Exploring Hodgson Lake
6 July 2009
A previously unexplored lake, hidden beneath four metres of ice in Antarctica, contains almost pure water with virtually nothing in it and no solid evidence for life. This is the first report on the exploration of the subglacial lake.
Citadel Bastion and the subglacial Hodgson Lake in Alexander Island in Antarctica.
Hodgson Lake was discovered in 2000, during an aerial survey of Alexander Island, offshore the Antarctic Peninsula. 'We spotted an area of flat ice from the aircraft and decided to investigate it further,' says Dr Dominic Hodgson, from the British Antarctic Survey (BAS).
The link between the freshwater lake's name and the lead author of the study is not a coincidence: 'We first proposed to call it Citadel Lake, after a nearby mountain,' says Hodgson, 'but the UK Antarctic Place-Names Committee objected to the idea and named the lake after me instead.'
Preliminary reports suggested that the lake is about 2km long by 1.5km wide and is about 90 metres deep. In this study, Hodgson sampled the four-metre thick ice cover, the lake's water and the bottom sediments, with the help of colleagues from the BAS and several universities from the UK and Belgium.
They found... nothing. The analyses show that the Hodgson Lake water 'is one of the clearest water lakes I have ever worked on, clearer than the distilled water we use in our lab, with almost nothing in it,' says Hodgson. The samples have virtually no nutrients such as nitrogen and phosphorus, and very low measurements of other chemical elements.
The water at Hodgson Lake is very clear because it was never contaminated by direct contact with the atmosphere and has 'no conclusive signs of life,' says Hodgson.
Water in subglacial lakes comes from ice that melted naturally at the bottom of the ice sheets, due to the pressure from the ice cap above and the heat released by the rocks from below. Nowadays, Hodgson Lake is blanketed by four-metres of ice, but in the past the cover was over 400 metres thick, making it a subglacial lake
Sediments at the bottom
Despite being sealed off by the ice, the bottom floor of Hodgson Lake is covered by a thick layer of sediments, just like any open lake. This is because 'glacial ice contains clays silts, sands and pebbles picked up from the surrounding rock surfaces,' explains Hodgson. These particles are trapped during ice formation together with particles and dust from the atmosphere. 'As the ice melts these particles are deposited,' he adds.
Hodgson and his colleagues used a 3.8m sediment core from the bottom to estimate the lake's age using a combination of radiocarbon dating and other analytical methods. The findings, published this week in Quaternary Science Reviews, suggest that the sediments at the bottom of the lake are between 30,000 and 90,000 years old.
What will happen to Hodgson Lake? 'If the Antarctic Peninsula ice continues to disappear at the present rate,' says Hodgson, 'the edges of the lake will melt and eventually cyanobacteria, green algae and other small organisms will become established.
In the meantime Hodgson Lake, with an ice cover of only four metres, is a perfect place to experiment with methods needed to study other subglacial lakes. Lake Ellsworth, for instance, lies under 3.4 km of ice beneath West Antarctica and is a big technical challenge. Hodgson Lake is a 'test run' to more technically demanding projects, used to 'refine techniques and calibrate detection limits to save time and expense,' says Hodgson.
D.A. Hodgson, S.J. Roberts, M.J. Bentley, J.A. Smith, J.S. Johnson, E. Verleyen, W. Vyverman, A.J. Hodson, M.J. Leng, A. Cziferszky, A.J. Fox, D.C.W. Sanderson. Exploring former subglacial Hodgson Lake, Antarctica Paper I: site description, geomorphology and limnology. Quaternary Science Reviews, available online 12 June 2009. doi:10.1016/j.quascirev.2009.04.011
D.A. Hodgson, S.J. Roberts, M.J. Bentley, E.L. Carmichael, J.A. Smith, E. Verleyen, W. Vyverman, P. Geissler, M.J. Leng, D.C.W. Sanderson. Exploring former subglacial Hodgson Lake, Antarctica. Paper II: palaeolimnology. Quaternary Science Reviews, available online 30 June 2009. doi:10.1016/j.quascirev.2009.04.014
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