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Over The Horizon

Rocky Images and Icy Depths

Researchers have been peering deep under the Ross Ice Shelf, using explosives to produce seismic reflection images of the rock layers thousands of metres below.

The 10-kilometre long profile shows sedimentary layers more than two kilometres thick lying beneath the ice and water layers of the Ross Ice Shelf. The rock has been found to dip steeply towards Ross Island. Scientists from the Institute of Geological and Nuclear Sciences are analysing the seismic data to see if the sedimentary rock continues on under the later volcanic flows associated with Ross Island.

Researcher Dr Stephen Bannister says that they hope to be able to interpret the data in terms of advances and retreats of the Antarctic ice sheet.

He believes that the sediments imaged by the work are likely to be of marine glacial origin. If so, this would indicate that the ice cap itself is rather ephemeral, geologically speaking, having retreated just a few million years ago to allow a marine seaway to advance well into the continent.

Meanwhile, a team of scientists led by Dr Clive Howard-Williams of the National Institute of Water and Atmospheric Research have been peering deep under the ice of Antarctic lakes, investigating the water and its inhabitants.

New measurements mean that Lake Wilson is now the deepest known lake in the Ross Dependency at 105 metres, and is probably one of the deepest lakes in Antarctica. It has risen at least ten metres since it was last measured in 1975.

Because the wind is unable to stir up the water under its cover of ice, the lake has an interesting layered structure, with the lower layers rich in salts and bacterial activity. All available oxygen in the bottom 20 metres has been used up.

Bacteria are also abundant in the surrounding ponds, and Dr Howard-Williams says that the sources of nutrients for the bacteria are particularly interesting. "For instance, nitrates in the ponds (containing cyanobacteria) were found to be up to 100 parts per million, which in New Zealand would be considered polluted water, he notes.