The Late Lutetian Thermal Maximum (middle Eocene): first record of deep-sea benthic foraminiferal response

Abstract

Understanding the role of deep-sea biota across global warming events in the past is key to unravel climate system dynamics during periods of increased pCO2 levels. Here we present the first record of the benthic foraminiferal response to a middle Eocene transient warming event named the Late Lutetian Thermal Maximum (LLTM; 41.52 Ma) at ODP Site 702 in the South Atlantic Ocean. Changes in benthic foraminiferal assemblages such as a decrease in absolute abundance of certain taxa (e.g. Bulimina elongata) are correlated with the negative carbon isotope excursion corresponding to the LLTM event. Paleoecological interpretations of the assemblage turnover suggest changes in the type of organic matter arriving to the seafloor during the LLTM. Benthic foraminifera and coarse fraction accumulation rates (BFARs and CFARs) decreased across the warming period of the LLTM, coeval with the negative δ18O excursion associated with ~2 °C deep-sea warming. We suggest that increased temperatures led to enhanced metabolic rates in heterotroph organisms such as foraminifera, triggering a population decline in food-limiting environments such as the meso-oligotrophic setting of Site 702. A similar ecological response and a decrease in export productivity, as inferred from decreased CFARs and BFARs, have also been reported across the Middle Eocene Climatic Optimum at this site, and support the hypothesis that metabolic rates accelerated during warming events, in spite of their different magnitude and duration.