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  • 1
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    Dynamic (in)stability of Thwaites Glacier, West Antarctica : THWAITES DYNAMICS
    American Geophysical Union (AGU) ; 2013
    In:  Journal of Geophysical Research: Earth Surface Vol. 118, No. 2 ( 2013-06), p. 638-655
    Details
    In: Journal of Geophysical Research: Earth Surface, American Geophysical Union (AGU), Vol. 118, No. 2 ( 2013-06), p. 638-655
    Type of Medium: Online Resource
    ISSN: 2169-9003
    URL: Article
    DOI: 10.1002/jgrf.20044
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2013
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  • 2
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    Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models
    Copernicus GmbH ; 2014
    In:  Earth System Dynamics Vol. 5, No. 2 ( 2014-08-14), p. 271-293
    Details
    In: Earth System Dynamics, Copernicus GmbH, Vol. 5, No. 2 ( 2014-08-14), p. 271-293
    Abstract: Abstract. The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02–0.14 m; 90% range: 0.0–0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04–0.21 m; 90% range: 0.01–0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.09 m (66% range: 0.04–0.17 m; 90% range: 0.02–0.25 m) for RCP-2.6 and 0.15 m (66% range: 0.07–0.28 m; 90% range: 0.04–0.43 m) for RCP-8.5. All probability distributions are highly skewed towards high values. The applied ice-sheet models are coarse resolution with limitations in the representation of grounding-line motion. Within the constraints of the applied methods, the uncertainty induced from different ice-sheet models is smaller than that induced by the external forcing to the ice sheets.
    Type of Medium: Online Resource
    ISSN: 2190-4987
    URL: Article
    DOI: 10.5194/esd-5-271-2014
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2014
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  • 3
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    Detection and monitoring of stratigraphic markers and temperature trends at the Greenland Ice Sheet Project 2 using passive‐microwave remote‐sensing data
    American Geophysical Union (AGU) ; 1997
    In:  Journal of Geophysical Research: Oceans Vol. 102, No. C12 ( 1997-11-30), p. 26877-26886
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 102, No. C12 ( 1997-11-30), p. 26877-26886
    Abstract: Satellite passive‐microwave sensors provide a sensitive means of studying ice‐sheet surface processes that assists ice‐core interpretation and can extend local observations across regional scales. Analysis of special sensor microwave/imager (SSM/I) brightness temperature ( T B ) data supports ice‐core research in two specific ways. First, the summer hoar complex layers used to date the Holocene portion of the Greenland Ice Sheet Project 2 ice core can be defined temporally and spatially by SSM/I 37‐GHz vertically (V) and horizontally (H) polarized B ratio (V/H) trends. Second, comparison of automatic weather station temperatures to SSM/I 37‐GHz V T B data shows that they are an effective proxy temperature record in this region. Also, the T B data can be correlated with proxy temperature trends from stable‐isotope‐ratio (δ 18 O and δD) profiles from snow pits and this allows the assignment of dates to specific snow depths.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/96JC02323
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1997
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    SSG: 16,13
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  • 4
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    Temperature history and accumulation timing for the snowpack at GISP2, central Greenland
    International Glaciological Society ; 1998
    In:  Journal of Glaciology Vol. 44, No. 146 ( 1998), p. 21-30
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 44, No. 146 ( 1998), p. 21-30
    Abstract: Previous research has documented a close association between high-resolution snow-pit profiles of hydrogen and oxygen stable-isotope ratios and multi-year Special Sensor Microwave/lmager (SSM/I) 37 GHz brightness temperature data in central Greenland. Comparison of the SSM/I data to profiles obtained during the 1989-91 field seasons indicated that δ D and δ 18 O data from the near-surface snow at the Greenland summit are a reliable, high-resolution temperature proxy. To test this new technique further, additional stable-isotope data were obtained from a 2 m snow pit constructed during late-June 1995 near the GISP2 site. This new profile, supported by pit stratigraphy and chemistry data, confirms the utility of comparing stable-isotope records with SSM/I brightness temperatures. The sub-annual variation of the δD record at the GISP2 site was determined using 15 match points, from approximately December 1991 through June 1995 and was guided in part by time-constrained hoar layers. The close association of these temperature proxies supports the assertion that snow accumulation occurs frequently through the year and that the isotope record initially contains temperature information from many times of the year. This is also independently confirmed by analysis of H 2 O 2 data. The slope of the multi-year T vs δ correlation was evaluated along with the sub-annual variation in the amount, rate and timing of accumulation. These new results are consistent with those from the previous study and they also demonstrate that the snow in this area initially contains temperature and chemical records with sub-annual resolution. This encourages confident interpretation of the paleoclimatic signal variations in the GISP2 and GRIP deep cores.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/S0022143000002318
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1998
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  • 5
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    Online Resource
