Identification and composition of secondary meniscus calcite in fossil coral and the effect on predicted sea surface temperature |
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| Authors: | Paul Dalbeck Maggie Cusack Phillip S Dobson Nicola Allison Anthony E Fallick Alexander W Tudhope |
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| Institution: | 1. Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore;2. The Tropical Marine Science Institute, National University of Singapore, Kent Ridge, Singapore 119227, Republic of Singapore;3. St. John''s Island National Marine Laboratory, National University of Singapore, Kent Ridge, Singapore 119227, Republic of Singapore;4. Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Republic of Singapore;1. Aix-Marseille Université, CNRS, CINaM UMR 7325, Marseille, France;2. Institut Ciències Mar, CSIC, 08003 Barcelona, Spain;3. Mediterranean Institute of Oceanography (MIO) UM 110, CNRS/INSU, IRD, Aix-Marseille Université, Université du Sud Toulon-Var, Marseille, France;4. Division of Chemistry, California Institute of Technology, Pasadena, CA, USA;5. Department of Chemistry and Applied Biosciences, ETH Zürich, Wolfgang Pauli Strasse 10, Hönggerberg, HCI, G113, CH-8093 Zurich, Switzerland;6. UBP-OPGC-CNRS, 5 rue Kessler, 63038 Clermont-Ferrand, France;7. Institut f. Geochemie und Petrologie, ETH Zürich, NW E 85, Clausiusstrasse 25, 8092 Zürich, Switzerland |
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| Abstract: | This study uses electron backscatter diffraction (EBSD) and atomic force microscopy (AFM) to identify secondary calcite in coral skeletons. Secondary calcite appears to have nucleated on the original aragonite dissepiments, producing horizontal structures that mimic the morphology of the original coral aragonite, forming dissepiment-like meniscus structures. The Sr/Ca and δ18O of the pristine aragonite and secondary calcite were analysed by secondary ion mass spectrometry (SIMS). The effect of calcite inclusion on the mean geochemistry of the coral carbonate and subsequent sea surface temperature (SST) calculations were determined for both Sr/Ca and δ18O. Inclusion of as little as 1% secondary calcite within the primary coral aragonite elevates the Sr/Ca-derived SST by 1.2 °C and could markedly offset estimates of past tropical climate. Conversely, inclusion of 10% secondary calcite has little effect on the SST estimated from δ18O (+ 0.6 °C) indicating that this proxy is relatively robust to even large amounts of calcite. The different extents to which the two proxies would be influenced by inadvertent inclusion of such meniscus calcite demonstrate the importance of a multi-proxy approach. |
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