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  • 1
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    Dynamic (In)stability of Thwaites Glacier, West Antarctica (2013)
    Wiley
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    Publication Date: 2013-02-26
    Description: [1]  Thwaites Glacier, West Antarctica has the potential to directly contribute ~1 m to sea level, and currently is losing mass and thinning rapidly. Here we report on regional results for the Sea-level Response to Ice Sheet Evolution (SeaRISE) experiments and investigate the impact of i) spatial resolution within existing data sets, ii) grounding-zone processes, and iii) till rheology on the dynamics of this outlet glacier. In addition to the SeaRISE datasets, we use detailed aerogeophysical and satellite data from Thwaites Glacier as input to a coupled ice-stream/ice-shelf/ocean-plume model that includes oceanic influences across a several-kilometers-wide grounding zone suggested by new, high resolution data. Our results indicate that the ice tongue provides limited stability, and that while future atmospheric warming will likely add mass to the surface of the glacier, strong ice-stream stabilization on bedrock highs narrower than the length of the grounding zone may be ephemeral if circulating waters substantially reduce basal resistance and enhance melting beneath grounded ice within this zone. However, we find that stability is significantly enhanced by effectively-plastic till beds. Accurate projections of future sea-level changerelies on correct understanding of the till rheology as well as local basal processes near the grounding line.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Seismic attenuation in glacial ice: A proxy for englacial temperature (2012)
    Wiley
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    Publication Date: 2012-04-12
    Description: Seismic attenuation α, or internal friction Q−1, in glacial ice is highly sensitive to temperature, particularly near the melting point. Here we detail a technique to estimate Q and apply it to active source seismic data from Jakobshavn Isbrae, Greenland. We compare our results to measured and modeled temperature profiles of the ice in the region. We find an excellent match, with differences between seismically estimated and modeled temperatures of less than 2°C. Mapping variations in seismic Q through glacial ice thus is shown to allow detailed estimation of englacial temperature profiles, which may be of special value in regions where in situ measurements are logistically difficult.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Surface elevation changes at the front of the Ross Ice Shelf: Implications for basal melting (2011)
    Wiley
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    Publication Date: 2011-02-04
    Description: Rapid melting beneath the Ross Ice Shelf (RIS) occurs near the ice front, likely in response to a secondary buoyant plume with tidal mixing, and is sensitive to seasonal water temperatures in front of the ice shelf. The front of the RIS is examined using GLAS ICESat laser altimetry data. Spatial and temporal changes in surface elevations are attributed to enhanced basal melting of the ice shelf near the ice front. Melt rates ($\dot{M}$b) increase exponentially as the front is approached, from approximately zero at 40 km from the front to an average of 2.8 ± 1.0 m a−1 within the front kilometer. Melt estimates within the front 60 km are best fit by the relationship $\dot{M}$b = 2.0 × exp(−x/11900) m a−1, where x denotes distance from the front. Frontal melt totals approximately 16 km3 a−1 in the front 40 km, which accounts for between 10% and 40% of current published estimates of total melt beneath the RIS. Spatial averaging along the front reveals a different pattern of melt in regions that have recently calved as compared to regions that have not calved. Frontal melt is modeled as a one-dimensional buoyant plume with tidal currents included. These model results imply that modest increases in sea surface temperatures will lead to considerable increases in melting beneath the ice shelf front.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Climate change. On thickening ice? (2002)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2002-01-19
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Alley, Richard B -- New York, N.Y. -- Science. 2002 Jan 18;295(5554):451-2.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉EMS Environment Institute and the Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA. ralley@essc.psu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11799228" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Changes in the west antarctic ice sheet (1991)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1991-11-15
    Description: The portion of the West Antarctic ice sheet that flows into the Ross Sea is thinning in some places and thickening in others. These changes are not caused by any current climatic change, but by the combination of a delayed response to the end of the last global glacial cycle and an internal instability. The near-future impact of the ice sheet on global sea level is largely due to processes internal to the movement of the ice sheet, and not so much to the threat of a possible greenhouse warming. Thus the near-term future of the ice sheet is already determined. However, too little of the ice sheet has been surveyed to predict its overall future behavior.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Alley, R B -- Whillans, I M -- New York, N.Y. -- Science. 1991 Nov 15;254(5034):959-63.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17731516" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
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    Possible Role for Tectonics in the Evolving Stability of the Greenland Ice Sheet (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The history of the Greenland Ice Sheet has been influenced by the geodynamic response to ice sheet fluctuations, and this interaction may help explain past deglaciations under modest climate forcing. We hypothesize that when the Iceland hot spot passed beneath north‐central Greenland, it thinned the lithosphere and left anomalous heat likely with partially melted rock; however, it did not break through the crust to supply voluminous flood basalts. Subsequent Plio‐Pleistocene glacial‐interglacial cycles caused large and rapidly migrating stresses, driving dike formation and other processes that shifted melted rock toward the surface. The resulting increase in surface geothermal flux favored a thinner, faster‐responding ice sheet that was more prone to deglaciation. If this hypothesis of control through changes in geothermal flux is correct, then the long‐term (105 to 106 years) trend now is toward lower geothermal flux, but with higher‐frequency (≤104 to 105 years) oscillations linked to glacial‐interglacial cycles. Whether the geothermal flux is increasing or decreasing now is not known but is of societal relevance due to its possible impact on ice flow. We infer that projections of the future of the ice sheet and its effect on sea level must integrate geologic and geophysical data as well as glaciological, atmospheric, oceanic, and paleoclimatic information.
