Life - But not as we know it
16 June 2008
Martin Siegert reports on a pioneering UK programme to explore Lake Ellsworth, a lake deep beneath the West Antarctic ice sheet.
On 21 July 1983, the thermometer at Vostok Station in East Antarctica, which usually hovers around -60°C, dropped to -89°C, the lowest temperature ever recorded on Earth. The notion of substantial volumes of liquid water existing in Antarctica seems incongruous with these extreme conditions.
But liquid water does exist here. At the base of the ice sheet 3.7 kilometres beneath the station, geothermal heating from Earth's interior at just a normal level is sufficient to keep the underside of the ice warm, permitting the existence of Lake Vostok, a body of water the size of Lake Ontario.
In fact, the Antarctic ice sheet base is warm in many places. Where the ice base melts, water flows under gravity and pressure of the ice above into troughs and valleys where it forms lakes, some small, others large.
These environments may be the closest Earth analogues to Jupiter's moon, Europa.
Glaciologists using ice-penetrating radar have discovered over 150 subglacial lakes scattered widely about the continent. The radar emits VHF radio-waves which travel well in cold ice. When they meet a boundary between two surfaces, say ice and rock, the change in electrical properties between the two media cause the waves to reflect back.
The type of reflection seen from a subglacial lake - a flat and uniformly strong echo - is distinct from an ice-rock contact - an undulating echo of variable strength - making detection of subglacial lakes surprisingly easy.
Extreme survival
Microbiologists think deep-water subglacial lakes are unique extreme environments where unusual microbes might adapt and survive. These environments may be the closest analogues on Earth to Jupiter's moon Europa, which has a thick icy crust above a liquid ocean. They could also be modern analogues to Snowball Earth - periods over 640 million years ago when thick ice may have covered the entire planet.
The locations of Antartic subglacial lakes. The colours refer to the nations who identified them. Lake Ellworth is circled in red. (Click on picture to view a larger version)
We think subglacial lakes are highly likely to have floors made of sediments accumulated over the lifetime of the lakes. For deep-water lakes, such sediments could be as old as the present-day ice sheet and may provide important information on past ice-sheet changes.
This is particularly relevant to the West Antarctic ice sheet, because we know so little about its glacial history, yet this information is critical to assessing ice-sheet stability. Sediments from West Antarctic subglacial lakes may help us understand the present-day risk of ice-sheet collapse.
To find life in subglacial lakes, and to extract sedimentary records of ice-sheet change, scientists must drill down through the ice and take direct measurements and samples. This is far easier said then done. Drilling into subglacial lakes is challenging from technical, logistical and environmental points of view. Because subglacial lakes are pristine environments, and because the levels of life and nutrients are likely to be low, we must ensure we investigate them in ultra-clean conditions.
Avoiding contamination
In other words, researchers must avoid contamination of the lake by the access technique, and equipment used to measure lake water and sediments must be sterile. Hot-water drilling is the best solution for clean lake access: ice coring usually uses an antifreeze drilling fluid and thermo-probing is notoriously unreliable, even over short (less than 100 metres) distances. Once into a lake, scientists will lower instruments down the borehole and into the water column and the lake-floor sediments.
Lake Vostok is not the only lake exciting scientists. A UK-led team has identified Lake Ellsworth in West Antarctica as a prime candidate for exploration (Siegert et al., 2004; Lake Ellsworth Consortium, 2007). In the 2007-08 season, a four-person group conducted a NERC-funded geophysical survey of the lake. From the survey, we estimate the lake is the size of Lake Windermere and is over 100m deep.
Schematic of planned drill mechanism and testing equipment, Cryobot and Hydrobot. (Click on image for a larger version)
As a result, we now know Lake Ellsworth is a deep-water body, and that is likely to have survived the glacial-interglacial cycles of the West Antarctic ice sheet intact. Because of this, the environment in which microscopic life has developed will be ancient, as will the sedimentary records on the lake floor. Lake Ellsworth is indeed an ideal candidate for exploration.
A UK consortium involving over 30 scientists from 15 universities and research centres plan to explore Lake Ellsworth. We will develop a probe, build a hot-water drill and arrange the logistics during the next three years. The access experiment will involve measurements of the lake water and sediment, and the recovery samples for laboratory studies.
The programme aims to answer basic questions such as is there life in subglacial lakes and what is the age of the West Antarctic ice sheet? Given the time needed to develop equipment, the lake access experiment could take place as early as 2012-13, around 100 years since the 'golden age' of Antarctic exploration and, of course, the centenary of the Scott expedition to South Pole!
For details of the UK's plans for the exploration of Lake Ellsworth see the project's website: www.geos.ed.ac.uk/ellsworth. Martin Siegert is the chair of the consortium, and Head of the School of GeoSciences, University of Edinburgh
Keywords:
Antarctic,
Biodiversity,
Environmental change,
Geology,
Oceans,
Polar,
Southern Ocean,
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