Neogene Modifications of Circulation in the Northeastern African-Southern Ocean Gateway

摘要

In the African-Southern Ocean gateway, several water masses originating in the Atlantic, Indian, and Southern oceans meet and mix. As a consequence, the gateway is crucial for the maintenance of the global thermohaline circulation. Newly acquired multichannel seismic reflection data collected across the southern Mozambique Ridge are used to reconstruct the impact of paleoceanographic modifications on the Neogene and Quaternary circulation in the northeastern African-Southern Ocean gateway. The data show the occurrence of mid-Miocene (~15 Ma) to early Pliocene (~5 Ma) contourite drifts and erosional features interpreted as evidence for the onset of current-controlled sedimentation in the late Neogene resulting from mid-Miocene cooling and closure of the Indonesian gateway. The Quaternary is characterized by a relocation of Antarctic Bottom Water inflow and the inception of two branches of the North Atlantic Deep Water circulation subsequent to the final closure of the Central American Seaway and the Northern Hemisphere Glaciation. Therefore, the two events triggered the onset of unhindered deep and bottom water circulation from the Atlantic into the Indian Ocean, whereas the Antarctic Intermediate Water circulation decreased due to the final closure of the Indonesian gateway. Our results show that tectonic and climatic events, which themselves may be linked, continuously modified the Cenozoic paleoceanic circulation in the African-Southern Ocean gateway, and indicate that ocean gateways governing the global water mass exchange act as an excellent location to reconstruct such modifications based on the interpretation of contourite drifts and erosional features.