Variability of Basal Meltwater Generation During Winter, Western Greenland Ice Sheet

Abstract

Abstract. Basal sliding in the ablation zone of the Greenland Ice Sheet is closely associated with water from surface melt introduced to the bed in summer, yet melting of basal ice also generates subglacial water year-round. Assessments of basal melt rely on modelling with results strongly dependent upon assumptions with poor observational constraint. Here we use surface and borehole measurements to investigate the generation and fate of basal meltwater in the ablation zone of Isunnguata Sermia basin, Western Greenland. The observational data are used to constrain estimates of the heat and water balances, providing insights into subglacial hydrology during the winter months when surface melt is minimal or non-existent. Despite relatively slow ice flow speeds during winter, the basal meltwater generation from sliding friction remains many fold greater than that due to geothermal heat flux. A steady acceleration of ice flow over the winter period at our borehole sites can cause the rate of basal water generation to increase by up to 20 %. Borehole measurements show high but steady basal water pressure, rather than monotonically increasing pressure. Ice and groundwater sinks for water do not likely have sufficient capacity to accommodate the meltwater generated in winter. Analysis of basal cavity dynamics suggests that cavity opening associated with flow acceleration likely accommodates only a portion of the basal meltwater, implying a residual is routed to the terminus through a poorly connected drainage system. A forcing from cavity expansion at high pressure may explain observations of winter acceleration in Western Greenland.

Future Atmospheric Rivers in Antarctica : intensity and impacts

“…Moreover, the GCM used cannot represent indirect effects such as the moistening of the firn and changes in snow albedo. The humidification of firn at depth also has an impact on melting processes (Harper et al, 2023) and on ice shelf destabilization (erosion and hydro-fracturing, (Pollard et al, 2015)) like at Amery ice shelf. Studies with more detailed models in key regions are thus needed to better quantify the total impacts on the overall mass balance, as well as other potential impacts, for example on ecosystems such as penguin colonies (Ganendran et al, 2016).…”

Seasonal evolution of basal environment conditions of Russell sector, West Greenland, inverted from satellite observation of surface flow

“…The most plausible hypothesis is that changes in point-B-like areas are mainly driven by changes in longitudinal stresses induced from the accelerating surroundings (such as point A) and are not a response to local variations in water pressure. In detail, we interpret annual friction and ice speed changes at point B as follows: from January to May, the gradual recharge of the subglacial water system locally reduces the friction, and the velocity slowly increases (Van De Wal et al, 2015;Harper et al, 2021). In May, when surface melting begins, local topography and/or organization of the hydrological system do not lead to an increase in water pressure and consequent facilitation of sliding.…”