Insight into Chemical, Biological, and Physical Processes in Coastal Waters from Dissolved Oxygen and Inert Gas Tracers

Cara Manning, Ph.D., 2017
David Nicholson, Co-Advisor
Rachel Stanley, Co-Advisor

In this thesis, I use coastal measurements of dissolved O₂ concentration and isotopic composition and inert gas concentrations to provide insights into the chemical, biological, and physical processes that impact the oceanic cycles of carbon and dissolved gases.  First, I developed a new field-deployable instrument for measuring noble gases in water that has precision and accuracy of 1 % or better, and higher throughput and lower cost compared to published laboratory-based methods. Second, I used time-series measurements of O₂ and noble gases in Monterey Bay, California, to evaluate the performance of published air-sea gas exchange parameterizations in simulating the inert gas data and to quantify productivity. Accurately parameterizing bubble-mediated gas exchange was necessary to simulate the He and Ne measurements. I found that net community production estimated from ¹⁵NO₃^- uptake and O₂/Ar gave equivalent results at steady state. Third, I conducted dual tracer release experiments and measured O₂ during seasonal ice melt in the Bras d'Or Lake, a Canadian inland sea. The gas transfer velocity at >90 % ice cover was 6 % of the rate for ice-free conditions. Rates of volumetric gross primary production were similar when the estuary was ice-covered and ice-free.