USING BENTHIC FORAMINIFERA TO EVALUATE THE RELATIONSHIP BETWEEN EOCENE HOTHOUSE CLIMATE FLUCTUATIONS AND ORBITAL CYCLICITY

Constraining the role of orbital forcing on Earth’s climate and carbon cycling is an important aspect of understanding past warm periods. The stable carbon and oxygen isotopes of benthic foraminifera are an effective proxy through which to study ancient global climate patterns, due to the integrative nature of the deep ocean. The natural shifts in Earth’s orbital patterns due to Milankovitch cycling have a repetitive, cyclical effect on oceanic and terrestrial climate and carbon cycling, which can be seen in intervals which range from 23,000 to 405,000 years. These patterns may have had an impact in forcing the onset of several major warming events throughout the Eocene, including the Paleocene-Eocene Thermal Maximum (PETM), and subsequent events (ETM2). In this project we investigate evidence of orbital cycling in ocean sediments collected at IODP Site U1553, which was located near New Zealand at 55S paleolatitude during the Eocene. We collected data across one suspected orbital cycle that shows a negative carbon isotope excursion as identified by a bulk sediment isotope stratigraphy (Röhl, unpublished data). Stable isotope ratios of two benthic foraminifera species, Nutallides truempyi and Ordorisalis umbonatus, reflect species-specific habitats, where N. truempyi reside on sediment surface, and O. umbonatus reside within. Our species-specific foraminifera data display similar trends to the bulk isotope record, and offer a higher resolution data set that we will use to investigate the nature of orbital forcing on different aspects of the oceanic system.