Cryoconite

Cryoconite is a dark, granular sediment that accumulates on the surface of glaciers and ice sheets. It typically consists of mineral dust and rock flour, soot or other black carbon, and organic material—including microbial biomass bound together by extracellular polymeric substances produced by bacteria and algae. The particles range in size from fractions of a millimeter up to a few millimeters and commonly form compact granules that cluster in depressions on the ice.

These sediments darken the ice surface, reducing albedo and increasing absorption of solar radiation. On many glaciers they create small meltwater holes, or cryoconite holes, where heat-driven melting concentrates water and light access, forming micro-ecosystems that host cyanobacteria, algae, and heterotrophic bacteria. The communities within cryoconite and the granules themselves can influence local melt rates and nutrient cycling on the glacier surface.

Cryoconite is found on glaciers and icefields worldwide, particularly where dust, volcanic ash, or soot deposition is substantial. Beyond affecting melt, it serves as a niche for microbial life in extreme environments and acts as a proxy for atmospheric deposition and past environmental conditions, since the mineral and organic components can preserve signals of climate and pollution histories.