CHARACTERISTICS AND DISTRIBUTION PATTERNS OF SNOW AND METEORIC ICE INTHE WEDDELL SEA AND THEIR CONTRIBUTION TO THE MASS-BALANCE OF SEA-ICE

Based on snow- and ice-thickness measurements at > 11000 points augmen ted by snow- and ice-core studies during 4 expeditions from 1986-92 in the Weddell Sea, we describe characteristics and distribution pattern s of snow and meteoric ice and assess their importance for the mass ba lance of sea ice. For first-year ice (FY) in the central and eastern W eddell Sea, mean snow depth amounts to 0.16 m (mean ice thickness 0.75 m) compared to 0.53 m (mean ice thickness 1.70 m) for second-year ice (SY) in the northwestern Weddell Sea. Ridged ice retains a thicker sn ow cover than level ice, with ice thickness and snow depth negatively correlated for the latter, most likely due to aeolian redistribution. During the different expeditions, 8, 15, 17 and 40% of all drill holes exhibited negative freeboard. As a result of flooding and brine seepa ge into the snow pack, snow salinities averaged 4 parts per thousand. Through O-18 measurements, the distribution of meteoric ice (i.e., pre cipitation) in the sea-ice cover was assessed. Roughly 4% of the total ice thickness consist of meteoric ice (FY 3%, SY 5%). With a mean den sity of 290 kg/m3, the snow cover itself contributes 8% to total ice m ass (7% FY, 11% SY). Analysis of deltaO-18 in snow indicates a local m aximum in accumulation in the 65 to 75-degrees-S latitude zone. Hydrog en peroxide in the snow has proven useful as a temporal tracer and for identification of second-year floes. Drawing on accumulation data fro m stations at the Weddell Sea coast, it becomes clear that the onset o f ice growth is important for the evolution of ice thickness and the i nteraction between ice and snow. Loss of snow to leads due to wind dri ft may be considerable, yet is reduced owing to metamorphic processes in the snow column. This is confirmed by a comparison of accumulation data from coastal stations and from snow depths over sea ice. Temporal and spatial accumulation patterns of snow are shown to be important i n controlling the sea-ice cover evolution.