Open AccessExploring the potential of clumped isotope thermometry on coccolith‐rich sediments as a sea surface temperature proxy
Author(s) -
Drury Anna Joy,
John Cédric M.
Publication year - 2016
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2016gc006459
Subject(s) - coccolith , seawater , geology , calcite , isotope , diagenesis , sediment , oceanography , mineralogy , dissolution , pelagic sediment , sea surface temperature , δ18o , stable isotope ratio , carbonate , paleontology , chemistry , physics , organic chemistry , quantum mechanics
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 δ 18 O) or reflect subsurface temperatures (TEX 86 ) or have a limited applicable temperature range (U 37 k '). We examine clumped isotope (Δ 47 ) 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 Δ 47 ‐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 Δ 47 ‐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 Δ 47 ‐derived temperatures are comparable to concurrentU 37 k 'SSTs. The <20, <10, and 2–5 μm c2 Δ 47 ‐derived temperatures are consistently cooler than expected. The Δ 47 ‐U 37 k '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.