Research Interests

The 13C-18O carbonate paleothermometer: The hottest thing off our presses is a carbonate paleothermometer based on the ordering of 13C and 18O into bonds with each other in the carbonate mineral lattice. This differs in important ways from Urey's classic carbonate-water oxygen isotope thermometer (or similar ones based on other sets of phases. Most significantly, the 13C-18O thermometer is based on a homogeneous equilibrium (an exchange reaction involving only components of a single phase). Therefore, it rigorously constrains temperature without needing to know the oxygen isotope composition of water, or anything else besides carbonate). This property of the 13C-18O thermometer promises to resolve many long-standing problems in paleoclimate research and paleothermometry. Our first application focused on determining the growth temperatures of soil carbonates from the Altiplano, which can be compared to the 'surface lapse rate' to constrain its uplift history. Ongoing applications include the thermal histories of aqueously altered meteorites, marine paleoclimate studies in 'deep' geologic history (the mesozoic, paleozoic and late pre-cambrian), and the body temperatures of the dinosaurs (roar!). These applications are anticipated to be the tip of a large iceberg. This is an ideal program for an ambitious new student or postdoc to join...

Multiply-substituted isotopologues of CO2 in air: The same set of instruments used to study 13C-18O ordering in carbonates can be used to measure the abundances of the rare carbon dioxide isotopologue, 13C18O16O, in air and other natural gases. This molecule has several interesting and exotic properties, and as a result it can provide unique constraints on the origins of CO2 and the budget of atmospheric CO2. For example, the concentration of this isotopologue is sensitive to whether or not CO2 comes from high temperature sources (car exhaust or forest fires) vs. low-temperature sources (e.g., respiration), independent of the ∂13C of that CO2. We are applying this measurement to understand the atmospheric budget of CO2 and the mechanisms of its production and consumption in model systems. In the near future, we will begin similar studies of multiply-substituted isotopologues of other atmospheric gases.

Earth's atmospheric H2 budget: Molecular hydrogen (H2) is the tenth most abundant molecule in earth's atmosphere, and the second most abundant reduced gas, after methane. It participates in or indirectly influences photochemical cycles of OH, methane and ozone, and has a poorly understood role in the microbiology of soils. The budget and environmental chemistry of H2 is not well known, and this ignorance poses a significant problem for predicting the possible consequences of anthropogenic emissions of H2 that might be associated with the transition to a 'hydrogen economy'. We have been examining

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