scholarly journals Inter-and Intra-annual Surface Velocity Variations at the Southern Grounding Line of Amery Ice Shelf from 2014 to 2018

2020 ◽  
Author(s):  
Zhaohui Chi ◽  
Andrew G. Klein
Keyword(s):  
Feature Tracking ◽  
Surface Velocity ◽  
Ice Shelf ◽  
Annual Increase ◽  
Amery Ice Shelf ◽  
Velocity Surface ◽  
Grounding Line ◽  
Velocity Variations ◽  
Mass Discharge

Abstract. The ice flow rate through the grounding line of the Amery Ice Shelf (AIS) is vital to understanding the mass discharge received from its three primary tributary glaciers. Previous studies have indicated a stable multiyear average surface velocity distribution in the convergence area of AIS. However, the surface velocity variations, especially short-term fluctuations, in the AIS have been relatively undocumented. This study investigated inter-annual and intra-annual surface velocity variations along the southern segment of AIS grounding line from 2014 to 2018. Using feature tracking to derive surface velocity for five consecutive austral summers and winters, it was found that AIS’s upstream end has experienced a steady ~ 5 % inter-annual increase in surface velocity. Surface velocity increases were observed in 2014/2015 (0.25 ± 0.02 m/d) and in 2017/2018 (0.21 ± 0.02 m/d) respectively. Surface velocities in winters were lower than the summers except for 2016, which had a 0.12 m/d surface velocity decrease from winter to summer. Although flowing slower than the other two glaciers, Fisher Glacier exhibited the highest inter-annual increase (8.56 ± 4.36 %) and the largest intra-annual variation (−5.41 ± 5.65 %) in surface velocity of the three studied glaciers. While the surface velocity observed in 2018 was generally close to the observed velocity in 1989, the magnitude of velocity variations observed during the 2014–2018 period is similar to the differences in velocities measured at the grounding line since 1989. This indicates continued relative stability in the surface velocities at the grounding line of these three tributary glaciers but also indicates that caution should be applied when interpreting long-term differences based on a limited number of measurements. This study demonstrated the capability of feature tracking to monitor the multidecadal changes of surface velocity.

scholarly journals Interannual surface velocity variations of Pine Island Glacier, West Antarctica

2003 ◽  
Vol 36 ◽  
pp. 205-214 ◽  
Author(s):  
Bernhard T. Rabus ◽  
Oliver Lang
Keyword(s):  
Feature Tracking ◽  
Surface Velocity ◽  
Synthetic Aperture ◽  
Clear Correlation ◽  
West Antarctica ◽  
Velocity Increase ◽  
Grounding Line ◽  
Velocity Variations ◽  
Independent Confirmation ◽  
Observation Period

AbstractThe surface velocity of Pine Island Glacier, West Antarctica, during the period 1992–2000 is measured with synthetic aperture radar feature-tracking techniques. Over the observation period, we find a monotonic acceleration with a spatially uniform amplitude of about 12% of the surface velocity. The acceleration extends > 80 km inland of the grounding line into a zone of prominent arcuate crevasses.The upper limit of these crevasses has migrated up-glacier by 0.2 km a−1 correlated with a velocity increase of similar size in the crevassed zone. On the other hand, there is no clear correlation between the velocity variations and observations of grounding-line migration. These findings suggest ongoing dynamic thinning of Pine Island Glacier, providing independent confirmation of recent interferometric results obtained by Rignot and others (2002).

scholarly journals Interannual velocity variations and recent calving of Thwaites Glacier Tongue, West Antarctica

2003 ◽  
Vol 36 ◽  
pp. 215-224 ◽  
Author(s):  
Bernhard T. Rabus ◽  
Oliver Lang ◽  
Ute Adolphs
Keyword(s):  
Feature Tracking ◽  
Surface Velocity ◽  
Synoptic Scale ◽  
West Antarctica ◽  
Weather Forecasts ◽  
Grounding Line ◽  
Medium Range ◽  
The Mean ◽  
Velocity Variations ◽  
Observation Period

AbstractThe surface velocity of Thwaites Glacier (TG), West Antarctica, during the period 1992–2000 is measured with synthetic aperture radar feature-tracking techniques. We find no indication of interannual velocity variations of the grounded ice further than about 20 km inland of the grounding line. The velocity of the floating TG Tongue shows cyclicalvariations with an amplitude of 10%; a minimum around 1997 is bracketed by similarly sized maxima in 1995 and 2000. The observed velocity variations can be explained by time-dependent rotation and deformation superimposed on the steady flow of TG Tongue. The orientation of the rotation is clockwise during the entire observation period; the mean center of the rotation is close to a small ice rise, situated at the east side of the tongue about 20 km past the grounding line. The recent calving of TG Tongue in February 2002 is consistent with continued clockwise rotation that eventually led to cracking from west to east across the tongue. The rotation and deformation of TG Tongue is caused by forces unrelated to glacier dynamics. Analysis of European Centre for Medium-Range Weather Forecasts wind data suggests a synoptic-scale origin for the external forcing that causes the rotation.

