Geoscience Reference
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Figure 7.6. Highly deformed sea ice near Barrow, Alaska, during the spring of 2008
(photograph by M.C. Serreze). (See plate section for color version.)
Beaufort Gyre circulation. When there is strong shear, there is also a component
of motion into the shore. This results in convergence and the formation of thick,
ridged ice (seen as the light colored streaks). There is also locally strong divergence,
producing leads. The very obvious lead north of (to the right of) Borden Island is
roughly 1-2 km wide. On the basis of submarine sonar data, Wadhams ( 1980 ) sug-
gests that the shear zone extends about 400 km off the coast of Ellesmere Island,
where ice motion is normal to the coast, and about 160 km off Alaska, where the
motion is more parallel to the coast.
Recall from Chapter 2 that the marginal ice zone (MIZ) represents the boundary
between the sea ice and open water. The boundary is generally (but not always)
gradual, perhaps 100-200 km in width. Figure 2.6 shows an example of conditions
along the MIZ. Penetration of surface waves into the ice pack breaks ice into small
floes with an average size increasing rapidly with distance from the ice edge. During
winter, the MIZ is associated with strong horizontal temperature gradients. Enhanced
baroclinicity along the MIZ may influence cyclone development. Horizontal varia-
tions in the density structure along the MIZ can also produce mesoscale phenomena
in the ocean, such as eddies, jets and upwelling. Biologic activity is high along
the MIZ.
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