</span>-5G forcing is always located over the Ross <span class="hlt">ice</span> <span class="hlt">shelf</span>. This demonstrates that not all 3D viscosity models can be approximated with a 1D viscosity model. Using CSR release 5 GRACE data from February 2003 to June 2013 mass balance estimates for the three preferred viscosity models are -131 to -171 Gt/year for the <span class="hlt">ICE</span>-5G model, and -48 to -57 Gt/year for the W12a model. The range due to Earth model uncertainty is larger than the error bar for GRACE (10 Gt/year), but smaller than the range resulting from the difference in <span class="hlt">ice</span> loading histories.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1991kul..rept.....D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1991kul..rept.....D"><span>Evaluation of solar flares and electron precipitation by nitrate distribution in <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dreschhoff, Gisela A.; Zeller, Edward J.</p> <p>1991-10-01</p> <p>Most of the time devoted to project research was spent in <span class="hlt">Antarctica</span>. A firm core was drilled by hand to a depth of 29 meters at Windless Bight on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. The main result is that all of the major peaks identified as resulting from ionization caused by SPEs that were found in the 1988-89 core could also be identified in the analytical sequence from the 1990-91 core. Following the Antarctic field season, a set of snow samples were obtained that had been collected by the International Trans-<span class="hlt">Antarctica</span> Expedition. The analysis of these samples showed nitrate flux that correlates closely with known spatial distribution of electron precipitation in the south polar region. A new apparatus has been build for field analysis on a continuous basis of nitrate and conductivity in a melt derived from the vertical melting of <span class="hlt">ice</span> cores.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1615919R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1615919R"><span>Airborne and ground based measurements in McMurdo Sound, <span class="hlt">Antarctica</span>, for the validation of satellite derived <span class="hlt">ice</span> thickness</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rack, Wolfgang; Haas, Christian; Langhorne, Pat; Leonard, Greg; Price, Dan; Barnsdale, Kelvin; Soltanzadeh, Iman</p> <p>2014-05-01</p> <p>Melting and freezing processes in the <span class="hlt">ice</span> <span class="hlt">shelf</span> cavities of the Ross and McMurdo <span class="hlt">Ice</span> Shelves significantly influence the sea <span class="hlt">ice</span> formation in McMurdo Sound. Between 2009 and 2013 we used a helicopter-borne laser and electromagnetic induction sounder (EM bird) to measure thickness and freeboard profiles across the <span class="hlt">ice</span> <span class="hlt">shelf</span> and the landfast sea <span class="hlt">ice</span>, which was accompanied by extensive field validation, and coordinated with satellite altimeter overpasses. Using freeboard and thickness, the bulk density of all <span class="hlt">ice</span> types was calculated assuming hydrostatic equilibrium. Significant density steps were detected between first-year and multi-year sea <span class="hlt">ice</span>, with higher values for the younger sea <span class="hlt">ice</span>. Values are overestimated in areas with abundance of sub-<span class="hlt">ice</span> platelets because of overestimation in both <span class="hlt">ice</span> thickness and freeboard. On the <span class="hlt">ice</span> <span class="hlt">shelf</span>, bulk <span class="hlt">ice</span> densities were sometimes higher than that of pure <span class="hlt">ice</span>, which can be explained by both the accretion of marine <span class="hlt">ice</span> and glacial sediments. For thin <span class="hlt">ice</span>, the freeboard to thickness conversion critically depends on the knowledge of snow properties. Our measurements allow tuning and validation of snow cover simulations using the Weather Research Forecasting (WRF) model. The simulated snowcover is used to calculate <span class="hlt">ice</span> thickness from satellite derived freeboard. The results of our measurements, which are supported by the New Zealand Antarctic programme, draw a picture of how oceanographic processes influence the <span class="hlt">ice</span> <span class="hlt">shelf</span> morphology and sea <span class="hlt">ice</span> formation in McMurdo Sound, and how satellite derived freeboard of ICESat and CryoSat together with information on snow cover can potentially capture the signature of these processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020030360','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020030360"><span>Geostatistical Methods For Determination of Roughness, Topography, And Changes of Antarctic <span class="hlt">Ice</span> Streams From SAR And Radar Altimeter Data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Herzfeld, Ute C.</p> <p>2002-01-01</p> <p>The central objective of this project has been the development of geostatistical methods fro mapping elevation and <span class="hlt">ice</span> surface characteristics from satellite radar altimeter (RA) and Syntheitc Aperture Radar (SAR) data. The main results are an Atlas of elevation maps of <span class="hlt">Antarctica</span>, from GEOSAT RA data and an Atlas from ERS-1 RA data, including a total of about 200 maps with 3 km grid resolution. Maps and digital terrain models are applied to monitor and study changes in Antarctic <span class="hlt">ice</span> streams and glaciers, including Lambert Glacier/Amery <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Mertz and Ninnis Glaciers, Jutulstraumen Glacier, Fimbul <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Slessor Glacier, Williamson Glacier and others.</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.osti.gov/pages/biblio/1255085-reactivation-kamb-ice-stream-tributaries-triggers-century-scale-reorganization-siple-coast-ice-flow-west-antarctica','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1255085-reactivation-kamb-ice-stream-tributaries-triggers-century-scale-reorganization-siple-coast-ice-flow-west-antarctica"><span>Reactivation of Kamb <span class="hlt">Ice</span> Stream tributaries triggers century-scale reorganization of Siple Coast <span class="hlt">ice</span> flow in West <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Bougamont, M.; Christoffersen, P.; Price, S. F.; ...</p> <p>2015-10-21</p> <p>Ongoing, centennial-scale flow variability within the Ross <span class="hlt">ice</span> streams of West <span class="hlt">Antarctica</span> suggests that the present-day positive mass balance in this region may reverse in the future. Here we use a three-dimensional <span class="hlt">ice</span> sheet model to simulate <span class="hlt">ice</span> flow in this region over 250 years. The flow responds to changing basal properties, as a subglacial till layer interacts with water transported in an active subglacial hydrological system. We show that a persistent weak bed beneath the tributaries of the dormant Kamb <span class="hlt">Ice</span> Stream is a source of internal <span class="hlt">ice</span> flow instability, which reorganizes all <span class="hlt">ice</span> streams in this region, leadingmore » to a reduced (positive) mass balance within decades and a net loss of <span class="hlt">ice</span> within two centuries. This hitherto unaccounted for flow variability could raise sea level by 5 mm this century. Furthermore, better constraints on future sea level change from this region will require improved estimates of geothermal heat flux and subglacial water transport.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008E%26PSL.265..246N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008E%26PSL.265..246N"><span>Conditions for a steady <span class="hlt">ice</span> sheet <span class="hlt">ice</span> <span class="hlt">shelf</span> junction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nowicki, S. M. J.; Wingham, D. J.</p> <p>2008-01-01</p> <p>This paper investigates the conditions under which a marine <span class="hlt">ice</span> sheet may adopt a steady profile. The <span class="hlt">ice</span> 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 <span class="hlt">ice</span> sheet and <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> flowing out over the ocean, we conclude that when sliding is present, Weertman's 'instability' hypothesis holds.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C34B..06P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C34B..06P"><span>An Antarctic stratigraphic record of step-wise <span class="hlt">ice</span>-sheet growth through the Eocene-Oligocene transition</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Passchier, S.; Ciarletta, D. J.; Miriagos, T.; Bijl, P.; Bohaty, S. M.</p> <p>2016-12-01</p> <p>The Antarctic cryosphere plays a critical role in the ocean-atmosphere system, but its early evolution is still poorly known. With a near-field record from Prydz Bay, <span class="hlt">Antarctica</span>, we conclude that Antarctic continental <span class="hlt">ice</span>-sheet growth commenced with the EOT-1 "precursor" glaciation, during a time of Subantarctic surface ocean cooling and a decline in atmospheric pCO2. Prydz Bay lies downstream of a major East Antarctic <span class="hlt">ice</span>-sheet drainage system and the Gamburtsev Mountains, a likely nucleation point for the first <span class="hlt">ice</span> sheets. Its sedimentary records uniquely constrain the timing of <span class="hlt">ice</span>-sheet advance onto the continental <span class="hlt">shelf</span>. We investigate a detrital record extracted from three Ocean Drilling Program drill holes in Prydz Bay within a new depositional and chronological framework spanning the late Eocene to early Oligocene ( 36-33 Ma). The chemical index of alteration (CIA) and the S-index, calculated from the major element geochemistry of bulk samples, yield estimates of chemical weathering intensities and mean annual temperature (MAT) on the East Antarctic continent. We document evidence for late Eocene mountain glaciation along with transient warm events at 35.8-34.8 Ma. These data and our sedimentological analyses confirm the presence of ephemeral mountain glaciers on East <span class="hlt">Antarctica</span> during the late Eocene between 35.9 and 34.4 Ma. Furthermore, we document the stepwise climate cooling of the Antarctic hinterland from 34.4 Ma as the <span class="hlt">ice</span> sheet advanced towards the edges of the continent during EOT-1. The youngest part of our data set correlates to the time interval of the Oi-1 glaciation, when the <span class="hlt">ice</span>-sheet in Prydz Bay extended to the outer <span class="hlt">shelf</span>. Cooling and <span class="hlt">ice</span> growth on <span class="hlt">Antarctica</span> was spatially variable and <span class="hlt">ice</span> sheets formed under declining pCO2. These results point to complex <span class="hlt">ice</span> sheet - atmosphere - ocean - solid-earth feedbacks.</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 <span class="hlt">Antarctica</span>, <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/2016AGUFM.C43B0751P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C43B0751P"><span>Seasonal and Interannual Fast-<span class="hlt">Ice</span> Variability from MODIS Surface-Temperature Anomalies, and its Link to External Forcings in Atka Bay, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paul, S.; Hoppmann, M.; Willmes, S.; Heinemann, G.</p> <p>2016-12-01</p> <p>Around <span class="hlt">Antarctica</span>, sea <span class="hlt">ice</span> is regularly attached to coastal features. These regions of mostly seasonal fast <span class="hlt">ice</span> interact with the atmosphere, ocean and coastal ecosystem in a variety of ways. The growth and breakup cycles may depend on different factors, such as water- and air temperatures, wind conditions, tides, ocean swell, the passage of icebergs and the presence of nearby polynyas. However, a detailed understanding about the interaction between these factors and the fast-<span class="hlt">ice</span> cycle is missing. In order to better understand the linkages between general fast-<span class="hlt">ice</span> evolution and external forcing factors, we present results from an observational case study performed on the seasonal fast-<span class="hlt">ice</span> cover of Atka Bay, eastern Weddell Sea. The <span class="hlt">ice</span> conditions in this region are critical for the supply of the German wintering station Neumayer III. Moreover, the fast <span class="hlt">ice</span> at Atka Bay hosts a unique ecosystem based on the presence of a sub-<span class="hlt">ice</span> platelet layer and a large emperor penguin colony. While some qualitative characterizations on the seasonal fast-<span class="hlt">ice</span> cycle in this region exist, no proper quantification was carried out to date. The backbone of this work is a new algorithm, which yields the first continuous time series of open-water fractions from Moderate-Resolution Imaging Spectroradiometer (MODIS) surface temperatures. The open-water fractions are derived from a range of running multi-day median temperature composites, utilizing the thermal footprint of warm open water and thin <span class="hlt">ice</span> in contrast to cold pack-<span class="hlt">ice/ice-shelf</span> areas. This unique, and manually validated dataset allows us to monitor changes in fast-<span class="hlt">ice</span> extent on a near daily basis, for a period of 14 years (2002-2015). In a second step, we combine these results with iceberg observations, data from the meteorological observatory, and auxiliary satellite data in order to identify the main factors governing fast-<span class="hlt">ice</span> formation and break-up.</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 calving 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 <span class="hlt">Antarctica</span> 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 <span class="hlt">Antarctica</span>-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://www.ncbi.nlm.nih.gov/pubmed/29540750','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29540750"><span>Recent high-resolution Antarctic <span class="hlt">ice</span> velocity maps reveal increased mass loss in Wilkes Land, East <span class="hlt">Antarctica</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Shen, Qiang; Wang, Hansheng; Shum, C K; Jiang, Liming; Hsu, Hou Tse; Dong, Jinglong</p> <p>2018-03-14</p> <p>We constructed Antarctic <span class="hlt">ice</span> velocity maps from Landsat 8 images for the years 2014 and 2015 at a high spatial resolution (100 m). These maps were assembled from 10,690 scenes of displacement vectors inferred from more than 10,000 optical images acquired from December 2013 through March 2016. We estimated the mass discharge of the Antarctic <span class="hlt">ice</span> sheet in 2008, 2014, and 2015 using the Landsat <span class="hlt">ice</span> velocity maps, interferometric synthetic aperture radar (InSAR)-derived <span class="hlt">ice</span> velocity maps (~2008) available from prior studies, and <span class="hlt">ice</span> thickness data. An increased mass discharge (53 ± 14 Gt yr -1 ) was found in the East Indian Ocean sector since 2008 due to unexpected widespread glacial acceleration in Wilkes Land, East <span class="hlt">Antarctica</span>, while the other five oceanic sectors did not exhibit significant changes. However, present-day increased mass loss was found by previous studies predominantly in west <span class="hlt">Antarctica</span> and the Antarctic Peninsula. The newly discovered increased mass loss in Wilkes Land suggests that the ocean heat flux may already be influencing <span class="hlt">ice</span> dynamics in the marine-based sector of the East Antarctic <span class="hlt">ice</span> sheet (EAIS). The marine-based sector could be adversely impacted by ongoing warming in the Southern Ocean, and this process may be conducive to destabilization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12.1415L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12.1415L"><span>Changes in flow of Crosson and Dotson <span class="hlt">ice</span> shelves, West <span class="hlt">Antarctica</span>, in response to elevated melt</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lilien, David A.; Joughin, Ian; Smith, Benjamin; Shean, David E.</p> <p>2018-04-01</p> <p>Crosson and Dotson <span class="hlt">ice</span> shelves are two of the most rapidly changing outlets in West <span class="hlt">Antarctica</span>, displaying both significant thinning and grounding-line retreat in recent decades. We used remotely sensed measurements of velocity and <span class="hlt">ice</span> geometry to investigate the processes controlling their changes in speed and grounding-line position over the past 20 years. We combined these observations with inverse modeling of the viscosity of the <span class="hlt">ice</span> shelves to understand how weakening of the shelves affected this speedup. These <span class="hlt">ice</span> shelves have lost mass continuously since the 1990s, and we find that this loss results from increasing melt beneath both shelves and the increasing speed of Crosson. High melt rates persisted over the period covered by our observations (1996-2014), with the highest rates beneath areas that ungrounded during this time. Grounding-line flux exceeded basin-wide accumulation by about a factor of 2 throughout the study period, consistent with earlier studies, resulting in significant loss of grounded as well as floating <span class="hlt">ice</span>. The near doubling of Crosson's speed in some areas during this time is likely the result of weakening of its margins and retreat of its grounding line. This speedup contrasts with Dotson, which has maintained its speed despite increasingly high melt rates near its grounding line, likely a result of the sustained competency of the <span class="hlt">shelf</span>. Our results indicate that changes to melt rates began before 1996 and suggest that observed increases in melt in the 2000s compounded an ongoing retreat of this system. Advection of a channel along Dotson, as well as the grounding-line position of Kohler Glacier, suggests that Dotson experienced a change in flow around the 1970s, which may be the initial cause of its continuing retreat.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010TCD.....4.1277W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010TCD.....4.1277W"><span>The Potsdam Parallel <span class="hlt">Ice</span> Sheet Model (PISM-PIK) - Part 1: Model description</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.</p> <p>2010-08-01</p> <p>We present the Potsdam Parallel <span class="hlt">Ice</span> Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale <span class="hlt">ice</span> sheet-<span class="hlt">shelf</span> systems. It is derived from the Parallel <span class="hlt">Ice</span> Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire <span class="hlt">ice</span> covered region: the shallow <span class="hlt">ice</span> approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow <span class="hlt">shelf</span> approximation (SSA) dominates the velocity field in <span class="hlt">ice</span> <span class="hlt">shelf</span> regions and serves as a basal sliding velocity in grounded regions. <span class="hlt">Ice</span> 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 <span class="hlt">ice</span> fronts. <span class="hlt">Ice</span> <span class="hlt">shelf</span> margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> Sheet Model Intercomparison Project (MISMIP) and is used for a dynamic equilibrium simulation of <span class="hlt">Antarctica</span> under present-day conditions in the second part of this paper (Martin et al., 2010).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JGRD..11522112S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JGRD..11522112S"><span>Synoptic controls on precipitation pathways and snow delivery to high-accumulation <span class="hlt">ice</span> core sites in the Ross Sea region, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sinclair, K. E.; Bertler, N. A. N.; Trompetter, W. J.</p> <p>2010-11-01</p> <p>Dominant storm tracks to two <span class="hlt">ice</span> core sites on the western margin of the Ross Sea, <span class="hlt">Antarctica</span> (Skinner Saddle (SKS) and Evans Piedmont Glacier), are investigated to establish key synoptic controls on snow accumulation. This is critical in terms of understanding the seasonality, source regions, and transport pathways of precipitation delivered to these sites. In situ snow depth and meteorological observations are used to identify major accumulation events in 2007-2008, which differ considerably between sites in terms of their magnitude and seasonal distribution. While snowfall at Evans Piedmont Glacier occurs almost exclusively during summer and spring, Skinner Saddle receives precipitation year round with a lull during the months of April and May. Cluster analysis of daily back trajectories reveals that the highest-accumulation days at both sites result from fast-moving air masses, associated with synoptic-scale low-pressure systems. There is evidence that short-duration pulses of snowfall at SKS also originate from mesocyclone development over the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and local moisture sources. Changes in the frequency and seasonal distribution of these mechanisms of precipitation delivery will have a marked impact on annual accumulation over time and will therefore need careful consideration during the interpretation of stable isotope and geochemical records from these <span class="hlt">ice</span> cores.</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 <span class="hlt">Antarctica</span>.</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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.C31F..01G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.C31F..01G"><span>Continued rapid glacier recession following the 1995 collapse of the Prince Gustav <span class="hlt">Ice</span> <span class="hlt">Shelf</span> on the Antarctic Peninsula (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glasser, N. F.; Scambos, T. A.</p> <p>2009-12-01</p> <p>We use optical satellite imagery (ASTER and Landsat) to document changes in the Prince Gustav <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice-shelf</span> break-up had commenced at least seven years before collapse. Meltwater ponds and streams were also common across its surface. After the <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice-shelf</span> removal by rapid and continued recession and that the response time of glaciers on the Antarctic Peninsula to <span class="hlt">ice-shelf</span> 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 <span class="hlt">ice-shelf</span> collapse.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AtmRe.107...42B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AtmRe.107...42B"><span>Aerosol size distribution at Nansen <span class="hlt">Ice</span> Sheet <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Belosi, F.; Contini, D.; Donateo, A.; Santachiara, G.; Prodi, F.</p> <p>2012-04-01</p> <p>During austral summer 2006, in the framework of the XXII Italian Antarctic expedition of PNRA (Italian National Program for Research in <span class="hlt">Antarctica</span>), aerosol particle number size distribution measurements were performed in the 10-500 range nm over the Nansen <span class="hlt">Ice</span> Sheet glacier (NIS, 74°30' S, 163°27' E; 85 m a.s.l), a permanently <span class="hlt">iced</span> branch of the Ross Sea. Observed total particle number concentrations varied between 169 and 1385 cm- 3. A monomodal number size distribution, peaking at about 70 nm with no variation during the day, was observed for continental air mass, high wind speed and low relative humidity. Trimodal number size distributions were also observed, in agreement with measurements performed at Aboa station, which is located on the opposite side of the Antarctic continent to the NIS. In this case new particle formation, with subsequent particle growth up to about 30 nm, was observed even if not associated with maritime air masses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017TCry...11.1283Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017TCry...11.1283Y"><span>Iceberg calving of Thwaites Glacier, West <span class="hlt">Antarctica</span>: full-Stokes modeling combined with linear elastic fracture mechanics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, Hongju; Rignot, Eric; Morlighem, Mathieu; Seroussi, Helene</p> <p>2017-05-01</p> <p>Thwaites Glacier (TG), West <span class="hlt">Antarctica</span>, 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 <span class="hlt">ice</span> fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-<span class="hlt">shelf</span> 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 <span class="hlt">Ice</span>Bridge 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> is shortened or when the <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> are more vulnerable to calving than glaciers developing a long <span class="hlt">ice</span> <span class="hlt">shelf</span>, especially as the <span class="hlt">ice</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1919075L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1919075L"><span><span class="hlt">Ice</span> Flows: A Game-based Learning approach to Science Communication</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Le Brocq, Anne</p> <p>2017-04-01</p> <p>Game-based learning allows people to become immersed in an environment, and learn how the system functions and responds to change through playing a game. Science and gaming share a similar characteristic: they both involve learning and understanding the rules of the environment you are in, in order to achieve your objective. I will share experiences of developing and using the educational game "<span class="hlt">Ice</span> Flows" for science communication. The game tasks the player with getting a penguin to its destination, through controlling the size of the <span class="hlt">ice</span> sheet via ocean temperature and snowfall. Therefore, the game aims to educate the user about the environmental controls on the behaviour of the <span class="hlt">ice</span> sheet, whilst they are enjoying playing a game with penguins. The game was funded by a NERC Large Grant entitled "<span class="hlt">Ice</span> shelves in a warming world: Filchner <span class="hlt">Ice</span> <span class="hlt">Shelf</span> system, <span class="hlt">Antarctica</span>", so uses data from the Weddell Sea sector of the West Antarctic <span class="hlt">Ice</span> Sheet to generate unique levels. The game will be easily expandable to other regions of <span class="hlt">Antarctica</span> and beyond, with the ultimate aim of giving a full understanding to the user of different <span class="hlt">ice</span> flow regimes across the planet.</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 <span class="hlt">Antarctica</span> 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('http://adsabs.harvard.edu/abs/2016TCry...10.2501P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016TCry...10.2501P"><span><span class="hlt">Ice</span> core evidence for a 20th century increase in surface mass balance in coastal Dronning Maud Land, East <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Philippe, Morgane; Tison, Jean-Louis; Fjøsne, Karen; Hubbard, Bryn; Kjær, Helle A.; Lenaerts, Jan T. M.; Drews, Reinhard; Sheldon, Simon G.; De Bondt, Kevin; Claeys, Philippe; Pattyn, Frank</p> <p>2016-10-01</p> <p><span class="hlt">Ice</span> cores provide temporal records of surface mass balance (SMB). Coastal areas of <span class="hlt">Antarctica</span> have relatively high and variable SMB, but are under-represented in records spanning more than 100 years. Here we present SMB reconstruction from a 120 m-long <span class="hlt">ice</span> core drilled in 2012 on the Derwael <span class="hlt">Ice</span> Rise, coastal Dronning Maud Land, East <span class="hlt">Antarctica</span>. Water stable isotope (δ18O and δD) stratigraphy is supplemented by discontinuous major ion profiles and continuous electrical conductivity measurements. The base of the <span class="hlt">ice</span> core is dated to AD 1759 ± 16, providing a climate proxy for the past ˜ 250 years. The core's annual layer thickness history is combined with its gravimetric density profile to reconstruct the site's SMB history, corrected for the influence of <span class="hlt">ice</span> deformation. The mean SMB for the core's entire history is 0.47 ± 0.02 m water equivalent (w.e.) a-1. The time series of reconstructed annual SMB shows high variability, but a general increase beginning in the 20th century. This increase is particularly marked during the last 50 years (1962-2011), which yields mean SMB of 0.61 ± 0.01 m w.e. a-1. This trend is compared with other reported SMB data in <span class="hlt">Antarctica</span>, generally showing a high spatial variability. Output of the fully coupled Community Earth System Model (CESM) suggests that, although atmospheric circulation is the main factor influencing SMB, variability in sea surface temperatures and sea <span class="hlt">ice</span> cover in the precipitation source region also explain part of the variability in SMB. Local snow redistribution can also influence interannual variability but is unlikely to influence long-term trends significantly. This is the first record from a coastal <span class="hlt">ice</span> core in East <span class="hlt">Antarctica</span> to show an increase in SMB beginning in the early 20th century and particularly marked during the last 50 years.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040015278&hterms=BALANCE+SHEET&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DBALANCE%2BSHEET','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040015278&hterms=BALANCE+SHEET&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DBALANCE%2BSHEET"><span>Antarctic <span class="hlt">Ice</span>-Sheet Mass Balance from Satellite Altimetry 1992 to 2001</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; Brenner, Anita C.; Cornejo, Helen; Giovinetto, Mario; Saba, Jack L.; Yi, Donghui</p> <p>2003-01-01</p> <p>A major uncertainty in understanding the causes of the current rate of sea level rise is the potential contributions from mass imbalances of the Greenland and Antarctic <span class="hlt">ice</span> sheets. Estimates of the current mass balance of the Antarctic <span class="hlt">ice</span> sheet are derived from surface- elevation changes obtained from 9 years of ERS - 1 & 2 radar altimeter data. Elevation time-series are created from altimeter crossovers among 90-day data periods on a 50 km grid to 81.5 S. The time series are fit with a multivariate linear/sinusoidal function to give the average rate of elevation change (dH/dt). On the major Rome-Filchner, Ross, and Amery <span class="hlt">ice</span> shelves, the W d t are small or near zero. In contrast, the <span class="hlt">ice</span> shelves of the Antarctic Peninsula and along the West Antarctic coast appear to be thinning significantly, with a 23 +/- 3 cm per year surface elevation decrease on the Larsen <span class="hlt">ice</span> <span class="hlt">shelf</span> and a 65 +/- 4 cm per year decrease on the Dotson <span class="hlt">ice</span> <span class="hlt">shelf</span>. On the grounded <span class="hlt">ice</span>, significant elevation decreases are obtained over most of the drainage basins of the Pine Island and Thwaites glaciers in West <span class="hlt">Antarctica</span> and inland of Law Dome in East <span class="hlt">Antarctica</span>. Significant elevation increases are observed within about 200 km of the coast around much of the rest of the <span class="hlt">ice</span> sheet. Farther inland, the changes are a mixed pattern of increases and decreases with increases of a few centimeters per year at the highest elevations of the East Antarctic plateau. The derived elevation changes are combined with estimates of the bedrock uplift from several models to provide maps of <span class="hlt">ice</span> thickness change. The <span class="hlt">ice</span> thickness changes enable estimates of the <span class="hlt">ice</span> mass balances for the major drainage basins, the overall mass balance, and the current contribution of the <span class="hlt">ice</span> sheet to global sea level change.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUFMIP31A..03S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUFMIP31A..03S"><span><span class="hlt">Ice</span> Sheet Temperature Records - Satellite and In Situ Data from <span class="hlt">Antarctica</span> and Greenland</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.; Comiso, J. C.</p> <p>2001-12-01</p> <p>Recently completed decadal-length surface temperature records from <span class="hlt">Antarctica</span> and Greenland are providing insights into the challenge of detecting climate change. <span class="hlt">Ice</span> and snow cover at high latitudes influence the global climate system by reflecting much of the incoming solar energy back to space. An expected consequence of global warming is a decrease in area covered by snow and <span class="hlt">ice</span> and an increase in Earth's absorption of solar radiation. Models have predicted that the effects of climate warming may be amplified at high latitudes; thinning of the Greenland <span class="hlt">ice</span> sheet margins and the breakup of Antarctic Peninsula <span class="hlt">ice</span> shelves suggest this process may have begun. Satellite data provide an excellent means of observing climate parameters across both long temporal and remote spatial domains but calibration and validation of their data remains a challenge. Infrared sensors can provide excellent temperature information but cloud cover and calibration remain as problems. Passive-microwave sensors can obtain data during the long polar night and through clouds but have calibration issues and a much lower spatial resolution. Automatic weather stations are generally spatially- and temporally-restricted and may have long gaps due to equipment failure. Stable isotopes of oxygen and hydrogen from <span class="hlt">ice</span> sheet locations provide another means of determining temperature variations with time but are challenging to calibrate to observed temperatures and also represent restricted areas. This presentation will discuss these issues and elaborate on the development and limitations of composite satellite, automatic weather station, and proxy temperature data from selected sites in <span class="hlt">Antarctica</span> and Greenland.