Detecting and monitoring subglacial lakes beneath the Greenland Ice Sheet

Bowling, Jade and McMillan, Mal and Leeson, Amber (2022) Detecting and monitoring subglacial lakes beneath the Greenland Ice Sheet. PhD thesis, Lancaster University.

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Abstract

In this thesis I develop novel methods and datasets, using airborne radio-echo sounding and high-resolution satellite-derived digital elevation models, to improve the understanding of subglacial lake distribution and activity beneath the Greenland Ice Sheet. First, I use 23 years of airborne radio-echo sounding data, totalling over 500,000 km, to conduct the first systematic ice sheet-wide survey of subglacial lakes beneath the Greenland Ice Sheet. Following classification of basal reflector properties, I detect over 50 new stable subglacial lakes beneath the Greenland Ice Sheet. Surface elevation data also revealed 2 previously unidentified collapsed ice-surface basins indicative of subglacial lake activity. The results indicate that subglacial lakes are more common than previously thought and differ from those found beneath the Antarctic Ice Sheet both in their size and spatial distribution. Next, I develop a new automated technique using statistical analysis of highresolution, satellite-derived surface elevation data to detect localised elevation changes which are characteristic of subglacial lake drainage events. I then apply this framework to the Greenland Ice Sheet within 50 km of the ice margin to classify 7 potential active subglacial lakes which could be used as candidates for future geophysical surveys and further monitoring to understand to understand the role they play within the subglacial hydrological system. Finally, using the results from the previous chapter, I utilise a variety of satellite datasets to analyse a unique active subglacial lake in Northern Greenland. From the observational record, the subglacial lake appears to have drained twice in the past 36 years, in 1990 and 2014, but each event with differing drainage characteristics. In particular, observations of downstream ice surface fracturing and excavation of ice blocks 20 m tall in 2014, suggests that drainage event caused a subglacial outburst flood which propagated to the ice surface. This is the first observation of supraglacial emergence of subglacial flood water in Greenland, indicating more varied drainage mechanisms that are currently not accounted for in numerical ice sheet models.