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Floating ice area loss is 10 times the area of Manhattan Is. (2000-2008)

Thursday, October 16th, 2008

Our survey of 32 of the largest Greenland tidewater glaciers indicates a continuous collective retreat end of summer 2000 onward to 2008.

A best-fit line indicates a -106.4 sq. km/yr area change around Greenland. The linear correlation coefficient is -0.98.

The cumulative area change from end of summer 2000 to 2008 is -920.5 sq km, an area loss equivalent with 10.5 times the area of Manhattan Is., New York.

The number of glaciers surveyed is increasing as graduate student David Decker continues to work.

http://bprc.osu.edu/~jbox/img/misc/32_Greenland_glaciers_cum_area_change.gif

The 32-glacier total for end of summer area change 2007-2008 was -183.8 sq km, 3 x that of the previous summer (2006-2007 area change was -62.9 sq km.). In other words, between 2007 and 2008, glaciers around Greenland lost an area more than two times the size of Manhattan Island.

* Manhattan Is. area is taken to be 87.5 sq km.

Upernavik Icestreams A and C retreat

Thursday, September 25th, 2008

See first this annotated image illustrating the Greenland region containing the Upernavik glaciers.


Terra/MODIS image of Upernavik region and its existing five glaciers (a, b, c, d, e). 30 August 2008. Image arranged by Russ Benson.

Five glaciers empty into the Upernavik archipelago, that, until the 1930s, could be considered a single glacier, but now, having disintegrated is five ice streams emptying into the sea. Up until the 1980s, A and B were joined at the front.  Below, we track the area changes for all five ice streams collectively using end of summer imagery from the years 2000-2010…

Timeseries arranged by David Decker.

Below, the area changes for each of Upernavik’s five glacier outlets are shown. Most of the action is at outlets A and more recently a sustained loss from Upernavik C between 2008 and 2009.

The cumulative area changes from each of the Upernavik outlets is illustrated.  Upernavik A and C has lost an area of approximately 24.3 and 35.7 sq. km, respectively.  The whole Upernavik glacier system has lost a net area of approximately 55.1 sq. km, net, considering all years since end of summer 2000.

Greenland ice sheet outlet glacier front changes: comparison of year 2008 with past years

Tuesday, September 16th, 2008

J. E. Box

Department of Geography, The Ohio State University, Columbus, Ohio, USA

Byrd Polar Research Center, The Ohio State University, Columbus, Ohio, USA

D. Decker*

Department of Geography, The Ohio State University, Columbus, Ohio, USA

Byrd Polar Research Center, The Ohio State University, Columbus, Ohio, USA

R. Benson

Byrd Polar Research Center, The Ohio State University, Columbus, Ohio, USA

* corresponding author

AGU Fall Meeting 2008 Abstract

NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) imagery are used to calculate inter-annual, end of summer, glacier front area changes at 10 major Greenland ice sheet outlets over the 2000-2008 period. To put the recent 8 end of summer net annual changes into a longer perspective, glacier front position information from the past century are also incorporated.

The largest MODIS-era area changes are losses/retreats; found at the relatively large Petermann Gletscher, Zachariae Isstrom, and Jakobshavn Isbrae. The 2007-2008 net ice area losses were 63.4 sq. km, 21.5 sq. km, and 10.9 sq. km, respectively. Of the 10 largest Greenland glaciers surveyed, the total net cumulative area change from end of summer 2000 to 2008 is -536.6 sq km, that is, an area loss equivalent with 6.1 times the area of Manhattan Is. (87.5 sq km) in New York, USA.

Ice front advances are evident in 2008; also at relatively large and productive (in terms of ice discharge) glaciers of Helheim (5.7 sq km), Store Gletscher (4.9 sq km), and Kangerdlugssuaq (3.4 sq km).

The largest retreat in the 2000-2008 period was 54.2 sq km at Jakobshavn Isbrae between 2002 and 2003; associated with a floating tongue disintegration following a retreat that began in 2001 and has been associated with thinning until floatation is reached; followed by irreversible collapse.

The Zachariae Isstrom pro-glacial floating ice shelf loss in 2008 appears to be part of an average ~20 sq km per year disintegration trend; with the exception of the year 2006 (6.2 sq km) advance. If the Zachariae Isstrom retreat continues, we are concerned the largest ice sheet ice stream that empties into Zachariae Isstrom will accelerate, the ice stream front freed of damming back stress, increasing the ice sheet mass budget deficit in ways that are poorly understood and could be surprisingly large.

By approximating the width of the surveyed glacier frontal zones, we determine and present effective glacier normalized length (L’) changes that also will be presented at the meeting. The narrow Ingia Isbrae advanced in L’ the most in 2006-2007 by 9.2 km. Jakobshavn decreased in L’ the most in 2002-2003 by 8.0 km. Petermann decreased in length the most in 2000-2001, that is, L’ = -5.3 km and again by L’ = -3.9 km in 2007-2008. Helheim Gl. retreated in 2004-2005 by L’ = -4.6 km and advanced 2005-2006 by L’ = 4.4 km. The 10 glacier average L’ change from end of summer 2000 end of summer 2008 was -0.6 km.

Results from a growing list of glaciers will be presented.

We attempt to interpret the observed glacier changes using glaciological theory and regional climate observations.

Keywords: glaciology, remote sensing, MODIS

Humboldt glacier retreats

Tuesday, September 16th, 2008

Humboldt is the widest tidewater glacier in the Northern Hemisphere.

