Winter sea-ice properties in Marguerite Bay, Antarctica

Abstract During the winter 2001 and 2002 cruises of the SO-GLOBEC experiment, we investigated the morphological properties, growth processes, and internal permeability of sea ice in the Marguerite Bay area of the Western Antarctic Peninsula. There was considerable interannual variability in ice thickness with, average values of 62 cm in 2001 and 102 cm in 2002, with medians of 43 and 68 cm, respectively. Snow depth averaged 16 cm in 2001 and 21 cm in 2002. At 40% of the thickness holes in 2001 and 17% in 2002, a combination of deep snow and thin ice resulted in negative freeboard and the potential for surface flooding. Ice production was strongly influenced by the snow cover. Deep snow resulted in negative freeboard, surface flooding, and the formation of snow–ice, but also limited columnar ice growth on the bottom of the ice. A stratigraphic analysis of ice thin sections showed that more than half of the ice sampled was granular and that virtually all of the upper 20 cm of the ice cover was granular. Stable isotope (δ 18 O) analysis of samples from 2001 indicated that snow–ice formation at the surface contributed significantly to ice formation. Two-thirds of the cores had some snow–ice and 15% of the ice sampled in 2001 was snow–ice. For 95% of the ice sampled the combination of warm ice temperatures and large salinities resulted in brine volumes that were greater than the percolation threshold of 5%. Autonomous mass balance buoys indicated that the ice was above the percolation threshold throughout late winter and spring. The exceeding of the percolation threshold allows continuous flooding to occur throughout the late winter–spring period. The WAP sea-ice therefore represents a warm “end-member” of the sea-ice covers of Antarctica. An expected consequence of the lengthy flooding condition at the snow/ice interface is an earlier onset of an algal bloom in the flooded snow than elsewhere in Antarctic sea ice.