The PAGES CoralHydro2k Seawater δ¹⁸O Database: A FAIR-aligned compilation of seawater δ¹⁸O data to uncover 'hidden' insights from the global ocean

Abstract. The stable isotope values of seawater (δ¹⁸O and δ²H) provide valuable information on the exchange of water between the ocean, atmosphere, and cryosphere and on ocean mixing processes. As such, observational seawater δ¹⁸O and δ²H data place powerful constraints on hydrologic changes in the modern ocean. Seawater δ¹⁸O data are also essential for calibrating paleoclimate proxies based on the δ¹⁸O of marine carbonates and are an increasingly critical diagnostic tool for assessing model performance and skill in isotope-enabled global climate models. Despite their broad value, no centralized and actively-curated database for this type of data exists, even though a growing number of new seawater δ¹⁸O datasets have been generated over the last decade. As such, many seawater δ¹⁸O datasets remain ‘hidden’. To improve the accessibility of seawater δ¹⁸O data for the Earth Science research community, the Past Global Changes (PAGES) CoralHydro2k project has created a new, machine-readable, and metadata-rich database of observational seawater δ¹⁸O data, paired with seawater δ²H and salinity data, that is compliant with findability, accessibility, interoperability, and reusability (FAIR) standards for digital assets. The data has been collected from public databases and repositories, direct researcher data submissions, scientific papers, and student theses. In total, the PAGES CoralHydro2k Seawater δ¹⁸O Database contains over 18,600 data points with extensive metadata that makes the database suitable for a myriad of research applications. For hidden data, we searched for and included all datasets within the global ocean. For public data, our data collation efforts were focused on the upper 50 m from 35° N to 35° S (to aid in CoralHydro2k’s seawater δ¹⁸O reconstruction studies using δ¹⁸O and Sr/Ca in tropical-subtropical coral skeletons). We also provide a set of best practices to the community for reporting seawater isotope data in the future.