Climate Fact: Antarctic Sea Ice
Much attention has been given to the decline of sea ice over the North Pole, which fell to a September minimum of 1.6 million square miles in 2007, about 40 percent below normal levels. On the other side of the world, the sea ice that extends from Antarctica’s continental ice sheets out over the ocean fluctuates between an average summertime (March) minimum extent of about 1.1 million square miles to an average of 6.9 million miles at the end of winter (September). In contrast to the Arctic ice, the average annual extent of the southern hemisphere ice has actually grown since the late 1970s at a rate of around one percent per decade. This trend has been linked to:
- Ozone Depletion: The most pronounced rates of ozone depletion have occurred over Antarctica, where the ozone hole forms during the spring months. While the strong westerly winds that “trap” frigid air around the continent during winter make the ozone hole possible, the hole itself works as a feedback by accentuating the pressure difference between the continent and the mid-latitudes of the Southern Hemisphere. This works to strengthen the winds responsible for the ozone hole in the first place.
- Wind Shifts: The accentuation of the pole to mid-latitude pressure difference linked to ozone depletion has deepened several of the continent’s low pressure zones, strengthening some of the winds that blow from the continent over the ocean during the autumn months. This has led to increases in sea ice over several of Antarctica’s coastal regions.
- Freshwater on the Ocean Surface: Increased precipitation around Antarctica and melting of the glaciers that sit on the land have led to freshening of the ocean surface waters. This promotes ice formation.
Shifts in the winds have also caused decreases in sea ice extent in some areas of the continent – specifically parts of the Southern Ocean adjacent to the Indian Ocean and the Amundsen-Bellingshausen Sea sectors. These losses have been more than compensated for by gains in other areas.
Seasons: Winter, Spring, Summer, Fall
Source: Turner, J et al. “Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase in Antarctic sea ice extent.” Geophysical Research Letters 36 (2009): L08502.
