Uncovering 'Hidden' Insights from the Ocean in the PAGES CoralHydro2k Seawater δ18O Database 

The oxygen isotope ratio (δ18O) of seawater is a powerful tracer of the global water cycle, providing valuable information on the exchange of water between the ocean, atmosphere, and cryosphere as well as on ocean mixing processes. As such, observational seawater δ18O data place powerful constraints on hydrologic changes in the modern ocean, are 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. In recognition of the broad value of seawater δ18O data to the Earth science community and the growing number of new seawater δ18O data sets that have been generated over the last decade, we launched the PAGES CoralHydro2k Seawater δ18O Database Project in 2020 to recover ‘hidden’ seawater oxygen isotope data sets. We have collated these records and combined them with public data to create a new, machine-readable, and metadata-rich database that aligns with findability, accessibility, interoperability, and reusability (FAIR) standards for digital assets. Here, we present a summary of our crowdsourcing efforts and description of the database to date, and report initial findings from the new database. The database consists of over 19,000 observations of seawater δ18O with more than 50 metadata fields. We compare seawater δ18O variability from the database to that simulated by a suite of isotope-enabled climate models and to seawater δ18O reconstructions derived from coral records and find substantial differences at annual to decadal timescales across different data sets. Lastly, we discuss the potential for future investments in water isotope observation networks to tackle 21st century science questions related to ocean changes in the past, present, and future.