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.C21B0585S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.C21B0585S"><span>Mass Balance of the Northern Antarctic Peninsula and its Ongoing Response to <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Loss</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.; Berthier, E.; Haran, T. M.; Shuman, C. A.; Cook, A. J.; Bohlander, J. A.</p> <p>2012-12-01</p> <p>An assessment of the most rapidly changing areas of the Antarctic Peninsula (north of 66°S) shows that <span class="hlt">ice</span> mass loss for the region is dominated by areas affected by eastern-Peninsula <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> drainages affected by recent <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> loss. Areas with <span class="hlt">shelf</span> losses occurring 30 to 100s of years ago seem to be relatively stable or losing mass only slowly (western glaciers, northernmost areas). The</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/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, <span class="hlt">Antarctica</span>, 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('https://ntrs.nasa.gov/search.jsp?R=19940007628&hterms=sea+ice+albedo&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dsea%2Bice%2Balbedo','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940007628&hterms=sea+ice+albedo&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dsea%2Bice%2Balbedo"><span>Modern <span class="hlt">shelf</span> <span class="hlt">ice</span>, equatorial Aeolis Quadrangle, Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brakenridge, G. R.</p> <p>1993-01-01</p> <p>As part of a detailed study of the geological and geomorphological evolution of Aeolis Quadrangle, I have encountered evidence suggesting that near surface <span class="hlt">ice</span> 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 <span class="hlt">ice</span> floes formed almost immediately, and that either grounded <span class="hlt">ice</span> or an <span class="hlt">ice</span>-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 <span class="hlt">ice</span> floes formed almost immediately, and that either grounded <span class="hlt">ice</span> or an <span class="hlt">ice</span>-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 <span class="hlt">ice</span> preservation, and at least the lower portions of this dust cover may be cemented by water <span class="hlt">ice</span>. Detailed mapping using Viking stereopairs and quantitative comparisons to terrestrial <span class="hlt">shelf</span> <span class="hlt">ice</span> geometries are underway.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C24C..05S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C24C..05S"><span>Meteorological Drivers of West Antarctic <span class="hlt">Ice</span> Sheet and <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Surface Melt</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scott, R. C.; Nicolas, J. P.; Bromwich, D. H.; Norris, J. R.; Lubin, D.</p> <p>2017-12-01</p> <p>We identify synoptic patterns and surface energy balance components driving warming and surface melting on the West Antarctic <span class="hlt">Ice</span> Sheet (WAIS) and <span class="hlt">ice</span> shelves using reanalysis and satellite remote sensing data from 1973-present. We have developed a synoptic climatology of atmospheric circulation patterns during the summer melt season using k-means cluster and composite analysis of daily 700-mb geopotential height and near-surface air temperature and wind fields from the ECMWF ERA-Interim reanalysis. Surface melt occurrence is detected in satellite passive microwave brightness temperature observations (K-band, horizontal polarization) beginning with the NASA Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR) and continuing with its more familiar descendants SMMR, SSM/I and SSMIS. To diagnose synoptic precursors and physical processes driving surface melt we combine the circulation climatology and multi-decadal records of cloud cover with surface radiative fluxes from the Extended AVHRR Polar Pathfinder (APP-x) project. We identify three distinct modes of regional summer West Antarctic warming since 1979 involving anomalous ridging over West <span class="hlt">Antarctica</span> (WA) and the Amundsen Sea (AS). During the 1970s, ESMR data reveal four extensive melt events on the Ross Sea sector of the WAIS also linked to AS blocking. We therefore define an Amundsen Sea Blocking Index (ASBI). The ASBI and synoptic circulation pattern occurrence frequencies are correlated with the tropical Pacific (ENSO) and high latitude Southern Annular Mode (SAM) indices and the West Antarctic melt index. Surface melt in WA is favored by enhanced downwelling infrared and turbulent sensible heat fluxes associated with intrusions of warm, moist marine air. Consistent with recent findings from the Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE), marine advection to the Ross sector is favored by El Niño conditions in the tropical Pacific and a negative SAM. We also find</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009GeCoA..73.5959G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009GeCoA..73.5959G"><span>Ultra-low rare earth element content in accreted <span class="hlt">ice</span> from sub-glacial Lake Vostok, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gabrielli, Paolo; Planchon, Frederic; Barbante, Carlo; Boutron, Claude F.; Petit, Jean Robert; Bulat, Sergey; Hong, Sungmin; Cozzi, Giulio; Cescon, Paolo</p> <p>2009-10-01</p> <p>This paper reports the first rare earth element (REE) concentrations in accreted <span class="hlt">ice</span> refrozen from sub-glacial Lake Vostok (East <span class="hlt">Antarctica</span>). REE were determined in various sections of the Vostok <span class="hlt">ice</span> core in order to geochemically characterize its impurities. Samples were obtained from accreted <span class="hlt">ice</span> and, for comparison, from the upper glacier <span class="hlt">ice</span> of atmospheric origin (undisturbed, disturbed and glacial flour <span class="hlt">ice</span>). REE concentrations ranged between 0.8-56 pg g -1 for Ce and 0.0035-0.24 pg g -1 for Lu in glacier <span class="hlt">ice</span>, and between <0.1-24 pg g -1 for Ce and <0.0004-0.02 pg g -1 for Lu in accreted <span class="hlt">ice</span>. Interestingly, the REE concentrations in the upper accreted <span class="hlt">ice</span> (AC 1; characterized by visible aggregates containing a mixture of very fine terrigenous particles) and in the deeper accreted <span class="hlt">ice</span> (AC 2; characterized by transparent <span class="hlt">ice</span>) are lower than those in fresh water and seawater, respectively. We suggest that such ultra-low concentrations are unlikely to be representative of the real REE content in Lake Vostok, but instead may reflect phase exclusion processes occurring at the <span class="hlt">ice</span>/water interface during refreezing. In particular, the uneven spatial distribution (on the order of a few cm) and the large range of REE concentrations observed in AC 1 are consistent with the occurrence/absence of the aggregates in adjacent <span class="hlt">ice</span>, and point to the presence of solid-phase concentration/exclusion processes occurring within separate pockets of frazil <span class="hlt">ice</span> during AC 1 formation. Interestingly, if the LREE enrichment found in AC 1 was not produced by chemical fractionation occurring in Lake Vostok water, this may reflect a contribution of bedrock material, possibly in combination with aeolian dust released into the lake by melting of the glacier <span class="hlt">ice</span>. Collectively, this valuable information provides new insight into the accreted <span class="hlt">ice</span> formation processes, the bedrock geology of East <span class="hlt">Antarctica</span> as well as the water chemistry and circulation of Lake Vostok.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.U53C..12B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.U53C..12B"><span>Ultra-low rare earth element content in accreted <span class="hlt">ice</span> from sub-glacial Lake Vostok, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barbante, C.; Gabrielli, P.; Turetta, C.; Planchon, F.; Boutron, C.; Petit, J. R.; Bulat, S.; Hong, S.; Cozzi, G.; Cescon, P.</p> <p>2009-12-01</p> <p>We report the first rare earth element (REE) concentrations in accreted <span class="hlt">ice</span> refrozen from sub-glacial Lake Vostok (East <span class="hlt">Antarctica</span>). REE were determined in various sections of the Vostok <span class="hlt">ice</span> core in order to geochemically characterize its impurities. Samples were obtained from accreted <span class="hlt">ice</span> and, for comparison, from the upper glacier <span class="hlt">ice</span> of atmospheric origin (undisturbed, disturbed and glacial flour <span class="hlt">ice</span>). REE concentrations ranged between 0.8-56 pg g-1 for Ce and 0.0035- 0.24 pg g-1 for Lu in glacier <span class="hlt">ice</span>, and between <0.1-24 pg g-1 for Ce and <0.0004-0.02 pg g-1 for Lu in accreted <span class="hlt">ice</span>. Interestingly, the REE concentrations in the upper accreted <span class="hlt">ice</span> (AC1;characterized by visible aggregates containing a mixture of very fine terrigenous particles) and in the deeper accreted <span class="hlt">ice</span> (AC2; characterized by transparent <span class="hlt">ice</span>) are lower than those in fresh water and seawater, respectively. We suggest that such ultra-low concentrations are unlikely to be representative of the real REE content in Lake Vostok, but instead may reflect phase exclusion processes occurring at the <span class="hlt">ice</span>/water interface during refreezing. In particular, the uneven spatial distribution (on the order of a few cm) and the large range of REE concentrations observed in AC1 are consistent with the occurrence/absence of the aggregates in adjacent <span class="hlt">ice</span>, and point to the presence of solid-phase concentration/exclusion processes occurring within separate pockets of frazil <span class="hlt">ice</span> during AC1 formation. Interestingly, if the LREE enrichment found in AC1 was not produced by chemical fractionation occurring in Lake Vostok water, this may reflect a contribution of bedrock material, possibly in combination with aeolian dust released into the lake by melting of the glacier <span class="hlt">ice</span>. Collectively, this valuable information provides new insight into the accreted <span class="hlt">ice</span> formation processes, the bedrock geology of East <span class="hlt">Antarctica</span> as well as the water chemistry and circulation of Lake Vostok.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20000070390&hterms=retreated&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dretreated','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20000070390&hterms=retreated&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dretreated"><span>Radar Interferometry Studies of the Mass Balance of Polar <span class="hlt">Ice</span> Sheets</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rignot, Eric (Editor)</p> <p>1999-01-01</p> <p>The objectives of this work are to determine the current state of mass balance of the Greenland and Antarctic <span class="hlt">Ice</span> Sheets. Our approach combines different techniques, which include satellite synthetic-aperture radar interferometry (InSAR), radar and laser altimetry, radar <span class="hlt">ice</span> sounding, and finite-element modeling. In Greenland, we found that 3.5 times more <span class="hlt">ice</span> flows out of the northern part of the Greenland <span class="hlt">Ice</span> Sheet than previously accounted for. The discrepancy between current and past estimates is explained by extensive basal melting of the glacier floating sections in the proximity of the grounding line where the glacier detaches from its bed and becomes afloat in the ocean. The inferred basal melt rates are very large, which means that the glaciers are very sensitive to changes in ocean conditions. Currently, it appears that the northern Greenland glaciers discharge more <span class="hlt">ice</span> than is being accumulated in the deep interior, and hence are thinning. Studies of temporal changes in grounding line position using InSAR confirm the state of retreat of northern glaciers and suggest that thinning is concentrated at the lower elevations. Ongoing work along the coast of East Greenland reveals an even larger mass deficit for eastern Greenland glaciers, with thinning affecting the deep interior of the <span class="hlt">ice</span> sheet. In <span class="hlt">Antarctica</span>, we found that glaciers flowing into a large <span class="hlt">ice</span> <span class="hlt">shelf</span> system, such as the Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in the Weddell Sea, exhibit an <span class="hlt">ice</span> discharge in remarkable agreement with mass accumulation in the interior, and the glacier grounding line positions do not migrate with time. Glaciers flowing rapidly into the Amudsen Sea, unrestrained by a major <span class="hlt">ice</span> <span class="hlt">shelf</span>, are in contrast discharging more <span class="hlt">ice</span> than required to maintain a state of mass balance and are thinning quite rapidly near the coast. The grounding line of Pine Island glacier (see diagram) retreated 5 km in 4 years, which corresponds to a glacier thinning rate of 3.5 m/yr. Mass imbalance is even more negative</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.2925F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.2925F"><span>Deglaciation of <span class="hlt">Antarctica</span> since the Last Glacial Maximum - what can we learn from cosmogenic 10Be and 26Al exposure ages?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fink, David</p> <p>2015-04-01</p> <p><span class="hlt">Ice</span> volume changes at the coastal margins of <span class="hlt">Antarctica</span> during the global LGM are uncertain. The little evidence available suggests that behaviour of the East and West Antarctic <span class="hlt">Ice</span> Sheets are markedly different and complex. It is hypothesised that during interglacials, thinning of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, a more open-water environment and increased precipitation, allowed outlet glaciers draining the Transantarctic Mnts and fed by interior <span class="hlt">Ice</span> Sheets to advance during moist warmer periods, out of phase with colder arid periods. In contrast, glacier dynamics along the vast coastal perimeter of East <span class="hlt">Antarctica</span> is strongly influenced by Southern Ocean conditions. Cosmogenic 10Be and 26Al chronologies, although restricted to <span class="hlt">ice</span>-free oasis and mountains flanking drainage glaciers, has become an invaluable, if not unique, tool to quantify spatial and temporal Pleistocene <span class="hlt">ice</span> sheet variability over the past 2 Ma. Despite an increasing number of well documented areas, extracting reliable ages from glacial deposits in polar regions is problematic. Recycling of previously exposed/ buried debris and continual post-depositional modification leads to age ambiguities for a coeval glacial landform. More importantly, passage of cold-based <span class="hlt">ice</span> can leave a landform unmodified resulting in young erratics deposited on ancient bedrock. Advances in delivering in-situ radiocarbon to routine application offer some relief. Exposure ages from different localities throughout East <span class="hlt">Antarctica</span> (Framnes Mnts, Lutzow-Holm Bay, Vestfold Hills) and West <span class="hlt">Antarctica</span> (Denton Ranges, Hatherton Glacier, Shackleton Range) highlight some of the new findings. This talk presents results which quantify the magnitude and timing of paleo-<span class="hlt">ice</span> sheet thickness changes, questions the validity of an Antarctic LGM and discusses the complexities encountered in the often excessive spread in exposure ages.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C41C1237P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C41C1237P"><span>Sensitivity of Totten Glacier <span class="hlt">Ice</span> <span class="hlt">Shelf</span> extent and grounding line to oceanic forcing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pelle, T.; Morlighem, M.; Choi, Y.</p> <p>2017-12-01</p> <p>Totten Glacier is a major outlet glacier of the East Antarctic <span class="hlt">Ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (TGIS) has been observed to accelerate <span class="hlt">ice</span> <span class="hlt">shelf</span> thinning and promote iceberg calving, a primary mechanism of mass discharge from Totten. As such, accurately simulating TGIS's <span class="hlt">ice</span> front dynamics is crucial to the predictive capabilities of <span class="hlt">ice</span> sheet models in this region. Here, we study the TGIS using the <span class="hlt">Ice</span> 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 <span class="hlt">ice</span> front dynamics and possible thresholds of instability. In addition, we artificially retreat Totten's <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23850279','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23850279"><span>Rapid glass sponge expansion after climate-induced Antarctic <span class="hlt">ice</span> <span class="hlt">shelf</span> collapse.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fillinger, Laura; Janussen, Dorte; Lundälv, Tomas; Richter, Claudio</p> <p>2013-07-22</p> <p>Over 30% of the Antarctic continental <span class="hlt">shelf</span> is permanently covered by floating <span class="hlt">ice</span> 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-<span class="hlt">ice</span> melting allows a patchy primary production supporting rich megabenthic communities dominated by glass sponges (Porifera, Hexactinellida). The catastrophic collapse of <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span>, a first biological survey interpreted the presence of hexactinellids as remnants of a former under-<span class="hlt">ice</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRC..122.5198L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRC..122.5198L"><span>Modeling modified Circumpolar Deep Water intrusions onto the Prydz Bay continental <span class="hlt">shelf</span>, East <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Chengyan; Wang, Zhaomin; Cheng, Chen; Xia, Ruibin; Li, Bingrui; Xie, Zelin</p> <p>2017-07-01</p> <p>An eddy-resolving coupled regional ocean-sea <span class="hlt">ice-ice</span> <span class="hlt">shelf</span> model is employed to locate the hot spots where modified Circumpolar Deep Water (mCDW) intrudes onto the continental <span class="hlt">shelf</span> within Prydz Bay, and locate the paths through which mCDW is transported to the Amery <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (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 <span class="hlt">ice</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.C13H..01B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.C13H..01B"><span><span class="hlt">Ice</span> flow in the Weddell Sea sector of West <span class="hlt">Antarctica</span> as elucidated by radar-imaged internal layering</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bingham, R. G.; Rippin, D. M.; Karlsson, N. B.; Corr, H.; Ferraccioli, F.; Jordan, T. A.; Le Brocq, A.; Ross, N.; Wright, A.; Siegert, M. J.</p> <p>2012-12-01</p> <p>Radio-echo sounding (RES) across polar <span class="hlt">ice</span> sheets reveals extensive, isochronous internal layers, whose stratigraphy, and especially their degree of continuity over multi-km distances, can inform us about both present <span class="hlt">ice</span> flow and past <span class="hlt">ice</span>-flow histories. Here, we bring together for the first time two recent advances in this field of cryospheric remote sensing to analyse <span class="hlt">ice</span> flow into the Weddell Sea sector of West <span class="hlt">Antarctica</span>. Firstly, we have developed a new quantitative routine for analysing the continuity of internal layers obtained over large areas of <span class="hlt">ice</span> by airborne RES surveys - we term this routine the "Internal-Layering Continuity-Index (ILCI)". Secondly, in the austral season 2010-11 we acquired, by airborne RES survey, the first comprehensive dataset of deep internal layering across Institute and Möller <span class="hlt">Ice</span> Streams, two of the more significant feeders of <span class="hlt">ice</span> into the Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. Applying the ILCI to SAR-processed (migrated) RES profiles across Institute <span class="hlt">Ice</span> Stream's catchment reveals two contrasting regions of internal-layering continuity behaviour. In the western portion of the catchment, where <span class="hlt">ice</span>-stream tributaries incise deeply through the Ellsworth Subglacial Highlands, the continuity of internal layers is most disrupted across the present <span class="hlt">ice</span> streams. We therefore interpret the <span class="hlt">ice</span>-flow configuration in this western region as predominantly spatially stable over the lifetime of the <span class="hlt">ice</span>. Further east, towards Möller <span class="hlt">Ice</span> Stream, and towards the interior of the <span class="hlt">ice</span> sheet, the ILCI does not closely match the present <span class="hlt">ice</span> flow configuration, while across most of present-day Möller <span class="hlt">Ice</span> Stream itself, the continuity of internal layers is generally low. We propose that the variation in continuity of internal layering across eastern Institute <span class="hlt">Ice</span> Stream and the neighbouring Möller results primarily from two factors. Firstly, the noncorrespondence of some inland tributaries with internal-layering continuity acts as evidence for past spatial</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 <span class="hlt">Antarcticas</span> PineIsland Glacier, less than 5 years after its lastlarge calving 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 <span class="hlt">Antarcticas</span> 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/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 <span class="hlt">Antarctica</span>. 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('https://pubs.er.usgs.gov/publication/70017680','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70017680"><span>Contrasts in Arctic <span class="hlt">shelf</span> sea-<span class="hlt">ice</span> regimes and some implications: Beaufort Sea versus Laptev 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>Reimnitz, E.; Dethleff, D.; Nurnberg, D.</p> <p>1994-01-01</p> <p>The winter <span class="hlt">ice</span>-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 <span class="hlt">ice</span>, and with a lack of compression, such deep-draft <span class="hlt">ice</span> is not generated in situ, as on the Beaufort Sea <span class="hlt">shelf</span>. 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 <span class="hlt">ice</span>, when compared to conditions in the short-fetched Beaufort Sea. We expect entrainment to occur yearly. Different from the intensely <span class="hlt">ice</span>-gouged Beaufort Sea <span class="hlt">shelf</span>, hydraulic bedforms probably dominate in the Laptev Sea. Corresponding with the large volume of <span class="hlt">ice</span> 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 <span class="hlt">ice</span> keels, may enhance benthic productivity and permit establishment of open-<span class="hlt">shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> settings. ?? 1994.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CliPa..14..193B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CliPa..14..193B"><span>The Ross Sea Dipole - temperature, snow accumulation and sea <span class="hlt">ice</span> variability in the Ross Sea region, <span class="hlt">Antarctica</span>, over the past 2700 years</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bertler, Nancy A. N.; Conway, Howard; Dahl-Jensen, Dorthe; Emanuelsson, Daniel B.; Winstrup, Mai; Vallelonga, Paul T.; Lee, James E.; Brook, Ed J.; Severinghaus, Jeffrey P.; Fudge, Taylor J.; Keller, Elizabeth D.; Baisden, W. Troy; Hindmarsh, Richard C. A.; Neff, Peter D.; Blunier, Thomas; Edwards, Ross; Mayewski, Paul A.; Kipfstuhl, Sepp; Buizert, Christo; Canessa, Silvia; Dadic, Ruzica; Kjær, Helle A.; Kurbatov, Andrei; Zhang, Dongqi; Waddington, Edwin D.; Baccolo, Giovanni; Beers, Thomas; Brightley, Hannah J.; Carter, Lionel; Clemens-Sewall, David; Ciobanu, Viorela G.; Delmonte, Barbara; Eling, Lukas; Ellis, Aja; Ganesh, Shruthi; Golledge, Nicholas R.; Haines, Skylar; Handley, Michael; Hawley, Robert L.; Hogan, Chad M.; Johnson, Katelyn M.; Korotkikh, Elena; Lowry, Daniel P.; Mandeno, Darcy; McKay, Robert M.; Menking, James A.; Naish, Timothy R.; Noerling, Caroline; Ollive, Agathe; Orsi, Anaïs; Proemse, Bernadette C.; Pyne, Alexander R.; Pyne, Rebecca L.; Renwick, James; Scherer, Reed P.; Semper, Stefanie; Simonsen, Marius; Sneed, Sharon B.; Steig, Eric J.; Tuohy, Andrea; Ulayottil Venugopal, Abhijith; Valero-Delgado, Fernando; Venkatesh, Janani; Wang, Feitang; Wang, Shimeng; Winski, Dominic A.; Winton, V. Holly L.; Whiteford, Arran; Xiao, Cunde; Yang, Jiao; Zhang, Xin</p> <p>2018-02-01</p> <p>High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually dated <span class="hlt">ice</span> core record from the eastern Ross Sea, named the Roosevelt Island Climate Evolution (RICE) <span class="hlt">ice</span> core. Comparison of this record with climate reanalysis data for the 1979-2012 interval shows that RICE reliably captures temperature and snow precipitation variability in the region. Trends over the past 2700 years in RICE are shown to be distinct from those in West <span class="hlt">Antarctica</span> and the western Ross Sea captured by other <span class="hlt">ice</span> cores. For most of this interval, the eastern Ross Sea was warming (or showing isotopic enrichment for other reasons), with increased snow accumulation and perhaps decreased sea <span class="hlt">ice</span> concentration. However, West <span class="hlt">Antarctica</span> cooled and the western Ross Sea showed no significant isotope temperature trend. This pattern here is referred to as the Ross Sea Dipole. Notably, during the Little <span class="hlt">Ice</span> Age, West <span class="hlt">Antarctica</span> and the western Ross Sea experienced colder than average temperatures, while the eastern Ross Sea underwent a period of warming or increased isotopic enrichment. From the 17th century onwards, this dipole relationship changed. All three regions show current warming, with snow accumulation declining in West <span class="hlt">Antarctica</span> and the eastern Ross Sea but increasing in the western Ross Sea. We interpret this pattern as reflecting an increase in sea <span class="hlt">ice</span> in the eastern Ross Sea with perhaps the establishment of a modern Roosevelt Island polynya as a local moisture source for RICE.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C23B1218P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C23B1218P"><span>Simple model of melange and its influence on rapid <span class="hlt">ice</span> retreat in a large-scale Antarctic <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>Pollard, D.; Deconto, R. M.</p> <p>2017-12-01</p> <p>Theory, modeling and observations point to the prospect of runaway grounding-line retreat and marine <span class="hlt">ice</span> loss from West <span class="hlt">Antarctica</span> 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 <span class="hlt">ice</span> from deep grounding lines generates substantial downstream melange (floating <span class="hlt">ice</span> debris). It is unknown whether this melange has a significant effect on <span class="hlt">ice</span> 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 <span class="hlt">ice</span> sheet-<span class="hlt">shelf</span> model. Continuum mechanics is used as aheuristic representation of discrete particle physics. Melange is createdby <span class="hlt">ice</span> calving and cliff failure. Its dynamics are treated similarly to <span class="hlt">ice</span> flow, but with little or no resistance to divergence. Melange providesback pressure where adjacent to grounded tidewater <span class="hlt">ice</span> faces or <span class="hlt">ice-shelf</span> edges. We examine the influence of the new melange component during rapid Antarctic retreat in warm-Pliocene and future warming scenarios.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMPP13A2047K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMPP13A2047K"><span>Biomarker-based reconstruction of late Holocene sea-<span class="hlt">ice</span> variability: East versus West Greenland continental <span class="hlt">shelf</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kolling, H. M.; Stein, R. H.; Fahl, K.</p> <p>2016-12-01</p> <p>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 <span class="hlt">ice</span> is not clearly reflected in climate models. This illustrates the need for high-resolution proxy-based sea-<span class="hlt">ice</span> reconstructions going beyond the time scale of direct measurements in order to understand the processes controlling present and past natural variability of sea <span class="hlt">ice</span> on short time scales. Here we present the first comparison of two high-resolution biomarker records from the East and West Greenland <span class="hlt">Shelf</span> for the late Holocene. Both areas are highly sensitive to sea-<span class="hlt">ice</span> changes as they are influenced by the East Greenland Current, the main exporter of Arctic freshwater and sea <span class="hlt">ice</span>. On the East Greenland <span class="hlt">Shelf</span>, we do not find any clear evidence for a long-term increase of sea <span class="hlt">ice</span> during the late Holocene Neoglacial. This sea-<span class="hlt">ice</span> 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 <span class="hlt">Ice</span> Age. In contrary, the West Greenland <span class="hlt">Shelf</span> record shows a strong and gradual increase in sea <span class="hlt">ice</span> concentration and a reduction in marine productivity markers starting near 1.6 ka. In general, the increase in sea <span class="hlt">ice</span> seems to follow the decreasing solar insolation trend. Short-term events are not as clearly pronounced as on the East Greenland <span class="hlt">Shelf</span>. 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5346486','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5346486"><span>Ultimate Eocene (Priabonian) Chondrichthyans (Holocephali, Elasmobranchii) of <span class="hlt">Antarctica</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>Kriwet, Jürgen; Engelbrecht, Andrea; Mörs, Thomas; Reguero, Marcelo; Pfaff, Cathrin</p> <p>2017-01-01</p> <p>The Eocene La Meseta Formation on Seymour Island, Antarctic Peninsula, is known for its remarkable wealth of fossil remains of chondrichthyans and teleosts. Chondrichthyans seemingly were dominant elements in the Antarctic Paleogene fish fauna, but decreased in abundance from middle to late Eocene, during which time remains of bony fishes increase. This decline of chondrichthyans at the end of the Eocene generally is related to sudden cooling of seawater, reduction in <span class="hlt">shelf</span> area, and increasing <span class="hlt">shelf</span> depth due to the onset of the Antarctic thermal isolation. The last chondrichthyan records known so far include a chimeroid tooth plate from TELM 6 (Lutetian) and a single pristiophorid rostral spine from TELM 7 (Priabonian). Here, we present new chondrichthyan records of Squalus, Squatina, Pristiophorus, Striatolamia, Palaeohypotodus, Carcharocles, and Ischyodus from the upper parts of TELM 7 (Priabonian), including the first record of Carcharocles sokolovi from <span class="hlt">Antarctica</span>. This assemblage suggests that chondrichthyans persisted much longer in Antarctic waters despite rather cool sea surface temperatures of approximately 5°C. The final disappearance of chondrichthyans at the Eocene–Oligocene boundary concurs with abrupt <span class="hlt">ice</span> sheet formation in <span class="hlt">Antarctica</span>. Diversity patterns of chondrichthyans throughout the La Meseta Formation appear to be related to climatic conditions rather than plate tectonics. PMID:28298806</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28298806','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28298806"><span>Ultimate Eocene (Priabonian) Chondrichthyans (Holocephali, Elasmobranchii) of <span class="hlt">Antarctica</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kriwet, Jürgen; Engelbrecht, Andrea; Mörs, Thomas; Reguero, Marcelo; Pfaff, Cathrin</p> <p>2016-01-01</p> <p>The Eocene La Meseta Formation on Seymour Island, Antarctic Peninsula, is known for its remarkable wealth of fossil remains of chondrichthyans and teleosts. Chondrichthyans seemingly were dominant elements in the Antarctic Paleogene fish fauna, but decreased in abundance from middle to late Eocene, during which time remains of bony fishes increase. This decline of chondrichthyans at the end of the Eocene generally is related to sudden cooling of seawater, reduction in <span class="hlt">shelf</span> area, and increasing <span class="hlt">shelf</span> depth due to the onset of the Antarctic thermal isolation. The last chondrichthyan records known so far include a chimeroid tooth plate from TELM 6 (Lutetian) and a single pristiophorid rostral spine from TELM 7 (Priabonian). Here, we present new chondrichthyan records of Squalus , Squatina , Pristiophorus , Striatolamia , Palaeohypotodus , Carcharocles , and Ischyodus from the upper parts of TELM 7 (Priabonian), including the first record of Carcharocles sokolovi from <span class="hlt">Antarctica</span>. This assemblage suggests that chondrichthyans persisted much longer in Antarctic waters despite rather cool sea surface temperatures of approximately 5°C. The final disappearance of chondrichthyans at the Eocene-Oligocene boundary concurs with abrupt <span class="hlt">ice</span> sheet formation in <span class="hlt">Antarctica</span>. Diversity patterns of chondrichthyans throughout the La Meseta Formation appear to be related to climatic conditions rather than plate tectonics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C11E..05F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C11E..05F"><span>Eastern Ross <span class="hlt">Ice</span> Sheet Deglacial History inferred from the Roosevelt Island <span class="hlt">Ice</span> Core</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fudge, T. J.; Buizert, C.; Lee, J.; Waddington, E. D.; Bertler, N. A. N.; Conway, H.; Brook, E.; Severinghaus, J. P.