By Avery Duncan

Faculty Mentor: Pamela Grothe

Abstract

One of the primary climate drivers of the central tropical Pacific (CTP) is the El Niño-Southern Oscillation (ENSO), a naturally occurring interannual ocean-atmosphere phenomenon that impacts global rainfall and temperature patterns. However, temporally limited instrumental climate records in the CPT prohibit the evaluation of long-term climate trends, limiting our understanding of the impacts of anthropogenic climate change on this region and ENSO. Kiritimati Island (1.8°N, 157.4°W) is ideally located in the CPT and is highly sensitive to the most substantial impacts of ENSO events. Reconstructions of ENSO variability using δ18O from Porites coral skeletons collected from this region have provided snapshots of ENSO variability over the last 6,000 years. However, since centuries-long coral samples are limited in this region, most paleo-ENSO reconstructions rely on short rubble coral samples from 7 to 20 years in length. Alternatively, the giant clam, Tridacna maximum, which has a long lifespan and fast growth rate, could provide decades-long, high-resolution records of ENSO variability. We focus on two modern Tridacna maximum samples collected from Kiritimati Island to investigate their potential as paleoclimate proxies and their ability to reproduce ENSO variability. Like corals, Tridacna clams have a calcium carbonate skeleton that incorporates the geochemistry from the seawater at the time they grew. Following similar methods for Porites corals, we will analyze δ18O and Sr/Ca from slabbed Tridacna skeletons and compare them to instrumental sea surface temperature (SST) data and the published Porites coral δ18O record from Kiritimati Island. If successful, the addition of Tridacna maximum for paleo ENSO studies would greatly improve our understanding of ENSO variability through the last several centuries and millennia, providing a better understanding of the natural versus anthropogenic influence on ENSO behavior.