Core Stratigraphy and Paleotemperature Estimates to Characterize Last Interglacial Tropical Pacific Climate Variability and El Nino Southern Oscillation During MIS 5e

Inter-annual climate variability is dominated by the El Niño Southern Oscillation (ENSO). ENSO is expressed as changes in tropical Pacific sea surface temperatures, and it impacts natural and human systems across the globe. Whether ENSO events will become stronger in the future is unclear, in part because the processes that control ENSO are not fully understood. Past ENSO activity can be reconstructed using geochemical proxy evidence from ocean sediments from the eastern equatorial Pacific. The last warm climate period, known as Marine Isotope Stage 5e (MIS 5e), occurred ~119,000-126,000 years ago. Thus, Eastern Pacific sediments from MIS 5e record ENSO behavior during a previous warm state. This research will characterize MIS 5e sediments in an eastern equatorial Pacific sediment core using the shell chemistry of foraminifera. These new records will provide reliable age control for the sediment core. The data from this core can then be compared with paleoclimate data from other locations. The study will support outreach efforts to broaden participation in STEM and in the geosciences through meaningful undergraduate research opportunities. Undergraduate research assistants will be involved in all phases of the project. The geochemical analyses will be a key component of a summer workshop for undergraduates. This will give the students valuable experience on modern analytical techniques. ENSO’s behavior in response to elevated atmospheric carbon dioxide is not well constrained as our understanding of the mechanisms controlling tropical Pacific variability is incomplete. Reconstructions of ENSO during previous warm periods, and in particular the last interglacial (MIS 5e) are limited. Such reconstructions would enable testing of ENSO’s relationship with changing climate background conditions, orbital forcing, and seasonal changes in the absence of modern carbon dioxide forcing. The eastern equatorial Pacific cold tongue region is a center-of-action for ENSO, but sediment cores with adequate material, resolution, and characteristic are sparse. This research will generate a stable isotope and trace elemental stratigraphy using surface and subsurface foraminifera to identify and characterize MIS 5e sediments in an eastern equatorial Pacific sediment core. Generation of a long-term surface and subsurface stratigraphy spanning the last glacial maximum to MIS 5e will allow the sediments to be characterized for composition, accumulation rates and resolution, enabling future, high-resolution analysis of tropical Pacific variability using foraminiferal geochemical proxies, and allow for testing of key hypotheses of ENSO control. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.