sea ice
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Sea ice is frozen seawater that forms when ocean water freezes at the surface. It matters because it plays an important role in Earth's climate system and ecosystems, affecting how much of the sun's heat is reflected back to space and providing habitat for various marine organisms.
AI-generated from the Wikipedia summary — may contain errors.
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Broken pieces of Arctic sea ice with a snow cover Sea ice forms as seawater freezes. Because ice is less dense than liquid water, it floats on the ocean's surface (just like fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world's sea ice is enclosed within the polar ice packs in the Earth's polar regions: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. Polar packs naturally undergo significant yearly cycling, reaching their greatest surface extent in winter and retreating in summer.
Within the ice, salty brine channels provide habitat for microorganisms that form the base of unique food webs. The presence or absence of sea ice also shapes navigation routes, regional weather, and global ocean circulation. Sea ice plays a key role in Earth's climate. Its white surface reflects the Sun's energy back into space, helping to keep the planet cool in a process known as the albedo effect. Sea ice also insulates the ocean below, limiting the transfer of heat, water vapor, and gases such as carbon dioxide between the sea and the atmosphere.