was less than half that of the CA NMS and non-NMS areas (Figure 3.2.18). 
Examination of the Bakun upwelling index at 48° N shows that there was 
downwelling occurring in the region of the OCNMS just prior to the sampling at 
this location, and only weak upwelling occurring during the sampling period. 
Silicate concentrations of water samples were analyzed by the states of 
Washington and California (exclusive of the SCB), but not Oregon. Therefore 
there were only 97 sample sites with silicate data available. The surface-water 
concentration of silicate in waters of the West Coast shelf within Washington and 
California ranged from 0 to 2040.5 pg/L. The 50 th percentile of area of the waters 
of the West Coast shelf sampled had a silicate concentration of 307 pg/L, with 
the 90 th percentile of area characterized by a concentration of 973 pg/L. The 
mean silicate concentration for surface waters was similar between Washington 
and California locations, while the mean silicate concentration for the CA NMSs 
was approximately twice that of the OCNMS and the non-NMS locations (Figure 
3.2.19) . These results are again consistent with the spatial patterns of upwelling 
on the shelf during the sampling period. 
3.2.8 Chlorophyll a 
The surface-water concentration of chlorophyll a for the 187 stations 
sampled in waters of the West Coast shelf ranged from 0 to 28 pg/L (Figure 
3.2.20) . The 50 th percentile of area of the waters of the West Coast shelf 
sampled had a chlorophyll a concentration of 3.9 pg/L, while the 90 th percentile 
had a chlorophyll a concentration of 14.5 pg/L. The mean chlorophyll a 
concentration for surface waters in California was less than half that of locations 
in Washington and Oregon locations (Figure 3.2.20 A). The lowest mean 
chlorophyll a concentration was for the CA non-NMS locations, while the mean 
for the CA NMS locations was approximately 60% of that found in the OCNMS 
(Figure 3.2.20 B). 
47 
