First-Year Ice

First-year ice is sea ice that has formed during one winter and not yet survived a summer melt season, the WMO stage of development above young ice (over 30 cm thick). Sub-stages run thin (30 to 70 cm), medium (70 to 120 cm), and thick (over 120 cm), reaching roughly 1.5 to 2 m by late Arctic winter. First-year ice retains high brine content, so it is more saline, weaker, and warmer than multi-year ice, and it carries the highest POLARIS risk values for a given ice class after thick first-year. Its salinity and rough surface make it bright in passive microwave and radar, aiding the AMSR and scatterometer discrimination from older ice.