Geophysical investigation of active subglacial lake dynamics in West Greenland

Abstract

Hydrologically active subglacial lakes modulate subglacial hydrology, ice motion, microbial habitats, biogeochemical fluxes, and subglacial and proglacial geomorphic activity. The recent potential identification of active subglacial lakes beneath the ablation area of the Greenland Ice Sheet from repeat satellite altimetry data suggests that they are a significant yet poorly constrained component of the ice sheet hydrological system. These subglacial lakes, which are presumably fed by both supraglacial and subglacial water inputs, appear to be highly dynamic features that fill gradually (i.e. over years) but drain rapidly (i.e. hours to days), causing high discharge flood events observed in the proglacial area. While remote sensing observations constrain lake dynamics to a coarse temporal and spatial resolution the precise timing of lake filling and drainage and the detailed effect on ice dynamics can only be determined from field-based measurements. Here we present initial results from a comprehensive geophysical investigation of subglacial lake dynamics beginning in April 2023. We report measurements of horizontal and vertical ice surface motion together with horizontal strain rates from an array of 11 GNSS receivers installed across three juxtaposed subglacial lakes on Isunnguata Sermia — an ~6 km wide land-terminating outlet glacier in West Greenland. We combine these GNSS data with autonomous phase-sensitive radio echo sounding measurements of ice thickness and vertical strain to construct a time series of lake filling and drainage spanning the 2023 melt season. To investigate inter-relationships between subglacial lake hydrology and ice dynamics at both short (hourly) and seasonal timescales, we supplement these time series with data from an array of seismometers installed in between two of the lakes and at the glacier terminus, together with several kilometres of radio echo sounding measurements of ice thickness.