SHAWN BROWN鈥橲 field trip got off to a bad start when he discovered that his experiment had disappeared. He had travelled thousands of kilometres from the University of Memphis to Finland to study blood-red snow algae when a heatwave had turned his plans to mush. The sun had melted the dark red living patches, and now only white snow remained.
With funders to satisfy, Brown and his team struck on a Plan B: look for algae in the pristine white snow. They didn鈥檛 expect to find much, but to their surprise they discovered a rich hidden ecosystem of algae, fungi and bacteria. 鈥淚 was just blown away by the biodiversity,鈥� says Brown.
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Until recently, microbes in snow were assumed to be rare and largely inactive. It is only in the past couple of years that scientists, including Brown, have used state-of-the-art DNA sequencing technology to reveal the secret life hidden there. As we learn more, it is becoming apparent that this is no mere curiosity: snow microbes play a role in cycling nutrients and carbon. They may be tiny but, given that snow covers a third of land on Earth, they could have an overlooked impact on the planet鈥檚 health and climate.
It may seem improbable that life could survive among ice crystals, given its dependence on liquid water, but microbes have evolved ingenious ways of eking out a living in snow. They grow in watery veins that run through the snow pack, melted either by impurities or by proteins that the microbes make. In extremely cold environments, some microbes that they can take hundreds of years to divide. Others might just tick over in snow then become active during a thaw. 鈥淲e鈥檙e just guessing at this point,鈥� says Brown. 鈥淲e don鈥檛 really know how they are making a living.鈥�
We are starting to understand where they come from, though. Some simply fall from the sky, swept up from Earth鈥檚 surface and carried on winds to new destinations. Some create the snow itself, acting as seeding points in clouds on which freezing water can take hold and grow into snowflakes. Others may simply lie low in the soil, biding their time, says Brown. Then a blanket of snow triggers a fleeting, invisible blossoming of specialist microbes, just as grass seeds in a desert briefly spring into life when the rains come. Even freshly fallen snow in your back garden has life lurking in it.
To explore the composition of these frigid ecosystems, Brown and his colleagues collected snow from different latitudes in Finland, Norway and Sweden, as well as in Colorado, and applied a technique called next-generation DNA sequencing, which let them study the organisms present without having to grow them, by looking at microbial genes in each sample. They found . Bacteria were pretty much the same everywhere in Europe although different from the US, but fungal species tended to stick to their own neighbourhoods. This makes sense because bacteria are much smaller than fungi, and so would more readily hitch a lift on the wind.
鈥淓ven freshly fallen snow in your back garden has life lurking in it鈥�
The algae were more surprising. Being relatively large, so harder to disperse, you might expect geographically distant populations to comprise distinct combinations of species. However, they were remarkably similar, even when comparing sites in Europe and the US, with one species dominating. The apparent similarity suggests that these algae are highly adapted to living in snow, says Brown, and may have had little pressure to change.
Brown has been studying temperate latitudes where snows form ephemeral, secret gardens that flower in winter and dissolve in spring. Things are different in permanently frozen regions where snow persists year on year, like Antarctica.
In 2012, a project began to drill through a glacier in West Antarctica to reach a lake that lay entombed beneath it and look for possible life cut off from the surface for half a million years. Before drilling began, David Pearce at Northumbria University, UK, and his team were asked to survey snow in the vicinity of the drill site to find out what microbes lived there as a precaution against contamination. Pearce was also keen to discover whether the same species lived across Antarctica, or whether there were local variations. So the researchers shouldered sterilised shovels and began digging at a range of locations with different types of snow, including islands north of the Antarctic peninsula and various sites in the continent鈥檚 interior.
They found . Some of the bacteria matched those known to exist in other parts of the world, but there were also some that seemed to be unique to Antarctica.
A major concern of Antarctic scientists is bio-contamination, bringing in microbes from elsewhere in the world or moving around those that are already present. In this regard, Pearce鈥檚 findings are reassuring because there was no evidence that humans had introduced any microbes. Yet they also indicate that intense activity could accidentally change the natural balance of species. Pearce suggests that there should be no-go zones in areas of special scientific interest until we understand the ecosystem better. 鈥淲e don鈥檛 know enough about the diversity of the Antarctic microbial flora to know that if we go somewhere and do something we鈥檙e not upsetting the environment,鈥� he says.
Microbes all around
What we do know is that snow microbes aren鈥檛 inert. 鈥淓verywhere we look, we find microbes, and they are active, and they are involved in biogeochemical cycling and climate active gas production,鈥� says Pearce.
In other words, snow microbes play a part in processes that are crucial for maintaining a healthy biosphere on Earth. For example, his team found that snow taken from the Arctic and Antarctic harboured , which degrade ozone in the atmosphere and affect the breakdown of other atmospheric gases such as the greenhouse gas methane.
Exactly how snow microbes affect Earth鈥檚 climate is unknown, for now. Their metabolism is very slow because of the extreme cold, says Pearce, but the sheer volume of snow on Earth suggests that they could make a significant contribution to the overall story.
Even as scientists start to explore snow life, its future is under threat from global warming. Snows are melting earlier in the season in some parts of the world, and other areas get more snow than they once did. All this will have unknown effects on snow microbes and the processes they might be involved in. 鈥淭here鈥檚 certainly a lot of new life and new biodiversity to be described in these systems,鈥� says Brown. 鈥淲e just don鈥檛 know enough about them to know what we鈥檙e going to lose.鈥�
