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Understanding Variability in Ice Dynamics at the Margins of the Greenland Ice Sheet

UTIG Seminars

Understanding Variability in Ice Dynamics
at the Margins of the Greenland Ice Sheet

Ginny Catania

When: Friday, August 31, 2012, 10:30 a.m. to 11:30 a.m.
Join us for coffee beginning at 10:00 a.m.
Where: Seminar Conference Room, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758
Host: Nick Hayman, UTIG

Click for a Live Broadcast.

image from Dr. Catania's talk

The margins of the Greenland Ice Sheet have undergone rapid and significant changes in recent years. This includes drawdown of the ice sheet surface, acceleration of both land and ocean-terminating ice, and retreat of outlet glaciers. Predicting the magnitude of and causes behind these changes is difficult. In part, this is because of a lack of observational data, but also because there is no consensus on the relative importance of various physical processes that control glacier changes. Much research has focused lately on the role that meltwater plays in ice sheet acceleration. Meltwater reaches the bed through moulins, which are likely formed from crevasses in locations where plentiful meltwater supply is generated. Some moulins can remain open and partially water-filled all year, which suggests that routing of meltwater to the bed remains spatially fixed for some period of time. Meltwater supplied via moulins causes ice sheet acceleration on daily, seasonal and event time scales although longitudinal flow coupling can explain many of the smaller variations in speed near and above the equilibrium line. Unlike in alpine glaciers, subglacial water pressure is out of phase with ice speed, while the water levels measured in moulins is in phase with ice speed. This suggests that the moulins are the primary pathway for getting water to the bed in Greenland and that water input through moulins drives localized fast flow. In addition to this we find that air temperature does not directly translate into increased sliding as suggested by many authors and this suggests evolution of the subglacial conduit system over time. These observations suggest that we need to model the subglacial hydrology of the Greenland ice sheet as supplied from point sources to an growing/shrinking conduit system that induces local slip events, which propagate outwards radially from the moulin.