NITROUS OXIDE PRODUCTION BY PHOTOCHEMODENITRIFICATION IN POLAR AND TROPICAL MARINE WATERS

Nitrous oxide (N₂O) is the main stratospheric ozone-depleting agent and a powerful greenhouse gas. Ammonia oxidizers and denitrifiers are microbial groups that are thought to control the N₂O budget in aquatic systems. Recently, a novel abiotic process known as photo(chemo)denitrification (PCD) has been identified as a significant contributor to N₂O production. It consists of photochemical reduction of nitrite and photoreduced nitrate to N₂O, and occurs at the oxic surface of freshwater and marine environments. Because it takes place at the water-air interface, PCD has the potential to contribute substantially to N₂O emissions. However, there were no measurements of PCD rates in the open ocean and at higher latitudes, which prevents evaluating the importance of PCD in the global ocean. Here, we quantified N₂O production by PCD and microbial sources in surface oxic waters from the coast of West Greenland (70^oN), and in the Eastern Tropical South Pacific Ocean (ETSP, 14-22^oS) using ¹⁵N-labelled tracer experiments. We detected PCD at both sites, at rates exceeding biological N₂O production in surface waters. Even at polar latitudes, sunlight is bright enough to drive PCD, at least during the summer period. At latitudes closer to the equator, with much more intense solar radiation, the PCD N₂O production rates may be comparable to N₂O production rates occurring in deeper layers due to biological activity. These new findings have critical implications for the global N₂O budget, suggesting that N₂O production in aquatic systems would be underestimated if PCD is not considered.

Presentation Preference: Oral

Primary Presenter: Elizabeth Leon-Palmero, Princeton University (el23@princeton.edu)

Authors:

Elizabeth Leon-Palmero, Department of Geosciences, Princeton University  (el23@princeton.edu)

Weiyi Tang, College of Marine Science, University of South Florida  (weiyitang@usf.edu)

Isabell Schlangen, Nordcee, Department of Biology, University of Southern Denmark  (schlangen@biology.sdu.dk)

Carolin Loescher, Nordcee, Department of Biology, University of Southern Denmark  (cloescher@biology.sdu.dk)

Bess Ward, Department of Geosciences, Princeton University  (bbw@princeton.edu)