This vital sign is primarily concerned with seasonal snow, seasonal river and lake ice, seasonal to inter-annual aufeis, and long-term glacial ice; sea ice is treated in a separate protocol. Seasonal snow, river and lake ice, and long-term glacial ice are dominant ecosystem influences in ARCN parks. Snow affects landscape vegetation patterns, drainage patterns, nutrient cycling, water quality, productivity of plants and animals, the degree and types of disturbance events, the timing of migratory and breeding events of organisms, predator-prey relationships, and the distribution of plants and animals. River and lake ice formation, thickness, and breakup are also key indicators of regional climate, especially in the data-sparse regions that characterize much of the network, and they exert dominant controls on aquatic productivity and aquatic ecosystem dynamics. In some areas of GAAR, changes in glacier ice also impact the landscapes, and these changes influence both terrestrial ecosystems via changes in glacier area and local microclimate, as well as stream ecosystems through impacts to the timing and flux of freshwater and sediments. Snow and river and lake ice are seasonal features which give us integrative information on the duration and severity of winter. Glaciers are persistent landscape features that give us integrative information of the decadal-scale climate trends. Comprehensively, measurements of all these features give us information on intra- and inter-annual climate trends that cannot be achieved through weather stations alone.
