Ice flow dynamics and surface meltwater flux at a land-terminating sector of the Greenland ice sheet

Abstract

ABSTRACT. We present satellite-derived velocity patterns for the two contrasting melt seasons of 2009-10 across Russell Glacier catchment, a western, land-terminating sector of the Greenland ice sheet which encompasses the K(angerlussuaq)-transect. Results highlight great spatial heterogeneity in flow, indicating that structural controls such as bedrock geometry govern ice discharge into individual outlet troughs. Results also reveal strong seasonal flow variability extending 57 km up-glacier to 1200 m elevation, with the largest acceleration (100% over 11 days) occurring within 10 km of the margin coincident with spring melt. By late July 2010, 2 weeks before peak melt and runoff, 48% of the 2400 km 2 catchment had slowed to less than the winter mean. This observation supports the hypothesis that the subglacial hydrological system evolves from an inefficient distributed to an efficient drainage system, regulating flow dynamics. Despite this, the cumulative surface flux over the record melt year of 2010 was still greater compared with the perturbation over the average melt year of 2009. This study supports the proposition that local surface meltwater runoff couples to basal hydrology driving ice-sheet dynamics, and although the effect is nonlinear, our observations indicate that greater meltwater runoff yields increased net flux over this sector of the ice sheet.

Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed

“…We isolated and tested the extent to which SGL drainage controls seasonal ice flow by performing experiments in which the model was driven by local runoff production delivered to the bed in each SGL sub-catchment (see Methods). Using total daily runoff volumes 43 , we found that modelled ice flow was fastest in late July ( 12,54 . This discrepancy is not surprising since both theory and observations demonstrate that it is the variability rather than the absolute volume of meltwater delivery to the bed that drives ice flow dynamics 19,27,28,51,55 .…”

“…The 2010 record of SGL drainage volumes was first used to drive the model. Patterns of surface velocity derived from TerraSAR-X satellite image pairs acquired with 11-day separation and centred on 19 June, 22 July and 11 November 53,54 are shown in Fig. 1 together with maps of modelled surface velocity averaged over the exact same periods.…”

Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

“…Increased water pressures reduce basal drag by decreasing ice-bed coupling, leading to faster ice flow. Early in the summer, surface runoff drains into an inefficient hydrological system, elevating water pressures, and accelerating ice flow Fitzpatrick et al, 2013;Sundal et al, 2011). As the melt season progresses, a channelized system that efficiently drains water develops.…”

“…Coupling recent hydrological models with ice sheet models allows for important feedback between the distributed system and ice velocities (Bartholomaus et al, 2011;Hoffman and Price, 2014) and allows explicit comparison between GPS velocities and model output. Comparisons to surface ice velocity measurements are an important means for validating subglacial hydrological models and provide a method for constraining poorly understood aspects of subglacial hydrology (see review by Flowers, 2015). Present challenges in applying coupled ice dynamicshydrology models to the GrIS margin for modelling seasonal evolution include the values of parameters, the form of the sliding law which relates water pressures to basal drag, and whether the models presently include the necessary elements.…”

“…This paper aims to model summer ice flow in the landterminating Russell Glacier area of western Greenland for three contrasting melt seasons using a multicomponent model approach similar to the previous work of Arnold et al (1998) and Flowers and Clarke (2002) on alpine glaciers. The model is then used to test the ice sheet response to higher melt input.…”