December 20, 2010

Cryosat-2 Maps Ocean Circulation In The Arctic Basin

The Cryosat-2 spacecraft has provided a new map of ocean circulation across the Arctic basin.

The spacecraft's primary mission is to measure sea-ice thickness, which has been in sharp decline in recent decades. However, Cryosat's ability to map the shape of the sea surface will allow scientists to determine if Arctic currents are changing as a result of winds being blown more easily on ice-free waters.

"Nobody really knows how the Arctic is going to behave as the ice retreats, but we do anticipate that significant changes will occur," said Seymour Laxon, a Cryosat science team member from University College London, told BBC News.

"This is just the first data, and it shows we now have the tool to monitor what is happening," he said.

Laxon presented the first Cryosat result in San Francisco at the American Geophysical Union (AGU) Fall Meeting, which is the world's largest annual gathering of Earth and planetary scientists.

The European Space Agency (ESA) satellite was launched this year in April.

The satellite carries one of the highest resolution synthetic aperture radars that was ever put into orbit.

The instrument sends down pulses of microwave energy with bounce off both the top of the Arctic sea-ice and the water in the cracks, or leads.

By measuring the difference in height between these surfaces, scientists will be able to work out the overall volume of the marine ice cover in the far north.

Cryosat becomes a powerful tool to study ocean behavior when it senses the surface of the water.

The opening months of observations have enabled the Cryosat team to build a unique map from the radar echoes bouncing off leads.

This map describes what researchers call ocean dynamic technology.

It is the height of the water surface above the gravitational level in the Arctic.

The map shows where water is piled up.

"What we've revealed is the first complete picture of ocean dynamic topography in the Arctic Ocean. All missions previously have had large holes in the middle of their Arctic data because of their orbits, even the American Icesat satellite which did a pretty good job of getting dynamic topography - it only went up to 86 degrees North. Cryosat goes up to 88 degrees North."

Ocean currents in the Northern Hemisphere move clockwise around high in topography and anti-clockwise around the lows.

The Cryosat team says that the map is built from early data and is only a first, static snapshot.

However, they said that over the course of the mission, this data-set will be improved and will provide telling evidence of any changes in Arctic Ocean circulation.

The region witnessed a dramatic retreat of Arctic sea-ice in summer months, which is far ahead of what the majority of climate computer models had forecast.

Scientists know that there is now a lot of warm water at depth in the Arctic.

This deep water's energy is not allowed to influence the sea-ice because of a buffer of colder, less dense water lying between it.

Cryosat is intended to help improve the performance of computer models that are used to try to forecast future climate behavior.

"The reason we believe all this is important is because we think from models that a retreat of the ice is going to significantly affect the circulation in the Arctic, and Cryosat is the only tool we've got to measure those changes," Laxon told BBC.


Image Caption: Artist's impression of CryoSat-2 in orbit. Credit: ESA


On the Net: