A team of researchers from the United States, Italy and the United Kingdom, has discovered a complex assemblage of bacteria and archaea in the waters and sediments of Lake Whillans, a lake that lies about 800 m beneath the surface of the West Antarctic ice sheet.
This false-color scanning electron microscopy image shows a microbial cell (arrow) with coccoid morphology found in a sample from Lake Whillans. Scale bar – 2 μm. Image credit: Brent C. Christner et al.
Using various methods, scientists have built a knowledge base about Antarctica’s subglacial hydrological system over the past forty years.
The largest of the Antarctic subglacial lakes, Lake Vostok, is one of the biggest lakes on Earth in terms of volume and depth and has been isolated beneath the ice sheet for more than 10 million years.
Samples of microbes from this lake have been collected indirectly by examining ice collected above its liquid part – on the bottom of the ice sheet.
These samples, which were first described in 1999, presented the first evidence for life beneath the Antarctic ice sheet.
However, the drilling techniques used to retrieve the samples and the low amount of microbial biomass present had called into question previous studies that concluded the lake supports a living microbial ecosystem.
In January 2013, scientists from the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project drilled into Lake Whillans using a clean hot-water drill and incorporated rigorous measures to avoid the introduction of foreign material into the lake.
This lake lies beneath 800 m of ice on the lower portion of the Whillans Ice Stream in West Antarctica and is part of an extensive and evolving subglacial drainage network.
Analysis of the samples from Lake Whillans shows that its water contains a diverse microbial community dominated by Betaproteobacteria (Sideroxydans lithotrophicus, Polaromonas glacialis, Nitrotoga sp., Thiobacillus denitrificans), Thaumarchaeota (Nitrososphaera viennensis, N. gargensis, Nitrosoarchaeum koreensis, Cenarchaeum symbiosum, Nitrosopumilus maritimus), Gammaproteobacteria (Methylobacter tundripaludum), Deltaproteobacteria, Actinobacteria, Chloroflexi, Bacteriodetes, etc.
“It is the first definitive evidence that there is not only life, but active ecosystems underneath the Antarctic ice sheet, something that we have been guessing about for decades,” said Dr Brent Christner of Louisiana State University, who is a researcher with the WISSARD project and the lead author of a paper published in the journal Nature.
The paper also raises a separate issue of the connectivity of Lake Whillans to the wider global ecosystem.
“Given the prevalence of subglacial water in Antarctica, our data lead us to contend that aquatic microbial systems are common features of the subsurface environment that exists beneath the Antarctic ice sheet,” the scientists concluded.
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Brent C. Christner et al. 2014. A microbial ecosystem beneath the West Antarctic ice sheet. Nature 512, 310–313; doi: 10.1038/nature13667
