PDF Nitrogen, oxygen and the noble gases as tracers of upper-ocean productivity and air-sea gas fluxes.
In this study, measurements and modeling of dissolved nitrogen, oxygen and the noble gases are used to investigate biogeochemical fluxes of elements and physical processes of gas exchange to better understand the cycling of carbon within the ocean/atmosphere system. The first aspect of my work involved a year-long deployment of autonomous underwater gliders, called Seagliders, equipped with oxygen sensors to study the upper ocean in the subtropical North Pacific gyre near Hawaii. Using data collected by Seagliders and an oxygen mass balance approach, I was able to constrain the annual net community production of oxygen and organic carbon at my study site. The continuous nature of Seaglider data also allowed me to investigate the role of mesoscale variability in driving primary productivity in the subtropical upper ocean. During Seaglider deployments, four productivity events were observed with elevated oxygen and fluorescence in the deep euphotic zone, each of which corresponded to isopycnal shoaling events induced by passing Rossby waves. Seaglider temperature and salinity measurements were also used to investigate mixing rates in the upper thermocline. In the second main component of this study I made measurements of Kr/Ar and delta 40Ar in deep ocean water and, along with other inert gas measurements, used a hierarchy of models to better understand ventilation processes during deepwater formation and rates of bubble fluxes. Using box models, I was able to demonstrate that most box models greatly overestimate the amount of ventilation at high latitudes because the surface-areas of high latitude boxes are too large. I used noble gas measurements to constrain an appropriate high latitude surface area of about 3% of total ocean surface area, which when applied in box models, results in gas cycling that is much more consistent with general circulation model results. Inert gas measurements were also used to constrain the flux of bubbles across the air-sea interface and I proposed new parameters to calculate bubble fluxes from 10-meter windspeed.
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