A comparison of supraglacial lake characteristics and drainage dynamics in Southwest Greenland between an extreme high, and an extreme low, melt season

Mass loss from the Greenland Ice Sheet (GrIS) is predicted to contribute up to 10 cm to global sea level rise by 2100. This mass loss is due to both increased meltwater production and therefore increased runoff, which is occurring at higher elevations on the ice sheet, as well as ice-dynamical feedback processes such as supraglacial lakes (SGLs) draining rapidly to the ice sheet bed; enhancing basal sliding. Therefore, the specific processes through which SGLs drain has an important control on mass loss from the GrIS. This highlights the need for high-resolution, integrated datasets that provide a comprehensive view of supraglacial hydrological networks, including SGL drainage events, on the GrIS.

Here, we compare SGL characteristics and drainage dynamics of a southwestern sector of the GrIS throughout both an extreme high melt season (2019) and an extreme low melt season (2018). SGLs are delineated throughout both the summer seasons from Sentinel-2 and Landsat 8 optical imagery using threshold-based normalized difference water index (NDWI) methods followed by extensive manual enhancement to increase accuracy. SGL depths are calculated using a radiative transfer model and individual lake volume is determined. The resulting meltwater maps have a spatial resolution of 10 to 30 m and have a temporal resolution of weekly to fortnightly. The following SGL characteristics are determined: i) area; ii) volume; iii) elevation; iv) ice surface slope; and v) solidity. SGL drainage dynamics are analysed by tracking lakes through the duration of each melt season and determining if a lake drains rapidly by hydrofracture, slowly drains via channel incision and overflow, or does not drain and instead refreezes at the end of the melt season. To do this, we use the Fully Automated supraglacial lake area and volume tracking at enhanced resolution (FASTER) algorithm, developed by Williamson et al. (2018).

As temperatures continue to increase, the frequency of high melt years like 2019 will also increase. As such, it ever more important to understand supraglacial meltwater characteristics and dynamics in high melt seasons, especially compared to years with limited melt.