Impacts of Mesoscale Eddies on Nitrous Oxide Production in the Eastern Tropical North Pacific Oxygen Deficient Zone

Nitrous oxide (N₂O) is a potent greenhouse gas and ozone depleting substance with important oceanic sources to the atmosphere. Yet the roles of mesoscale or sub mesoscale features (e.g., eddies, chlorophyl intrusions), oxygen concentrations, or organic matter fluxes on N₂O dynamics are still poorly constrained. We sampled 23 stations along a transect from Costa Rica to San Diego in the Eastern Tropical North Pacific (ETNP) for N₂O concentrations, stable isotopes and isotopomers in January 2022. The transect crossed contrasting oxygen and productivity regimes in the ETNP Oxygen Deficient Zone (ODZ), including the highly productive Costa-Rica Dome. In addition, we observed at least two mesoscale eddies along the cruise track. We measured rates of N₂O production from nitrification and denitrification using ¹⁵N-labeled incubations. We also performed kinetic experiments to evaluate the effect of substrate additions on N₂O production rates. We observed highest N₂O concentrations and production rates at low-O₂ concentrations near the ODZ oxycline in elevated productivity areas, as evaluated by satellite-derived surface chlorophyll a and ship transmissometer data. Consistent with previous studies in ODZs, our isotopomer data suggest that incomplete denitrification is responsible for these high N₂O accumulations above the ODZ. We will further expand on the role of mesoscale eddies for N₂O production both along vertical and horizontal gradients. 

Presentation Preference: Either

Primary Presenter: Annie Bourbonnais, University of South Carolina (abourbonnais@seoe.sc.edu)

Authors:

Annie Bourbonnais, School of the Earth, Ocean and Environment, University of South Carolina, Columbia, USA  (abourbonnais@seoe.sc.edu)

Darcy Perin, School of the Earth, Ocean and Environment, University of South Carolina, Columbia, USA  (dperin@email.sc.edu)

Laura Bristow, Department of Marine Sciences, University of Gothenburg, Sweden  (laura.bristow@gu.se)

Mark Altabet, School for Marine Science and Technology, University of Massachusetts Dartmouth, New Bedford, MA, USA  (maltabet@umassd.edu)