The Greenland ice sheet is vast, majestic, pristine....and peppered with bacteria that seem equipped to survive in industrial waste, according to a new study. Which really makes you question the whole the pristine bit, now, doesn't it?
In fact, scientists know that industrial contaminants, including heavy metals, pesticides, and polychlorinated biphenyls (PCBs), have been accumulating at our planet's north polar region for decades. So, a group of microbial ecologists wondered if this was impacting the local flora -- the diverse collection of microbes that call the Greenland ice sheet (GrIS) home. Through DNA sequencing, the scientists found evidence that these bacteria have what it takes to tolerate industrial toxins, suggesting the local environment may be more contaminated than we thought.
But contrary to some headlines, that doesn't mean Greenland is a toxic wasteland, nor that we should be panicking about all that pollution oozing back into the sea as ice caps melt. (Free climate disaster movie idea, by the way.) The research offers an intriguing clue, one that scientists now need to follow up on.
For the study, scientists from Denmark, the Czech Republic and elsewhere collected samples of "glacial surface debris" from five locations up and down the Greenland ice sheet between May and September 2013. They extracted bacterial DNA from the ice, and examined the sequences using metagenomics -- an approach that allows you to look at the genes of potentially hundreds of different species at once. The researchers scanned their ice-hardy DNA brews for genes associated with the ability to degrade industrial pollutants, or to resist their toxic effects. They compared the results with DNA from healthy human gut bacteria, which were presumed to harbour no special resistance to environmental pollution.
What they found might surprise those who picture Greenland as a pristine environment. In each location, microbes had the genetic potential to degrade or resist toxic pollutants (including PCBs) and polycyclic aromatic hydrocarbons (PAHs) that formed during the burning of fossil fuels or garbage, mercury, chromium, and lead.
"Our results show that microbial communities on the GrIS have the potential for resistance to and degradation of contaminants known to be transported to the Arctic," the researchers wrote in their paper published in Environmental Research Letters. They concluded: "Since the genetic potential of contaminant resistance and degradation usually indicates the presence of the relevant contaminants, the Greenland ice sheet should not be considered a pristine environment, and more attention should be paid to the potential release of anthropogenic contaminants from this fast-changing environment," i.e., due to climate change.
It's certainly worrisome to hear that industrial pollutants may be fouling up Greenland, especially given the propensity of things like PCBs to bio-accumulate up the food chain and harm humans. Still, the new study's findings have some important caveats. For one thing, as Antje Boetius of the Max Planck Institute for Marine Microbiology points out, the researchers didn't compare the "contaminated" bacterial communities to samples from truly pristine ice, as a control.
"This is important to back up the conclusion that 'glaciers are not pristine,' Boetius, who was not involved with the new study, told Gizmodo. "The only reference used was human gut microbiome, which we cannot call 'pristine,' and which is an awkward reference for a study on glaciers. Why have they not used deeper core sections from before industrial revolution, to test whether these are free of the contaminants and contaminant-associated genes?"
Boetius added that she looked at the microbes detected in the new survey, "and they seem not particularly connected to anthropogenic contamination. Many of them were reported before as members of glacial ice communities." She pointed out that lots of bacteria have the ability to degrade all sorts of wacky, toxic stuff, and that isn't necessarily a sign of contamination.
But Janet Jansson, a microbial ecologist at Pacific Northwest National Lab, agreed with study's conclusions. "I am not surprised to see evidence of bacteria that can degrade contaminants on the Greenland ice sheet because I have been to Greenland and have personally seen how dirty the surface ice is on some regions of the ice cap, and how contaminants are concentrated," she told Gizmodo. In Jansson's view, the results "convincingly show that the Greenland ice sheet harbours microorganisms that have genes typical of microbes from other contaminated environments on our planet and therefore the Greenland ice sheet is not pristine."
What's not clear to anyone, yet, is how these microbes would respond to contaminants melting out from the ice due to climate warming -- would they mobilize a resistance, snarfing down industrial toxins as they ooze away? Maybe. But until we do follow up studies, what we have is an interesting observation that poses more questions than answers.
Until those answers are forthcoming, maybe pass on the snow cones next time you're in Qaqortoq.