Sea ice
Frozen seawater that shapes climate, navigation, and polar ecosystems.
Sea ice forms as seawater freezes and floats on the ocean's surface due to its lower density compared to liquid water. It covers about 7% of the Earth's surface and about 12% of the world's oceans, primarily within the polar ice packs of the Arctic and Antarctic regions. Sea ice is dynamic, shaped by winds, currents, and temperature fluctuations, and plays a key role in Earth's climate through the albedo effect and insulation of the ocean.
- coverage
- 7% of Earth's surface, 12% of world's oceans
- thickness_range_first_year
- 0.3 m to 2 m
- thickness_range_old_ice
- 2 m to 4 m
- brine_volume_growth_period
- typically below 5%
- air_volume_growth_period
- typically 1–2%, up to 15% in summer
Lore & Background
Sea ice is classified by whether it is attached to the shoreline (fast ice) or free to drift (drift ice or pack ice). Drift ice consists of floes, individual pieces of sea ice 20 meters or more across, with sizes ranging from small (20–100 m) to giant (over 10 km). The marginal ice zone is the transition region between open ocean and consolidated pack ice, characterized by fragmented floes. Sea ice is also classified by age: new ice, nilas, young ice, first-year ice, and old ice (which includes second-year and multiyear ice). Multi-year ice is more common in the Arctic than in the Antarctic due to drift patterns.
Reader's Guide
Sea ice is significant for its role in Earth's climate system, reflecting solar energy via the albedo effect and insulating the ocean, which limits heat and gas exchange with the atmosphere. It provides habitat for microorganisms in brine channels, forming the base of unique food webs. Satellite records show a marked decline in Arctic sea ice extent and thickness in recent decades, linked to global climate change, while Antarctic sea ice shows regional variability with recent declines. Sea ice also shapes navigation routes, regional weather, and global ocean circulation. Its physical properties—density, thermal conductivity, and mechanical strength—depend on brine and air volumes, which vary with age and temperature. Leads and polynyas, areas of open water within ice expanses, are important for wildlife and navigation. Sea ice differs from icebergs, which originate from ice shelves or glaciers.
Did You Know?
- Sea ice covers about 7% of Earth's surface and about 12% of the world's oceans.
- Multi-year ice is much more common in the Arctic than in the Antarctic.
- Leads are narrow, linear open-water areas within sea ice, varying in width from meters to kilometers.
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