Coastal water and to a lesser extent Bering Shelf water; both 

 these water masses show a decrease in S over the summer, 

 which can amount to as much as one-half part per thousand. 



There are also interannual variations in the water mass 

 salinities that are the same magnitude as those of the seasonal 

 cycle (about 0.5). Figure 5 showstherangesofS values for the 

 water masses for all the years when sections in June or early 

 July encompassing Anadyr and Shpanberg Straits have been 

 taken; similar times of year must be compared to avoid the 

 seasonal variations. We see that, interannually, the salinities 

 are not constant. Small year-to-year differences are probably 

 not significant because definition of water mass boundary 

 values can sometimes be somewhat fuzzy, but the long-term 

 variation with either a 10 or 20-year period is definitely real. 

 Anadyr Current water in the 1960"s frequently had S values 

 >33.0, but during the 1970's and beginning of the 1980's, 

 values this high were never observed; only in 1988 have 

 salinities >33 reappeared. 



Similar sized interannual variations in S have also been 

 observed in the central shelf water of the southeast Bering Sea 

 Shelf; ranges of S observed there (Coachman, 1986) are also 

 plotted in Fig. 5. Clearly we are seeing the effects of large-scale 

 climatic fluctuation causing similar property variations ovei; 

 the entire Bering Sea Shelf. This variation effects also the 

 bottom water temperatures of central shelf waters, and the T 

 and S are correlated — wanner with more saline and colder 

 with fresher. The few measurements available of bottom water 

 temperatures in the central Gulf of Anadyr, where the coldest 

 water of the whole Bering Sea Shelf is always found (the so- 

 called "cold center" of the Bering Sea; Barnes & Thompson, 

 1938), suggest an interannual variation incoldestTof at least 

 2°C may obtain, not unlike that of T on the southeast shelf 

 (Fig. 5). The interannual climate variation is also manifested 

 in interannual variablity of ice cover of the Bering Shelf, which 

 is primarily responsible for establishing the T and S conditions 

 of bottom waters for the following year: minimum ice/warmer 

 bottom temperatures/more saline, and vice versa. 



^m^ Southeast Central Shelf Bottom Woter T Ronge 

 J Southeast Central Shelf Water S Range 



;^ 



I960 65 



Fig. 5. Interannual variation ofsalinity ranges ofthclhrec basic water masses. 

 Over the 2.'i years of observations, water masses were most saline in the 

 late I960's, and least saline in the mid-mVO's. Temperatures and 

 salinities of southeastern Bering Shelf water suggest similar variations, 

 showing the changes to be part of a large-scale climatic variation. 



The water mass sources are all to the south of the northern 

 shelf area, and the advection carries them northward. As 

 Alaskan Coastal, Bering Shelf, and Anadyr Current water 

 masses are arranged sequentially east to west and there is very 

 little lateral mixing or diffusion in the system, these waters 

 maintain their east to west relationship as they are advected 

 north. Figure 6 shows their distribution during August 1988, 

 based on the Korolev data. The water masses were distinguished 

 primarily by salinity of the deeper water, but temperature and 

 water column structure (depth and degree of layering) were 

 also considered. Anadyr Current water mass (Fig. 6, 1) originates 

 from water of the Bering Slope Current (Kinder et ai, 1975), 

 a branch of which enters the Gulf of Anadyr in the west near 

 Cape Navarin. This water hugs the western Siberian shore and 

 remains identifiable as a distinct entity to Bering Strait. North 

 of this strait, the water merges with and becomes 

 indistinguishable from Bering Shelf water. 



"180 



175° 



170° 



165° 



160° 



Fig. 6. Spatial distribution of water masses in August 1988 (Korolev liala). 

 I: Anadyr Current. II: Bering Shelf. Ill: Alaskan Coastal. 

 IV: Gulf of Anadyr. V: Siberian Coastal. 



On the east side of the system, Alaskan Coastal water 

 (Fig. 6, III) originates well to the south of the region. It has the 

 lowest salinities because it is the recipient of runoff from all 

 along the coast, from the rivers of Bristol Bay and the 

 Kuskokwim River. As Alaskan Coastal water enters the 

 region, additions of Yukon River water near the east side of 

 Shpanberg Strait "reinforce" the low salinities, which happens 

 again when the water passes through Kotzebue Sound north of 

 Bering Strait. Thus some parts of this water mass can become 

 quite fresh in late summer (S<30), and its area expands westward, 

 but by the following winter the freshwater has flushed from the 

 system and Alaskan Coastal water salinities are again >32. 



Bering Shelf water (Fig. 6, II) is the resident water mass 

 of the whole central shelf region south of St. Lawrence Island. 

 The waters filling the central shelf are basically mixtures of the 

 two extremes: least saline coastal water and the most saline 



19 



