CHANGING NORTH ATLANTIC OSTRACODE ABUNDANCE AND DIVERSITY IN RESPONSE TO AN EOCENE HYPERTHERMAL EVENT

The rapidly changing climate of the early Cenozoic represents one of our best opportunities to study the effect of the sudden addition of carbon into the atmosphere and oceans. During the late Paleocene and early Eocene, climate on earth was distinguished by multiple hyperthermal events that have been identified globally by rapid increases in temperature and negative carbon isotope excursions. The Paleocene-Eocene Thermal Maximum is the largest of these hyperthermal events; the following Eocene Thermal Maximum 2 (ETM2, ~54 Ma) event is characterized by about half of the magnitude of carbon and oxygen isotope excursions that have been observed for the PETM. ETM2 has been identified in terrestrial and marine records around the world. Using the multitude of ocean drill cores containing early Cenozoic sediments, a variety of studies have analyzed how single-celled organisms, such as foraminfera, have been impacted by these hyperthermal events, identifying a benthic foramifera extinction event at the PETM and changes in abundance at other hyperthermals. Ostracodes (small, bivalved crustaceans) provide an opportunity to conduct similar investigations that evaluate how multicellular animals have responded to these changing environments.

Here we investigate patterns of ostracode abundance and diversity across ETM2 at IODP site U1409 off the coast of Newfoundland. Using proxies for temperature and carbon cycle indicators, we evaluate the effect of environmental changes associated with the rapid input of isotopically light carbon to the ocean-atmosphere system on this group of multicellular animals. In this core, several carbon and oxygen isotope excursions, including ETM2, have been identified using bulk carbonate and benthic foraminfera isotope records. At this site, ostracode abundance and diversity both decrease at ETM2, with some samples at the peak of the isotope excursions preserving no ostracodes. Ostracodes also recover within the recovery period of the isotope excursions. Throughout the record there are more than ten ostracode genera, and the ostracode assemblages present before and after ETM2 are similar to one another.