What is the pack ice?
Pack-ice is an area of ice that forms on the surface of the sea. It's made of seawater that gradually freezes over and becomes ice, which then forms a huge white (of course) expanse called pack-ice. The main feature of pack-ice is that it floats on the surface of the sea and can move about. This movement sometimes causes the pack-ice to break up. The fragments of ice jostle and bang against one another to create the familiar compression ridges that we see in photos of the Arctic.