    Temperature history and accumulation timing for the snowpack at GISP2, central Greenland
    Cambridge University Press (CUP) ; 1998
    In:  Journal of Glaciology Vol. 44, No. 146 ( 1998), p. 21-30
    Details
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 44, No. 146 ( 1998), p. 21-30
    Abstract: Previous research has documented a close association between high-resolution snow-pit profiles of hydrogen and oxygen stable-isotope ratios and multi-year Special Sensor Microwave/lmager (SSM/I) 37 GHz brightness temperature data in central Greenland. Comparison of the SSM/I data to profiles obtained during the 1989-91 field seasons indicated that δ D and δ 18 O data from the near-surface snow at the Greenland summit are a reliable, high-resolution temperature proxy. To test this new technique further, additional stable-isotope data were obtained from a 2 m snow pit constructed during late-June 1995 near the GISP2 site. This new profile, supported by pit stratigraphy and chemistry data, confirms the utility of comparing stable-isotope records with SSM/I brightness temperatures. The sub-annual variation of the δD record at the GISP2 site was determined using 15 match points, from approximately December 1991 through June 1995 and was guided in part by time-constrained hoar layers. The close association of these temperature proxies supports the assertion that snow accumulation occurs frequently through the year and that the isotope record initially contains temperature information from many times of the year. This is also independently confirmed by analysis of H 2 O 2 data. The slope of the multi-year T vs δ correlation was evaluated along with the sub-annual variation in the amount, rate and timing of accumulation. These new results are consistent with those from the previous study and they also demonstrate that the snow in this area initially contains temperature and chemical records with sub-annual resolution. This encourages confident interpretation of the paleoclimatic signal variations in the GISP2 and GRIP deep cores.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.1017/S0022143000002318
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1998
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    SSG: 14
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  • 6
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    Composite Temperature Record from the Greenland Summit, 1987–1994: Synthesis of Multiple Automatic Weather Station Records and SSM/I Brightness Temperatures
    American Meteorological Society ; 1996
    In:  Journal of Climate Vol. 9, No. 6 ( 1996-06), p. 1421-1428
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 9, No. 6 ( 1996-06), p. 1421-1428
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/1520-0442(1996)009〈1421:CTRFTG〉2.0.CO;2
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 1996
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  • 7
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    Continued deceleration of Whillans Ice Stream, West Antarctica : CONTINUED DECELERATION OF WHILLANS ICE STREAM
    American Geophysical Union (AGU) ; 2005
    In:  Geophysical Research Letters Vol. 32, No. 22 ( 2005-11), p. n/a-n/a
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 32, No. 22 ( 2005-11), p. n/a-n/a
    Type of Medium: Online Resource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2005GL024319
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2005
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  • 8
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    Mass-Balance Studies of Ice Streams A, B, and C, West Antarctica, and Possible Surging Behavior of Ice Stream Β
    International Glaciological Society ; 1988
    In:  Annals of Glaciology Vol. 11 ( 1988), p. 137-149
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 11 ( 1988), p. 137-149
    Abstract: Recent airborne radar sounding has made it possible to map accurately three of the West Antarctic ice streams that flow into Ross Ice Shelf. In previous work we have shown that ice streams A and Β have negative mass balances, whereas inactive Ice Stream C has a strongly positive balance. In this paper we examine in more detail the balance of ice streams A and Β by constructing several gates across them where velocities and ice thicknesses have been measured. We then examine the net fluxes in blocks of the ice streams delimited by successive pairs of gates. Ice Stream A as a whole is apparently discharging more ice than is being accumulated in the catchment area, and currently thinning at the rate of 0.08 ± 0.03 m a −1 . The situation on Ice Stream Β is more complex. We have calculated separately the fluxes from tributary ice streams Bl and B2, and examined their individual fluxes within Ice Stream Β by tracing the suture zone between them down-stream of their confluence. The flow band that is the farthest up-stream (girdle), encompassing both Ice Stream Bl and Ice Stream B2, shows a strongly negative net flux that we attribute to lateral and headward expansion of the ice streams within the band. Such expansion can occur by lateral movement of an ice-stream boundary, by temporally accelerating ice flow at the head of the ice stream, or by activation of formerly slowly moving “island” or “peninsula” ice. The imbalance in this flow band, 8 ± 2 km 3 a −1 (equivalent mean rate of change in ice thickness, is nearly half of the total excess outflow for the Ice Stream Β system (20 ± 4 km 3 a −1 ), — the remainder is mostly the difference between flow through the uppermost gate and mass input to the catchment area . When for the whole of Ice Stream Β is plotted against the distance along the entire Ice Stream B, the overall pattern appears to be of mild thinning in the catchment, intense thinning in the girdle, and thickening in the main body of the ice stream, which decreases with distance from the girdle. This global behavior is suggestive of a major transient response, resulting from either a change in the internal dynamics or an internal adjustment to a change in the external forcings. We argue that there are a number of conditions which could lead to this type of response pattern. One possibility is a surge. Although the distribution of the changes in thickness is one characteristic of a surge, we caution that this alone is not sufficient to classify the behavior as a surge. Several other possibilities that support a picture of Ice Stream Β as a system in the process of dynamic change and in unsteady state are discussed. At present, Ice Stream C and its catchment area are thickening over their entire area The present surface elevation does not suggest that Ice Stream Β has captured part of Ice Stream C. Moreover, the shut-down of Ice Stream C and the large mass imbalance of Ice Stream Β are not related.