</p> <p>2017-12-01</p> <p>The Ross <span class="hlt">Ice</span> Sheet drains large portions of both West and East <span class="hlt">Antarctica</span>. Understanding the retreat of the Ross <span class="hlt">Ice</span> Sheet following the Last Glacial Maximum is particularly difficult in the eastern Ross area where there is no exposed rock and the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> prevents extensive bathymetric mapping. Coastal domes, by preserving old <span class="hlt">ice</span>, can be used to infer the establishment of grounded <span class="hlt">ice</span> and be used to infer past <span class="hlt">ice</span> thickness. Here we focus on Roosevelt Island, in the eastern Ross Sea, where the Roosevelt Island Climate Evolution project recently completed an <span class="hlt">ice</span> core to bedrock. Using <span class="hlt">ice</span>-flow modeling constrained by the depth-age relationship and an independent estimate of accumulation rate from firn-densification measurements and modeling, we infer <span class="hlt">ice</span> thickness histories for the LGM (20ka) to present. Preliminary results indicate thinning of 300m between 15ka and 12ka is required. This is similar to the amount and timing of thinning inferred at Siple Dome, in the central Ross Sea (Waddington et al., 2005; Price et al., 2007) and supports the presence of active <span class="hlt">ice</span> streams throughout the Ross <span class="hlt">Ice</span> Sheet advance during the LGM.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017TCry...11..319G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017TCry...11..319G"><span>Marine <span class="hlt">ice</span> sheet model performance depends on basal sliding physics and sub-<span class="hlt">shelf</span> melting</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gladstone, Rupert Michael; Warner, Roland Charles; Galton-Fenzi, Benjamin Keith; Gagliardini, Olivier; Zwinger, Thomas; Greve, Ralf</p> <p>2017-01-01</p> <p>Computer models are necessary for understanding and predicting marine <span class="hlt">ice</span> sheet behaviour. However, there is uncertainty over implementation of physical processes at the <span class="hlt">ice</span> base, both for grounded and floating glacial <span class="hlt">ice</span>. Here we implement several sliding relations in a marine <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> basal melting.Sliding relations that reduce the magnitude of the step change in basal drag from grounded <span class="hlt">ice</span> to floating <span class="hlt">ice</span> (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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span>: melt parameterisations that reduce the abruptness of change in basal melting from grounded <span class="hlt">ice</span> (where basal melt is set to zero) to floating <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> basal melt rates next to the grounding line, may mean that some marine <span class="hlt">ice</span> sheet systems can be reliably simulated at</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140008935','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140008935"><span>Validation of Airborne FMCW Radar Measurements of Snow Thickness Over Sea <span class="hlt">Ice</span> in <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Galin, Natalia; Worby, Anthony; Markus, Thorsten; Leuschen, Carl; Gogineni, Prasad</p> <p>2012-01-01</p> <p>Antarctic sea <span class="hlt">ice</span> and its snow cover are integral components of the global climate system, yet many aspects of their vertical dimensions are poorly understood, making their representation in global climate models poor. Remote sensing is the key to monitoring the dynamic nature of sea <span class="hlt">ice</span> and its snow cover. Reliable and accurate snow thickness data are currently a highly sought after data product. Remotely sensed snow thickness measurements can provide an indication of precipitation levels, predicted to increase with effects of climate change in the polar regions. Airborne techniques provide a means for regional-scale estimation of snow depth and distribution. Accurate regional-scale snow thickness data will also facilitate an increase in the accuracy of sea <span class="hlt">ice</span> thickness retrieval from satellite altimeter freeboard estimates. The airborne data sets are easier to validate with in situ measurements and are better suited to validating satellite algorithms when compared with in situ techniques. This is primarily due to two factors: better chance of getting coincident in situ and airborne data sets and the tractability of comparison between an in situ data set and the airborne data set averaged over the footprint of the antennas. A 28-GHz frequency modulated continuous wave (FMCW) radar loaned by the Center for Remote Sensing of <span class="hlt">Ice</span> Sheets to the Australian Antarctic Division is used to measure snow thickness over sea <span class="hlt">ice</span> in East <span class="hlt">Antarctica</span>. Provided with the radar design parameters, the expected performance parameters of the radar are summarized. The necessary conditions for unambiguous identification of the airsnow and snowice layers for the radar are presented. Roughnesses of the snow and <span class="hlt">ice</span> surfaces are found to be dominant determinants in the effectiveness of layer identification for this radar. Finally, this paper presents the first in situ validated snow thickness estimates over sea <span class="hlt">ice</span> in <span class="hlt">Antarctica</span> derived from an FMCW radar on a helicopterborne platform.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2007/1047/srp/srp097/of2007-1047srp097.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2007/1047/srp/srp097/of2007-1047srp097.pdf"><span>Subglacial conditions at a sticky spot along Kamb <span class="hlt">Ice</span> Stream, West <span class="hlt">Antarctica</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>Peters, L.E.; Anandakrishnan, S.</p> <p>2007-01-01</p> <p>We present the results of a seismic reflection experiment performed transverse to flow a few tens of kilometers above the main trunk of Kamb <span class="hlt">Ice</span> Stream, West <span class="hlt">Antarctica</span>, where we image a basal high surrounded by variable subglacial conditions. This high rises as much as 200 m above the surrounding bed, acting as a major sticking point that resists fast flow. Application of the amplitude variation with offset (AVO) seismic technique has highlighted regions of frozen sediments along our profile, suggesting that the <span class="hlt">ice</span> stream is experiencing basal freeze-on in the region. The bedrock high appears to be at least partially draped in sediment cover, with a concentrated area of weak, dilatant till flanking one edge. This dilatant till is further dispersed along our profile, though it does not possess enough continuity to maintain streaming <span class="hlt">ice</span> conditions. These results support the hypothesis that the ongoing shutdown of Kamb <span class="hlt">Ice</span> Stream is due to a loss in continuous basal lubrication.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRF..122.1827B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRF..122.1827B"><span>Post-LGM Grounding-Line Positions of the Bindschadler Paleo <span class="hlt">Ice</span> Stream in the Ross Sea Embayment, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bart, Philip J.; Anderson, John B.; Nitsche, Frank</p> <p>2017-10-01</p> <p>The West Antarctic <span class="hlt">Ice</span> Sheet (WAIS) retreated more than 1,000 km since last grounding at the Ross Sea outer continental <span class="hlt">shelf</span>. Here we show an interpretation of former grounding line positions from a new large-area multibeam survey and a regional grid of chirp cross-sectional data from the Whales Deep Basin in eastern Ross Sea. The basin is a paleo-glacial trough that was occupied by the Bindschadler <span class="hlt">Ice</span> Stream when grounded <span class="hlt">ice</span> advanced to the <span class="hlt">shelf</span> edge during the Last Glacial Maximum. These new geophysical data provide unambiguous evidence that the WAIS occupied at least seven grounding line positions within 60 km of the <span class="hlt">shelf</span> edge. Four of seven grounding zone wedges (GZWs) are partly exposed over large areas of the trough. The overlapping stratal arrangement created a large-volume compound GZW. Some of the groundings involved local readvance of the grounding line. Subsequent to these seven outer continental <span class="hlt">shelf</span> groundings, the <span class="hlt">ice</span> sheet retreated more than 200 km towards Roosevelt Island on the middle continental <span class="hlt">shelf</span>. The major retreat across the middle continental <span class="hlt">shelf</span> is recorded by small-scale moraine ridges that mantle the top of GZW7, and these are suggestive of relatively continuous grounding line recession. The results indicate that retreat was considerably more complex than was possible to reconstruct with reconnaissance-level data. The added details are important to climate models, which must first be able to reproduce the recent retreat pattern in all of its complexities to improve confidence in model predictions of the system's future response.</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 <span class="hlt">Antarctica</span>. 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://adsabs.harvard.edu/abs/2017JMS...166..108L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JMS...166..108L"><span>Processes influencing formation of low-salinity high-biomass lenses near the edge of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Yizhen; McGillicuddy, Dennis J.; Dinniman, Michael S.; Klinck, John M.</p> <p>2017-02-01</p> <p>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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> and irregularity of the <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> edge.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.1721F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.1721F"><span>Cosmogenic 10Be ages from the Meirs and Garwood Valleys, Denton Hills, West <span class="hlt">Antarctica</span>, suggest an absence in LGM <span class="hlt">Ice</span> Sheet expansion.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fink, David; Joy, Kurt; Storey, Bryan</p> <p>2014-05-01</p> <p>It has been hypothesised that during interglacials, thinning of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> allowed a more open water environment with increased local precipitation. This resulted in outlet glaciers, which drain the Transantarctic Mountains and fed by the East Antarctic <span class="hlt">Ice</span> Sheet, advancing during moist warmer periods, apparently out of phase with colder arid dry periods. Significantly the <span class="hlt">ice</span> core record during these warm periods also shows increased accumulation continent wide The geomorphology of the Denton Hills in the Royal Society Range, West <span class="hlt">Antarctica</span>, is a result of Miocene fluvial incision reworked by subsequent glacial advances throughout the Quaternary. The Garwood and Miers glacial valleys drain <span class="hlt">ice</span> across the Denton Hills into the <span class="hlt">Shelf</span>, and should thus show maximum extent during interstadials. To understand the chronology of late Quaternary glaciations, 15 granitic boulders from terminal moraines were sampled for 10Be and 26Al cosmogenic dating. Obtaining reliable exposure ages of erratics within moraines that represent timing of deposition (i.e. glacial advances) is problematic in polar regions, where glacial activity is principally controlled by <span class="hlt">ice</span> sheet dynamics. Recycling of previously exposed debris, uncertainty in provenance of glacially transported boulders and a lack of a post-depositional hydrologic process to remove previously exposed material from a valley system, leads to ambiguities in multiple exposure ages from a single coeval glacial landform. More importantly, cold-based <span class="hlt">ice</span> advance can leave a landform unmodified resulting in young erratics deposited on bedrock that shows weathering and/or inconsistent age-altitude relationships. Primarily, inheritance becomes a difficulty in qualifying exposure ages from polar regions. Preliminary results from the Garwood and Miers Valleys indicate that glaciers in the Denton Hills had begun to retreat from their last maximum positions no later than 23-37 ka, and thus the local last glacial maximum</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C51B0991K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51B0991K"><span>Field Observations and Modeling Results of the McMurdo Shear Zone, <span class="hlt">Antarctica</span>: Implications on Shear Margin Dynamics and Long- Term Viability of the South Pole Traverse</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaluzienski, L. M.; Koons, P. O.; Enderlin, E. M.; Courville, Z.; Campbell, S. W.; Arcone, S.; Jordan, M.; Ray, L.</p> <p>2017-12-01</p> <p><span class="hlt">Antarctica</span>'s <span class="hlt">ice</span> shelves modulate the flow of inland <span class="hlt">ice</span> towards the ocean. Understanding the controls on <span class="hlt">ice-shelf</span> stability are critical to predicting the future evolution of the Antarctic <span class="hlt">Ice</span> Sheet. For the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (RIS), an important region of lateral resistance is the McMurdo Shear Zone (MSZ), a 5-10 km wide strip of heavily crevassed <span class="hlt">ice</span>. On a yearly basis the United States Antarctic Program (USAP) mitigates crevasse hazards along the South Pole Traverse (SPoT) route that crosses this region. However, as <span class="hlt">ice</span> advects northward past the lateral buttress of White Island into a region of greater flow divergence, intensified crevassing has been observed which will continue to place a substantial burden on safety mitigation efforts. The route has advected down-glacier towards this complex region since 2002 so the USAP currently has plans to relocate the shear zone crossing upstream in the near future. Our work aims to assess the feasibility of moving the route to several potential locations based on results from an integrated project incorporating detailed field-based observations of crevasse distributions and orientation from ground-penetrating radar (GPR), GPS and remote sensing observations of the flow and stress field within the MSZ, and finite element numerical modeling of local and regional kinematics within the region. In addition, we assess plausible dynamic forcings both upstream and downstream of the MSZ that could influence shear zone stability. These include changes in mass flux across the grounding lines of tributary glaciers such as the observed increase in <span class="hlt">ice</span> discharge from of Byrd Glacier (Stearns et al., 2008) as well as changes at the MIS front due to recent intensified rift propagation (Banwel et al., 2017). Results from this work will increase our understanding of <span class="hlt">ice</span> <span class="hlt">shelf</span> shear margin dynamics and provide a firm basis for predicting the long-term behavior of the MSZ and viability of the SPoT. Stearns, Leigh A., Benjamin E. Smith, and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140005256','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140005256"><span><span class="hlt">Ice</span> Velocity Mapping of Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, <span class="hlt">Antarctica</span> by Matching Surface Undulations Measured by Icesat Laser Altimetry</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lee, Choon-Ki; Han, Shin-Chan; Yu, Jaehyung; Scambos, Ted A.; Seo, Ki-Weon</p> <p>2012-01-01</p> <p>We present a novel method for estimating the surface horizontal velocity on <span class="hlt">ice</span> shelves using laser altimetrydata from the <span class="hlt">Ice</span> Cloud and land Elevation Satellite (ICESat; 20032009). The method matches undulations measured at crossover points between successive campaigns.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GeoRL..45..201C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GeoRL..45..201C"><span><span class="hlt">Ice</span> Stream Slowdown Will Drive Long-Term Thinning of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, With or Without 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>Campbell, Adam J.; Hulbe, Christina L.; Lee, Choon-Ki</p> <p>2018-01-01</p> <p>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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. First, a numerical model of <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">Ice</span> Streams is clearly detectable in remotely sensed thickness change. Moreover, those past events will continue to drive thinning into the future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24349517','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24349517"><span>Edwardsiella andrillae, a new species of sea anemone from Antarctic <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>Daly, Marymegan; Rack, Frank; Zook, Robert</p> <p>2013-01-01</p> <p>Exploration of the lower surface of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in <span class="hlt">Antarctica</span> by the Submersible Capable of under-<span class="hlt">Ice</span> Navigation and Imaging (SCINI) remotely operated vehicle discovered a new species of sea anemone living in this previously undocumented ecosystem. This discovery was a significant outcome of the Coulman High Project's geophysical and environmental fieldwork in 2010-2011 as part of the ANDRILL (ANtarctic geologic DRILLing) program. Edwardsiella andrillae n. sp., lives with most of its column in the <span class="hlt">ice</span> <span class="hlt">shelf</span>, with only the tentacle crown extending into the seawater below. In addition to being the only Antarctic representative of the genus, Edwardsiella andrillae is distinguished from all other species of the genus in the number of tentacles and in the size and distribution of cnidae. The anatomy and histology of Edwardsiella andrillae present no features that explain how this animal withstands the challenges of life in such an unusual habitat.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C11E..03B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C11E..03B"><span>Neoglacial Antarctic sea-<span class="hlt">ice</span> expansion driven by mid-Holocene retreat of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2017-12-01</p> <p>Recent decades have seen expanding Antarctic sea-<span class="hlt">ice</span> coverage, coeval with thinning West Antarctic <span class="hlt">Ice</span> Sheet (WAIS) <span class="hlt">ice</span> 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-<span class="hlt">ice</span> 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-<span class="hlt">ice</span>. 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (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-<span class="hlt">ice</span> from 4.5 ka. This is coeval with cosmogenic nuclide evidence for a rapid thinning of the Antarctic <span class="hlt">ice</span> sheet during the mid-Holocene (Hein et al., 2016). We suggest this represents a final major pulse of deglaciation from the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, which initiates the Neoglacial, driving cool surface waters along the coast and greater sea-<span class="hlt">ice</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2007/1047/srp/srp074/of2007-1047srp074.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2007/1047/srp/srp074/of2007-1047srp074.pdf"><span>Miocene-Pliocene <span class="hlt">ice</span>-volcano interactions at monogenetic volcanoes near Hobbs Coast, Marie Byrd Land, <span class="hlt">Antarctica</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>Wilch, T.I.; McIntosh, W.C.</p> <p>2007-01-01</p> <p>Ar geochronology of seven eroded monogenetic volcanoes near the Hobbs Coast, Marie Byrd Land, West <span class="hlt">Antarctica</span> provide proxy records of WAIS paleo-<span class="hlt">ice</span>-levels in Miocene-Pliocene times. Interpretations, based on lithofacies analysis, indicate whether the volcanoes erupted below, near, or above the level of the <span class="hlt">ice</span> sheet. Our interpretations differ significantly from previous interpretations as they highlight the abundant evidence for <span class="hlt">ice</span>-volcano interactions at emergent paleoenvironments but limited evidence of higher-than-present syn-eruptive <span class="hlt">ice</span>-levels. Evidence for subglacial volcanic paleoenvironments is limited to Kennel Peak, a ~8 Ma volcano where a pillow lava sequence extending 25 m above current <span class="hlt">ice</span> level overlies an inferred glacial till and unconformity. A major complication in the Hobbs Coast region is that the volcanism occurred on interfluves between regions of fast-flowing <span class="hlt">ice</span>. Such a setting precludes establishing precise regional paleo-<span class="hlt">ice</span>-levels although the presence or absence of <span class="hlt">ice</span> at times of eruptions can be inferred.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C51A0635N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C51A0635N"><span>Amundsen Sea simulation with optimized ocean, sea <span class="hlt">ice</span>, and thermodynamic <span class="hlt">ice</span> <span class="hlt">shelf</span> model parameters</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nakayama, Y.; Menemenlis, D.; Schodlok, M.; Heimbach, P.; Nguyen, A. T.; Rignot, E. J.</p> <p>2016-12-01</p> <p><span class="hlt">Ice</span> shelves and glaciers of the West Antarctic <span class="hlt">Ice</span> 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 <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice-shelf</span> ocean interactions in the ECCO (Estimating the Circulation and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1910394W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1910394W"><span>Geoengineering Outlet Glaciers and <span class="hlt">Ice</span> Streams</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wolovick, Michael</p> <p>2017-04-01</p> <p>Mass loss from Greenland and <span class="hlt">Antarctica</span> is highly sensitive to the presence of warm ocean water that drives melting of <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice-shelf</span> cavities. Glaciers with a floating <span class="hlt">shelf</span> 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, <span class="hlt">Antarctica</span> 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 <span class="hlt">Antarctica</span>, 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 <span class="hlt">ice</span> streams remain far from their non-geoengineered trajectories throughout the 1000 year duration of our model runs. In both cases, an</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.G31B0907M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.G31B0907M"><span>Regionally Optimized GRACE Processing and Inter-comparison on 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>Mohajerani, Y.; Velicogna, I.; Sutterley, T. C.; Rignot, E. J.</p> <p>2017-12-01</p> <p>The Antarctic <span class="hlt">ice</span> sheet is losing mass at an accelerating rate, with a sea level contribution that changed from 0.08mm/yr from 1992 to 2001 to 0.4mm/yr from 2002 to 2011. While most of this contribution comes from West <span class="hlt">Antarctica</span>, Totten Glacier has the largest discharge of <span class="hlt">ice</span> in East <span class="hlt">Antarctica</span>, with a sea level rise potential of 3.9 m. Furthermore, the drainage basin of Totten Glacier, along the neighboring Moscow University Glacier are below sea level, extending hundreds of kilometers inland. Therefore, obtaining regional estimates of both western and eastern Antarctic basins are of critical importance. The GRACE (Gravity Recovery and Climate Experiment) satellite has been providing mass balance time-series from geoid changes since 2002. Several mascon and harmonic GRACE solutions are available from different processing centers. Here, we evaluate the various solutions across the <span class="hlt">ice</span> sheet and a new set of regionally optimized mascons to study the mass balance of Totten and Moscow University glaciers. We obtain a trend of -16.5±4.1Gt/yr with an acceleration of -2.0±1.8Gt/yr2 for the two glaciers for the period April 2002 to December 2016 using the Ivins et al (2013) GIA model (errors include leakage, GIA, and regression errors). We compare the results with the Mass Budget Method that combines <span class="hlt">ice</span> discharge (D) and surface mass balance (SMB) from two models: 1) RACMO2.3, and 2) MAR3.6.4. MBM/RACMO2.3 shows the best agreement with the GRACE estimates. Within the common period from April 2002 to December 2015, the MBM/RACMO2.3 and MAR3.6.4 results are -15.6±1.8Gt/yr and -6.7±1.5Gt/yr respectively, while the GRACE time-series has a trend of -14.8±2.7 Gt/yr. We extend the study to the Getz <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, the third largest <span class="hlt">ice</span> <span class="hlt">shelf</span> in West <span class="hlt">Antarctica</span> after Ronne and Ross West <span class="hlt">ice</span> shelves. We compare our gravity-derived mass estimates, the mass budget estimates, and the volume changes from altimetry data to compare the estimates and obtain a multi-sensor assessment</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C21B0673W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C21B0673W"><span>Damage Mechanics in the Community <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>Whitcomb, R.; Cathles, L. M. M., IV; Bassis, J. N.; Lipscomb, W. H.; Price, S. F.</p> <p>2016-12-01</p> <p>Half of the mass that floating <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> evolve over time. Here, we demonstrate the application of a damage model to <span class="hlt">ice</span> shelves that predicts realistic geometries. We incorporated this solver into the Community <span class="hlt">Ice</span> Sheet Model, a three dimensional <span class="hlt">ice</span> 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 <span class="hlt">ice</span> tongue lengths that match well with observations for a selection of natural <span class="hlt">ice</span> tongues, including Erebus, Drygalski, and Pine Island in <span class="hlt">Antarctica</span>, as well as Petermann in Greenland. We also apply the model to more generalized ideal <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> extent and how the calving margins of <span class="hlt">ice</span> shelves respond to climate change.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20060035638&hterms=migration&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dmigration','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20060035638&hterms=migration&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dmigration"><span>Radar Interferometry Detection of Hinge Line Migration on Rutford <span class="hlt">Ice</span> Stream and Carlson Inlet, <span class="hlt">Antarctica</span></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>1997-01-01</p> <p>Satellite synthetic-aperture radar (SAR) Interferometry is employed to map the hinge line, or limit of tidal flexing, of Rutford <span class="hlt">Ice</span> Stream and Carlson Inlet, <span class="hlt">Antarctica</span>, and detect its migration between 1992 and 1996. The hinge line is mapped using a model fit from an elastic beam theory.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830037367&hterms=Skylight&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DSkylight','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830037367&hterms=Skylight&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DSkylight"><span>Effects on skylight at South Pole Station, <span class="hlt">Antarctica</span>, by <span class="hlt">ice</span> crystal precipitation in the atmosphere</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Fitch, B. W.; Coulson, K. L.</p> <p>1983-01-01</p> <p>Measurements of the radiance and polarization of the skylight at South Pole Station, <span class="hlt">Antarctica</span>, were made for clear cloud-free skies and cloudless skies with <span class="hlt">ice</span> crystal precipitation. The measurements were made at six narrowband wavelengths from 321 to 872 nm in the principal plane. The data show that scattering by <span class="hlt">ice</span> crystals increases the radiance in the backscatter plane, decreases it in the solar plane, and shifts the radiance minimum to a point closer to the sun. The crystals decrease the maximum value of linear polarization and shift the position of the maximum away from the sun. The influence of <span class="hlt">ice</span> crystal scattering is greatest at the longer wavelengths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18195749','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18195749"><span>Effects on skylight at South Pole Station, <span class="hlt">Antarctica</span>, by <span class="hlt">ice</span> crystal precipitation in the atmosphere.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fitch, B W; Coulson, K L</p> <p>1983-01-01</p> <p>Measurements of the radiance and polarization of the skylight at South Pole Station, <span class="hlt">Antarctica</span>, were made for clear cloud-free skies and cloudless skies with <span class="hlt">ice</span> crystal precipitation. The measurements were made at six narrowband wavelengths from 321 to 872 nm in the principal plane. The data show that scattering by <span class="hlt">ice</span> crystals increases the radiance in the backscatter plane, decreases it in the solar plane, and shifts the radiance minimum to a point closer to the sun. The crystals decrease the maximum value of linear polarization and shift the position of the maximum away from the sun. The influence of <span class="hlt">ice</span> crystal scattering is greatest at the longer wavelengths.</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/2014GeoRL..41.5506D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeoRL..41.5506D"><span>Basal terraces on melting <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>Dutrieux, Pierre; Stewart, Craig; Jenkins, Adrian; Nicholls, Keith W.; Corr, Hugh F. J.; Rignot, Eric; Steffen, Konrad</p> <p>2014-08-01</p> <p>Ocean waters melt the margins of Antarctic and Greenland glaciers, and individual glaciers' responses and the integrity of their <span class="hlt">ice</span> shelves are expected to depend on the spatial distribution of melt. The bases of the <span class="hlt">ice</span> shelves associated with Pine Island Glacier (West <span class="hlt">Antarctica</span>) and Petermann Glacier (Greenland) have similar geometries, including kilometer-wide, hundreds-of-meter high channels oriented along and across the direction of <span class="hlt">ice</span> flow. The channels are enhanced by, and constrain, oceanic melt. New meter-scale observations of basal topography reveal peculiar glaciated landscapes. Channel flanks are not smooth, but are instead stepped, with hundreds-of-meters-wide flat terraces separated by 5-50 m high walls. Melting is shown to be modulated by the geometry: constant across each terrace, changing from one terrace to the next, and greatly enhanced on the ~45° inclined walls. Melting is therefore fundamentally heterogeneous and likely associated with stratification in the <span class="hlt">ice</span>-ocean boundary layer, challenging current models of <span class="hlt">ice</span> <span class="hlt">shelf</span>-ocean interactions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.C32B..06D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.C32B..06D"><span>Basal Terraces on Melting <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>Dutrieux, P.; Stewart, C.; Jenkins, A.; Nicholls, K. W.; Corr, H. F. J.; Rignot, E. J.; Steffen, K.</p> <p>2014-12-01</p> <p>Ocean waters melt the margins of Antarctic and Greenland glaciers and individualglaciers' responses and the integrity of their <span class="hlt">ice</span> shelves are expected to depend on thespatial distribution of melt. The bases of the <span class="hlt">ice</span> shelves associated with Pine IslandGlacier (West <span class="hlt">Antarctica</span>) and Petermann Glacier (Greenland) have similar geometries,including kilometers-wide, hundreds-of-meter-high channels oriented along and acrossthe direction of <span class="hlt">ice</span> flow. The channels are enhanced by, and constrain, oceanic melt.New, meter-scale observations of basal topography reveal peculiar glaciated landscapes.Channel flanks are not smooth, but are instead stepped, with hundreds-of-meters-wideflat terraces separated by 5-50 m-high walls. Melting is shown to be modulated by thegeometry: constant across each terrace, changing from one terrace to the next, and greatlyenhanced on the ~45°-inclined walls. Melting is therefore fundamentally heterogeneousand likely associated with stratification in the <span class="hlt">ice</span>-ocean boundary layer, challengingcurrent models of <span class="hlt">ice</span> <span class="hlt">shelf</span>-ocean interactions.</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 <span class="hlt">Antarctica</span>. 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/2017AGUFMGC34A..06R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMGC34A..06R"><span>Assessing the Global Climate Response to Freshwater Forcing from the Antarctic <span class="hlt">Ice</span> Sheet Under Future Climate Scenarios</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rogstad, S.; Condron, A.; DeConto, R.; Pollard, D.</p> <p>2017-12-01</p> <p>Observational evidence indicates that the West Antarctic <span class="hlt">Ice</span> Sheet (WAIS) is losing mass at an accelerating rate. Impacts to global climate resulting from changing ocean circulation patterns due to increased freshwater runoff from <span class="hlt">Antarctica</span> in the future could have significant implications for global heat transport, but to-date this topic has not been investigated using complex numerical models with realistic freshwater forcing. Here, we present results from a high resolution fully coupled ocean-atmosphere model (CESM 1.2) forced with runoff from <span class="hlt">Antarctica</span> prescribed from a high resolution regional <span class="hlt">ice</span> sheet-<span class="hlt">ice</span> <span class="hlt">shelf</span> model. Results from the regional simulations indicate a potential freshwater contribution from <span class="hlt">Antarctica</span> of up to 1 m equivalent sea level rise by the end of the century under RCP 8.5 indicating that a substantial input of freshwater into the Southern Ocean is possible. Our high resolution global simulations were performed under IPCC future climate scenarios RCP 4.5 and 8.5. We will present results showing the impact of WAIS collapse on global ocean circulation, sea <span class="hlt">ice</span>, air temperature, and salinity in order to assess the potential for abrupt climate change triggered by WAIS collapse.