Date of Award

Spring 1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean/Earth/Atmos Sciences

Program/Concentration

Oceanography

Committee Director

Eileen E. Hofmann

Committee Member

Larry P. Atkinson

Committee Member

Dale B. Haidvogel

Committee Member

John M. Klinck

Committee Member

Philip R. Wohl

Abstract

Two time- and space-dependent, physical-bio-optical models have been developed for the California Coastal Transition Zone (CTZ) region with the overall objective of understanding and quantifying the processes th at contribute to the spatial and temporal development of nutrient and plankton distributions in the CTZ. The first of these models considers only time- and vertical processes at specific locations in the CTZ. The model food web components include: silicate, nitrate, ammonium, two phytoplankton size fractions, copepods, doliolids, euphausiids and a detritus pool. The wavelength dependent attenuation of the subsurface irradiance field, due to sea water, phytoplankton pigment concentrations and dissolved organic m atter, is incorporated as a depth-dependent energy flux which balances the phytoplankton energy uptake and the kinetic energy flux (ΔT) into the water. The one-dimensional model adequately simulates the development and maintenance of a subsurface chlorophyll maximum at different regions within the CTZ. An analysis of the individual terms in the model governing equations reveals that phytoplankton in situ growth is primarily responsible for the creation and maintenance of the subsurface chlorophyll maximum. The depth to which maximum in situ growth occurs is controlled by the combined effect of light and nutrient limitation. Also, the simulated bio-optical fields demonstrate the effect of nonlinear couplings between food web components and the subsurface irradiance field on vertical biological distributions. In particular, the depth of the 10% light (PAR) level is influenced by the level of zooplankton grazing.

The second model considers the three-dimensional time-dependent structure of plankton populations in the CTZ. A three-dimensional primitive equation model, developed to simulate the circulation features (filaments) observed in the CTZ, is used to advect the food web constituents of the bio-optical model. The simulated nutrient, plankton and submarine light fields agree well with those observed within the CTZ. Specifically, high nutrient and plankton biomass occur onshore and within the core of the simulated filament. The depth of the 1% light (PAR) level, which results from the simulated plankton distributions, shallows to < 30 m in regions of high phytoplankton biomass, and deepens to > 75 m in regions of low phytoplankton biomass. The onshore and offshore surface carbon flux patterns are similar in shape due to the meander-like flow patterns of the filament; however, the net cross-shelf area-integrated carbon flux is predominantly offshore. The total 20-day integrated carbon transport for the model domain varies with distance from shore and is highest, (35 x 109 g C), in the region where the filament circulation pattern develops into an anticyclonic and cyclonic pair of eddies. Integrated carbon transport by filaments along the California coast is estimated to be 1.89 x 1012 g C over one year.

DOI

10.25777/k0r1-d292

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