Geoscience Reference
In-Depth Information
The ice becomes translucent and blue. The different stages of
formation have been given informal names in local languages: grease,
slush, pancakes, hummocks, floes, etc.
Sea ice is important in the surface energy balance:
- on the atmospheric side, the main ice characteristic (covered or
not by a snow layer) is its high albedo: solar flux is strongly reflected,
and so barely contributes to ocean warming. Moreover, the ice
sublimation process does not lead to a significant increase of
atmospheric water vapor, contrary to the evaporation of water, in polar
climatic conditions. On the ice, the energy balance is nearly reduced
to the radiative balance. During the polar night, almost nothing but the
net long wave radiation remains. Note that the polar atmosphere is
characterized by a very thin atmospheric boundary layer, at the bottom
of a thin troposphere (less than 10 km), in which clouds of ice very
often occupy the entire depth. The radiative balance is strongly
constrained by this cloud cover. However, as soon as the sea ice
fissures, evaporation dominates the energy balance, contributing
further to the generation of fogs and mists;
- on the oceanic side, the brine pockets differ strongly from the
overall OML characteristics; the OML is not very salty at these
latitudes (30-35 per thousand). Moreover, the heat and fresh water
fluxes are not significant at the ice base once this has been formed.
However, the ice formation is associated with a significant release of
brine, which increases the density of the surface water under the ice.
These fluxes can be enough, particularly in certain regions beside the
continental plateau, to cause the formation of dense waters that can
sink into the deep ocean.
Another interaction among the ocean, sea ice and atmosphere, is the
impact of the wind and currents on the ice fields: displaced by friction,
the ice floes fragment or collide with each another, creating temporary
channels of free water between plates and polynyas (close to
the continents, these are “lakes” of free water created by the action of
the wind blowing from the continent). These free water areas are
characterized, contrary to the ice, by a flux of intense evaporation, since
the polar atmosphere is very dry (because of the low air temperature).
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