A seismic approach to the paleoceanography of the eastern South Atlantic

Geochemical proxies (such as δ13C or εNd) measured on drilled samples helped to decipher variations of water masses related to climate changes in the South Atlantic (e.g. Billups 2002; Scher and Martin, 2008). Information on how these changes in transport influenced the intensity and position of current systems is currently very sparse but can be gained by seismic investigations of contourites (e.g. Gruetzner et al., 2014). With a new proposal, which is based on 5400 km of high-resolution multichannel seismic reflection data acquired during RV Maria S. Merian cruise MSM 19/2 in the Agulhas Ridge area, we aim at a better understanding of both pathways and intensity of the current system in the eastern South Atlantic. With its high topography the Agulhas Ridge has prevented a direct N-S water mass exchange between the Southern Ocean and the Atlantic and hence has restricted the energy and heat transfer since its formation ∼83 Ma. 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 (Fig. 1). Sediment drifts have been formed due to this flow pattern since the Oligocene (Wildeboer Schut and Uenzelmann-Neben, 2005). By mapping the drift shapes and distributions we aim to monitor oceanographic variations caused by global climate changes like the onset of the glaciations of East and West Antarctica, the Mid Miocene Climatic Optimum (MMCO), and the glacial/interglacial cycles since the Pliocene. Furthermore the seismic interpretation will help to decipher the influence of tectonic events as the opening of Drake Passage and the closure of the Isthmus of Panama on the position of oceanic fronts and pathways of water masses in the region. A first interpretation of the seismic lines collected across the northern Agulhas Ridge shows two formation levels of sediment drifts corresponding to the activity depths of AABW/CDW and the Agulhas Rings (Gruetzner and Uenzelmann-Neben, 2014). A correlation with ODP Leg 177 age-depths model and water mass information based on εNd values (Scher and Martin, 2008) as well as the seismostratigraphic model of Wildeboer Schut et al. (2002) will allow the development of a chronology for the formation of the sediment drifts. A subsidence analysis in two dimensions along a series of selected profiles will be performed in order to correct for the effects of compaction and determine the volumes and masses of sediment (eroded rock) deposited during each time interval