Bering Sea
Little is known about bird distribution in the Bering Sea during ice formation because cruises in rapidly forming ice are potentially hazardous. It is not known if the large numbers of birds found at the ice edge in March are present in December and January.
Discussion
The principal effect of the arctic pack ice is to lower biological productivity and bird densities in the areas it covers. Unlike the antarctic pack ice, which supports a large biomass of pagophilic species, the number of pagophilic species supported by the arctic pack ice is small. Only the ivory gull, Ross' gull, and black guillemot have specific adaptations to the ice environment. The Ross' gull and guillemot winter in the pack ice, and the ivory gull is associated with ice throughout the year. The total biomass of these species is low. Other species which are regularly associated with the arctic pack, such as murres and black-legged kittiwakes, are also found in large numbers away from the ice. In addition, these species are usually associated with ice for limited periods during the year—murres primarily in winter and spring and kittiwakes primarily in summer.
The difference in the antarctic and arctic pack ice systems is largely due to the antarctic pack ice being surrounded by ocean, whereas the arctic pack ice is, in general, surrounded by land. The high productivity associated with the antarctic pack ice is due primarily to the mixing that occurs at the edge of the pack ice. There is little opportunity for mixing to occur next to the arctic pack ice, except where it is next to large expanses of boreal waters. This occurs in the Bering Sea in winter and spring, in the North Atlantic, and to a minor extent in the Chukchi Sea in summer and fall (Dunbar 1968). The limited geographic range and seasonal nature of high productivity at the arctic pack ice edge has been a major factor in preventing a well-developed pagophilic avifauna.
The importance of the in-ice algal bloom and its associated under-ice fauna is not yet clear. It is probably most important in areas such as the Beaufort Sea, where productivity in the water column is low. Although considerable numbers of seabirds are regularly found in the summer pack ice feeding on arctic cod and zooplankton associated with the ice, bird densities south of the ice are usually greater than those in the ice. The only species that appear to depend on the ice-associated fauna for much of their food are the three pagophilic species mentioned above.
References
Alexander, V. 1974. Primary productivity regimes of the nearshore Beaufort Sea, with reference to potential roles of ice biota. Pages 609-632 in J. C. Reed and J. E. Sater, eds. The coast and shelf of the Beaufort Sea. Arctic Institute of North America, Arlington, Virginia.
Andriashev, A. P. 1968. The problem of the life community associated with the antarctic fast ice. Pages 147-155 in R. I. Currie, ed. Symposium on antarctic oceanography. Scott Polar Research Institute, Cambridge.