Contourites at the eastern Agulhas Ridge and Cape Rise seamount shaped by Southern Ocean derived water masses

摘要

Constituting a topographic barrier the Agulhas Ridge has a strong influence on the exchange of water masses between high and lower latitudes in the South Atlantic. While Antarctic Bottomwater (AABW) and Circumpolar Deepwater (CDW) originating in the Southern Ocean provide the inflow of cold water masses in larger water depths, the Agulhas leakage is the main source of warm and salty waters carried towards the Subpolar North Atlantic. In order to track past changes in this circulation pattern 5400 km of high-resolution multichannel seismic reflection data were acquired during RV Maria S. Merian cruise MSM 19/2 in the Agulhas Ridge area. Here we present first results from the eastern plateau of the ridge and the area between the plateau and the Cape Rise Seamount. Via crosscorrelation with ODP Leg 177 drillsites, prominent reflectors marking the early Oligocene, the middle Miocene and the base of the Pleistocene were identified. Sediment drifts deposited between these erosional surfaces indicate steady contour current acitivity at various depth levels. Extensive current derived deposits in this area and a mounded drift northwest of the Cape Rise Seamounts formed by clockwise circulating bottom water appear to have been built contemporaneously by AABW flow after the early Oligocene.