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C43B0753X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C43B0753X"><span>Sea <span class="hlt">Ice</span> Freeboard and Thickness from the 2013 <span class="hlt">Ice</span>Bridge ATM and DMS Data in Ross Sea, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xie, H.; Tian, L.; Tang, J.; Ackley, S. F.</p> <p>2016-12-01</p> <p>In November (20, 21, 27, and 28) 2013, NASA's <span class="hlt">Ice</span>Bridge mission flew over the Ross Sea, <span class="hlt">Antarctica</span> and collected important sea <span class="hlt">ice</span> data with the ATM and DMS for the first time. We will present our methods to derive the local sea level and total freeboard for <span class="hlt">ice</span> thickness retrieval from these two datasets. The methods include (1) leads classification from DMS data using an automated lead detection method, (2) potential leads from the reflectance of less than 0.25 from the ATM laser shots of L1B data, (3) local sea level retrieval based on these qualified ATM laser shots (L1B) within the DMS-derived leads (after outliers removal from the mean ± 2 standard deviation of these ATM elevations), (4) establishment of an empirical equation of local sea level as a function of distance from the starting point of each <span class="hlt">Ice</span>Bridge flight, (5) total freeboard retrieval from the ATM L2 elevations by subtracting the local sea level derived from the empirical equation, and (6) <span class="hlt">ice</span> thickness retrieval. The <span class="hlt">ice</span> thickness derived from this method will be analyzed and compared with ICESat data (2003-2009) and other available data for the same region at the similar time period. Possible change and potential reasons will be identified and discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017TCry...11.1851P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017TCry...11.1851P"><span>Sea-level response to melting of Antarctic <span class="hlt">ice</span> shelves on multi-centennial timescales with the fast Elementary Thermomechanical <span class="hlt">Ice</span> Sheet model (f.ETISh v1.0)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pattyn, Frank</p> <p>2017-08-01</p> <p>The magnitude of the Antarctic <span class="hlt">ice</span> sheet's contribution to global sea-level rise is dominated by the potential of its marine sectors to become unstable and collapse as a response to ocean (and atmospheric) forcing. This paper presents Antarctic sea-level response to sudden atmospheric and oceanic forcings on multi-centennial timescales with the newly developed fast Elementary Thermomechanical <span class="hlt">Ice</span> Sheet (f.ETISh) model. The f.ETISh model is a vertically integrated hybrid <span class="hlt">ice</span> sheet-<span class="hlt">ice</span> <span class="hlt">shelf</span> model with vertically integrated thermomechanical coupling, making the model two-dimensional. Its marine boundary is represented by two different flux conditions, coherent with power-law basal sliding and Coulomb basal friction. The model has been compared to existing benchmarks. Modelled Antarctic <span class="hlt">ice</span> sheet response to forcing is dominated by sub-<span class="hlt">ice</span> <span class="hlt">shelf</span> melt and the sensitivity is highly dependent on basal conditions at the grounding line. Coulomb friction in the grounding-line transition zone leads to significantly higher mass loss in both West and East <span class="hlt">Antarctica</span> on centennial timescales, leading to 1.5 m sea-level rise after 500 years for a limited melt scenario of 10 m a-1 under freely floating <span class="hlt">ice</span> shelves, up to 6 m for a 50 m a-1 scenario. The higher sensitivity is attributed to higher <span class="hlt">ice</span> fluxes at the grounding line due to vanishing effective pressure. Removing the <span class="hlt">ice</span> shelves altogether results in a disintegration of the West Antarctic <span class="hlt">ice</span> sheet and (partially) marine basins in East <span class="hlt">Antarctica</span>. After 500 years, this leads to a 5 m and a 16 m sea-level rise for the power-law basal sliding and Coulomb friction conditions at the grounding line, respectively. The latter value agrees with simulations by DeConto and Pollard (2016) over a similar period (but with different forcing and including processes of hydrofracturing and cliff failure). The chosen parametrizations make model results largely independent of spatial resolution so that f.ETISh can potentially be</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3859642','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3859642"><span>Edwardsiella andrillae, a New Species of Sea Anemone from Antarctic <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>Daly, Marymegan; Rack, Frank; Zook, Robert</p> <p>2013-01-01</p> <p>Exploration of the lower surface of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in <span class="hlt">Antarctica</span> by the Submersible Capable of under-<span class="hlt">Ice</span> Navigation and Imaging (SCINI) remotely operated vehicle discovered a new species of sea anemone living in this previously undocumented ecosystem. This discovery was a significant outcome of the Coulman High Project’s geophysical and environmental fieldwork in 2010-2011 as part of the ANDRILL (ANtarctic geologic DRILLing) program. Edwardsiella andrillae n. sp., lives with most of its column in the <span class="hlt">ice</span> <span class="hlt">shelf</span>, with only the tentacle crown extending into the seawater below. In addition to being the only Antarctic representative of the genus, Edwardsiella andrillae is distinguished from all other species of the genus in the number of tentacles and in the size and distribution of cnidae. The anatomy and histology of Edwardsiella andrillae present no features that explain how this animal withstands the challenges of life in such an unusual habitat. PMID:24349517</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.5000F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.5000F"><span>Long-term monitoring of glacier dynamics of Fleming Glacier after the disintegration of Wordie <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, 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>Friedl, Peter; Seehaus, Thorsten; Wendt, Anja; Braun, Matthias</p> <p>2017-04-01</p> <p>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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, located at the south-western side of the Antarctic Peninsula. Since the <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span>, 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. <span class="hlt">ice</span> extent, velocity, grounding line position, <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> anymore, but</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C41E..07D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C41E..07D"><span>Foehn and temperature-based melt patterns over the Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span> as simulated by the MAR regional 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>Datta, R.; Tedesco, M.; Agosta, C.; Fettweis, X.; Kuipers Munneke, P.; van den Broeke, M. R.</p> <p>2017-12-01</p> <p>Surface melting has been implicated in the collapse of Antarctic Peninsula <span class="hlt">ice</span> shelves, most dramatically in the Larsen A (1995) and Larsen B (2002) <span class="hlt">ice</span> shelves. In July of this year, a rift in the remaining Larsen C <span class="hlt">ice</span> <span class="hlt">shelf</span> broke away one of the largest icebergs ever recorded. <span class="hlt">Ice-shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span>. 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 <span class="hlt">ice</span> <span class="hlt">shelf</span>, as well as glaciers previously feeding to the former Larsen B <span class="hlt">ice</span> <span class="hlt">shelf</span>, 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 <span class="hlt">ice</span> <span class="hlt">shelf</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.A23C0308K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.A23C0308K"><span>Abrupt Late Holocene Shift in Atmospheric Circulation Recorded by Mineral Dust in the Siple Dome <span class="hlt">Ice</span> Core, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koffman, B. G.; Goldstein, S. L.; Kaplan, M. R.; Winckler, G.; Bory, A. J. M.; Biscaye, P.</p> <p>2015-12-01</p> <p>Atmospheric dust directly influences Earth's climate by altering the radiative balance and by depositing micronutrients in the surface ocean, affecting global biogeochemical cycling. In addition, mineral dust particles provide observational evidence constraining past atmospheric circulation patterns. Because dust can originate from both local and distant terrestrial sources, knowledge of dust provenance can substantially inform our understanding of past climate history, atmospheric transport pathways, and differences in aerosol characteristics between glacial and interglacial climate states. Dust provenance information from Antarctic <span class="hlt">ice</span> cores has until now been limited to sites in East <span class="hlt">Antarctica</span>. Here we present some of the first provenance data from West <span class="hlt">Antarctica</span>. We use Sr-Nd isotopes to characterize dust extracted from late Holocene <span class="hlt">ice</span> (~1000-1800 C.E.) from the Siple Dome <span class="hlt">ice</span> core. The data form a tight array in Sr-Nd isotope space, with 87Sr/86Sr ranging between ~0.7087 and 0.7102, and ɛNd ranging between ~ -7 and -16. This combination is unique for <span class="hlt">Antarctica</span>, with low Nd and low Sr isotope ratios compared to high-elevation East Antarctic sites, requiring a dust source from ancient (Archean to early Proterozoic) and unweathered continental crust, which mixes with young volcanic material. Both components are likely sourced from <span class="hlt">Antarctica</span>. We also observe significant, systematic variability in Sr and Nd isotopic signatures through time, reflecting changes in the mixing ratio of these sources, and hypothesize that these changes are driven by shifts in circulation patterns. A large change occurs over about 10 years at ca. 1125 C.E. (ΔɛNd = +3 and Δ87Sr/86Sr = -0.0014). This shift coincides with changes in climate proxies in Southern Hemisphere paleoclimate records reflecting variability in the Westerlies. We therefore interpret the shift in dust provenance at Siple Dome to be related to larger-scale circulation changes. In general, the observed shifts</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1916368J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1916368J"><span>In situ-measurement of <span class="hlt">ice</span> deformation from repeated borehole logging of the EPICA Dronning Maud Land (EDML) <span class="hlt">ice</span> core, East <span class="hlt">Antarctica</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jansen, Daniela; Weikusat, Ilka; Kleiner, Thomas; Wilhelms, Frank; Dahl-Jensen, Dorthe; Frenzel, Andreas; Binder, Tobias; Eichler, Jan; Faria, Sergio H.; Sheldon, Simon; Panton, Christian; Kipfstuhl, Sepp; Miller, Heinrich</p> <p>2017-04-01</p> <p>The European Project for <span class="hlt">Ice</span> Coring in <span class="hlt">Antarctica</span> (EPICA) <span class="hlt">ice</span> core was drilled between 2001 and 2006 at the Kohnen Station, <span class="hlt">Antarctica</span>. During the drilling process the borehole was logged repeatedly. Repeated logging of the borehole shape is a means of directly measuring the deformation of the <span class="hlt">ice</span> sheet not only on the surface but also with depth, and to derive shear strain rates for the lower part, which control the volume of <span class="hlt">ice</span> transported from the inner continent towards the ocean. The logging system continuously recorded the tilt of the borehole with respect to the vertical (inclination) as well as the heading of the borehole with respect to magnetic north (azimuth) by means of a compass. This dataset provides the basis for a 3-D reconstruction of the borehole shape, which is changing over time according to the predominant deformation modes with depth. The information gained from this analysis can then be evaluated in combination with lattice preferred orientation, grain size and grain shape derived by microstructural analysis of samples from the deep <span class="hlt">ice</span> core. Additionally, the diameter of the borehole, which was originally circular with a diameter of 10 cm, was measured. As the <span class="hlt">ice</span> flow velocity at the position of the EDML core is relatively slow (about 0.75 m/a), the changes of borehole shape between the logs during the drilling period were very small and thus difficult to interpret. Thus, the site has been revisited in the Antarctic summer season 2016 and logged again using the same measurement system. The change of the borehole inclination during the time period of 10 years clearly reveals the transition from a pure shear dominated deformation in the upper part of the <span class="hlt">ice</span> sheet to shear deformation at the base. We will present a detailed analysis of the borehole parameters and the deduced shear strain rates in the lower part of the <span class="hlt">ice</span> sheet. The results are discussed with respect to <span class="hlt">ice</span> microstructural data derived from the EDML <span class="hlt">ice</span> core. Microstructural</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4928901','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4928901"><span>Pan–<span class="hlt">ice</span>-sheet glacier terminus change in East <span class="hlt">Antarctica</span> reveals sensitivity of Wilkes Land to sea-<span class="hlt">ice</span> changes</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Miles, Bertie W. J.; Stokes, Chris R.; Jamieson, Stewart S. R.</p> <p>2016-01-01</p> <p>The dynamics of ocean-terminating outlet glaciers are an important component of <span class="hlt">ice</span>-sheet mass balance. Using satellite imagery for the past 40 years, we compile an approximately decadal record of outlet-glacier terminus position change around the entire East Antarctic <span class="hlt">Ice</span> Sheet (EAIS) marine margin. We find that most outlet glaciers retreated during the period 1974–1990, before switching to advance in every drainage basin during the two most recent periods, 1990–2000 and 2000–2012. The only exception to this trend was in Wilkes Land, where the majority of glaciers (74%) retreated between 2000 and 2012. We hypothesize that this anomalous retreat is linked to a reduction in sea <span class="hlt">ice</span> and associated impacts on ocean stratification, which increases the incursion of warm deep water toward glacier termini. Because Wilkes Land overlies a large marine basin, it raises the possibility of a future sea level contribution from this sector of East <span class="hlt">Antarctica</span>. PMID:27386519</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27386519','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27386519"><span>Pan-<span class="hlt">ice</span>-sheet glacier terminus change in East <span class="hlt">Antarctica</span> reveals sensitivity of Wilkes Land to sea-<span class="hlt">ice</span> changes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Miles, Bertie W J; Stokes, Chris R; Jamieson, Stewart S R</p> <p>2016-05-01</p> <p>The dynamics of ocean-terminating outlet glaciers are an important component of <span class="hlt">ice</span>-sheet mass balance. Using satellite imagery for the past 40 years, we compile an approximately decadal record of outlet-glacier terminus position change around the entire East Antarctic <span class="hlt">Ice</span> Sheet (EAIS) marine margin. We find that most outlet glaciers retreated during the period 1974-1990, before switching to advance in every drainage basin during the two most recent periods, 1990-2000 and 2000-2012. The only exception to this trend was in Wilkes Land, where the majority of glaciers (74%) retreated between 2000 and 2012. We hypothesize that this anomalous retreat is linked to a reduction in sea <span class="hlt">ice</span> and associated impacts on ocean stratification, which increases the incursion of warm deep water toward glacier termini. Because Wilkes Land overlies a large marine basin, it raises the possibility of a future sea level contribution from this sector of East <span class="hlt">Antarctica</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMPP31E..02J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP31E..02J"><span>Forced Climate Changes in West <span class="hlt">Antarctica</span> and the Indo-Pacific by Northern Hemisphere <span class="hlt">Ice</span> Sheet Topography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jones, T. R.; Roberts, W. H. G.; Steig, E. J.; Cuffey, K. M.; Markle, B. R.; White, J. W. C.</p> <p>2017-12-01</p> <p>The behavior of the Indo-Pacific climate system across the last deglaciation is widely debated. Resolving these debates requires long term and continuous climate proxy records. Here, we use an ultra-high resolution and continuous water isotope record from an <span class="hlt">ice</span> core in the Pacific sector of West <span class="hlt">Antarctica</span>. In conjunction with the HadCM3 coupled ocean-atmosphere GCM, we demonstrate that the climate of both West <span class="hlt">Antarctica</span> and the Indo-Pacific were substantially altered during the last deglaciation by the same forcing mechanism. Critically, these changes are not dependent on ENSO strength, but rather the location of deep tropical convection, which shifts at 16 ka in response to climate perturbations induced by the Laurentide <span class="hlt">Ice</span> Sheet. The changed rainfall patterns in the tropics explain the deglacial shift from expanded-grasslands to rainforest-dominated ecosystems in Indonesia. High-frequency climate variability in the Southern Hemisphere is also changed, through a tropical Pacific teleconnection link dependent on the propogration of Rossby Waves.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17314977','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17314977"><span>Large subglacial lakes in East <span class="hlt">Antarctica</span> at the onset of fast-flowing <span class="hlt">ice</span> streams.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bell, Robin E; Studinger, Michael; Shuman, Christopher A; Fahnestock, Mark A; Joughin, Ian</p> <p>2007-02-22</p> <p>Water plays a crucial role in <span class="hlt">ice</span>-sheet stability and the onset of <span class="hlt">ice</span> streams. Subglacial lake water moves between lakes and rapidly drains, causing catastrophic floods. The exact mechanisms by which subglacial lakes influence <span class="hlt">ice</span>-sheet dynamics are unknown, however, and large subglacial lakes have not been closely associated with rapidly flowing <span class="hlt">ice</span> streams. Here we use satellite imagery and <span class="hlt">ice</span>-surface elevations to identify a region of subglacial lakes, similar in total area to Lake Vostok, at the onset region of the Recovery Glacier <span class="hlt">ice</span> stream in East <span class="hlt">Antarctica</span> and predicted by <span class="hlt">ice</span>-sheet models. We define four lakes through extensive, flat, featureless regions of <span class="hlt">ice</span> surface bounded by upstream troughs and downstream ridges. Using <span class="hlt">ice</span> velocities determined using interferometric synthetic aperture radar (InSAR), we find the onset of rapid flow (moving at 20 to 30 m yr(-1)) of the tributaries to the Recovery Glacier <span class="hlt">ice</span> stream in a 280-km-wide segment at the downslope margins of these four subglacial lakes. We conclude that the subglacial lakes initiate and maintain rapid <span class="hlt">ice</span> flow through either active modification of the basal thermal regime of the <span class="hlt">ice</span> sheet by lake accretion or through scouring bedrock channels in periodic drainage events. We suggest that the role of subglacial lakes needs to be considered in <span class="hlt">ice</span>-sheet mass balance assessments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12..521G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12..521G"><span>Increased West Antarctic and unchanged East Antarctic <span class="hlt">ice</span> discharge over the last 7 years</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gardner, Alex S.; Moholdt, Geir; Scambos, Ted; Fahnstock, Mark; Ligtenberg, Stefan; van den Broeke, Michiel; Nilsson, Johan</p> <p>2018-02-01</p> <p><span class="hlt">Ice</span> discharge from large <span class="hlt">ice</span> sheets plays a direct role in determining rates of sea-level rise. We map present-day Antarctic-wide surface velocities using Landsat 7 and 8 imagery spanning 2013-2015 and compare to earlier estimates derived from synthetic aperture radar, revealing heterogeneous changes in <span class="hlt">ice</span> flow since ˜ 2008. The new mapping provides complete coastal and inland coverage of <span class="hlt">ice</span> velocity north of 82.4° S with a mean error of < 10 m yr-1, resulting from multiple overlapping image pairs acquired during the daylight period. Using an optimized flux gate, <span class="hlt">ice</span> discharge from <span class="hlt">Antarctica</span> is 1929 ± 40 Gigatons per year (Gt yr-1) in 2015, an increase of 36 ± 15 Gt yr-1 from the time of the radar mapping. Flow accelerations across the grounding lines of West <span class="hlt">Antarctica</span>'s Amundsen Sea Embayment, Getz <span class="hlt">Ice</span> <span class="hlt">Shelf</span> and Marguerite Bay on the western Antarctic Peninsula, account for 88 % of this increase. In contrast, glaciers draining the East Antarctic <span class="hlt">Ice</span> Sheet have been remarkably constant over the period of observation. Including modeled rates of snow accumulation and basal melt, the Antarctic <span class="hlt">ice</span> sheet lost <span class="hlt">ice</span> at an average rate of 183 ± 94 Gt yr-1 between 2008 and 2015. The modest increase in <span class="hlt">ice</span> discharge over the past 7 years is contrasted by high rates of <span class="hlt">ice</span> sheet mass loss and distinct spatial patters of elevation lowering. The West Antarctic <span class="hlt">Ice</span> Sheet is experiencing high rates of mass loss and displays distinct patterns of elevation lowering that point to a dynamic imbalance. We find modest increase in <span class="hlt">ice</span> discharge over the past 7 years, which suggests that the recent pattern of mass loss in <span class="hlt">Antarctica</span> is part of a longer-term phase of enhanced glacier flow initiated in the decades leading up to the first continent-wide radar mapping of <span class="hlt">ice</span> flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016TCry...10..811D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016TCry...10..811D"><span>Constraining variable density of <span class="hlt">ice</span> shelves using wide-angle radar measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Drews, Reinhard; Brown, Joel; Matsuoka, Kenichi; Witrant, Emmanuel; Philippe, Morgane; Hubbard, Bryn; Pattyn, Frank</p> <p>2016-04-01</p> <p>The thickness of <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 data sets (10 MHz) collected at five sites on Roi Baudouin <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (RBIS), Dronning Maud Land, <span class="hlt">Antarctica</span>. We reconstruct depth to internal reflectors, local <span class="hlt">ice</span> thickness, and firn-air content using a novel algorithm that includes traveltime inversion and ray tracing with a prescribed shape of the depth-density relationship. For the particular case of an <span class="hlt">ice-shelf</span> channel, where <span class="hlt">ice</span> thickness and surface slope change substantially over a few kilometers, the radar data suggest 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 that the firn inside the channel is 4.7 % denser than that outside the channel. Hydrostatic <span class="hlt">ice</span> thickness calculations used for determining basal melt rates should account for the denser firn in <span class="hlt">ice-shelf</span> channels. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/imap/2600/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/imap/2600/"><span>Coastal-change and glaciological maps of <span class="hlt">Antarctica</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>Williams, Richard S.</p> <p>2004-01-01</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 the western part is thickening, the northern part is thinning. Joughin and Tulaczyk (2002), based on 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. The mass balance of the East Antarctic 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 Programs. On the basis of these recommendations, the U.S. Geological Survey (USGS) decided that the archive of early 1970s Landsat 1, 2, and 3 Multispectral Scanner (MSS) images of <span class="hlt">Antarctica</span> and the subsequent repeat coverage made possible with Landsat and other satellite images provided an excellent means of documenting changes in the coastline of <span class="hlt">Antarctica</span> (Ferrigno and Gould, 1987). The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMPP13A2042M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMPP13A2042M"><span>Ocean Observations Below Petermann Gletscher <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, Greenland From a Cabled Observatory</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.; Nicholls, K. W.; Padman, L.; Washam, P.</p> <p>2016-12-01</p> <p>Petermann Gletscher in North Greenland features the second largest floating <span class="hlt">ice</span> <span class="hlt">shelf</span> by area in the northern hemisphere. In August of 2015 we drilled three holes through the <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRC..120.5545A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRC..120.5545A"><span>Environmental controls of marine productivity hot spots around <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arrigo, Kevin R.; van Dijken, Gert L.; Strong, Aaron L.</p> <p>2015-08-01</p> <p>Antarctic coastal polynyas are biologically rich ecosystems that support large populations of mammals and birds and are globally significant sinks of atmospheric carbon dioxide. To support local phytoplankton blooms, these highly productive ecosystems require a large input of iron (Fe), the sources of which are poorly known. Here we assess the relative importance of six different environmental factors in controlling the amount of phytoplankton biomass and rates of net primary production (NPP) in 46 coastal polynyas around <span class="hlt">Antarctica</span>. Data presented here suggest that melting <span class="hlt">ice</span> shelves are a primary supplier of Fe to coastal polynyas, with basal melt rates explaining 59% of the between-polynya variance in mean chlorophyll a (Chl a) concentration. In a multiple regression analysis, which explained 78% of the variance in chlorophyll a (Chl a) between polynyas, basal melt rate explained twice as much of the variance as the next most important variable. Fe upwelled from sediments, which is partly controlled by continental <span class="hlt">shelf</span> width, was also important in some polynyas. Of secondary importance to phytoplankton abundance and NPP were sea surface temperature and polynya size. Surprisingly, differences in light availability and the length of the open water season explained little or none of the variance in either Chl a or NPP between polynyas. If the productivity of coastal polynyas is indeed sensitive to the release of Fe from melting <span class="hlt">ice</span> shelves, future changes in <span class="hlt">ice</span> <span class="hlt">shelf</span> melt rates could dramatically influence Antarctic coastal ecosystems and the ability of continental <span class="hlt">shelf</span> waters to sequester atmospheric carbon dioxide. This article was corrected on 26 AUG 2015. See the end of the full text for details.</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/2018TCry...12...49L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12...49L"><span>Modelling present-day basal melt rates for Antarctic <span class="hlt">ice</span> shelves using a parametrization of buoyant meltwater plumes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lazeroms, Werner M. J.; Jenkins, Adrian; Hilmar Gudmundsson, G.; van de Wal, Roderik S. W.</p> <p>2018-01-01</p> <p>Basal melting below <span class="hlt">ice</span> shelves is a major factor in mass loss from the Antarctic <span class="hlt">Ice</span> Sheet, which can contribute significantly to possible future sea-level rise. Therefore, it is important to have an adequate description of the basal melt rates for use in <span class="hlt">ice</span>-dynamical models. Most current <span class="hlt">ice</span> models use rather simple parametrizations based on the local balance of heat between <span class="hlt">ice</span> and ocean. In this work, however, we use a recently derived parametrization of the melt rates based on a buoyant meltwater plume travelling upward beneath an <span class="hlt">ice</span> <span class="hlt">shelf</span>. This plume parametrization combines a non-linear ocean temperature sensitivity with an inherent geometry dependence, which is mainly described by the grounding-line depth and the local slope of the <span class="hlt">ice-shelf</span> base. For the first time, this type of parametrization is evaluated on a two-dimensional grid covering the entire Antarctic continent. In order to apply the essentially one-dimensional parametrization to realistic <span class="hlt">ice-shelf</span> geometries, we present an algorithm that determines effective values for the grounding-line depth and basal slope in any point beneath an <span class="hlt">ice</span> <span class="hlt">shelf</span>. Furthermore, since detailed knowledge of temperatures and circulation patterns in the <span class="hlt">ice-shelf</span> cavities is sparse or absent, we construct an effective ocean temperature field from observational data with the purpose of matching (area-averaged) melt rates from the model with observed present-day melt rates. Our results qualitatively replicate large-scale observed features in basal melt rates around <span class="hlt">Antarctica</span>, not only in terms of average values, but also in terms of the spatial pattern, with high melt rates typically occurring near the grounding line. The plume parametrization and the effective temperature field presented here are therefore promising tools for future simulations of the Antarctic <span class="hlt">Ice</span> Sheet requiring a more realistic oceanic forcing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70026030','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70026030"><span><span class="hlt">Ice</span> cover, landscape setting, and geological framework of Lake Vostok, East <span class="hlt">Antarctica</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>Studinger, M.; Bell, R.E.; Karner, G.D.; Tikku, A.A.; Holt, J.W.; Morse, D.L.; David, L.; Richter, T.G.; Kempf, S.D.; Peters, M.E.; Blankenship, D.D.; Sweeney, R.E.; Rystrom, V.L.</p> <p>2003-01-01</p> <p>Lake Vostok, located beneath more than 4 km of <span class="hlt">ice</span> in the middle of East <span class="hlt">Antarctica</span>, is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment. Melting and freezing at the base of the <span class="hlt">ice</span> sheet, which slowly flows across the lake, controls the flux of water, biota and sediment particles through the lake. The influx of thermal energy, however, is limited to contributions from below. Thus the geological origin of Lake Vostok is a critical boundary condition for the subglacial ecosystem. We present the first comprehensive maps of <span class="hlt">ice</span> surface, <span class="hlt">ice</span> thickness and subglacial topography around Lake Vostok. The <span class="hlt">ice</span> flow across the lake and the landscape setting are closely linked to the geological origin of Lake Vostok. Our data show that Lake Vostok is located along a major geological boundary. Magnetic and gravity data are distinct east and west of the lake, as is the roughness of the subglacial topography. The physiographic setting of the lake has important consequences for the <span class="hlt">ice</span> flow and thus the melting and freezing pattern and the lake's circulation. Lake Vostok is a tectonically controlled subglacial lake. The tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small, but significant amounts of thermal energy into the lake. ?? 2002 Elsevier Science B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.C11A0465M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.C11A0465M"><span>Characteristics of basal <span class="hlt">ice</span> and subglacial water at Dome Fuji, <span class="hlt">Antarctica</span> <span class="hlt">ice</span> sheet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Motoyama, H.; Uemura, R.; Hirabayashi, M.; Miyake, T.; Kuramoto, T.; Tanaka, Y.; Dome Fuji Ice Core Project, M.</p> <p>2008-12-01</p> <p>(Introduction): The second deep <span class="hlt">ice</span> coring project at Dome Fuji, <span class="hlt">Antarctica</span> reached a depth of 3035.22 m during the austral summer season in 2006/2007. The recovered <span class="hlt">ice</span> cores contain records of global environmental changes going back about 720,000 years. (Estimation of basal <span class="hlt">ice</span> melt): The borehole measurement was carried out on January 2nd in 2007 when the temperature disturbance in the borehole calmed down by the rest of drilling for 2 days. Temperature measurement was performed after 0 C thermometer test was done in the ground. The temperature sensor of pt100 installed in the skate-like anti-torque was used. We did not have the enough time until the temperature of thermometer was matched with the temperature of <span class="hlt">ice</span> sheet. Some error was included in <span class="hlt">ice</span> temperature data. The resistance of pt100 sensor was converted to temperature in the borehole measurement machine. But we used only two electrical lines for pt100 sensor. Rate of heat flow in the <span class="hlt">ice</span> sheet was calculated using the vertical temperature gradient of the <span class="hlt">ice</span> sheet and rate of heat conductivity of <span class="hlt">ice</span>. The deepest part of heat flux using temperatures at 3000m and 3030m was about 45mW/m2. We assumed that this value was the heat flux from the bedrock in the <span class="hlt">ice</span> sheet. Heat flux to the bedrock surface in the ground was assumed 54.6mW/m2 adopted by <span class="hlt">ice</span> sheet model (P. Huybrechts, 2006). Then the heat flux for basal <span class="hlt">ice</span> melt was about 10mW/m2. This value was equaled to melting of 1.1mm of <span class="hlt">ice</span> thickness per year. On the other hand, the annual layer thickness under 2500m was not changed so much and its average was 1.3mm of <span class="hlt">ice</span> thickness. So the annual layer thickness and melting rate of basal <span class="hlt">ice</span> was the same in ordering way. Or <span class="hlt">ice</span> equivalent in annual layer is melting every year. The age of the deepest part of <span class="hlt">ice</span> core is guessed at 720,000 years old and the <span class="hlt">ice</span> older than basal <span class="hlt">ice</span> has melted away. (The state of basal <span class="hlt">ice</span>): When the <span class="hlt">ice</span> core drilling depth passed 3031.44m, amount of <span class="hlt">ice</span> chip more abundant</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160012483','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160012483"><span>Modeling the Thickness of Perennial <span class="hlt">Ice</span> Covers on Stratified Lakes of the Taylor Valley, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Obryk, M. K.; Doran, P. T.; Hicks, J. A.; McKay, C. P.; Priscu, J. C.