Microbes have been trapped in an icy capsule cut off from the world beneath this glacier for more than 1.5 million years. In the summer a gush of water dyed red from the iron compounds trapped with them manages to escape (Image: Benjamin Urmston/Science) Analysing DNA fragments from the “blood falls” has revealed that the bacteria survive on organic compounds trapped with them all those years ago that will eventually run out. (Image: Ralph Maestas/Science)

A bacterial lost world trapped beneath Antarctic ice may help explain how life persisted during the “snowball Earth” period when almost all of the globe’s surface was frozen over.


Isolated for at least 1.5 million years from close relatives that live in the ocean, the Antarctic microbes live in a super-salty lake sealed with a 400-metre slab of ice, called Taylor Glacier. But each summer, the temperature warms enough for a trickle of extremely cold water to flow to the surface.

Antarctic explorers and scientists noted the deep red colour left by these flows, created by iron in the water, and called them “blood falls”.

“‘Wow’ moment”

“When I came on the scene, I was definitely determined to see whether there was life associated with this feature or not,” says Jill Mikucki, a geomicrobiologist at Dartmouth College in Hanover, New Hampshire, who led a new study into the blood falls.

Her team’s first look at the water turned up bacterial DNA and living cells. “That was a ‘wow’ moment, when you could actually see the microbes,” she says. DNA sequence analysis suggested that most of the bacteria were related to marine microbes.

After proving that bacteria were living in the lake, Mikucki’s team turned their attention to explaining just how life could flourish in such an inhospitable spot.

Hard life

During the Pliocene epoch plummeting sea levels isolated the lake from the ocean before falling global temperatures during concentrated its salt content through evaporation to several times that of the sea. An advancing Taylor Glacier completed the lake’s total isolation, leaving it sealed off from the world for the last 1.5 to 2 million years.

The bacteria inside are lodged nearly half a kilometre beneath a glacier, making photosynthesis impossible. The sulphurous metabolic reactions that sustain bacteria in other ecosystems independent of the sun – for example, in deep-sea cold seeps – are not an option because the lake’s abundant iron minerals would interfere, reacting with the sulphur to make the inert mineral iron pyrite.

Instead, the bacteria use the sulphur compounds as chemical catalysts to shuttle energy-bearing electrons from organic compounds in their icy prison to iron leached from bedrock surrounding the lake. The organic feedstock was probably sealed in the lake when the bacteria were locked in by the Taylor Glacier, while the iron comes from surrounding rock.

It’s a way of sustaining life believed to be unique. “Trust microbes to do something clever given an unusual niche,” says Julia Foght, a microbiologist at the University of Alberta, Canada, who was not involved in the study.

Death sentence

With no other source of energy, the bacteria will eventually eat all of their food, says Ann Pearson, a team member at Harvard University. “This is eventually going to run down to nothing.” Mikucki’s team has no way to know how long the bacteria will survive.

A similar situation may have occurred roughly 600 to 800 million years ago when snow caps extended to the tropics – perhaps even to the equator – during a period often referred to as “snowball Earth”.

Photosynthesis probably ground to a halt across the planet, and marine bacteria may have only managed to eke out a living in the same way as those living under Taylor Glacier, Pearson says. “Life in sea water, as we know it, could maintain reasonable continuity through an event like this.”

Ron Ormeland, a microbiologist at the US Geological Survey in Menlo Park, California, told New Scientist that this theory is reasonable, if somewhat speculative.

“It is intriguing to extrapolate the data to the early Earth,” he says. “That and whatever is in the rock record are the only bits of evidence we have.”

Journal reference: Science (DOI: 10.1126/science.1167350) (in press)