did not grow, their presence might confound measurements based on macromolecules (e.g., DNA, proteins).

Unless these microbes are introduced along with substrates that provide them a nutritional edge, it is less likely that allochthonous microbes would outcompete autochthonous (already present) ones. Microbes recovered from subglacial aquatic environments may not survive in surface environments due to a variety of factors. For example, it is more likely that microbes released from the overlying ice sheet into the atmosphere would survive more readily than microbes recovered from subglacial lakewater, given that long-term preservation would be more effective in deep frozen ice than in liquid-water conditions.

In addition, subglacial microbes may be light sensitive, may not be able to adapt to a more nutritionally rich environment, may not be able to survive under lower pressures or they may be more sensitive to new populations of grazers or other predators. These features would place them at a disadvantage relative to other taxa if they were transferred into less severe environmental conditions, where they would likely be outcompeted by the native microbiota. As discussed in Chapter 3, even microbes isolated in ice for 1 million years are unlikely to have a genome exhibiting significant genetic divergence because of the slow pace of prokaryotic evolution.

The work of Karl et al. (1999) on water from accretion ice, however, does suggest that some fraction of recovered microbes could remain viable at the surface. Spores that might be either introduced to or removed from subglacial aquatic environments represent a potentially different situation because they are able to survive under many extreme conditions over very long time frames (millions of years) (Vreeland et al. 2000). For example, spores present in a subglacial lake environment such as Lake Vostok might have been deposited millions of years ago prior to the formation of the lake and, if returned to the surface, could become viable once more.

OTHER POTENTIAL SOURCES OF CONTAMINATION—PARTICULATES IN THE FLUID

This category includes biotic constituents such as bacterial cells, viruses, and fungi. Drilling fluids at the Vostok site (Alekhina et al. 2007) and at the EPICA sites (S. Bulat, personal communication) are known to contain many microbial taxa, including genera such as Sphingomonas that have also been detected in hydrocarbon-contaminated soils in Antarctica and elsewhere and on Greenland ice cores (Alekhina et al. 2007). Technologies that are under development for the detection of life in subglacial lakes (e.g., fluorescence-based systems; see Bay et al. 2005) may also provide sensitive detection of dissolved and particulate organic contaminants.

Abiotic particulates are probably best monitored via turbidity sensors that could be lowered down the access holes. A variety of optical backscattering instruments are used routinely for water column profiling in limnology and oceanography, and these have detection limits at or below 1 NTU (nephelometric turbidity unit).7

7

Drinking water should not have a turbidity above 1 NTU, although values up to 5 NTU are usually considered safe.



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