Calcareous Nannoplankton Assemblages across the Pliocene-Pleistocene Transition in the Southwestern Indian Ocean, IODP Site U1475

Abstract

International Ocean Discovery Program (IODP) Expedition 361 cored six sites along the greater Agulhas Current system. An objective of this expedition was to determine the dynamics of the Indian-Atlantic Ocean Gateway circulation during Pliocene-Pleistocene climate changes in association with changing wind fields and migrating ocean fronts. The Indian-Atlantic Ocean Gateway contains a pronounced oceanic frontal system, the position of which has the potential to influence global climate on millennial scales. Owing to the physical differences between the frontal zones, this region has complex biogeochemistry, changes in phytoplankton distribution, and variations in primary productivity. Site U1475 was cored on the Agulhas Plateau in the Southwestern Indian Ocean and recovered a complete sequence of calcareous ooze spanning the last ~7 Ma. The calcareous nannoplankton assemblage shows an increase of taxa associated with cooler water across the Pliocene-Pleistocene Transition (PPT) interval suggesting that a long- term change in sea surface temperature and nutrient availability took place across the PPT, potentially linked to the northward migration of the Subtropical Front.