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/S0260305500006455
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1988
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  • 9
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    Thinning and Grounding-Line Retreat on Ross Ice Shelf, Antarctica
    International Glaciological Society ; 1988
    In:  Annals of Glaciology Vol. 11 ( 1988), p. 165-172
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 11 ( 1988), p. 165-172
    Abstract: Detailed measurements of surface topography, ice motion, snow accumulation, and ice thickness were made in January 1974 and again in December 1984, along an 8 km stake network extending from the ice sheet, across the grounding line, and on to floating ice shelf in the mouth of slow-moving Ice Stream C, which flows into the eastern side of Ross Ice Shelf, Antarctica. During the 11 years between surveys, the grounding line retreated by approximately 300 m. This was caused by net thinning of the ice shelf, which we believe to be a response to the comparatively recent, major decrease in ice discharge from Ice Stream C. Farther inland, snow accumulation is not balanced by ice discharge, and the ice stream is growing progressively thicker. There is evidence that the adjacent Ice Stream B has slowed significantly over the last decade, and this may be an early indication that this fast-moving ice stream is about to enter a period of stagnation similar to that of Ice Stream C. Indeed, these large ice streams flowing from West Antarctica into Ross Ice Shelf may oscillate between periods of relative stagnation and major activity. During active periods, large areas of ice shelf thicken and run aground on seabed to form extensive “ice plains” in the mouth of the ice stream. Ultimately, these become too large to be pushed seaward by the ice stream, which then slows down and enters a period of stagnation. During this period, the grounding line of the ice plain retreats, as we observe today in the mouth of Ice Stream C, because nearby ice shelf, no longer compressed by ice-stream motion, progressively thins. At the same time, water within the deformable till beneath the ice starts to freeze on to the base of the ice stream, and snow accumulation progressively increases the ice thickness. A new phase of activity would be initiated when the increasing gravity potential of the ice stream exceeds the total resistance of the shrinking ice plain and the thinning layer of deformable till at the bed. This could occur rapidly if the effects of the shrinking ice plain outweigh those of the thinning (and therefore stiffening) till. Otherwise, the till layer would finally become completely frozen, and the ice stream would have to thicken sufficiently to initiate significant heating by internal deformation, followed by basal melting and finally saturation of an adequate thickness of till; this could take some thousands of years.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/S0260305500006492
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 1988
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  • 10
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    Surface elevation contours of greenland and Antarctic Ice Sheets
    American Geophysical Union (AGU) ; 1983
    In:  Journal of Geophysical Research: Oceans Vol. 88, No. C3 ( 1983-02-28), p. 1589-1596
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 88, No. C3 ( 1983-02-28), p. 1589-1596
    Abstract: Surface elevations of the ice sheets are contoured at 50‐m intervals for the region of Greenland covered by SEASAT radar altimetry south of 72°N and at 100‐m intervals for a region of East Antarctica north of 72°S. The surface elevations were obtained from computer retracking of the radar altimeter waveforms, which were recorded at 0.1‐s intervals corresponding to 662‐m spacings on the surface. The precision of the elevation measurements before adjustment for radial orbit errors is 1.9 m as shown by analysis of elevation differences at orbital crossover points. This precision is partly determined by radial errors of approximately 1.0 m in orbit determination and partly by noise due to ice surface irregularities. Adjustment of the radial components of the orbits to minimize the differences in elevations at crossovers over a small, relatively flat region reduces the rms difference to 0.25 m, which is indicative of the optimum precision obtainable over the ice sheets. However, the precision degrades as the slope of the surface or amplitude of the undulations increases, yielding an overall precision of ±1.6 m. The preliminary contour maps are not corrected for slope‐induced displacements. A 2‐m contour map in a region of highest data density illustrates the three‐dimensional characteristics of some surface undulations.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/JC088iC03p01589
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1983
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    SSG: 16,13
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