OSTRACODE RESPONSE TO CHANGING ENVIRONMENTS DURING EOCENE THERMAL MAXIMUM 2 IN THE EQUATORIAL ATLANTIC

The climate of the late Paleocene and early Eocene is characterized by the presence of multiple hyperthermal events that have been distinguished by relatively rapid increases in temperature and corresponding negative carbon isotope excursions. These early Cenozoic events represent some of the most relevant analogs with which we can study the effects of the sudden input of carbon into the atmosphere and/or oceans. While the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) is the largest of these hyperthermal events, several other smaller hyperthermals followed in the early Eocene. Records of Eocene Thermal Maximum 2 (ETM2, ~54 Ma), the second-largest Eocene event, indicate that it was characterized by about half of the magnitude of warming and carbon isotope excursion that has been observed for the PETM. Like the PETM, ETM2 has been documented globally from both terrestrial and marine settings, particularly in deep sea drill cores. Although previous studies have investigated the response of unicellular organisms such as foraminifera to these hyperthermals, relatively little work has been done to evaluate the response of multicellular organisms to these episodes of environmental change. Ostracode (small, bivalved crustacean) microfossils can provide insight to the impacts of these events on multicellular groups.

Here we investigate patterns of ostracode abundance and diversity across ETM2 at ODP Site 1258 in the equatorial Atlantic. ETM2 has been identified in these sediments using carbon and oxygen isotopes from bulk carbonate. Preliminary results of ostracode abundance at this site suggest that ostracodes persisted throughout the ETM2 interval in varying levels of abundance. We further analyze the relationship between ostracode accumulation rate, temperature, and carbon cycle indicators (wt% CaCO₃ and carbon isotopes). In this way, we evaluate the effect of environmental changes associated with rapid input of isotopically light carbon to the ocean and atmosphere on this group of multicellular animals.