My research is focused on the biogeochemical oceanographic processes that affect climate. I am particularly interested in the cycling of nitrogen (N), an essential nutrient for all organisms that limits primary productivity in most of the ocean. The capacity of the ocean to take up and sequester carbon dioxide, through the biological pump, is regulated in part by the availability of bioavailable, or fixed, N in surface waters. Moreover, the ocean is an important source of nitrous oxide (N2O), a by-product of nitrification and an intermediate product during denitrification. N2O is a greenhouse gas ~300 times more potent than CO2, and is currently the most important ozone-depleting substance.

I use complementary approaches to address questions related to marine N-cycling, including geochemical and microbial molecular ecology techniques as well as simple box modeling. Stable isotopes are widely used to elucidate marine N cycle processes as they integrate over space and time. I exploit the stable isotope ratios of reactive N pools as a primary tool and tracer to study N transformations in different marine environments. The coupled (δ  N and δ  O) isotopic compositions of nitrate (NO3 ), nitrite (NO2 ) or N2O is particularly valuable, since the O and N atoms are affected differently during biological consumption and production. This allows co-occurring N processes in oceanic environments to be disentangled. I also measure N2O isotopomers, the intramolecular distribution of   N in the N2O molecule, in order to resolve N source and sink terms.

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New graduate student position available here!