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Dynamic Behavior and Disintegration of the Northern Larsen Ice Shelf, Antarctic Peninsula

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Citation:
Rack, W. (2000): Dynamic Behavior and Disintegration of the Northern Larsen Ice Shelf, Antarctic Peninsula , PhD thesis, Leopold-Franzens-Universität Innsbruck.
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Abstract:

The dynamic behavior and retreat of the northern Larsen Ice Shelf, Antarctic Peninsula, and its relation to climatic parameters areinvestigated. The analysis concentrates on the period after 1986 and is based on satellite remote sensing methods and fieldmeasurements.Temperature series of the eastern coast of the Antarctic Peninsula are analyzed. They show a significant warming trend since the 1970s,which caused a shift of the climatic limit for the existence of ice shelves further to the south. Major retreat of the ice shelf was observed inyears with mean summer temperatures above average. Extensive surface melting is observed in satellite images of those summers. Theduration of the melt periods is estimated from ERS scatterometer data.Based on satellite images and topographic data five ice shelf sections and their corresponding grounded catchment basins were analyzed.The sections are from north to south: Prince Gustav Channel (P-G), Larsen Inlet (L-I), the ice shelf between Sobral Peninsula and SealNunataks (S-S), the stagnant part around the Seal Nunataks (S-N), and the ice shelf between Seal Nunataks and Jason Peninsula (S-J).The three northern ice shelf sections were already in a state of retreat in 1986 and disintegrated until 1995.Stake measurements at the ice shelf sections S-S, S-N, and S-J provide information on mass balance, ice thickness, and ice motion. Thesurface mass balance turned to negative values in the beginning of the 1990s but was roughly balanced after 1995 at section S-N andS-J. Ice thickness and bottom melting rates are estimated from surface elevation measurements between 1996 and 1999 for section S-Nand the northern part of S-J. An increase in ice motion was observed since the beginning of the 1990s at section S-S and S-J andreached values up to 15% until 1997 at section S-J. The mass balance measurements and dynamic behavior suggest that the ice shelf isno more in equilibrium.High resolution Synthetic Aperture Radar (SAR) images which were acquired by the European Remote Sensing Satellites ERS-1/2between 1992 and 1999 represent the main remote sensing data base. Additional information is derived from declassified intelligencesatellite photographs from 1962/63, Landsat images between 1986 and 1990, and Radarsat SAR images for 1998 and 1999.The motion field is derived from satellite images by means of cross correlation for various periods between 1986 and 1993. SAR dataacquired during the ERS Tandem Mission in October/November 1995 enabled the interferometric analysis of motion at the two southernice shelf sections. Satellite derived velocities are in good agreement with field measurements. A comparison of satellite derived velocitiesfrom 1986/88 and 1995 at selected flow lines of section S-J shows an increase in velocity of 7% to 16%, with higher values towards theice edge. The vertical displacement in the tidal flexure zone is analyzed using interferometry and GPS measurements and shows goodagreement with a tidal model. An automatic algorithm is defined for the detection of the grounding line and hinge zone by means ofinterferometry.The changes of ice extent are documented by means of satellite images. Since 1986 continuous retreat of the ice shelf was observednorth of Seal Nunataks. Large parts of section L-I disintegrated already in 1989. The sections P-G and S-S collapsed in early 1995, andsimultaneously a major calving event occurred at the ice shelf section S-J after decades of continuous advance. Based on a close ERS-1SAR image sequence and meteorological information this break up event is analyzed in detail. Within one week about 3800 km2 of icecalved off. The occurrence of many small icebergs indicates the ice was fractured already before. After the disintegration some of theinput glaciers retreated beyond the former grounding line.Between 1986 and 1999 the investigated ice shelf area decreased from 15500 km2 to 8300 km2. The analysis suggests that the furtherdisintegration of the remnant parts of the ice shelf has to be expected in the near future. The re-formation of the ice shelf is extremelyunlikely under the current climatic conditions.

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