Seasonal and interannual characteristics of supra-glacial lake formation on Nioghalvfjerdsbrae (79 glacier) in northeast Greenland

The retreat and thinning of the large outlet glaciers of the Greenland Ice Sheet, especially in western Greenland, is documented by numerous studies and generally attributed to global warming. Rising temperatures are also responsible for enhanced surface melt during boreal summer, which is reflected by the inland-advancing distribution of supra-glacial lakes (SGL) in the ablation areas. Recently, the marine-terminating glaciers of the northeast Greenland Icestream (NEGIS) have been recognized as reacting sensitively to variations in climate regarding mass conservation, velocities or grounding line position. Still, these glaciers, including Nioghalvfjerdsbrae as the largest outlet glacier of NEGIS, are notoriously understudied.

Here, we present a spatiotemporal time series of SGL on the NEGIS based on Sentinel-2 data from 2016 to 2019, covering the ablation areas of 79 glacier and Zachariae isstrom. Due to the size of the input data, the algorithm series were designed to run fully automated and with open source software alone. Over 1000 individual lakes were identified and tracked over the melting seasons of the four years, including more than 450 time steps with an average temporal resolution of less than two days. Based on this dataset, we analyzed the variations in the melt seasons regarding onset, speed of progression and extent (area- and altitude-wise). Our findings illustrate the difference in magnitude between record-breaking warm (2016) and particularly cold (2018) years, enabling further in-depth analyses of climate-glacier feedback mechanisms. A challenge for the estimation of lake depths/volumes is the lack of in situ measurement, as all available data sets originate from western Greenland. Hence, the accuracy of the calculation based on a digital elevation model would benefit from a future measurement campaign.