PRIMARY PRODUCTION IN THE MID-SUBARCTIC 

 PACIFIC REGION, 1966-68 



Jeery D. Larrance' 



ABSTRACT 



Primary productivity, chlorophyll a, net zooplankton, nutrients, and associated physical variables were 

 measured on seven cruises in the mid-Subarctic Pacific Region in 1966-68. Most of the data were col- 

 lected between lat 46° N and the central Aleutian Islands, although several measurements were made 

 as far south as lat 40° N. Primary productivity and chlorophyll were higher in Aleutian coastal waters 

 than in areas to the south, but no other major differences among upper zone domains were consistent 

 seasonally. Production was low in winter, high in spring, and intermediate throughout the summer. 

 Annual productivity was between 80 and 100 g C/nfi. Chlorophyll a concentrations changed only slightly 

 except in March when chlorophyll was high during the early part of the phytoplankton bloom. 



Low light intensities limited primary production during the winter, and zooplankton grazing appeared 

 to limit production in summer and part of spring. Nutrients and light were always sufficient to sup- 

 port high productivity during spring and summer except in late summer when some nutrients, particu- 

 larly nitrate, were very low south of lat 44° N; however, the productivity did not appear severely 

 limited. The main source of phosphate replenishment in the upper layers during spring and summer 

 was probably in situ regeneration by zooplankton rather than upwelled deep water. 



The pelagic biota of the Subarctic Pacific Region 

 has long been recognized as distinct from that 

 in the Subtropical Region, and the Subarctic is 

 thought to be generally more productive. Until 

 the introduction of the carbon-14 technique by 

 Steemann Nielsen (1952) , however, no adequate 

 means existed for directly measuring primary 

 productivity in the open ocean. Since that time 

 thousands of measurements of primary produc- 

 tion have been made throughout the Tropical 

 and Subtropical North Pacific. Measurements 

 in the Subarctic Pacific have been fewer and 

 more localized. 



Koblents-Mishke (1965), who summarized 

 data from the Pacific Ocean, estimated that pri- 

 mary productivity in the mid-Subarctic Region 

 averaged about 150 to 250 mg C/m- per day 

 or 55 to 91 g C/m^ per year. She estimated 

 average production in the Gulf of Alaska and 

 along the Washington and Oregon coasts to be 

 between 250 and 650 mg C/m^ per day (90-240 g 

 C/m- per year) and in the transition area of 

 the southern Subarctic to be 100 to 150 mg C/m- 



' National Marine Fisheries Service, Biological Lab- 

 oratory, Seattle, Wash. 98102. 



Manuscript accepted February 1971. 



FISHERY BULLETIN: VOL. 69. NO. 3, 1971. 



per day (35-55 g C/m^ per year). As discussed 

 by Koblents-Mishke, these estimates are rather 

 imprecise because productivity at most of the 

 stations was measured only at the surface and 

 not throughout the euphotic zone and because 

 many of the measurements were made in artifi- 

 cial light of various intensities. Comprehensive 

 analyses of annual cycles were seldom possible 

 because surveys have been made during all 

 seasons in only a few studies. 



From detailed year-round surveys, Anderson 

 (in press) estimated annual primary produc- 

 tion in oceanic waters off^ Washington and Ore- 

 gon to be 125 g C/m-. Mean annual primary pro- 

 duction at Ocean Station "P" (lat 50° N, long 

 145° W) in the Gulf of Alaska was 48 g C/m= 

 in 1960-66 (McAllister, 1969). Although pri- 

 mary productivity has been measured on several 

 individual cruises through the region (McGary 

 and Graham, 1960; Faculty of Fisheries, Hok- 

 kaido University, 1961; Doty, 1964; Koblents- 

 Mishke, 1965), no previous time-series studies 

 of productivity have been made in the central 

 Subarctic Region west of Station "P." 



Primary productivity, zooplankton abundance, 

 and related physical and chemical oceanographic 



595 



