SYDNEY, Aug 12, 2008 (AFP) - Huge elephant seals have been recruited to help scientists break through a critical blind spot and chart climate change under the Antarctic sea ice in winter, researchers said Tuesday.

The seals, which can weigh up to three tonnes, are fitted with sensors that transmit previously unavailable data to satellites when they surface to breathe.

"They have made it possible for us to observe large areas of the ocean under the sea ice in winter for the first time," said Steve Rintoul of Australia's Antarctic Climate and Ecosystem Cooperative Research Centre.

"Satellites can't see the ocean through the ice and the profiling floats we are using throughout the world's oceans now are also unable to surface through the ice and transmit their data by satellite."

The seals, however, measure temperature, salinity and depth as they dive up to nearly two kilometres (1.25 miles) and cover distances of up to 65 kilometres a day.

They have provided a 30-fold increase in data over conventional methods, Rintoul and French, Australian, US and British scientists say in a paper published in the American publication, Proceedings of the National Academy of Sciences.

The polar regions play an important role in the Earth's climate system and are changing more rapidly than any other part of the world, with the potential to accelerate the rate of change elsewhere, scientists say.

One of the most innovative aspects of the seal-borne research was using the data on changes in salinity that the animals provided to infer how much sea ice had formed during the winter, Rintoul said.

"The sea ice is important for climate because it is bright and reflects the sun's energy back into space, so if we have less sea ice the Earth tends to absorb more energy and so warm up.

"We've never been able to measure how much sea ice is actually forming before and the seal data is allowing us to do that for the first time," he said.

The sensors, about the size of a mobile phone, are fitted when the seals return to sub-Antarctic islands to breed and to moult during the summer.

Once they have grown the next season's fur, the sensors are glued to the fur on the back of the animal's head, so when it surfaces to breathe the sensor is out of the water and the antennae can transmit the data to satellite.

Though the seals are not particularly concerned about humans and scientists can approach them quite close, the animals are sedated with a syringe on the end of a pole to ensure the sensors can be attached safely, Rintoul said.

The sensors stay on through the winter season and fall off when the seals return to the islands and shed their fur for the summer.

Rintoul said the researchers have a new experiment under way in connection with the International Polar Year and involving scientists from a number of countries.

"We will be instrumenting a total of about 160 seals both in the Arctic and Antarctic, using several different species of seal because different seals go to different places to feed so we can get information from different parts of the ocean."

The data from the Antarctic seals does not yet allow scientists to draw firm conclusions about changes in the world under the sea ice since it is so new there is nothing to compare it with.

But the information from the seals will provide a baseline for future climate change studies, Rintoul said.