FIG. 3.

Sea ice that appears solid to the eye and hand is deceptive. Peering into the unmelted ice matrix using light microscopy, on a scale relevant to microorganisms, reveals a network of liquid brine inclusions as thin veins along ice-grain boundaries, at triple-point junctures between ice grains, and in small pockets (visible by transmitted light in the upper and lower left images) that house bacteria. At least some of these bacteria remain metabolically active in these fluids, even as temperatures drop severely during the Arctic winter (Junge et al., 2004). These images were taken at −15°C, when the liquid phase of the ice is approaching its minimum volume. The area outlined in red is (A) enlarged in (B) and (C), where (C) was taken by epifluorescence microscopy following staining with the DNA-specific stain DAPI. [Adapted from Junge et al. (2001)]