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Tropical Sea Surface Temperatures following the Middle Miocene Climate Transition from Laser-Ablation ICP-MS analysis of glassy foraminifera
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  • Michael Grahame Nairn,
  • Caroline H. Lear,
  • Sindia Sosdian,
  • Trevor Bailey,
  • Simon Beavington-Penney
Michael Grahame Nairn
Cardiff University, Cardiff University

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Caroline H. Lear
Cardiff University, Cardiff University
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Sindia Sosdian
Cardiff University, Cardiff University
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Trevor Bailey
National Museums and Galleries of Wales, National Museums and Galleries of Wales
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Simon Beavington-Penney
University of Manchester, University of Manchester
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The mid-to-late Miocene is proposed as a key interval in the transition of the Earth’s climate state towards that of the modern-day. However, it remains a poorly understood interval in the evolution of Cenozoic climate, and the sparse proxy-based climate reconstructions are associated with large uncertainties. In particular, tropical sea surface temperature (SST) estimates largely rely on the unsaturated alkenone Uk37 proxy, which fails to record temperatures higher than 29˚C, the TEX86 proxy which has challenges around its calibration, and Mg/Ca ratios of poorly preserved foraminifera. We reconstruct robust, absolute, SSTs between 13.5 Ma and 9.5 Ma from the South West Indian Ocean (paleolatitude ~5.5˚S) using Laser-Ablation (LA-) ICP-MS microanalysis of glassy planktic foraminiferal Mg/Ca. Employing this microanalytical technique, and stringent screening criteria, permits the reconstruction of paleotemperatures using foraminifera which although glassy, are contaminated by authigenic coatings. Our absolute estimates of 24-31⁰C suggest that SST in the tropical Indian Ocean was relatively constant between 13.5 and 9.5 Ma, similar to those reconstructed from the tropics using the Uk37 alkenone proxy. This finding suggests an interval of enhanced polar amplification between 10 and 7.5 Ma, immediately prior to the global late Miocene Cooling.
Mar 2021Published in Paleoceanography and Paleoclimatology volume 36 issue 3. 10.1029/2020PA004165