[pccgrads] Christianson on "Oceanic forcing of ice-sheet retreat" Nov 15 at 2:30 in OCN 425

UW PCC uwpcc at u.washington.edu
Mon Nov 13 13:55:17 PST 2017


Oceanography Seminar



Knut Christianson,

Assistant Professor, Department of Earth and Space Sciences & Quaternary Research Center

University of Washington



Wednesday November 15th
2:30 pm
Ocean Sciences Building 425
Tea and cookies at 2:15 pm



"Oceanic forcing of ice-sheet retreat"



Abstract:

Ice sheets resting on beds below sea level that deepen toward the ice-sheet interior are susceptible to marine ice-sheet instability. Flow speed at the grounding line (the transition from grounded to floating ice) increases with ice thickness. Thus, initial grounding-line retreat down a sloping bed into thicker ice causes additional ice discharge, thinning, and retreat: a positive feedback. For at least the last two decades, ocean-induced melting has thinned floating ice shelves in West Antarctica’s Amundsen Sea Embayment, initiating widespread grounding-line retreat and increasing ice discharge. Models projecting these changes forward often, but not always, yield eventual ice-sheet collapse. These projections do not generally include ocean temperature forcing on short (seasonal, interannual or decadal) timescales, and thus the cumulative effects of ocean temperature fluctuations on ice flow are unclear. Simultaneous observations of the ice sheet and adjacent ocean remain scarce, so that observational validation of model simulations is rare.



In this talk, I present the first concurrent multiyear (2009–2014) observations of Pine Island Glacier (PIG), its ice shelf, and the adjacent Amundsen Sea. These observations document a low-amplitude glacier slowdown in response to a single transient high-amplitude ocean cooling. The long-term effects of ocean temperature variability on ice flow, however, are not yet known. Furthermore, the inland propagation of ocean-induced changes in ice flow forced from the coast depends critically on basal conditions beneath the grounded ice, which remain difficult to assess using conventional geophysical methods. I close by discussing future plans from two perspectives: (1) efforts to enable longer-term ocean measurements in ice-shelf cavities where observational data are particularly sparse, and (2) advances in geophysical techniques (3-D radar tomography) that allow better diagnosis of ice-sheet bed conditions.





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