Date of Award

Summer 2023

Document Type

Open Access Thesis


Marine Science

First Advisor

Annie Bourbonnais


Nitrous oxide (N2O) is a potent greenhouse gas and ozone depleting substance. It is estimated that the ocean accounts for about one third of total atmospheric emissions, which mostly occur in Oxygen Deficient Zones (ODZs) connected to coastal upwelling regions. Modeling efforts and high-resolution datasets are starting to provide a clearer picture of global marine N2O fluxes, spatiotemporal variability, and the impacts of submesoscale processes on N2O distributions. We measured nitrous oxide concentrations, stable isotope ratios and isotopomers at 7 open ocean stations along a transect crossing the Eastern Tropical North Pacific ODZ as well as at 1 background station outside the ODZ during a research expedition onboard the R/V Sally Ride in winter 2020. 15N labeled substrates were used to track the formation of 15N products during time series incubations, to quantify N2O production pathways and rates across horizontal and vertical O2 gradients. We observed important variations in the concentrations, isotopic signatures, and N2O production rates at the ODZ open ocean stations. Highest N2O concentrations were observed near the oxycline with the highest value (160 nmol L-1) at station 5, in the presence of a chlorophyll intrusion which may support the hypothesis that submesoscale features stimulate N2O production. N2O consumption during denitrification was evidenced by elevated δ15Nbulk, δ15Nα, SP, and δ18O of N2O due to kinetic isotope fractionation, and may alleviate emissions of this greenhouse gas to the atmosphere in this region.


© 2023, Margaret Ann Gaspar

Available for download on Sunday, August 31, 2025