Figure 1 shows the climatological mean circulation patterns of the subarctic Pacific based on geostrophic flow (e.g., Reed, 1984; Reed et al., 1993), and direct current measurements (Stabeno and Reed, 1994; Schumacher and Kendall, 1995; Schumacher and Stabeno, in press). The values of velocity given are estimates of typical flow. In the swifter currents, peak speeds can be substantially larger than the values given.
Oceanic conditions in the Bering Sea are also influenced by the extent of ice cover (Fig. 2). During extreme conditions, ice covers the entire eastern shelf, however interannual variability of coverage can be as great as 40% (Niebauer, 1988). The buoyancy flux from melting ice initiates both baroclinic transport along the marginal ice zone and stratification.
Evidence of decadal-scale variability in climate conditions and regime shifts is prevalent in the North Pacific and Bering Sea. The climate of the Subarctic Pacific changed during the late 1970s. The Aleutian Low intensified (Trenberth and Hurrell, 1994) and coastal sea surface temperatures rose rapidly by several degrees (Rogers and Ruggerone, 1993; Royer, 1989; Graham, 1995). The most recent shift occurred in the late 1970s.