Award: OCE-1140404

Nitrogen (N) is required by all living organisms, and its availability can limit ecosystem productivity on a variety of space and time scales. Humans have profoundly changed the availability of N on a global scale by manufacturing synthetic fertilizer in amounts equivalent to natural terrestrial N fixation each year. This fertilizer has increased food production throughout the world, but its runoff and atmospheric transport to the ocean have negative environmental impacts, such as stimulating harmful algal blooms and coastal hypoxia, as well as enhancing production of nitrous oxide (N₂O), a potent greenhouse gas. The goals of this research project were to develop a framework for using the ratios of naturally occurring stable isotopes in marine nitrate (NO₃^-), nitrite (NO₂^-) and N₂O to quantify the fluxes and to understand the mechanisms of N cycling in the marine environment. In so doing, we can better anticipate how enhanced N delivery to the ocean will be processed and what impacts it will have on ocean biogeochemistry.