The Bering Slope Current (BSC; Kinder et al., 1975, 1986; Schumacher and Reed, 1992) has a transport of 3-5 x 106 m3 s-1, and contains Alaskan Stream water that flows through Amchitka and Amukta Passes and then eastward along the northern side of the Aleutian Islands. The BSC influences slope water properties (Schumacher and Stabeno, 1994; Reed and Stabeno, 1994) which flux onto the outer continental shelf. A subsurface temperature maximum is a characteristic of the southern Bering Sea. It is >4°C when the Alaskan Stream flows northward through Amukta Pass (Schumacher and Reed, 1992). Eddies are a common feature in the southeastern Bering Sea; some are formed by flow through Amukta Pass (Schumacher and Stabeno, 1994).
The northwestward flow of the BSC (3-15 cm s-1) along the eastern shelf break is concentrated in the upper 300 m (Schumacher and Reed, 1992: Muench and Schumacher, 1985). Although wind energy approximately doubles in winter, kinetic energy of the current fluctuations and the vector mean currents do not; only a small fraction of the current fluctuations measured here can be accounted for by the wind. Small (5-30 km) eddies with strong (20-30 cm s-1) rotational speeds are features of the current regime. Estimates of salt fluxes indicate some significant shoreward transport (Schumacher and Reed, 1992).
The BSC separates from the slope near 58°N; it then flows across the basin. This flow is the main source of the Kamchatka Current (Stabeno and Reed, 1994: Khen, 1989). Much of the remaining BSC flow likely recirculates over the basin (Overland et al., 1994). The Kamchatka Current, which originates near 175°E and exhibits both strong speed (40-100 cm s-1) and numerous meanders and eddies, dominates circulation off the western shelf of the Bering Sea (Stabeno et al., 1994: Cokelet et al., in press). This current exits the basin through Kamchatka Strait.
The Kamchatka Current forms the western boundary and the Bering Slope Current (BSC) the eastern boundary of the cyclonic gyre in the Bering Sea (Reed et al., 1993). This gyre is mainly an extension of the Alaskan Stream, with the majority of volume transport entering through the deeper western passes of the Aleutian Islands (Near Strait and Amchitka Pass) and exiting via the Kamchatka Current (Stabeno and Reed, 1994). Occasionally, the Alaskan Stream does not flow into the Bering Sea through Near Strait (Stabeno and Reed, 1992) which results in a reduction of transport (by ~50%) in the Kamchatka Current (Verkhunov and Tkachenko, 1992). After a disrupted or weak inflow that started in late 1990, normal flow resumed in early 1992 (Reed and Stabeno, 1993). A numerical study (Overland et al., 1994) suggests that flow instabilities, both in the Alaskan Stream and within the basin, contribute to substantial interannual variability in the circulation.
A climatology of the wind forcing shows that eastward and northward-propagating storm systems dominate the surface stress at short periods (<1 month), which serves principally to mix the upper ocean (Bond et al., 1994). At longer periods (> months), the wind-driven transports account for roughly one-half of the observed transport within the Kamchatka Current. The interannual variations in the Sverdrup transports are ~25% of the mean.
The Alaska Coastal Current flows through Unimak Pass (~0.3 x 106 m3 s-1). Some turns eastward resulting in a current along the coastline (2-5 cm s-1) with the remainder flowing toward the northwest along the 100-m isobath (Reed and Stabeno 1994). The coastal flow (< 3 cm s-1) follows the 50-m isobath turning northward along near 58°N. The coastal current has a seasonal pattern in strength, with flow increasing in winter concomitant with increased storm activity (Schumacher and Kinder, 1983).
Over the outer-shelf domain of the Bering Sea, flow (5-10 cm s-1) containing water from both Unimak Pass and the slope follows the 100-m isobath toward the northwest. Near the shelf break, the inshore edge of the Bering Slope Current results in stronger (10-20 cm s-1) currents. Like the coastal flow, much of this flow is baroclinic. While pulses of cross-shelf flow (5-10 cm s-1) occur, their inherent variability precludes establishing a mean from existing moored current data. Propagation of eddies onto the shelf provides one possible mechanism for generation of pulses of cross-shelf current.
The northward mean transport through Bering Strait is driven by the surface height difference between the Pacific and the Arctic Ocean and modified by the wind. Strong (5 x 106 m3 s-1) wind-driven reversals occur mainly during winter. During summer, maximum northward transport exceeds 3 x 106 m3 s-1. An annual mean of 0.8 x 106 m3 s-1 has been estimated (Coachman, 1993). Transport through Shpanberg Strait provides about one-third of the northward transport through Bering Strait.
It has been hypothesized that the northward mean flow over the shelf undergoes westward intensification as water column depth decreases from south to north (Kinder et al., 1986). Flow through Anadyr Strait (15-40 cm s-1) provides about two-thirds of the transport through Bering Strait (Coachman, 1993). The current in Anadyr Strait is more stable in strength and location than that observed in Shpanberg Strait. Some of the flow continues eastward along the south coast of St. Lawrence Island and then turns northward, joining the coastal flow through Shpanberg Strait.
The suggested coastal flow from the Gulf of Anadyr westward past Cape Navarin (Overland and Roach, 1987) is supported by water property distributions. At the mouth of the Anadyr River, low salinities (~10 psu) occur during summer (Favorite et al., 1976). Dilute (<31.0 psu) surface waters, whose origin lies in the Gulf of Anadyr (Verkhunov and Tkachenko, 1992), exist over the shelf between Capes Navarin and Olyutorski. Satellite-tracked buoys (drogue at 40 m) transited here at speeds of ~40 cm s-1 (Stabeno and Reed, 1994). Buoy observations from the Gulf of Olyutorski show the strong (30-50 cm s-1) flow of the Kamchatka Current over the slope, while more moderate (15-25 cm s-1) speeds occur over the adjacent shelf. These observation suggest a coastal current over the western shelf.
In both the Gulf of Olyutorski and Karaginski Bay, quasi-stationary eddies exist, and similar features also occur in embayments along the Kamchatka coast (Stabeno et al., 1994; S. Gladyshev, unpublished manuscript). Satellite-tracked buoy trajectories substantiate such a feature in the bay centered at 54°N. Generation of these features likely results from meanders in the inshore flow interacting with topography and/or formation of saline lenses due to brine expulsion (Verkhunov, 1994).
Ice production and cold bottom water exert an important influence on distributions of biota over both the western (Radchenko and Sobolevskiy, 1993) and eastern (Ohtani and Azumaya, 1995: Wyllie-Echeverria, 1995) shelves. The production of dense water has a marked impact on the halocline of the Arctic Ocean (Cavalieri and Martin, 1994), with water from the Anadyr and Anadyr Strait polynyas providing a substantial fraction of the total dense water. From 9 to 25 m of ice formation occurs depending on the location and duration of a given season (Cavalieri and Martin, 1994), but the average thickness of ice over most of the eastern shelf is only ~0.5 m (Coachman, 1986).