Correction factors for δ 18 O-derived global sea surface temperature reconstructions from diagenetically altered intervals of coral skeletal density banding

Sivaguru, Mayandi, Fouke, Kyle W., Todorov, Lauren, Kingsford, Michael J., Fouke, Kaitlyn E., Trop, Jeffrey M., and Fouke, Bruce W. (2019) Correction factors for δ 18 O-derived global sea surface temperature reconstructions from diagenetically altered intervals of coral skeletal density banding. Frontiers in Marine Science, 6. 306.

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Abstract

Reconstruction of sea surface temperature (SST) from the δ18O and Sr/Ca composition of coral skeletal density banding (CSDB), identified with x-ray diffraction and micro computed tomography, provides invaluable centuries-long records of ocean circulation and climate change. Comparison with age-equivalent instrument measurements of SST over the last 125 years has proven these δ18O-derived SST reconstructions to be generally reliable. However, notable exceptions occur within discrete CSDB stratigraphic intervals that yield δ18O-derived SST underestimates of as much as 9°C with respect to instrument measured SST. Here we combine high-resolution optical and electron microscopy with geochemical modeling to establish correction factors for the impact of marine seafloor physical, chemical, and biological alteration (diagenesis) within these altered intervals of CSDB stratigraphy. Four cores were collected from Porites coral heads across a 4-24 m water depth bathymetric transect at Myrmidon Reef, Great Barrier Reef, Australia. Precise mapping of diagenetic aragonite cementation was completed within CSDB patterns digitally overlaid on 35 petrographic thin sections fully covering 2.1 m of core. The vast majority of core skeletal material exhibited little to no diagenetic aragonite cementation. However, extensive diagenetic alteration was observed within discrete CSDB intervals near the base of the two deeper water Porites heads. This diagenesis serves to modify skeletal density and CSDB stratigraphy in these intervals, as well as structurally reinforce the coral skeleton. Reliable δ18O-based SST correction factors for these diagenetically altered CSDB intervals are established here by applying the percent mixing of diagenetic aragonite cement to a binary mixing model. This approach, with quantitative extents of mixing established with both microscopy and existing globally distributed coral δ18O and Sr/Ca data sets, accurately restores modern and fossil coral δ18O-derived SST records. Results indicate that as little as 5% mixing of diagenetic aragonite cement with original coral skeleton will cause δ18O-based SST anomalies of 0.9°C.

Item ID: 62038
Item Type: Article (Research - C1)
ISSN: 2296-7745
Keywords: Coral skeletal density banding, Correction factors, Diagenetic alteration, Marine carbonate geochemistry, Paleoclimate reconstruction, Paleothermometry, Porites, Sea surface temperature
Copyright Information: Copyright © 2019 Sivaguru, Fouke, Todorov, Kingsford, Fouke, Trop and Fouke. This is an open-access article distributed under the terms of the Creative CommonsAttribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Funders: National Aeronautics and Space Administration (NASA), Office of Naval Research (ONR), ARC Centre of Excellence for Coral Reef Studies
Projects and Grants: NASA Astrobiology Institute No. NNA13AA91A, ONR N00014-00-1-0609
Date Deposited: 06 Mar 2020 01:34
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 60%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 40%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 60%
96 ENVIRONMENT > 9603 Climate and Climate Change > 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts) @ 40%
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