Archive for September, 2008

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