By Sophia Pedroza

Faculty Mentor: Pamela Grothe

Abstract

The geochemistry of the coral genus Porites is a robust proxy for reconstructing sea surface temperature (SST) and sea surface salinity (SSS) in the central tropical Pacific (CTP), using oxygen isotope ratios (δ18O). Recent paleoclimate reconstructions from Kiritimati Island (1.8° N, 157.4° W) have relied on coral rubble collected primarily from storm deposits on ocean-facing beaches. However, many older samples (3,000 – 6,000 yrs BP) were collected from the island interior, which possibly originated from lagoonal environments. This research investigates the geochemistry (δ18O ratios) from a modern Porites coral collected near the mouth of the Kiritimati Island lagoon to assess its reliability in recording open ocean conditions. Given that mid-Holocene sea levels were higher, the lagoon was likely more open to ocean exchange, suggesting that corals near the present-day mouth of the lagoon may reflect the higher sea-level conditions of the mid-to-late Holocene. By analyzing geochemical signals from this modern lagoonal coral, we aim to determine whether preserved SST and SSS variability are influenced by lagoonal processes or reflect open ocean conditions. We will compare δ18O time series derived from a modern Porites spp. coral recovered from the mouth of the lagoon of Kiritimati Island to in-situ SST instrumental data and published modern Porites δ18O records. This validation is essential for interpreting paleoclimate records derived from spatially unconstrained samples and for refining reconstructions of the El Niño Southern Oscillation (ENSO) variability and CTP hydroclimate shifts. The results will enhance confidence in coral-based climate archives and inform sampling strategies for similar environments.