Antarctica normally conjures images of white and blue, but the frozen continent can sometimes bear more unexpected colours. Take the Taylor Glacier - when geologist Griffith Taylor first explored it a century ago, he found a bizarre reddish stain that seemed to spill waterfall-like from the glacier's snout. The area became evocatively known as Blood Falls.
The source of the blood-red colour is an underground saltwater lake that was trapped by the encroaching glacier at least 1.5 million years ago. The temperature of the water is -5 Celsius, but it's so salty that it doesn't freeze. It's also rich in iron salts, which are slowly leaching the ice - these are the source of the distinctive red hue. Blood Falls is a rust glacier.
But it also houses another secret, which scientists from Harvard University have started to uncover - it's home to an entire ecosystem of bacteria, trapped for millennia in conditions that could hardly be more inhospitable to life.
Neither water from the surface nor light from the sun penetrates the thick ice of Taylor Glacier to the lake lying 400 metres beneath. As the glacier slides overhead, trace amounts of gases might seep through, but nothing substantial. There's hardly any oxygen dissolved in the water, and radioactive-dating of the little carbon suggests that it is incredibly old. But despite the extremely salty water and the lack of light, oxygen and carbon, the microbes have lived there for millions of years, using sulphate ions as their only source of energy.
Jill Mikucki from Harvard University discovered life in Blood Falls a few years ago. It took her several years to get a sample of water from it, but when she did so, an analysis of its chemical composition revealed that its bacterial community have lived a truly sheltered existence. For millennia, the Blood Falls bacteria have been trapped underground with no nutrients coming in from the outside world. How do they survive? Again, the water provides a clue. It's very rich in sulphate ions (SO42-), which many bacteria can use as an energy source.
That seemed like a plausible explanation for the bacteria's survival, but something didn't add up. Bacteria typically subsist off sulphate ions through a chemical reaction that converts them into sulphide ions (S2-). These can usually be detected as hydrogen sulphide, but Mikucki couldn't find any hydrogen sulphide in the water. And in the genomes of the bacteria, she couldn't find any traces of the group of genes (dsrA) that would normally catalyse this reaction. She even found, by analysing the proportion of different sulphur isotopes, that the overall levels of sulphate ions in the water hadn't fallen for millions of years.
The bacteria must have some way of recycling their energy source. Mikucki suggests that they do so using a unique system, where they reduce sulphate to sulphite (SO32-) instead. The sulphite then reacts with iron (which the glacier scours from the underlying rock), and is oxidised back into sulphate, replenishing the original supply. The bacteria do this with a special enzyme called PAPS, or phosphoadenosine-5'-phosphosulphate-reductase, to give it its fuller, catchier name!
This system may be unique, but that's only because life beneath glaciers has hardly been studied. Perhaps such ecosystems were commonplace during Snowball Earth periods when much of the planet was covered in ice. And perhaps many similar communities exist elsewhere beneath the planet's glaciers. After all, Mikucki notes that iron is such an abundant part of the Earth's crust that it's entirely possible that other bacterial ecosystems have adapted to survive on little else besides it and sulphate ions.
Reference: Science doi:10.1126/science.1167350
Images: Glacier diagram by Zina Deretsky; Blood Falls by Ralph Maestas
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Another obvious, for me, implication would be greatly increased support that life exists on ice-shelled rocks orbiting planets in our solar system.
Fascinating. Thanks very much for blogging on this.
What I'd like to know is, where do these bacteria get the carbon for their DNA and other cellular structures? I assume that they're fanatical about recycling carbon from dead creatures, but in every system there's some loss. But perhaps some carbon trickles in, enough to make up for the loss, but not enough to make it an attractive to use in producing energy.
gillt: "Another obvious, for me, implication would be greatly increased support that life exists on ice-shelled rocks orbiting planets in our solar system."
I will add: and the other planets.
arensb -- i was wondering about that, too. Ed?
It's amazing that under ice-cap there is still something alive. But what's more interesting to me is how the bacteria survived becoming almost self-sufficient. If it is possible for the bacteria to renew its energy source - why should it be impossible to us? Maybe it's just a matter of time that we can learn from it how to cooperate with our environment.
I'm not sure one can make that leap of faith. Life exists on earth (and I realize there is some debate as to how abiogenesis occurred), so a 1.5 million year old population of these organisms is hardly surprising given that bacteria are so ubiquitous on this planet. Bacteria living in this type of environment would lead me to believe that bacteria from earth could live in an ice shelled asteroid somewhere, but it provides no evidence that life could arise under such conditions, since these blood falls bacteria did not arise independent of all other life on earth.
I forgot to mention one thing: what a cool (yeah, I know, pun) story!
More than 20 years ago a friend of mine did his doctoral and postdoctoral work on cryptoendolithic bacteria in Antarctica. They live hidden deep in cold, dry, dark, rock.
This is only the latest batch of this sort of life studied in Antarctica.
arensb -- i was wondering about that, too. Ed?
On the comment made by Michael Simpson, First off your remarks seems to be unbelievable for the simple fact that you made the statement that bacteria from Earth could live else where in an ice shelled asteroid which are called comets. Comet's do not come from Earth, secondly humanity evolved from cellular microbials just the same way that a human develops in the womb and begins as a series of cells which over a nine month period of cellular growth develops or primarily evolves into a human being. How life would evolve from the the above discussed topic could be achived by introducing an new element into the environment of the microbial. A change in the microbials habitat could be a few degrees rise in temperature where seeds been grow which would attract new life in the form of bugs, birds and other species. When these species die the microbials would feed off of the carcass of the dead animal. The protein ingested and digested would then cause the microbial to split again into a new type of bacteria. As the evolution of the microbial continues due to the splitting of the cells to create new bacteria, the bacteria will begin to develop thought patterns based upon repeative actions. These actions could be as simple as the microbial traveling from it's resting place during non-feeding times to areas where consistent foliage builds up every year. During the journey from rest to feeding and over many generations of cellular growth, the microbial would have remembered the path that it traveled to get to the food bank and then back again to it's home by using landmarks such as pebbles that are bigger then they are but smaller for us to see. This would then equate inside of the microbials mind as taking a certain number of pulls and pushes to get to one landmark in it's journey to and from the food storage and home. Other millions of years and a constant change in the food supply will have caused the microbial to split it's cells billions of times which each new microbial split resulting a more intelligent and evolved bacteria that if the certain enviromental factors arre encountered then bipedal creatures then evolve just as Earthlings did.