scholarly journals Properties of a marine ice layer under the Amery Ice Shelf, East Antarctica

2009 ◽  
Vol 55 (192) ◽  
pp. 717-728 ◽  
Author(s):  
Mike Craven ◽  
Ian Allison ◽  
Helen Amanda Fricker ◽  
Roland Warner
Keyword(s):  
Sea Water ◽  
Average Rate ◽  
East Antarctica ◽  
Ice Shelf ◽  
Closure Rate ◽  
Southern Limit ◽  
Amery Ice Shelf ◽  
Average Porosity ◽  
Grounding Line ◽  
Ocean Properties

AbstractThe Amery Ice Shelf, East Antarctica, undergoes high basal melt rates near the southern limit of its grounding line where 80% of the ice melts within 240 km of becoming afloat. A considerable portion of this later refreezes downstream as marine ice. This produces a marine ice layer up to 200 m thick in the northwest sector of the ice shelf concentrated in a pair of longitudinal bands that extend some 200 km all the way to the calving front. We drilled through the eastern marine ice band at two locations 70 km apart on the same flowline. We determine an average accretion rate of marine ice of 1.1 ± 0.2 m a−1, at a reference density of 920 kg m−3 between borehole sites, and infer a similar average rate of 1.3 ± 0.2 m a−1 upstream. The deeper marine ice was permeable enough that a hydraulic connection was made whilst the drill was still 70–100 m above the ice-shelf base. Below this marine close-off depth, borehole video imagery showed permeable ice with water-filled cavities and individual ice platelets fused together, while the upper marine ice was impermeable with small brine-cell inclusions. We infer that the uppermost portion of the permeable ice becomes impermeable with the passage of time and as more marine ice is accreted on the base of the shelf. We estimate an average closure rate of 0.3 m a−1 between the borehole sites; upstream the average closure rate is faster at 0.9 m a−1. We estimate an average porosity of the total marine ice layer of 14–20%, such that the deeper ice must have even higher values. High permeability implies that sea water can move relatively freely through the material, and we propose that where such marine ice exists this renders deep parts of the ice shelf particularly vulnerable to changes in ocean properties.

scholarly journals Modelling the response of the Lambert Glacier–Amery Ice Shelf system, East Antarctica, to uncertain climate forcing over the 21st and 22nd centuries

2014 ◽  
Vol 8 (3) ◽  
pp. 1057-1068 ◽  
Author(s):  
Y. Gong ◽  
S. L. Cornford ◽  
A. J. Payne
Keyword(s):  
Climate Model ◽  
Global Environmental Change ◽  
Ice Sheet ◽  
Adaptive Mesh ◽  
Ocean Model ◽  
East Antarctica ◽  
Ice Shelf ◽  
Amery Ice Shelf ◽  
Grounding Line ◽  
Lambert Glacier

Abstract. The interaction between the climate system and the large polar ice sheet regions is a key process in global environmental change. We carried out dynamic ice simulations of one of the largest drainage systems in East Antarctica: the Lambert Glacier–Amery Ice Shelf system, with an adaptive mesh ice sheet model. The ice sheet model is driven by surface accumulation and basal melt rates computed by the FESOM (Finite-Element Sea-Ice Ocean Model) ocean model and the RACMO2 (Regional Atmospheric Climate Model) and LMDZ4 (Laboratoire de Météorologie Dynamique Zoom) atmosphere models. The change of ice thickness and velocity in the ice shelf is mainly influenced by the basal melt distribution, but, although the ice shelf thins in most of the simulations, there is little grounding line retreat. We find that the Lambert Glacier grounding line can retreat as much as 40 km if there is sufficient thinning of the ice shelf south of Clemence Massif, but the ocean model does not provide sufficiently high melt rates in that region. Overall, the increased accumulation computed by the atmosphere models outweighs ice stream acceleration so that the net contribution to sea level rise is negative.

scholarly journals Changes in ice-shelf buttressing following the collapse of Larsen A Ice Shelf, Antarctica, and the resulting impact on tributaries

2016 ◽  
Vol 62 (235) ◽  
pp. 905-911 ◽  
Author(s):  
SAM ROYSTON ◽  
G. HILMAR GUDMUNDSSON
Keyword(s):  
Antarctic Peninsula ◽  
Surface Velocity ◽  
Ice Shelf ◽  
Mass Redistribution ◽  
Grounding Line ◽  
Modelling Studies ◽  
Speed Up ◽  
Stringent Test ◽  
The Antarctic ◽  
The Impact

