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Viable microorganisms (e.g. fungi, bacteria, Archaea and viruses) are distributed by wind over great distances, including globally. Microbes may settle out of the atmosphere or may be incorporated into fog, rain, sleet, hail, or snow. These organisms fall into lakes, streams, oceans, or onto the land or glaciers. When they become incorporated into environmental ice (e.g. glaciers, ice sheets, and snow), those that survive freezing and thawing may persist for years, centuries, millennia, or longer. Once they melt from the ice, they may enter contemporary populations. This mixing of ancient and modern genotypes (i.e. temporal gene flow, or what we term “genome recycling”) may lead to a change of allele proportions in the population, which may have effects on mutation rates, fitness, survival, pathogenicity and other characteristics of the organisms. Pathogenic microbes that survive freezing and thawing (e.g. influenza …