    Print ISSN: 2169-9003
    Electronic ISSN: 2169-9011
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Enhanced Firn Densification in High‐Accumulation Shear Margins of the NE Greenland Ice Stream (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Firn thickness across the NE Greenland Ice Stream is a function of accumulated strain, with thinner firn in the high‐strain margins of the ice stream. We present a novel technique for extracting firn density from previously collected seismic reflection profiles and apply this technique across both shear margins of NE Greenland Ice Stream. Firn is up to 30 m thinner in the vicinity of the ice stream shear margins. Snow accumulation rates across the ice stream were calculated from airborne ice‐penetrating radar data, calibrated with ground‐based firn density measurements from a shallow core. We find that accumulation is ~20% higher in the shear margins compared to the surroundings. The higher density firn adjacent to shear margins is due to high along‐flow stresses that accelerate firn densification and develops despite the higher accumulation rate favoring lower density. These firn density variations influence subglacial hydropotential by changing the ice surface slope and overburden pressure and may influence subglacial water flow. These results demonstrate the importance of high‐resolution firn surveys in studies of shear‐margin dynamics.
    Print ISSN: 2169-9003
    Electronic ISSN: 2169-9011
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Paleoclimatic evidence for future ice-sheet instability and rapid sea-level rise (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-03-25
    Description: Sea-level rise from melting of polar ice sheets is one of the largest potential threats of future climate change. Polar warming by the year 2100 may reach levels similar to those of 130,000 to 127,000 years ago that were associated with sea levels several meters above modern levels; both the Greenland Ice Sheet and portions of the Antarctic Ice Sheet may be vulnerable. The record of past ice-sheet melting indicates that the rate of future melting and related sea-level rise could be faster than widely thought.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Overpeck, Jonathan T -- Otto-Bliesner, Bette L -- Miller, Gifford H -- Muhs, Daniel R -- Alley, Richard B -- Kiehl, Jeffrey T -- New York, N.Y. -- Science. 2006 Mar 24;311(5768):1747-50.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for the Study of Planet Earth, Department of Geosciences, and Department of Atmospheric Sciences, University of Arizona, Tucson, AZ 85721, USA. jto@u.arizona.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16556837" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Discovery of till deposition at the grounding line of Whillans Ice Stream (2007)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2007-03-03
    Description: We report on the discovery of a grounding-line sedimentary wedge ("till delta") deposited by Whillans Ice Stream, West Antarctica. Our observation is that grounding-line deposition serves to thicken the ice and stabilize the position of the grounding line. The ice thickness at the grounding line is greater than that of floating ice in hydrostatic equilibrium. Thus, the grounding line will tend to remain in the same location despite changes in sea level (until sea level rises enough to overcome the excess thickness that is due to the wedge). Further, our observation demonstrates the occurrence of rapid subglacial erosion, sediment transport by distributed subglacial till deformation, and grounding-line sedimentation, which have important implications for ice dynamics, numerical modeling of ice flow, and interpretation of the sedimentation record.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Anandakrishnan, Sridhar -- Catania, Ginny A -- Alley, Richard B -- Horgan, Huw J -- New York, N.Y. -- Science. 2007 Mar 30;315(5820):1835-8. Epub 2007 Mar 1.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA. sak@essc.psu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17332378" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    Climate change. Understanding glacier flow in changing times (2008)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2008-11-15
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Alley, Richard B -- Fahnestock, Mark -- Joughin, Ian -- New York, N.Y. -- Science. 2008 Nov 14;322(5904):1061-2. doi: 10.1126/science.1166366.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geosciences and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA. rba6@psu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19008435" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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