Another Massive Iceberg is Calved in Antarctica, With Implications for Local Ocean Circulation and Wildlife

Researchers announced yesterday (26 February 2010) that a giant iceberg has collided with a seaward extension of East Antarctica's Mertz Glacier, breaking a huge chunk off of the glacier to form a second iceberg 78 km (48 miles) long, 33 to 39 km (21-24 miles) wide and 400 m (0.25 mile) thick.  A team of Australian and French scientists say that "[t]he future behavior of the two icebergs is of great interest," with potential impacts on local ocean circulation, and on the region's marine biology -- including emperor penguins.

Until earlier this month, the "tongue" of the Mertz Glacier extended 160 km into the Southern Ocean from the glacier's "grounding line," the point beyond which the tongue of ice floats on the ocean's surface.  Since 1992, a large iceberg called B-9B, sat 100 km to the east on the Ninnis Bank where it had run aground.  B-9B was a piece of a larger iceberg called B-9 that had broken off of (or "calved" from) the Ross Ice Shelf in 1987.  See What's Happening: Another Massive Iceberg is Born [PDF] (2002) for an illustration showing the tracks of these and other icebergs around Antarctica.  See the image below, showing the relationship between the Mertz Glacier tongue and iceberg B-9B at the end of December 2007.

The image below, from the European Space Agency, showing the Mertz Glacier Tongue on the left and the very large Iceberg B-9B to the right on 11 December 2007. 

After about 18 years in the same place, iceberg B-9B -- now 97 km by 20-35 km -- floated free and rotated into the Mertz Glacier tongue.  The iceberg collided with the Mertz Glacier tongue around 7 February, and by 12/13 February a large piece of the tongue broke off at a point where existing rifts on the glacier tongue created a weak spot. By 20 February, the newly calved iceberg from the Mertz Glacier was drifting free from the glacier.  The three images below document the changes from 7 January through 20 February. 

B9B approaches the Mertz Glacier tongue 7 January 2010.  Photo: Neal Young
Above: B9B approaches the Mertz Glacier tongue 7 January 2010. Photo: Neal Young

B9B makes contact 7 February 2010.  Photo: Neal Young
Above: B9B makes contact 7 February 2010.  Photo: Neal Young

 The Mertz Glacier tongue breaks off 20 February 2010.  Photo: Neal Young
Above: The Mertz Glacier tongue breaks off 20 February 2010. Photo: Neal Young

The Mertz Glacier tongue now extends only 80 km from the glacier's grounding line, i.e. the length beyond the grounding line has been cut in half.

The dramatic change in the Mertz Glacier tongue, and the movement of the two massive icebergs is particularly important because of the Mertz Glacier Polynya that forms each Winter to the West of the glacier tongue.  According to the Antarctic Climate & Ecosystems Cooperative Research Centre (ACE CRC) (Antarctic polynyas: Nature’s sea ice factories):

"A polynya is a large body of open water or an area covered by very thin ice that persists in the middle of winter sea ice in the polar regions... Although relatively small in area, coastal polynyas play a disproportionately important role in many important physical and biological processes in the high-latitude Southern Ocean, as well as having an impact on global ocean circulation."

ACE CRC says, for example that "the Mertz Glacier Polynya ... covers only 0.001% of the overall Antarctic sea ice zone at its maximum winter extent, but is responsible for 1% of the total sea ice production in the Southern Ocean."

The collision of the B-9B glacier into the Mertz Glacier tongue was detected and initially reported by a joint French-Australian team working on a project called “CRACICE” (Cooperative Research into Antarctic Calving and Iceberg Evolution).  According to a press release [PDF] issued by the team, the volume of ice in the new iceberg "represents about 70 years of glacier advance." 

The press release [PDF] said:

The future behavior of the two icebergs is of great interest. Satellite images show that the recently-calved Mertz iceberg is moving into the Adélie Depression, a coastal basin situated between the Mertz Glacier and the French Antarctic station of Dumont D’Urville to the west. This depression one of the major sites of dense water formation which drives the world’s deep ocean circulation. The dense water is formed from ocean water that circulates onto the continental shelf and interacts with the glacier tongue, and by high rates of sea ice formation within the Mertz Glacier polynya to the immediate west of the former glacier tongue. The future position of the two giant icebergs will likely affect local ocean circulation, the extent (and timing?) of the polynya, sea ice production, and deep water formation...This calving is indeed a unique in-situ sensitivity experiment that will help to evaluate the climatic impacts of this region on the large scale ocean circulation." [emphasis added]

The scientists also report that the event has "important implications for the marine biology of this region." It says that the region's polynyas "constitute places of high biodiversity and food concentration for birds and marine mammals, in particular emperor penguins the only birds to reproduce during winter in Antarctica. The emperor colony at Pointe Géologie, next to Dumont d’Urville, is closely dependent on the ocean resources. Therefore significant modifications in the marine environment may have large consequences, not only on the local biodiversity but also on this emblematic penguin colony that was brought to prominence in the movie by Luc Jacquet March of the Penguins..." [emphasis added]

Aptenodytes forsteri Emperor penguin Adults and chicks Dawson-Lambton Glacier, Antarctica.  Source: Fritz Polking / WWF.
Above: Aptenodytes forsteri Emperor penguin Adults and chicks Dawson-Lambton Glacier, Antarctica.  Source: Fritz Polking / WWF.

We reported in January that Antarctica is losing more than 24 cubic miles of ice annually -- and the pace is accelerating.  Last year was the warmest on record for the Southern Hemisphere, and January 2010 was the warmest January on record (see NASA: After Warmest Year on Record, Southern Hemisphere Starts 2010 With Record-Shattering January, 17 Feb 2010). 

Online Resources:

NASA's Earth Observatory:

Mertz Glacier.  MODIS image from 26 September 2001, 23:00.  From the U.S. National Snow and Ice Data Center.

Massive iceberg calves from the Mertz Glacier.  Press release (26 Feb 2010) from Australian Antarctic Division.

National Snow and Ice Data Center:

Antarctic Climate & Ecosystems Cooperative Research Centre. "The ACE CRC is a unique collaboration between core partners the Australian Antarctic Division, CSIRO Marine and Atmosphere, the University of Tasmania, the Bureau of Meteorology and a consortium of supporting partners. It is funded by the Australian Government’s Cooperative Research Centre Program. The ACE CRC’s mission is to understand the crucial role played by Antarctica and the Southern Ocean in global climate, and the impacts of climate change on Australia and the world, and to inform governments, industry, the community and scientists about climate change to guide our future."

Modeling water mass formation in the Mertz Glacier Polynya and Adélie Depression, East Antarctica.  By Marsland, S. J., N. L. Bindoff, G. D. Williams, and W. F. Budd in  J. Geophys. Res., 109, 4 November 2004.

State of Antarctica: red or blue?  Realclimate, 21 January 2009.

What's Happening: Another Massive Iceberg is Born [PDF] .  By Neal Young in Australian Antarctic Magazine, Spring 2002.

New Research Sheds Light On Antarctic Ice Melting.  National Public Radio, All Things Considered, 28 Feb 2010.



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