ABSTRACT

Measurements of suspended material and temperature have been made at 32 stations on the shelf off the State of Oregon, U.S.A. The thermal structure of shelf waters shows three layers divided by a strong seasonal thermocline and a weaker permanent thermocline. The latter slopes upwards towards the coast indicating that upwelling was taking place. Clearer water below the surface mixed layer enters the shelf region from offshore by upwelling. Total suspended material concentrations are higher in surface and bottom waters than at mid-depth. Wave and current activity generates the higher concentrations close to the bed both nearshore and over the mud bed of the outer shelf. Percentages of "organic" and inorganic material plus refractory organic matter ("inorganic") were obtained by treatin the suspended material with H₂O₂ to oxidise the labile part of the organic matter. The concentration of organic matter is highest in the surface and bottom layers but the percentage organic is greatest in the intruding water mass below the surface layer. No mid-water turbid layers were found, but several samples had a tow percentage of organic matter just above the permanent thermocline. Fluxes of inorganic material on- and offshore are approximately equal and, at a point, are ten times less than the longshore flux.