Award: OCE-1657868

Nitrous oxide is a potent greenhouse gas that contributes to human-induced climate change. On a molecular basis, nitrous oxide absorbs as much heat as 300 molecules of carbon dioxide. The oceans are an important source of nitrous oxide to the atmosphere. Coastal upwelling induces high rates of biological activity, and many of these microbially-mediated processes contribute to nitrous oxide production and emission to the atmosphere. Previous research has shown that the eastern tropical Pacific Ocean is one such region, with persistent upwelling and high rates of nitrous oxide emission to the atmosphere. The goals of this project were to identify the source mechanisms, rates, and the environmental conditions that favor high rates of nitrous oxide production in the eastern tropical Pacific ocean. The first phase of our research took place onboard the research vessel R/V Sally Ride in the spring of 2018. From the ship, we collected seawater samples, and conducted experiments with water collected from different depths in the water column, experiencing different conditions that might favor nitrous oxide production. Those samples were brought home to our laboratories at Stanford and Princeton University, and chemically analyzed to determine the rates and mechanisms of nitrous oxide production. Our findings to date show that the highly productive, low oxygen waters favor nitrous oxide production from nitrite and nitrate, through a process known as denitrification. In addition, nitrous oxide is produced from ammonium via a novel hybrid mechanism. These results will allow us to better model and predict the production and emission of nitrous oxide under a variety of possible future conditions, as our planet and oceans continue to change. This project has also supported the research and training of two PhD students at Stanford, as well as the education of undergraduate students who have been introduced to oceanographic research, and learned about ocean chemistry and the interactions between the ocean's chemical and biological processes. The model we developed and data we collected as part of this project is freely available to the public, and can be used for teaching and learning about the ocean. Last Modified: 12/17/2020 Submitted by: Karen L Casciotti