Firn structure of Larsen C Ice Shelf, Antarctic Peninsula, from in-situ geophysical surveys

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Bernd Kulessa1, Alex Brisbourne2, Peter Kuipers Munneke3, Suzanne Louise Bevan4, Adrian J Luckman4, Bryn P Hubbard5, David Ashmore5, Paul Holland2, Daniela Jansen6, Edward C King2, Martin O'Leary4 and Daniel McGrath7, (1)Swansea University, College of Science, Cardiff, CF5, United Kingdom, (2)NERC British Antarctic Survey, Cambridge, United Kingdom, (3)Institute for Marine and Atmospheric Research Utrecht, Utrecht, Netherlands, (4)Swansea University, Swansea, United Kingdom, (5)Aberystwyth University, Aberystwyth, United Kingdom, (6)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany, (7)USGS Alaska Science Center, Anchorage, AK, United States
Rising surface temperatures have been causing firn layers on Antarctic Peninsula ice shelves to compact, a process that is strongly implicated in ice shelf disintegration. Firn compaction is expected to warm the ice column and given sufficiently wet and compacted firn layers, to allow meltwater to penetrate into surface crevasses and thus enhance the potential for hydrofracture. On Larsen C Ice Shelf a compacting firn layer has previously been inferred from airborne radar and satellite data, with strongly reduced air contents in Larsen C’s north and north-west. The hydrological processes governing firn compaction, and the detailed firn structures they produce, have so far remained uncertain however. Using integrated seismic refraction, MASW (Multi-Channel Analysis of Surface Waves), seismoelectric and ground-penetrating radar (GPR) data, we reveal vertical and horizontal changes in firn structure across Larsen C Ice Shelf. Particular attention is paid to the spatial prevalence of refrozen meltwaters within firn, such as the massive subsurface ice layer discovered recently by the NERC-funded MIDAS project in Cabinet Inlet in Larsen C’s extreme northwest. Such ice layers or lenses are particularly dramatic manifestations of increased ice shelf densities and temperatures, and contrast sharply with the relatively uncompacted firn layers present in the ice shelf’s southeast. We consider our observations in the context of a one-dimensional firn model for Larsen C Ice Shelf that includes melt percolation and refreezing, and discuss temporal changes in firn layer structures due to surface melt and ponding.