The phrase "drift ice" refers to chunks or sheets of frozen seawater that are carried along by ocean currents and wind. It is called "drift" because it moves slowly and does not stay in one place. Full definition
He has been recording the sounds of the ship breaking through rafts of drifting ice in the hopes of turning it all into music. (dotearth.blogs.nytimes.com)
Writing in 1953, arctic researcher Hans Ahlmann noted that «The extent of drift ice in Arctic waters has also diminished considerably in the last decades. (uscentrist.org)
They uniformly reject the idea that heat from the bottom — either from the general geothermal activity beneath the seabed or the occasional outbursts of lava or vents — could have a significant impact on the veneer of floating, drifting ice on the surface. (dotearth.blogs.nytimes.com)