4-yr study of seasonal biomass cycles at distances 

 of 28 km from shore and beyond, which employed 

 mid-water trawls and dlO-fjm plankton nets. 



Peterson (1972) summarized the results of 434 

 zooplankton samples collected off Oregon and 

 Washington with 110-ju,m mesh Clarke-Bumpus 

 nets at an irregular set of stations in 1961 and 

 1962. Most of the samples were taken beyond the 

 continental shelf break. His conclusion that 

 copepods attain larger inshore populations in 

 winter than in summer is not in agreement with 

 our results for the Oregon nearshore zone. We 

 have found winter densities to be several orders of 

 magnitude lower than summer densities. This 

 discrepancy makes his work difficult to evaluate. 



All of these studies share two shortcomings: 

 First, few or no samples were collected within 10 

 km of the coast. Second, the time intervals 

 between samplings were large, ranging from 

 monthly (Hebard 1966) to quarterly and longer 

 (Cross 1964; Laurs 1967; Peterson 1972). Under 

 such sampling programs the authors could only 

 document large scale phenomena, such as faunal 

 changes associated with seasonal hydrographic 

 changes, and faunal differences between 

 nearshore and offshore stations. 



THE COASTAL ENVIRONMENT 

 OF OREGON 



Aspects of descriptive physical oceanography of 

 Oregon coastal waters can be found in Burt and 

 Wyatt 1964; Pattullo and Denner 1965; Cross and 

 Small 1967; Collins et al. 1968; Bourke 1972; Pills- 

 bury 1972; Huyer 1974; and Smith 1974. 



Circulation Patterns 



The California Current is a slow, southward- 

 flowing current situated within a band 300 to 800 

 km off the Oregon coast. Inshore of this per- 

 manent feature the circulation changes with 

 season. During spring and summer months 

 nearshore flow is southward, driven by northerly 

 winds. During fall and winter months, after ces- 

 sation of upwelling, flow is northward. This flow is 

 called the Davidson Current. 



Wind and Coastal Upwelling 



Northerly winds predominate from April to 



September. They produce a generally southward 

 transport of surface water with a component to 

 the right of the wind away from the coastline. This 

 offshore, near-surface transport is balanced by 

 northward and onshore transport at depth of cool, 

 high salinity, nutrient rich water. When northerly 

 winds are strong and/or persistent, cold, high 

 salinity water appears on the beach and 

 throughout the entire water column out to about 

 10 km. This condition is called active or intense 

 upwelling. When north wind stress is weak or 

 nonexistent, this onshore deep transport is 

 weakened and nearshore waters are warmed by 

 solar radiation. 



Intense upwelling is not a continuous process 

 during summer, but occurs sporadically. If 

 northerly winds blow for a day or two, upwelling 

 will develop. If wind ceases or changes direction, 

 upwelling ceases. During July and August 

 northerly winds are often persistent, so that in- 

 tense upwelling may continue for several weeks 

 without interruption. 



Waters offshore of 10-20 km do not experience 

 these rapid changes. In these deeper waters, up- 

 welling is indicated in hydrographic sections by 

 upward sloping isolines of temperature, salinity, 

 and density (see Smith 1974). The upward slope 

 develops in April or May and persists until ces- 

 sation of upwelling in September or October. 

 Offshore surface waters are warm (as high as 

 17°C) and a mixed layer is well developed. Salini- 

 ties are reduced as a result of the Columbia River 

 plume. 



Temperature and Salinity Relationships 



Pillsbury (1972) has summarized all temperature 

 and salinity data collected within the top 10 m of 

 the water column at stations 5 and 9 km from 

 shore during the April-September upwelling 

 seasons of 1960 through 1970, a total of 188 obser- 

 vations. Pillsbury used the modal cell technique of 

 Pattullo and Denner (1965) to summarize the data. 

 The portion of a temperature-salinity plot con- 

 taining the most data points was one bounded by 

 8.1°-9.0°C and 33.1-34.0°/ oo. That "cell" accounted 

 for 28% of the data. Pillsbury identified two 

 general water types that occur at the two stations: 

 1) cold-upwelled water (7.5°-8.5°C and 33.5-34Voo) 

 and 2) warm, low salinity water (11.0°-12.0°C and 

 30.5-31.5 °/oo) which is a mixture of Columbia River 

 plume water and surface oceanic water. 



643 



