Ice block with sediment aggregates

Permanent ice covers on Antarctic lakes in the McMurdo Dry Valleys, (76° 30’ - 78° 20’S, 160° - 164° E) are unique geophysical features of our planet which have only recently been recognized as being capable of supporting resident microbial life. Previously, the permanent ice covers have been considered primarily as physical barriers to wind mixing, material transport, and solar radiation necessary for photosynthesis in the lake’s water columns. The realization that these features support viable microbial habitats and populations was only recognized once 1) anomalous nitrous oxide gas was measured in the ice cover, 2) microalgal (primarily cyanobacterial) and bacterial cells were found in tight association with resident sediment inclusions within the interior of several permanent ice covers, and 3) historical temperature records were analyzed which indicated that substantial amounts of liquid water (up to 70% by ice volume) were generated in the regions of sediment inclusions in the ice during the summer months. Based on the temperature records and bubble morphologies it was inferred that the absorption of penetrating radiation by the sediments in the absence of conductive processes (which could dissipate the resultant heat energy) led to localized ice melting and refreezing of generated liquid water pockets (thus the arching bubble patterns). Together, these findings show that the most geographically unique ice covers on this planet present an extreme environment where microbial persistence and growth occurs along the fringe of the physiocochemical gradients which are currently known to support life.