Accessing the potential of clumped isotope thermometry to constrain temperatures in the Arctic during the Pliocene

The specific goal of this research is to identify whether carbonate "clumped isotope" thermometry can be applied to mollusks to accurately and precisely reconstruct temperatures in the Arctic. Previous work has shown that the occurrence of multiple rare isotope substitutions in carbonate minerals, also referred to as the "clumping" of heavy isotopes into bonds with each other, is temperature dependent. This temperature proxy is also independent of the del-18O of water and the del-13C of dissolved inorganic carbon. Initial studies of biologically-precipitated calcite and aragonite by the PI and co-PI and collaborators indicate that the measurements of 13C-18O bond abundance should allow one to make a relatively assumption-free determination of the temperature at which a mineral formed. Although this new proxy looks promising, calibration of the clumped isotope thermometer at low temperatures (i.e., below 15C) is limited. Therefore the utility of this proxy for climate reconstructions in the Arctic is unclear. This project will determine the accuracy and precision of the technique when applied to biological samples grown at Arctic temperatures and, consequently, the ability of this technique to assess paleo ocean temperatures in polar regions. The instrumental record of temperature only goes back in time a few hundred years, at most. In order to understand the natural variability of temperature, either locally or globally, we require much longer records. To develop such records, we rely on proxy measurements for temperature. Use of such proxies requires assumptions and often imposes large error bars on the estimated temperature. This project will determine the usefulness of a new proxy in the polar regions. This research is an Early-concept Grant for Exploratory Research (EAGER) proposal.