Assessing the Viability of Pristine Fossil Corals from the Dominican Republic as Indicators of ENSO at the Miocene/Pliocene Boundary

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The El Nino-Southern Oscillation (ENSO) represents the single largest source of interannual climate variability on Earth, and because numerous studies have suggested that ENSO is sensitive to greenhouse warming of the atmosphere and surface ocean, it is critical that we better understand how ENSO may respond over coming decades and centuries. Studies of marine sediments have examined centennial- to millennial-scale dynamics of the mean state of the tropical Pacific, but these results have mostly lacked the temporal resolution necessary to identify variability within the ENSO band (2-7 yr). Corals preserve records of sea surface temperature and upwelling in their annually-banded aragonite skeletons, and thus can be used for spectral frequencies consistent with ENSO. The results of this study will contribute broadly to our understanding of the nature of ENSO during a time period considered the most recent analog for an anthropogenically-warmed world.The research project will generate a roughly half-century-long record of monthly-resolved oxygen and carbon isotopic ratios from a pristine fossil coral from the Gurabo Formation of the Dominican Republic as a test of ENSO variability in the latest Miocene. The record will allow the researchers to test three proposed states of the Pacific during the Miocene: entrenched El Nino conditions, entrenched La Nina conditions, or a modern ENSO pattern. The results may also have implications for modeling of flow through the Central American Seaway (CAS) prior to its final closure. Complete formation of the Central American Isthmus (and closure of the CAS) around 3.5 ma led to pulses of extinction and speciation in both the eastern Pacific and the Caribbean, and may have contributed to Northern Hemisphere glaciation through changes to ocean circulation. However, modeling these effects are limited by the still considerable uncertainties in the nature of flow through the CAS, largely owing to ambiguities surrounding the width of the opening(s) and depth of the sill. An undergraduate student from Cornell College (a small, four-year liberal arts school with no graduate programs) will receive advanced training in paleoclimatology research methods by actively participate in all aspects of this project, including presentation of results at a national meeting.