</p> <p>2016-01-01</p> <p>A one-dimensional <span class="hlt">ice</span> cover model was developed to predict and constrain drivers of long term <span class="hlt">ice</span> thickness trends in chemically stratified lakes of Taylor Valley, <span class="hlt">Antarctica</span>. The model is driven by surface radiative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 years (between 1996 and 2012) of <span class="hlt">ice</span> thickness changes for west lobe of Lake Bonney (average <span class="hlt">ice</span> thickness = 3.53 m; RMSE = 0.09 m, n = 118) and Lake Fryxell (average <span class="hlt">ice</span> thickness = 4.22 m; RMSE = 0.21 m, n = 128). Long-term <span class="hlt">ice</span> thickness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or facilitate <span class="hlt">ice</span> thickness change depending on the predominant climatic trend (temperature cooling or warming). As such, shallow (< 20 m deep water columns) perennially <span class="hlt">ice</span>-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term <span class="hlt">ice</span> thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C33B1183H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C33B1183H"><span>Multi-method Quantification of Sea-<span class="hlt">ice</span> Production in Weddell Sea Polynyas (<span class="hlt">Antarctica</span>)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Heinemann, G.; Zentek, R.; Stulic, L.; Paul, S.; Preusser, A.; Timmermann, R.</p> <p>2017-12-01</p> <p>Coastal polynyas occur frequently during winter in the Weddell Sea, which leads to strong sea <span class="hlt">ice</span> production and to the formation of a highly saline water mass which is considered to be a major source of bottom water and one of the main drivers of the circulation beneath the Filchner-Ronne <span class="hlt">Ice</span> <span class="hlt">Shelf</span>. Thus the quantification of sea <span class="hlt">ice</span> production in Weddell Sea polynyas is of vital interest for understanding water mass modification in this region. We use a multi-method approach to quantify sea <span class="hlt">ice</span> production. Method 1) is based on the energy balance simulated by the regional climate model COSMO-CLM (CCLM) with 15 / 5 km resolution for the period 2002-2015 (nested in ERA-Interim data). Daily sea <span class="hlt">ice</span> concentrations were taken from microwave satellite measurements. Method 2) is based on remote sensing using MODIS thermal infrared data at a resolution of 1-2km and a surface energy balance model taking atmospheric data from different reanalyses (ERA-Interim, JRA55, NCEP2) as well as data of CCLM. Method 3) relies on simulations using the Finite Element Sea <span class="hlt">ice</span>-Ocean Model (FESOM). FESOM is run on a global grid with a resolution of about 5 km along the coast of the Weddell Sea using atmospheric forcing from reanalyses (ERA-Interim (80km) and CFSR (38km)) as well as from CCLM. In addition, an experiment with assimilation of MODIS thin <span class="hlt">ice</span> retrievals was conducted. Estimates of polynya area (POLA) and sea <span class="hlt">ice</span> production (IP) from the different methods are presented. The MODIS-based method with ERA-Interim shows the largest POLA as well as the largest IP for the Ronne polynya (RO, POLA / IP = 2800 km² / 29 km³/a) and for the polynya off Brunt <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (BR, 3400 km² / 30 km³/a). Sensitivity to the choice of atmosphere data is high. In particular, too low temperatures in JRA55 cause very large <span class="hlt">ice</span> production events and a strong overestimation of IP rates. Estimates based on CCLM simulations agree generally well with MODIS/ERA-Interim. FESOM yields a generally larger <span class="hlt">ice</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5425240','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5425240"><span>Australian <span class="hlt">shelf</span> sediments reveal shifts in Miocene Southern Hemisphere westerlies</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Groeneveld, Jeroen; Henderiks, Jorijntje; Renema, Willem; McHugh, Cecilia M.; De Vleeschouwer, David; Christensen, Beth A.; Fulthorpe, Craig S.; Reuning, Lars; Gallagher, Stephen J.; Bogus, Kara; Auer, Gerald; Ishiwa, Takeshige</p> <p>2017-01-01</p> <p>Global climate underwent a major reorganization when the Antarctic <span class="hlt">ice</span> sheet expanded ~14 million years ago (Ma) (1). This event affected global atmospheric circulation, including the strength and position of the westerlies and the Intertropical Convergence Zone (ITCZ), and, therefore, precipitation patterns (2–5). We present new shallow-marine sediment records from the continental <span class="hlt">shelf</span> of Australia (International Ocean Discovery Program Sites U1459 and U1464) providing the first empirical evidence linking high-latitude cooling around <span class="hlt">Antarctica</span> to climate change in the (sub)tropics during the Miocene. We show that Western Australia was arid during most of the Middle Miocene. Southwest Australia became wetter during the Late Miocene, creating a climate gradient with the arid interior, whereas northwest Australia remained arid throughout. Precipitation and river runoff in southwest Australia gradually increased from 12 to 8 Ma, which we relate to a northward migration or intensification of the westerlies possibly due to increased sea <span class="hlt">ice</span> in the Southern Ocean (5). Abrupt aridification indicates that the westerlies shifted back to a position south of Australia after 8 Ma. Our midlatitude Southern Hemisphere data are consistent with the inference that expansion of sea <span class="hlt">ice</span> around <span class="hlt">Antarctica</span> resulted in a northward movement of the westerlies. In turn, this may have pushed tropical atmospheric circulation and the ITCZ northward, shifting the main precipitation belt over large parts of Southeast Asia (4). PMID:28508066</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.2275R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.2275R"><span>Understanding <span class="hlt">ice</span> sheet evolution to avoid massive sea level rise instead of experiencing it (Louis Agassiz Medal Lecture)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rignot, Eric</p> <p>2017-04-01</p> <p>With unabated climate warming, massive sea level rise from the melting of <span class="hlt">ice</span> sheets in Greenland and <span class="hlt">Antarctica</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> sheets, including the coupling of ocean and <span class="hlt">ice</span> 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 <span class="hlt">ice</span> sheets as we know it today and the fundamental processes that will drive fast <span class="hlt">ice</span> sheet retreat and sea level change: <span class="hlt">ice</span>-ocean interaction and iceberg calving. <span class="hlt">Ice</span>-ocean interaction are dominated by the wind-forced intrusion of warm, salty, subsurface waters toward the <span class="hlt">ice</span> sheet periphery to melt <span class="hlt">ice</span> 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 <span class="hlt">ice</span> melt along vertical calving faces of meters per day, along with undercutting of the <span class="hlt">ice</span> 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 <span class="hlt">Antarctica</span>, 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 <span class="hlt">ice</span> within the sub-<span class="hlt">ice-shelf</span> cavities. I will describe progress made in mapping the bathymetry of the <span class="hlt">ice</span> shelves and how</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GeoRL..45.2706D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GeoRL..45.2706D"><span>Basal Settings Control Fast <span class="hlt">Ice</span> Flow in the Recovery/Slessor/Bailey Region, East <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Diez, Anja; Matsuoka, Kenichi; Ferraccioli, Fausto; Jordan, Tom A.; Corr, Hugh F.; Kohler, Jack; Olesen, Arne V.; Forsberg, René</p> <p>2018-03-01</p> <p>The region of Recovery Glacier, Slessor Glacier, and Bailey <span class="hlt">Ice</span> Stream, East <span class="hlt">Antarctica</span>, has remained poorly explored, despite representing the largest potential contributor to future global sea level rise on a centennial to millennial time scale. Here we use new airborne radar data to improve knowledge about the bed topography and investigate controls of fast <span class="hlt">ice</span> flow. Recovery Glacier is underlain by an 800 km long trough. Its fast flow is controlled by subglacial water in its upstream and topography in its downstream region. Fast flow of Slessor Glacier is controlled by the presence of subglacial water on a rough crystalline bed. Past <span class="hlt">ice</span> flow of adjacent Recovery and Slessor Glaciers was likely connected via the newly discovered Recovery-Slessor Gate. Changes in direction and speed of past fast flow likely occurred for upstream parts of Recovery Glacier and between Slessor Glacier and Bailey <span class="hlt">Ice</span> Stream. Similar changes could also reoccur here in the future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C51A0959A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51A0959A"><span>Twenty-three years of height changes on Antarctic Peninsula <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>Adusumilli, S.; Siegfried, M. R.; Paolo, F. S.; Fricker, H. A.; Padman, L.</p> <p>2017-12-01</p> <p>Over the past few decades, several <span class="hlt">ice</span> shelves in the Antarctic Peninsula (AP), the northernmost region of <span class="hlt">Antarctica</span>, have collapsed or undergone significant retreat. While the disintegration of these <span class="hlt">ice</span> shelves appears to be linked primarily to hydrofracture initiated by widespread surface melting, it has also been proposed that some of these <span class="hlt">ice</span> shelves could have weakened prior to collapse due to increased basal melt rates induced by thermal ocean forcing. To determine the long-term evolution of <span class="hlt">ice</span> shelves in this region, we compiled data from four radar altimeters (ERS-1, ERS-2, Envisat, and CryoSat-2) spanning twenty-three years (1994-2017). Over Larsen C, the largest AP <span class="hlt">ice</span> <span class="hlt">shelf</span>, a surface lowering of around 1 m between 1992 and 2009 has been partially offset by a height increase of around 0.75 m between 2009 and 2017. We use four independent, repeat airborne laser altimetry surveys from NASA's Operation <span class="hlt">Ice</span>Bridge to confirm the recent height increase, and a firn densification model (IMAU-FDM) forced by a regional atmospheric model (RACMO), to show that the recent height increase is primarily due to density changes in the firn column. In contrast, George VI <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in the Bellingshausen Sea remains in a state of continuous thinning through excess basal melting attributed to higher fluxes of ocean heat under the <span class="hlt">ice</span> <span class="hlt">shelf</span>. Changes such as these, which can occur on seasonal to decadal timescales, can potentially impact the dynamics of the grounded <span class="hlt">ice</span> sheet behind the floating <span class="hlt">ice</span> shelves, consequently affecting sea-level rise. Therefore, it is vital to continue the long-term, uninterrupted monitoring of <span class="hlt">ice</span> shelves through the modern satellite and airborne altimetry missions, and lengthen our existing time series to investigate the climate drivers causing changes in the <span class="hlt">ice</span> shelves from above (accumulation and density changes) and below (basal melting).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/984088-modeling-fracture-ice-sheets-parallel-computers','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/984088-modeling-fracture-ice-sheets-parallel-computers"><span>Modeling the fracture of <span class="hlt">ice</span> sheets on parallel computers.</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>Waisman, Haim; Bell, Robin; Keyes, David</p> <p>2010-03-01</p> <p>The objective of this project is to investigate the complex fracture of <span class="hlt">ice</span> and understand its role within larger <span class="hlt">ice</span> sheet simulations and global climate change. At the present time, <span class="hlt">ice</span> fracture is not explicitly considered within <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice</span> shelves inmore » <span class="hlt">Antarctica</span> (e.g. partial collapse of the Wilkins <span class="hlt">shelf</span> in March of 2008 and the diminishing extent of the Larsen B <span class="hlt">shelf</span> from 1998 to 2002). Other fracture examples include <span class="hlt">ice</span> calving (fracture of icebergs) which is presently approximated in simplistic ways within <span class="hlt">ice</span> sheet models, and the draining of supraglacial lakes through a complex network of cracks, a so called <span class="hlt">ice</span> sheet plumbing system, that is believed to cause accelerated <span class="hlt">ice</span> 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 <span class="hlt">ice</span>. To model <span class="hlt">ice</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-ED04-0056-110.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-ED04-0056-110.html"><span>An AirSAR 2004 view from the DC-8 as it approaches the Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, which is part of the Antarctic Peninsula</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>An AirSAR 2004 view from the DC-8 as it approaches the Larsen <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, which is part of the Antarctic Peninsula. AirSAR 2004 is a three-week expedition in Central and South America by an international team of scientists that is using an all-weather imaging tool, called the Airborne Synthetic Aperture Radar (AirSAR), located onboard NASA's DC-8 airborne laboratory. Scientists from many parts of the world are combining ground research with NASA's AirSAR technology to improve and expand on the quality of research they are able to conduct. These photos are from the DC-8 aircraft while flying an AirSAR mission over <span class="hlt">Antarctica</span>. 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('http://adsabs.harvard.edu/abs/2016GeoRL..43.9103K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoRL..43.9103K"><span><span class="hlt">Ice</span>-flow reorganization in West <span class="hlt">Antarctica</span> 2.5 kyr ago dated using radar-derived englacial flow velocities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kingslake, Jonathan; Martín, Carlos; Arthern, Robert J.; Corr, Hugh F. J.; King, Edward C.</p> <p>2016-09-01</p> <p>We date a recent <span class="hlt">ice</span>-flow reorganization of an <span class="hlt">ice</span> divide in the Weddell Sea Sector, West <span class="hlt">Antarctica</span>, using a novel combination of inverse methods and <span class="hlt">ice</span>-penetrating radars. We invert for two-dimensional <span class="hlt">ice</span> flow within an <span class="hlt">ice</span> divide from data collected with a phase-sensitive <span class="hlt">ice</span>-penetrating radar while accounting for the effect of firn on radar propagation and <span class="hlt">ice</span> flow. By comparing isochronal layers simulated using radar-derived flow velocities with internal layers observed with an impulse radar, we show that the divide's internal structure is not in a steady state but underwent a disturbance, potentially implying a regional <span class="hlt">ice</span>-flow reorganization, 2.5 (1.8-2.9) kyr B.P. Our data are consistent with slow <span class="hlt">ice</span> flow in this location before the reorganization and the <span class="hlt">ice</span> divide subsequently remaining stationary. These findings increase our knowledge of the glacial history of a region that lacks dated constraints on late-Holocene <span class="hlt">ice</span>-sheet retreat and provides a key target for models that reconstruct and predict <span class="hlt">ice</span>-sheet behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12..491G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12..491G"><span>Crustal heat production and estimate of terrestrial heat flow in central East <span class="hlt">Antarctica</span>, with implications for thermal input to the East 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>Goodge, John W.</p> <p>2018-02-01</p> <p>Terrestrial heat flow is a critical first-order factor governing the thermal condition and, therefore, mechanical stability of Antarctic <span class="hlt">ice</span> sheets, yet heat flow across <span class="hlt">Antarctica</span> is poorly known. Previous estimates of terrestrial heat flow in East <span class="hlt">Antarctica</span> come from inversion of seismic and magnetic geophysical data, by modeling temperature profiles in <span class="hlt">ice</span> boreholes, and by calculation from heat production values reported for exposed bedrock. Although accurate estimates of surface heat flow are important as an input parameter for <span class="hlt">ice</span>-sheet growth and stability models, there are no direct measurements of terrestrial heat flow in East <span class="hlt">Antarctica</span> coupled to either subglacial sediment or bedrock. As has been done with bedrock exposed along coastal margins and in rare inland outcrops, valuable estimates of heat flow in central East <span class="hlt">Antarctica</span> can be extrapolated from heat production determined by the geochemical composition of glacial rock clasts eroded from the continental interior. In this study, U, Th, and K concentrations in a suite of Proterozoic (1.2-2.0 Ga) granitoids sourced within the Byrd and Nimrod glacial drainages of central East <span class="hlt">Antarctica</span> indicate average upper crustal heat production (Ho) of about 2.6 ± 1.9 µW m-3. Assuming typical mantle and lower crustal heat flux for stable continental shields, and a length scale for the distribution of heat production in the upper crust, the heat production values determined for individual samples yield estimates of surface heat flow (qo) ranging from 33 to 84 mW m-2 and an average of 48.0 ± 13.6 mW m-2. Estimates of heat production obtained for this suite of glacially sourced granitoids therefore indicate that the interior of the East Antarctic <span class="hlt">ice</span> sheet is underlain in part by Proterozoic continental lithosphere with an average surface heat flow, providing constraints on both geodynamic history and <span class="hlt">ice</span>-sheet stability. The ages and geothermal characteristics of the granites indicate that crust in central</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1210736S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1210736S"><span>Neogene sea surface temperature reconstructions from the Southern McMurdo Sound and the McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (ANDRILL Program, <span class="hlt">Antarctica</span>)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sangiorgi, Francesca; Willmott, Veronica; Kim, Jung-Hyun; Schouten, Stefan; Brinkhuis, Henk; Sinninghe Damsté, Jaap S.; Florindo, Fabio; Harwood, David; Naish, Tim; Powell, Ross</p> <p>2010-05-01</p> <p>During the austral summers 2006 and 2007 the ANtarctic DRILLing Program (ANDRILL) drilled two cores, each recovering more than 1000m of sediment from below the McMurdo <span class="hlt">Ice-Shelf</span> (MIS, AND-1B), and sea-<span class="hlt">ice</span> in Southern McMurdo Sound (SMS, AND-2A), respectively, revealing new information about Neogene Antarctic cryosphere evolution. Core AND-1B was drilled in a more distal location than core AND-2A. With the aim of obtaining important information for the understanding of the history of Antarctic climate and environment during selected interval of the Neogene, we applied novel organic geochemistry proxies such as TEX86 (Tetra Ether IndeX of lipids with 86 carbon atoms) using a new calibration equation specifically developed for polar areas and based on 116 surface sediment samples collected from polar oceans (Kim et al., subm.), and BIT (Branched and Isoprenoid Tetraether), to derive absolute (sea surface) temperature values and to evaluate the relative contribution of soil organic matter versus marine organic matter, respectively. We will present the state-of-the-art of the methodology applied, discussing its advantages and limitations, and the results so far obtained from the analysis of 60 samples from core AND-2A covering the Miocene Climatic Optimum (and the Mid-late Miocene transition) and of 20 pilot samples from core AND-1B covering the late Pliocene.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29899456','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29899456"><span>Extensive retreat and re-advance of the West Antarctic <span class="hlt">Ice</span> Sheet during the Holocene.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kingslake, J; Scherer, R P; Albrecht, T; Coenen, J; Powell, R D; Reese, R; Stansell, N D; Tulaczyk, S; Wearing, M G; Whitehouse, P L</p> <p>2018-06-01</p> <p>To predict the future contributions of the Antarctic <span class="hlt">ice</span> sheets to sea-level rise, numerical models use reconstructions of past <span class="hlt">ice</span>-sheet retreat after the Last Glacial Maximum to tune model parameters 1 . Reconstructions of the West Antarctic <span class="hlt">Ice</span> Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so) 2-4 . Here we show, however, that over this period the grounding line of the West Antarctic <span class="hlt">Ice</span> Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating <span class="hlt">ice</span> <span class="hlt">shelf</span>) retreated several hundred kilometres inland of today's grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the <span class="hlt">ice</span> streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, <span class="hlt">ice</span>-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating <span class="hlt">ice-shelf</span> grounding. We explore the implications of these findings with an <span class="hlt">ice</span>-sheet model. Modelled re-advance of the grounding line in the Holocene requires <span class="hlt">ice-shelf</span> grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West <span class="hlt">Antarctica</span>, and corroborate previous suggestions of <span class="hlt">ice</span>-sheet re-advance 5 . Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated <span class="hlt">ice</span> loss. Whether these processes can reverse present-day <span class="hlt">ice</span> loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity-parameters that are difficult to measure and to incorporate into <span class="hlt">ice</span>-sheet models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018RvGeo..56..142P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018RvGeo..56..142P"><span>Ocean Tide Influences on the Antarctic and Greenland <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>Padman, Laurie; Siegfried, Matthew R.; Fricker, Helen A.</p> <p>2018-03-01</p> <p>Ocean tides are the main source of high-frequency variability in the vertical and horizontal motion of <span class="hlt">ice</span> sheets near their marine margins. Floating <span class="hlt">ice</span> shelves, which occupy about three quarters of the perimeter of <span class="hlt">Antarctica</span> and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of <span class="hlt">ice</span> sheets near their marine margins can also include a tidal component. These tide-induced signals provide insight into the processes by which the oceans can affect <span class="hlt">ice</span> sheet mass balance and dynamics. In this review, we summarize in situ and satellite-based measurements of the tidal response of <span class="hlt">ice</span> shelves and grounded <span class="hlt">ice</span>, and spatial variability of ocean tide heights and currents around the <span class="hlt">ice</span> sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, <span class="hlt">ice</span> <span class="hlt">shelf</span> thickness, and <span class="hlt">ice</span> sheet mass and extent. We then describe coupled <span class="hlt">ice</span>-ocean models and analytical glacier models that quantify the effect of ocean tides on lower-frequency <span class="hlt">ice</span> sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future <span class="hlt">ice</span> sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, <span class="hlt">ice</span> <span class="hlt">shelf</span> draft, spatial variability of the drag coefficient at the <span class="hlt">ice</span>-ocean interface, and higher-resolution models with improved representation of tidal energy sinks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.S31D..02C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.S31D..02C"><span>Near-surface elastic changes in the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> arising from transient storm and melt forcing observed with high-frequency ambient seismic noise</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chaput, J.; Aster, R. C.; Baker, M. G.; Gerstoft, P.; Bromirski, P. D.; Nyblade, A.; Stephen, R. A.; Wiens, D.</p> <p>2017-12-01</p> <p><span class="hlt">Ice</span> <span class="hlt">shelf</span> collapse can herald subsequent grounded <span class="hlt">ice</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> properties. Using nearly three years of continuous data from a recently deployed 34-station broadband seismic array on the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span>, 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 <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> elasticity and structure using long-duration seismic recordings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C23A1213G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C23A1213G"><span>The frequency response of a coupled <span class="hlt">ice</span> sheet-<span class="hlt">ice</span> <span class="hlt">shelf</span>-ocean system to climate forcing variability</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.; Snow, K.; Jordan, J. R.; Holland, P.; Arthern, R. J.</p> <p>2017-12-01</p> <p>Changes at the West Antarctic <span class="hlt">ice</span>-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 <span class="hlt">ice</span>-ocean boundary, transported on-<span class="hlt">shelf</span> via warm Circumpolar Deep Water (CDW). However, the processes in which ocean heat drives <span class="hlt">ice</span>-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 <span class="hlt">ice</span>-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 <span class="hlt">ice</span>-ocean system. Feedbacks and response are assessed in an idealised <span class="hlt">ice</span>-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 <span class="hlt">ice</span>-sheet to periodic variations in thermocline depth. These non-linearities illustrate the heightened sensitivity of fast flowing <span class="hlt">ice</span>-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 <span class="hlt">ice</span>-sheet response.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.2520T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.2520T"><span>Geoethical approach to mineral activities in <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Talalay, Pavel</p> <p>2013-04-01</p> <p><span class="hlt">Antarctica</span> is the outermost from civilization space continent. From 14.0 million km2 of surface area about 98% of <span class="hlt">Antarctica</span> is covered by <span class="hlt">ice</span> that averages at least 1.6 km in thickness. Geologically, the continent is the least explored in the world, and it is almost absolutely unknown what mineral resources <span class="hlt">Antarctica</span> has as they are buried in rock that is covered by a thick <span class="hlt">ice</span> sheet. It is thought to have large and valuable mineral deposits under the <span class="hlt">ice</span>. This is because of what has been found in samples taken from the small areas of rock that are exposed, and also from what has been found in South Africa and South America. Up until 180 million years ago, <span class="hlt">Antarctica</span> was a part of the Gondwanaland super continent, attached to South America, the Southern part of Africa, India and Australia, these continents then drifted apart until they reached their current positions. This leads to a possibility that <span class="hlt">Antarctica</span> may also share some of the mineral wealth of these continents. Right now on the <span class="hlt">ice</span>-free areas of <span class="hlt">Antarctica</span> iron ore, chromium, copper, gold, nickel, platinum, coal and hydrocarbons have been found. The Protocol on Environmental Protection to the Antarctic Treaty, also known as the Madrid Protocol, was signed in 1991 by the signatories to the Antarctic Treaty and became law in January 1998. The Protocol provides for comprehensive protection of the Antarctic environment and associated ecosystems and includes a ban on all commercial mining for at least fifty years (this is up for review in 2041). Current climate change and melting <span class="hlt">ice</span> in Polar Regions is opening up new opportunities to exploit mineral and oil resources. Even <span class="hlt">Antarctica</span>'s weather, <span class="hlt">ice</span> and distance from any industrialized areas mean that mineral extraction would be extremely expensive and also extremely dangerous, the depletion of mineral recourses on the Earth can reverse banning of mining in <span class="hlt">Antarctica</span> in future. There is no question that any resource exploitation in <span class="hlt">Antarctica</span> will cause</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4024921','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4024921"><span>Radiometric 81Kr dating identifies 120,000-year-old <span class="hlt">ice</span> at Taylor Glacier, <span class="hlt">Antarctica</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>Buizert, Christo; Baggenstos, Daniel; Jiang, Wei; Purtschert, Roland; Petrenko, Vasilii V.; Lu, Zheng-Tian; Müller, Peter; Kuhl, Tanner; Lee, James; Severinghaus, Jeffrey P.; Brook, Edward J.</p> <p>2014-01-01</p> <p>We present successful 81Kr-Kr radiometric dating of ancient polar <span class="hlt">ice</span>. Krypton was extracted from the air bubbles in four ∼350-kg polar <span class="hlt">ice</span> samples from Taylor Glacier in the McMurdo Dry Valleys, <span class="hlt">Antarctica</span>, and dated using Atom Trap Trace Analysis (ATTA). The 81Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) 85Kr and 39Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the <span class="hlt">ice</span> did not experience gas loss. We estimate the error in the 81Kr ages due to past geomagnetic variability to be below 3 ka. We show that <span class="hlt">ice</span> from the previous interglacial period (Marine Isotope Stage 5e, 130–115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient <span class="hlt">ice</span> in blue <span class="hlt">ice</span> areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old <span class="hlt">ice</span> and meteorites. At present, ATTA 81Kr analysis requires a 40–80-kg <span class="hlt">ice</span> sample; as sample requirements continue to decrease, 81Kr dating of <span class="hlt">ice</span> cores is a future possibility. PMID:24753606</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24753606','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24753606"><span>Radiometric 81Kr dating identifies 120,000-year-old <span class="hlt">ice</span> at Taylor Glacier, <span class="hlt">Antarctica</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Buizert, Christo; Baggenstos, Daniel; Jiang, Wei; Purtschert, Roland; Petrenko, Vasilii V; Lu, Zheng-Tian; Müller, Peter; Kuhl, Tanner; Lee, James; Severinghaus, Jeffrey P; Brook, Edward J</p> <p>2014-05-13</p> <p>We present successful (81)Kr-Kr radiometric dating of ancient polar <span class="hlt">ice</span>. Krypton was extracted from the air bubbles in four ∼350-kg polar <span class="hlt">ice</span> samples from Taylor Glacier in the McMurdo Dry Valleys, <span class="hlt">Antarctica</span>, and dated using Atom Trap Trace Analysis (ATTA). The (81)Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) (85)Kr and (39)Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the <span class="hlt">ice</span> did not experience gas loss. We estimate the error in the (81)Kr ages due to past geomagnetic variability to be below 3 ka. We show that <span class="hlt">ice</span> from the previous interglacial period (Marine Isotope Stage 5e, 130-115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient <span class="hlt">ice</span> in blue <span class="hlt">ice</span> areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old <span class="hlt">ice</span> and meteorites. At present, ATTA (81)Kr analysis requires a 40-80-kg <span class="hlt">ice</span> sample; as sample requirements continue to decrease, (81)Kr dating of <span class="hlt">ice</span> cores is a future possibility.