Bitter cold and floating sea ice long frustrated scientists seeking to study the ocean around Antarctica in winter. The solution: Send in the seals.
The polar regions are expected to be especially sensitive to climate change, but collecting data has been a problem, especially in the wind-whipped Southern Ocean surrounding Antarctica.
So researchers led by Jean-Benoit Charrassin of the National Museum of Natural History in Paris decided to recruit help from residents of the area.
They glued electronic data-collecting equipment to dozens of elephant seals that lived in the region. The animals can dive more than a mile deep in search of food.
The machines radioed back information on temperature, pressure, salinity and position whenever the seals surfaced.
The seals swimming under winter sea ice have overcome a "blind-spot" for scientists by allowing them to calculate how fast sea ice forms during winter.
Sea ice reflects sunlight back into space, so less sea ice means more energy is absorbed by the earth, causing more warming.
"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 from Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO), co-author of a new study documenting the work.
Thousands of ice profiles
The result: Nine times more data than had been previously available from buoys and ships and 30 times more information than had been known from beneath the winter sea ice, the researchers report in Tuesday's edition of Proceedings of the National Academy of Sciences.
Between 2004 and 2005, the seals swam up to 40 miles a day, supplying scientists with 16,500 ice profiles, including 4,520 from beneath the sea ice. The seals dived to a depth of more than 1,500 feet on average and to a maximum depth of nearly a mile.
With the information, the scientists are mapping the water properties of the Southern Ocean, including the main fronts where the properties of the water change. They report that formation of sea ice peaked in April and May — early winter in the Southern Hemisphere.
"If we want to understand what's going to happen to climate in the future we need to know what the sea ice is going to do. Will there be more or less and will it form more or less rapidly?" Rintoul told Australian Broadcasting Corp. radio.
"Until now, our ability to represent the high-latitude oceans and sea ice in oceanographic and climate models has suffered as a result," said Rintoul, who also works with the Antarctic Climate and Ecosystems Cooperative Research Center in Hobart.
Rapidly warming seas
The polar regions play an important role in the earth's climate and are changing more rapidly than any other part of the world, with the Southern Ocean warming more rapidly than the global ocean average.
Sea ice not only affects the amount of energy reflected back into space, but also the amount of dense water around the Antarctic which drives ocean currents that transports heat around the globe.
Sea ice also provides a critical habitat for krill, penguins and seals.
Funding for the study was provided by government and research agencies in France, Australia, the United States and United Kingdom.