sciencetech-blog

comments

Scientists have made the first ever detailed 3D images of polar sea ice, using an underwater robot.

The depth of Antarctic ice has previously been difficult to measure using satellites because it is often covered in a thick blanket of snow.

But now, the high-resolution maps of Antarctic sea ice will help scientists investigate dramatic changes in the polar region - and the results have already revealed the ice is thicker than first thought.

A team of UK, US and Australian researchers have measured Antarctic sea ice. They found it was up to 56ft (17 metres) thick in places - much thicker than expected. The measurements were made using an underwater robot called SeaBed, also called 'Jaguar', which is pictured mapping under the sea ice

The measurements were carried out by an autonomous underwater vehicle (AUV) known as SeaBed, which provides a new way of mapping sea ice, from below.

It was built and operated by engineers from Woods Hole Oceanographic Institution (WHOI) in Massachusetts, while the project also involves scientists from the UK, US and Australia.

In some areas, the team found ice up to 56ft (17 metres) thick - much thicker than that measured by previous techniques - but the exact thickness, and the differences in thickness is not known. 

The research was reported in the journal Nature Geoscience.

The submarine is 6.5ft (two metres) long and operates at a depth of 66ft to 98ft (20 to 30 metres), bouncing sound waves off the under-surface of the ice.

Satellites can measure large-scale ice thickness, but their data is often difficult to interpret because of snow covering the ice.

Man-made measurements carried out by drilling holes and observations from ships, meanwhile, are more accurate but are limited by lack of access.

But the submarine can measure the thickness of the ice much more accurately.

Three locations around the Antarctic Peninsula were mapped - the Weddell, Bellingshausen and Wilkes Land sectors covering an area of 5.4 million square feet (500,000 square meters). 

'Our surveys indicate that the floes are much thicker and more deformed than reported by most drilling and ship-based measurements of Antarctic sea ice,' the researchers wrote in their paper.

'We suggest that thick ice in the near-coastal and interior pack may be under-represented in existing in situ assessments of Antarctic sea ice and hence, on average, Antarctic sea ice may be thicker than previously thought.' 

Ice floes - packs of floating ice - are shown in various regions of Antarctica. Previous data is in green (ship-based) and red (drill data), while the latest data using the SeaBed robot is shown in the blue squares. The team measured sectors covering an area of 5.4 million square feet (500,000 square meters)

The submarine was built and operated by engineers from Woods Hole Oceanographic Institution (WHOI) in Massachusetts, US. In some areas they found ice up to 56 feet (17 metres) thick - much thicker than that measured by previous techniques (stock image of Weddell Sea ice shown)

The data from SeaBed, combined with airborne measurements of sea-ice surface elevation, ice coring surveys, and satellite observations, vastly improves scientists' estimates of ice thickness and total sea ice volume. 

The next step is for the scientists to carry out large-scale surveys that can be compared to large-scale observations from aircraft and satellites.

Dr Jeremy Wilkinson, from the British Antarctic Survey, said: 'The AUV missions have given us a real insight into the nature of Antarctic sea ice - like looking through a microscope.

'We can now measure ice in far greater detail and were excited to measure ice up to 17 metres [56 feet] thick.'

Here, researchers drill through the sea ice in the Bellingshausen Sea to position a navigational transceiver before a deployment of SeaBed. The data from SeaBed, combined with airborne measurements of sea-ice surface elevation, ice coring surveys, and satellite observations, improves estimates of ice thickness

The mapping by the submarine was undertaken in two expeditions during 2010 and 2012.

Routine surveys will now allow the team to monitor changes over long periods of time.

Dr Hanumant Singh, a member of the WHOI team, added: 'Putting an AUV together to map the underside of sea ice is challenging from a software, navigation and acoustic communications standpoint.

'SeaBed's manoeuvrability and stability made it ideal for this application where we were doing detailed floe-scale mapping and deploying, as well as recovering in close-packed ice conditions.

'It would have been tough to do many of the missions we did, especially under the conditions we encountered, with some of the larger vehicles.' 

The submarine (shown) is 6.5ft (two metres) long and operates at a depth of 66ft to 98ft (20 to 30 metres), bouncing sound waves off the under-surface of the ice. Satellites can measure large-scale ice thickness, but their data is often difficult to interpret because of snow covering the ice

And Professor Mike Meredith, deputy director of science at the British Antarctic Survey, said: 'Sea ice is changing in both polar regions, with important consequences for climate and the ecosystem.

'In contrast to the Arctic, the changes around Antarctica vary from region to region, but full understanding of the causes and impacts of these changes requires detailed knowledge of how thick the ice is, which has historically proven very hard to get.

'Satellites can now give information about this over large areas, but proper interpretation of the satellite data requires direct measurements also. 

'This new paper presents important results obtained from a novel underwater vehicle that radically change our concepts of the structure of Antarctic sea ice, and the processes that influence it. Such understanding is key to improving our models of how sea ice will change into the future.'