Research Interests

My research is in the areas of climate and biogeochemistry. For the last two decades my colleagues and I have measured variations in the concentration of oxygen and its isotopic composition to characterize rates of photosynthesis and respiration at different scales of time and space. We have made our measurements in the modern atmosphere, in air in the snowpack of polar ice sheets, in seawater-dissolved gases, and in fossil air samples trapped in ice cores. Our atmospheric measurements have characterized the fertility of the oceans and, together with snowpack studies, constrained rates of fossil fuel carbon dioxide uptake by the oceans and the land biosphere during recent decades. Seawater measurements have characterized regional rates of photosynthesis and respiration in the oceans. Ice core measurements constrain glacial-interglacial changes in the fertility of Earth's marine and land biospheres. They also provide a means for correlating ice cores, yielding information about the timing (and hence dynamics) of large-scale climate changes.

Membership Type


Election Year


Primary Section

Section 15: Geology

Secondary Section

Section 16: Geophysics