Early-Middle Pleistocene to recent paleoceanographic variability in the Agulhas system (southwestern Indian Ocean) induced by fluctuations in the Antarctic Circumpolar Current

The Agulhas system, in the southwestern Indian Ocean, plays a crucial role in the global circulation patterns as it supplies warm, salty waters from the Indo-Pacific region to the Atlantic Ocean, via Agulhas Leakage (AL). The intensity of the leakage can vary based on the fluctuations of the subtropical front and the northward expansion of the Antarctic Circumpolar Current (ACC). Despite its importance, the characterization of the Agulhas system and its development through time is still poorly constrained. In this work, we performed high-resolution statistical and isotopic analyses on the planktonic foraminiferal assemblages from IODP Expedition 361, Hole U1474A, which is under the direct influence of the Agulhas Current (AgC). Our dataset provided detailed paleoceanographic variations of the Agulhas system for the last 1.5 Ma. The foraminiferal assemblages reflected the interactions between the AgC and ACC, which were linked to variations in the permanent and seasonal thermocline. Furthermore, we reconstructed ACC fluctuations and its interaction with the AL intensity at a glacial-interglacial scale during the Pleistocene. The interval before 900 kyr was mostly under the AgC regime during both glacials and interglacials, with limited fluctuation of the ACC. Conversely, after 900 kyr, an increase in frequency of the ACC ingressions occurred during glacials. These ingressions became stronger after the Mid-Bruhnes Transition. We propose that the difference in the frequency of ACC expansions before and after 900 kyr is linked to changes in the amplitude and frequency of glacial-interglacial cycles. • High-resolution proxies reveal 1.5 Ma Agulhas system variability. • Foraminiferal data track Agulhas–ACC interactions through the Pleistocene. • ACC incursions increase after 900 ka, intensifying post-MBT. • Thermocline changes reflect shifts in Agulhas leakage dynamics. • Results link ACC behavior to glacial–interglacial cycle amplitude and frequency.