Characteristics: Arctic vs. Antarctic

Ice Formation

Salinity and Brine

Multiyear Ice

Features

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• Polynyas

Arctic vs. Antarctic

Because the Arctic and Antarctic are cold, dark, and remote, we often think these two places are nearly the same. However, they are quite different. One notable difference is that polar bears live only in the Arctic, and penguins live only in the Antarctic. But what about the differences in sea ice between the two regions?

Geography

Sea ice differs between the Arctic and Antarctic, primarily because of their different geography. The Arctic is a semi-enclosed ocean, almost completely surrounded by land. As a result, the sea ice that forms in the Arctic is not as mobile as sea ice in the Antarctic. Although sea ice moves around the Arctic basin, it tends to stay in the cold Arctic waters. Floes are more prone to converge, or bump into each other, and pile up into thick ridges. These converging floes makes arctic ice thicker. The presence of ridge ice and its longer life cycle leads to ice that stays frozen longer during the summer melt. So some arctic sea ice remains through the summer and continues to grow the following autumn. Of the 15 million square kilometers (5.8 million square miles) of sea ice that exist during winter, on average, 7 million square kilometers (2.7 million square miles) remain at the end of the summer melt season.

The Antarctic is almost a geographic opposite of the Arctic, because Antarctica is a land mass surrounded by an ocean. The open ocean allows the forming sea ice to move more freely, resulting in sea ice that is highly deformed due to high drift speeds. However, Antarctic sea ice forms ridges much less often than sea ice in the Arctic. Also, because there is no land boundary to the north, the sea ice is free to float northward into warmer waters where it eventually melts. As a result, almost all of the sea ice that forms during the antarctic winter melts during the summer. During the winter, up to 18 million square kilometers (6.9 million square miles) of ocean is covered by sea ice, but by the end of summer, only about 3 million square kilometers (1.1 million square miles) of sea ice remain.

Minimum and maximum sea ice cover for the Arctic and Antarctic. Winter in the Southern Hemisphere is opposite that of the Northern Hemisphere, which explains why Antarctica has less sea ice during February. The black circles in the center of the Northern Hemisphere images are areas lacking data due to limitations in satellite coverage at the North Pole. Image courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder, Colorado.

Thickness

Because sea ice does not stay in the Antarctic as long as it does in the Arctic, it does not have the opportunity to grow as thick as sea ice in the Arctic. While thickness varies significantly within both regions, antarctic ice is typically 1 to 2 meters (3 to 6 feet) thick, while most of the Arctic is covered by sea ice 2 to 3 meters (6 to 9 feet) thick. Some arctic regions are covered with ice that is 4 to 5 meters (12 to 15 feet) thick.

Patterns of Ice Extent

The above images reveal another notable difference in sea ice. The pattern of antarctic maximum sea ice is roughly symmetric around the pole, forming a circle around Antarctica. In contrast, the Arctic is asymmetric, with much more ice in some longitudes than others. For example, sea ice off the eastern coast of Canada extends south of Newfoundland to 50 degrees north latitude, and ice off the eastern coast of Russian extends to Bohai Bay, China, at about 38 degrees north latitude. Conversely, in western Europe, the northern coast of Norway at 70 degrees north latitude (2,000 kilometers, or 1,243 miles, farther north than Newfoundland or Japan) generally remains ice-free. Ocean currents and winds explain these differences.

In the Antarctic, the currents and winds tend to flow without interruption around the continent in a west-to-east direction, acting like a barricade to warmer air and water to the north. In contrast, the Arctic region north of the Atlantic Ocean is open to the warmer waters from the south, because of the way the ocean currents flow. These warmer waters can flow into the Arctic and prevent sea ice from forming in the North Atlantic. The waters off the eastern coasts of Canada and Russia are affected by cold air moving off the land from the west. The eastern Canadian coast is also fed by southward-flowing cold water currents that make it easier for sea ice to grow.

Snow Cover over Sea Ice

Because the Arctic Ocean is mostly covered by ice and surrounded by land, precipitation is relatively rare. Snowfall tends to be low, except near the ice edge. Antarctica, however, is entirely surrounded by ocean, so moisture is more readily available. Antarctic sea ice tends to be covered by thicker snow, which may accumulate to the point that the weight of snow pushes the ice below sea level, causing the snow to become flooded by salty ocean waters.

Other Differences

Antarctic sea ice does not reach the South Pole, extending only to about 75 degrees south latitude (in the Ross and Weddell Seas), because of the Antarctic continent. However, arctic sea ice can extend all the way to the North Pole. Here, the arctic sea ice receives less solar energy at the surface because the sun's rays strike at a more oblique angle, compared to lower latitudes.

Water from the Pacific Ocean and several rivers in Russia and Canada provide fresher, less dense water to the Arctic Ocean. So the Arctic Ocean has a layer of cold, fresh water near the surface with warmer, saltier water below. This cold, fresh water layer typically allows more ice growth in the Arctic than the Antarctic.

Variations in Extent

Both Arctic and Antarctic sea ice extent are characterized by fairly large variations from year to year. The monthly average extent can vary by as much as 1 million square kilometers (386,102 square miles) from the year-to-year monthly average. The area covered by antarctic sea ice has shown a small (not statistically significant) increasing trend.

The annual average extent of arctic sea ice has slightly decreased by approximately 3 percent per decade over the last 25 years, which corresponds to an area of approximately 750,000 square kilometers (289,576 square miles). The extent of arctic ice in September, when extent is at its annual minimum, is decreasing at a rate of 7.7 percent per decade, which corresponds to approximately 1.4 million square kilometers (540,543 square miles). The Septembers of 2002 to 2004 showed dramatically lower arctic ice extent. This trend is a major sign of climate change in the polar regions and may be an indicator of the effects of global warming. (See Trends in the Environment section).

Total Arctic sea ice extent, 1978 to 2006. Image courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder, CO.

Total Antarctic sea ice extent, 1978 to 2006. Image courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder, CO.