In contrast to the atmospherically deposited microbial life found at depths down to 2,750 m in the Vostok ice core (9), life in Lake Vostok might have emerged from sediments, from cracks in bedrock, or even from thermal vents and might have migrated upward into the accretion ice.

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Using a scanning electron microscope equipped with a cold stage and an energy-dispersive x-ray microanalyzer, Wolff and coworkers (18, 19) showed that sulfur was concentrated in veins and was undetectable in the bulk of the ice.

They estimated that, in a region where a vein roughly 1 μm in cross section intersected the surface of an ice sample, the concentration of sulfuric acid was about 2.5 M.

The explanation for how foreign ions migrate into veins has to do with the fact that micrometer-size droplets of acids and sea salts deposited as aerosols are essentially insoluble in ice crystals.

Coarsening and recrystallization of deep ice, in response to the shear stress induced by the weight of the overlying ice, take place by migration of grain (crystal) boundaries, which sweep through and scavenge the droplets.

From the mean crystal size of their sample, they estimated that the melt water concentration of acid was ≈7 μM and thus that most, and perhaps all, of the acid was concentrated in veins.

They later showed that hydrochloric acid can also concentrate in veins (20).

No one has yet observed living, motile organisms Fig.

1 shows a habitat that I argue can provide microbes in polar ice with the three ingredients essential for life: water, energy, and carbon.

At the Cambridge workshop, Priscu (15) also reported evidence for microbial life in their sample of melted accretion ice: the presence of dissolved organic carbon (7 μM), including ≈100 pg/liter of lipopolysaccharides, and sluggish uptake of into biomolecules.