Sea ice is frozen seawater floating on the surface of the ocean. Some sea ice is permanent, persisting from year to year, and some is seasonal, melting and refreezing from season to season. Each winter existing sea ice thickens and new, thinner ice is formed. This conceptual animation shows a cut-away view of the seasonal advance and retreat of Arctic sea ice, demonstrating the current trend toward a thinning ice pack, with less of the thicker multi-year ice surviving each summer's melt.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 184.108.40.206.0