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

Stable oxygen isotopic ratios in corals (δ¹⁸O_coral) 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 (δ¹⁸O_sw) 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 δ¹⁸O_coral to provide information on past salinity. Using ‘‘pseudocorals’’ to represent δ¹⁸O_coral as a function of observed or simulated temperature and salinity/δ¹⁸O_sw, we find that δ¹⁸O_sw contributes up to 89% of δ¹⁸O_coral variability in the Western Pacific Warm Pool. Although uncertainty in the δ¹⁸O_sw-salinity relationship influences the inferred salinity variability, corals from these sites could provide valuable δ¹⁸O_sw reconstructions. Coordinated in situ monitoring of salinity and δ¹⁸O_sw is vital for improving estimates of hydroclimatic change.