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 Sagavanirktok, 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 nesting species, since the overflow surrounds islands 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 decomposes quickly, and patches of open water occur early in areas just seaward of major river deltas. For this reason the largest breeding 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 recede northward as is frequently thought. Rather, there is a general decomposition of ice throughout the pack. The leads that are constantly 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 provide 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 (Stercorarius 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 information is available on fish and invertebrate populations that are associated with the decomposing 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 dominated 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 almost 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 begins 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 swimming in these channels. Bird use of these channels is not extensive.