shelf seas, the East Siberian Sea and the Laptev Sea. ponds freeze over, snow falls on the surface and new ice
There, sea ice forms during the Arctic autumn and win- forms at the underside of the ice floe. Individual floes
ter, grows thicker and joins the transpolar drift towards freeze together to form larger floes. Rafting and ridg-
and over the North Pole. Finally, after some two to seven ing occurs (Figure 5.13) and leads (narrow channels of
years, the ice floe enters Fram Strait. This transport of open water) are formed. Ridges, which can be several
ice influences, among other things, the processes gov- metres high, and ice keels, which can extend more than
erning ocean circulation and the flow of nutrients in 20 m below sea level, affect wind drag and water drag.
Arctic marine ecosystems. Dust and sediments are incorporated into snow and ice
through atmospheric and oceanic processes, and ice al-
Many factors influence the formation, evolution and gae and other organisms colonize the brine channels
degradation of sea ice. Monitoring and research is un- and the under-sides of ice floes.
derway to improve understanding of these factors, how
they are linked, and the influence of climate change (see In the Southern Hemisphere sea-ice conditions are very
boxes on sea ice research). different. The Southern Ocean surrounds the Antarctic
continent, in contrast to the Arctic Ocean, which is sur-
Large parts of the Arctic are characterized by complex, rounded by land. Since the highest latitude areas in the
multi-year ice
35
. During Arctic summers, ponds form south are land covered, Antarctic sea ice is on average fur-
as snow melts on the ice surface. In autumn the melt ther away from the South Pole than is Arctic sea ice from
Figure 5.13: Several metre-high
pressure ridge on a multi-year sea
ice floe in Western Fram Strait.
Photo: Sebastian Gerland, Norwegian
Polar Institute
78 GLOBAL OUTLOOK FOR ICE AND SNOW
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