Late Quaternary Paleoceanographic Changes over the Conrad Rise and off Lutzow-Holm Bay in the Indian Sector of the Southern Ocean

The Southern Ocean plays a very important role in the global climate system on the present and geologic past. The Southern Ocean has also become a region of paleoceanographic focus because of its key role in global deep-water circulation and its potential significance for the global carbon. For example, it has been proposed that primary production was higher and utilization of preformed nutrients in surface waters was more efficient in the glacial Southern Ocean than today, effectively lowering the glacial atmospheric CO2 concentration. To resolve the causes and processes of atmospheric CO2 change, it is important to understand mechanisms and processes of sub-systems in the Antarctic Cryosphere such as a change of biological productivity, sea surface temperature, surface water frontal system, sea-ice distribution, and East Antarctic ice sheet during the glacial-interglacial climate cycle. We collected three sediment cores from the Conrad Rise (COR-1PC, 54.27°S, 39.77°E, 2864m), the Gunnerus Ridge (GUR-1MC, 66.27°S, 33.42°E, 1348m), and off Lutzow-Holm Bay (LHB-3PC, 66.00°S, 40.00°E, 4469m) in the Indian Sector of the Southern Ocean during the R/V Hakuho- maru cruise KH07-4 Leg.3. Age models of the cores were established by radiocarbon dating of planktonic foraminifera, diatom biostratigraphy and relative paleointensity curve of the geomagnetic field. At the core LHB-3PC, biogenic opal contents indicate that the marine productivity was enhanced at interglacials in the high-latitudinal Southern Ocean. Based on the bathymetric mapping, subbottom profiling, and multi-channel seismic reflection survey, a dune- like bedform (mudwave) exists on the southwest slope of the Conrad Rise. The mudwaves are about 30 m in altitude and a few hundred meters in wavelength. The wave-field is located in water depths of 2000-3200 m. Similar wavy sedimentary structures are recognized below the seafloor in the seismic profile on the Conrad Rise. Such deep-sea mudwaves have been reported at the northern Weddell Sea, which influenced by the Antarctic Bottom Water (AABW) (Howe et al., 1998), and at the Gardar Drift in the North Atlantic, where is also influenced by the North Atlantic Deep Water (NADW) (e.g., Manley and Caress, 1994). Lithology of core COR-1PC is diatom ooze, and sedimentation rate is very high up to about 40 cm/ka. Thus, the sediment drift was deposited with mudwaves on the Conrad Rise, which was developed by influences of NADW and/or AABW.