Lake Ice Break-Up in Greenland: Timing and Spatio-Temporal Variability.

Synthetic aperture radar (SAR) data from the Sentinel-1 (S1) mission with its high temporal and spatial resolution allows for an automated detection of lake ice break-up timings from surface backscatter differences across South (S), Southwest (SW) and Northwest (NW) Greenland (< 71° N latitude) during the period 2017 to 2021. Median break-up dates of the 563 studied lakes range between 8 June and 10 July, being earliest in 2019 and latest in 2018. There is a strong correlation between break-up date and elevation, while no relationship with latitude and lake area could be observed. Lake-specific median break-up timings for 2017–2021 increase (i.e., are later) by 3 days per 100 m elevation gain. When assuming an earlier break- up timing of 8 days which corresponds to the observed median variability of ± 8 days, the introduced excess energy due to a changing surface albedo from ice to water translates to melting 0.5 m thick ice at the melting point or heating up a water depth down to 35 m by 1 K across the entire surface area of each respective lake. Upscaling the results to 100486 lakes across the regions S, SW and NW which correspond to 64.5 % of all lakes or 62.1 % of the overall lake area in Greenland yields an estimate of 1.8 * 10⁶ TJ additional energy input. This translates to melting 5.8 Gt ice at the melting point or warming 432.3 Gt water by 1 K. [ABSTRACT FROM AUTHOR]