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.

Automated summary

Dual clumped isotope thermometry of coral carbonate can accurately reconstruct paleotemperatures and may require different corrections for cold-water and warm-water corals.