Sea ice is a thin, fragile, solid layer that forms in the North (Arctic) and South (Antarctic) Polar Regions. In the Arctic, sea ice is about 10 feet (or, three meters) thick on average, while ice at the South Pole averages one mile thick. Sea ice floats on the surface of the ocean and moves in response to winds and ocean currents. Because sea ice is in constant motion, ice floes are pushed against each other. When pushed together with enough force, the edges of the ice floes start giving way and ice breaks into pieces and piles up along the floe boundary forming ridges.
Sea ice is generally divided into two categories:
- First-year ice floes - grow during one winter. This ice is usually smooth and is commonly two to three feet (or, one-half to one meter) thick.
- Multi-year ice floes - have survived at least one summer melt season. Generally multi-year ice floes are about 10 to 16 feet (or, three to five meters) thick, and are not smooth like first-year ice.
Polar sea ice undergoes changes every year. During the winter, the Arctic ice pack grows to the size of the United States; in the summer, half of the ice disappears. The sea ice surrounding Antarctica ranges from 4 million square miles in February (the Antarctic summer) to 19 million square miles in August.
Given the amount of water that sea ice alternately puts into or pulls out of the ocean and the atmosphere, sea ice variability plays a role in global climate change . In addition to altering salinity (the amount of salt in water), melting sea ice also raises worldwide sea levels , with potentially significant effects for coastal cities and towns. The National Oceanic and Atmospheric Administration's (NOAA) Arctic Future web page also shows that changes in the Arctic can influence weather globally. Aimed at everyone from students to researchers, the Arctic Future page brings together easy-to-understand cause-and-effect-graphics with links to scientific literature.
Additional Resources:
- The National Snow and Ice Data Center's (NSIDC) Sea Ice Index
- Additional Sea Ice Data from the NSIDC
- The Study of Environmental Arctic Change's (SEARCH) Sea Ice Outlook
- NOAA's Arctic Change Indicator Website's Arctic Report on Sea Ice
- The Cold Regions Research and Engineering Laboratory's (CRREL) web page on Monitoring the Mass Balance, Motion and Thickness of Sea Ice
- The CRREL's Sea Ice Dynamics Program
- The National Science Foundation's (NSF) Information on the Importance of Sea Ice
- The National Weather Service's (NWS) Sea Ice Group
- The National Ice Center (NIC)
- The U.S. National Ice Core Laboratory (NICL)
- The Status of the Polar Bear
- Permafrost
- Coastal Changes
- The Ocean Observing System
- Oil and Gas Development and Exploration on the U.S. Outer Continental Shelf (OCS)