Posts Tagged ‘Ross ice shelf’

Japan quake shifts Antarctic glacier, New Scientist reports

March 23, 2011

15:45 15 March 2011 by Anil Ananthaswamy
Original article here

The major earthquake that hit Japan on Friday caused a massive ice stream in Antarctica to momentarily speed up.

As the surface seismic waves generated by the quake travelled around the world, they appear to have given the Whillans ice stream in West Antarctica a nudge, causing it to slide by about half a metre.

The movement was picked up by Jake Walter of the University of California, Santa Cruz, and his colleagues, who monitor the glacier remotely from California. They say the event is an “interesting insight”, but are not suggesting it will destabilise the ice stream in any way.

The Whillans ice stream drains ice from the West Antarctic Ice Sheet into the Ross Ice Shelf. Since 2007, Walter and colleagues have been using GPS field stations on the ice sheet to monitor its movements. They have shown that the ice stream speeds up twice a day in slip events which last about 30 minutes.

The glacier normally creeps along at an average speed of about 1 metre per day. But during a slip event, it slides almost half a metre in one go. The sudden slips are related to the tides, and are strong enough to generate seismic waves that are recorded by stations at the South Pole and the Antarctic Dry Valleys (Journal of Geophysical Research, DOI: 10.1029/2010JF001754).

Slipping glacier

Now it looks like the magnitude 9.0 earthquake that shook Japan last Friday caused the glacier to slip in a similar way.

When Walter and his colleagues were analysing GPS data from the ice stream on Monday, they noticed that one slip event had happened earlier than expected. Further analysis revealed that it happened exactly when surface seismic waves generated by the Japanese earthquake would have hit Antarctica.

Large earthquakes are known to create seismic waves which can circle the planet several times before dying down.

“The Chile earthquake from last year also had a similar effect” on the Whillans ice stream, Walter told New Scientist. “It’s an interesting insight into how large earthquakes might affect glacier motion.”

Walter and colleagues now want to examine data from other large earthquakes to see if any others are linked to slip events of the Whillans ice stream.

Giant iceberg breaks off from Antarctic glacier

June 29, 2010

This undated photo released on February 26, 2010 from the Australian Antarctic Division shows the Mertz Glacier, a 160-kilometer spit of floating ice protruding into the Southern Ocean from East Antarctica. Researchers said on February 25, 2010 that the iceberg the size of Luxembourg - or some 2550 square kilometres in size - knocked loose from the Antarctic continent earlier this month and could disrupt the ocean currents driving weather patterns around the globe. Photograph by: Tony Worby, Australian Antarctic Division/AFP/Getty Images/Handout

Reuters February 26, 2010

SINGAPORE – An iceberg the size of Luxembourg has broken off from a glacier in Antarctica after being rammed by another giant iceberg, scientists said on Friday, in an event that could affect ocean circulation patterns.

The 2,500 sq km (965 sq mile) iceberg broke off earlier this month from the Mertz Glacier’s 160 km (100 miles) floating tongue of ice that sticks out into the Southern Ocean.

The collision has since halved the size of the tongue that drains ice from the vast East Antarctic ice sheet.

“The calving itself hasn’t been directly linked to climate change but it is related to the natural processes occurring on the ice sheet,” said Rob Massom, a senior scientist at the Australian Antarctic Division and the Antarctic Climate and Ecosystems Co-operative Research Centre in Hobart, Tasmania.

Both organisations, along with French scientists, have been studying existing giant cracks in the ice tongue and monitored the bumper-car-like collision by the second iceberg, B-9B.

This 97 km long slab of ice is a remnant of an iceberg of more than 5,000 sq km that broke off, or calved, in 1987, making it one of the largest icebergs ever recorded in Antarctica.

The Mertz glacier iceberg is among the largest recorded for several years. In 2002, a iceberg about 200 km long broke off from Antarctica’s Ross Ice Shelf. In 2007, a iceberg roughly the size of Singapore broke off from the Pine Island Glacier in West Antarctica.

Massom said the shearing off of the ice tongue and the presence of the Mertz and B-9B icebergs could affect global ocean circulation.

The area is an important zone for the creation of dense, salty water that is a key driver of global ocean circulation. This is produced in part through the rapid production of sea ice that is continually blown to the west.

“Removal of this tongue of floating ice would reduce the size of that area of open water, which would slow down the rate of salinity input into the ocean and it could slow down this rate of Antarctic bottom water formation,” he said.

He said there was a risk both icebergs would become grounded on banks or shoals in the area, disrupting the creation of the dense, salty water and the amount that sinks to the bottom of the ocean, he said.

Oceans act like a giant flywheel for the planet’s climate by shifting heat around the globe via myriad currents above and below the surface.

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Original article here