6.1 Primary Production of Organic Matter 



MIKHAIL N. KORSAK 



Institute of Global Climate and Ecology, State Committee for Hydrometeorology and Academy of Sciences, Moscow, USSR 



Introduction 



The Bering and Chukchi Seas are situated in the subarctic 

 and arctic regions of the Pacific and Arctic Oceans. They are 

 among the most productive regions of the oceans. Consequently, 

 these areas are of great significance from the standpoint of 

 fisheries. For example, the annual output of the sea products in 

 the region of the Bering Sea is approximately 3 million tons, 

 including I million tons of fish (Sorokin et al., 1983). The 

 results of previous research conducted in the Bering Sea 

 showed that, from the point of view of productivity, this basin 

 is comparable to the upwelling regions of the Pacific and 

 Atlantic Oceans (Sorokin, 1973;Izrael&Tsyban, 1981;Korsak, 

 1982, \985; Sorokin etal., 1983; Tsyban, 1985; Tsy ban (-/«/.. 

 1985). 



The amount of annual gross primary production in the 

 Bering Sea is about 1-1.5% of the total primary production of 

 the Worid Ocean (Sorokin et al.. 1983; Korsak, 1985). 



The amount of organic production reaches 7 g C m - d ' in 

 some regions of the sea during the period of biological succession 

 of the plankton community. This allows us to classify the 

 Bering Sea as a eutrophic water basin (Sorokin. I973;Korsak, 

 1982; Sorokin era/., 1983; Tsyban efrt/., 1985). 



In contrast to the Bering Sea. the ecological system of the 

 Chukchi Sea has been explored to a much lesser degree. The 

 existing data from the literature, however, allow one to presume 

 that the productivity of this basin is also rather high (Sorokin. 

 1973; Korsak. 1982). According to the classification of waters 

 of the World Ocean, proposed by O. A. Koblents-Mishke etal. 

 ( 1970), the Chukchi Sea is considered to be mesotrophic. The 

 amount of net production of the region is 35-55 g C m- 

 annually (Sorokin, 1973). For the purpose of comparison, it 

 should be noted that this amount for the Bering Sea is 

 90 g C m -. 



The amounts of primary organic production in the Bering 

 Sea and in the Chukchi Sea were determined during the course 

 of the Third Joint US-USSR Bering & Chukchi Seas Expedition 

 on the Research Vessel (R/V) Akademik Korolev in July- 

 August of 1988. In contrast to the previous expeditions of 1 98 1 

 and of 1984, the research conducted this time covered a much 

 larger area of the Bering Sea. including the insufficiently 

 studied northwestern and northern regions of the sea, the 

 Bering Strait, and the southern part of the Chukchi Sea. 



Materials and Methods 



The measurements of phytoplankton primary production 

 were performed at 23 stations in the Bering Sea and 1 1 stations 

 in the Chukchi Sea during the period from July 28 through 



August, 1988. The determination of phytoplankton production 

 was conducted with the bottle method and '^C modification 

 proposed by Sorokin (Sorokin, 1973; Sorokin et al., 1983). 

 The depth of the euphotic zone was assumed to be equal to 

 triple the Secchi disk transparency. The samples were taken 

 with 5-1 Niskin bottles from depths of 0.5, 5, 10, 15, 25, and 

 45 m. As a rule, incubations were started in the morning and 

 continued for a 6-hour exposure period. 



Seawater samples were incubated in a flowing seawater 

 bath, located on the deck of the ship in conditions of natural 

 light. Special experiments determining photosynthetic 

 dynamics during the day were performed in order to calculate 

 the daily production values. Radioactivity of the '^C labeled 

 phytoplankton retained on the filters and of '^C isotope solutions 

 was measured with the use of a scintillation counter, "Rack-P ,"' 

 in the course of the voyage. The biomass of phytoplankton was 

 calculated on the basis of chlorophyll concentration, with the 

 assumption that chlorophyll accounted forO.3% of total organic 

 content of phytoplankton. For calculation of daily values of 

 F/B coefficients, it was assumed that the amount of organic 

 carbon in the biomass of seaweeds is 6%. 



Results and Discussion 



The third complex ecological expedition started its work 

 at the end of July 1988 in the region called East Polygon. This 

 area is situated in the central part of the Bering Sea, near Pearle 

 canyon. According to the results obtained during the expeditions 

 of 1981 and 1984, the amounts of primary organic production 

 in this area of the sea during the middle-to-end of biological 

 summer were 430-530 mg C m - d ', and the values of P/B 

 coefficients were 0.48-0.56 (Izrael & Tsyban, 1981; Korsak, 

 1982, 1985; Sorokin e/ a/., 1983; Tsyban, 1985; Tsyban era/., 

 1 985 ). The results of the measurements of primary production 

 in the East Polygon during the third ecological expedition give 

 ground to suppose that the development of phytoplankton on 

 Stations 1-5 took place rather actively. The average values of 

 primary production at these stations were approximately 

 1,300 mg C m- d ', with a station-to-station range of 

 840 to 2,600 mg C m' d ' (Tables 1, 2; Fig. 1 ). The value of 

 P/B coefficient varied from 0.84 to 1.6. It is obvious that 

 significant variations of the primary production indicate high 

 heterogeneity of water masses in this region during the research 

 period. 



Further experiments on determination of primary organic 

 production were done in the Gulf of Anadyr. This region is 

 comparatively less studied, from the point of view of production 

 biology, than the rest ofthe Bering Sea (Fig. 1). At the entrance 

 to the gulf, on Stations 6 and 7. the level of primary production 



215 



