FORAMINIFERA STABLE ISOTOPES AS INDICATORS OF WATER COLUMN TEMPERATURE AND CARBON CYCLING DURING THE EOCENE

Deep ocean sediments provide biogeochemical records of ancient climates as case studies for global processes that cannot be adequately reconstructed in a lab. One example is the Eocene hothouse that lasted from 56 to 47 million years ago, which serves as a partial analog for projected anthropogenic warming because both are characterized by high levels of atmospheric carbon dioxide, a lack of ice caps, and subsequently slower thermohaline ocean circulation. The shells of single-celled foraminifera living in the surface and deep ocean record the climatic conditions under which they grew, and can be used to reconstruct past temperature and carbon cycling. In this study, we analyzed the stable and carbon isotopic composition of benthic and planktic foraminifera in order to reconstruct water column conditions in multiple time slices throughout the Eocene. Foraminifera species from the genera Acarinina, Subbotina, and Nuttalides were picked and analyzed as representatives of the surface, intermediate, and deep ocean isotopic environments, respectively. The oxygen isotope results show the expected temperature gradient correlating to cooler temperatures with depth for most of the Eocene. Similar to the results of Shepherd et al. (2021), the water column homogenizes through the Eocene as the benthic genera show warming and planktic genera display cooling. Such a contradiction with the expectation for a warming climate may be due to recrystallization or the changing of ocean circulation patterns increasing vertical mixing (Shepherd et al. 2021). The carbon isotope gradient also weakens, possibly indicating a less efficient carbon biological pump. Higher resolution data at this site and others will aim to reconstruct full column gradients to view 3D ocean circulation and mixing patterns possibly responsible for the striking homogenization of oxygen isotopes in the late Eocene.