Collaborative Research: US GEOTRACES GP17-OCE: Mapping nitrous oxide sources and sinks through isotopic measurements in the Pacific Ocean

Nitrous oxide is a powerful greenhouse gas that is produced by microbial activity in soils and the ocean. The Pacific Ocean is an important component of oceanic nitrous oxide production and emission to the atmosphere due to its large area and pockets of low oxygen in the eastern tropical Pacific. The largest amounts of nitrous oxide observed in the global ocean occur in these pockets of low oxygen.

These regions appear to impact nitrous oxide distributions throughout the Pacific Ocean, but the sources of nitrous oxide in these regions may be quite different. This work will provide a better understanding of both the natural distribution of nitrous oxide in the global ocean, as well as the mechanisms and controls on its production for future emission projections.

This will be accomplished by collecting nitrous oxide isotopic measurements at different water depths from the central Pacific, where relatively little work has focused. Measurements of nitrous oxide isotopic composition is a powerful analytical tool that will help to answer these important questions about this powerful greenhouse gas. The Stanford component of this project will be carried out primarily by a PhD student, who will be trained in a variety of laboratory techniques, data analysis, and computer modeling.

We will also use support from this project to increase diversity in the Geosciences by providing first-time research experiences to underrepresented minority students through Stanford’s SURGE (Summer Undergraduate Research in Geoscience and Engineering) Program. One of the project’s lead investigators, Bourbonnais, will also give a series of introductory Chemical Oceanography lectures at Benedict College, a private historically black, liberal arts college in Columbia, SC and support two undergraduate students from Benedict College through summer internships at the University of South Carolina.

This project will address three main questions related to N2O cycling in the Pacific Ocean: (1) What features of N2O distribution in the central Pacific Ocean are driven primarily through mixing and circulation vs. biological processes; (2) Which biogeochemical processes control the distribution of biologically produced N2O in the central Pacific Ocean; and (3) How does the production (amount, mechanism, yield) of N2O relate to the availability of oxygen in situ? This collaborative project will be carried under the GEOTRACES program, an international effort to understand the distribution of elements in the global ocean.

With the synthesis of the GEOTRACES GP17 and GP15 sections, we will have an opportunity to examine the distributions of N2O and its isotopes (an indicator of production mechanisms) relative to oxygen, trace elements, and water mass tracers. Data from this project will be made available to the public through the Biological and Chemical Oceanography-Data Management Office (www.bco-dmo.org). The data will also be compiled in GEOTRACES data products that will be freely available.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.