14 



G. J. DIVOKY 



or sudden freezes were presented by Palmer 

 (1976). 



In late May, rivers that empty into the 

 northern Chukchi and Beaufort seas begin to 

 flow. The shorefast ice is still present at this 

 time and the rivers flow over the ice. For large 

 rivers, such as the Colville and the Saga- 

 vanirktok, the area of ice covered by water is 

 considerable. Openings in the ice develop 

 sometime after the river runoff starts and the 

 river water drains through the ice. 



This river overflow plays an important role 

 in the breeding biology of certain island nest- 

 ing species, since the overflow surrounds is- 

 lands and prevents arctic foxes from reaching 

 the islands. The overflow also allows birds to 

 sit in the water near breeding sites. It is not 

 known whether river overflow contains prey 

 items available to birds. After the overflow 

 drains through the ice, the shorefast ice that 

 has been covered with river overflow decom- 

 poses quickly, and patches of open water 

 occur early in areas just seaward of major 

 river deltas. For this reason the largest breed- 

 ing colonies on barrier islands in the northern 

 Chukchi and Beaufort seas are all found near 

 the mouths of large rivers. Islands away from 

 rivers become isolated from the pack ice by 

 moats, which are caused by the absorption of 

 solar radiation by the islands and the melting 

 of the ice immediately adjacent to them. Moat 

 formation is not as predictable and uniform as 

 river overflow. 



Bering Sea 



When the ice in the Bering Sea begins to 

 melt in April, the edge of the pack does not re- 

 cede northward as is frequently thought. 

 Rather, there is a general decomposition of ice 

 throughout the pack. The leads that are con- 

 stantly forming in the ice no longer freeze. As 

 melt continues and ice becomes rotten, leads 

 form with increasing frequency. This manner 

 of ice decomposition is important to birds. 

 The leads that form deep in the pack ice pro- 

 vide feeding and roosting areas near the large 

 seabird colonies found north of the ice edge, 

 and are used by certain tundra-nesting ocean 

 migrants such as eiders, red phalaropes 

 (Phalaropus fulicarius), and jaegers (Sterco- 

 rarius spp.). If ice decomposition is retarded 

 by persistent low temperatures, the initiation 



of breeding may be delayed at northern 

 Bering Sea colonies and for some tundra 

 species. 



At the time of decomposition the large 

 standing stock of phytoplankton present in 

 the pack ice is released into the water. No in- 

 formation is available on fish and invertebrate 

 populations that are associated with the de- 

 composing ice. The quantity of organic carbon 

 released is considerable, although it is not 

 known what fish or invertebrate populations 

 are supported by this plankton as soon as it is 

 released. For birds breeding in areas where ice 

 is present in the initial stages of breeding, the 

 phytoplankton released by the disintegrating 

 ice could play an important part in the birds' 

 energy budgets. 



Summer 



Chukchi and Beaufort Seas 



In the northern Chukchi and Beaufort seas 

 the nearshore marine environment is domi- 

 nated by sea ice in June and July. In June the 

 coastal areas are characterized by a snow-free 

 tundra teeming with nesting waterfowl and 

 shorebirds next to an expanse of sea ice al- 

 most completely devoid of bird life. In areas 

 where river outflow does not occur, the use of 

 nearshore waters usually begins when a moat 

 forms along the shoreline. Amphipods and 

 other invertebrates are found in this moat, 

 especially at stream mouths. Limited but 

 regular use of the moat occurs, primarily by 

 loons (Gavia spp.), oldsquaws, and arctic 

 terns (Sterna paradisaea). 



As the snow on top of the shorefast ice be- 

 gins to melt, ponds form on top of the ice. As 

 melt proceeds, these melt ponds merge into 

 long, parallel channels and may cover well 

 over 50% of the ice surface. Only when thaw 

 holes form and the melt ponds are connected 

 to the water under the ice is food present in 

 the channels. Amphipods are then seen swim- 

 ming in these channels. Bird use of these 

 channels is not extensive. 



It is usually late July before the nearshore 

 ice begins its rapid decomposition. Ice in the 

 lagoons is the first to melt. Ice seaward of the 

 barrier islands decomposes more slowly be- 

 cause of the presence of keels and pressure 

 ridges. As the ice melts, the in-ice algal bloom 



