Reconstruction of Deep-Water Temperatures in the Drake Passage Over the Last Glacial Cycle: Application of Carbonate Clumped Isotope Thermometer to Absolutely-Dated Deep-Sea Corals

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This proposed research aims to produce high resolution, precise and accurate records of deep water temperatures in the Drake Passage over the past ~40,000 years, by applying the newly developed carbonate clumped isotope thermometer to a unique collection of modern and fossil deep-sea corals, and thus advance the understanding of the role of the Southern Ocean in modulating global climate. In addition, this study will provide further evaluation on the potential of this new thermometer to derive accurate estimates of past ocean temperatures from deep-sea coral skeletons. Funding will support an early-career junior scientist and a graduate student. Despite its crucial role in modulating global climate, rates and amplitudes of environmental changes in the Southern Ocean are often difficult to constrain. In particular, the knowledge about the deep water temperatures in the Southern Ocean during the last glacial cycle is extremely limited. This results both from the lack of well-dated climate archives for the deep Southern Ocean and from the fact that most existing temperature proxies (e.g. del18O and Mg/Ca of foraminifera and corals) suffer from the biological 'vital effects'. The latter is especially problematic; it causes substantial challenges in interpreting these geochemical proxies and can lead to biases equivalent to tens of degrees in temperature estimates. Recent development of carbonate clumped isotope thermometer, holds new promises for reconstructing deep water temperatures in the Southern Ocean, since calibration studies of this thermometer in deep-sea corals suggest it is largely free of vital effects. This proposed research seeks to refine the calibration of carbonate clumped isotope thermometer in deep-sea corals at low temperatures, improve the experimental methods to obtain high precision in temperature estimates, and then apply this thermometer to a unique collection of modern and fossil deep-sea corals collected from the Drake Passage during two recent Office of Polar Programs (OPP)-funded cruises, that have already been dated by radiocarbon and U-series methods. By combining the reconstructed temperatures with the radiocarbon and U-Th ages for these deep-sea corals, this study will explore the relationships between these temperature changes and global climate changes.