Unlike the Arctic—an ocean basin surrounded by land—the Antarctic is a large continent surrounded by an ocean. Because of this geography, sea ice has more room to expand in the winter. But that ice also stretches into warmer latitudes and is exposed to the open ocean, leading to more melting in summer. Antarctic sea ice peaks in September (the end of Southern Hemisphere winter) and retreats to a minimum in February.
These image pairs show Antarctic sea ice extent at the September maximum (left) and the following February minimum (right) from September 1999 to February 2015. Land is dark gray, and ice shelves—thick slabs of glacial ice grounded along the coast—are light gray. The yellow outline shows the median sea ice extent in September and February from 1979 to 2000. Extent is the total area in which the ice concentration is at least 15 percent. The median is the middle value; that is, half of the extents were larger than the line, and half were smaller.
Since the start of regular satellite observations in 1979, total Antarctic sea ice has increased by about 1 percent per decade. Whether the increase is a sign of meaningful change is uncertain because ice extents vary considerably from year to year around Antarctica. For three consecutive Septembers from 2012 to 2014, satellites observed new record highs for winter sea ice extent. These highs occurred while the Arctic was seeing record lows.
Within Antarctic sea ice, there is great variation from place to place around the continent. The Ross Sea sector has had a significant positive trend, while sea ice extent has decreased in the Bellingshausen and Amundsen Seas. In short, Antarctic sea ice shows a small positive trend, but large-scale variations make the trend very noisy.
This time series above is made from a combination of observations from the Special Sensor Microwave/Imagers (SSM/Is) flown on a series of Defense Meteorological Satellite Program missions. The sensors measure microwave energy radiated from the Earth’s surface (sea ice and open water emit microwaves differently), which can be used to map sea ice concentrations.
- Cavalieri, D. J., and C. L. Parkinson (2008) Antarctic sea ice variability and trends, 1979–2006, Journal of Geophysical Research Oceans. 113, C07004.
- NASA Earth Observatory (2009, April 20) Sea Ice.
- NSIDC State of the Cryosphere.
- NSIDC Frequently Asked Questions about Sea Ice.
- NSIDC Sea Ice Index.
- NSIDC (2007, September 25). Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I.
- Raphael, M.N. (2007) The influence of atmospheric zonal wave three on Antarctic sea ice variability. Journal of Geophysical Research. 112, D12112.
- Steig, E.J., Schneider, D.P., Rutherford, S.D., Mann, M.E., Comiso, J.C., Shindell, D.T. (2009) Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year. Nature. 457, 459-463.
Antarctic Sea Ice
By Rebecca Lindsey
September 1999 & February 2000
- Water Level in Lake Powell
- Recovery at Mt. St. Helens
- Antarctic Sea Ice
- Arctic Sea Ice
- Growing Deltas in Atchafalaya Bay
- Global Temperatures
- Columbia Glacier, Alaska
- Coastline Change
- Shrinking Aral Sea
- Antarctic Ozone Hole
- Amazon Deforestation
- Mountaintop Mining, West Virginia
- Fire in Etosha National Park
- Green Seasons of Maine
- Drought Cycles in Australia
- Athabasca Oil Sands
- Burn Recovery in Yellowstone
- Severe Storms
- Seasons of the Indus River
- Urbanization of Dubai
- Seasons of Lake Tahoe
- Solar Activity
- Larsen-B Ice Shelf
- Mesopotamia Marshes
- Yellow River Delta
- El Niño, La Niña, and Rainfall
- Global Biosphere