The early to mid-Pliocene latitudinal migration of the Southern Ocean subtropical front (IODP Site U1475, Agulhas Plateau)

The latitudinal migration of the Southern Ocean hydrographic fronts has been suggested to influence oceanographic conditions within the Indian-Atlantic Ocean gateway by restricting the amount of warm, saline water from the Indo-Pacific, transported by Agulhas Current, feeding into the South Atlantic via the Agulhas leakage. The Agulhas Current is an integral part of the global thermohaline circulation system as it acts as potential modulator of the Atlantic Meridional Overturning Circulation, which drives changes in regional and global climate, over at least the last 1.4 million years. However, the dynamics of this frontal system and associated changes in surface ocean biogeochemistry have not been explored beyond this time period due to absence of long continuous records spanning the Pliocene. Using International Ocean Discovery Program Site U1475 located on the southwestern flank of the Agulhas Plateau (41°25.61′S; 25°15.64′E; 2669 m water depth), we present high-resolution palaeoclimate records spanning the early to mid-Pliocene (~2.8 to ~5 Ma), from assemblage composition and morphometry of coccoliths, combined with oxygen and carbon stable isotopes from the bulk coccolith fraction. Our new Pliocene reconstructions offer evidence of the changing position of the subtropical front in the Southern Indian Ocean, driving variations in surface ocean conditions (e.g., nutrients, temperature, stratification), and thus biological productivity. We also explore expressions of coccolith δ¹³C vital effects from size-separated coccolith fractions together with planktic foraminifer carbon and oxygen stable isotopes from co-registered samples, that have been linked to cell size, growth rate, and calcification degree, providing empirical correlation with aqueous and atmospheric CO₂ concentrations.