Change in Deep Water Circulation in Southern Drake Passage during the Mid-Pleistocene Transition

Abstract:

Seven gravity cores (2.5~8-m long) from southern Drake Passage were analyzed for magnetic susceptibility, grain size distribution, total organic carbon, and total inorganic carbon content to reconstruct paleoceanographic changes in late Quaternary. Glacial sediments from southern Drake Passage are distinguished from interglacial sediments by their higher magnetic susceptibility and lower total organic carbon, due to the increased influx of magnetic minerals from nearby source areas (South Shetland Islands and northern Antarctic Peninsula) during glacial periods and increased marine productivity during interglacial periods. Correlation among the cores based on magnetic susceptibility indicates that sedimentation rates are higher in northeastern cores than in southwestern cores. Northeastern cores record paleoceanographic changes since the last glacial period, whereas a southwestern core of the lowest sedimentation rate show records of last ~900 thousand years. Carbonate content is higher in interglacial sediments than in glacial sediments prior to mid-Pleistocene transition (MPT), reflecting higher productivity during interglacial periods. Since the MPT carbonate dissolution occurs widely, and carbonates are preserved only in some glacial sediment. Absence of carbonate in post-MPT interglacial sediments suggests an invasion of corrosive deep water, possibly from Weddell Sea, since the MPT. Influence of Weddell Deep Water decreased during glacial periods due to extensive ice sheets and weakened current from the Weddell Sea, and carbonates are preserved in some post-MPT glacial sediment.