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Exploring the Temperature Dependence of Clumped Isotopes in Modern Porites Corals
Author(s) -
Guo Yangrui,
Deng Wenfeng,
Wei Gangjian,
Chen Xuefei,
Liu Xi,
Wang Xijie,
Lo Li,
Cai Guanqiang,
Zeng Ti
Publication year - 2020
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2019jg005402
Subject(s) - porites , coral , sea surface temperature , oceanography , geology
Porites corals are valuable geological archives for reconstructing past sea surface temperature (SST) in tropical oceans. Their clumped isotope compositions (indicated by Δ 47 values) provide a potential proxy for SST. The Δ 47 value in Porites coral usually departs from thermodynamic equilibrium due to vital effects. To explore the temperature dependence of Δ 47 values in corals, we determined δ 13 C, δ 18 O, and Δ 47 values in two modern Porites corals from the South China Sea. Our results indicate no intercolony or intracolony biases in Δ 47 values on annual timescales. However, on seasonal timescales, Δ 47 enrichment associated with δ 13 C depletion is observed at an intracolony level. This cannot be explained by incomplete hydration and/or hydroxylation of metabolic CO 2 ; instead, we interpret this new pattern of isotopic anomalies as a peculiar evidence of vital effects on Δ 47 and δ 13 C fractionation. Although complicated by vital effects, the Δ 47 signature in Porites corals still preserved a robust SST dependence, similar to those of recently published Δ 47 ‐T calibrations. The observed Δ 47 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 Δ 47 thermometer in Porites corals and strengthens its capacity to be used to reconstruct past SST.