zeeijs

Zeeijs, or sea ice, refers to frozen ocean water that forms on the surface of polar seas. It forms when surface seawater cools to its freezing point, aided by calm and windy conditions that allow the surface to freeze. Sea ice floats on the ocean surface and is distinct from land-based ice such as glaciers and ice sheets.

Formation and structure: As seawater freezes, most salt is expelled, producing brine pockets within the ice and giving sea ice its characteristic salinity and permeability. Ice can be categorized by age: first-year ice forms during a single winter and melts in the summer, while multiyear ice survives multiple summers and tends to be thicker and more consolidated.

Seasonal cycle and measurement: In the Arctic, sea-ice extent grows in winter and recedes in summer. The Antarctic shows a somewhat different pattern due to regional wind and ocean dynamics, but also exhibits a seasonal cycle. Since the late 20th century, satellite observations have tracked sea-ice concentration, extent, and to some extent thickness, providing long-term records used in climate research.

Significance: Sea ice influences the climate system through higher albedo, limiting heat absorption, and through insulation of the ocean. It also affects ocean circulation via brine rejection during freezing. Ecologically, it provides habitat and hunting grounds for polar species and shapes human activities such as shipping and resource exploration in polar regions. Changes in zeeijs are widely cited as indicators of climate change.