Science News‘ long piece on a study, conducted by Russian scientists at Lake Vostok, reveals evidence of a complex subglacial ecosystem:
Lake Vostok is a behemoth, and not just by Antarctic standards. It is nearly as big as Lake Ontario and much deeper — estimated to be more than 900 meters in some places. By volume, Vostok is the seventh largest lake in the world. While there were clues that a large body of water lay beneath Vostok station, the lake’s existence wasn’t confirmed until the mid-1990s. Almost as soon as its existence was confirmed, murmurs began that the buried lake might harbor life (SN: 10/2/99, p. 216). Russian members of the team now have samples of lake water that gushed up into the borehole, and they expect to publish an analysis of it this fall. But Scott Rogers, an expert in ancient DNA at Bowling Green State University in Ohio, got his hands on some of the American share of the core, which is stored at the National Ice Core Laboratory in Denver. More than 3,000 meters long, the core is mostly glacier ice. But near its bottom, the core contains lake ice that has frozen to the bottom of the overlying glacier as it crawls across eastern Antarctica. Rogers and colleagues, including his student Yury Shtarkman, took more than two years to analyze their samples of this “accretion ice.” As expected, they found genetic material indicating bacterial life (SN: 3/9/13, p. 12). The team had samples from two parts of the lake: In one, about 77 percent of the identifiable genetic sequences were from bacteria, with most of the rest from fungi. In the other, about 95 percent of what the researchers could identify was bacterial. And then there were the standouts: The researchers detected DNA similar to that of small water animals called tardigrades, or water bears, which are known for withstanding extreme environments. Some genetic material was nearly identical to the little swimmers called rotifers. Other sequences suggested a whole mess of algae (yellow-green, green, red). The real surprise was sequences indicating larger organisms like clams and jellyfish. Strangest of all were genetic signatures resembling parasites or symbiotic partners of large aquatic organisms: a rainbow trout intestinal bacterium, a sponge symbiont, a lobster gut bacterium. Finding those DNA sequences doesn’t mean that those exact organisms are swimming around kilometers under the Antarctic ice. But the mix of genetic signatures is suggestive of a functioning rudimentary ecosystem: There are what ecologists call primary producers — bacteria and other critters that extract nitrogen and carbon from the environment and make it usable for other organisms. There are also consumers — various amoebae, zooplankton and perhaps others living off them. And completing the loop are decomposers, including fungi, that make a living breaking dead things down. Many of the DNA sequences are similar to those of organisms with a high tolerance for extremes, be it cold, salt or pressure. In the July report, published in PLOS ONE, Rogers and his colleagues present a Vostok scenario that goes something like this: About 35 million years ago, much of Antarctica was green and free of ice. Sea levels were higher, so Lake Vostok may have been connected to the Southern Ocean. It could have been a saltwater bay that had reverted to brackish. Bring in a glacier, and the top of the lake becomes freshwater, says Rogers. This scenario might lead to a variety of distinct zones within the lake. At different depths and locations there may be vastly different temperatures, salinities and other chemical concentrations. “You could have organisms surviving there and possibly evolving into different niches in the lake,” he says. Hard to fathom Even so, some scientists cannot wrap their minds around the idea of a thriving Vostokian ecosystem. “Here’s probably the most extreme ecosystem on the planet and it’s teeming with life? And we can go to other less extreme environments and these fauna are absent?” says microbiologist Brent Christner of Louisiana State University in Baton Rouge. It’s not just the numbing cold of Lake Vostok, which at its surface hovers around 0° Celsius. Nor is it the crushing pressure exerted on a lake beneath almost 4,000 meters of ice. The problem is energy, without which life can’t exist. Lake Vostok sits in permanent darkness, far beyond the reach of any photons. “If you put all these organisms in a lake, they have to eat something. What do they eat?” Christner says. “I’m not saying it’s impossible that more than a bacterium lives in these lakes. Maybe you have a nematode, but that would be an apex predator.” Earlier this year, Christner and his colleagues reported finding cells containing DNA in Lake Whillans, which lies beneath a mere 800 meters of ice in West Antarctica (SN: 3/9/13, p. 12). But unlike Lake Whillans and many of the continent’s other subglacial lakes, there aren’t known streams and rivers feeding into Vostok that might bring life or nutrients from afar. “On the extreme-o-meter, Vostok is an order of magnitude more extreme than these other lakes,” says Christner. “It’s a lot to ask of a multicellular organism to be living like that.” But if Lake Vostok does harbor an energy source, then the existence of multicellular life seems much less far-fetched. Data from ice-penetrating radar and laser altimetry suggest that Lake Vostok sits on a major geological boundary. “Recent minor tectonic activity could have the potential to introduce small, but significant amounts of thermal energy into the lake,” a team of geoscientists wrote in 2003 in Earth and Planetary Science Letters. In 2006, a research team that included microbial geneticist Sergey Bulat of the Petersburg Nuclear Physics Institute in Russia, one of the more vocal critics of the current study, reported DNA from Vostok ice cores closely resembling that of microbes thriving in the high temperatures and strange chemistry of volcanic vents and hot springs. For extremophile microbes like those, Lake Vostok might even seem cushy. After all, there are bacteria that live in the Earth’s upper atmosphere, a freezing place with little oxygen that’s bombarded with UV radiation. Other microbes, like Picrophilus torridus, live in highly acidic volcanic vents that spit out scalding-hot gases. And there are fish that survive just fine in toxic, hydrogen sulfide–laden waters inside permanently dark caves.