Carbonate clumped isotope thermometry of deep-sea corals and implications for vital effects

Here we calibrate the carbonate clumped isotope thermometer in modern deep-sea corals. We examined 11 specimens of three species of deep-sea corals and one species of a surface coral spanning a total range in growth temperature of 2–25 C. External standard errors for individual measurements ranged from 0.005& to 0.011& (average: 0.0074&) which corresponds to 1–2 C. External standard errors for replicate measurements of D47 in corals ranged from 0.002& to 0.014& (average: 0.0072&) which corresponds to 0.4–2.8 C. We find that skeletal carbonate from deep-sea corals shows the same relationship of D47 (the measure of C–O ordering) to temperature as does inorganic calcite. In contrast, the d C and dO values of these carbonates (measured simultaneously with D47 for every sample) differ markedly from equilibrium with seawater; i.e., these samples exhibit pronounced ‘vital effects’ in their bulk isotopic compositions. We explore several reasons why the clumped isotope compositions of deep-sea coral skeletons exhibit no evidence of a vital effect despite having large conventional isotopic vital effects. 2011 Elsevier Ltd. All rights reserved.