. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering 466 Fisheries oceanography I960 1963 1966 1969 1972 1975. Figure 29-11. Monthly mean wind (m/sec) components at 57°N, 170°W, 1946-75. (Positive values indicate northward component, negative values indicate southward component.) Twelve-month running mean showing annual mean trends. winds (cold conditions). Kihara (1971) has reported the extreme variability of the extent of Alaskan Stream Extension water over the southern part of the outer shelf. Although polar wav
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering 466 Fisheries oceanography I960 1963 1966 1969 1972 1975. Figure 29-11. Monthly mean wind (m/sec) components at 57°N, 170°W, 1946-75. (Positive values indicate northward component, negative values indicate southward component.) Twelve-month running mean showing annual mean trends. winds (cold conditions). Kihara (1971) has reported the extreme variability of the extent of Alaskan Stream Extension water over the southern part of the outer shelf. Although polar waves considerably alter air temperature, wind, and precipitation, annual variability in shelf conditions is most easily shown by the extent of ice cover and by bottom temperatures. Ice In recent years (1976-78) the extent of ice cover for November (when ice first extends seaward) was minimal in 1976 and maximal in 1977; whereas for April (usually the month of greatest ice cover), the maximum extent occurred in 1976 and the ice edge has been farther north each succeeding year, with the greatest changes occurring on the eastern side of the shelf (Fig. 29-12). Thus, there is no correlation between spring conditions and subsequent fall con- ditions (, summer conditions can obliterate cold trends established in the spring). Furthermore, although the normal southerly winds in spring result in a compact ice edge and hasten its northerly retreat, northerly winds can cause anoma- lous conditions. In April 1976 an unusual and large southward displacement of part of the ice edge in the Bristol Bay area resulted in ice immediately north of the Alaska Peninsula which forced vessels out of the area (Northwest Fisheries Center 1976).' This displacement not only caused water in the open area in the northern Bristol Bay to be subjected to early insolation (and thus warming), but because spring warming at the surface had already begun, considera- bly altered the temperature structure of the
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