zooplankton-to-phy toplankton biomass ratio calculated for the 

 Bering Sea is higher than most oceanic areas (Motoda & 

 Minoda, 1974) suggests that there is an efficient transfer of 

 phytoplankton carbon to higher trophic levels. However, 

 recent work by Springer et cil. ( 1 989 ) indicates that on average 

 the zooplankton of the northern Bering Sea are unable to 

 control the large blooms of diatoms that occur during springtime 

 in this region. 



Sambrotto etal. ( 1 986 ) have shown that there is a significant 

 degree of seasonal variability in both phytoplankton biomass 

 and production on the southeastern Bering Sea Shelf. The 

 shallowing of the mixed layer was the most important process 

 responsible for bloom initiation, which occurs annually during 

 early May. The investigators also concluded that vertical 

 mixing forced by atmospheric events is important in controlling 

 the magnitude of the spring bloom. Innerannual variations in 

 zooplankton biomass have also been documented for the Bering 

 Sea, which may reflect variations in meteorological conditions 

 (Motoda & Minoda, 1974). 



During early to midsummer, boreal-oceanic diatoms 

 dominate the phytoplankton community of the open 

 western/central Bering Sea and the eastern Bering Sea Shelf, 

 while temperate-neritic diatoms are characteristically found in 

 the vicinity of the Aleutian Island chain (Motoda & Minoda. 

 1974: Whitledgeeffl/., 1988). The dominant offshore diatoms 

 include representatives from the following genera: 

 Chaetoceros sp., Rhizosolenia sp., Denticula sp., 

 Thalassiosira sp., Nilzschia sp., Fragilaria sp., and 

 Thalassiothrix sp. On the southeastern Bering Sea Shelf, 

 diatoms are dominated by Thalassiosira aestivalis and 

 T. nordenskioldii during prebloom conditions (April) and 

 Chaetoceros spp. (especially C. debilis) during bloom 

 conditions that occur during May (Sambrotto 

 et al.. 1986). Kisselev (1937) also reported the presence of 

 dinoflagellates and green algae in the northern Bering Sea. 



' To further investigate the distributions of phytoplankton 

 in the Bering and Chuckchi Seas, near-surface water samples 

 were analyzed for pigment content by high-performance liquid 

 chromatography (HPLC). This study was part of the Third 

 Joint US-USSR Bering & Chukchi Seas Expedition, designed 

 to examine biological-chemical-physical interactions in the 

 Bering Sea. 



Materials and Methods 



A series of stations were occupied during July-August 

 1988 aboard the R/V Akademik Korolev in the Bering and 

 Chukchi Seas. Near-surface samples were collected at 1 12 of 

 these stations for the determination of photosynthetic pigment 

 concentrations (Figs. 1-12). One-liler water samples were 

 filtered through 47 mm GF/F glass fiber filters and transported 

 to Texas A&M University for HPLC pigment analysis. Filters 

 were extracted in 6 ml lOO'/f acetone (final acetone concentration 

 - -90%) for 24-48 h (-20 "C). Following extraction, pigment 

 samples were centrifuged for 5 min to remove cellular debris. 

 Pigment extracts were analyzed for pigment content by HPLC 



(Bidigare, 1989). Briefly, chlorophylls and carotenoids were 

 separated using a Spectra-Physics Model SP8700 liquid 

 chromatograph equipped with a Radial-PAK C.s column 

 (0.8 X 10 cm, 5 |i particle size; Waters Chrom. Div.) at a flow 

 rate of 6 ml/min '. Prior to injection, 1 ml aliquots of the 

 standards and algal extracts were mixed separately with 

 300 |i 1 of ion pairing solution (Mantoura& Llewellyn, 1983). 

 A two-step solvent program was used to separate the algal 

 pigments. After injection (500 \i\ sample), mobile phase A 

 (80: 1 5:5; methanol:water:ion-pairing solution) was ramped to 

 mobile phase B (methanol) over a 12-min period. Mobile 

 phase B was then pumped for 18 min for a total analysis time 

 of 30 min. Individual peaks were detected and quantified (by 

 area) with a Waters Model 440 Fixed Wavelength Detector 

 (436 nm) and a Spectra-Physics Model SP4400 integrator, 

 respectively. The identities of the peaks were determined by 

 comparing their retention times with those of pure standards 

 and extracts prepared from "standard" plant materials of known 

 pigment composition. On-line diode array spectroscopy 

 (HPLC/DAS; 350-550 nm for carotenoids and 400-700 nm for 

 chlorophylls) using a Hewlett-Packard Model HP8451 Diode 

 Array Spectrophotometer was performed to confirm the 

 identities of the major chlorophylls and carotenoids. The 

 HPLC system was calibrated with pure standards whose 

 concentrations were determined spectrophotometrically in 

 1-cm cuvettes (Bidigare, 1989). Known pigment quantities 

 were injected and resultant peak areas were used to calculate 

 individual standard response factors (ng area'). Pigment 

 concentrations (ng pigment 1 ' ) of the samples were calculated 

 with these response factors and knowledge of the extraction 

 and sample volumes. The HPLC method employed is not 

 capable of separating chlorophyll c, from chlorophyll r,, nor 

 zeaxanthin from lutein. 



Results 



The quantitatively important algal pigments measured in 

 suspended particulate samples collected from near-surface 

 waters of the Bering and Chukchi Seas were chlorophyll a; 

 chlorophyllide a; chlorophyll b\ chlorophylls c, -i- c,; 

 chlorophyll c,; 19'-hexanoyloxyfucoxanthin: 



19- butanoyloxyfucoxanthin; fucoxanthin; peridinin; 

 diadinoxanthin; diatoxanthin: and p,p-carotene (Table 2). 

 Concentrations of zeaxanthin plus lutein, prasinoxanthin, and 

 alloxanthin were near or below the limit of HPLC quantification. 

 Phytoplankton pigments in the study area were not uniformly 

 distributed. Chlorophyll a concentrations ranged from 

 1 2 to 26,6 1 8 ng 1 ' , wi th highest concentrations measured in the 

 Gulf of Anadyr and the Chukchi Sea (Fig. 1). Distributions of 

 chlorophyllide a, chlorophyll c, fucoxanthin, diadinoxanthin, 

 diatoxanthin, and |3,P-carotene all displayed patterns similar to 

 that of chlorophyll rt (Figs. 2,4,7,10,1 1,12). In contrast, 

 elevated concentrations of chlorophyll /' and peridinin were 

 measured in a narrow zone extending from the Chirikov basin 

 to just north of the Bering Strait (Figs. 3,6). Chlorophyll c„ 

 19'-hexanoyloxyfucoxanthin.and 1 9 -butanoyloxyfucoxanthin 



128 



