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

Stable oxygen isotopic ratios in corals (delta O-18(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 delta O-18 (delta O-18(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 delta O-18(coral) to provide information on past salinity. Using ''pseudocorals'' to represent delta O-18(coral) as a function of observed or simulated temperature and salinity/delta O-18(sw), we find that delta O-18(sw) contributes up to 89% of delta O-18(coral) variability in the Western Pacific Warm Pool. Although uncertainty in the delta O-18(sw)-salinity relationship influences the inferred salinity variability, corals from these sites could provide valuable delta O-18(sw) reconstructions. Coordinated in situ monitoring of salinity and delta O-18(sw) is vital for improving estimates of hydroclimatic change.

Automated summary

Stable oxygen isotopic ratios in corals can be used to reconstruct past climate variability. The contribution of seawater δ18O to coral δ18O variability is up to 89% in the Western Pacific Warm Pool. However, uncertainty in the δ18O(sw)-salinity relationship influences the inferred salinity variability.