Greenland Glacier Calves the Arctic's Largest Ice Chunk in Nearly a Half-Century

One of the largest of Greenland's marine "outlet" glaciers (i.e. glaciers ending in the sea) has calved an enormous "ice island" that reportedly extends over 100 square miles.  Not since 1962, when a 250 square mile island was formed from the Ward Hunt Ice Shelf, has such a large area of ice been calved in the Arctic.

Above: Satellite image from Aug. 5, 2010, shows the huge ice island calved from Greenland's Petermann Glacier. Source: Prof. Andreas Muenchow, University of Delaware.

“In the early morning hours of August 5, 2010, an ice island four times the size of Manhattan was born in northern Greenland,” says Andreas Muenchow, associate professor of physical ocean science and engineering at the University of Delaware's College of Earth, Ocean, and Environment in a press release (Greenland Glacier Calves Island 4 times the Size of Manhattan, UD Scientist Reports, 6 August 2010) from University of Delaware. The ice island was calved by the Petermann Glacier on the Northwest corner of Greenland.

The Byrd Polar Research Center in Petermann Glacier Front Breakup, July-August 2008 (August 19th, 2008) said that Between 2001 and 2007, 86.8 sq. km (33.5 sq. mi.) broke away from the glacier.  Then in 2008, the center reported that the glacier during the July-August period calved a 29 sq. km. (11 sq. mi.) area of ice. It warned that "more breakup is imminent in the next year, for a large crack has widened while moving toward the calving front."

Writing in RealClimate's What links the retreat of Jakobshavn Isbrae, Wilkins Ice Shelf and the Petermann Glacier?, Mauri Pelto said in October 2008 that the glacier's floating tongue extended 80 km into the sea and covered an area of roughly and 1300 km2 (in area).  "This makes it (by area) the largest floating glacier in the Northern Hemisphere," said Peltro. 

Greenland's Petermann Glacier in 2009. Source: Prof. Andreas Muenchow, University of Delaware.

Above: Greenland's Petermann Glacier in 2009. Source: Prof. Andreas Muenchow, University of Delaware.

"We expected Petermann Glacier to lose up to 100 sq. km ice area this summer," the Byrd Polar Research Center reported last October (2009) in Greenland glaciers continue to lose ice area (15 October 2009), "but it held together and even advanced 2 sq km despite warmer than normal surface air temperatures."

With the massive ice island calved by the glacier on August 5, 2010, the Petermann Glacier made up for lost time.  The glacier lost not just the 100 square km the Byrd Polar Research Center  had anticipated in 2009, but lost at least 260 square km (100 square miles) of ice -- about a quarter of its floating ice-shelf

According to the University of Delaware press release on Friday, the ice island has a "thickness up to half the height of the Empire State Building."  Professor Muenchow said:  “The freshwater stored in this ice island could keep the Delaware or Hudson rivers flowing for more than two years. It could also keep all U.S. public tap water flowing for 120 days,”

The calving of the ice island is part of a larger trend of ice loss in the area.  In Greenland glaciers continue to lose ice area (15 October 2009) the Byrd Polar Research Center said:

"Our 2009 area change survey of 34 of the widest Greenland marine-terminating glacier outlets from the inland ice sheet is complete. We find a net marine-terminating ice area loss of 109 sq km. The total net cumulative area change from year 2000 (when our survey begins) to 2009 is -990.2 sq. km, a loss equivalent [to]... an area more than 11 times the area of Manhattan Is. (87.5 sq. km) in New York, USA. The marine-terminating ice area change for these glaciers is -106 sq. km per year, the 2009 loss being within 3% of the linear fit. In other words, and as you can see below, the loss rate has been nearly constant. Though, on a glacier by glacier basis, the loss rate is not constant."

Above: cumulative annual area changes for 34 of the widest Greenland ice sheet marine-terminating outlets.  Source: Byrd Polar Research Center.

To put the Petermann Glacier's latest ice island in perspective, the island's area of at least 260 sq. km is well over twice what all 34 glaciers surveyed by the  Byrd Polar Research Center have been losing annually (-106 sq.km per year).

A month ago, on July 6 and 7, scientist documented the breakup up of a 7 square kilometer (2.7 square mile) section of another glacier in the region, the Jakobshavn Isbrae glacier. According to Researchers Witness Overnight Breakup, Retreat of Greenland Glacier, a feature article (9 July 2010) from NASA, "[t]he calving front – where the ice sheet meets the ocean – retreated nearly 1.5 kilometers (a mile) in one day and is now further inland than at any time previously observed."  See figure below. 

