Late Miocene to Pleistocene deep water Productivity in the Southeast Atlantic: Evidence from Benthic Foraminiferal Assemblages

Benthic foraminifera are widely considered as marker proxy for past changes in surface and deep water productivity, organic matter flux, bottom water oxygenation, and deep water circulation. This study presents benthic foraminiferal relative abundance records from ODP Site 1087 (31°27.9137’S, 15°18.6541’E, water depth 1374m), located in the southeast Atlantic Ocean beneath the productive Benguela Upwelling System (BUS). The main objective is to assess long-term productivity and oceanographic variability in the region from the Late Miocene to Pleistocene. Our results indicate a major shift in regional oceanographic conditions at ~10 Ma. A distinct increase in the relative abundance of Bulimina striata, a dysoxic, infaunal species associated with elevated flux of organic matter, suggests enhanced surface productivity and marks the emergence of the BUS. This timing closely matches with the onset of the BUS as inferred from multiple independent proxy records. The late Miocene–early Pliocene biogenic bloom (~ 8–5 Ma), characterised by sustained and widespread high productivity across the Indian, Pacific and Atlantic Oceans, is often indicated by higher relative abundance of Uvigerina proboscidea, a suboxic, infaunal species associated with high delivery rates of organic matter to the seafloor. A similarly higher relative abundance of U. proboscidea is clearly recorded in our benthic assemblages, pointing to intensified export productivity during this interval. Additionally, an increased relative abundances of the opportunistic species Epistominella exigua during ~8 to 6 Ma and ~3.7 to 3.0 Ma indicate seasonal input of phytodetritus from the surface waters due to extensive phytoplankton blooms associated with the strengthening of the upwelling. The early Pliocene interval between ~5 and 3.7 Ma is marked by the co-occurrence of Globocassidulina subglobosa, U. proboscidea, and B. striata. This assemblage reflects alternating oxic and suboxic–dysoxic benthic environments, which might be linked to oligotrophic and eutrophic surface conditions, respectively. Decreased surface productivity related to reduced upwelling and enhanced oxygenation of bottom waters favoured oxic species, but the continued presence of dysoxic-suboxic species indicate a continuous nutrient supply, perhaps related to Agulhas Leakage. A rapid increase in U. proboscidea and Uvigerina peregrina during the Plio–Pleistocene cooling reflects re-intensification of BUS-related productivity. Overall, benthic foraminiferal assemblages at ODP Site 1087 provide a robust record of productivity and associated oceanographic changes in the Southeast Atlantic Ocean between the Late Miocene and Pleistocene.