cyclonic gyre over the Eurasian Basin and an anti-cyclonic gyre over the Canadian
Basin. Those central basins are surrounded by six shelf seas that comprise over 50%
of Arctic Ocean area (Fig. 11.17). Sea ice is the dominant physical factor nearly year
round in the central basins and seasonally in the surrounding shelf seas. The overall
extent of summer melting and open water has been increasing markedly in recent
decades. Formation of sea ice excludes salt, increasing salinity and density in the
water just below the surface. Melting of ice releases fresh water.
Fig. 11.17 Map of the Arctic Ocean showing the shelf seas and central basins. The
Nansen and Amundsen basins together form the Eurasian Basin, and the Makarov and
Canada basins form the Canadian Basin. The Lomonosov Ridge separates the
Eurasian and Canadian Basins.
(^) (After Aagaard et al. 2008.)
The Arctic biome is structured by freshwater entrainment, sea-ice cover and
resulting stratification of the water column. Fresh water is entrained from increasing
seasonal ice-melt (∼800–1100 km^3 yr−1), inflowing rivers (3559 km^3 yr−1), and