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29239353','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29239353"><span>Initiation and long-term instability of the East 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>Gulick, Sean P S; Shevenell, Amelia E; Montelli, Aleksandr; Fernandez, Rodrigo; Smith, Catherine; Warny, Sophie; Bohaty, Steven M; Sjunneskog, Charlotte; Leventer, Amy; Frederick, Bruce; Blankenship, Donald D</p> <p>2017-12-13</p> <p><span class="hlt">Antarctica</span>'s continental-scale <span class="hlt">ice</span> sheets have evolved over the past 50 million years. However, the dearth of <span class="hlt">ice</span>-proximal geological records limits our understanding of past East Antarctic <span class="hlt">Ice</span> Sheet (EAIS) behaviour and thus our ability to evaluate its response to ongoing environmental change. The EAIS is marine-terminating and grounded below sea level within the Aurora subglacial basin, indicating that this catchment, which drains <span class="hlt">ice</span> to the Sabrina Coast, may be sensitive to climate perturbations. Here we show, using marine geological and geophysical data from the continental <span class="hlt">shelf</span> seaward of the Aurora subglacial basin, that marine-terminating glaciers existed at the Sabrina Coast by the early to middle Eocene epoch. This finding implies the existence of substantial <span class="hlt">ice</span> volume in the Aurora subglacial basin before continental-scale <span class="hlt">ice</span> sheets were established about 34 million years ago. Subsequently, <span class="hlt">ice</span> advanced across and retreated from the Sabrina Coast continental <span class="hlt">shelf</span> at least 11 times during the Oligocene and Miocene epochs. Tunnel valleys associated with half of these glaciations indicate that a surface-meltwater-rich sub-polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming. Cooling since the late Miocene resulted in an expanded polar EAIS and a limited glacial response to Pliocene warmth in the Aurora subglacial basin catchment. Geological records from the Sabrina Coast <span class="hlt">shelf</span> indicate that, in addition to ocean temperature, atmospheric temperature and surface-derived meltwater influenced East Antarctic <span class="hlt">ice</span> mass balance under warmer-than-present climate conditions. Our results imply a dynamic EAIS response with continued anthropogenic warming and suggest that the EAIS contribution to future global sea-level projections may be under-estimated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27..209R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27..209R"><span>Marine Isotope Stage 11 : The Role of Co2, Insolation and <span class="hlt">Antarctica</span> <span class="hlt">Ice</span> Sheet On This Interglacial</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Raynaud, D.; Loutre, M. F.; Ritz, C.; Barnola, J.-M.; Berger, A.; Chappellaz, J.; Jouzel, J.; Lipenkov, V.; Petit, J.-R.; Vimeux, F.</p> <p></p> <p>The Marine Isotopic Stage 11 (MIS 11), around 400kyr BP ago, has been suggested as an analogue for a future climate under natural forcing because of the similar condi- tions of orbitally driven insolation during this interglacial period and the one covering the Holocene and the near future. There are many open questions about unusual MIS 11 climatic conditions (length of the interglacial, temperature, sea level, marine car- bonate system), as recorded in different marine and continental records. The Antarctic Vostok <span class="hlt">ice</span> core provides the only atmospheric record extending back to MIS 11 and we use it to discuss the Antarctic temperature, the atmospheric CO2 concentration and the <span class="hlt">ice</span> sheet stability in the central part of East <span class="hlt">Antarctica</span> during this interglacial. The unique nature of the Vostok atmospheric record leads us to use the available Vos- tok data to drive climate and <span class="hlt">ice</span> sheet models for MIS 11. A model of intermediate complexity (LLN-2D model) is used to investigate the sensitivity of the simulated MIS 11 deglaciation to the interplay between insolation and CO2. It is shown that the length of the simulated interglacial depends strongly on the phasing between these two climate forcings. We also investigate the response of the Antarctic <span class="hlt">Ice</span> Sheet to changing climate through simulations performed with the LGGE 3-D <span class="hlt">ice</span> sheet model. The results indicate that sea level stands during MIS 11 as high as 20 m. above present level, as suggested by different elevated marine terraces, cannot be explained, except by assuming that MIS 11 was very dry over <span class="hlt">Antarctica</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016QSRv..140..101P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016QSRv..140..101P"><span>Sedimentology and chronology of the advance and retreat of the last British-Irish <span class="hlt">Ice</span> Sheet on the continental <span class="hlt">shelf</span> west of Ireland</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 L.; Benetti, Sara; Dunlop, Paul; Ó Cofaigh, Colm; Moreton, Steven G.; Wheeler, Andrew J.; Clark, Christopher D.</p> <p>2016-05-01</p> <p>The last British-Irish <span class="hlt">Ice</span> Sheet (BIIS) had extensive marine-terminating margins and was drained by multiple large <span class="hlt">ice</span> streams and is thus a useful analogue for marine-based areas of modern <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> break by ∼24,000 Cal BP. <span class="hlt">Ice</span> margin retreat was likely preceded by thinning, grounding zone retreat and <span class="hlt">ice</span> <span class="hlt">shelf</span> formation on the outer <span class="hlt">shelf</span> by ∼22,000 Cal BP. This <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> and records a significant stillstand in BIIS retreat. Geomorphic relationships indicate that the BIIS experienced continued thinning during its retreat across the <span class="hlt">shelf</span>, which led to increased topographic influence on its flow dynamics following <span class="hlt">ice</span> <span class="hlt">shelf</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1610000A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1610000A"><span>Simulations of Antarctic <span class="hlt">ice</span> shelves and the Southern Ocean in the POP2x ocean model coupled with the BISICLES <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>Asay-Davis, Xylar; Martin, Daniel; Price, Stephen; Maltrud, Mathew</p> <p>2014-05-01</p> <p>We present initial results from Antarctic, <span class="hlt">ice</span>-ocean coupled simulations using large-scale ocean circulation and <span class="hlt">ice</span>-sheet evolution models. This presentation focuses on the ocean model, POP2x, which is a modified version of POP, a fully eddying, global-scale ocean model (Smith and Gent, 2002). POP2x allows for circulation beneath <span class="hlt">ice</span> <span class="hlt">shelf</span> cavities using the method of partial top cells (Losch, 2008). Boundary layer physics, which control fresh water and salt exchange at the <span class="hlt">ice</span>-ocean interface, are implemented following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard <span class="hlt">ice</span>-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013) and with results from other idealized <span class="hlt">ice</span>-ocean coupling test cases (e.g., Goldberg et al., 2012). A companion presentation, 'Fully resolved whole-continent <span class="hlt">Antarctica</span> simulations using the BISICLES AMR <span class="hlt">ice</span> sheet model coupled with the POP2x Ocean Model', concentrates more on the <span class="hlt">ice</span>-sheet model, BISICLES (Cornford et al., 2012), which includes a 1st-order accurate momentum balance (L1L2) and uses block structured, adaptive-mesh refinement to more accurately model regions of dynamic complexity, such as <span class="hlt">ice</span> streams, outlet glaciers, and grounding lines. For idealized test cases focused on marine-<span class="hlt">ice</span> sheet dynamics, BISICLES output compares very favorably relative to simulations based on the full, nonlinear Stokes momentum balance (MISMIP-3d; Pattyn et al., 2013). Here, we present large-scale (Southern Ocean) simulations using POP2x at 0.1 degree resolution with fixed <span class="hlt">ice</span> <span class="hlt">shelf</span> geometries, which are used to obtain and validate modeled submarine melt rates against observations. These melt rates are, in turn, used to force evolution of the BISICLES model. An offline-coupling scheme, which we compare with the <span class="hlt">ice</span>-ocean coupling work of Goldberg et al. (2012), is then used to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C43A..02P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C43A..02P"><span>Theory of buttressed marine <span class="hlt">ice</span> sheet dynamics and its application to the assessment of tipping-point conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pegler, S.</p> <p>2017-12-01</p> <p>Understanding the fate of the West Antarctic <span class="hlt">Ice</span> Sheet is constrained by difficulties of resolving the buttressing effect of <span class="hlt">ice</span> shelves and its dynamic response to grounding-line migration. This effect may be responsible for protecting a large majority of outlet glaciers in <span class="hlt">Antarctica</span> 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 <span class="hlt">ice-shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">ice-shelf</span> buttressing force, with a loss of sensitivity to basal conditions, contrasting with the conclusion from one-dimensional theory that the <span class="hlt">ice</span> <span class="hlt">shelf</span> is irrelevant. The results provide an interpretive framework for understanding grounding-line dynamics, its coupling with <span class="hlt">ice-shelf</span> dynamics, an efficient exploration of parameter variation, and a complement to large-scale simulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C13G..06H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C13G..06H"><span>The transient response of <span class="hlt">ice-shelf</span> melting to ocean change</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Holland, P.</p> <p>2017-12-01</p> <p>Idealised modelling studies show that the melting of <span class="hlt">ice</span> shelves varies as a quadratic function of ocean temperature. This means that warm-water <span class="hlt">ice</span> shelves have higher melt rates and are also more sensitive to ocean warming. However, this result is the equilibrium response, derived from a set of ice—ocean simulations subjected to a fixed ocean forcing and run until steady. This study considers instead the transient response of melting, using unsteady simulations subjected to forcing conditions that are oscillated in time with a range of periods. The results show that when the ocean forcing is varied slowly, the melt rates follow the equililbrium response. However, for rapid ocean change melting deviates from the equilibrium response in interesting ways. The residence time of water in the sub-<span class="hlt">ice</span> cavity offers a critical timescale. When the forcing varies slowly (period of oscillation >> residence time), the cavity is fully-flushed with forcing anomalies at all stages of the cycle and melting follows the equilibrium response. When the forcing varies rapidly (period ≤ residence time), multiple cold and warm anomalies coexist in the cavity, cancelling each other in the spatial mean and thus inducing a relatively steady melt rate. This implies that all <span class="hlt">ice</span> shelves have a maximum frequency of ocean variability that can be manifested in melting. The results also show that <span class="hlt">ice</span> shelves forced by warm water have high melt rates, high equilibrium sensitivity, and short residence times, hence a short timescale over which the equilibrium sensitivity is manifest. The most rapid melting adjustment is induced by warm anomalies that are also saline. Thus, <span class="hlt">ice</span> shelves in the Amundsen and Bellingshausen seas, <span class="hlt">Antarctica</span>, are highly sensitive to ocean change.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009QSRv...28.1291D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009QSRv...28.1291D"><span>Holocene glacier and deep water dynamics, Adélie Land region, East <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Denis, Delphine; Crosta, Xavier; Schmidt, Sabine; Carson, Damien S.; Ganeshram, Raja S.; Renssen, Hans; Bout-Roumazeilles, Viviane; Zaragosi, Sebastien; Martin, Bernard; Cremer, Michel; Giraudeau, Jacques</p> <p>2009-06-01</p> <p>This study presents a high-resolution multi-proxy investigation of sediment core MD03-2601 and documents major glacier oscillations and deep water activity during the Holocene in the Adélie Land region, East <span class="hlt">Antarctica</span>. A comparison with surface ocean conditions reveals synchronous changes of glaciers, sea <span class="hlt">ice</span> and deep water formation at Milankovitch and sub-Milankovitch time scales. We report (1) a deglaciation of the Adélie Land continental <span class="hlt">shelf</span> from 11 to 8.5 cal ka BP, which occurred in two phases of effective glacier grounding-line retreat at 10.6 and 9 cal ka BP, associated with active deep water formation; (2) a rapid glacier and sea <span class="hlt">ice</span> readvance centred around 7.7 cal ka BP; and (3) five rapid expansions of the glacier-sea <span class="hlt">ice</span> systems, during the Mid to Late Holocene, associated to a long-term increase of deep water formation. At Milankovich time scales, we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier-sea <span class="hlt">ice</span>-ocean system throughout the Holocene, in the Adélie Land region. In addition, the orbitally-forced seasonality seems to control the coastal deep water formation via the sea <span class="hlt">ice</span>-ocean coupling, which could lead to opposite patterns between north and south high latitudes during the Mid to Late Holocene. At sub-Milankovitch time scales, there are eight events of glacier-sea <span class="hlt">ice</span> retreat and expansion that occurred during atmospheric cooling events over East <span class="hlt">Antarctica</span>. Comparisons of our results with other peri-Antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier-sea <span class="hlt">ice</span>-ocean interactions and their Holocene evolutions reflect a more global Antarctic Holocene pattern.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-GSFC_20171208_Archive_e001782.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-GSFC_20171208_Archive_e001782.html"><span>Mackenzie Bay, <span class="hlt">Antarctica</span></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>Off the northeastern edge of Antarctica’s Amery <span class="hlt">Ice</span> <span class="hlt">Shelf</span> lies Mackenzie Bay, which was painted with a ghostly blue-green mass in early February 2012. Similarly colored tendrils also streamed northward across the ocean, their flow sometimes interrupted by icebergs. Multiple factors might account for the ghostly shapes, including low-lying clouds or katabatic winds—downslope winds blowing toward the coast, which can freeze the water at the ocean surface. But an intriguing and perhaps more likely explanation involves processes occurring below the <span class="hlt">ice</span> <span class="hlt">shelf</span>. An <span class="hlt">ice</span> <span class="hlt">shelf</span> is a thick slab of <span class="hlt">ice</span> often fed by glaciers attached to the coastline. The <span class="hlt">shelf</span> floats on the ocean surface, with seawater circulating underneath. Like most <span class="hlt">ice</span> shelves, the Amery is very thick in the upstream area near the shore. It thins significantly as it stretches northward away from the continent. Water at depth is subject to much greater pressure than water at the surface, and one effect of this intense pressure is that it effectively lowers the freezing point. So water circulating at depth beneath the Amery <span class="hlt">Ice</span> <span class="hlt">Shelf</span> may be slightly below the temperature at which it would normally begin to freeze. As some that water wells up along the underbelly of the <span class="hlt">shelf</span>, the pressure is reduced and the water begins to freeze even though the temperature may not change. As it freezes, this deep-ocean water forms needle-like crystals known as frazil. The crystals are only 3 to 4 millimeters (0.12 to 0.16 inches) wide, but a sufficient concentration of frazil can change the appearance of the water. A frazil-rich plume probably accounts for the blue-green waters off the Amery <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in the image above. Modeling of ocean circulation beneath the <span class="hlt">shelf</span> indicates just such a plume emerging in that location. Frazil-rich water explains the plume, and wind transport of the surface water explains the long streams extending northward. As the sub-iceshelf water mixes with surface water around the Antarctic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1817840B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1817840B"><span>Phase-sensitive radar on thick Antarctic <span class="hlt">ice</span> - how well does it work?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Binder, Tobias; Eisen, Olaf; Helm, Veit; Humbert, Angelika; Steinhage, Daniel</p> <p>2016-04-01</p> <p>Phase-sensitive radar (pRES) has become one of the mostly used tools to determine basal melt rates as well as vertical strain in <span class="hlt">ice</span> sheets. Whereas most applications are performed on <span class="hlt">ice</span> shelves, only few experiments were conducted on thick <span class="hlt">ice</span> in Greenland or <span class="hlt">Antarctica</span>. The technical constrains on an <span class="hlt">ice</span> <span class="hlt">shelf</span> to deduce basal melt rates are less demanding than on inland <span class="hlt">ice</span> of more than 2 km thickness. First, the <span class="hlt">ice</span> itself is usually only several 100s of meters thick; and, second, the reflection coefficient at the basal interface between sea water and <span class="hlt">ice</span> is the second strongest one possible. Although the presence of marine <span class="hlt">ice</span> with higher conductivities might increase attenuation in the lower parts, most experiments on shelves were successful. To transfer this technology to inland regions, either for the investigation of basal melt rates of subglacial hydrological networks or for determining vertical strain rates in basal regions, a reliable estimate of the current system performance is necessary. To this end we conducted an experiment at and in the vicinity of the EPICA deep <span class="hlt">ice</span> core drill site EDML in Dronning Maud Land, <span class="hlt">Antarctica</span>. That site has been explored in extraordinary detail with different geophysical methods and provides an already well-studied <span class="hlt">ice</span> core and borehole, in particular with respect to physical properties like crystal orientation fabric, dielectric properties and matching of internal radar horizons with conductivity signals. We present data from a commercially available pRES system initially recorded in January 2015 and repeated measurements in January 2016. The pRES data are matched to existing and already depth-calibrated airborne radar data. Apart from identifying prominent internal layers, e.g. the one originating from the deposits of the Toba eruption at around 75 ka, we put special focus on the identification of the basal reflection at multiple polarizations. We discuss the potential uncertainty estimates and requirements to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSHE44B1515S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSHE44B1515S"><span>Spatial and temporal variation of <span class="hlt">Shelf</span> Water and its connection with Antarctic Bottom Water in Prydz Bay, East <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sun, Y.; Shi, J.; Yuan, X.</p> <p>2016-02-01</p> <p>Hydrographic surveys from 1981 to 2015, instrumented seal data from 2004 to 2014, and mooring data were used to reveal spatial and temporal variation of <span class="hlt">Shelf</span> Water (SW) and the connection between SW and Antarctic Bottom Water (AABW) in Prydz Bay. The basic spatial pattern of the SW properties was presented and 5 subregions were distinguished based on the pattern and the topography. The change of water masses and the processes on the <span class="hlt">shelf</span> are investigated in these subregions. A high salinity SW(S>34.6) is observed in the central and northern part of the Amery Basin in summer, which is like to be caused by the Circumpolar Deep Water (CDW) intrusion, and the eddy activities could be the primary impact to the CDW intrusion. There could be less CDW intrusion in winter because of the <span class="hlt">ice</span> cover in this subregion, which is supported by the mooring in Prydz Bay Channel. A high salinity SW is observed near the Mackenzie polynya in winter, which is caused by brine rejection in <span class="hlt">ice</span> production process. But the high salinity SW seems unlikely to form the overflow denser SW and locally form AABW. A dense water mass with low salinity, low temperature and high oxygen was observed on the <span class="hlt">shelf</span> break in the 70.5°E section, which could be caused by the <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Water (ISW) export from Amery <span class="hlt">Shelf</span>. According to the hydrographic data, the dense water can form overflow DSW and flow downslope to west, which can be observed in the bottom of slope near 1500m in the 70°E section. The water will form AABW if it can flow downslope to the deep basin and keep mixing with CDW, suggesting a new type of DSW overflow in Prydz Bay.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GeoRL..45.4096K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GeoRL..45.4096K"><span>Evaluating the Duration and Continuity of Potential Climate Records From the Allan Hills Blue <span class="hlt">Ice</span> Area, East <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kehrl, Laura; Conway, Howard; Holschuh, Nicholas; Campbell, Seth; Kurbatov, Andrei V.; Spaulding, Nicole E.</p> <p>2018-05-01</p> <p>The current <span class="hlt">ice</span> core record extends back 800,000 years. Geologic and glaciological evidence suggests that the Allan Hills Blue <span class="hlt">Ice</span> Area, East <span class="hlt">Antarctica</span>, may preserve a continuous record that extends further back in time. In this study, we use <span class="hlt">ice</span>-penetrating radar and existing age constraints to map the internal stratigraphy and age structure of the Allan Hills Main <span class="hlt">Ice</span> Field. The dated isochrones provide constraints for an <span class="hlt">ice</span> flow model to estimate the age of <span class="hlt">ice</span> near the bed. Previous drilling in the region recovered stratigraphically disturbed sections of <span class="hlt">ice</span> up to 2.7 million years old. Our study identifies a site 5 km upstream, which likely preserves a continuous record through Marine Isotope Stage 11 with the possibility that the record extends back 1 million years. Such records would provide new insight into the past climate and glacial history of the Ross Sea Sector.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70197380','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70197380"><span>Seismic experiment ross <span class="hlt">ice</span> <span class="hlt">shelf</span> 1990/91: Characteristics of the seismic reflection data</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p></p> <p>1993-01-01</p> <p>The Transantarctic Mountains, with a length of 3000-3500 km and elevations of up to 4500 m, are one of the major Cenozoic mountain ranges in the world and are by far the most striking example of rift-shoulder mountains. Over the 1990-1991 austral summer Seismic Experiment Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (SERIS) was carried out across the Transantarctic Mountain front, between latitudes 82 degrees to 83 degrees S, in order to investigate the transition zone between the rifted area of the Ross Embayment and the uplifted Transantarctic Mountains. This experiment involved a 140 km long seismic reflection profile together with a 96 km long coincident wide-angle reflection/refraction profile. Gravity and relative elevation (using barometric pressure) were also measured along the profile. The primary purpose was to examine the boundary between the rift system and the uplifted rift margin (represented by the Transantarctic Mountains) using modern multi-channel crustal reflection/refraction techniques. The results provide insight into crustal structure across the plate boundary. SERIS also represented one of the first large-scale and modern multi-channel seismic experiments in the remote interior of <span class="hlt">Antarctica</span>. As such, the project was designed to test different seismic acquisition techniques which will be involved in future seismic exploration of the continent. This report describes the results from the analysis of the acquisition tests as well as detailing some of the characteristics of the reflection seismic data. (auths.)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.C11C0828S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.C11C0828S"><span>Velocities along Byrd Glacier, East <span class="hlt">Antarctica</span>, derived from Automatic Feature Tracking</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stearns, L. A.; Hamilton, G. S.</p> <p>2003-12-01</p> <p>Automatic feature tracking techniques are applied to recently acquired ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) imagery in order to determine the velocity field of Byrd Glacier, East <span class="hlt">Antarctica</span>. The software IMCORR tracks the displacement of surface features (crevasses, drift mounds) in time sequential images, to produce the velocity field. Due to its high resolution, ASTER imagery is ideally suited for detecting small features changes. The produced result is a dense array of velocity vectors, which allows more thorough characterization of glacier dynamics. Byrd Glacier drains approximately 20.5 km3 of <span class="hlt">ice</span> into the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> every year. Previous studies have determined <span class="hlt">ice</span> velocities for Byrd Glacier by using photogrammetry, field measurements and manual feature tracking. The most recent velocity data is from 1986 and, as evident in the West Antarctic <span class="hlt">ice</span> streams, substantial changes in velocity can occur on decadal time scales. The application of ASTER-based velocities fills this time lapse, and increased temporal resolution allows for a more complete analysis of Byrd Glacier. The ASTER-derived <span class="hlt">ice</span> velocities are used in updating mass balance and force budget calculations to assess the stability of Byrd Glacier. <span class="hlt">Ice</span> thickness information from BEDMAP, surface slopes from the OSUDEM and a compilation of accumulation rates are used to complete the calculations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23627111','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23627111"><span>[Bacterial diversity within different sections of summer sea-<span class="hlt">ice</span> samples from the Prydz Bay, <span class="hlt">Antarctica</span>].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ma, Jifei; Du, Zongjun; Luo, Wei; Yu, Yong; Zeng, Yixin; Chen, Bo; Li, Huirong</p> <p>2013-02-04</p> <p>In order to assess bacterial abundance and diversity within three different sections of summer sea-<span class="hlt">ice</span> samples collected from the Prydz Bay, <span class="hlt">Antarctica</span>. Fluorescence in situ hybridization was applied to determine the proportions of Bacteria in sea-<span class="hlt">ice</span>. Bacterial community composition within sea <span class="hlt">ice</span> was analyzed by 16S rRNA gene clone library construction. Correlation analysis was performed between the physicochemical parameters and the bacterial diversity and abundance within sea <span class="hlt">ice</span>. The result of fluorescence in situ hybridization shows that bacteria were abundant in the bottom section, and the concentration of total organic carbon, total organic nitrogen and phosphate may be the main factors for bacterial abundance. In bacterial 16S rRNA gene libraries of sea-<span class="hlt">ice</span>, nearly complete 16S rRNA gene sequences were grouped into three distinct lineages of Bacteria (gamma-Proteobacteria, alpha-Proteobacteria and Bacteroidetes). Most clone sequences were related to cultured bacterial isolates from the marine environment, arctic and Antarctic sea-<span class="hlt">ice</span> with high similarity. The member of Bacteroidetes was not detected in the bottom section of sea-<span class="hlt">ice</span>. The bacterial communities within sea-<span class="hlt">ice</span> were little heterogeneous at the genus-level between different sections, and the concentration of NH4+ may cause this distribution. The number of bacteria was abundant in the bottom section of sea-<span class="hlt">ice</span>. Gamma-proteobacteria was the dominant bacterial lineage in sea-<span class="hlt">ice</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-200910220008HQ.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-200910220008HQ.html"><span><span class="hlt">Ice</span> Bridge Antarctic Sea <span class="hlt">Ice</span></span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2009-10-21</p> <p>Sea <span class="hlt">ice</span> is seen out the window of NASA's DC-8 research aircraft as it flies 2,000 feet above the Bellingshausen Sea in West <span class="hlt">Antarctica</span> on Wednesday, Oct., 21, 2009. This was the fourth science flight of NASA’s Operation <span class="hlt">Ice</span> Bridge airborne Earth science mission to study Antarctic <span class="hlt">ice</span> sheets, sea <span class="hlt">ice</span>, and <span class="hlt">ice</span> shelves. Photo Credit: (NASA/Jane Peterson)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016DSRII.131....7H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016DSRII.131....7H"><span>SIPEX 2012: Extreme sea-<span class="hlt">ice</span> and atmospheric conditions off East <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Heil, P.; Stammerjohn, S.; Reid, P.; Massom, R. A.; Hutchings, J. K.</p> <p>2016-09-01</p> <p>In 2012, Antarctic sea-<span class="hlt">ice</span> coverage was marked by weak annual-mean climate anomalies that consisted of opposing anomalies early and late in the year (some setting new records) which were interspersed by near-average conditions for most of the austral autumn and winter. Here, we investigate the ocean-<span class="hlt">ice</span>-atmosphere system off East <span class="hlt">Antarctica</span>, prior to and during the Sea <span class="hlt">Ice</span> Physics and Ecosystems eXperiment [SIPEX] 2012, by exploring relationships between atmospheric and oceanic forcing together with the sea-<span class="hlt">ice</span> and snow characteristics. During August and September 2012, just prior to SIPEX 2012, atmospheric circulation over the Southern Ocean was near-average, setting up the ocean-<span class="hlt">ice</span>-atmosphere system for near-average conditions. However, below-average surface pressure and temperature as well as strengthened circumpolar winds prevailed during June and July 2012. This led to a new record (19.48×106 km2) in maximum Antarctic sea-<span class="hlt">ice</span> extent recorded in late September. In contrast to the weak circum-Antarctic conditions, the East Antarctic sector (including the SIPEX 2012 region) experienced positive sea-<span class="hlt">ice</span> extent and concentration anomalies during most of 2012, coincident with negative atmospheric pressure and sea-surface temperature anomalies. Heavily deformed sea <span class="hlt">ice</span> appeared to be associated with intensified wind stress due to increased cyclonicity as well as an increased influx of sea <span class="hlt">ice</span> from the east. This increased westward <span class="hlt">ice</span> flux is likely linked to the break-up of nearly 80% of the Mertz Glacier Tongue in 2010, which strongly modified the coastal configuration and hence the width of the westward coastal current. Combined with favourable atmospheric conditions the associated changed coastal configuration allowed more sea <span class="hlt">ice</span> to remain within the coastal current at the expense of a reduced northward flow in the region around 141°-145°E. In addition a westward propagating positive anomaly of sea-<span class="hlt">ice</span> extent from the western Ross Sea during austral winter</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1513583C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1513583C"><span><span class="hlt">Ice</span> <span class="hlt">shelf</span> breaking and increase velocity of glacier: the view from analogue experiment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Corti, Giacomo; Iandelli, Irene</p> <p>2013-04-01</p> <p>Collapse of the Larsen II platform during the late 90s has generated an increase in velocity if <span class="hlt">ice</span> sheet discharge, highlighting that these processes may strongly destabilize large <span class="hlt">ice</span> masses speeding up the plateau discharge toward the sea. Parameters such as <span class="hlt">ice</span> thickness, valley width and slope, <span class="hlt">ice</span> pack dimensions may contribute to modulate the effect of increase in <span class="hlt">ice</span> flow velocity following the removal of <span class="hlt">ice</span>. We analyze this process through scale analogue models, aimed at reproducing the flow of <span class="hlt">ice</span> from a plateau into the sea through a narrow valley. The <span class="hlt">ice</span> 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 <span class="hlt">ice</span>, PDMS floats on water and simulate the <span class="hlt">ice-shelf</span> 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 <span class="hlt">ice</span> pack. Additional tests are designed to verify the influence of the above-mentioned parameters on the increase in <span class="hlt">ice</span> velocity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.8308R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.8308R"><span>Antarctic sub-<span class="hlt">shelf</span> melt rates via SIMPEL</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reese, Ronja; Albrecht, Torsten; Winkelmann, Ricarda</p> <p>2017-04-01</p> <p>Ocean-induced melting below <span class="hlt">ice</span>-shelves is currently suspected to be the dominant cause of mass loss from the Antarctic <span class="hlt">Ice</span> Sheet (e.g. Depoorter et al. 2013). Although thinning of <span class="hlt">ice</span> shelves does not directly contribute to sea-level rise, it may have a significant indirect impact through the potential of <span class="hlt">ice</span> shelves to buttress their adjacent <span class="hlt">ice</span> sheet. Hence, an appropriate representation of sub-<span class="hlt">shelf</span> melt rates is essential for modelling the evolution of <span class="hlt">ice</span> sheets with marine terminating outlet glaciers. Due to computational limits of fully-coupled <span class="hlt">ice</span> and ocean models, sub-<span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> base or its local slope but do not include the physical processes in <span class="hlt">ice</span> <span class="hlt">shelf</span> cavities. Here, we present the Sub <span class="hlt">Ice</span> <span class="hlt">shelf</span> Melt Potsdam modEL (SIMPEL) which mimics the first-order large-scale circulation in <span class="hlt">ice</span> <span class="hlt">shelf</span> cavities based on an ocean box model (Olbers & Hellmer, 2010), implemented in the Parallel <span class="hlt">Ice</span> 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-<span class="hlt">shelf</span> melt rates are highest, and then rises along the <span class="hlt">shelf</span> base towards the calving front where refreezing can occur. Melt rates are computed by a description of <span class="hlt">ice</span>-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 <span class="hlt">ice</span> shelves (Rignot et al. 2013).