Seeing in the dark: evolution of supraglacial lakes on the Greenland and Antarctic ice sheets during polar night

格陵兰和南极冰盖造成了全球海平面上升的三分之一，这是由于冰川融化加剧和冰流变化造成的。冰川上湖（SGLs）由于融化的增加而变得越来越丰富，并且在它们干涸时可以加速冰的流动（Leeson et al., 2015）。SGLs可能是冰盖系统中的一个潜在反馈，因为更快的冰流导致变薄，从而导致更多的融化和SGLs形成。仅在格陵兰岛就有成千上万的SGLs，因此了解它们的演变是很重要的，特别是关于它们的排水行为。直到最近，人们还认为SGL排水只发生在夏季，但我们现在有令人信服的证据表明冬季有少量排水事件（Benedeck et al., 2021）。冬季湖泊排水可能比夏季湖泊排水对冰流的影响更大，因为冬季冰下更滑。通常使用光学卫星图像（例如Corr et al., 2021）对SGLs进行大规模研究，但是由于极夜的黑暗，光学卫星无法在冬季对冰盖表面进行成像。然而，机器学习和数据科学的最新进展意味着现在可以“在黑暗中看到”，并在冬季使用合成孔径雷达（SAR）数据绘制冰川上的湖泊。本博士将利用这些进展，在冬季对格陵兰岛和南极洲的冰川上湖泊进行第一次大规模的清查，并将利用这些清查来了解冬季湖泊排水的规模，并检查其对冰流的影响。

The Greenland and Antarctic Ice Sheets are responsible for about a third of global sea level rise as a result of increased melting and changes to ice flow. Supraglacial lakes (SGLs) are becoming more abundant as a result of increased melting, and can act to speed up ice flow when they drain (Leeson et al., 2015). SGLs may be a potential feedback in the ice sheet system, since faster ice flow leads to thinning, which leads to more melting and SGL formation. There are tens of thousands of SGLs on Greenland alone, and so understanding their evolution is important, especially with respect to their drainage behavior. Until recently it was thought that SGL drainage occurs only during the summer months, however we now have compelling evidence for a small number of winter time drainage events (Benedeck et al., 2021). Winter lake drainage is likely to have a larger impact on ice flow than summer lake drainage because it is more slippery under the ice in winter. SGLs are typically studied at scale using optical satellite imagery (e.g. Corr et al., 2021), however optical satellites are unable to image the ice sheet surface in winter due to the darkness of the polar night. Recent advances in machine learning and data science however mean that it is now possible to 'see in the dark' and map supraglacial lakes during winter using Synthetic Aperture Radar (SAR) data. This PhD will exploit these advances to perform the first wide scale inventory of supraglacial lakes on Greenland and Antarctica during winter, and will use this inventory to understand the scale of wintertime lake drainage and examine its impact on ice flow.