probably as the result of strong vertical mixing; however, 

 values larger than 20 |imole/l were observed on the west side 

 of all three regions (Gulf of Anadyr, Chirikov basin, Chukchi 

 Sea). The presence of these large near-bottom nitrate 

 concentrations are almost certainly due to some nitrification 

 (ammonium conversion to nitrate by bacteria) occurring in the 

 Chirikov basin and Chukchi Sea. 



Ammonium, the regenerated form of nitrogen, was found 

 to have very low concentrations (Fig. 2C) in surface waters. 

 The very high affinity of phytoplankton to ammonium reduces 

 concentrations to very low levels unless unusually large surface 

 ammonium regeneration rates are occurring. The bottom 

 ammonium concentrations (Fig. 2D ) reflect the active nature of 

 nutrient regeneration in the near bottom waters and sediments. 

 Decomposition of organic matter releases large amounts of 



ammonium especially where high priinary 

 production/deposition is occurring. This process is best shown 

 in the central Chukchi Sea and to a smaller extent in the western 

 Chirikov basin. Remember that the east side of the Bering and 

 Chukchi Seas has very small organic production rates compared 

 to the western portions. The highest near bottom ammonium 

 concentrations were found in the low temperature "winter 

 water" in the Gulf of Anadyr and along the Soviet coast in the 

 Chukchi Sea. These large ammonium concentrations reflect 

 the accumulation that occurred over the several months since 

 the cold water was produced. In both cases more than 

 4 (iniole/1 concentrations were observed in the two regions. 

 The Gulf of Anadyr ammonium probably contributes to the 

 surface increases of ammonium that are observed downstream 

 after vertical mixing in Anadyr Strait. 



180 



175 



170 



165 



==V 



-+- 



-+- 



180 



175 



170 



165 



180 175 170 165 



Fig. 2. The surface (A) and bottom (Bl distribution of nitrate ()i mole/1), the surface (C) and bottom (D) distribution of ammonium 

 ((J mole/1) measured in the northern Bering and Chukchi Seas. 



41 



