Particle size distributions and the vertical distribution of suspended matter in the upwelling region off Oregon : final report Public Deposited


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  • Various methods of presenting and mathematically describing particle size distribution are explained and evaluated. The hyperbolic distribution is found to be the most practical but the more complex characteristic vector analysis is the most sensitive to changes in the shape of the particle size distributions. Particle size distribution, nutrient concentrations, temperature and other biological and hydrographic data were taken during two cruises off the Oregon coast. The first, in late July, 1973, was during a period of consistent upwelling-favorable winds. The second cruise, in August, 1974, was during a period of intermittently favorable winds. Thus the data presented represent several different upwelling situations. Two distinct vertical structures of suspended particulates and two types of particle size distributions were found, separated by a particle front. On the offshore side of the front, the structure was characterized by dominantly small particles and a subsurface maximum of suspended matter. On the other side of the front, the structure shows a particle maximum at or very near the surface with dominantly large particles. A method for determining onshore-offshore flow patterns from the distribution of particulates was presented. The method was applied to the data from the two cruises. A further experiment was suggested with an emphasis on determining three-dimensional current patterns at the same time as particle distributions. Such data would be used for a three-dimensional numerical model. A numerical model of the vertical structure of two size classes of particles was developed. The results show a close similarity to the observed distributions but overestimate the particle concentration by forty percent. This was attributed to ignoring grazing by zooplankton. Sensitivity analyses showed the size preference was most responsive to the maximum specific growth rates and nutrient half saturation constants. The vertical structure was highly dependent on the eddy diffusivity followed closely by the growth terms.
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