Using DNA and RNA sequencing, an international team of researchers has revealed a surprising variety of life forms living in the subglacial Lake Vostok.
Radar satellite image of Lake Vostok (Goddard Space Flight Center)
Lake Vostok is the fourth-deepest lake on Earth and the largest of the 400-some subglacial lakes known in Antarctica. The ice that has covered it for the past 15 million years is now more than 2 miles deep.
Not only had most scientists believed Lake Vostok completely inhospitable to life, some thought it might even be sterile.
Working with core sections removed from the deep layer of ice that accreted from lake water that froze onto the bottom of the glacier where it meets the lake, the scientists examined ice as clear as diamonds that formed in the great pressure and relatively warm temperatures found at that depth. They sampled cores from two areas of the lake, the southern main basin and near an embayment on the southwestern end of the lake.
“We found much more complexity than anyone thought. It really shows the tenacity of life, and how organisms can survive in places where a couple dozen years ago we thought nothing could survive,” said Dr Scott Rogers of the Bowling Green State University, senior author of a paper reporting the findings in the open-access journal PLoS ONE.
An artist’s cross-section of Lake Vostok (Nicolle Rager-Fuller / NSF)
The team identified more than 3,000 of bacteria, including some that are commonly found in the digestive systems of fish, crustaceans and annelid worms, in addition to fungi and two species of archaea, or single-celled organisms that tend to live in extreme environments. Other species they identified are associated with habitats of lake or ocean sediments. Psychrophiles, or organisms that live in extreme cold, were found, along with heat-loving thermophiles, which suggests the presence of hydrothermal vents deep in the lake.
“The presence of marine and freshwater species supports the hypothesis that the lake once was connected to the ocean, and that the freshwater was deposited in the lake by the overriding glacier,” Dr Rogers said.
The largest number of species overall was found in the area near the embayment, including many that are common to freshwater environments, as well as marine species, psychrophiles and thermophiles. Numerous others were found that remain unidentified. The embayment appears to contain much of the biological activity in the lake.
Schematic cross-section of Lake Vostok, above, and metagenomic summary (Shtarkman YM et al)
“Many of the species we sequenced are what we would expect to find in a lake. Most of the organisms appear to be aquatic (freshwater), and many are species that usually live in ocean or lake sediments,” Dr Rogers said.
Before 35 million years ago, Antarctica had a temperate climate and was inhabited by a diverse assemblage of plants and animals.
“About 34 million years ago, a huge drop in temperature occurred and ice covered the lake, when it was probably still connected to the Southern Ocean. This lowered sea level by about 300 feet, which could have cut off Lake Vostok from the ocean. The ice cover was intermittent until a second big plunge in temperature took place 14 million years ago, and sea level dropped even farther,” Dr Rogers said.
As the ice crept across the lake, it plunged the lake into total darkness and isolated it from the atmosphere, and led to increasing pressure in the lake from the weight of the glacier. While many species probably disappeared from the lake, many seem to have survived, as indicated by the new results.
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Bibliographic information: Shtarkman YM et al. 2013. Subglacial Lake Vostok (Antarctica) Accretion Ice Contains a Diverse Set of Sequences from Aquatic, Marine and Sediment-Inhabiting Bacteria and Eukarya. PLoS ONE 8 (7): e67221; doi: 10.1371/journal.pone.0067221
