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

Abstract

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 Δ_47 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 Δ47 (the measure of ^(13)C–^(18)O ordering) to temperature as does inorganic calcite. In contrast, the δ^(13) C and δ^(18)O values of these carbonates (measured simultaneously with Δ_47 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.

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