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Exploring the potential of clumped isotope thermometry on coccolith-rich sediments as a sea surface temperature proxy

Drury, AJ; John, CM; (2016) Exploring the potential of clumped isotope thermometry on coccolith-rich sediments as a sea surface temperature proxy. Geochemistry, Geophysics, Geosystems , 17 (10) pp. 4092-4104. 10.1002/2016GC006459. Green open access

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Abstract

Understanding past changes in sea surface temperatures (SSTs) is crucial; however, existing proxies for reconstructing past SSTs are hindered by unknown ancient seawater composition (foraminiferal Mg/Ca and δ18O) or reflect subsurface temperatures (TEX86) or have a limited applicable temperature range ( urn:xwiley:15252027:media: ggge21148:ggge21148-math-0001). We examine clumped isotope (Δ47) thermometry to fossil coccolith‐rich material as an SST proxy, as clumped isotopes are independent of original seawater composition and applicable to a wide temperature range and coccolithophores are widespread and dissolution resistant. The Δ47‐derived temperatures from <63, <20, <10, and 2–5 μm size fractions of two equatorial Pacific late Miocene‐early Pliocene sediment samples (c1; c2) range between ∼18 and 29°C, with c1 temperatures consistently above c2. Removing the >63 μm fraction removes most nonmixed layer components; however, the Δ47‐derived temperatures display an unexpected slight decreasing trend with decreasing size fraction. This unexpected trend could partly arise because larger coccoliths (5–12 μm) are removed during the size fraction separation process. The c1 and <63 μm c2 Δ47‐derived temperatures are comparable to concurrent urn:x-wiley: 15252027:media:ggge21148:ggge21148-math-0002 SSTs. The <20, <10, and 2–5 μm c2 Δ47‐derived temperatures are consistently cooler than expected. The Δ47‐ urn:x-wiley: 15252027:media:ggge21148:ggge21148-math-0003 temperature offset is probably caused by abiotic/ diagenetic calcite present in the c2 2–5 μm fraction (∼53% by area), which potentially precipitated at bottom water temperatures of ∼6°C. Our results indicate that clumped isotopes on coccolith‐rich sediment fractions have potential as an SST proxy, particularly in tropical regions, providing that careful investigation of the appropriate size fraction for the region and time scale is undertaken.

Type: Article
Title: Exploring the potential of clumped isotope thermometry on coccolith-rich sediments as a sea surface temperature proxy
Open access status: An open access version is available from UCL Discovery
DOI: 10.1002/2016GC006459
Publisher version: https://doi.org/10.1002/2016GC006459
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: clumped isotope thermometry, coccolith‐rich sediments, late Miocene to early Pliocene, equatorial Pacific, sea surface temperature proxy, sediment size fraction
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10076961
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