The surface silicate concentrations (Fig. 3 A) are similar to 

 those of nitrate, especially the strong east-west gradient in the 

 Chirikov basin. Silicate is mainly utilized by diatom populations 

 but other phytoplankton may also have a silicate requirement. 

 Even the areas where high silicate concentrations have been 

 reported in river discharge contained less than 5 |imole/l. Near- 

 bottom silicate concentrations (Fig. 3B) reflect the large 

 concentrations present in deep Bering Sea water with values 

 above 50 [imole/l. Vertical mixing in Anadyr Strait and 

 subsequent uptake by phytoplankton reduce concentrations to 

 the range of 10-30 |imole/l. The east side of the ecosystem all 

 had values less than 10 |imole/l. 



The surface phosphate concentrations (Fig. 3C) were 

 adequate to support primary production processes throughout 

 the area of investigation. Areas with phosphate concentrations 



less than 0.5 |imole/l also contained small amounts of nitrate 

 and silicate; therefore, phosphate was always in plentiful 

 supply compared to other nutrient forms. Near-bottom 

 phosphate concentrations ( Fig. 3D) reflect both the enrichment 

 from the deep Bering Sea into the Gulf of Anadyr and the 

 cumulative effects of phosphate regeneration in the Chirikov 

 basin and Chukchi Sea. 



The Gulf of Anadyr serves as the conduit for flow of water 

 from the deep Bering Sea into the confined Chirikov basin. The 

 center of the Gulf of Anadyr is stratified with the warmer 

 surface waters depleted of nutrients ( Fig. 4), but near the coast, 

 all isopleths rise toward the surface, indicative of active coastal 

 upwelling. Surface concentrations of all nutrients were low 

 enough to reduce primary production. The highest chlorophyll 

 measured in this region (24-28 |ig/l) was on Station 26 at a 



180 



175 



170 



165 



180 



175 



170 



165 



180 



175 



170 



165 



180 175 170 165 



Fig. .^. The surface (A) and boltcim (Bl dislrihulion ol silicate (n mole/1), the surface (C) and hcitlcim (D) distribution of phosphate 

 (|i mole/I) measured in the northern Bering and Chukchi Seas. 



42 



