Project: Equatorial transport of nitrous oxide from the eastern tropical Pacific Ocean

NSF Award Abstract:
Nitrous oxide (N2O) is a powerful greenhouse gas, ~300 times stronger than carbon dioxide and is also implicated in the destruction of the ozone layer. Thus, it is important to understand the magnitude and sources of N2O to the atmosphere in order to predict future climate impacts. The ocean is a significant source of N2O to the atmosphere, but its overall contribution is uncertain. A significant amount of the marine N2O delivered to the atmosphere comes from the eastern tropical Pacific (ETP). This region is host to some of the lowest oxygen concentrations in the entire ocean, which is favorable to a massive production of N2O. Previous estimates of the amount of N2O diffusing out of the ETP to the atmosphere considered only the area directly over the high N2O region of the ETP. However, there are strong subsurface currents that flow away from the ETP, westward along the equator, and N2O carried away in these equatorial currents has been overlooked when determining the contribution of the ETP to marine emissions of N2O. This proposed work will use new, high-quality N2O data collected on 3 Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) cruises through the tropical Pacific to investigate N2O cycling across the entire tropical Pacific Ocean. Low oxygen regions, like the ETP, are predicted to expand in the future, potentially leading to an increase in N2O production, underscoring the importance of understanding N2O cycling in this region. This project will support mentoring up to two undergraduate summer interns.

Recent advances in analytical capabilities within the NOAA/PMEL Trace Gas group, and their application to three Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) repeat hydrography cruises through the tropical Pacific, have facilitated the collection of nitrous oxide measurements of unprecedented quality and coverage of the region, together with complementary hydrographic parameters. We propose to use this new, high-quality GO-SHIP N2O data in concert with the stable isotopic composition of nitrous oxide, tracers of ventilation rates, and current velocities to investigate the transport, production, and efflux of nitrous oxide in the tropical Pacific Ocean. Using both observation data and idealized modeling, the research will (i) estimate the magnitude of the physical transport of N2O to/from the ETP, and losses to the atmosphere, and (ii) differentiate the sources of N2O in equatorial currents between advection from the ETP and in situ production. The work proposed here will lead to a more nuanced understanding of N2O production, transport, and fate in the tropical Pacific.

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.