Knowra Firn Firn Firn is granular snow that has survived at least one melt season but has not yet become glacier ice. Compaction and recrystallization gradually turn it into glacier ice.
Snow metamorphism : The physical transformation of snow grains through temperature-driven changes, compaction, and recrystallization. Snow metamorphism rounds and bonds firn grains as the layer densifies.
Ice core : A cylinder of ice drilled from a glacier or ice sheet, preserving layers of snowfall and trapped atmospheric gases. Firn becomes the upper, porous portion of many ice-core records.
Glacier : A persistent body of land ice that moves under its own weight. Firn accumulates and transforms within the upper reaches of glaciers.
Greenland Ice Sheet : The vast ice sheet covering most of Greenland, with extensive surface melting and firn accumulation. Its firn stores meltwater and varies strongly between the cold interior and warmer margins.
Firnification : The compaction and recrystallization by which snow and firn become glacier ice. This process carries firn across the boundary into glacier ice.
Paleoclimatology : The study of past climates using natural records such as ice, sediments, and tree rings. Firn processes shape how ice cores preserve evidence of past climate.
Accumulation zone : The part of a glacier where annual snowfall exceeds annual ice loss. Firn commonly persists where snowfall adds mass faster than ablation removes it.
Antarctic Ice Sheet : The continental ice mass covering most of Antarctica, containing thick, cold firn over much of its interior. Its firn preserves snowfall layers and atmospheric records in a comparatively cold setting.
Snow density : The mass of snow per unit volume, shaped by grain structure, liquid water, and compaction. Increasing density tracks firn’s progressive loss of pore space.
Firn air : Air contained in the interconnected pore space of firn before it becomes trapped in ice bubbles. Sampling firn air measures atmospheric gases before bubble close-off.
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