Exploring the Temperature Dependence of Clumped Isotopes in Modern Porites Corals
Journal
Journal of Geophysical Research: Biogeosciences
Journal Volume
125
Journal Issue
1
Pages
-
Date Issued
2020
Author(s)
Abstract
Porites corals are valuable geological archives for reconstructing past sea surface temperature (SST) in tropical oceans. Their clumped isotope compositions (indicated by Δ47 values) provide a potential proxy for SST. The Δ47 value in Porites coral usually departs from thermodynamic equilibrium due to vital effects. To explore the temperature dependence of Δ47 values in corals, we determined δ13C, δ18O, and Δ47 values in two modern Porites corals from the South China Sea. Our results indicate no intercolony or intracolony biases in Δ47 values on annual timescales. However, on seasonal timescales, Δ47 enrichment associated with δ13C depletion is observed at an intracolony level. This cannot be explained by incomplete hydration and/or hydroxylation of metabolic CO2; instead, we interpret this new pattern of isotopic anomalies as a peculiar evidence of vital effects on Δ47 and δ13C fractionation. Although complicated by vital effects, the Δ47 signature in Porites corals still preserved a robust SST dependence, similar to those of recently published Δ47-T calibrations. The observed Δ47 offset relative to inorganic carbonate due to the vital effects is consistent, and relative variations in seasonal SST can be obtained. This study refines the Δ47 thermometer in Porites corals and strengthens its capacity to be used to reconstruct past SST. ©2019. American Geophysical Union. All Rights Reserved.
Other Subjects
calibration; carbon dioxide; carbon isotope; carbonate; coral; hydration; isotopic composition; isotopic fractionation; oxygen isotope; proxy climate record; reconstruction; sea surface temperature; thermodynamics; Pacific Ocean; South China Sea; Anthozoa; Porites
Type
journal article