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V31B2706F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V31B2706F"><span>Gas discharges in fumarolic <span class="hlt">ice</span> caves of Erebus volcano, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fischer, T. P.; Curtis, A. G.; Kyle, P. R.; Sano, Y.</p> <p>2013-12-01</p> <p> reactions. We are confident that the atmospheric component is not the result of sampling procedure but intrinsic to the <span class="hlt">ice</span> cave system. In addition to carbon dioxide, magmatic gases emitted from Erebus lava lake contain significant amounts of SO2, HCl, HF, CO and H2 [1,2]. The acid magmatic gases (SO2, HCl, HF) and a significant amount of the CO2 are likely absorbed by the subsurface <span class="hlt">ice</span>/water system. The atmospheric components (Ar, nitrogen, oxygen) likely enter the system at shallow levels. The relative abundances of these components reflect degassing fractionation of these volatiles from liquid water at low temperatures, suggesting the presence of liquid water in the subsurface. [1] Oppenheimer, C., Kyle, P.R., 2008. Probing the magma plumbing of Erebus volcano, <span class="hlt">Antarctica</span>, by open-path FTIR spectroscopy of gas emissions. J. Vol. Geoth. Res. 177, 743-754. [2] Moussallam, Y., Oppenheimer, C., et al., 2012. Hydrogen emission from Erebus volcano, <span class="hlt">Antarctica</span>. Bull. Volcan 74, 2109-2120.</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/2017GeoRL..44.4159H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..44.4159H"><span>Increased <span class="hlt">ice</span> flow in Western Palmer Land linked to ocean melting</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hogg, Anna E.; Shepherd, Andrew; Cornford, Stephen L.; Briggs, Kate H.; Gourmelen, Noel; Graham, Jennifer A.; Joughin, Ian; Mouginot, Jeremie; Nagler, Thomas; Payne, Antony J.; Rignot, Eric; Wuite, Jan</p> <p>2017-05-01</p> <p>A decrease in the mass and volume of Western Palmer Land has raised the prospect that <span class="hlt">ice</span> speed has increased in this marine-based sector of <span class="hlt">Antarctica</span>. To assess this possibility, we measure <span class="hlt">ice</span> velocity over 25 years using satellite imagery and an optimized modeling approach. More than 30 unnamed outlet glaciers drain the 800 km coastline of Western Palmer Land at speeds ranging from 0.5 to 2.5 m/d, interspersed with near-stagnant <span class="hlt">ice</span>. Between 1992 and 2015, most of the outlet glaciers sped up by 0.2 to 0.3 m/d, leading to a 13% increase in <span class="hlt">ice</span> flow and a 15 km3/yr increase in <span class="hlt">ice</span> discharge across the sector as a whole. Speedup is greatest where glaciers are grounded more than 300 m below sea level, consistent with a loss of buttressing caused by <span class="hlt">ice</span> <span class="hlt">shelf</span> thinning in a region of shoaling warm circumpolar water.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C23C1227E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C23C1227E"><span>Experimental Analysis of Sublimation Dynamics for Buried Glacier <span class="hlt">Ice</span> in Beacon Valley, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ehrenfeucht, S.; Dennis, D. P.; Marchant, D. R.</p> <p>2017-12-01</p> <p>The age of the oldest known buried <span class="hlt">ice</span> in Beacon Valley, McMurdo Dry Valleys (MDV) <span class="hlt">Antarctica</span> is a topic of active debate due to its implications for the stability of the East Antarctic <span class="hlt">Ice</span> Sheet. Published age estimates range from as young as 300 ka to as old as 8.1 Ma. In the upland MDV, ablation occurs predominantly via sublimation. The relict <span class="hlt">ice</span> in question (ancient <span class="hlt">ice</span> from Taylor Glacier) lies buried beneath a thin ( 30-70 cm) layer of sublimation till, which forms as a lag deposit as underlying debris-rich <span class="hlt">ice</span> sublimes. As the <span class="hlt">ice</span> sublimates, the debris held within the <span class="hlt">ice</span> accumulates slowly on the surface, creating a porous boundary between the buried-<span class="hlt">ice</span> surface and the atmosphere, which in turn influences gas exchange between the <span class="hlt">ice</span> and the atmosphere. Additionally, englacial debris adds several salt species that are ultimately concentrated on the <span class="hlt">ice</span> surface. It is well documented the rate of <span class="hlt">ice</span> sublimation varies as a function of overlying till thickness. However, the rate-limiting dynamics under varying environmental conditions, including the threshold thicknesses at which sublimation is strongly retarded, are not yet defined. To better understand the relationships between sublimation rate, till thickness, and long-term surface evolution, we build on previous studies by Lamp and Marchant (2017) and evaluate the role of till thickness as a control on <span class="hlt">ice</span> loss in an environmental chamber capable of replicating the extreme cold desert conditions observed in the MDV. Previous work has shown that this relationship exhibits exponential decay behavior, with sublimation rate significantly dampened under less than 10 cm of till. In our experiments we pay particular attention to the effect of the first several cm of till in order to quantify the dynamics that govern the transition from bare <span class="hlt">ice</span> to debris-covered <span class="hlt">ice</span>. We also examine this transition for various forms of glacier <span class="hlt">ice</span>, including <span class="hlt">ice</span> with various salt species.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eric.ed.gov/?q=ice+AND+antarctica&id=EJ826146','ERIC'); return false;" href="https://eric.ed.gov/?q=ice+AND+antarctica&id=EJ826146"><span>The Landsat Image Mosaic of <span class="hlt">Antarctica</span> (LIMA): A Cutting-Edge Way for Students and Teachers to Learn about <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Campbell, Brian; Bindschadler, Robert</p> <p>2009-01-01</p> <p>By studying <span class="hlt">Antarctica</span> via satellite and through ground-truthing research, we can learn where the <span class="hlt">ice</span> is melting and why. The Landsat Image Mosaic of <span class="hlt">Antarctica</span> (LIMA), a new and cutting-edge way for scientists, researchers, educators, students, and the public to look at <span class="hlt">Antarctica</span>, supports this research and allows for unprecedented views of our…</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> troughs were carved by glaciers issuing from distant highlands of Marie Byrd Land and not from East <span class="hlt">Antarctica</span>. Late Oligocene through mid Miocene and younger prograding and unconformities farther north in Eastern Basin indicate grounded <span class="hlt">ice</span> there. One possible interpretation is that "Red" was cut by thick, grounded <span class="hlt">ice</span> that affected all of the Eastern Ross Sea paleo-<span class="hlt">shelf</span>, while the pre-25 Ma glaciers affected only the area proximal to Marie Byrd Land. Late Oligocene glaciation on the outer <span class="hlt">shelf</span> above deep Eastern Basin may have been sourced from East <span class="hlt">Antarctica</span> and/or Central High. Evidence for pre-25 Ma glaciation proximal to Marie Byrd Land, combined with evidence for Oligocene <span class="hlt">ice</span> caps at widely-separated localities of West <span class="hlt">Antarctica</span>, allow the interpretation that portions of the West Antarctic <span class="hlt">Ice</span> Sheet developed during Oligocene time. The broad troughs and the stack of prograding sequences may be related to dynamic <span class="hlt">ice</span> caps and sea level falls in mid Oligocene and earliest Oligocene time. The Middle Miocene Red unconformity may be related to development of polar (cold-base) <span class="hlt">ice</span> sheets. Oligocene glaciation implies that Marie Byrd Land and eastern Ross Sea have subsided from higher elevation due to cooling after late Cretaceous crustal thinning.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.C33D..02V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.C33D..02V"><span>Subglacial Volcanism in West-<span class="hlt">Antarctica</span> - A Geologic and <span class="hlt">Ice</span> Dynamical Perspective</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vogel, S. W.; Tulaczyk, S.; Carter, S.; Renne, P.; Turrin, B. D.; Joughin, I.</p> <p>2004-12-01</p> <p> means to resolve any further questions on the existence of subglacial volcanism in West-<span class="hlt">Antarctica</span> and its potential impact on the dynamic of the <span class="hlt">ice</span> sheet, requires drilling into potential volcanic centers and the recovery of volcanic rocks for dating and geochemical analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950050449&hterms=Ross+1986&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DRoss%2B1986','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950050449&hterms=Ross+1986&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DRoss%2B1986"><span>Spatial patterns in the length of the sea <span class="hlt">ice</span> season in the Southern Ocean, 1979-1986</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Parkinson, Claire L.</p> <p>1994-01-01</p> <p>The length of the sea <span class="hlt">ice</span> season summarizes in one number the <span class="hlt">ice</span> coverage conditions for an individual location for an entire year. It becomes a particularly valuable variable when mapped spatially over a large area and examined for regional and interannual differences, as is done here for the Southern Ocean over the years 1979-1986, using the satellite passive microwave data of the Nimbus 7 scanning multichannel microwave radiometer. Three prominent geographic anomalies in <span class="hlt">ice</span> season lengths occur consistently in each year of the data set, countering the general tendency toward shorter <span class="hlt">ice</span> seasons from south to north: (1) in the Weddell Sea the tendency is toward shorter <span class="hlt">ice</span> seasons from southwest to northeast, reflective of the cyclonic <span class="hlt">ice</span>/atmosphere/ocean circulations in the Weddell Sea region. (2) Directly north of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> anomalously short <span class="hlt">ice</span> seasons occur, lasting only 245-270 days, in contrast to the perennial <span class="hlt">ice</span> coverage at comparable latitudes in the southern Bellingshausen and Amundsen Seas and in the western Weddell Sea. The short <span class="hlt">ice</span> season off the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> reflects the consistently early opening of the <span class="hlt">ice</span> cover each spring, under the influence of upwelling along the continental slope and <span class="hlt">shelf</span> and atmospheric forcing from winds blowing off the Antarctic continent. (3) In the southern Amundsen Sea, anomalously short <span class="hlt">ice</span> seasons occur adjacent to the coast, owing to the frequent existence of coastal polynyas off the many small <span class="hlt">ice</span> shelves bordering the sea. Least squares trends in the <span class="hlt">ice</span> season lengths over the 1979-1986 period are highly coherent spatially, with overall trends toward shorter <span class="hlt">ice</span> seasons in the northern Weddell and Bellingshausen seas and toward longer <span class="hlt">ice</span> seasons in the Ross Sea, around much of East <span class="hlt">Antarctica</span>, and in a portion of the south central Weddell Sea.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994JGR....9916327P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994JGR....9916327P"><span>Spatial patterns in the length of the sea <span class="hlt">ice</span> season in the Southern Ocean, 1979-1986</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Parkinson, Claire L.</p> <p>1994-08-01</p> <p>The length of the sea <span class="hlt">ice</span> season summarizes in one number the <span class="hlt">ice</span> coverage conditions for an individual location for an entire year. It becomes a particularly valuable variable when mapped spatially over a large area and examined for regional and interannual differences, as is done here for the Southern Ocean over the years 1979-1986, using the satellite passive microwave data of the Nimbus 7 scanning multichannel microwave radiometer. Three prominent geographic anomalies in <span class="hlt">ice</span> season lengths occur consistently in each year of the data set, countering the general tendency toward shorter <span class="hlt">ice</span> seasons from south to north: (1) In the Weddell Sea the tendency is toward shorter <span class="hlt">ice</span> seasons from southwest to northeast, reflective of the cyclonic <span class="hlt">ice</span>/atmosphere/ocean circulations in the Weddell Sea region. (2) Directly north of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> anomalously short <span class="hlt">ice</span> seasons occur, lasting only 245-270 days, in contrast to the perennial <span class="hlt">ice</span> coverage at comparable latitudes in the southern Bellingshausen and Amundsen Seas and in the western Weddell Sea. The short <span class="hlt">ice</span> season off the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> reflects the consistently early opening of the <span class="hlt">ice</span> cover each spring, under the influence of upwelling along the continental slope and <span class="hlt">shelf</span> and atmospheric forcing from winds blowing off the Antarctic continent. (3) In the southern Amundsen Sea, anomalously short <span class="hlt">ice</span> seasons occur adjacent to the coast, owing to the frequent existence of coastal polynyas off the many small <span class="hlt">ice</span> shelves bordering the sea. Least squares trends in the <span class="hlt">ice</span> season lengths over the 1979-1986 period are highly coherent spatially, with overall trends toward shorter <span class="hlt">ice</span> seasons in the northern Weddell and Bellingshausen seas and toward longer <span class="hlt">ice</span> seasons in the Ross Sea, around much of East <span class="hlt">Antarctica</span>, and in a portion of the south central Weddell Sea.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=PIA03431&hterms=Antarctic+icebergs&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DAntarctic%2Bicebergs','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=PIA03431&hterms=Antarctic+icebergs&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DAntarctic%2Bicebergs"><span>Birth of a Large Iceberg in Pine Island Bay, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2001-01-01</p> <p><p/>A large tabular iceberg (42 kilometers x 17 kilometers) broke off Pine Island Glacier, West <span class="hlt">Antarctica</span> (75oS latitude, 102oW longitude) sometime between November 4 and 12, 2001. Images of the glacier were acquired by the Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard NASA's Terra spacecraft. This event was preceded by the formation of a large crack across the glacier in mid 2000. Data gathered by other imaging instruments revealed the crack to be propagating through the <span class="hlt">shelf</span> <span class="hlt">ice</span> at a rate averaging 15 meters per day, accompanied by a slight rotation of about one percent per year at the seaward margin of the rift.<p/>The image set shows three views of Pine Island Glacier acquired by MISR's vertical-viewing (nadir) camera. The first was captured in late 2000, early in the development of the crack. The second and third views were acquired in November 2001, just before and just after the new iceberg broke off. The existence of the crack took the glaciological community by surprise, and the rapid rate at which the crack propagated was also not anticipated. Glaciologists predicted that the rift would reach the other side of the glacier sometime in 2002. However, the iceberg detached much sooner than anticipated, and the last 10-kilometer segment that was still attached to the <span class="hlt">ice</span> <span class="hlt">shelf</span> snapped off in a matter of days.<p/>The animated sequence consists of 11 snapshots acquired by MISR's nadir camera between September 16, 2000 and November 12, 2001. Due to frequent cloud cover, the time interval between successive frames is not uniform. The flow of the glacier, widening of the rift, and subsequent break-off of the iceberg are evident. A 'jump' in the position of the rift near the middle of the sequence is due to a gap in image acquisition during Antarctic winter, when the glacier was in continuous darkness.<p/> <p/>Pine Island Glacier is the largest discharger of <span class="hlt">ice</span> in <span class="hlt">Antarctica</span> and the continent's fastest moving glacier. This area of the West</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018TCry...12.1969R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018TCry...12.1969R"><span>Antarctic sub-<span class="hlt">shelf</span> melt rates via PICO</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reese, Ronja; Albrecht, Torsten; Mengel, Matthias; Asay-Davis, Xylar; Winkelmann, Ricarda</p> <p>2018-06-01</p> <p>Ocean-induced melting below <span class="hlt">ice</span> shelves is one of the dominant drivers for mass loss from the Antarctic <span class="hlt">Ice</span> Sheet at present. An appropriate representation of sub-<span class="hlt">shelf</span> melt rates is therefore essential for model simulations of marine-based <span class="hlt">ice</span> sheet evolution. Continental-scale <span class="hlt">ice</span> sheet models often rely on simple melt-parameterizations, in particular for long-term simulations, when fully coupled <span class="hlt">ice</span>-ocean interaction becomes computationally too expensive. Such parameterizations can account for the influence of the local depth of the <span class="hlt">ice-shelf</span> draft or its slope on melting. However, they do not capture the effect of ocean circulation underneath the <span class="hlt">ice</span> <span class="hlt">shelf</span>. Here we present the Potsdam <span class="hlt">Ice-shelf</span> Cavity mOdel (PICO), which simulates the vertical overturning circulation in <span class="hlt">ice-shelf</span> cavities and thus enables the computation of sub-<span class="hlt">shelf</span> melt rates consistent with this circulation. PICO is based on an ocean box model that coarsely resolves <span class="hlt">ice</span> <span class="hlt">shelf</span> cavities and uses a boundary layer melt formulation. We implement it as a module of the Parallel <span class="hlt">Ice</span> 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 <span class="hlt">ice</span> shelves, with an average of about 0.1 m a-1 for cold sub-<span class="hlt">shelf</span> cavities, for example, underneath Ross or Ronne <span class="hlt">ice</span> 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 <span class="hlt">ice</span> draft geometry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA613425','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA613425"><span>Bearing Capacity of Floating <span class="hlt">Ice</span> Sheets under Short-Term Loads: Over-Sea-<span class="hlt">Ice</span> Traverse from McMurdo Station to Marble Point</span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>2015-01-01</p> <p>crafts on floating <span class="hlt">ice</span> sheets near McMurdo, <span class="hlt">Antarctica</span> (Katona and Vaudrey 1973; Katona 1974; Vaudrey 1977). To comply with the first criterion, one...Nomographs for operating wheeled aircraft on sea- <span class="hlt">ice</span> runways: McMurdo Station, <span class="hlt">Antarctica</span> . In Proceedings of the Offshore Mechanics and Arctic Engineering... <span class="hlt">Ice</span> Thickness Requirements for Vehicles and Heavy Equipment at McMurdo Station, <span class="hlt">Antarctica</span> . CRREL Project Report 04- 09, “Safe Sea <span class="hlt">Ice</span> for Vehicle</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26811794','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26811794"><span>Community dynamics of nematodes after Larsen <span class="hlt">ice-shelf</span> collapse in the 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; Ballesteros-Redondo, Laura; Gutt, Julian; Vanreusel, Ann</p> <p>2016-01-01</p> <p>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 <span class="hlt">ice-shelf</span> 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 <span class="hlt">ice-shelf</span> 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 <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> areas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3729O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3729O"><span>Marine geological and geophysical records of the last British-Irish <span class="hlt">Ice</span> Sheet on the continental <span class="hlt">shelf</span> west of Ireland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>O'Cofaigh, Colm; Callard, S. Louise; Benetti, Sara; Chiverell, Richard C.; Saher, Margot; van Landeghem, Katrien; Livingstone, Stephen J.; Scourse, James; Clark, Chris D.</p> <p>2015-04-01</p> <p>The record of glaciation on the continental <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> west of Ireland during cruise JC106 of the RRS James Cook in 2014. Across the western Irish <span class="hlt">shelf</span>, offshore of counties Galway and Clare, a series of large arcuate moraines record the former presence of a grounded <span class="hlt">ice</span> sheet on the <span class="hlt">shelf</span>. 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 <span class="hlt">ice</span> across the northern Porcupine Bank and thus much further west on the Irish margin than has previously been considered. This <span class="hlt">ice</span> underwent retreat in a glacimarine setting. The large 'Olex Moraine' on the western Irish <span class="hlt">shelf</span> 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 <span class="hlt">Ice</span> Sheet.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.C51A0638W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.C51A0638W"><span>On thin <span class="hlt">ice</span>/in hot water: Rapid drawdown of Wordie <span class="hlt">Ice</span> <span class="hlt">Shelf</span> glaciers in the decades after collapse in response to a changing 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>2016-12-01</p> <p>Over the past 50 years, several Antarctic Peninsula <span class="hlt">ice</span> shelves have retreated or collapsed completely. One such collapse was the Wordie <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (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 <span class="hlt">Ice</span>Bridge 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 <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> 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 <span class="hlt">shelf</span> break, along which the southern boundary</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.C13B0445M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.C13B0445M"><span><span class="hlt">Ice</span> Elevation Changes in the Ellsworth Mountains, <span class="hlt">Antarctica</span> Using Multiple Cosmogenic Nuclides</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marrero, S.; Hein, A.; Sugden, D.; Woodward, J.; Dunning, S.; Reid, K.</p> <p>2014-12-01</p> <p>Well-dated geologic data points provide important indicators that can be used for the reconstruction of <span class="hlt">ice</span> sheet dynamics and as constraints in <span class="hlt">ice</span> sheet models predicting future change. Cosmogenic nuclides, which accumulate in rocks exposed at the earth's surface, can be used to directly date the exposure age of the rock surfaces that have been created through glacial erosion or deposition. The technique requires a detailed understanding of the local geomorphology as well as awareness of the post-depositional processes that may affect the interpretation of exposure ages. Initial surface exposure ages (10Be, 26Al, 21Ne, and 36Cl ) from local limestone bedrock and other glacially deposited exotic lithologies provide a history spanning from 0 to 1.1 Ma in the Patriot, Independence, and Marble Hills in the southern Ellsworth Mountains, <span class="hlt">Antarctica</span>. Using the new surface exposure ages combined with geomorphological mapping, we will discuss the implications for the glacial history of the southern Ellsworth Mountains.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GGG....18.2657D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GGG....18.2657D"><span>Geothermal heat flux in the Amundsen Sea sector of West <span class="hlt">Antarctica</span>: New insights from temperature measurements, depth to the bottom of the magnetic source estimation, and thermal modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dziadek, R.; Gohl, K.; Diehl, A.; Kaul, N.</p> <p>2017-07-01</p> <p>Focused research on the Pine Island and Thwaites glaciers, which drain the West Antarctic <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (WAIS) into the Amundsen Sea Embayment (ASE), revealed strong signs of instability in recent decades that result from variety of reasons, such as inflow of warmer ocean currents and reverse bedrock topography, and has been established as the Marine <span class="hlt">Ice</span> Sheet Instability hypothesis. Geothermal heat flux (GHF) is a poorly constrained parameter in <span class="hlt">Antarctica</span> and suspected to affect basal conditions of <span class="hlt">ice</span> sheets, i.e., basal melting and subglacial hydrology. Thermomechanical models demonstrate the influential boundary condition of geothermal heat flux for (paleo) <span class="hlt">ice</span> sheet stability. Due to a complex tectonic and magmatic history of West <span class="hlt">Antarctica</span>, the region is suspected to exhibit strong heterogeneous geothermal heat flux variations. We present an approach to investigate ranges of realistic heat fluxes in the ASE by different methods, discuss direct observations, and 3-D numerical models that incorporate boundary conditions derived from various geophysical studies, including our new Depth to the Bottom of the Magnetic Source (DBMS) estimates. Our in situ temperature measurements at 26 sites in the ASE more than triples the number of direct GHF observations in West <span class="hlt">Antarctica</span>. We demonstrate by our numerical 3-D models that GHF spatially varies from 68 up to 110 mW m-2.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.C51C..01R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.C51C..01R"><span>Exploration of the Climate Change Frontier in Polar Regions at the Land <span class="hlt">Ice</span>-Ocean Boundary.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rignot, E. J.</p> <p>2014-12-01</p> <p><span class="hlt">Ice</span> sheets are the largest contributors to sea level rise at present, and responsible for the largest uncertainty in sea level projections. <span class="hlt">Ice</span> 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 <span class="hlt">Antarctica</span> (Amundsen Sea), and East <span class="hlt">Antarctica</span> (Filchner basin and Wilkes Land). Fast changes require an increase in <span class="hlt">ice</span> 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 <span class="hlt">shelf</span>, along bays and glacial fjords and at <span class="hlt">ice</span>-ocean boundaries, beneath kilometers of <span class="hlt">ice</span> (<span class="hlt">Antarctica</span>) 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 <span class="hlt">Antarctica</span>, 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 <span class="hlt">ice</span> melting by the ocean even if the ocean temperature remains the same. Near <span class="hlt">ice</span>-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 <span class="hlt">ice</span> sheet evolution in a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.C51B0973H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.C51B0973H"><span>Ground-penetrating radar evidence of refrozen meltwater in the firn column of Larsen C <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>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.</p> <p>2017-12-01</p> <p>Firn densification, which has been strongly implicated in <span class="hlt">ice</span> <span class="hlt">shelf</span> 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 <span class="hlt">shelf</span> collapse. Meltwater ponds on Larsen C's Cabinet (CI) and Whirlwind (WI) inlets form where foehn winds reach and influence the <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> shelves affected by surface melt and ponding can contain spatially extensive bodies of <span class="hlt">ice</span> that are warmer and denser than assumed so far, with significant implications for <span class="hlt">ice</span> <span class="hlt">shelf</span> flow and fracturing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRG..122.2409A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRG..122.2409A"><span>Late Spring Nitrate Distributions Beneath the <span class="hlt">Ice</span>-Covered Northeastern Chukchi <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>Arrigo, Kevin R.; Mills, Matthew M.; van Dijken, Gert L.; Lowry, Kate E.; Pickart, Robert S.; Schlitzer, Reiner</p> <p>2017-09-01</p> <p>Measurements of late springtime nutrient concentrations in Arctic waters are relatively rare due to the extensive sea <span class="hlt">ice</span> cover that makes sampling difficult. During the SUBICE (Study of Under-<span class="hlt">ice</span> 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 <fi>a</fi> 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 μ<fi>M</fi> in surface waters and 14.0 ± 1.91 μ<fi>M</fi> 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 <span class="hlt">shelf</span> break within the upper halocline waters of the Canada Basin and along the eastern side of the <span class="hlt">shelf</span> 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 <span class="hlt">ice</span> to the waters below the <span class="hlt">ice</span> could fuel large phytoplankton blooms over a much wider area than previously known.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22932387','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22932387"><span>Potential methane reservoirs beneath <span class="hlt">Antarctica</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wadham, J L; Arndt, S; Tulaczyk, S; Stibal, M; Tranter, M; Telling, J; Lis, G P; Lawson, E; Ridgwell, A; Dubnick, A; Sharp, M J; Anesio, A M; Butler, C E H</p> <p>2012-08-30</p> <p>Once thought to be devoid of life, the <span class="hlt">ice</span>-covered parts of <span class="hlt">Antarctica</span> are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the <span class="hlt">ice</span>, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick and an estimated 21,000 petagrams (1 Pg equals 10(15) g) of organic carbon are buried beneath the Antarctic <span class="hlt">Ice</span> Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West <span class="hlt">Antarctica</span> and 700 metres in East <span class="hlt">Antarctica</span>. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the <span class="hlt">ice</span>-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic <span class="hlt">Ice</span> Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during <span class="hlt">ice</span>-sheet wastage.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRF..122..973L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRF..122..973L"><span>Slow-slip events on the Whillans <span class="hlt">Ice</span> Plain, <span class="hlt">Antarctica</span>, described using rate-and-state friction as an <span class="hlt">ice</span> stream sliding law</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lipovsky, Bradley Paul; Dunham, Eric M.</p> <p>2017-04-01</p> <p>The Whillans <span class="hlt">Ice</span> Plain (WIP), <span class="hlt">Antarctica</span>, experiences twice daily tidally modulated stick-slip cycles. Slip events last about 30 min, have sliding velocities as high as ˜0.5 mm/s (15 km/yr), and have total slip ˜0.5 m. Slip events tend to occur during falling ocean tide: just after high tide and just before low tide. To reproduce these characteristics, we use rate-and-state friction, which is commonly used to simulate tectonic faulting, as an <span class="hlt">ice</span> stream sliding law. This framework describes the evolving strength of the <span class="hlt">ice</span>-bed interface throughout stick-slip cycles. We present simulations that resolve the cross-stream dimension using a depth-integrated treatment of an elastic <span class="hlt">ice</span> layer loaded by tides and steady <span class="hlt">ice</span> inflow. Steady sliding with rate-weakening friction is conditionally stable with steady sliding occurring for sufficiently narrow <span class="hlt">ice</span> streams relative to a nucleation length. Stick-slip cycles occur when the <span class="hlt">ice</span> stream is wider than the nucleation length or, equivalently, when effective pressures exceed a critical value. <span class="hlt">Ice</span> streams barely wider than the nucleation length experience slow-slip events, and our simulations suggest that the WIP is in this slow-slip regime. Slip events on the WIP show a sense of propagation, and we reproduce this behavior by introducing a rate-strengthening region in the center of the otherwise rate-weakening <span class="hlt">ice</span> stream. If pore pressures are raised above a critical value, our simulations predict that the WIP would exhibit quasi-steady tidally modulated sliding as observed on other <span class="hlt">ice</span> streams. This study validates rate-and-state friction as a sliding law to describe <span class="hlt">ice</span> stream sliding styles.