The area south of South Africa is an important gateway for the interoceanic exchange of water masses from the Atlantic, Indian and Southern Oceans. Three major water masses are involved: the Agulhas Current (AC), the North Atlantic Deep Water (NADW), and Antarctic Bottom Water (AABW). The interplay of these currents is widely believed to control the sediment transport pathways along the South African continental slope, the Agulhas Passage as well as the Transkei Basin.During the research cruise SO-182 with R/V SONNE in spring 2005 extensive reflection seismic data were recorded along the Agulhas Passage, the Agulhas Plateau as well as the Transkei Basin to reconstruct sediment transport pattern through time. Thereby, the Agulhas Drift situated in the Transkei Basin, was surveyed by a dense profile grid. This large sediment body could be identified as major sediment deposition center which was developed since mid-Miocene. Furthermore, seismic data indicate that current conditions were highly variable in this region: a north-south directed inflow of AABW dominated the sediment transport and deposition in the Transkei Basin from middle Miocene to early Pliocene times, while after that an eastward flow of NADW responded to this sedimentation and the inflow of AABW must have shifted back to the Agulhas Passage gateway.To get to better understanding of the temporal evolution of the Agulhas Drift and the development of the palaeocirculation south of South Africa, the Regional Ocean Modeling System (ROMS) coupled with a sediment model is applied. This is an advanced open-source model which solves the free surface, hydrostatic, primitive equations over variable topography using stretched, terrain-following coordinates in the vertical, orthogonal coordinates in the horizontal. Based on these current simulations sediment transport pattern have been calculated simultaneously. We started with a 3D model under recent current conditions for a one year model run. Levitus is used as model input. These simulations show that the sediment transport patterns along the Agulhas Drift are strongly influenced by mesoscale eddies under recent conditions. In general, sediment resuspension occurs during the eddy events, and materials are transported away from the Transkei basin if the eddy breaks up. In addition seasonal variations in erosion and depositional pattern along the continental shelf and slope areas north of the Transkei Basin could be observed.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > MAR2-Palaeo Climate Mechanisms and Variability