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Warm middle Miocene Indian Ocean bottom water temperatures: comparison of clumped isotope and Mg/Ca based estimates

Modestou, S. E., Leutert, T. J., Fernandez, A., Lear, C. H. and Meckler, A. N. 2020. Warm middle Miocene Indian Ocean bottom water temperatures: comparison of clumped isotope and Mg/Ca based estimates. Paleoceanography and Paleoclimatology 35 (11) , e2020PA003927. 10.1029/2020PA003927

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The middle Miocene is an important analogue for potential future warm climates. However, few independent deep ocean temperature records exist, though these are important for climate model validation and estimates of changes in ice volume. Existing records, all based on the foraminiferal Mg/Ca proxy, suggest that bottom water temperatures were 5–8°C warmer than present. In order to improve confidence in these bottom water temperature reconstructions, we generated a new record using carbonate clumped isotopes (Δ47) and compared our results with Mg/Ca‐based estimates for the Indian Ocean at ODP Site 761. Our results indicate temperatures of 11.0 ± 1.7°C during the middle Miocene Climatic Optimum (MCO, 14.7–17 Ma) and 8.1 ± 1.9°C after the middle Miocene Climate Transition (MCT, 13.0–14.7 Ma), values 6 to 9°C warmer than present. Our record also indicates cooling across the MCT of 2.9 ± 2.5°C (uncertainties 95% confidence level). The Mg/Ca record derived from the same samples indicates temperatures well within uncertainty of Δ47. As the two proxies are affected by different non‐thermal biases, the good agreement provides confidence in these reconstructed temperatures. Our Δ47 temperature record implies a ~0.6‰ seawater δ18O change over the MCT, in good agreement with previously published values from other sites. Our data furthermore confirm overall high seawater δ18O values across the middle Miocene, at face value suggesting ice volumes exceeding present‐day despite the warm bottom water temperatures. This finding suggests previously underappreciated additional influences on seawater δ18O and/or a decoupling of ice volume and ocean temperature.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Additional Information: This is an open access article under the terms of the Creative Commons Attribution License
Publisher: American Geophysical Union (AGU)
ISSN: 2572-4525
Date of First Compliant Deposit: 2 October 2020
Date of Acceptance: 9 September 2020
Last Modified: 11 Feb 2021 14:02

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