ABSTRACTThe dominant mass-loss process on the Antarctic Peninsula has been ice-shelf collapse, including the Larsen A Ice Shelf in early 1995. Following this collapse, there was rapid speed up and thinning of its tributary glaciers. We model the impact of this ice-shelf collapse on upstream tributaries, and compare with observations using new datasets of surface velocity and ice thickness. Using a two-horizontal-dimension shallow shelf approximation model, we are able to replicate the observed large increase in surface velocity that occurred within Drygalski Glacier, Antarctic Peninsula. The model results show an instantaneous twofold increase in flux across the grounding line, caused solely from the reduction in backstress through ice shelf removal. This demonstrates the importance of ice-shelf buttressing for flow upstream of the grounding line and highlights the need to explicitly include lateral stresses when modelling real-world settings. We hypothesise that further increases in velocity and flux observed since the ice-shelf collapse result from transient mass redistribution effects. Reproducing these effects poses the next, more stringent test of glacier and ice-sheet modelling studies.

scholarly journals Ice-shelf Response to Ice-stream Discharge Fluctuations: I. Unconfined Ice Tongues

1988 ◽  
Vol 34 (116) ◽  
pp. 121-127 ◽  
Author(s):  
Douglas R. MacAyeal ◽  
Victor Barcilon
Keyword(s):  
Ice Shelf ◽  
Lagrangian Particle ◽  
Sea Level Fluctuations ◽  
Stream Discharge ◽  
Discharge Fluctuations ◽  
Ice Stream ◽  
Grounding Line ◽  
Velocity Changes ◽  
Particle Paths

AbstractIce-stream discharge fluctuations constitute an independent means of forcing unsteady ice-shelf behavior, and their effect must be distinguished from those of oceanic and atmospheric climate to understand ice-shelf change. In addition, ice-stream-generated thickness anomalies may constitute a primary trigger of ice-rise formation in the absence of major sea-level fluctuations. Such triggering may maintain the current ice-rise population that, in turn, contributes to long-term ice-sheet stability. Here, we show that ice-stream-generated fluctuations of an ideal, two-dimensional ice shelf propagate along two characteristic trajectories. One trajectory permits instantaneous transmission of grounding-line velocity changes to all points down-stream. The other trajectory represents slow transmission of grounding-line thickness changes along Lagrangian particle paths.

Seasonal glacier surface velocity fluctuation and contribution of the Eastern and Western Tributary Glaciers in Amery Ice Shelf, East Antarctica

2019 ◽  
Vol 9 (1) ◽  
pp. 49-60
Author(s):  
Shridhar Digambar Jawak ◽  
Shubhang Kumar ◽  
Alvarinho Joaozinho Luis ◽  
Prashant Hemendra Pandit ◽  
Sagar Filipe Wankhede
Keyword(s):  
Remote Sensing ◽  
Root Mean Square ◽  
Winter Season ◽  
Maximum Velocity ◽  
Surface Velocity ◽  
Mean Square ◽  
Ice Shelf ◽  
Amery Ice Shelf ◽  
Rms Error ◽  
Western Side

Glaciers play a crucial role in the study of the climate change pattern of the Earth. Remote sensing with access to large archives of data has the ability to monitor glaciers frequently throughout the year. Therefore, remote sensing is the most beneficial tool for the study of glacier dynamics. Fed by many tributaries from different sides, the Amery Ice Shelf (AIS) is one of the largest ice shelves that drains ice from the Antarctic ice sheet into the Southern Ocean. This study focuses on the eastern and the western tributaries of the AIS. The primary objective of the study was to derive the velocity of the tributary glaciers and the secondary objective was to compare variations in their velocities between the summer and winter season. This study was carried on using the European Space Agency’s (ESA) Sentinel-1 satellite’s Synthetic Aperture Radar (SAR) data acquired from the Sentinel data portal. Offset tracking method was applied to the Ground Range Detected (GRD) product of the Sentinel-1 interferometric wide (IW) swath acquisition mode. The maximum velocity in summer was observed to be around 610 m/yr in the eastern tributary glacier meeting the ice shelf near the Pickering Nunatak, and around 345 m/yr in the Charybdis Glacier Basin from the western side. The maximum velocity in the winter was observed to be 553 m/yr in the eastern side near the Pickering Nunatak whereas 323 m/yr from the western side in the Charybdis Glacier Basin. The accuracy of the derived glacier velocities was computed using bias and root mean square (RMS) error. For the analysis, the publicly available velocity datasets were used. The accuracy based on RMS error was observed to be 85-90% for both seasons with bias values up to 25 m/yr and root mean square error values up to 30 m/yr.

scholarly journals The supply of subglacial meltwater to the grounding line of the Siple Coast, West Antarctica

