packice

Pack ice, or pack ice, refers to large areas of floating sea ice that are not attached to land or to the sea floor. It forms in polar and subpolar regions where ocean water freezes and drifts with winds and ocean currents. Pack ice is composed of many individual ice floes that have broken apart and consolidated as they move, rather than a single solid sheet.

Formation and structure: Pack ice develops from lead-filled expanses of frozen seawater and from the breakup and consolidation of existing sea ice. Floes vary greatly in size, from tens to hundreds of meters across, and sometimes many kilometers in extent. The thickness ranges from a few tenths of a meter for young ice to several meters for multi-year pack ice. Ridges and hummocks form where floes collide and compress, creating uneven topography on the ice surface.

Dynamics and variability: Pack ice is highly mobile, driven by winds, currents, and ocean waves. It undergoes continual rearrangement, with open-water channels called leads that intermittently appear and close. Its extent and thickness vary seasonally and interannually, and are influenced by air and ocean temperatures. In recent decades, changes in climate have affected the distribution, concentration, and stability of pack ice in both the Arctic and Antarctic regions.

Ecological and climatic role: Pack ice affects planetary albedo, heat exchange, and ocean salinity through brine rejection as ice forms. It provides habitat and hunting platforms for marine mammals and birds, and influences primary production by modulating light and nutrient exchange beneath the ice.

Human activity: Pack ice shapes Arctic navigation, offshore operations, and resource considerations. It presents hazards to ships due to moving floes and pressure ridges but also shapes historical and contemporary sea routes as ice conditions fluctuate.