Areas further to the west (region 13, in the north Pacific gyral water, Fig. 1 ) show 

 low surface concentrations which increase to 30 /ag-at/liter NO3-N at near 450 meters of 



depth. From limited data, there appears to be a seasonal near-surface increase of concentra- 

 tion from winter to summer (Figs. A. 7 to A. 9) to a value of approximately 1 ixg-at in the 

 spring and summer. 



In Hawahan offshore waters (area 14, Pacific north equatorial region, Fig. 1), near- 

 surface nitrate concentrations are again low (less than 0.5 //g-at/Iiter) and do not reach 30 

 ;ug-at/liter levels until a depth of between 325 and 500 meters is reached (Figs. A. 10 to 

 A. 1 2). Average nitrate levels for Hawaiian offshore waters are given in Table 3. There is 

 little upwelhng in the Hawaiian area except in some very localized near-shore sites; overall 

 the area can be considered nutrient-limited. 



In area 18, the western extreme of California water (Fig. 1), nutrient values are low 

 in the upper 100 meters (less than 0.2 /ig-at/liter) (Figs. B.54 through B.61). Nitrate levels 

 of 30 /zg-at/liter are reached at approximately 300 meters of depth. Further to the south 

 (3°N to 15°N) in the North Equatorial Countercurrent region (region 17, Fig. 1), nutrient 

 concentrations are again low in the upper 50 meters, but rise rapidly to between 1 5 and 25 

 /Lig-at N03/liter at 100 meters of depth. Below 100 meters, the concentration remains rela- 

 tively constant, approaching 30 /zg-at/liter at 250-300 meters of depth but in some measure- 

 ments not going above 20 to 25 jUg-at/liter at depths of 350 meters (Fig. A. 13). In this area, 

 therefore, little would be apparently accomplished by upwelling water artificially from 

 deeper than 1 50 meters. 



Further to the east, (area 19 in the southern portion of the west Mexican water), 

 surface concentrations are low to about 30 meters of depth (Figs. A. 16 to A. 19). There are 

 a few liigh surface values (between 2 and 7 ;ug-atN03/liter) during the winter (Fig. A. 16), a 



phenomenon which might be caused by local wind-induced upwelling. Below 30 to 50 

 meters there is a very rapid increase in concentration which reaches 20-25 /ig-at/liter at a 

 depth of 100 meters. A nitrate concentration of 30 //g-at/Uter is reached between 100 and 

 500 meters. Nitrate concentrations are generally directly related to the temperature profile 

 (thermocline). Nutrient concentration increases rapidly near the base of the thermochne. 



Table 3. Average nitrate concentration for Hawaiian offshore waters (Ref. 33). 



DEPTH (m) 



NO3-N (jug-at/liter) 







0.05 



100 



0.08 



200 



2.18 



300 



11.90 



400 



23.92 



500 



33.03 



600 



34.77 



19 



