Alexander Hafemann/istockphoto

DCL

Floating ice that has been driven together into a single mass is called pack ice.

There are three different types of ice in the sea: sea ice, river ice, and land ice: "Land ice is principally icebergs. River ice is carried into the sea during spring breakup and is important only near river mouths. The greatest part, probably 99% of ice in the sea, is sea ice."

Pack ice can be very flat, but it is "usually covered with very rough areas caused by the movement of sheets of ice against one other. These pressure ridges can increase the thickness of the ice from just a few inches or centimeters to tens of meters (many feet) thick." Like free-floating ice floes, pack ice moves with ocean currents and wind but it is not always continuous and can be very broken. Pack ice dominates the polar regions and is "important to global ocean circulation and climate patterns." As with just about everything else, pack ice is now endangered because of global warming.

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