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B-15 iceberg
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In mid-December, a NASA satellite snapped an image of the disintegration of a large iceberg that first broke away from Antarctica nearly 12 years ago, and has been wandering the Southern Ocean ever since.
It's not unusual for icebergs to survive for up to a quarter century if they stay near their birthplace, in the frigid waters surrounding Antarctica; yet if they stray too far north, the massive chunks of ice can quickly disappear, said Ted Scambos, a glaciologist at the National Snow and Ice Data Centre at the University of Colorado, Boulder.

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B-15J iceberg
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On February 1, 2007, one of the pieces from the giant iceberg, named B-15, called B-15J was imaged by NASA’s Aqua satellite. Three smaller bergs were captured splitting off the southeastern quadrant of B-15J. The largest piece, about 18.5 kilometres on its longest axis and 3.7 kilometres at its widest, was named B-15S.

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Credit: NASA

New bergs in Antarctic waters are often first spotted from the remotest of vantage points: space. The new berg was first spotted by scientists at the Antarctic Meteorological Research Centre at the Space Science and Engineering Centre at University of Wisconsin-Madison. The Antarctic Meteorological Research Centre uses daily MODIS imagery along with images from other NASA and NOAA satellites to track the formation and movement of icebergs in Antarctica for both scientific and navigational purposes.

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RE: B-15A iceberg
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This image was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua and Terra satellite on November 4.


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NASA images courtesy Jeff Schmaltz.

The shrinking B-15A iceberg was moving out of the Ross Sea on the East Wind Drift, an ocean surface current that circles Antarctica counterclockwise. The iceberg’s departure was, no doubt, a relief to denizens of the Ross Sea region. From 2000 to 2003, the iceberg lurked off Ross Island, the location of the U.S. Antarctic Program’s McMurdo Research Station. In 2004, the berg began to drift north, trapping sea ice in McMurdo Sound. The excess sea ice stranded penguins, who could not reach open water and return with food for their young. The shifting berg also made planning a shipping route through the ice to McMurdo Station difficult.

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The B-15A iceberg has finally broken into smaller pieces off Antarctica's Cape Adare, after five years of being the world's largest free-floating object.

ESA's Envisat satellite's Advanced Synthetic Aperture Radar (ASAR) has been tracking the movement of the drifting ice object continuously since the beginning of this year. Its latest imagery reveals the bottle-shaped iceberg split into nine knife-shaped icebergs and a myriad of smaller pieces on 27-28 October, the largest being formed by fractures along the long axis of the original single iceberg.

Measuring – until last week - around 115 kilometres in length with an area exceeding 2500 square kilometres, the B-15A tabular iceberg had apparently run aground off Cape Adare, the northernmost corner of the Victoria Land Coast. This stranding appears to have led to flexing and straining which resulted in the break-up.

"The long knife-shaped pieces suggest the iceberg has split along existing lines of weakness within the iceberg. These would have been pre-existing fractures and crevasses in the ice shelf" - Mark Drinkwater of ESA's Ocean and Ice Unit.


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These new icebergs, named by the US National Oceanic and Atmospheric Administration (NOAA) National Ice Centre, will retain their parent's title: the three largest island-sized pieces have been called B-15M, B-15N and B-15P.

B-15A was the largest remaining section of the even larger B-15 iceberg that calved from the nearby Ross Ice Shelf in March 2000 before breaking up into smaller sections off McMurdo Island.

Since then its B-15A section drifted into McMurdo Sound, where its presence blocked ocean currents and led to a build-up of sea ice that decimated local penguin colonies, deprived of open waters for feeding. During the spring of this year prevailing currents took B-15A slowly past the Drygalski ice tongue. A full-fledged collision failed to take place, but a glancing blow broke the end off Drygalski in mid-April.

The iceberg sailed on to have a less-destructive close encounter with the Aviator Glacier ice tongue at Lady Newnes Bay before becoming stranded off Cape Adare in mid-October.

ASAR is extremely useful for tracking changes in polar ice. ASAR can peer through the thickest polar clouds and work through local day and night. And because it measures surface texture, the instrument is also extremely sensitive to different types of ice – so the radar image clearly delineates the older, rougher surface of icebergs from surrounding sea ice, while optical sensors simply show a continuity of snow-covered ice.

Envisat's ASAR instrument monitors Antarctica in two different modes: Global Monitoring Mode (GMM) provides 400-kilometre swath one-kilometre resolution images, enabling rapid mosaicing of the whole of Antarctica to monitor changes in sea ice extent, ice shelves and iceberg movement.

Wide Swath Mode (WSM) possesses the same swath but with 150-metre resolution for a detailed view of areas of particular interest.

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The mammoth B-15A iceberg appears poised to strike another floating Antarctic ice feature, a month on from a passing blow that broke off the end of the Drygalski ice tongue.

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As this Envisat image reveals, this time its target is the ice tongue of the Aviator Glacier.
Measuring around 115 kilometres in length with an area exceeding 2500 square kilometres, the B-15A iceberg is the world's largest free-floating object. It is the largest remaining section of the even larger B-15 iceberg that calved from the Ross Ice Shelf in March 2000 before breaking up into smaller sections.

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