Sea ice and a polar bear in the Fram Strait (Arctic Circle).Sea ice is frozen seawater that floats o

Sea ice and a polar bear in the Fram Strait (Arctic Circle).Sea ice is frozen seawater that floats on the ocean’s surface.  Itforms in the winter (in both the Arctic and Antarctic) and retreatsin the summer, but does not completely disappear.Ice crystals form on the surface of the ocean.  They expel salt,which increases the water salinity below them.  This cold salty wateris dense, and it can sink to the ocean floor, whence it flows backtowards the equator.Sea ice has an important influence on polar environments (e.g.weather, regional climate and ocean circulation).  The sea ice layerrestricts wind and wave movement near coastlines, which reducescoastal erosion and protects ice shelves.It also creates an insulating “cap” on the ocean, reducingevaporation and heat loss to the atmosphere.  Because of this, theweather in ice-covered areas tends to be colder and drier than inareas not covered by ice.When the ice melts in the summer, it releases nutrients into thewater.  This stimulates the growth of phytoplankton, which are at thecentre of the marine food web.  The melting ice exposes the oceanwater to sunlight, which encourages photosynthesis in plankton.When ice freezes and the saltier, denser water sinks, it mixes thewater column and brings nutrients to the surface.  The sea ice is ahabitat for animals including polar bears, seals, penguins and Arcticfoxes.The influence of sea ice is global.  The white surface reflects moresunlight back into space than the water does (i.e. the ice has ahigher albedo).  When it begins to melt, it exposes more dark waterto the sun, and this water absorbs more sunlight.  The sun-warmedwater then melts more ice, creating a self-reinforcing cycle.  Overseveral years, this ice-albedo feedback can influence global climate. -- source link

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