Microbial Activity in Solid Ice: Implications for Modifying the CO₂ Record in Ice Cores
 

Project participants:
 

Recent studies of microbial longevity in ancient glacial ice indicate that bacteria remain viable for hundreds of thousands of years while frozen. In the absence of metabolic activity, the cells within the ice must incur a significant amount of macromolecular damage (e.g, amino acid racemization and DNA depurination). Perhaps the species recovered are particularly successful at surviving metabolic dormancy over extended time frames, but it is also possible that the entrapped microbes might carry out a slow rate of metabolism to repair incurred macromolecular damage. Microbial activity within glacial ice would alter the gas composition of bubbles in the ice, skewing paleoclimatic inferences based on these data. Furthermore, confirming that microorganisms in permanently frozen environments remain metabolically active would support the view that ice sheets are an active biome.

The objective of our research is to examine the ability of bacteria to metabolize and respire CO₂ in the liquid fraction of ice. We are using a laboratory model to conduct a detailed analysis of the physiological, biochemical, and genetic mechanisms responsible for subzero metabolism. Importantly, the proposed research represents the first attempt to measure microbial CO₂ respiration and macromolecular synthesis under environmental conditions (-5 to -20^oC) in which elevated CO₂ concentrations have been reported in glacial ice cores and basal ice from cold based glaciers.

Cross-polarized image of ice crystal structure and interstitial
liquid veins at -15 ^oC. The letter “C” designates four
adjacent ice crystals. Image courtesy of Steve Jepsen.

Incorporation of [³H]thymidine into TCA-precipitable
material by frozen suspensions of Sporosarcina
species TGTB5-5B at -15 °C.

Disclaimer: Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).