LARRANCE: PRIMARY PRODLCTIONJ !N MID-SL BARCTIC REGION 



average daily light intensity for the cruise. Al- 

 though the relation was based on data tal<en 

 north of lat 46° N, it was used to estimate pro- 

 ductivity in June 1966 for stations as far south 

 as lat 44° N (Figure 4). 



These methods give rough approximations at 

 best but probably indicate productivity responses 

 to seasonal-average light conditions more accu- 

 rately than those given by measured produc- 

 tivity values affected by large day-to-day fluc- 

 tuations of light. The means of Pu for each 

 cruise were higher than means of Pk except in 

 September (Table 2, Figure 5). The higher Pr 

 values may mean that the photosynthetic effi- 

 ciency of the subarctic Pacific phytoplankton is 

 lower than the average efficiency of populations 

 represented in Ryther and Yentsch's (1957) 

 analysis. Other ]30ssible explanations might in- 

 volve differences between our experimental pro- 

 cedures and Ryther's (1956). 



AREAL AND SEASONAL 



DISTRIBUTIONS OF PRIMARY 



PRODUCTIVITY AND CHLOROPHYLL ^4 



Differences in ])roductivity and chlorophyll a 

 among the upper zone domains do not appear 

 to be consistent from season to season except 

 that mean values in the Coastal Domain and 

 Adak Bay were higher than those farther from 

 shore (Figure 4, Table 2). The Coastal and 

 Alaskan Stream Domains can be compared only 

 in June- July 1967 because both areas were not 

 sampled on any other single cruise. Productivity 

 and chlorophyll o were substantially higher in 

 coastal water than in the Alaskan Stream. Un- 

 like other times of the year, productivity and 

 chlorophyll values were similar in nearshore and 

 offshore areas in March 1966 and January-Feb- 

 ruary 1967, probably because low light inten- 

 sities in these months limited production to about 

 similar levels throughout the northern Subarctic 

 Region. This effect was especially pronounced 

 at Adak Bay, where productivity estimates in 

 March were between 350 and 460 mg C/m- per 

 day but ranged between 840 and 2,400 mg C m- 

 per day in late spring and through the summer. 

 The lowest productivity during each cruise was 

 in the Central Subarctic Domain except in win- 



ter, when productivity was uniformly low 

 throughout the region. The mean ijroductivity, 

 however, was lower in the Central Subarctic 

 Domain than in the other areas only in March 

 1966 and June 1967. 



Daily carbon assimilation was normalized 

 (,P/C„) above to estimate productivity from 

 chlorophyll and light measurements. The com- 

 monly used P 'Ca ratio may also be considered 

 as an index of the capacity of a population to 

 photosynthesize under natural light and ambient 

 nutrient and temperature conditions, and pro- 

 vides a basis for seasonal and areal comparisons. 

 This ratio is similar to "turnover rate" (Cushing 

 et al., 1958) and to the ratio discussed by Currie 

 (1958), except that Currie used the concentra- 

 tion of the total complement of plant pigments 

 instead of only chlorophyll 0. Piatt (1969) used 

 an efficiency index (productivity/light energy) 

 to normalize productivity measurements for 

 comparison at designated chlorophyll concentra- 

 tions by means of a regression of the efficiency 

 index on chlorophyll. His method was similar 

 to that used here except he could estimate pro- 

 ductivity at individual depths. For analysis in 

 this study, ratios of P 'C„ were computed for 

 measured productivities (P,,,) and productivities 

 adjusted for differences in light (Pr) by the 

 curve of Ryther and Yentsch (1957). 



Ratios of Pr 'C, were high at four of the nine 

 stations at or south of lat 46° N (Figure 6). 

 The southernmost stations in March and Sep- 

 tember 1966 were in subtropical water. In 

 March, Pr (515 mg Cm- per day) and Pr /Ca 

 (39) were high, suggesting conditions of a phy- 

 toplankton bloom, whereas in September, Pn/Ca 

 was lowest (10) of any observed during summer 

 (Table 2). At lat 44° N in June 1966 and at 

 lat 42°50' N in September, Pr/C, ratios were 

 high (41 and 49), but Pr values were moderate 

 (232 and 275 mg C/m- per day) and chlorophyll 

 values were unusually low (5.6 mg 'm- in each 

 case) . This combination of high Pr/Co and low 

 chlorophyll may be due to high carbon to chlor- 

 ophyll ratios in the cells. At lat 46° N in August 

 1967, however, Pr and chlorophyll a were both 

 relatively high (664 mg C 'm= per day and 16.8 

 mg/m') ; thus the high productivity and photo- 

 synthetic capacity (Pr/Cu = 40) of the popu- 



601 



