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What is sea ice? (Text Level 3)

Adelie penguins in Antarctica

Sea ice is frozen seawater. It floats on the ocean. It forms in both the Arctic and the Antarctic each winter. The Arctic is a continent in the North Pole. The Antarctic is a continent in the South Pole. Sea ice shrinks in summer but does not completely disappear. This ice affects ocean water and weather around the world. Seals, polar bears, and penguins live on sea ice.

The Sea Ice Life Cycle

Sea ice has a life cycle of its own.
Sea ice has a life cycle of its own.       Credit:  NASA

Seawater begins to freeze. It forms tiny crystals. When the water is calm, the crystals form thin sheets of ice. They are very smooth. They look oily or greasy. These sheets form into thicker ice. In rough water, ice crystals form into slushy pancakes.

Water and air temperatures rise each summer. Some sea ice melts. Antarctic sea ice melts more than Arctic sea ice.

Monitoring Sea Ice

Vikings lived a thousand years ago. They recorded the ice in Iceland.

In modern times, there are sea ice records from 1953.

Satellites and planes also keep track of Earth’s sea ice. Satellites are spaceships that orbit Earth.

Arctic Sea Ice

Arctic sea ice is on an ocean. It is mostly surrounded by land.

In the Arctic, March has the most sea ice. It covers about 5.4 to 6.2 million square miles. September has the least. Then the ice is only about 2.7 million square miles. In the last few years, there has been a lot less ice.

There a couple of reasons for the melting ice. Global warming is one reason. The Earth is heating up. Scientists call this global warming or climate change. Eventually, seals and polar bears will lose their homes. Native peoples in the Arctic have already said there are fewer polar bears. They are also sicker.


Maps of the North Pole
Maps of the North Pole                                Images courtesy of NASA

Antarctic Sea Ice

The Antarctic is the opposite of the Arctic. The Antarctic is land surrounded by ocean.

There is more sea ice in the Antarctic sea in winter. The Antarctic is in the Southern Hemisphere. September is the end of winter. The total ice covers about 6.6 to 7.7 million square miles. Ice covers the least area in February. It dips down to about 1.2 to 1.5 million square miles.

In the Arctic, ice is shrinking all the time. The Antarctic is different. There, sea ice increased between 1979 and 2013.

Scientists think sea ice in the Antarctic will melt more slowly than in the Arctic. Still, there will be less sea ice there, too. It may just take longer.


South Pole show how sea ice changes during winter and summer.
South Pole show how sea ice changes during winter and summer.   Credit :  NASA


The Arctic and Antarctic are different. Their sea ice is also different. Global warming may affect sea ice in different ways. Scientists want to know how. They have to compare it to the past.

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