wind mixing, advection, and continental run- 

 off. The presence in the summer of the cold 

 bottom water masses which are probably a 

 residue of winter water, suggests week warm- 

 ing of the region and weak circulation in the 

 Gulf which prevents extensive mixing. 



DISTRIBUTION OF DISSOLVED OXYGEN 

 AND NUTRIENTS 



The Gulf of Anadyr has a uniform vertical 

 and horizontal distribution of oxygen and nu- 

 trients in the spring as a result of vigorous 

 vertical circulation in the fall and winter 

 (Mokievskaya, 1956). With the formation of 

 a two-layer .system due to warming and ad- 

 vection of warm North Pacific water into the 

 Gulf, an intense phytoplankton bloom occurs 

 in June in the surface waters depleting the 

 nutrients and increasing the oxygen concentra- 

 tion to supersaturation in many places in the 

 Gulf (Zenkevitch, 1963). The Anadyr phyto- 

 plankton are mainly Arctic or Arctic-boreal, 

 the boreal forms being predominant only in the 

 surface layer in the summer (Zenkevitch, 

 1963). 



The dissolved oxygen distribution in the Gulf 

 of Anadyr during Augu-st 1970 is shown in 

 Figures 5, 12, 19, 26, and 33. The degree of 

 saturation for all the oxygen data was calcu- 

 lated from the solubility of oxygen in sea water 

 given by Green and Carritt (1967). The sur- 

 face waters had saturation values near or 

 greater than 100 ^^ except near the Anadyr 

 River where .saturations down to 70' , were ob- 

 served. The maximum .saturation values 

 (>100%) were found .iu.st above or at the 

 thermocline. The supersaturation at the sur- 

 face may be caused by rapid surface heating 

 which occurs in the Gulf under calm summer 

 conditions, as well as by phytoplankton activ- 

 ity. The maximum super.saturation values at 

 the thermocline are probably caused by pri- 

 mary production. Fourteen vertical plankton 

 tows were made in the Gulf and the .samples 

 revealed large concentrations of phytoplankton. 



The three bottom water masses in the Gulf 

 of Anadyr can be distinguished by their dis- 

 .solved oxygen content (fig. 53). The oxygen 

 content of the cold bottom water in the .south- 

 east section of the Gulf ranged from 6.1 to 

 7.8 ml 1 with .saturations of 70 to 90%. The 



high saturation values suggest recent contact 

 of the water with the surface. The dissolved 

 oxygen content of the cold bottom water near 

 Holy Cross Bay ranged from 4.2 to 5.5 ml/1 

 with saturation values of 51 to 64%. The low 

 values support the hypothesis that the cold 

 water was trapped and has escaped from the 

 i.solated bay. The warm bottom water separat- 

 ing the two cold bottom water masses exhibited 

 dissolved oxygen values of 6.1 to 6.7 ml/1 with 

 saturations of 77 to 87' , . 



The general distribution of nutrients in the 

 Gulf of Anadyr during August 1970 resembled 

 tho.se distributions observed previously (Mo- 

 kievskaya, 1956) . although none of the previous 

 investigations provided as much detail as the 

 CGC NORTHWIND survey. The observed dis- 

 tributions of phosphate, nitrate, nitrite, and 

 silicate in the Gulf are shown in Figures 6-9, 

 13-16, 20-23, 27-30, and 34-37. 



The surface concentrations of nutrients were 

 much lower than those of the bottom waters. 

 Phosphate and nitrate concentrations were 

 often so low as to suggest nutrient limitation 

 of phytoplankton production. Silicate concen- 

 trations in the surface waters were also low 

 but almost always greater than 3.0 ^ig-at/1. 

 The near-surface nutrient concentrations near 

 the Anadyr River Plume (Stations 8, 9, 22, 

 23) were high and indicate that the river is an 

 important source of nutrients in the western 

 Gulf of Anadyr. All the nutrients increased in 

 concentration as the Plume was approached. 

 Silicate showed the greate.st increase. 



A strong seasonal thermocline acts as a bar- 

 rier to recirculation of the nutrients in the 

 shallow gulf. Below the thermocline, nutrient 

 concentrations were many times greater than 

 in the surface waters (PO4>1.20, NO, > 10.0, 

 SiO.,>20.0 /j,g-at/l) . Source of the high nutrient 

 content of the bottom waters may be advection 

 of Pacific water into the Gulf of Anadyr from 

 the southwestern Bering Sea. This water is 

 characterized by high nutrient concentrations 

 (especially nitrate and silicate) and is known 

 to flow into the gulf ( Ar.sen'yev. 1967) near the 

 bottom the entire year. 



The two cold bottom water masses in the 

 Gulf of Anadyr .show slightly different nutrient 

 concentrations, reflecting the different .sources 

 suggested above. The nutrient concentrations 

 in the cold bottom water near Holy Cross Bay 



