Seismic evidence for bottom current activity at the Agulhas Ridge

In the South Atlantic water masses from the Atlantic and Indian Oceans meet Antarctic water masses. The Agulhas Ridge, a pronounced elevation of the ocean bottom in the eastern South Atlantic, has acted as a barrier for deep oceanic currents since the Cretaceous, such as the North Atlantic Deep Wate...

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Bibliographic Details
Published in:Global and planetary change 2002-11, Vol.34 (3), p.185-198
Main Authors: Wildeboer Schut, Etienne, Uenzelmann-Neben, Gabriele, Gersonde, Rainer
Format: Article
Language:English
Subjects:
Agulhas Ridge
bottom currents
Marine
palaeo-reconstruction
seismic reflection
South Atlantic
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Summary:In the South Atlantic water masses from the Atlantic and Indian Oceans meet Antarctic water masses. The Agulhas Ridge, a pronounced elevation of the ocean bottom in the eastern South Atlantic, has acted as a barrier for deep oceanic currents since the Cretaceous, such as the North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW), or water masses derived from AABW such as Circumpolar Deep Water (CDW). The history of these currents is recorded in the sedimentary sequence in the adjacent Cape and Agulhas Basins. Seismic profiles over the Agulhas Ridge show sediment packages in the Cape Basin which are interpreted as contourite sheets. These consist of thick sequences interrupted by widespread hiatuses, with a predominantly low seismic reflectivity. The seismic data shows prominent reflectors inside contourite drift bodies which, at the location of the drill-sites of Ocean Drilling Program (ODP) Leg 177, can be attributed to hiatuses in the Early Oligocene, the Middle Miocene, around the Miocene/Pliocene boundary and in the early Pleistocene. In this way, ODP Leg 177 cores were used to date an elongate contourite drift in the Cape Basin. This drift shows sediments deposited by a westward current, implying that the bottom current in the Oligocene followed the same trajectory as present-day CDW does.
ISSN:0921-8181
1872-6364
DOI:10.1016/S0921-8181(02)00114-5