. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering 16 16 20 22 24 26 29 30 ^^'' '^*" « â "â ' ""TTT 1 1 I ' ^g C/(/)(hf) / SURVEYOR 2 / ICE TRANSECT II ^â a I Q Station 13 in ice t O Station 14 ice-edge k A Station 15 out of ice ââ Chloroptiyll Primary Productivity Figure 44-5. Depth profiles of primary production and ciiioropiiyll a at three stations at different distances from the ice edge. Redrawn from Alexander and Cooney (1979). concentrations are not so distinct, the general trend appea
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering 16 16 20 22 24 26 29 30 ^^'' '^*" « â "â ' ""TTT 1 1 I ' ^g C/(/)(hf) / SURVEYOR 2 / ICE TRANSECT II ^â a I Q Station 13 in ice t O Station 14 ice-edge k A Station 15 out of ice ââ Chloroptiyll Primary Productivity Figure 44-5. Depth profiles of primary production and ciiioropiiyll a at three stations at different distances from the ice edge. Redrawn from Alexander and Cooney (1979). concentrations are not so distinct, the general trend appears to be the oppositeâammonia concentrations are higher in ice-covered areas than in the open water. As the bloom progresses, after stratification is estab- lished near the ice edge, ammonia concentrations tend to increase. An increase is also evident in areas of open water. Although the source of this increase is not clear, in ice-dominated areas in-situ ammoni- fication may be the mechanism. Ice-edge model The general elements of the ice-edge ecosystem can be described in a spatial and temporal concep- tual model (Fig. 44-6). The proximity of the ice-edge zone to the shelf break in the southeast Bering Sea depends on the severity of the preceding winter; the duration and strength of the seasonal cooling cycle determines the location of the southern terminus of the pack. There is increasing evidence that cycles of water temperatures are related to fluctuations in the long-term atmospheric circulation over the northern North Pacific Ocean (Niebauer 1980; Chapters 3 and 9, Volume 1). For periods of one or more years, the atmospheric distribution of spatial pressure patterns forms a predominantly southerly or northerly mean air flow above the ocean surface. If the air flow is mainly southerly, the winters are warm and the seasonal ice is restricted to northern shelf regions. During periods of mean air flow from the north, the converse is true: the cooling cycle is longer
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