Estimating supraglacial lake bottom ablation rates by integrating ICESat-2 repeat track data and multi-temporal sentinel-2 imagery

Abstract

Supraglacial lakes are widely distributed across the Greenland Ice Sheet (GrIS) each summer. The resulting meltwater-enhanced ablation effect plays a critical role in understanding the GrIS surface mass balance but remains poorly quantified. Inspired by the insight that longer meltwater persistence leads to stronger meltwater-enhanced ablation, this study proposes a novel method to directly estimate supraglacial lake bottom ablation rates at centimeter-per-day scale using satellite observations. First, we map multi-temporal supraglacial lake extents from Sentinel-2 imagery to estimate cumulative meltwater-covered days. Then, we derive ablation depths at the lake bottom and surrounding bare ice by differencing ICESat-2 repeat track data acquired before and during the melt season. Next, we perform linear fitting between lake bottom ablation depths and cumulative meltwater-covered days along the ICESat-2 tracks to calculate both the lake bottom ablation rate and the bare ice ablation rate. Finally, we evaluate the magnitude of the meltwater-enhanced ablation effect. We apply this method to 26 supraglacial lakes across the GrIS and identify a positive linear relationship between lake bottom ablation depths and cumulative water-covered days (mean Pearson correlation coefficient r = 0.70 ± 0.14, p < 0.001). The fitted mean lake bottom ablation rate (4.50 ± 1.15 cm/day) significantly exceeds the mean bare ice ablation rate (1.98 ± 0.52 cm/day). Meltwater in supraglacial lakes therefore enhances ablation rate by ∼ 1.3 ± 0.5 times, with values ranging from 0.6 to 2.4, consistent with previous field measurements (1.1–1.4 times) and numerical model simulations (1.1–1.7 times). In summary, this study provides a first quantitative satellite-based estimate of meltwater-enhanced ablation across the GrIS under varying ablation intensities, and may improve our understanding of GrIS surface melt process.