Burial-induced oxygen-isotope re-equilibration of fossil foraminifera explains ocean paleotemperature paradoxes

S. Bernard (), D. Daval, P. Ackerer, S. Pont and A. Meibom
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S. Bernard: IMPMC, Sorbonne Universités, CNRS UMR 7590, MNHN, UPMC, IRD UMR 206
D. Daval: LHyGeS, CNRS UMR 7517, Université de Strasbourg/EOST
P. Ackerer: LHyGeS, CNRS UMR 7517, Université de Strasbourg/EOST
S. Pont: IMPMC, Sorbonne Universités, CNRS UMR 7590, MNHN, UPMC, IRD UMR 206
A. Meibom: Laboratory for Biological Geochemistry, School of Architecture, Civil and Environmental Engineering, École Polytechnique Fédérale de Lausanne (EPFL)

Nature Communications, 2017, vol. 8, issue 1, 1-10

Abstract: Abstract Oxygen-isotope compositions of fossilised planktonic and benthic foraminifera tests are used as proxies for surface- and deep-ocean paleotemperatures, providing a continuous benthic record for the past 115 Ma. However, visually imperceptible processes can alter these proxies during sediment burial. Here, we investigate the diffusion-controlled re-equilibration process with experiments exposing foraminifera tests to elevated pressures and temperatures in isotopically heavy artificial seawater (H2 18O), followed by scanning electron microscopy and quantitative NanoSIMS imaging: oxygen-isotope compositions changed heterogeneously at submicrometer length scales without any observable modifications of the test ultrastructures. In parallel, numerical modelling of diffusion during burial shows that oxygen-isotope re-equilibration of fossil foraminifera tests can cause significant overestimations of ocean paleotemperatures on a time scale of 107 years under natural conditions. Our results suggest that the late Cretaceous and Paleogene deep-ocean and high-latitude surface-ocean temperatures were significantly lower than is generally accepted, thereby explaining the paradox of the low equator-to-pole surface-ocean thermal gradient inferred for these periods.

Date: 2017
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DOI: 10.1038/s41467-017-01225-9

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