From Biogeochemical Pathways to Eddy-driven Variability: Understanding Nitrous Oxide Production and Outgassing from Oxygen Minimum Zones

Speaker: Danny McCoy
Institution: UCLA
Location: MSA 7124
Date: May 31, 2023
Time: 3:30 pm to 4:30 pm


Oceanic emissions of the potent greenhouse gas nitrous oxide (N2O) account for roughly one-third of all natural sources to the atmosphere. The Eastern Tropical South Pacific (ETSP) is a prominent hot-spot for N2O cycling due to the presence of a widespread and persistent oxygen-minimum-zone (OMZ), where steep oxygen gradients leads to enhanced production from both nitrification and stepwise denitrification. However, the relative contributions from these biogeochemical pathways to the ultimate outgassing of N2O remains poorly constrained, in part due to shared intermediary nitrogen tracers, and the tight coupling of denitrification sources and sinks. To shed light on this problem, we embed a new, mechanistic model of the OMZ nitrogen cycle within a three-dimensional eddy-resolving physical-biogeochemical model of the ETSP, tracking contributions from remote advection, atmospheric exchange, and local nitrification and denitrification. The model reveals a decoupling between denitrification steps that allows this pathway to dominate local N2O production within the ETSP OMZ, while also providing new insights into the role the physical circulation plays in regulating N2O accumulation. I will further highlight the tight interaction between mesoscale-driven tracer heterogeneity in the ETSP and the response of nonlinear N cycle transformations triggered by such perturbations. Using a Reynolds-averaging framework, I will demonstrate that coarse grained biogeochemical models may overestimate the fluxes of N2O to the atmosphere from the ETSP