This award will provide funds to test the hypothesis that the early Pliocene "permanent El Nino" was caused by a deeper seasonal thermocline, which shoaled in association with a global cooling trend over the last 5 Myr. This hypothesis will be tested by reconstructing sea surface temperatures and sub-surface temperatures at ODP site 1264 in the South Atlantic subtropical gyre, which is the source region for upwelling water in the tropical Atlantic, and comparing these data to a tropical Atlantic temperature time series at ODP site 662/3. Funds will also be used to measure the d18O and Mg/Ca composition of three depth-stratified species of planktonic foraminifera to quantify changes in the depth of the thermocline at the subtropical, non-upwelling site. These new data will be used to explore the details of the transition from an "El Nino-like" to "La Nina-like" climate state in the Atlantic Ocean. Specific objectives include the generation of high-resolution benthic and planktonic foraminiferal records to investigate the 41Kyr Milankovitch cycles in the data. Broader Impacts include support for an early career scientist who is now a new faculty member at a RUI as well as research on a societally-relevant issue to understand the origin of the ENSO system on Earth. This project will involve both undergraduate and graduate students in its research.
