Due to offshore archipelagos and shallow shelves along the NSR, extensive landfast ice is always present in the region in winter. The fast ice grows out from the mainland or islands into the sea, and can attain thicknesses of over 2m. In two key regions the fast-ice boundary extends extraordinary distances from the mainland. In the first, the landfast ice boundary usually extends from the eastern Kara Sea to the northern extremity of Severnaya Zemlya. The second region is a fast-ice region surrounding the New Siberian Islands, located far from the mainland (Figure 4.2-3). As described in Chapter 3, the formation of fast ice is governed by marine geography: In these regions shallow continental shelves extend far out to sea, and are fed with fresh water by large river systems such as the Ob, Yenisey and Lena. The inflow of a large volume of fresh water generates a surface water layer of a low salinity that facilitates the growth of sea ice. Conversely, the seas from the Chukchi Sea to the eastern East Siberian Sea lack these features and receive a warm ocean current from the North Pacific Ocean, limiting the formation of fast ice to narrow coastal bands.
Figure 4.2-3 Fast ice
The polynyas are found in all regions of the Russian Arctic. Flaw polynyas created by prevailing offshore winds are dominant features of sea ice along the outer edges of the fast ice, between the fast ice and drifting ice in the adjacent open seas (Figure 4.2-3). The flaw polynyas are often used as passageways for NSR navigation. In the Barents Sea, a large area exists where no ice is found, due to the warming influence of the Gulf Stream.
As the sea ice expands, the thickness of the ice becomes the key parameter affecting navigation. Generally, first-year ice begins growing at the beginning of the winter, and as the months progress its speed of growth declines, so that it reaches its maximum extent at the end of the winter. Figure 4.2-4 illustrates the growth of first-year ice. In this figure, the ice thicknesses at the end of each month are calculated from the growth rate of level ice in each region. Naturally the growth rate is different in each region. In the eastern Laptev Sea and western East Siberian Sea in the middle of the NSR, sea ice grows fastest, reaching a thickness of over 2m at the end of May. At both the eastern and western sides of the NSR, ice growth is relatively moderate.
