Modeling subglacial water routing at Paakitsoq, W Greenland

Abstract

The functioning of the Greenland Ice Sheet's subglacial drainage system and its effect on ice dynamics have been inferred largely from hypothetical hydrology dynamics models and from analysis of satellite data and in situ GPS measurements. Despite this, there is still uncertainty about how the surface hydrology interacts with the subglacial drainage system and affects basal water pressures and ice flow, especially over annual time scales. To address this, we developed a high spatial (100 m) and temporal (1 h) resolution, distributed, physically based, subglacial hydrological model, and applied it to the Paakitsoq region, western Greenland. The model is driven with moulin input hydrographs calculated by a surface routing and lake filling/draining model, forced ultimately with distributed hourly runoff calculated by a surface mass balance model. Key outputs from the model are spatially and temporally varying subglacial water pressures and proglacial stream hydrographs. Early in the melt season, short spikes in water pressure lasting less than a day occur as a result of lake drainage events. During midsummer, there are sustained periods of high water pressure lasting days to weeks, even at times when the subglacial system is inferred to be predominantly efficient. Later in the summer, large diurnal fluctuations in water pressure occur with peaks regularly exceeding ice overburden pressure superimposed on a gradually declining trend. These phenomena support the results of previous hypothetical modeling efforts and inferences drawn from GPS measurements.