On the paleo footprint of Cape Darnley Bottom Water off MacRobertson Land Shelf, East Antarctica

Abstract

Cape Darnley Bottom Water (CDBW) is a major contributor to Antarctic Bottom Water (AABW) formation in the MacRobertson Land continental shelf area, East Antarctica. As the production of CDBW is dependent on intense sea ice formation in the Cape Darnley Polynya Region, it is sensitive to climatic changes, such as global warming. Studying paleo-conditions of CDBW during Antarctica's transition from coolhouse to icehouse during the middle to late Miocene allows to gain knowledge about the onset of bottom water production in the Cosmonaut/Prydz Bay region as well as changes in the strength and outflow path of the CDBW.In order to study the paleo-conditions of the CDBW, we have investigated the formation history of a 200 km long, 70 km wide sediment drift (Darnley Drift herein) at the western flank of Wild Canyon. In the early Miocene, the upper rise was dominated by turbiditic channel-levee growth and large continental sediment supply off the MacRobertson Land continental shelf. Therefore, no indications of CDBW formation were observed. During the middle Miocene, the dominant sediment transport regime transformed from turbiditic to contouritic mode, mirroring Antarctica's climatic transition into an icehouse world. This climatic transformation caused the initiation of CDBW, which is inferred from the onset of Darnley Drift formation as a levee-drift and its growth to a maximum areal extent of 60,000 km2, four times the size of today. Since the late Miocene/early Pliocene the sedimentation rate has been strongly reduced and bottom current controlled deposition dominated. The growth of mixed levee-drifts along the continental slope-rise transition parallel to Darnley Drift suggests an intensification of paleo CDBW generation and outflow to be comparable to observations of recent CDBW, in addition to an intensification of the Antarctic Slope Front and Circumpolar Deep Water.