Abstracts Category : Other

Insight into chemical, biological, and physicalprocesses in coastal waters from dissolved oxygen and inert gastracers

by Cara Charlotte Manning

In this thesis, I use coastal measurements ofdissolved O and inert gases to provide insight into the chemical,biological, and physical processes that impact the oceanic cyclesof carbon and dissolved gases. Dissolved O concentration andtriple isotopic composition trace net and gross biologicalproductivity. The saturation states of inert gases trace physicalprocesses, such as air-water gas exchange, temperature change, andmixing, that affect all gases. First, I developed afield-deployable system that measures Ne, Ar, Kr, and Xe gas ratiosin water. It has precision and accuracy of 1 % or better, enablesnear-continuous measurements, and has much lower cost compared toexisting laboratory-based methods. The system will increase thescientific community's access to use dissolved noble gases asenvironmental tracers. Second, I measured O and five noble gasesduring a cruise in Monterey Bay, California. I developed a verticalmodel and found that accurately parameterizing bubble-mediated gasexchange was necessary to accurately simulate the He and Nemeasurements. I present the first comparison of multiple gastracer, incubation, and sediment trap-based productivity estimatesin the coastal ocean. Net community production estimated fromNO uptake and 02 /Ar gave equivalent results at steady state.Underway O/Ar measurements revealed submesoscale variability thatwas not apparent from daily incubations. Third, I quantifiedproductivity by O mass balance and air-water gas exchange by dualtracer (He/SF ) release during ice melt in the Bras d'Or Lakes, aCanadian estuary. The gas transfer velocity at >90 % ice coverwas 6 % of the rate for nearly ice-free conditions. Rates ofvolumetric gross primary production were similar when the estuarywas completely ice-covered and ice-free, and the ecosystem was onaverage net autotrophic during ice melt and net heterotrophicfollowing ice melt. I present a method for incorporating theisotopic composition of HO into the O isotope-based productivitycalculations, which increases the estimated gross primaryproduction in this study by 46-97 %. In summary, I describe a newnoble gas analysis system and apply O and inert gas observationsin new ways to study chemical, biological, and physical processesin coastal waters.Advisors/Committee Members: Rachel H.R. Stanley, Nicholson (advisor).