Measurements of Amery Ice Shelf, East Antarctica, thickness change from surface elevation observations 1968-present

Lead Research Organisation: Newcastle University
Department Name: Civil Engineering and Geosciences

Abstract

Antarctica's large floating ice shelves are perhaps the most sensitive of its regions to climate change. During the 1990s, the collapse of several ice shelves in the Antarctic Peninsula region were witnessed. While the much colder ice shelves of East Antarctica are thought to be presently safe from such dramatic destruction, little is known about their present rate of change. This study focusses on the largest ice shelf in East Antarctica, the Amery Ice Shelf (AIS), which drains 16% of the grounded Antarctic continent. How has it changed during the past few decades? What is driving these changes? To answer this, we will compare surface elevation measurements on the northern AIS made during the 1960s with more recent elevation measurements using satellite technology, such as Global Positioning System (GPS). Together with an understanding of the ice shelf density, we will be able to determine the amount of ice mass gained/lost during this period and it will provide important indicators to the driving mechanisms behind any changes.

Publications

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King M (2009) A 4-decade record of elevation change of the Amery Ice Shelf, East Antarctica in Journal of Geophysical Research

 
Description We report on long-term surface elevation changes of the central Amery Ice Shelf (AIS) by comparing elevation records spanning four decades (1968-2007). We use elevation records acquired with the following methods: optical leveling (1968-69); ERS radar altimetry (1992-2003); GPS (1995-2006); and ICESat laser altimetry (2003-2007). We compute multi-decadal elevation trend (dh/dt) values at crossovers between the leveling route and each of the GPS and ICESat tracks, as well as shorter period dh/dt at ERS-ERS, GPS-GPS and ICESat-ICESat crossovers. At GPS-leveling crossovers the mean long-term dh/dt is -0.003 m/yr and at ICESat-leveling crossovers the mean dh/dt is 45+0.013 m/yr; neither trend is significantly different from zero. The data do however exhibit variable trends: near-zero change between 1991 and mid-1996, then thickening to ~2003, followed by thinning ~2003-2007, with 5 year dh/dt averages exceeding ~±0.1 m/yr. The changes in dh/dt pattern in mid-1996 and again in 2003 occur with unexpected speed. The ice shelf exhibits different dh/dt patterns than does the surrounding grounded ice, suggesting that surface mass balance variations or longer term variations in firn densification processes are unlikely to be major causes. We conclude that these observed multi-year elevation changes must be due to currently unexplained or presently poorly quantified phenomena involving surface, basal processes and/or ice dynamics. With the multi-decadal stability of the AIS established, the short-term fluctuations that we observe suggests that, for other ice shelves, observed strong dh/dt signals over short time periods do not necessarily indicate ice shelf instability.
Exploitation Route Antarctic research of the Amery ice shelf can be continued through longer GNSS times series.
Sectors Education,Environment