2012 ◽  
Vol 53 (60) ◽  
pp. 267-280 ◽  
Author(s):  
S.P. Carter ◽  
H.A. Fricker
Keyword(s):  
Temporal Variability ◽  
Freshwater Flux ◽  
Spatial And Temporal Variability ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Lake Volume ◽  
Grounding Line ◽  
Subglacial Lakes

AbstractRecent satellite studies have shown that active subglacial lakes exist under the Antarctic ice streams and persist almost to their grounding lines. When the lowest-lying lakes flood, the water crosses the grounding line and enters the sub-ice-shelf cavity. Modeling results suggest that this additional freshwater influx may significantly enhance melting at the ice-shelf base. We examine the spatial and temporal variability in subglacial water supply to the grounding lines of the Siple Coast ice streams, by combining estimates for lake volume change derived from Ice, Cloud and land Elevation Satellite (ICESat) data with a model for subglacial water transport. Our results suggest that subglacial outflow tends to concentrate towards six embayments in the Siple Coast grounding line. Although mean grounding line outflow is ~60m3 s–1 for the entire Siple Coast, maximum local grounding line outflow may temporarily exceed 300 m3 s–1 during the synchronized flooding of multiple lakes in a hydrologic basin. Variability in subglacial outflow due to subglacial lake drainage may account for a substantial portion of the observed variability in freshwater flux out of the Ross Ice Shelf cavity. The temporal variability in grounding line outflow results in a net reduction in long-term average melt rate, but temporary peak melting rates may exceed the long-term average by a factor of three.

scholarly journals Ice-shelf Response to Ice-stream Discharge Fluctuations: I. Unconfined Ice Tongues

1988 ◽  
Vol 34 (116) ◽  
pp. 121-127 ◽  
Author(s):  
Douglas R. MacAyeal ◽  
Victor Barcilon
Keyword(s):  
Ice Shelf ◽  
Lagrangian Particle ◽  
Sea Level Fluctuations ◽  
Stream Discharge ◽  
Discharge Fluctuations ◽  
Ice Stream ◽  
Grounding Line ◽  
Velocity Changes ◽  
Particle Paths

AbstractIce-stream discharge fluctuations constitute an independent means of forcing unsteady ice-shelf behavior, and their effect must be distinguished from those of oceanic and atmospheric climate to understand ice-shelf change. In addition, ice-stream-generated thickness anomalies may constitute a primary trigger of ice-rise formation in the absence of major sea-level fluctuations. Such triggering may maintain the current ice-rise population that, in turn, contributes to long-term ice-sheet stability. Here, we show that ice-stream-generated fluctuations of an ideal, two-dimensional ice shelf propagate along two characteristic trajectories. One trajectory permits instantaneous transmission of grounding-line velocity changes to all points down-stream. The other trajectory represents slow transmission of grounding-line thickness changes along Lagrangian particle paths.

scholarly journals Glaciological study in Terra Nova Bay, Antarctica, inferred from remote sensing analysis

1993 ◽  
Vol 17 ◽  
pp. 63-71 ◽  
Author(s):  
Massimo Frezzotti
Keyword(s):  
Aerial Photographs ◽  
Surface Velocity ◽  
Ice Shelf ◽  
Limit Values ◽  
Glacier Tongue ◽  
Outer Limit ◽  
Ice Melt ◽  
Terra Nova Bay ◽  
Grounding Line ◽  
Terra Nova

Analysis of satellite images (Landsat 1 MSS, 4 TM and SPOT 1 XS), of U.S. Navy aerial photographs (TMA) and of U.S.G.S. maps has made it possible to assess a number of parameters relating to the surface dynamics (between 1956 and 1990) of eight ice tongues and of two ice shelves in the Terra Nova Bay area. The study shows that between 1960–63 and 1972–73 there was a decided decrease in the areas of some of the tongues and shelves: −53 km2 for the Aviator Glacier Tongue and −124 km2 for the Nansen Ice Sheet. On the other hand, the areas generally increased in the period 1972–73 to 1988. An exception to this situation is the small Hells Gate ice shelf whose area diminished by 1.15 km2 between 1956–57 and 1988. The calculated surface velocity of the ice tongues shows that they increase from the grounding line to their outer limit. Values of longitudinal strain rate generally increase from the grounding line to just after the start of the ice tongue, after which they diminsh proceeding towards its outer limit. Integration of the areal values with radio-echo sounding data has enabled the ice discharges of the southern flow of the David Glacier (12km3a−1) and of the Aviator Glacier Tongue (0.62 km3 a−1) to be calculated. Furthermore, on the basis of the data available, basal melting values of between 25 cm a−1 and 100 cm a−1 are deduced for these two ice tongues, and bottom freezing values of 20 cm a−1 for the Drygalski Ice Tongue. Different spectral responses of the glacial areas have made it possible to discriminate ablation areas from those of accumulation and to differentiate various typologies of ice (glacier ice, melt lake ice, and sea ice formed at the ice shelf-ocean interface).

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