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Southern African Climates, Agulhas Warm Water Transports and Retroflection, and Interocean Exchanges - SAFARI -

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Citation:
Zahn, R. , Hall, I. R. , Barker, S. , Schneider, R. , Spiess, V. , Uenzelmann-Neben, G. , Lee-Thorp, J. , Hoernle, K. and Rickaby, R. (2006): Southern African Climates, Agulhas Warm Water Transports and Retroflection, and Interocean Exchanges - SAFARI - , IODP Past Achievements and Future Opportunities, EuroForum 2006, 8-9 May, Cardiff, UK. .
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Abstract:

Agulhas Current warm water transports and their leakage into the Atlantic form a key link in the global thermohaline circulation (THC) as they feed the warm upper limb of the northward THC in the South Atlantic. The interocean exchange off southern Africa is potentially involved in the initiation, maintenance and stability of North Atlantic THC and thus, it bears importance within the Plio-Pleistocene climate development. On regional scales it is involved with setting past environmental conditions in continental southern Africa with plausible significance for the evolution of mammals including hominins. While the southwest African margin has been the target of scientific ocean drilling several times in the past, only a single drill site has presently been occupied within the direct reaches of the warm water Agulhas Current along the southeast African margin. With this IODP drilling initiative we target 9 sites to retrieve multiple APC-XCB cores spanning the main routing of the Agulhas head waters, the Agulhas corridor linking the Indian and Atlantic Oceans, and the retroflected waters returning into the Indian Ocean. One additional RCB hole is planned to drill >200 m deep into the Agulhas Plateau basement.The SAFARI drilling proposal combines four overarching themes: (i) Variability of warm water transports along the southeast African margin during the late Neogene and its linking with regional to hemisphere-wide climate changes; (ii) the role of gateway circulation around South Africa and ensuing Indian-Atlantic Ocean water exchanges in changing Atlantic THC modes during key-periods of the Plio-Pleistocene climatic evolution; (iii) place southern African terrestrial climates and the evolution of mammals including hominins into a framework of long-term changes of ocean circulation and marine heat budgets in the SW Indian; (iv) origin and development of the Agulhas plateau as a continental fragment vs. a large igneous province of oceanic origin.Specific palaoceanographic objectives, on Plio-Pleistocene timescales, of the SAFARI drill sites are: variations of Agulhas Current warm-water transports during orbital and faster climate changes; role of such variations during key-periods of global change: mid-Pliocene onset of northern hemisphere glaciation and mid-Pleistocene revolution; influence of upstream forcing i.e., monsoonal, Indonesian Throughflow and Red Sea outflow, on SE African warm water transports in the 41-kyr and 100-kyr worlds; advective salinity feedback between Agulhas Leakage and Atlantic MOC mode changes at these times; contribution of Southern Ocean deep and bottom water masses to global ocean THC circulation prior to and after the onset of northern hemisphere glaciation; linking between ocean circulation changes in the SW Indian, southern African terrestrial climates and mammal / hominin evolution; extending the southern hemisphere paleoclimatic record beyond EPICA.Specific tectonic objectives of the SAFARI drill sites are: basement petrology and geochemical composition and hence, the origin of the Agulhas Plateau; age of the basement and timing of lava flows relative to the separation of Africa from Antarctica; age and composition of Agulhas Plateau lava flows within the framework of worldwide LIP occurrence and excessive volcanism; emplacement of volcanics on the southern Agulhas Plateau in the light of a possible volcanic period; age and composition of the sediments on the Agulhas Plateau as an indication for the earliest occurrence of modern-type current systems.

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