SYDNEY, 3 July 2006 – Even in the frigid gloom of an Antarctic lake, 18 metres below the surface, algae is converting light into energy.

Scientists from New Zealand's National Institute of Water and Atmospheric Research (NIWA) have been studying the microscopic algae that live under these extreme conditions and were excited to find that these microbes are still able to photosynthesise in the near-dark.

"We had seen them photosynthesise in the lab," said Kay Vopel, one of the aquatic ecologists who made the discovery. "But we couldn't say for certain how they would behave until we actually went down and studied them in situ."

Vopel and fellow scientist Ian Hawes made the measurements in November 2004 at Lake Hoare, an 18-metre deep ice-covered melt-water lake in the Dry Valleys of Antarctica. Scientists have long been interested in the bacteria and microscopic algae that inhabit such lakes, because they offer insights into the extreme conditions under which life can exist.

The major issue that could affect the photosynthesis is the light. The ice that covers the lake is so thick that the scientists weren't sure whether the microbes would still be able to photosynthesise with such a small amount of light reaching those depths. They found that these algae can use what little light is available and photosynthesise quite successfully.

These are among the lowest natural light levels at which photosynthesis has ever been recorded. "There are some tantalising observations of marine plants growing on rocks in very deep water, and of algae and cyanobacteria growing in caves where there may be even less light, but these are certainly amongst the lowest where field observations have been made," says Hawes.

This discovery, published in the July issue of Limnology and Oceanography, can not only help to shed light on the past Antarctic climate, but could even glean an insight into finding life on other planets. If microbes can survive in these harsh conditions, it may provide insight into where and how life originated on earth, and where evidence of life might occur on other planets in our solar system.

But this is not the end of the Lake's role in understanding hostile environments. Since the photosynthesising microbes were only measured in a certain part of the lake, Vopel and Hawes plan to return in November to measure bacteria that use other chemicals such as hydrogen sulphide.