Measurement and modeling of optical, physical, and photochemical processes in the open-ocean mixed layer: Peroxide and dissolved organic matter

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine and Atmospheric Chemistry

First Committee Member

Rod G. Zika, Committee Chair


The goals of this work were to model H$\sb2$O$\sb2$ cycling in aquatic systems, and to study the photoproperties of bulk dissolved organic matter (DOM). H$\sb2$O$\sb2$ is produced photochemically from DOM with an "apparent" quantum yield (AQY; normalized to DOM absorbance) which decreases exponentially as wavelength increases.The primary task of this project was to develop a vertical-flux model of undersea irradiance (300-500 nm). The model varied the path-length and geometry of undersea light with solar zenith angle according to scattering in the atmosphere and water column, and according to the ratio of collimated light to diffuse light. This optical model was then combined with a one-dimensional model of marine surface mixing, which derived structure and dynamics by applying empirically determined stability limits to calculated bulk turbulent kinetic energy and shear turbulence.Using data collected in the eastern Caribbean during 1988, modeled H$\sb2$O$\sb2$ mixed-layer depth and diel distributions were controlled by mixing dynamics. Preliminary model results made it possible to identify two classes of photoproductive waters, based on the ratio of UV DOM absorption, 330 nm, to visible absorption, 460 nm. H$\sb2$O$\sb2$ photoproduction was primarily due to 320-360 nm irradiance in the model, while a surprisingly significant fraction of total production occurred at wavelengths greater than 400 nm at depth and at zenith angles greater than 15 degrees. The diel photoproduction of H$\sb2$O$\sb2$ was notably deeper at midday than would be predicted in a simple non-scattering optical model.DOM fluorescence decayed with irradiation above 330 nm, and intensified with irradiation below 330 nm. The processes were partially photo-reversible, and also reversed slowly in the dark. For new river input, irradiation at 296.7 nm initially bleached fluorescence, with re-intensification occurring upon longer irradiation at the same wavelength. Full-spectral solar irradiation bleached fluorescence. The rates of these processes fit a linear function of the initial fluorescence intensity. DOM absorbance was altered irreversibly by monochromatic irradiation, with an initial rate of absorbance change that was fairly constant in all samples.


Physical Oceanography; Biogeochemistry; Physics, Optics

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