Exploring the Temperature Dependence of Clumped Isotopes in Modern Porites Corals. Issue 1 (10th January 2020)

• Record Type: Journal Article
• Authors: Guo, Yangrui; Deng, Wenfeng; Wei, Gangjian; Chen, Xuefei; Liu, Xi; Wang, Xijie; Lo, Li; Cai, Guanqiang; Zeng, Ti
• Is Part Of: Journal of geophysical research. Volume 125:Issue 1(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-01-10
• Subjects: clumped isotope -- oxygen isotope -- carbon isotope -- coral -- carbonate -- SST reconstruction; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2019JG005402
• Languages: English
• ISSNs: 2169-8953

Abstract

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 δ 13 C, δ 18 O, 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 δ 13 C 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 δ 13 C 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. Plain Language Summary: Sea surface temperature (SST) is a fundamental parameter of climate variation. Understanding how SST has changed in the past is important to inform climate predictions. One way to do this is by developing a reliable thermometer based on the clumped isotope composition (Δ47 ) of corals. However, the thermometer based on coral Δ47 values may be complicated by biological factors that affect the Δ47 values as the coral grows. We investigated two modern Porites corals from the South China Sea by measuring their oxygen, carbon, and clumped isotope compositions. By comparing two samples from the same coral colony, we found that the impact of biological factors is significant, causing unusual patterns in the carbon and clumped isotopes. The biological factors also likely lead to differences in the coral Δ47 values from two different colonies. To account for these potential intracolony and intercolony effects, we established a relationship between the Δ47 values and SST based on the two corals. This relationship has the same temperature dependence as other Δ47 thermometers established on synthetic carbonates in which no biological factors are involved and can be used as a thermometer to reconstruct seasonal SST. Key Points: There is no evidence of intercolony or intracolony variations in mean Δ47 values of Porites corals on an annual timescale Coral vital effects are found to cause relative disequilibrium of isotopic composition at an intracolony level Clumped isotopes analysis of Porites corals is suitable for reconstructing relative changes in seasonal sea surface temperature