2.1 Northern Bering-Chukchi Sea Ecosystem: 

 The Physical Basis 



LAWRENCE K. COACHMAN^ and VIKTOR V. SHIGAEV^ 



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



• Institute of Global Climate and Ecology, State Committee for Hydrometeorology and Academy of Sciences, Moscow. USSR 



Introduction 



The northern Bering and Chukchi Seas, encompassing the 

 Bering Strait (Fig. 1 ). together constitute the most enormous 

 shelf sea of the World Ocean — that is, over 1,000 km in north- 

 south extent with depths less than 100 m. The longer-term 

 (>1 month) average flow is northward of Bering Sea water 

 across the whole area into the Arctic Ocean, providing the 

 Northern Hemisphere oceanic link between Pacific and Atlantic 

 Ocean systems. It has been known that North America and 

 Asia are separated by the Bering Strait since Simeon Dezhnev 

 transited the strait inadvertently (blown by a storm) in 1648; 

 and that the general flow of the water through the strait is 

 northward since the voyages of Bering and Cook in the 18th 

 century. 



178* 180* 173" t7S* 



164- I6r iW 158* ISA* 



76' leO- I7B' 176* 174- 17;- 170" i68' i66- lei* 



Fig. 1. Bathymetry of the northern Bering and Chukchi Seas. 



Modem studies of the physical oceanography of various 

 parts of this large regime, begun in the 1930"s by G. E. 

 Ratmanov ( 19,^7a,b) and C. A. Barnes (Barnes & Thompson, 

 1938), were )iyn[he^izedinBering Strait: The Regional Physical 

 Oceanography {Coachman etal., 1975). This study summarized 

 the water masses, theirdistributions, something of the temporal 

 and spatial variations in properties and causes thereof, and 

 quantified the northward flow and its variations. It showed the 



integrated nature of the whole system: that the waters and its 

 transported properties were intimately connected across the 

 entire shelf sea from the Bering Sea basin to the Arctic Ocean 

 and that the dominant property distribution inechanism is 

 everywhere is advection (with the generally northward flow). 

 Investigations of various biochemical properties within 

 the region, from which the production of organic matter and its 

 subsequent fate can be determined and explained, began much 

 later than the physical studies. These were also much more 

 piecemeal and limited in scope until the advent of the Inner 

 Shelf Transfer and Recycling Program (ISHTAR) in 1985 

 (Walsh et al.. 1990), which undertook an integrated 

 physical/chemical/biological study (i.e., ineasuremenls of all 

 fundamentals of the basic ecosystem) of those portions of the 

 region to which they had access, viz. the Chirikov basin and 

 eastern part of the Chukchi Sea. The results from ISHTAR, 

 after four years of intensive sampling and analysis, clearly 

 demonstrate that the whole region, integrated into one regime 

 by the north advection, is also integrated as an enormous 

 ecosystem containing some of the highest primary production 

 values ever measured in the World Ocean. The ecosystem is 

 sketched schematically in Fig. 2. The generally northward' 

 water flow is composed mostly of water from the northern 

 Bering Sea basin, which enters the region in the 



Fig. 2. Schematic of the northern Bering Sea ecosystem. Open arrows 

 indicate advection along which ecosystem activity is aligned; 

 dashed Imes encompass the three production/deposition centers. 



17 



