Systematics and application of the carbonate 'clumped isotope'thermometer in foraminifera and coccoliths

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Research has shown that 18O/16O ( 18O) and metal/calcium ratios in carbonates, and the structure of organic biomarkers, can be used to give quantitative estimates of temperature and water composition. However, the sensitivity of inorganic ( 18O, Mg/Ca) and organic (UK'37 and TEX86) temperature proxies to biological, ecological, and non-temperature environmental factors can result in systematic errors or ambiguities in climate reconstructions. Almost all temperature proxies are subject to 'vital effects' and other non-temperature environmental parameters. Most existing proxies must be referenced to water composition - use of 18O or Mg/Ca ratios in foraminifera as a proxy for temperature requires knowledge of water 18O or Mg/Ca, respectively. Both proxies are somewhat sensitive to carbonate ion concentration. In addition, a detailed mechanistic understanding does not exist for many temperature proxies (e.g., UK'37, TEX86, Mg/Ca). All of these factors contribute to uncertainties in the interpretation of past conditions, particularly for extinct taxa, for which one cannot establish robust empirical calibrations of the proxy. A technique that may not be subject to these limitations is the new carbonate 'clumped isotope' thermometer. Clumped isotope thermometry is based on the principle that ordering, or 'clumping', of heavy isotopes into bonds with or near each other in molecules, minerals or organic moieties is a temperature dependent phenomenon. In carbonates, rare heavy isotopes (13C, 18O) occur in a pool of abundant light isotopes. The proportion of 13C and 18O that are bound to each other within the carbonate mineral lattice is predicted to be temperature dependent based on principles of statistical thermodynamics. In practice, the carbonate clumped isotope thermometer is based on analyses of 13C18O16O in CO2 produced by acid digestion of carbonates. With this fellowship, I propose to develop the first calibration of the carbonate 'clumped isotope' thermometer in planktic and benthic foraminifera, and coccoliths. To date, a limited number of measurements have been made to calibrate ?47 in inorganic calcite precipitated at known temperatures (4 samples), in fish otoliths (8 samples), mollusks (3 samples), brachiopods (3 samples), and coral (3 samples). There has not yet been a validation of the clumped isotope thermometer from cultured biogenic samples, detailed field-based sampling, and no measurements have been made of foraminifera and coccoliths - all of which are requisite for paleoceanographic studies. In addition to calibrating this new isotopic thermometer in cultured and coretop foraminifera and coccoliths, I will use these data to test models for the origin of 'vital effects' in 18O and 13C. I will also apply this this thermometer to Last Glacial Maximum samples from the warm pool in the western tropical Pacific Ocean. The West Pacific warm pool is the warmest open ocean region and a benchmark for climate models. Reconstructions of the glacial-interglacial change in sea surface temperatures in the region vary from 1 to 6°C, differing systematically between methods. Finally, I will apply this thermometer to Paleocene-Eocene boundary samples from the Southern Ocean, in order to constrain the warming associated with the massive release of carbon.