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

Abstract

Tropical sea surface temperature (SST) and sea surface salinity (SSS), variables driven by large-scale oceanic-atmospheric interactions, are recorded in the stable oxygen isotopic ratio of coral skeletal aragonite (δ 18 O coral ). Coral δ 18 O values thus preserve key information on past ocean-atmosphere variability on interannual to centennial timescales, such as the interannual El Niño-Southern Oscillation (ENSO) in the tropical Indo-Pacific (e.g.,

Equatorial Undercurrent Influence on Surface Seawater δ18O Values in the Galápagos

“…Our work provides an important new context for interpreting such data. Although atmospheric moisture balance is the common focus of δ 18 O sw interpretations (Thompson et al, 2022;Walter et al, 2022), our findings show stronger potential for Galápagos δ 18 O sw values to be used to reconstruct the strength of the EUC. Such a reconstruction would be novel and useful, given the critical role of the EUC in supporting the zonal gradient of sea surface temperature across the tropical Pacific and contributing to regional productivity.…”

“…Many paleoceanographic records from the Galápagos have been developed from fossil coral and foraminifera δ 18 O values over the last three decades (Dunbar et al, 1994;Koutavas et al, 2006;Lea et al, 2000;Rustic et al, 2015;Shen et al, 1992). These records are a mixed contribution of δ 18 O sw values and temperature, with evaluations to date showing the dominance of temperature on coral carbonate δ 18 O values in this region (Thompson et al, 2022). However, more recent work pairing foraminifera Mg/Ca and δ 18 O measurements and coral Sr/Ca and δ 18 O measurements from around the archipelago offer the potential for future δ 18 O sw and salinity reconstructions (Cheung et al, 2021;Jimenez et al, 2018;Rustic et al, 2015).…”

“…If the temperature component can be isolated, such as with paired measurements of the temperature proxy Sr/Ca in corals (McCulloch et al., 1994; Walter et al., 2022), past δ 18 O sw values can be calculated and used to interpret past salinity, hydroclimate, and ocean dynamics. In some regions, where δ 18 O sw controls a larger portion of carbonate δ 18 O variance, δ 18 O sw and salinity can also be directly inferred from carbonate δ 18 O measurements (Thompson et al., 2022).…”

“…δ 18 O variance, δ 18 O sw and salinity can also be directly inferred from carbonate δ 18 O measurements (Thompson et al, 2022).…”

Machine Learning Solutions to Regional Surface Ocean δ18O‐Salinity Relationships for Paleoclimatic Reconstruction

“…In high latitudes, seasonal sea ice melt/formation and runoff can also affect the δ 18 O sw -salinity relationship (Bauch et al, 2005;Dubinina et al, 2017Dubinina et al, , 2019. The y-intercept of the δ 18 O sw -salinity relationship, the "freshwater endmember," is thought to be an integrated measure of evaporation, precipitation, and the isotope signal of each, providing additional information about regional hydroclimate (Delaygue et al, 2001), along with the slope, which is critical for isotope-based proxy forward models of marine paleoclimate archives (Thompson et al, 2022). Consequently, it is essential to have an accurate understanding of the modern spatial variability in δ 18 O sw -salinity relationship to begin to tease apart its numerous controls and to provide a framework suitable for stable isotope-based paleoceanographic and paleoclimate interpretations.…”