178" 176" 174*' I72« 170" 168" 166" 164" 162" 160" 158" 156" 



^ — - VARIABLE 

 — • — • "CORES" (vonoua posi 



ifions) / V 



178" 176° 174° 172° 170° 168° 166° 164° 162° 160° 158° 156° 



Fig. 19. A best guess of the circulation in the Chukchi Sea (from Coachman, 

 Aagaard & Tripp, 1975). Notice that Herald Island and Shoal are in 

 the main pathway of Bering Shell water. However, there actually must 

 be more movement of water toward the Siberian Coast near Wrangel 

 Island than suggested in this schematic. 



L'envoi 



We have summarized the important physical oceanographic 

 factors of the northern Bering Sea ecosystem. A unique set of 

 features combine to make it one of the World Ocean's largest 

 and most productive ecosystems. The key feature is advection 

 of waterfrom a rich pool of nutrients (the Bering Sea Continental 

 Shelf edge), across an enormous distance in shallow water. 

 The nutrient supply continuously injected by the current is 

 sufficient that they never become depleted and limiting, even 



with high production. There are two constrictions in the 

 advective stream, dividing the system into three basins and 

 three production centers. These are spaced such that the transit 

 time of water across each basin, two to four weeks, is the same 

 as a complete biological production-utilization-regeneration 

 cycle. Turbulent energy injected into the water columns at the 

 constrictions stirs them, "resetting" the system for the next 

 round of production. 



The advection is driven northward from the Bering Sea 

 into the Arctic Ocean by a sea surt'ace slope (the Arctic Ocean 

 stands lower than the Bering). But there are important variations 

 in the transport related to the local winds, which drive water 

 against the land boundaries modifying the surface slope. Primary 

 variations are over a few days (storm time scale), and as these 

 are greatest and most frequent in winter, there is a seasonal 

 cycle of lower net north transport in winter and greater in 

 summer. Interannual variations are also significant. They 

 affect mostly the geographically constricted Chirikov basin; 

 here water parcel transit (residence) times can differ by a factor 

 of five. The variability seems to have only a small influence on 

 the actual amount of primary production in the ecosystem; 

 rather, its importance lies in varying the amount of production 

 that becomes deposited in the centers versus the amount that is 

 transported through into the Arctic Ocean. 



The downstream (Chukchi Sea) end of the ecosystem is 

 virtually unknown. Nutrients supporting very large production 

 are supplied to this center by Bering Shelf water entering 

 directly via Bering Strait and from a second source presumed 

 to be Bering Shelf water enhanced in salt content through 

 freezing during the previous winter and recirculated via the 

 Siberian Coastal Current. But this is hypothesis; the circulation 

 of the Chukchi is not known, nor the amount and extent of 

 production, nor the amount of carbon that is exported to the 

 Arctic Ocean. Considering the possible significant role of 

 Chukchi Sea carbon export in global carbon budgets and 

 climate warming (Walsh el cil.. 1989), further study of the 

 Chukchi Sea end of the northern Bering Sea ecosystem has a 

 very high priority. 



2.2 Water Mass Modification from the Bering 

 into the Chukchi Sea 



ANTHONY F. AMOS' and LAWRENCE K. COACHMAN* 



'Marine Science Institute. University of Texas. Port Aransas. USA 

 ' School of Oceanography. University of Washington. Seattle. USA 



Introduction 



The only Northern Hemisphere connection between the 

 Pacific and Atlantic Oceans is across the shallow waters of the 

 northern Bering and Chukchi Seas connected by the Bering 



Strait. The seminal work on the oceanography of the northern 

 Bering Sea (Barnes & Thompson, 1938) led to further 

 investigations on this important region that continue to this 

 day. Coachman et al. (1975) reviewed the regional physical 

 oceanography in the most comprehensive work on the Bering 



27 



