Understanding spatial and temporal variability in Supraglacial Lakes on an Antarctic Ice Shelf : A 31-year study of George VI

Barnes, Thomas and Leeson, Amber and McMillan, Mal (2020) Understanding spatial and temporal variability in Supraglacial Lakes on an Antarctic Ice Shelf : A 31-year study of George VI. Masters thesis, Lancaster University.

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Abstract

Floating ice shelves cover ~1.5million km2 of Antarctica’s area, and are important as they buttress land ice, which limits sea level rise. In recent years, several such Antarctic ice shelves have collapsed or retreated. Supraglacial lakes are linked to warm periods and influence the stability of ice shelves through hydrofracture. Climate change induced temperature increases may increase lake presence, thus decreasing stability. Monitoring ‘at risk’ ice shelves is therefore important to understand their likelihood of fracture. George VI is located on the western Antarctic Peninsula, covering ~23200 km2, and has had high lake densities in its northern sector. This study analyses 31 years of imagery to understand the long-term and seasonal dynamics of lake evolution. This is the first study to characterise supraglacial lake variability in the long- and short-term on George VI, thus producing a comprehensive picture of lake evolution. Here I use a semi-automated technique to map lakes in >160 satellite images from Sentinel 2 and Landsat 4-8. Additional influences on stability and lake presence are gauged using climatic and glaciological data. Analysis of recent imagery shows that the apparent high lake density in summer 2020 is not unique on George VI, with 1989-90 having similar densities persisting over ≥3 years. Decadal average temperature and annual summer snowfall are found to be primary controls on lake density at their respective timescales, the former being influenced by changes in the southern annular mode. Climatic controls on an intra-annual scale are complex, with melt, snowfall and temperature influencing lake density. Although lakes are widespread in several years, little evidence has been found of the unstable drainage which preceded neighbouring ice shelf collapse. This study demonstrates the value of frequent monitoring by current generations of optical satellites in lake analysis; and provides the first long-term catalogue of lakes on George VI.