Paleoceanographic changes in the Southern Ocean off Elephant Island since the Last Glacial Maximum

Abstract

Three sediment cores were collected from the Southern Ocean off Elephant Island by R/V Yuzhmorgeologiya during 2003/2004 Korea Antarctic Research Program. The core site is ideal for reconstructing paleoceanographic changes in response to glacial retreat since the last glacial period because of its location. In order to reveal how the oceanographic changes are associated with ice sheet/sea ice changes since the last glacial period, we measured geochemical proxies, bulk nitrogen isotope, physical properties, and sediment grain size from all cores. Surface water productivity was dominated by diatom production. Surface water productivity was low during the last glacial period under extensive sea ice conditions and became high during the interglacial period under more open ocean conditions. Apparently, surface water productivity seems to be controlled by sea ice concentration. However, bulk nitrogen isotope, nutrient utilization proxy, showed decreased nutrient utilization with increased surface water productivity and increased utilization with decreased surface water productivity, indicating that surface water productivity in the core site is controlled by nutrient availability in association with changes in sea ice extent. Our result indicates that the surface current system, Antarctic Circumpolar Current, is closely related to changes in cryosphere and oceanographic condition. In addition, our result showed surface water productivity decrease during mid to late Holocene with decreasing nutrient utilization, suggesting deepening of mixed layer depth with intensifying surface current. At the same time, sortable silt also supported stronger bottom current intensity. During this time period atmospheric pCO2 in the Antarctic ice core was also increasing. This suggests the strong coupling of cryosphere-ocean-atmosphere in the Southern Ocean off Elephant Island.