MODIS Studies of Greenland

We’ve been impressed by the size and persistence of an area of open water and unconsolidated sea ice between Greenland and Ellesmere Island, Arctic Canada. This phenomenon goes by the Russian term polynya.

NASA satellite view of the Nares St. polynya. Image ground resolution is 250 m. Blue and green reflectance is resampled from 500 m resolution data to the 250 m resolution red image. Click for a medium or full resolution version of the above graphic.

Polynyi (plural) are formed by a combination of wind action and ocean heat not allowing sea ice to form thick enough to bridge between land masses as land fast ice. More rare are polynyi formed only by wind or only by ocean heat. Prevailing winds in Nares St. above are southward, like in the below graphic from , the lower atmosphere channeled between 1000-2000 m terrain on either side of the channel.

Meteorological model output from Roger M. Samelson, Professor of Oceanic & Atmospheric Sciences
College of Oceanic & Atmospheric Sciences Oregon State University

The usual location of the Nares St. polynya is Smith Sound ~400 km south of this winter 2008/2009 position. Click for a location map with place names. The Smith Sound polynya is commonly referred to at the “North Water” polynya.

Polynyi (plural) can be associated with a tremendous heat loss from the ocean surface to the atmosphere. The sea surface is 20-40 degrees C (55-75 degrees F) warmer than the overlying air. Plumes of condensed water/ice release latent heat into the lower atmosphere. Sensible heat is also released into the lower atmosphere. Being so much warmer than the surroundings, the open water radiates much stronger in the thermal infrared than the surroundings. Infrared imagery from NASA’s MODIS sensor indicate the thin ice and open water having apparent temperatures (brightness temperatures) 20-30 deg. C greater than the surroundings. Clearly, sea ice caps ocean heat from the cold Arctic winter…

Click for a medium resolution version of the above graphic. Image resolution is 1000 m.

MODIS nicely captures the “sea smoke” plumes of condensed water vapor streaming downwind to the south…

Sea smoke to the north of Robeson Channel and Nares St. Image ground resolution is 250 m. Blue and green reflectance is resampled from 500 m resolution data to the 250 m resolution red image.

Polynyi (plural of polynya) are special for additional reasons.
•    Sometimes called an “ice factory”, a polynya can produce ice that is continually exported down wind. The ice rejects salt, leading to sinking (more dense than surroundings) salty ‘deep water’. Evaporation cools the surface, helping the cool dense water sink, helping set up a thermohaline circulation.
•    Polynyi are wildlife hot spots for beluga whales and narwhals that feed on plankton that can bloom because the ice is thin or absent. The whales can come up for air, reliably in the polynya.

Find an animation of the polynya for the month of March here.

Rink Isbrae is ranked 2nd or 3rd for iceberg production for all west Greenland (Weidick and Bennicke, 2007).

ASTER 3D view of Rink Isbrae.

There have been no major front position change in the past 9 summers imaged by MODIS, see figure below. A 10 sq. km ice area loss in 2004 was built up in previous years and is followed by subsequent net build up.

Rink sheds 1+ km long ~0.5 km wide “ice islands” periodically.

Ingia has  built up a longer floating tongue that was lost in 2007. The building accelerated before breakup.

The Zachariæ and the “79N” glacier to its north, are two massive outlets draining the gradually-sloping northeast Greenland ice sheet. An annotated image (below) illustrates a 23 sq. km (9 sq. mi.) retreat of Zachariæ Isstrøm from the end of summer 2007 to end of summer 2008.

The trend in ice loss is visible since MODIS observations began in 2000, see below…

Thinning has been observed near the grounding line since 1999 [1].

Lakes form here in northeast Greenland and may play an important role in future disintegration of this glacier, provided that warming continues, as predicted. View an animation of 2008 melt lake formation in northeast Greenland.

MODIS image showing the 79 N glacier outlet and supra-glacial melt lakes in the north east region of Greenland.

Figures:

• Zachariæ front change 2007-2008: small (710×540), large (1420×1080)
• Zachariae front change 2002-2008: small (710×540), large (1420×1080)

Animations:

• Zachariæ end of summer front position 2002-2008: small (853×480), large (1280×720)
• Melt Lakes NE Greenland 2008: small (853×480), large (1280×720)

Works Cited

1. Eric Rignot, Sivaprasad Gogineni, Ian Joughin, Wiliam Krabil, Contribution to the glaciology of northern Greenland from satellite radar interferometry, Journal of Geophysical Research, vol. 106, no. D24, Pages 34,007-34,019, December 27, 2001

Break-off Event East of the 79 fjord in Greenland

Credit Image courtesy of Byrd Polar Research Center

A large piece (55 km x 36 km) of sea ice broke away from land at 79˚N, 15˚W, 193 km (120 mi.) from the edge of the 79 N glacier in Northeast Greenland 16-20 June, 2008. The breakup was preceded by a 4 day period of fracturing before completely disinetgrating 20 June, 2008.

