Late Quaternary palaeoceanography of the Southern Benguela upwelling and interoceanic exchange between the Indian and Atlantic Oceans

The Benguela Upwelling System (BUS) is one of the world’s major coastal upwelling zones, playing a critical role in regional marine productivity and global climate modulation due to its influence on interoceanic exchanges between the Indian and Atlantic Oceans. This study presents a comprehensive million-year palaeoceanographic reconstruction of the southern BUS by examining planktic foraminiferal assemblages and stable oxygen isotopes from Ocean Drilling Programme (ODP) Hole 1085A, located in the mid-Cape Basin of the southeastern Atlantic. Our multiproxy analysis—including dominant species Neogloboquadrina pachyderma (Dex), Globigerina inflata and the Agulhas Leakage Fauna (ALF)—reveals three distinct phases of upwelling evolution: latest Early Pleistocene intense and sustained upwelling (1000–800 kyr), middle Pleistocene transition with marked oligotrophic events and system reorganisation (800–400 kyr), and the development of pronounced glacial–interglacial cyclicity in the Late Pleistocene (400 kyr-present). Results indicate that the latest Early Pleistocene upwelling was both more intense and stable than in later periods, coinciding with the dominance of obliquity-driven climate cycles. The middle Pleistocene records show dramatic shifts, including the near-collapse of upwelling and the northward migration of oceanic fronts during the mid-Pleistocene transition. In the Late Pleistocene, upwelling intensity tracks glacial cycles, with intensified activity during glacials and reduced Agulhas Leakage indicative of complex interplay between trade winds, oceanic fronts and global ice volume. We demonstrate that interoceanic exchange via the Agulhas Leakage, tightly coupled to upwelling variability and larger-scale climate processes, has profoundly shaped the evolution of the BUS and its role in the Atlantic Meridional Overturning Circulation over the past million years.