Identifying Hydro-Sensitive Coral δ18O Records for Improved High-Resolution Temperature and Salinity Reconstructions

Abstract

Stable oxygen isotopic ratios in corals (δ18Ocoral) are commonly utilized to reconstruct climate variability beyond the limit of instrumental observations. These measurements provide constraints on past seawater temperature, due to the thermodynamics of isotopic fractionation, but also past salinity, as both salinity and seawater δ18O (δ18Osw) are similarly affected by precipitation/evaporation, advection, and other processes. We use historical observations, isotope-enabled model simulations, and the PAGES Iso2k database to assess the potential of δ18Ocoral to provide information on past salinity. Using ‘‘pseudocorals’’ to represent δ18Ocoral as a function of observed or simulated temperature and salinity/δ18Osw, we find that δ18Osw contributes up to 89% of δ18Ocoral variability in the Western Pacific Warm Pool. Although uncertainty in the δ18Osw-salinity relationship influences the inferred salinity variability, corals from these sites could provide valuable δ18Osw reconstructions. Coordinated in situ monitoring of salinity and δ18Osw is vital for improving estimates of hydroclimatic change. © 2022. American Geophysical Union. All Rights Reserved.