The stable oxygen isotope composition of tunicate cellulose 

 and its relationship to the water mass the animal grows in was 

 studied for the first time in a polar system during the 1 988 field 

 season in the major water masses of the northern Bering and 

 Chukchi Seas. The 5 '''O values in the major water masses were 

 mirrored in the 8 '"O values of the cellulose in the benthic 

 tunicates living in/on the underlying sediments (Figs. 3,4 ). Our 

 objective was to test for possible short- and long-term signals 

 for water mass location in this region. By measuring the "*0 

 content of cellulose in tunicates, which are immobile as adults, 

 we found evidence that these animals provide a long-term 

 indication (over a 1-3-yr. lifespan) of water mass location 

 during the growing season, presumably during the ice-free 

 summer months (Fig. 4). Due to oxygen isotope fractionation 

 during cellulose synthesis, the 8 "'O values of tunicate cellulose 



Fig. 4. Distribution of tunicate cellulose 8 '"O values for stations occupied 

 during R/V Akademik Korolev cruise 47 (•) and R/V Alpha Helix 

 cruise 1 I3(»)in 1988. Isotope ratio units: '7„|(Grcbmeierf/(7/.. 1990). 



are positive, but the relative ~2T/,„ enrichment in "O is 

 consistent with differences between each water mass. This 

 signal was also observed in tunicates underlying the Siberian 

 Coastal water. 



Sediment Oxygen Uptake Rates 



The high nutrient load of the Anadyr water provides a 

 continuous source of nutrients for high primary production in 

 the water column during the open- water season on the west side 

 of the shelf from the Gulf of Anadyr to north of Bering Strait, 

 but nutrient depletion limits production along the Alaska 

 coastline after the spring bloom (Fig. 5; Walsh et ai, 1989). 



Fig. 5. Depth-integrated distribution of chlorophyll a ( mg m - ) during August 

 1988 (after Walsh et ai. 1989). 



KEY 



' 1964-1987 stations 

 1988 stations 

 values < 10 mmol Op m' d' 



Fig. 6. Distribution of sediment oxygen uptake rates (mmol O., m • d ') for 

 1984-1986 {from Grcbmcier & McRoy. 1989) and 1988 (this study). 



247 



