A theoretical study of growth and vertical distribution of phytoplankton in a temperate ocean during summer
Jamart, B.M.; Anderson, G.C.; Lam, R.K.; Winter, D.F. (1976). A theoretical study of growth and vertical distribution of phytoplankton in a temperate ocean during summer, in: Persoone, G. et al. (Ed.) Proceedings of the 10th European Symposium on Marine Biology, Ostend, Belgium, Sept. 17-23, 1975: 2. Population dynamics of marine organisms in relation with nutrient cycling in shallow waters. pp. 337-338 In: Persoone, G.; Jaspers, E. (Ed.) (1976). Proceedings of the 10th European Symposium on Marine Biology, Ostend, Belgium, Sept. 17-23, 1975: 2. Population dynamics of marine organisms in relation with nutrient cycling in shallow waters. European Marine Biology Symposia, 10(2). IZWO/Universa Press: Wetteren. ISBN 90-6281-002-0. 712 pp., more In: European Marine Biology Symposia., more |
| Available in | Authors | | Document type: Conference paper
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| Authors | | Top | - Jamart, B.M.
- Anderson, G.C.
- Lam, R.K.
- Winter, D.F.
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| Abstract | A numerical two-dimensional (i.e. time and depth) model of primary production in the Pacific Ocean off the northwestern U.S. coast has been constructed in an effort to identify and quantify the physical and biological processes that govern the spring and summer variations in the vertical distribution of phytoplankton in the offshore zone. The investigation concentrated on the development of one of the more prominent features of the region, namely, the subsurface chlorophyll maximum. The presence of this layer over extensive areas of the ocean can be expected to have a considerable effect on related biological and chemical characteristics (e.g. total biological production, distribution of nutrients and oxygen). The dependent variables in the model were the concentrations of chlorophyll a, nitrate- nitrogen, and ammonium-nitrogen. Since it was assumed that average horizontal gradients of both nutrients and phytoplankton were small, the dominant transport processes were vertical turbulence and sinking of algal cells. The biological terms were algal gross production, algal respiration, and zooplankton grazing for the phytoplankton equation, and selective uptake and regeneration for the nitrogen equations. The computation of light intensity included the self-shading effect and seasonal as well as daily variations of the daylength and the incident radiation. Most of the parameters and forcing functions varied with time and depth. The resulting set of coupled, nonlinear, integro-partial, differential equations was solved by using an iterative, implicit, finite-difference method. Our experience showed that much care should be given to the numerical technique applied to this problem. The simulation over spring and summer months represented the main features of the chemical and biological data reasonably well. A relatively shallow and moderate spring bloom was caused by the stabilization of the water column and controlled by grazing. After the bloom, the maxima of both the chlorophyll concentration and primary productivity were found at the level of optimum light intensity -between 10 and 20 m -as long as the 20 m deep wind-mixed layer was not depleted of nutrients. When nutrient depletion occurred, the chlorophyll maximum crossed the bottom of the mixed layer and then continued to grow, deepen, and sharpen nearly until the end of the simulation. The nutricline followed with some delay the motion of the chlorophyll maximum. The development of the subsurface chlorophyll maximum requires in situ production ; the rate of development is essentially controlled by the grazing pressure and the light intensity. Sinking and differential grazing cause the deepening of the chlorophyll maximum. One major drawback of the model is that grazing processes, although relatively important, are poorly understood. This points out the need for improved quantitative information concerning secondary productivity. |
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