How are Arctic and Antarctic sea ice different?

There are a number of important differences between Arctic and Antarctic sea ice.

Distribution of land and water:

Antarctica is a continent that is completely surrounded by water. In fact, this is the only place in the world where all the ocean basins connect without being blocked by land. Strong prevailing winds at approximately 50° to 65°S latitude create a surface ocean current that flows from west to east around Antarctica. The Antarctic Circumpolar Current (ACC) is the only ocean current that completely circles the globe, moving around 130 million cubic meters of water per second – the largest volume of water of any ocean current in the world. This partially isolates the Southern Ocean and Antarctica, restricting the transfer of heat from the tropics.

The Arctic is an ocean surrounded by land and this confines the sea ice in the Arctic basin, which can only drift south through the Bering Strait and Fram Strait. However, sea ice can also form in the northern hemisphere at lower latitudes (meaning closer to the equator) than in the Antarctic. This is because there is much more land, which heats up and cools down more rapidly than water, leading to an effect known as continentality. The Arctic also has an ice-free region in the North Atlantic because of the flow of warm Gulf Stream waters.

Seasons:

When it is winter in the Arctic, it is summer in the Antarctic. When ice is forming in one polar region, it is melting in the other, so the total amount of sea ice on Earth remains fairly constant. On average, between 16 and 23 million square kilometres of the polar oceans are covered by sea ice.

Seasonal variations in extent:

Antarctic sea ice covers about 19 million square kilometres at its maximum winter extent. Approximately 80% of this ice melts each summer, reducing the extent to around 4 million square kilometres.

About 50% of Arctic sea ice melts in the summer months, decreasing the area covered from approximately 13.5 million to about 6 million square kilometers.

Arctic summer	Arctic winter
Antarctic winter	Antarctic summer

Images courtesy of NASA SeaWiFS

Click here for an animation of seasonal changes in sea ice extent.

Differences in the ice characteristics:

Strong winds and ocean currents around Antarctica keep the water in constant motion. Newly formed sea ice gets carried away to the north at speeds of up to 10-20 km per day. There is more open water and generally thinner ice within the Antarctic ice pack.

Most of the area around the North Pole remains ice covered all year. Multiyear sea ice in the Arctic can be up to 6 metres thick, and drifting ice floes can ram together to form ridges tens of metres thick.

Long-term trends in sea ice extent:

Satellite records show that the mean winter sea ice cover has declined by about 2.6% per decade over the past 27 years in the Arctic, while the minimum summer extent has decreased even faster.

In Antarctica, no discernable trends have been documented for the continent as a whole, although there have been noticeable decreases in sea ice extent around the Antarctic Peninsula. It is possible, however, that Antarctic sea ice may be changing more in thickness than in extent. To date, there are few broad-scale data about sea ice thickness and this is a key area of research for SIPEX voyage. In addition, a summary of climate models from the Intergovernmental Panel on Climate Change indicates that sea ice extent in Antarctica will decrease in the future, perhaps by as much as 50% by the end of the 21st century.