Images of the breakup were gathered from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA’s Terra satellite.

The recent shelf ice breakup will not raise sea level rise as the ice is already afloat. Loss of land-connected (land-fast) ice can reduce back-stress on glaciers, leading to their acceleration, e.g. Scambos et al 2002.

Satellite images indicate that the ice shelf break off began its collapse 16 June; data reveled a large ice plate, 84 km x 40 km (52.2 x 24.9 mi.), triggering disintegration of 2539 sq. km (1578 mi.). The city of Columbus, Ohio would fit in the shallow tabular “ice island” four times.

Figures: (800×600), (600×450)

Animation: (720×480) (Requires Quicktime)

Break-off at Skærfjorden Northeast Greenland

Credit Image courtesy of Byrd Polar Research Center

Another large tabular ice berg, (76 km X 23 km), seperated from Skærfjorden at 77˚N, 18˚W, 117 miles southwest of the Zachariæ Isstrøm on 4 July, 2008.

The 2970 km^2 (1875 mi^2) area superceeds that of the previous event from 20 June, 2008. Similarly, the mass is shelf ice…

The shelf ice in this region has deteriorated in each year from year 2000 to present. Large shelf ice break-offs such of this magnitude are becoming increasingly common in the Northeast region. Over the past 8 melt seasons there have been cases of significant shelf ice loss greater than 1700 km^2 on a year by year basis. Comparing the images on 4 July and 6 July we have an area deformation of 2970km^2. In relation to Columbus, Oh, this glacier change would fit into the metropolitan area of Columbus twice.

The animation below is a three day period where the event is taking place east of the fjord.

Figure: (675×263), (900×350)

Animation: (720×480)

Northeast Shelf Breakup Continues

On 18 July, 2007 Modis Satillite imagry (shown above) reported a large (63.5 km X 25.4 km) sea ice breakoff at 79.6˚N, 17˚W. It is located 278km (173 mi) from the middle of the of the 79 fjord in Northeast Greenland.

Credit Image courtesy of Byrd Polar Research Center

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Figure: (coming soon)

Animation: (505×505)

Sea Ice Collision South of Zachariæ Isstrøm

On 13 July 13, a small tabular piece of sea ice broke free after a region of melt below Store Koldewey disintegrated. The tabluar piece [size km^2] headed Northwest from 12 July to 18 July and collided with another region of sea ice in Dove Bugt (Dove Bay). The collision triggered the continuous breakup in the bay following 18 July, taking 4 days for the sea ice to break up completely.

Credit Image courtesy of Byrd Polar Research Center

In the figure and animation below we show the collision of sea ice that occured south of Store Koldewey between 13 July and 24 July of 2008. The region of interest is located 1,914km (1189 mi) south east of Zachariæ Isstrøm.

Figure: (714×316)

Animation: (705×705)

Store Gletscher, 5.5 km wide at its front, is ranked 2nd or 3rd in iceberg discharge for west Greenland at 13.2 - 17.5 km3 y-1 [1,2]. Store Gl. is one of a number of remarkably stable Greenland ice sheet outlets. Having not significantly changed its front position in available imagery going back to 1964 [2]. Why? We suspect this glacier is heavily grounded, dragging securely along its steep bed, that is, without significant buoyancy. Ice that reaches the grounding line either simply falls off into the 900 m deep fjord or the buoyancy force also wrenches the ice free.

Store Glacier, seen from the air, looking south, 13 June 2007. Photo: J. Box

Comparing multiple years of end of summer MODIS imagery, we find that Store Gl. advanced 5 sq km in 2008 (Figure 1).

[1] Bauer, A., Baussart, M., Carbonnell, M., Kasser, P. Perroud, P. & Renaud, A. 1968a: Missions aériennes de reconnaissance au Groenland 1957–1958. Observations aériennes et terrestres, exploitation des photographies aériennes, détermination des vitesses des glaciers vêlant dans Disko Bugt et Umanak Fjord. Meddelelser om Grønland 173(3), 116 pp.

[2] Carbonnell, M. & Bauer, A. 1968: Exploitation des couvertures photographiques aériennes répétées du front des glaciers vélant dans Disko Bugt et Umanak Fjord, juin–juillet 1964. Meddelelser om Grønland 173(5), 78 pp.

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.

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.

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. Below, we track the area changes for all five ice streams collectively using end of summer imagery from the years 2000-2008…

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.

The cumulative area changes from each of the Upernavik outlets is illustrated.  Upernavik C has lost an area of approximately 34.0 sq. km.  The whole Upernavik glacier system has lost a net area of approximately 43.8 sq. km, net, considering all years since end of summer 2000.

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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