The PAGES CoralHydro2k Seawater <i>δ</i> ¹⁸ O Database: a FAIR-aligned compilation of seawater <i>δ</i> ¹⁸ O 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 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. The database is available on the NOAA NCEI World Data Service for Paleoclimatology landing page: https://www.ncei.noaa.gov/access/paleo-search/study/34575 (last access: 11 February 2026; https://doi.org/10.25921/ap7d-2k16, Atwood et al., 2026). A Seawater Oxygen Isotopes Community was also developed within the EarthChem Library (https://www.earthchem.org/communities/seawater-oxygen-isotopes/, last access: 20 February 2026) to help researchers submit new datasets and obtain a dataset DOI. This template is aligned with the CoralHydro2k Seawater δ18O Database to facilitate future updates to the database.