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Abstract

Despite making up a relatively small proportion of total ocean area, coastal marine waters play a disproportionate role in the biogeochemical cycling of climate-active gases, including nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄). Sea-air fluxes from these coastal regions remain subject to significant uncertainty, due to limited sampling resolution and high spatio-temporal variability in surface water properties. Using continuous ship-board measurements to map spatial distributions of N₂O, CO₂ and CH₄, coupled with discrete depth profiles and numerical model analysis, this thesis provides insight into the biogeochemical and physical processes that influence the surface water concentrations and sea-air fluxes of these gases. Chapter two presents a methodology for high resolution measurements of dissolved gases in surface waters, based on a rapid dissolved gas extraction module coupled with a Cavity Ring-down Spectroscopy gas analyzer. The gas extraction module was first deployed and tested in the Canadian Arctic Archipelago. These field measurements demonstrate that surface water N₂O concentrations largely followed a temperature-dependent solubility distribution, while CH₄ concentrations were more variable, and influenced by a range of processes, including vertical mixing, sea-ice dynamics and tidewater glacier melt. In chapter three, the role of sea-ice and tidewater glacier melt in coastal biogeochemical cycling of methane is further explored, with a focus on the coastal Arctic regions near Svalbard, Norway, and other areas of the Canadian Arctic Archipelago. Measurements from these areas further illustrate an important role of sea ice and tidewater glaciers in controlling surface water CH4 concentrations in the Arctic Ocean. In chapter four, the biogeochemical cycling of CH₄, N₂O and CO₂ are explored in a wind-driven coastal upwelling system off the coast of Oregon and California, where high frequency observations of dissolved gases and stable carbon isotopes were paired with numerical model output to explore the importance of vertical mixing and source water masses in the surface fluxes of these gases. Overall, this thesis describes an automated trace gas analysis system and demonstrates the utility of high frequency measurements in examining biogeochemical and physical processes controlling the spatial distribution and sea-air fluxes of climate active gases in dynamic coastal marine waters.