Image:  Terra/MODIS satellite image of Humboldt Glacier August 30, 2008

Image:  Terra/MODIS satellite image of Humboldt Glacier August 31, 2000

View an animation here

Sermeq Avannarleq retreats

Wednesday, August 27th, 2008

Sermeq Avannarleq, the next glacier north of the enormous Jakobshavn Isbrae lost more than 2 sq. mi of its ice front by the end of summer 2008. This loss is on top of more than 2 sq. mi lost by end of summer 2007. These recent breakups added to smaller losses in earlier years have generated a retreat pattern illustrated in the lower panel of the figure below.

Sermeq Avannarleq had been dubbed “dead glacier” by local dog sledders that take tourists to the bay in front of this glacier. The name is now illogical. Beginning in 2003, Dead Glacier came alive, shedding floating ice into the forebay and continuing its retreat during 2007 and 2008 summers.

Factoid: Greenlandic glacier names describe the relative location of the feature. Sermeq Avannarleq translated literally means “northern glacier”, north, that is, of Sermeq Kujaleq (southern glacier), that is, Jakobshavn Isbrae.

Petermann Glacier front breakup, July-August 2008

Tuesday, August 19th, 2008

A 29 sq. km. (11 sq. mi.) area of the Petermann Glacier in northern Greenland (80˚N, 60˚W) broke away between July 10th and by July 24th.

Petermann has a floating section 16 km (10 mi) wide and 80 km (50 mi) long, that is, 1295 sq. km (500 sq mi); the longest floating glacier in the Northern Hemisphere.

Here is an animation of the breakup.

This 2008 breakup is actually not the largest observed. Between 2001 and 2000, 86.8 sq. km (33.5 sq. mi.) broke away from the Petermann front. However, more breakup is immenent in the next year, for, a large crack has widened while moving toward the calving front.

ASTER image courtesy of Ian Howat showing Petermann Glacier crack

Here is an annual (2001-2007) animation Ian Howat made of the crack flowing toward the glacier front while widening.

If the Petermann glacier breaks up back to the upstream rift, the loss would be as much as and additional 160 sq. km (60 sq. mi); a loss of one third of the massive Petermann ice tongue.

The Petermann glacier thins from 600 m thickness at the grounding line to 70 m at the terminus, see [1]. The crack is advancing to a point where a massive breakup seems imminent, in which case, the area of break-up would be 56-60 sq. miles (147-160 sq. km).

Animations:

  • Petermann front breakup: small (480×480), large (720×720)
  • End of summer 2000 – 2008: small (720×405), large (960×540)
  • Annual (2001-2007) animation Ian Howat made of the crack flowing toward the glacier front while widening.

Figures:

  • Initial Breakup 1: small (638×826), large (1276×1650)
  • Initial Breakup 2: small (975×413), large (1950×825)
  • Glacier Front Position 2007-25 July 2008: small (720×540), large (1420×1080)
Addendum (25 Dec, 2008)
Petermann Glacier thins from 600-700 m at the grounding line primarilly due to basal melting [1] calves 0.6 km3 (Higgins, 1990). “The lower 80 km (in length) and 1300 km2 (in area) of the glacier is afloat. This makes it (by area) the largest floating glacier in the Northern Hemisphere. “…”The calving front protrudes a mere 5-10 m above sea level, reflecting the fact that the ice at the front is only 60-70 m thick.” M. Pelto, Real Climate.
Work Cited
  1. Rignot, E., and K. Steffen (2008), Channelized bottom melting and stability of floating ice shelves, Geophys. Res. Lett., 35, L02503, doi:10.1029/2007GL031765
  2. Higgins, A. 1990. Northern Greenland glacier velocities and calf ice production. Polar Forschung, 60, 1-23.

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Jakobshavn Glacier Retreats to New Minimum

Tuesday, August 19th, 2008

MODIS image of Jakobshavn Glacier with lines indicating continued retreat.

The Jakobshavn Glacier front retreated 14 sq. km (5 sq. mi.) between 6-15 August 2008.

Jakobshavn Glacier is the world’s fastest continuously flowing glacier and the main outlet from the vast 1.69 million sq. km Greenland ice sheet. Jakobshavn drains 6.5% of the ice sheet, producing 35–50 cubic km of icebergs per year [1].

The 2008 retreat is to a position further inland than any time over the past 150 years of direct observation and likely is further back than during any time since the Holocene Thermal Maximum 4-8 thousand years before present, because the interim period ends with the Little Ice Age c. 1250 AD – 1850 AD glacier advance.

Of distinction from a retreat trend mainly at the faster southern branch of Jakobshavn Glacier since 2001, is the northern branch has retreated in the past weeks. Repeat altimeter measurements show the northern branch thinning in recent years at an accelerated rate (Ian Howat, personal communication).

Image with end of summer positions indicated. We measure interannual changes using end of summer images because glaciers reach a seasonal minimum at the end of summer.

Between 2001 and 2005, a collapse of the Jakobshavn Glacier floating tongue removed 94 sq. km (36 sq. mi.).

Additional Figures:

  • End of summer 2000-2008: small (720×540), large (1420×1080)
  • End of summer 2007-2008: small (720×540), large (1420×1080)

Animations:

References:

Weidick, Anker and Ole Bennick. Quarternary glaciation history and glaciology of Jakobshavn Isbrae and the Disko Bugt region, West Greenland: a review. Boreas 14 (2007).

Page Constructed by Jason Box, Russ Benson, and David Decker, Byrd Polar Research Center.

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