The distribution of sediment oxygen uptake rates measured in 

 the Bering and Chukchi Seas in 1 988 ( Fig. 6) is similar to water 

 column chlorophyll a concentrations ( Fig. 5 ). It further indicates 

 the extension of a high sediment respiration zone, which can be 

 used as an indicator of food supply to the benthos, to the west 

 of the previously known zone in US waters (Grebmeier & 

 McRoy. 1989). 



The highest benthic respiration rates in the southern 

 Chukchi Sea occurred in the central region where a similar 

 value was measured in 1985 (-35 mmol O, m-d'; Fig. 6). In 

 contrast to the sediment regimes under Alaska Coastal water, 

 sediment uptake rates in Siberian Coastal water and offshore 

 Bering Shelf- Anadyr water had high respiration rates, indicating 

 enhanced food supply to the benthos. Only a limited number 

 of sediment respiration measurements were made in the Gulf of 

 Anadyr, with values ranging from 10 to 40 mmol O, m-d '. 

 Further sampling is necessary to determine realistically organic 

 carbon supply to the various regions of the gulf. 



Benthic Macrofaiinal Biomass and Community Structure 



The highest benthic macrofaunal biomass for the study 

 area was recorded in the southern Chukchi Sea in 1 988 and was 

 coincident with the location of highest macrofaunal biomass 

 measured in the previous 1984-86 study period 

 (-30-60 g C m-; Fig. 7). The extension of this high biomass 

 zone to the west, both under Siberian Coastal water and 

 Anadyr-Bering Shelf water, suggests a major depositional 

 regime for high quality organic matter to support the high 

 secondary productivity in the underlying benthos. This western 

 region of the Chukchi Sea contrasts greatly with the nearshore 

 Alaskan waters, where benthic biomass nomially remained 

 below 10 g C m-. Ampeliscid and isaeid amphipods and 

 tellinid and nuculid bivalves dominated the benthic fauna in the 

 offshore region of the southern Chukchi Sea (Fig. 8). Benthic 

 regions closer to the Alaska coastline were characterized by a 

 mixture of communities, including tellinid and nuculid bivalves, 

 echiurids, brittle stars, phoxocephalid, isaeid and ampeliscid 

 amphipods, maldanid and oweniid polychaetes, and styelid 

 tunicates. The variability in benthic community composition 

 indicates the heterogeneity of the sediments underlying the 

 Alaska Coastal water (Grebmeier et ai, 1989). 



The highest biomass in the northern Bering Sea, north of 

 St. Lawrence Island, was observed in the central basin, with 

 lowest values once again along the Alaskan coast (Fig. 7; 

 Grebmeier «'/«/., 1989). Ampeliscid and isaeid amphipods and 

 tellinid bivalves dominated sandy sediments in this central 

 region. Brittle stars and sea urchins were common in Anadyr 

 Strait. A variety of benthic fauna characterized the region 

 under Alaska Coastal water, which included ampeliscid and 

 isaeid amphipods, tellinid and nuculid bivalves, echinarachniid 

 sand dollars, and echiurids. 



The Gulf of Anadyr is characterized by two major faunal 

 populations. The inner gulf is composed of a high biomass 

 (10-^0 g C m-) of tellinid and nuculid bivalves and capitellid 

 and scalibregmid polychaetes. These animals are deposit 

 feeders, indicative of the fine-grained sediment structure in 



Fig. 7. Distribution of macrofaunal benthic biomass (g Cm ') for 1984-1986 

 (from Grebmeier ('/((/., 1988) and 1988. 



this region. The outer gulf is composed of a more variable 

 biomass ( 1^0 g C m -) of nuculanid and nuculid bivalves and 

 capitellid and scalibregmid polychaetes. 



The area of high organic carbon supply to the benthos, 

 indicated by high sediment respiration rates (Fig. 6). supports 

 a rich benthic biomass of amphipods and bivalves (Figs. 7,8), 

 which in turn support the dominant benthic-feeding marine 

 mammals in the region, the California gray whale (Eschrichtius 

 gibbosus) and Pacific walrus ( Odobenus ros marus). Sediment 

 oxygen uptake rates and benthic biomass show a strong pelagic- 

 benthic coupling north of St. Lawrence Island into the southern 

 Chukchi Sea, with the lowest apparent food supply to the 

 benthos occurring in the low biomass regions underlying the 

 Alaska Coastal water (Figs. 6,7). Sediment respiration and 

 benthic biomass data were collected concurrently in the Gulf of 

 Anadyr for the first time in 1988. The results support a high 

 organic carbon flux to the benthos in the shallow nearshore 

 Siberian waters and offshore regions southwest of St. Lawrence 

 Island, with lower values in the central Gulf of Anadyr and 

 deeper slope regions ( Figs. 6,7 ). The increased benthic biomass 

 and sediment respiration on the shelf in the eastern part of the 

 Gulf of Anadyr is in an area affected by the St. Lawrence Island 

 polynya (SLIP) in the winter/spring (Arctic Ocean Sciences 

 Board. 1 989), which indicates the region may be exposed to an 

 additional carbon supply from enhanced open-water polynya 

 primary production in the late winter-early spring. 



248 



