Wednesday, April 16, 2014
Environmental Science and Engineering Seminar
Is there a need for an ice-sheet—ocean observation system?
Knut Christianson, Postdoctoral Scientist, Department of Environmental Studies and Physics, St. Olaf College
As the sole remaining marine ice sheet (an ice sheet grounded below sea level), the future stability of West Antarctica is uncertain. Paleoglaciology and modern observations show that marine ice sheets can exhibit threshold behavior, with intervals of stability punctuated by rapid retreat, but stabilizing factors are poorly understood due to lack of data on the ice-sheet bed. Much of this threshold behavior is thought to result from processes occurring at the grounding zone, where the ice sheet gradually goes afloat. Here we review geophysical data and modeling results that show interactions between ocean water, subglacial hydrology, sediment, and tidal processes are complex and occur across the several-kilometers-wide grounding zone. Our results indicate that ongoing sediment deposition can stabilize grounding-line position. However, this competes with ocean-driven melt across the grounding zone. Our modeling indicates that ice-stream stabilization on bedrock highs narrower than the length of the tidally-influenced grounding zone may be ephemeral if warm ocean water is present. Stabilization is, however, significantly enhanced by effectively plastic beds and zones of high bed friction, which can be created via till compaction from tidal flexure. Thus accurate future projections of sea level require additional mapping of bed conditions, better understanding of grounding-zone processes, and inclusion of these processes in whole-ice-sheet models. A key advance would be the establishment of an integrated ice-sheet—ocean observation system, which would allow development of benchmark datasets and alert scientists to monitor areas of the ice sheet prone to especially rapid change.