Collaborative Research: Opening the black box of oxygen deficient zone biogeochemistry through integrative tracers

The oxygen deficient zones are regions in the ocean where dissolved oxygen disappears. These regions harbor unique ecosystems only found in waters without oxygen, and they are important for Earth’s climate. Specifically, the production of nitrogen gas by two microbial processes, anammox and denitrification can control how productive the oceans are. Yet how much each process shapes ocean chemistry within these areas remains unknown. This project aims to study the oxygen deficient waters of the eastern tropical North Pacific ocean to better understand the mechanisms shaping marine nitrogen and carbon chemistry. Through this work, the project will train undergraduate and graduate students at three universities. The project aims to broaden participation in and understanding of ocean sciences by developing public videos about the methods used and the science behind the project. The investigators will conduct a research cruise in the eastern tropical North Pacific ocean, the largest oxygen deficient zone. They will measure many nutrients including inorganic carbon and nitrogen and natural abundance stable isotopes of nitrogen compounds. They will use these patterns to establish how the major reactions work together to control nitrogen cycling and gaseous nitrogen production. In addition, a high-resolution model of the ocean will reveal the influence of ocean mixing, set the timescales for reactions, and enable synthesis of the measurements into a global context. The work will determine how the input of oxygen through mixing controls chemistry, and it will distinguish between the processes restricted to the permanently anoxic core vs. those that tolerate (or are enhanced by) occasional oxygenation. Overall, the project will provide new information about nitrogen cycling pathways (anammox, denitrification, and nitrite oxidation) across the region and link the resulting isotopic signals to the global nitrogen budget. 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.