C41E-07
Rapid growth and seasonal persistence of efficient subglacial drainage under kilometre thick Greenland ice

Thursday, 17 December 2015: 09:30
3007 (Moscone West)
Jemma Wadham1, Dave Chandler1, Pete Nienow2, Samuel Huckerby Doyle3, Andrew J Tedstone4 and Alun Hubbard II5, (1)School of Geographical Sciences, University of Bristol, Bristol, United Kingdom, (2)University of Edinburgh, Edinburgh, United Kingdom, (3)Aberystwyth University, Aberystwyth, SY23, United Kingdom, (4)University of Edinburgh, School of Geosciences, Edinburgh, United Kingdom, (5)University of Tromsø, Tromsø, Norway
Abstract:
The relationship between surface melt and ice motion partly determines the sensitivity of the Greenland Ice Sheet to climate, and the structure of the subglacial drainage system may be critical in controlling how changing melt-rates will impact on future ice dynamics. However, the extent to which efficient subglacial drainage develops tens of km inland from the ice margin under thick (>1km) ice remains equivocal. In particular, several numerical modelling studies suggest that under such conditions subglacial channels cannot evolve on seasonal timescales, even under extreme inputs of surface meltwater.

Here, we present hydrological and ice-motion data collected in summer 2012 in the vicinity of a moulin located ~40 km from the western margin of the Greenland Ice Sheet, where ice is ~1km thick. Supraglacial discharge into the moulin was monitored from the onset of surface drainage and the tracer sulphur hexafluoride (SF6) was injected into the moulin at repeat intervals and its emergence was monitored at its proglacial river outlet. The tracer results indicate rapid evolution from a slow, inefficient drainage system to a fast, hydraulically efficient system within ~three weeks from the onset of surface drainage. Once an efficient hydrological pathway was established, it remained open - as evidenced by the fast tracer return times - even during periods of low surface melt (~0.01m/d), when discharge into the moulin was <4 m3 s-1 and ceased overnight. Ice motion in the vicinity of the moulin slowed following the establishment of the efficient drainage pathway with a clear diurnal cyclicity driven by variations in supraglacial discharge. 

Our results confirm that hydraulically-efficient subglacial drainage can exist 10s km from the ice sheet margin where ice is ~1km thick, that the drainage configuration can form in a matter of weeks, and that it persists even during cool periods when local surface melt rates and inputs are low.

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