3.2 Water Column Characteristics 
3.2.1 Salinity 
Salinity in the surface waters of the West Coast shelf for the 140 stations 
for which data were obtained ranged from 21.2 to 34.0 psu. The 50 th percentile 
of area had a surface salinity of 33.3 psu, while the 90 th percentile had a salinity 
of 33.9 psu. An estimated 8% of area had a surface salinity of < 31 psu. The 
majority of stations with surface salinity < 31 psu were located off the mouth of 
the Columbia River or farther south along the Oregon coast, presumably within 
the plume from the Columbia River (Figure 3.2.1). Surface salinity was generally 
less than 33 psu to the north of Cape Blanco, Oregon, and greater than 33 psu to 
the south of Cape Blanco (Figure 3.2.1). Reflecting this pattern, mean surface 
salinities were slightly lower in Washington and Oregon than California (Figure 
3.2.2 A), and slightly lower in the OCNMS as compared to the CA NMSs (Figure 
3.2.2 B). 
Bottom salinity ranged only between 31.6 and 34.4 psu for the 164 
stations for which data were obtained. The 50 th percentile of area had a bottom 
salinity of 33.9 psu, while the 90 th percentile had a salinity of 34.0 psu. An 
estimated 3.3% of the area of the shelf surveyed had a bottom salinity of < 33 
psu, represented by seven stations all located within the northern region of the 
Washington shelf. There was virtually no difference in the mean bottom salinity 
among states or between NMS and non-NMS stations (Figure 3.2.3). 
3.2.2 Water Temperature 
Temperature in the surface water of the West Coast shelf for the 140 
stations for which data were obtained ranged from 8.5 °C to 19.9 °C. The 50 th 
percentile of area had a surface-water temperature of 11.9 °C, while the 90 th 
percentile had a surface water temperature of 13.5 °C. Mean surface-water 
temperatures were similar between Washington and Oregon, while the California 
average was several °C higher (Figure 3.2.4 A). Highest mean surface 
temperatures were observed in the CA non-NMS stations. The CA NMS stations 
were similar to the OCNMS (Figure 3.2.4 B), reflecting the fact that most 
measurements were obtained from the NMS off the central California coast, while 
temperature data were missing from the Channel Islands NMS. 
Temperature in the bottom water of the West Coast shelf for the 164 
stations for which data were obtained ranged from 5.8 °C to 14.7 °C. The 50 th 
percentile of area had a bottom-water temperature of 7.8 °C, while the 90 th 
percentile had a bottom water temperature of 9.7 °C. Bottom-water temperatures 
for stations on the California coast were generally warmer by several °C than 
those from Oregon and Washington (Figure 3.2.5 A). The bottom-water 
temperatures for the CA NMS stations were slightly higher than the OCNMS 
(Figure 3.2.5 B) and probably would be much higher if temperature data from the 
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