Sea Ice

Sea ice is the biome of frozen seawater that forms and floats on the surface of the ocean, most extensively in the polar regions as the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. Roughly seven percent of the planet surface, or about twelve percent of its oceans, is covered by sea ice at any given time, and the ice expands each winter and retreats each summer in a strong seasonal cycle. Within the ice itself, channels of salty brine form microhabitats that host distinctive microbial communities forming the base of polar food webs, while the ice white surface reflects solar energy back to space and insulates the ocean beneath it from the atmosphere, giving the biome an outsized role in regulating the planet climate. Satellite records show marked declines in Arctic sea ice extent and thickness in recent decades, with Antarctic sea ice showing more regionally variable trends.