The notion of digging so deep for life raises a darker question: Could some prehistoric pestilence be lurking in that ice waiting for a chance to come back and terrorize a defenseless population? An Amundsen Strain, perhaps, named after Norwegian explorer Roald Amundsen, who led the first expedition to reach the South Pole 100 years ago.
''There are some possible adaptations by surviving in ice that could be advantageous to these pathogens," said Scott Rogers, an evolutionary biologist and professor in the Department of Biological Sciences at Bowling Green State University in Ohio. For instance, a virus becomes unable to cause infections when its host population builds up antibodies to it. "So if [viruses] can survive in the ice, they could come back at a time when the population is naïve again and hasn't been exposed to that particular genotype," he said.
Rogers has found a living 140,000-year-old plant virus in glacial ice from Greenland. He speculates that it could be possible for some hardy viruses, like the one that causes polio, to survive in ice and come back to infect susceptible humans. However, he and other scientists think there's little possibility that melting glaciers will unleash virulent viruses that trigger pandemics like the one depicted in the recent Hollywood horror film, Contagion. Human and animal pathogens have evolved to live in a warm, cozy place and would have a hard time surviving the extremely harsh conditions in ice. Viruses tend to be especially fragile.
"The chances aren't zero," said Rogers, "but they're very close to zero."
More likely is prospect that thawing ice sheets will allow ancient microbial genes to mix with modern ones, flooding the oceans with never-before-seen types of organisms. Rogers believes this is already taking place. "What we think is happening is that things are melting out all the time and you're getting mixing of these old and new genotypes," he said.
The biggest effect of these newly liberated – and potentially newly remade –microbes will likely be seen in the oceans, Christner said. Earth's glaciers and sub-glacial sediments contain more microbial cells and carbon than all the lakes and rivers on the surface of the planet – a huge load of organic matter that, if thawed, would end up in the sea, he said.
"Potential climate impacts are more in the direction of introducing nutrients into marine systems," Christner said. One scenario: The nutrients trigger growth bursts of bacteria that would then use up all the oxygen in the water, destroying fish habitats and exacerbating ocean dead zones that are already occurring from other causes.
"We have always thought about the ocean as being this sink that can handle everything," said Montana State's Foreman. "But we know now that's not true. There are going to be tipping points where things are going to happen… But we don't know what point that's going to be."
Enormous compost piles
Thawing glaciers could also churn out enormous compost piles of decaying biomass. All the carbon from organic matter in and under the ice sheets, if converted to carbon dioxide, would equal a decade's worth of emissions from vehicles on roads worldwide, scientists estimate. Of course, not all of the carbon would convert directly to greenhouse gases. But any release would add to the huge amount expected from thawing permafrost. "This is a big pool of carbon to be considered," Priscu said. "The carbon cycle is so important right now, especially in terms of climate change, that we really should look at this."