Improved monitoring of subglacial lake activity in Greenland

Abstract. Subglacial lakes form beneath ice sheets and ice caps if water is available and if bedrock and surface topography are able to retain the water. On a regional scale, the lakes modulate the timing and rate of freshwater flow through the subglacial system to the ocean by acting as reservoirs. More than 100 hydrologically active subglacial lakes that drain and recharge periodically have been documented under the Antarctic Ice Sheet, while only approximately 20 active lakes have been identified in Greenland. Active lakes may be identified by local changes in ice topography caused by the drainage or recharge of the lake beneath the ice. The small size of the Greenlandic subglacial lakes puts additional demands on mapping capabilities to resolve the evolving surface topography in sufficient detail to record their temporal behaviour. Here, we explore the potential for using CryoSat-2 swath-processed data, together with TanDEM-X digital elevation models, to improve the monitoring capabilities of active subglacial lakes in Greenland. We focus on four subglacial lakes previously described in the literature and combine the data with ArcticDEMs to obtain improved measurements of the evolution of these four lakes. We find that with careful tuning of the swath processor and filtering of the output data, the inclusion of these data, together with the TanDEM-X data, provides important information on lake activity, documenting, for example, that the ice surface collapse basin on Flade Isblink Ice Cap was 50 % (30 m) deeper than previously recorded. We also present evidence of a new, active subglacial lake in southwestern Greenland, which is located close to an already known lake. Both lakes probably drained within 1 month in the summer of 2012, which suggests either that they are hydrologically connected or that the drainages were independently triggered by extensive surface melt. If the hydrological connection is confirmed, this would to our knowledge be the first indication of hydrologically connected subglacial lakes in Greenland.