Accurate knowledge of glacier bed topography is critical for quantifying ice volumes and modelling ice and subglacial hydrology dynamics. Bed topography observations are traditionally obtained from airborne and ice penetrating radar, which offers the crucial advantage of recovering the detailed glacier structure over a range of scales. A main difficulty with radar, however, is that waves can be strongly scattered and attenuated by englacial heterogeneities, in particular by water inclusions, which can potentially limit the applicability of the technique under certain conditions. Here we present a case study on Isunguata Sermia, West Greenland, where we conducted an ice penetrating radar survey together with dense seismic array acquisitions from 87 nodes spread over a 1 km2 area. We show that, in the area of investigation, radar observations were only partially successful in identifying the ice-bed interface, likely due to the thick warm ice, presence of some surface water and near-surfacing crevassing and other englacial structures. The H/V analysis performed over the seismic array yielded surprisingly coherent estimates of ice thickness, along with its spatial variation along and across the glacier. These findings raise questions about the interpretation of traditional radar measurements under certain glacier conditions, and how dense seismic arrays could retrieve bed topography more systematically.

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.

This study presents high resolution mapping of moulins located above three subglacial lakes at Isunguata Sermia. Moulins are the primary pathway for transferring supraglacial melt to englacial and subglacial environments. The formation of moulins has been explained by the flow of water into a notch, associated with glacier structures and incision of supraglacial streams, which are directly related to glacier morphology and dynamics. Meltwater input to subglacial systems, along with glacier dynamics, will in turn affect the development of subglacial meltwater networks, which control glacier morphology and dynamics. This study focusses on Isunguata Sermia, West Greenland, which has an active subglacial drainage system that includes distinct subglacial lakes. Hydrologically connected or active subglacial lakes may be directly influenced by water input from supraglacial to englacial systems via moulins during the ablation season. Moulins were mapped using a combination of high resolution orthomosaics and digital elevation models derived from uncrewed aerial vehicle flights. Moulin locations and morphologies were compared with glacier structures, ice flow velocities, and bed topography. We reveal a distinct pattern of moulin locations relative to each subglacial lake and the locations of primary and secondary glacier structures an supraglacial hydrology. Furthermore, we also outline a clear morphological pattern, wherein morphology of moulins varies distinctly at with the location of each subglacial lake between vertical shafts, crevasse associated and keyhole morphology. These observations will be used to consider the efficiency of meltwater routing from the surface to the bed, and the potential for inputs to subglacial lakes, and the wider implications for varying ice flow velocity and evolution of the subglacial drainage system.