FISHERY BULLETIN: VOL. 69, NO. 3 



Table 3.— Computed standing stock (S,), expressed in units of chlorophyll, 

 for various cell chlorophyll to carbon ratios (l/F) during spring 1966 in 

 the mid-Subarctic Pacific Region. 



l/F 



P/C^ 



la 



Feb. -Mar. 

 Mar.-June 

 Mar. -June 

 Mar.-June 



11.2 

 19.3 

 19.3 

 19.3 



50 

 80 

 80 

 80 



S, 



.04 



.04-0) 



.04 



.01 



7-15 

 15-20 

 15-20 

 15-20 



0.433 

 0,472 

 0.701 

 0.398 



20.422 

 0.422 

 0.422 

 0.422 



19.3 

 21096. 

 29.3X10'° 

 228.0 



ifl is the mean growth coefficient calculated by assuming that />/Ca varied linearly with time 

 as did ]/f in the second computation. 



: e-l 



: "0 + 



where Aa= AP/C„ [(:/F)„ -|- 1/f • Al/F] 



the initial and final values for the period. 

 2 Computed values. 



A g 

 t 



S . 



= 1 



AREAL AND SEASONAL DISTRIBUTION 

 OF NUTRIENTS 



Nutrient concentrations were always higher 

 in Adak Bay and the Coastal Domain than in 

 the other areas and generally decreased toward 

 the south (Table 4, Figure 7). Average con- 

 centrations of nutrients in the Central Sub- 

 arctic water exceeded those in the Alaskan 

 Stream only in June 1967. In winter of 1967, 

 the nutrients were relatively high and varied 

 little throughout the cruise ai-ea. Low nutrient 

 concentrations at a few stations to the south 

 in September correspond to lower PR/Ca ratios. 

 The lowest average phosphate concentration in 

 the upper 50 m, 10 mg-at/m-, was in subtropical 

 water. Nitrate-nitrite was undetectable in the 

 upper 10 m at one station in area T-2 (lat 43° N) 

 and totaled only 12 mg-at/m- in the upper 50 m, 

 whereas the minimum silicate observed was 187 

 mg-at/m- at the same station. Apart from the 

 low nutrient values measured south of about lat 

 44° N in September and possibly in subtropical 

 water in Mai-ch, nutrients appeared to be in 

 sufficient abundance to support vigorous phyto- 

 plankton growth. Even for these areas of low 

 concentrations, productivity did not appear to 

 be severely limited, as evidenced by the Pr/C„ 

 ratios, but was probably somewhat suppressed. 



To obtain a seasonal pattern of changes, the 

 data on nutrients, like those on productivity, 

 were ti'eated as composite measurements from 

 the same year. The changes of mean nutrient 

 concentrations between lat 46° and 51°40' N 

 from season to season were not large. In mid- 



(P/Ca)a ' Al/F and A is the difference between 



winter all nutrients were relatively abundant, 

 as were phosphate and silicate in March. (Ni- 

 trate was not measured in March.) Phosphate 

 decreased between March and June 1966 from 78 

 to 56 mg-at/m-, the largest fractional change 

 measured during this study for any of the nu- 

 trients. In June 1967, nitrate and phosphate 

 concentrations were nearly equal to those in 

 winter, but concentrations of silicate were lower. 

 The apparent difference in the phosphate fluc- 

 tuations between the 2 years could be the result 

 of a shift in timing of the periods of high pri- 

 mary productivity, differences in supply by 

 circulation, or an overall net difference in the 

 balance between phosphate assimilation and 

 supply for the year. By August phosphate and 

 silicate had increased to quantities considerably 

 higher than those in winter, but in September 

 phosphate was lower and silicate was only slight- 

 ly higher than in winter. 



The low nutrient concentrations to the south 

 in the summer lend support to the proposal by 

 Anderson (1969) that a trans- Pacific band of 

 chlorophyll occurs between the seasonal and 

 permanent pycnoclines in the summer. His 

 measurements indicate that the algae are pro- 

 duced in situ at these depths (50 to 75 m) which 

 receive less than 1 % of the light energj' at the 

 sea surface. This band lies between lat 35° and 

 45° N and is coincident with and could explain 

 the occurrence of a layer of maximum oxygen 

 content (Reid, 1962). Anderson also found that 

 nitrate in the surface mixed layer above the 

 chlorophyll band was nearly absent, having been 

 used up in the spring during high primary pro- 

 duction. A nitrate gradient through the deep 



606 



