Sea ice facts for kids
Sea ice is frozen ocean water that forms, grows, and melts right in the sea. It's different from icebergs, glaciers, ice sheets, and ice shelves, which all start on land. You can find sea ice in both the Arctic (North Pole) and the Antarctic (South Pole).
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What is Sea Ice?
Sea ice is made of frozen seawater, so it's a bit salty. Unlike the ice cubes in your drink, sea ice is not perfectly clear. It usually grows bigger in winter, when it's often dark all day and night in the polar regions. Then, it melts in the summer, when the sun can shine for 24 hours!
Sea ice usually covers more area around the Antarctic than the Arctic. Because it's salty, sea ice is heavier, less see-through, and easier to break than fresh water ice.
How Sea Ice Behaves
Sea ice isn't completely solid like a block of ice. It has tiny pockets of salty water inside it. Older ice can also have many air bubbles. This makes it easier to squish, break, and snap compared to a normal ice cube.
When two pieces of sea ice push against each other, they can crumple and break. This forms a raised area called a 'ridge' where they meet. Sometimes, they might just bend. It's also fairly easy to pull a single piece of sea ice apart by pulling its edges in opposite directions.
How Light Interacts with Sea Ice
Because sea ice has air bubbles and saltwater pockets, it's harder to see through than clear, fresh water ice. Light struggles to pass through without hitting these bubbles and pockets. In winter, most sea ice is covered by a layer of snow, which also blocks light.
This means that when the sun shines on sea ice, not much light gets through to the ocean below. This limits how much algae and tiny plants can grow in the sea. When the ice melts, much more light gets through, allowing these tiny plants to grow well. This effect also helps keep the water below the ice cooler.
Why Sea Ice Matters to People
About four million people live in the Arctic, and many of them live near the sea. These communities have lived there for hundreds of years. They have learned to use and depend on the sea ice for their way of life.
People living along the coast often travel over the sea ice. They use it to hunt animals for food and to make clothes. Because some people spend so much of their lives on the ice, it becomes very important to them and their communities.
Why Sea Ice Matters to Animals
Many animals live on top of and under the sea ice. For some, the ice makes life harder, but for others, it makes life easier. Animals like seals and polar bears live both on top of the sea ice and swim in the ocean.
Tiny plants and algae don't grow well under the sea ice because they need sunlight. This means that animals that eat these plants, like many fish, also spend less time under the ice.
Why Sea Ice Matters to Our Climate
Even though it's not perfectly smooth, sea ice is very shiny. Most of the sunlight that hits it bounces off and goes back into space. By reflecting a lot of sunlight, the Earth's poles stay cold.
Having cold regions at the top and bottom of the Earth is important for global weather patterns. It affects how cold and warm air moves around the planet. When cold air moves down from the Arctic, it can cause very strong storms. When warm air moves up into the Arctic, it can make the sea ice melt and break apart.
Sea ice also acts like a barrier between the ocean and the air. In other parts of the world, water often evaporates from the sea into the air, eventually leading to rain. Sea ice greatly reduces this process, which is why the air in polar regions is very dry and there isn't much rain or snow.
The ice also stops a lot of heat from moving from the warm ocean water into the colder air above.
Sea ice is important for how the ocean surface mixes. When wind blows over the open ocean, it stirs the water. But when wind blows sea ice around, it can mix the water much deeper. This mixing is important because it affects the tiny animals that live at the ocean surface and how salty the surface water is.
How Sea Ice is Changing
Humans have been releasing a lot of greenhouse gases, which are making the Earth warmer. The Arctic, in particular, has been getting much warmer. One reason for this is that sea ice formation and melting are very sensitive to temperature changes. When the air is warmer, sea ice grows slower and melts faster.
These rising temperatures mean that sea ice starts growing later in the year and begins melting earlier. It also means that the total area covered by sea ice is getting smaller.
Satellites and Sea Ice
Going to the sea ice is difficult and sometimes dangerous. This makes it impossible to track all the sea ice at once and see how it's changing. To solve this, scientists often study sea ice from space using satellites.
There are many ways to do this. Some satellites use cameras similar to the ones you might use. Others create pictures of the sea ice using microwave energy, which can even go through clouds. Some satellites don't just look at the ice; they send down energy from laser and radar machines and then record how it bounces off the ice.
These satellites help scientists measure the area covered by sea ice quite well. However, they are still not completely sure how thick the sea ice is. This is partly because it's hard to know how much snow is resting on the ice at any given time. Measuring the amount of snow on sea ice is tricky. European scientists are currently designing a new satellite called CRISTAL to help study it.
Images for kids
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Nilas in Baffin Bay
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Satellite image of sea ice forming near St. Matthew Island in the Bering Sea.
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Volume of arctic sea ice over time using a polar coordinate system draw method (time goes counter clockwise; one cycle per year)
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As ice melts, the liquid water collects in depressions on the surface and deepens them, forming these melt ponds in the Arctic. These fresh water ponds are separated from the salty sea below and around it, until breaks in the ice merge the two.
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Aerial view showing an expanse of drift ice offshore Labrador (Eastern Canada) displaying floes of various sizes loosely packed, with open water in several networks of leads. (Scale not available.)
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Aerial view showing an expanse of drift ice in southeastern Greenland, comprising loosely packed floes of various sizes, with a lead developing in the centre.(Scale not available.)
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Aerial view showing an expanse of drift ice consisting mostly of water. (Scale not available.)
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Close-up view inside a drift ice zone: several small rounded floes are separated from each other by slush or grease ice. (Bird at lower right for scale.)
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Example of hummocky ice: an accumulation of ice blocks, here about 20 to 30 cm (7.9 to 11.8 in) in thickness (with a thin snow cover).
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Field example of a pressure ridge. Only the sail (the part of the ridge above the ice surface) is shown in this photograph – the keel is more difficult to document.
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Aerial view of the Chukchi Sea between Chukotka and Alaska, displaying a pattern of leads. Much of the open water inside those leads is already covered by new ice (indicated by a slightly lighter blue color)(scale not available).
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Sea ice off Baffin Island.
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Sea ice imitates the shoreline along the Kamchatka Peninsula.
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Clear view of the Antarctic Peninsula, the Larsen Ice Shelf and the sea ice-covered waters around the region.
See also
In Spanish: Banquisa para niños