Location of the successive calving fronts of the Jakobshavn Isbrae glacier between 1851 and 2009, overlain on a Landsat image from 7/29/2009.  Source: NASA/Goddard Space Flight Center Scientific Visualization Studio. Historic calving front locations courtesy of Anker Weidick and Ole Bennike, Geological Survey of Denmark and Greenland.

Climate Change is accelerating the rate of ice loss from Greenland -- and the ice loss is adding to sea level rise

As we reported in our earlier post, Warm Ocean Waters are Speeding Greenland Glacier Melt (21 Feb 2010), the floating ice of outlet glaciers is vulnerable to basal melting by seawater circulating under the ice.  The glaciers are melting much faster from below than they are from above  where warm air temperatures drive the melting. In its report,Abrupt Climate Change , the U.S. Global Change Research Program (USGCRP) in December 2008 highlighted the potential importance of such melting. "The interaction of warm waters with the periphery of the large ice sheets represents one of the most significant possibilities for abrupt change in the climate system," it said.

Writing in RealClimate's What links the retreat of Jakobshavn Isbrae, Wilkins Ice Shelf and the Petermann Glacier? (2008), Mauri Pelto explained that a key to Petermann's major ice losses during the last decade is thinning of the glacier's floating tongue of ice.  That weakens the ice, increasing ice losses through calving. The melting and calving together reduce the downward pressure of the glacier at the grounding line where the floating portion of the glacier meets the rest of the glacier that rests on land.  As that downward pressure at the groundlng line is reduced, the glacier can move more quickly  to the sea.  Ultimately, more ice mass is lost to the sea and the glacier recedes.

We reported in Dramatic Ice Loss Spreads to Northwest Coast of Greenland (23 March 2010) that the region was losing much more ice in the area where the Petermann glacier is located.  "Our speculation is that some of the big glaciers in this region are sliding downhill faster and dumping more ice in the ocean," said John Wahr, a coauthor of Spread of ice mass loss into northwest Greenland observed by GRACE and GPS published in Geophysical Research Letters (19 March 2010).  Shfaqat Abbas Khan, lead author of the article, says: "If this activity in northwest Greenland continues and really accelerates some of the major glaciers in the area -- like the Humboldt Glacier and the Petermann Glacier -- Greenland's total ice loss could easily be increased by an additional 50 to 100 cubic kilometers (12 to 24 cubic miles) within a few years." [emphasis added].

Above: The mass changes of the Greenland Ice Sheet (GIS) for the period April 5, 2003 - July 25, 2009.  The spatial variation in surface mass is shown in centimeters equivalent height of water. The time variation of the GIS mass (in Gigtons) is shown in the x-y plot insert.  Source: NASA/Goddard Space Flight Center Scientific Visualization Studio. 

Dr. David Carlson, Director of the International Polar Year International Program Office said in a statement before the Senate Foreign Relations Committee hearing on "The Global Implications of a Warming Arctic" in May 5, 2009:  “A clear consensus has emerged during IPY [International Polar Year] that the Greenland Ice sheet will disappear as a consequence of this current global warming.”  Carlson added that a “very plausible outcome” is  “a meter or more of sea level rise in this century from Greenland alone.”  

Online Resources

NASA Polar Ice Expert on Climate Change and Greenland's Ice Loss: "We Need to Take this Seriously."  WWF Climate Change Blog, 13 Aug 2010.

Greenland glacier calves island 4 times the size of Manhattan, UD scientist reports.  Press release (6 September 2010) from Univeristy of Delaware. 

Ice Island calves off Petermann Glacier. Image of the Day from NASA's Earth Observatory (August 10, 2010).

Petermann Glacier front breakup, July-August 2008.  Posting (August 19th, 2008) in MODIS Studies of Greenland, by Byrd Polar Research Center.

Greenland’s Ice Island Alarm.  Feature article (28 August 2007) from NASA's Earth Observatory.  Includes sidebar on Why Does the Greenland Ice Sheet Matter?

What links the retreat of Jakobshavn Isbrae, Wilkins Ice Shelf and the Petermann Glacier? By  Mauri Pelto in RealClimate (7 October 2008)

In Greenland glaciers continue to lose ice area.  Posting (15 October 2009) in MODIS Studies of Greenland, by Byrd Polar Research Center

Spread of ice mass loss into northwest Greenland observed by GRACE and GPS. By Shfaqat Abbas Khan, John Wahr, Michael Bevis, Eric Kendrick and Isabella Velicogna in Geophysical Research Letters, vol. 37 (19 March 2010).

WWF Climate Change Blog

Extreme Ice Survey.  "The Extreme Ice Survey is the most wide-ranging glacier study ever conducted using ground-based, real-time photography."  See its photos of the following glaciers in the same region as those that were the focus of the research reported in Nature Geoscience: 

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