pack ice 
noun [mass noun]
A mass of ice floating in the sea, formed by smaller pieces freezing together.By contrast with pack ice, ice floes in the Chukchi Sea flaw zone move independently....
- In two years, observed densities on pack ice were much greater than those on fast ice; in the other two years, the densities on pack ice and fast ice were similar.
- There are two kinds of sea ice in Antarctica: fast ice and pack ice.