Abstracts Category : Other

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

by Cara C Manning

In this thesis, I use coastal measurements of dissolved O2 and inert gases to provide insightinto the chemical, biological, and physical processes that impact the oceanic cycles of carbonand dissolved gases. Dissolved O2 concentration and triple isotopic composition trace net andgross biological productivity. The saturation states of inert gases trace physical processes,such as air-water gas exchange, temperature change, and mixing, that affect all gases.First, I developed a field-deployable system that measures Ne, Ar, Kr, and Xe gasratios in water. It has precision and accuracy of 1 % or better, enables near-continuousmeasurements, and has much lower cost compared to existing laboratory-based methods.The system will increase the scientific communitys access to use dissolved noble gases asenvironmental tracers.Second, I measured O2 and five noble gases during a cruise in Monterey Bay, California.I developed a vertical model and found that accurately parameterizing bubble-mediated gasexchange was necessary to accurately simulate the He and Ne measurements. I present thefirst comparison of multiple gas tracer, incubation, and sediment trap-based productivityestimates in the coastal ocean. Net community production estimated from 15NO 3 uptakeand O2/Ar gave equivalent results at steady state. Underway O2/Ar measurements revealedsubmesoscale variability that was not apparent from daily incubations.Third, I quantified productivity by O2 mass balance and air-water gas exchange by dualtracer (3He/SF6) release during ice melt in the Bras dOr Lakes, a Canadian estuary. Thegas transfer velocity at >90% ice cover was 6% of the rate for nearly ice-free conditions.Rates of volumetric gross primary production were similar when the estuary was completelyice-covered and ice-free, and the ecosystem was on average net autotrophic during ice meltand net heterotrophic following ice melt. I present a method for incorporating the isotopiccomposition of H2O into the O2 isotope-based productivity calculations, which increases theestimated gross primary production in this study by 4697%.In summary, I describe a new noble gas analysis system and apply O2 and inert gasobservations in new ways to study chemical, biological, and physical processes in coastalwaters.