Geoscience Reference
In-Depth Information
Figure 2.4.
Mean sea ice extent for March (all shaded areas) and September (dark
shading), based on data from the Special Sensor Microwave/Imager (SSM/I) over the
1979-2001 period. SSM/I has a nominal resolution of 25 km (courtesy of K. Knowles,
NSIDC, Boulder, CO).
stress on the upper surface of the sea ice cover, water stress on the lower surface
of the ice, floe-to-floe interactions, and ocean tilt (see
Chapter 7
for discussion of
the sea ice momentum budget). Ice motion varies strongly from day to day, largely
in response to variations in the wind field. Leads and polynyas in the pack ice are
largely the result of differential ice motion. Divergent (spreading) ice motion acts
to reduce the ice concentration; convergent motion increases it. Convergent motion
can force one floe to ride over another, a process known as rafting, producing thicker
deformed ice characterized by ridges and corresponding underwater keels. Much of
the ice cover consists of deformed ice.
Thermodynamic ice growth occurs at the bottom of the ice cover (the ice- inter-
face), but melt can occur at both the top and bottom. During autumn, the marginal
seas and openings in the pack ice refreeze, forming new ice that thickens during the
