Brine inclusions are particularly sensitive in this regard; even small changes in thermal conditions can causes significant changes in the size, shape and distribution patterns of the inclusions and concentration of the entrapped brine. Because the strength of sea ice depends on its brine component, when air temperatures rises in spring the sea ice quickly becomes brittle.
An expanse of ice floe less than 10km in diameter is called an ice patch, and an expanse of ice floe more than 10km is called an ice field. Ice fields are further classified as small, medium and large ice fields. Very large compact ice fields, having an area of 1,000km2 or more and ice concentration of 70% or more, are referred to as ice massifs.
Ice massifs composed of multi-year ice in the Arctic Ocean are called Arctic ice massifs. Arctic ice massifs are further divided into Canadian and Siberian ice massifs, and other ice massifs extending into peripheral areas such as Spitsbergen, the Kara Sea, the Taymyr peninsula, Ion and Wrangel Island are named accordingly. In coastal regions as well, areas of relatively stable ice massifs have been found; these are named for their respective regions, Novaya Zemlya, Severnaya Zemlya and Yana.
3.2.4 The Extent of Sea Ice in the Northern Hemisphere
Beginning in 1973, satellite-borne microwave radiometry came to be adopted for year-round, all-weather and day-and-night surveillance of the ice cover in the Arctic. The monthly average distribution of sea ice in the northern hemisphere during March, the month of maximum extent, and September, the month of minimum extent, for 1986 is illustrated below as an example. Areas of open water are indicated in light blue, while areas where the sea ice is so concentrated that no water can be seen are colored a purplish dark red. The color scale between these two extremes is indicated accordingly.
In winter (March), the region of sea ice extends throughout the Arctic Ocean as far as Hudson Bay, Baffin Bay, the Sea of Labrador, the Greenland Sea, the Baltic Sea, the Sea of Okhotsk and the Bering Sea, except for some regions of the Barents Sea. Because the line of 66.5｡? runs close to the north shore of Iceland, the eastern Greenland Sea, northern Sea of Norway and southern Barents Sea comprise a vast region free from sea ice even in the long Arctic nights.