Blanketing snow and ice; constraints on radiocarbon dating deglaciation in East Antarctic oases

Abstract

Radiocarbon dating of marine, lacustrine or terrestrial biogenic deposits is the main technique used to determine when deglaciation of the oases of East Antarctica occurred. However, at many of the oases of East Antarctica, including the Schirmacher Oasis, Stillwell Hills, Amery Oasis, Larsemann Hills, Taylor Islands and Grearson Oasis, snow and ice presently forms extensive blankets that fills valleys and some lake basins, covers perennial lake ice and in places overwhelms local topography to form ice domes up to hundreds of square kilometres in area. Field observations from Larsemann Hills and Taylor Islands suggest that under these conditions, terrestrial and lacustrine biogenic sedimentation is neither widespread nor abundant. If similar conditions prevailed in and around the oases immediately following retreat of the ice sheet, then a lengthy hiatus might exist between deglaciation and the onset of widespread or abundant biogenic sedimentation. As a result, radiocarbon dating might be a clumsy tool with which to reconstruct deglaciation history, and independent dating methods that record emergence of the hilltops from the continental ice must be employed as well.

Late Quaternary deglaciation and climate history of the Larsemann Hills (East Antarctica)

“…In Palmer Deep and the Prydz Bay region these sediments are considered as glacial sediments, deposited after melting of the ice sheet (Domack et al, 1998;Brachfeld et al, 2002), but the precise origin of these sediments in lake-sediment cores is still debated. On the continent, these sediments are considered to be reworked glacial till, washed into the lake basins from drift deposits that covered the oases after the LGM (Zwartz et al, 1998) or derived directly from floating glacier ice mass or blanketing snow and ice (sensu Gore, 1997) in the lake basin (Verkulich et al, 2002). In both cases significant melting has occurred of glacial or snow coverage of the catchment area, suggesting that warmer conditions than before may have occurred in the region.…”

Evidence for the continued existence of Abraxas Lake, Vestfold Hills, East Antarctica during the Last Glacial Maximum

“…These lakes typically have extremely clear ice covers; in contrast, the ice cover on Abraxas Lake would, as a result of the salinity of the lake, have optical characteristics much more like sea ice which transmits far less solar radiation. Any snow present on the ice surface would further reduce the PAR reaching the water column (Gore 1997). Primary productivity in the McMurdo Dry Valleys lakes also occurs in moats that form during summer; the near absence of organic carbon from this part of the sediment in Abraxas Lake suggests that moat formation did not occur, as within lake processes would be expected to transport at least some of this material to the depocentre of the lake.…”

Deglaciation and weathering of Larsemann Hills, East Antarctica

“…Larsemann Hills is a Proterozoic terrain consisting of a layered complex of cordierite-and iron-titanium-rich gneiss, leucogneiss and a dominant heterogeneous migmatitic paragneiss composed of discontinuous lenses of metapelite with abundant sillimanite, spinel, cordierite, garnet, K-feldspar and biotite (Stuwe et al 1989, Dirks et al 1993, Carson et al 1995. The two main peninsulas -Broknes to the east and Stornes to the west -are different in that the former is largely free of ice and snow whereas the latter is largely snow covered, and hosts an ice dome 4.9 km 2 in area and 170 m altitude (Gore 1997). Hill summits reach 170 m above sea level, with the highest terrain occurring near the ice edge.…”