Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers
Citable URI
https://hdl.handle.net/1912/8589DOI
10.1575/1912/8589Keyword
Gases; Chemical oceanographyAbstract
In this thesis, I use coastal measurements of dissolved O2 and inert gases to provide insight
into the chemical, biological, and physical processes that impact the oceanic cycles of carbon
and dissolved gases. Dissolved O2 concentration and triple isotopic composition trace net and
gross 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 gas
ratios in water. It has precision and accuracy of 1 % or better, enables near-continuous
measurements, and has much lower cost compared to existing laboratory-based methods.
The system will increase the scientific community’s access to use dissolved noble gases as
environmental 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 gas
exchange was necessary to accurately simulate the He and Ne measurements. I present the
first comparison of multiple gas tracer, incubation, and sediment trap-based productivity
estimates in the coastal ocean. Net community production estimated from 15NO –3 uptake
and O2/Ar gave equivalent results at steady state. Underway O2/Ar measurements revealed
submesoscale variability that was not apparent from daily incubations.
Third, I quantified productivity by O2 mass balance and air-water gas exchange by dual
tracer (3He/SF6) release during ice melt in the Bras d’Or Lakes, a Canadian estuary. The
gas 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 completely
ice-covered and ice-free, and the ecosystem was on average net autotrophic during ice melt
and net heterotrophic following ice melt. I present a method for incorporating the isotopic
composition of H2O into the O2 isotope-based productivity calculations, which increases the
estimated gross primary production in this study by 46–97%.
In summary, I describe a new noble gas analysis system and apply O2 and inert gas
observations in new ways to study chemical, biological, and physical processes in coastal
waters.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2017
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Suggested Citation
Thesis: Manning, Cara C., "Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers", 2017-02, DOI:10.1575/1912/8589, https://hdl.handle.net/1912/8589Related items
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