Subglacial lake activity beneath the ablation zone of the Greenland Ice Sheet

Abstract. Hydrologically active subglacial lakes can drain large volumes of water and sediment along subglacial pathways, affecting the motion and mass balance of ice masses, and impacting downstream sediment dynamics. Only seven active lakes have been reported beneath the Greenland Ice Sheet (GrIS) to date, and thus a systematic understanding of their spatial distribution and dynamic processes is still lacking. Here, using the ICESat-2 ATL11 data, we identified 61 active subglacial lakes, 59 of which have not been previously reported. The identification of active subglacial lakes beneath the GrIS is complicated by the occurrence of supraglacial lakes, which also fill and drain, and are hypothesized to be almost co-located. However, the ability of ICESat-2 to penetrate through shallow surface water allowed us to correct the elevation provided by the ATL11 data. A significant localized elevation anomaly was still measured in all detected subglacial lakes after correction, revealing that 18 subglacial lakes are twinned with supraglacial lakes. The active subglacial lakes have large upstream hydrological catchments and are located near or below the equilibrium line. These observations suggest that active subglacial lakes are widespread components of the subglacial drainage system and provide critical information for understanding their activity.