</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('http://adsabs.harvard.edu/abs/2017GeoRL..44.7328C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..44.7328C"><span>Mass balance reassessment of glaciers draining into the Abbot and Getz <span class="hlt">Ice</span> Shelves of West <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chuter, S. J.; Martín-Español, A.; Wouters, B.; Bamber, J. L.</p> <p>2017-07-01</p> <p>We present a reassessment of input-output method <span class="hlt">ice</span> mass budget estimates for the Abbot and Getz regions of West <span class="hlt">Antarctica</span> using CryoSat-2-derived <span class="hlt">ice</span> thickness estimates. The mass budget is 8 ± 6 Gt yr-1 and 5 ± 17 Gt yr-1 for the Abbot and Getz sectors, respectively, for the period 2006-2008. Over the Abbot region, our results resolve a previous discrepancy with elevation rates from altimetry, due to a previous 30% overestimation of <span class="hlt">ice</span> thickness. For the Getz sector, our results are at the more positive bound of estimates from other techniques. Grounding line velocity increases up to 20% between 2007 and 2014 alongside mean elevation rates of -0.67 ± 0.13 m yr-1 between 2010 and 2013 indicate the onset of a dynamic thinning signal. Mean snowfall trends of -0.33 m yr-1 water equivalent since 2006 indicate recent mass trends are driven by both <span class="hlt">ice</span> dynamics and surface processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-200910220009HQ.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-200910220009HQ.html"><span><span class="hlt">Ice</span> Bridge Antarctic Sea <span class="hlt">Ice</span></span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2009-10-21</p> <p>An iceberg is seen out the window of NASA's DC-8 research aircraft as it flies 2,000 feet above the Amundsen Sea in West <span class="hlt">Antarctica</span> on Wednesday, Oct., 21, 2009. This was the fourth science flight of NASA‚Äôs Operation <span class="hlt">Ice</span> Bridge airborne Earth science mission to study Antarctic <span class="hlt">ice</span> sheets, sea <span class="hlt">ice</span>, and <span class="hlt">ice</span> shelves. Photo Credit: (NASA/Jane Peterson)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70031611','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70031611"><span>Modeling englacial radar attenuation at Siple Dome, West <span class="hlt">Antarctica</span>, using <span class="hlt">ice</span> chemistry and temperature data</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>MacGregor, J.A.; Winebrenner, D.P.; Conway, H.; Matsuoka, K.; Mayewski, P.A.; Clow, G.D.</p> <p>2007-01-01</p> <p>The radar reflectivity of an <span class="hlt">ice</span>-sheet bed is a primary measurement for discriminating between thawed and frozen beds. Uncertainty in englacial radar attenuation and its spatial variation introduces corresponding uncertainty in estimates of basal reflectivity. Radar attenuation is proportional to <span class="hlt">ice</span> conductivity, which depends on the concentrations of acid and sea-salt chloride and the temperature of the <span class="hlt">ice</span>. We synthesize published conductivity measurements to specify an <span class="hlt">ice</span>-conductivity model and find that some of the dielectric properties of <span class="hlt">ice</span> at radar frequencies are not yet well constrained. Using depth profiles of <span class="hlt">ice</span>-core chemistry and borehole temperature and an average of the experimental values for the dielectric properties, we calculate an attenuation rate profile for Siple Dome, West <span class="hlt">Antarctica</span>. The depth-averaged modeled attenuation rate at Siple Dome (20.0 ?? 5.7 dB km-1) is somewhat lower than the value derived from radar profiles (25.3 ?? 1.1 dB km-1). Pending more experimental data on the dielectric properties of <span class="hlt">ice</span>, we can match the modeled and radar-derived attenuation rates by an adjustment to the value for the pure <span class="hlt">ice</span> conductivity that is within the range of reported values. Alternatively, using the pure <span class="hlt">ice</span> dielectric properties derived from the most extensive single data set, the modeled depth-averaged attenuation rate is 24.0 ?? 2.2 dB km-1. This work shows how to calculate englacial radar attenuation using <span class="hlt">ice</span> chemistry and temperature data and establishes a basis for mapping spatial variations in radar attenuation across an <span class="hlt">ice</span> sheet. Copyright 2007 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA526813','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA526813"><span>Worldwide Emerging Environmental Issues Affecting the U.S. Military. March 2008 Report</span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>2008-03-01</p> <p><span class="hlt">Shelf</span> of western <span class="hlt">Antarctica</span>, a chunk of <span class="hlt">ice</span> with an area of about 400 sq km broke up into icebergs . This might trigger the disintegration of a larger...allafrica.com/stories/200803041273.html Earth from Space: Further break-up of Antarctic <span class="hlt">ice</span> <span class="hlt">shelf</span> http://www.esa.int/esaEO/SEMMX4R03EF_index_0.html...200803041273.html Antarctic <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Disintegration Underscores a Warming World http://nsidc.org/news/press/20080325_Wilkins.html Antarctic <span class="hlt">ice</span> <span class="hlt">shelf</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014QSRv..100...31A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014QSRv..100...31A"><span>Ross Sea paleo-<span class="hlt">ice</span> sheet drainage and deglacial history during and since the LGM</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anderson, John B.; Conway, Howard; Bart, Philip J.; Witus, Alexandra E.; Greenwood, Sarah L.; McKay, Robert M.; Hall, Brenda L.; Ackert, Robert P.; Licht, Kathy; Jakobsson, Martin; Stone, John O.</p> <p>2014-09-01</p> <p>Onshore and offshore studies show that an expanded, grounded <span class="hlt">ice</span> sheet occupied the Ross Sea Embayment during the Last Glacial Maximum (LGM). Results from studies of till provenance and the orientation of geomorphic features on the continental <span class="hlt">shelf</span> show that more than half of the grounded <span class="hlt">ice</span> sheet consisted of East Antarctic <span class="hlt">ice</span> flowing through Transantarctic Mountain (TAM) outlet glaciers; the remainder came from West <span class="hlt">Antarctica</span>. Terrestrial data indicate little or no thickening in the upper catchment regions in both West and East <span class="hlt">Antarctica</span> during the LGM. In contrast, evidence from the mouths of the southern and central TAM outlet glaciers indicate surface elevations between 1000 m and 1100 m (above present-day sea level). Farther north along the western margin of the Ross <span class="hlt">Ice</span> Sheet, surface elevations reached 720 m on Ross Island, and 400 m at Terra Nova Bay. Evidence from Marie Byrd Land at the eastern margin of the <span class="hlt">ice</span> sheet indicates that the elevation near the present-day grounding line was more than 800 m asl, while at Siple Dome in the central Ross Embayment, the surface elevation was about 950 m asl. Farther north, evidence that the <span class="hlt">ice</span> sheet was grounded on the middle and the outer continental <span class="hlt">shelf</span> during the LGM implies that surface elevations had to be at least 100 m above the LGM sea level. The apparent low surface profile and implied low basal shear stress in the central and eastern embayment suggests that although the <span class="hlt">ice</span> streams may have slowed during the LGM, they remained active. <span class="hlt">Ice</span>-sheet retreat from the western Ross Embayment during the Holocene is constrained by marine and terrestrial data. Ages from marine sediments suggest that the grounding line had retreated from its LGM outer <span class="hlt">shelf</span> location only a few tens of kilometer to a location south of Coulman Island by ˜13 ka BP. The <span class="hlt">ice</span> sheet margin was located in the vicinity of the Drygalski <span class="hlt">Ice</span> Tongue by ˜11 ka BP, just north of Ross Island by ˜7.8 ka BP, and near Hatherton Glacier by </p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V11F..07P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V11F..07P"><span>Neogene <span class="hlt">ice</span> sheet, paleoclimatic and geological history of the McMurdo Sound region, Victoria Land Basin, <span class="hlt">Antarctica</span>: overview of ANDRILL's first two drilling projects</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Powell, R.; Naish, T.; Harwood, D.; Florindo, F.; Levy, R.; Teams, M. S.</p> <p>2008-12-01</p> <p>The ANtarctic geological DRILLing Program (ANDRILL), an international collaboration within IPY, has recovered 2 cores: from under the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> (McMurdo <span class="hlt">Ice</span> <span class="hlt">Shelf</span> Project (MIS) - AND-1B), and from the land-fast sea-<span class="hlt">ice</span> of McMurdo Sound (Southern McMurdo Sound Project (SMS) - AND-2A). Drill cores reached respective total depths of 1285mbsf in c. 850m of water (MIS) and 1138.54mbsf in c. 380m of water (SMS). Repetitive facies successions in AND-1B core imply at least 60 fluctuations, of probable Milankovitch- duration, between subglacial, <span class="hlt">ice</span> proximal and <span class="hlt">ice</span> distal open marine environments. These are grouped into 3 types of facies cycles corresponding to glacial-interglacial variability during climatically distinct periods of Late Neogene: (1) cold-polar climate and <span class="hlt">ice</span> (late Miocene and Pleistocene); (2) relatively warmer climate, polythermal <span class="hlt">ice</span> and interglacials dominated by pelagic diatomite (Pliocene); (3) warmer climate, polythermal <span class="hlt">ice</span> with interglacials dominated by hemipelagites (early late Miocene). A c. 80m-thick interval of diatomite of mid to late Pliocene age shows no apparent glacial cyclicity and represents an extended period of <span class="hlt">ice</span>-free conditions indicating reduced or absent WAIS. Late Pliocene glacial-interglacial cycles characterized by abrupt alternations between subglacial/<span class="hlt">ice</span>-proximal facies and open marine diatomite units imply significant WAIS dynamism, and contribution to global <span class="hlt">ice</span> volume changes coeval with the initiation of Northern Hemisphere glaciations. A c. 4m-thick interval of diatomaceous mudstone in the mid-Pleistocene also represents warm-interglacial <span class="hlt">ice</span>-free conditions. Intriguingly, glacial deposits interrupted by periodic, small- scale grounding-line retreats dominate the last 1m.y. Inter-hemispheric <span class="hlt">ice</span> sheet coupling was probably controlled by Northern Hemispheric insolation and consequent glacial eustasy to account for much of the orbital-scale WAIS variability since 2.5Ma. A further expansion of WAIS occurred across</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/6648212-fire-beneath-ice','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/6648212-fire-beneath-ice"><span>Fire beneath the <span class="hlt">ice</span></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>Monastersky, R.</p> <p>1993-02-13</p> <p>A volcano discovered six years ago by researchers Blankenship and Bell under <span class="hlt">Antarctica</span> poses questions about a potential climatic catastrophe. The researchers claim that the volcano is still active, erupting occasionally and growing. A circular depression on the surface of the <span class="hlt">ice</span> sheet has <span class="hlt">ice</span> flowing into it and is used to provide a portrait of the heat source. The volcano is on a critical transition zone within West <span class="hlt">Antarctica</span> with fast flowing <span class="hlt">ice</span> streams directly downhill. Work by Blankenship shows that a soft layer of water-logged sediments called till provide the lubricating layer on the underside of the icemore » streams. Volcanos may provide the source of this till. The <span class="hlt">ice</span> streams buffer the thick interior <span class="hlt">ice</span> from the ocean and no one know what will happen if the <span class="hlt">ice</span> streams continue to shorten. These researchers believe their results indicate that the stability of West <span class="hlt">Antarctica</span> ultimately depends less on the current climate than on the location of heat and sediments under the <span class="hlt">ice</span> and the legacy of past climatic changes.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JMS...175...46M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JMS...175...46M"><span>22-year surface salinity changes in the Seasonal <span class="hlt">Ice</span> Zone near 140°E off <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Morrow, Rosemary; Kestenare, Elodie</p> <p>2017-11-01</p> <p>Seasonal and interannual variations in sea surface salinity (SSS) are analyzed in the Sea <span class="hlt">Ice</span> Zone south of 60°S, from a 22-year time series of observations near 140°E. In the northern sea-<span class="hlt">ice</span> 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-<span class="hlt">ice</span> 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 <span class="hlt">shelf</span> 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-<span class="hlt">ice</span> cover than surface forcing. SSS and sea-<span class="hlt">ice</span> 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-<span class="hlt">ice</span> cover and widespread freshening of the surface layers from 2011 onwards. Summer freshening in the northern sea-<span class="hlt">ice</span> zone is 0.05-0.07 per decade, increasing to 0.08 per decade in the southern sea-<span class="hlt">ice</span> zone, largely influenced by the Mertz Glacier calving event at the end of our time series. The summer time series of SSS on the <span class="hlt">shelf</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004DSRI...51.1601M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004DSRI...51.1601M"><span>Effects of summer <span class="hlt">ice</span> coverage on phytoplankton assemblages in the Ross Sea, <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mangoni, O.; Modigh, M.; Conversano, F.; Carrada, G. C.; Saggiomo, V.</p> <p>2004-11-01</p> <p>An oceanographic cruise was conducted in the Ross Sea (<span class="hlt">Antarctica</span>) during summer 2001 as part of the Italian National Program for Antarctic Research (PNRA). Extensive areas of pack <span class="hlt">ice</span> occurred over the Ross Sea, atypical for summer when offshore waters are normally free of <span class="hlt">ice</span>. The present study focuses on the effects of increased <span class="hlt">ice</span> coverage on phytoplankton assemblages. Water samples collected at various depths at 72 hydrographical stations in offshore and coastal waters were used to determine size-fractionated phytoplankton biomass as chlorophyll a (chla) concentrations, and HPLC photosynthetic pigments. For the offshore waters, the average chla concentration was 57.8 mg m-2, approximately three times the values recorded under <span class="hlt">ice</span>-free conditions during summer 1996. In coastal waters, the average chla concentrations were 102 and 206 mg m-2 during January and February, respectively, i.e., up to 2.5 times those of 1996. Micro- and nano-phytoplankton size fractions made up about 90% of the phytoplankton biomass over the entire study area and were composed primarily of diatoms with a pico-phytoplankton fraction dominated by prymnesiophyceans. The broken pack and melting <span class="hlt">ice</span> was strongly coloured by an extensive algal biomass suggesting that the phytoplankton was a result of seeding from <span class="hlt">ice</span> algal communities. The Ross Sea considered to be one of the most productive areas of the Southern Ocean, had primary production values about four-fold those of other areas. The lengthening of the <span class="hlt">ice</span> season observed in the Western Ross Sea, associated with a considerable increase in phytoplankton biomass as observed in summer 2001, would have a major impact on the trophic structure of the entire ecosystem, and presumably, also on carbon export.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016DSRII.131...53T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016DSRII.131...53T"><span>On the extraordinary snow on the sea <span class="hlt">ice</span> off East <span class="hlt">Antarctica</span> in late winter, 2012</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Toyota, Takenobu; Massom, Robert; Lecomte, Olivier; Nomura, Daiki; Heil, Petra; Tamura, Takeshi; Fraser, Alexander D.</p> <p>2016-09-01</p> <p>In late winter-early spring 2012, the second Sea <span class="hlt">Ice</span> Physics and Ecosystems Experiment (SIPEX II) was conducted off Wilkes Land, East <span class="hlt">Antarctica</span>, onboard R/V Aurora Australis. The sea-<span class="hlt">ice</span> conditions were characterized by significantly thick first-year <span class="hlt">ice</span> and snow, trapping the ship for about 10 days in the near coastal region. The deep snow cover was particularly remarkable, in that its average value of 0.45 m was almost three times that observed between 1992 and 2007 in the region. To reveal factors responsible, we used in situ observations and ERA-Interim reanalysis (1990-2012) to examine the relative contribution of the different components of the local-regional snow mass balance equation i.e., snow accumulation on sea <span class="hlt">ice</span>, precipitation minus evaporation (P-E), and loss by (i) snow-<span class="hlt">ice</span> formation and (ii) entering into leads due to drifting snow. Results show no evidence for significantly high P-E in the winter of 2012. <span class="hlt">Ice</span> core analysis has shown that although the snow-<span class="hlt">ice</span> layer was relatively thin, indicating less transformation from snow to snow-<span class="hlt">ice</span> in 2012 as compared to measurements from 2007, the difference was not enough to explain the extraordinarily deep snow. Based on these results, we deduce that lower loss of snow into leads was probably responsible for the extraordinary snow in 2012. Statistical analysis and satellite images suggest that the reduction in loss of snow into leads is attributed to rough <span class="hlt">ice</span> surface associated with active deformation processes and larger floe size due to sea-<span class="hlt">ice</span> expansion. This highlights the importance of snow-sea <span class="hlt">ice</span> interaction in determining the mean snow depth on Antarctic sea <span class="hlt">ice</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890011969','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890011969"><span>Volcanic ash layers in blue <span class="hlt">ice</span> fields (Beardmore Glacier Area, <span class="hlt">Antarctica</span>): Iridium enrichments</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Koeberl, Christian</p> <p>1988-01-01</p> <p>Dust bands on blue <span class="hlt">ice</span> fields in <span class="hlt">Antarctica</span> have been studied and have been identified to originate from two main sources: bedrock debris scraped up from the ground by the glacial movement (these bands are found predominantly at fractures and shear zones in the <span class="hlt">ice</span> near moraines), and volcanic debris deposited on and incorporated in the <span class="hlt">ice</span> by large-scale eruptions of Antarctic (or sub-Antractic) volcanoes. <span class="hlt">Ice</span> core studies have revealed that most of the dust layers in the <span class="hlt">ice</span> cores are volcanic (tephra) deposits which may be related to some specific volcanic eruptions. These eruptions have to be related to some specific volcanic eruptions. These eruptions have to be relatively recent (a few thousand years old) since <span class="hlt">ice</span> cores usually incorporate younger <span class="hlt">ice</span>. In contrast, dust bands on bare blue <span class="hlt">ice</span> fields are much older, up to a few hundred thousand years, which may be inferred from the rather high terrestrial age of meteorites found on the <span class="hlt">ice</span> and from dating the <span class="hlt">ice</span> using the uranium series method. Also for the volcanic ash layers found on blue <span class="hlt">ice</span> fields correlations between some specific volcanoes (late Cenozoic) and the volcanic debris have been inferred, mainly using chemical arguments. During a recent field expedition samples of several dust bands found on blue <span class="hlt">ice</span> fields at the Lewis Cliff <span class="hlt">Ice</span> Tongue were taken. These dust band samples were divided for age determination using the uranium series method, and chemical investigations to determine the source and origin of the dust bands. The investigations have shown that most of the dust bands found at the <span class="hlt">Ice</span> Tongue are of volcanic origin and, for chemical and petrological reasons, may be correlated with Cenozoic volcanoes in the Melbourne volcanic province, Northern Victoria Land, which is at least 1500 km away. Major and trace element data have been obtained and have been used for identification and correlation purposes. Recently, some additional trace elements were determined in some of the dust band</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5954474','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5954474"><span>Icebergs, sea <span class="hlt">ice</span>, blue carbon and Antarctic climate feedbacks</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Fleming, Andrew; Sands, Chester J.; Quartino, Maria Liliana; Deregibus, Dolores</p> <p>2018-01-01</p> <p>Sea <span class="hlt">ice</span>, including icebergs, has a complex relationship with the carbon held within animals (blue carbon) in the polar regions. Sea-<span class="hlt">ice</span> losses around West <span class="hlt">Antarctica</span>'s continental <span class="hlt">shelf</span> generate longer phytoplankton blooms but also make it a hotspot for coastal iceberg disturbance. This matters because in polar regions <span class="hlt">ice</span> scour limits blue carbon storage ecosystem services, which work as a powerful negative feedback on climate change (less sea <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 (<span class="hlt">ice</span> <span class="hlt">shelf</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29760118','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29760118"><span>Icebergs, sea <span class="hlt">ice</span>, blue carbon and Antarctic climate feedbacks.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Barnes, David K A; Fleming, Andrew; Sands, Chester J; Quartino, Maria Liliana; Deregibus, Dolores</p> <p>2018-06-28</p> <p>Sea <span class="hlt">ice</span>, including icebergs, has a complex relationship with the carbon held within animals (blue carbon) in the polar regions. Sea-<span class="hlt">ice</span> losses around West <span class="hlt">Antarctica</span>'s continental <span class="hlt">shelf</span> generate longer phytoplankton blooms but also make it a hotspot for coastal iceberg disturbance. This matters because in polar regions <span class="hlt">ice</span> scour limits blue carbon storage ecosystem services, which work as a powerful negative feedback on climate change (less sea <span class="hlt">ice</span> 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 <span class="hlt">ice</span> 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 (<span class="hlt">ice</span> <span class="hlt">shelf</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980151107','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980151107"><span>West-Antarctic <span class="hlt">Ice</span> Streams: Analog to <span class="hlt">Ice</span> Flow in Channels on Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lucchitta, B. K.</p> <p>1997-01-01</p> <p>Sounding of the sea floor in front of the Ross <span class="hlt">Ice</span> <span class="hlt">Shelf</span> in <span class="hlt">Antarctica</span> recently revealed large persistent patterns of longitudinal megaflutes and drumlinoid forms, which are interpreted to have formed at the base of <span class="hlt">ice</span> streams during the list glacial advance. The flutes bear remarkable resemblance to longitudinal grooves and highly elongated streamlined islands found on the floors of some large martian channels, called outflow channels. ln addition, other similarities exist between Antarctic <span class="hlt">ice</span> streams and outflow channels. <span class="hlt">Ice</span> streams are 30 to 80 km wide and hundreds of kilometers long, as are the martian channels. <span class="hlt">Ice</span> stream beds are below sea level. Floors of many martian outflow channels lie below martian datum, which may have been close to or below past martian sea levels. The Antarctic <span class="hlt">ice</span> stream bed gradient is flat and locally may go uphill, and surface slopes are exceptionally low. So are gradients of martian channels. The depth to the bed in <span class="hlt">ice</span> streams is 1 to 1.5 km. At bankful stage, the depth of the fluid in outflow channels would have been 1 to 2 km. These similarities suggest that the martian outflow channels, whose origin is commonly attributed to gigantic catastrophic floods, were locally filled by <span class="hlt">ice</span> that left a conspicuous morphologic imprint. Unlike the West-Antarctic-<span class="hlt">ice</span> streams, which discharge <span class="hlt">ice</span> from an <span class="hlt">ice</span> sheet, <span class="hlt">ice</span> in the martian channels came from water erupting from the ground. In the cold martian environment, this water, if of moderate volume, would eventually freeze. Thus it may have formed <span class="hlt">icings</span> on springs, <span class="hlt">ice</span> dams and jams on constrictions in the channel path, or frozen pools. Given sufficient thickness and downhill surface gradient, these <span class="hlt">ice</span> masses would have moved; and given the right conditions, they could have moved like Antarctic <span class="hlt">ice</span> streams.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eosweb.larc.nasa.gov/project/misr/gallery/larsen_c_rift','SCIGOV-ASDC'); return false;" href="https://eosweb.larc.nasa.gov/project/misr/gallery/larsen_c_rift"><span>Larsen C Rift Growth</span></a></p> <p><a target="_blank" href="http://eosweb.larc.nasa.gov/">Atmospheric Science Data Center </a></p> <p></p> <p>2017-04-17</p> <p>... NASA's MISR Tracks Growth of Rift in the Larsen C <span class="hlt">Ice</span> <span class="hlt">Shelf</span>     View Larger Image ... figures image   A rift in <span class="hlt">Antarctica</span>'s Larsen C <span class="hlt">ice</span> <span class="hlt">shelf</span> has grown to 110 miles (175 km) long, making it inevitable that an ...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.G23C..06W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.G23C..06W"><span>In Situ Observational Constraints on GIA in <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wilson, T. J.; Bevis, M. G.; Kendrick, E. C.; Konfal, S.; Dalziel, I. W.; Smalley, R.; Willis, M. J.; Wiens, D. A.; Heeszel, D. S.</p> <p>2012-12-01</p> <p>Geodetic and seismologic data sets have been acquired across a significant portion of <span class="hlt">Antarctica</span> through deployment of autonomous, remote instrumentation by the Antarctic Network (ANET) project of the Polar Earth Observing Network (POLENET). Continuous GPS measurements of bedrock crustal motions are yielding a synoptic picture of vertical and horizontal crustal motion patterns from the Transantarctic Mountains to the Ellsworth-Whitmore Mountains and Marie Byrd Land regions. Vertical motion patterns are broadly compatible with predictions from current GIA models, but the magnitudes of the vertical motions are substantially lower than predicted. Slower rates of uplift due to GIA can be attributed to factors including errors in <span class="hlt">ice</span> history, a superposed solid earth response to modern <span class="hlt">ice</span> mass change, and/or the influence of laterally varying earth properties on the GIA response. Patterns of horizontal motions measured by ANET show that the role of laterally varying earth rheology is extremely important in <span class="hlt">Antarctica</span>. Crustal motion vectors are closely aligned and document motion from East toward West <span class="hlt">Antarctica</span>, in contradiction to <span class="hlt">ice</span> sheet reconstructions placing maximum LGM <span class="hlt">ice</span> mass loss in West <span class="hlt">Antarctica</span> and GIA models that predict motions in the opposite direction. When compared to earth structure mapped by seismology, the horizontal crustal motions are consistently near-perpendicular to the very strong gradient in crust and mantle properties, perhaps the first confirmation of predictions from modeling studies that horizontal motions can be deflected or even reversed where such a lateral earth property exists. Accurate GIA models for <span class="hlt">Antarctica</span> clearly require a laterally-varying earth model and tuning based on these new GPS and seismological constraints.</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('http://adsabs.harvard.edu/abs/2009AGUFM.G43B0727W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.G43B0727W"><span>Estimating <span class="hlt">Antarctica</span> land topography from GRACE gravity and ICESat altimetry data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wu, I.; Chao, B. F.; Chen, Y.</p> <p>2009-12-01</p> <p>We propose a new method combining GRACE (Gravity Recovery and Climate Experiment) gravity and ICESat (<span class="hlt">Ice</span>, Cloud, and land Elevation Satellite) altimetry data to estimate the land topography for <span class="hlt">Antarctica</span>. <span class="hlt">Antarctica</span> is the fifth-largest continent in the world and about 98% of <span class="hlt">Antarctica</span> is covered by <span class="hlt">ice</span>, where in-situ measurements are difficult. Some experimental airborne radar and ground-based radar data have revealed very limited land topography beneath heavy <span class="hlt">ice</span> sheet. To estimate the land topography for the full coverage of <span class="hlt">Antarctica</span>, we combine GRACE data that indicate the mass distribution, with data of ICESat laser altimetry that provide high-resolution mapping of <span class="hlt">ice</span> topography. Our approach is actually based on some geological constraints: assuming uniform densities of the land and <span class="hlt">ice</span> considering the Airy-type isostasy. In the beginning we construct an initial model for the <span class="hlt">ice</span> thickness and land topography based on the BEDMAP <span class="hlt">ice</span> thickness and ICESat data. Thereafter we forward compute the model’s gravity field and compare with the GRACE observed data. Our initial model undergoes the adjustments to improve the fit between modeled results and the observed data. Final examination is done by comparing our results with previous but sparse observations of <span class="hlt">ice</span> thickness to reconfirm the reliability of our results. As the gravitational inversion problem is non-unique, our estimating result is just one of all possibilities constrained by available data in optimal way.</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/2016DSRII.131...28T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016DSRII.131...28T"><span>Formation processes of sea <span class="hlt">ice</span> floe size distribution in the interior pack and its relationship to the marginal <span class="hlt">ice</span> zone off East <span class="hlt">Antarctica</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Toyota, Takenobu; Kohout, Alison; Fraser, Alexander D.</p> <p>2016-09-01</p> <p>To understand the behavior of the Seasonal <span class="hlt">Ice</span> Zone (SIZ), which is composed of sea-<span class="hlt">ice</span> floes of various sizes, knowledge of the floe size distribution (FSD) is important. In particular, FSD in the Marginal <span class="hlt">Ice</span> Zone (MIZ), controlled by wave-<span class="hlt">ice</span> interaction, plays an important role in determining the retreating rates of sea-<span class="hlt">ice</span> extent on a global scale because the cumulative perimeter of floes enhances melting. To improve the understanding of wave-<span class="hlt">ice</span> interaction and subsequent effects on FSD in the MIZ, FSD measurements were conducted off East <span class="hlt">Antarctica</span> during the second Sea <span class="hlt">Ice</span> Physics and Ecosystems eXperiment (SIPEX-2) in late winter 2012. Since logistical reasons limited helicopter operations to two interior <span class="hlt">ice</span> regions, FSD in the interior <span class="hlt">ice</span> region was determined using a combination of heli-photos and MODIS satellite visible images. The possible effect of wave-<span class="hlt">ice</span> interaction in the MIZ was examined by comparison with past results obtained in the same MIZ, with our analysis showing: (1) FSD in the interior <span class="hlt">ice</span> region is basically scale invariant for both small- (<100 m) and large- (>1 km) scale regimes; (2) although fractal dimensions are quite different between these two regimes, they are both rather close to that in the MIZ; and (3) for floes <100 m in diameter, a regime shift which appeared at 20-40 m in the MIZ is absent. These results indicate that one role of wave-<span class="hlt">ice</span> interaction is to modulate the FSD that already exists in the interior <span class="hlt">ice</span> region, rather than directly determine it. The possibilities of floe-floe collisions and storm-induced lead formation are considered as possible formation processes of FSD in the interior pack.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <div class="footer-extlink text-muted" style="margin-bottom:1rem; text-align:center;">Some links on this page may take you to non-federal websites. 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