Seawater carbonate chemistry and skeletal isotopic composition and calcifying fuid composition in co-occurring Porites and Diploastrea specimens across the Pacifc ocean

Abstract

The Tara Pacifc expedition (2016–2018) provided an opportunity to investigate calcifcation patterns in extant corals throughout thePacifc Ocean. Cores from colonies of the massive Porites and Diploastrea genera were collected fromdiferent environments to assess calcifcation parameters of long-lived reef-building corals. In this study, we compared the calcifcation and carbonate chemistryup-regulation of Diploastrea heliopora and Porites corals from across a range of environments. To this, we analyzed the skeletal geochemistry and growth parameters of 39 colonies of Porites (n=33) and Diploastrea (n=6) collected across the tropical Pacifc Ocean during the Tara Pacifc expedition (2016–2018). Te collected corals represent a suite of cores exposed to various hydrological conditions of seawater temperature (SST: 22.4–29.8 °C), salinity (SSS: 31.5–36.1), and carbonate chemistry (total scale pHsw: 8.01–8.09). Te average chemical composition of the calcifying fuid (pHcf, [CO32−]cf, DICcf, Ωcf) was derived from paired boron isotope (δ11B) and B/Ca analyses of core-top samples corresponding to the last 6 years of growth (2010–2016). Based on these data, we assessed the impact of the ambient seawater properties (SST, salinity, carbonate chemistry) on the cf composition of these slow-growing reef-building genera at the Pacifc basin scale.