Correction Factors for δ18O-Derived Global Sea Surface Temperature Reconstructions From Diagenetically Altered Intervals of Coral Skeletal Density Banding

Mayandi Sivaguru, Kyle W. Fouke, Lauren Todorov, Michael J. Kingsford, Kaitlyn E. Fouke, Jeffrey M. Trop, Bruce W Fouke

Research output: Contribution to journalArticle

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.

Original languageEnglish (US)
Article number306
JournalFrontiers in Marine Science
Volume6
Issue numberJUN
DOIs
StatePublished - Jun 18 2019

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surface temperature
corals
coral
sea surface temperature
aragonite
Temperature
Stratigraphy
Reefs
Cements
stratigraphy
cement
cementation
skeleton
diagenesis
Climate change
Electron microscopy
Optical microscopy
Tomography
micro-computed tomography
Water

Keywords

  • Coral skeletal density banding
  • Correction factors
  • Diagenetic alteration
  • Marine carbonate geochemistry
  • Paleoclimate reconstruction
  • Paleothermometry
  • Porites
  • Sea surface temperature

ASJC Scopus subject areas

  • Oceanography
  • Global and Planetary Change
  • Aquatic Science
  • Water Science and Technology
  • Environmental Science (miscellaneous)
  • Ocean Engineering

Cite this

Correction Factors for δ18O-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.; Fouke, Bruce W.

In: Frontiers in Marine Science, Vol. 6, No. JUN, 306, 18.06.2019.

Research output: Contribution to journalArticle

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AB - 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.

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