"old sea ice" is sea ice that has survived at least one melting season ("i.e." one summer). for this reason, this ice is generally thicker than first-year sea ice. old ice is commonly divided into two types: "second-year ice", which has survived one melting season, and "multiyear ice", which has survived more than one. (in some sources, "old ice" is more than 2-years old.) multi-year ice is much more common in the arctic than it is in the antarctic. the reason for this is that sea ice in the south drifts into warmer waters where it melts. in the arctic, much of the sea ice is land-locked.