Assessing the impact of Sr/Ca-SST calibrations on coral-based seawater δ18O reconstructions - First results from PAGES CoralHydro2k

Corals are distributed throughout the tropical oceans, making them useful for resolving climate information covering time before the satellite era when instrumental data is often scarce. Coral δ¹⁸O has been used to reconstruct changes in both sea surface temperature (SST) and hydrology, while coral Sr/Ca is thought to mainly record SST. Coral δ¹⁸O data, when used in conjunction with Sr/Ca, can therefore be used to reconstruct seawater δ¹⁸O (δ¹⁸O_sw), an indicator of the local precipitation-evaporation balance as well as other surface ocean hydrological changes. Coral Sr/Ca-SST relationships are critical for reconstructing δ¹⁸O_sw from paired Sr/Ca and δ¹⁸O records, but vary across existing literature. Some of this variation is due to existing natural differences between corals, but variation also stems from differences in calibration methods or SST products used to determine the Sr/Ca-SST relationship. Such methodological differences complicate the comparison of results across studies and slow efforts to create a global picture of reconstructed tropical ocean hydroclimate.

Here, we use the PAGES CoralHydro2k database - a collection of 45 paired coral Sr/Ca-δ¹⁸O records and 70 coral δ¹⁸O records - to assess different methodological choices such as SST product and regression method and develop a calibration framework to use as a set of “best practices” moving forward. We also examine the sensitivity of δ¹⁸O_sw to our calibration framework and to existing δ¹⁸O_sw calculation methods. The PAGES CoralHydro2k project aims to leverage its coral database and apply these best practices and insights to a global reconstruction of tropical marine hydrology over the past 200 years.