Gulf of Anadyr. The continuity of this flow, entirely through 

 the system into the Arctic Ocean, provides integration between 

 three serially-aligned production/deposition/regeneration 

 centers; the output of the upstream Gulf of Anadyr center 

 materially effects the biochemical activity of the Chirikov 

 basin center, which in turn feeds the center in the Chukchi Sea. 

 Confirmation of the integrated nature of the ecosystem is 

 provided by measurements made during the first synoptic 

 survey of the whole region from the Gulf of Anadyr through the 

 southern Chukchi. The opportunity arose from amalgamation 

 of ISHTAR into the Third Joint US-USSR Bering & Chukchi 

 Seas E.\pedition, 25 July-2 September 1988, on board the 

 research vessel (RfV ) Akademik Korolev (Korolev). The areal 

 distribution of integrated chlorophyll ( Fig. 3 ) clearly shows in 

 essence the ecosystem arrangement sketched in Fig. 2 — three 

 high-production centers arranged sequentially along the 

 pathway of flow of Bering Sea water from the northern Bering 

 through the Gulf of Anadyr, then the Chirikov basin and 

 Bering Strait, and on through the southern Chukchi. Thus, we 

 are dealing with a single ecosystem. It is the purpose of this 

 paper to describe, to the extent of current knowledge, the 

 physical basis of this ecosystem: the water masses and their 

 characteristics, the flow field, and the variabilities of the 

 physical features. The paper concludes with a discussion of the 

 downstream end of the system in the Chukchi Sea, about which 

 very little is as yet known. 



175° 



165° 



160° 



Fig. 



}. Integrated chlorophyll from the cruise odheAkmleinik K(iroU'\\ August 

 1988. Notice the three major production centers, and the edge of a 

 fourth area of high chlorophyll biomass off Kolyuchm Bay in the 

 Chukchi Sea (after Springer, McRoy & Whitledge, in press). 



Water Masses 



Salinity is the variable delimiting the water masses because 

 in the colder high-latitude waters, it, rather than temperature, 

 has the primary influence on water density. Based on sources 



and modifications, there are three water masses fundamental to 

 the sy.stem (Coachman el ai. 1975), and it is convenient to 

 define two others, more local products of modifications. 



The three basic water masses, Alaskan Coastal, Bering 

 Shelf, and Anadyr Current, are arranged side-by-side in the 

 east-west direction. Identification ofthe water mas.ses obtained 

 at any particular time are done from T/S diagrams of stations 

 from sections crossing Anadyr and Shpanberg Straits; these 

 capture the characteristics of the three basic water masses at the 

 same time. Figure 4 shows an example. Typically, in the T/S 

 plane, values beneath the surface layer fall naturally into three 

 groups; a group with intermediate values of S but very cold; 

 and somewhat warmer groups to each side, both less and more 

 saline. Spatial continuity shows the least saline group ( Alaskan 

 Coastal) to occupy the eastern part of Shpanberg Strait, the 

 most saline group ( Anadyr Current ) are always stationed in the 

 western part of Anadyr Strait, while Bering Shelf water of 

 intermediate salinities can usually be found near both ends of 

 St. Lawrence Island. Thus, from Fig. 4, the ranges of salinity 

 for the three water masses were Anadyr Current — 33.0 to 

 32.75; Bering Shelf— 32.75 to 3 1 .9 ; Alaskan Coastal— <3 1 .9. 



ALASKAN 

 COASTAL 



31 32 



SALINITY %o 



Fig. 



4. T/S diagram of stations crossing Anadyr and Shpanberg Straits, 

 illustrating the definition of the basic water masses. Station numbers 

 are at the bottom of each water mass curve. Notice the natural 

 separation into three salinity groups. 



But salinity values of the water masses are not constant. 

 There is a seasonal cycle because runoff at these high latitudes 

 is markedly seasonal. Yukon River discharge peaks in June, 

 when the flow grows in about one month's time to two orders 

 of magnitude greater than in winter. The regional north flow is 

 insufficient to flush all of this freshwater from the system 

 immediately, so part of the freshwater accumulates over the 

 summer and is only completely flushed by late fall (Coachman 

 t'l ai. 1975). This effects primarily salinities of Alaskan 



18 



