Dual clumped isotope thermometry of coral carbonate

The stable (618O and 613C) and clumped (A47) isotope compositions of coral carbonate are valuable archives for paleoclimate reconstructions. However, the A47-temperature relationships of warm and cold-water corals deviate from that of inorganic carbonate precipitated at equilibrium. Dual clumped iso-tope thermometry of carbonates (i.e., simultaneous A47 and A48 measurements on a single carbonate) has the potential to achieve more accurate paleotemperature reconstruction, identifying and correcting for kinetically driven isotopic disequilibrium. Here we present the first extensive dual clumped isotope data -set of coral carbonate, spanning a broad range of cold and warm-water coral species. We confirm that corals are enriched in A47 and depleted in A48 relative to equilibrium, a pattern corresponding to the mix-ing of an equilibrium DIC pool with kinetically derived HCO3- produced by hydration and hydroxylation of CO2. Dual clumped isotope measurements of cold-water corals fall on the initial linear portion of model (IsoDIC) predicted departure from equilibrium. The dual clumped isotope composition of cold-water cor-als, corrected by the model-predicted A47/A48 offset slope (-0.78), yield accurate reconstruction of coral growth temperature with a precision of < 3 & DEG;C at the 68% confidence level. In contrast, disequilibrium off-sets in the A47 and A48 of warm-water corals correspond to precipitation from a more equilibrated DIC pool, which we attribute to the action of carbonic anhydrase in the calcifying fluid. It may be possible to correct warm-water coral growth temperatures, using an empirically derived correction (A47/ A48 offset slope of-0.4). Dual clumped isotope thermometry of coral carbonate opens new possibilities to recon-struct both sea surface temperatures and ocean dynamics of intermediate to deep water masses.(c) 2022 Elsevier Ltd. All rights reserved.