The ~250 square km Petermann floating ice “island” has drifted into Nares St. The drift out of Petermann fjord has been slow, as tides wash in and out and the berg was jammed in the fjord 20-25 August. Prevailing winds blowing toward the south will push the berg in that direction.
29 August MODIS image
The recent ice island detachment at Petermann glacier is part of a larger pattern of deglaciation observed at 31/34 glaciers (91%) in our survey.
We just updated our survey to include year 2010. Retreat continues at the 110 km (68 mi) wide Humboldt glacier and at the 23 km (14 mi) wide Zachariae ice stream. Humboldt, Zachariae, and Petermann (16 km or 10 mi wide) have bedrock trenches that lead inland below sea level to the thickest parts of the ice sheet. Sleeping giants are awakening…
Cumulative area change at Greenland’s glacier top 5 “losers”. 2010 areas are measured ~1 month prior to the end of summer melt when the survey usually is made . We do not expect 2010 area changes to be much different using the future data. If anything, we expect the losses to be larger. Click here for a full resolution graphic.
The front areas at Jakobshavn glacier, the world’s overall fastest glacier, and at 79 N glacier, are not losing area in 2010. Jakobshavn area changes are probably less indicative of its stability because the ice is moving so fast it just jams into it’s ice-choked fjord resulting in growth of the front area (see Amundson, Fahnestock, Truffer, Brown, Lüthi and Motyka. 2010. Ice me´lange dynamics and implications for terminus stability, Jakobshavn Isbræ, Greenland. J. Geophys. Res., 115 (F1), 1–12. F01005.). Jakobshavn remains flowing ~2x faster than it was prior to the loss of it’s ice shelf 1997-2003. Ian Howat has likened this glacier to a fire hose spewing about as fast as it can.
The 79 N and Zacharaiae glaciers are outlets to the Northeast Greenland Ice Stream (see: Joughin, Fahnestock, MacAyeal, Bamber, and Gogineni. 2001, Observation and analysis of ice flow in the largest Greenland ice stream, J. Geophys. Res., 106, 34,021–34,034). The northeast ice stream has not accelerated much. If surface climate is any indicator (J. Box is convinced it is), the lesser warming rates in northeast Greenland may partly explain the relative stability.
The Bottom Line Importance
Losses at the front of glaciers translate to less ice flow-resistance and in turn accelerated flow. Flow acceleration leads to further thinning by stretching. In turn the “grounding line”, where the glacier begins to float migrates inland. For the largest glaciers that have bedrock trenches leading inland to the thickest parts of the ice sheet, there is no expected mechanism to prevent retreat from continuing, hastening ice sheet volume losses. Ice movement from land to sea rises global sea level. As climate warming continues, we expect some acceleration of global sea level rise; by how much remains the subject of intense scientific inquiry that’s making gradual progress.
This blog entry was composed by Jason Box with assistance from David Decker.
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 with 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.
cumulative annual area changes for 34 of the widest Greenland ice sheet marine-terminating outlets
Below, we tabulate the area changes for each of the surveyed glaciers. 12 of 34 glaciers advanced (blue). 22 of 34 glaciers retreated (red). The widest glaciers lost the most marine-terminating ice area. We expected Petermann Glacier to lose up to 100 sq. km ice area this summer, but it held together and even advanced 2 sq km despite warmer than normal surface air temperatures. We will soon post an individual glacier change discussion.
|
Glacier Name |
Width [km] |
Area Change [sq km] |
|
Storstrommen |
27.8 |
4.00 |
|
Store |
5.3 |
-2.80 |
|
Upernavik |
26.1 |
3.20 |
|
Ikertivaq |
16.6 |
2.80 |
|
Petermann |
20.0 |
2.60 |
|
Sermeq Avannarleq |
2.5 |
2.10 |
|
Kangia Nunata |
4.9 |
0.90 |
|
Kangigdleq |
4.9 |
0.80 |
|
79 |
62.6 |
0.60 |
|
Kong Oscars |
4.1 |
0.50 |
|
Allison |
4.9 |
0.50 |
|
Docker/Smith |
4.3 |
0.02 |
|
Sermeq Avangnardleq |
0.7 |
-0.20 |
|
Ostenfeld |
7.0 |
-0.40 |
|
Perdlerfiup Sermia |
3.1 |
-0.40 |
|
Lille |
2.2 |
-0.50 |
|
Kangerdlugssup Sermerssua |
4.7 |
-0.60 |
|
Daugaard Jensen |
6.0 |
-0.90 |
|
Tingmjarmiut |
2.2 |
-0.90 |
|
Fenris |
2.5 |
-1.00 |
|
Sermeq Silardleq |
4.5 |
-1.20 |
|
Ingia |
3.2 |
-1.30 |
|
Umiamiko |
3.5 |
-1.30 |
|
Hayes |
10.7 |
-1.40 |
|
Rink |
4.5 |
-1.70 |
|
Kangerdluarssup Sermia |
3.6 |
-2.30 |
|
Steenstrup |
15 |
-2.70 |
|
Helheim |
5.5 |
-3.70 |
|
Kangerdlugssauq |
8.6 |
-5.20 |
|
Sermilik (South Greenland) |
2.2 |
-2.10 |
|
Jakobshavn |
6.8 |
-11.40 |
|
Midgard |
3.5 |
-15.80 |
|
Zachariae |
22.8 |
-31.00 |
|
Humboldt |
110.0 |
-36.90 |
|
|
Total |
-106.4 |
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:
Animations:
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
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.
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.
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.
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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.
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.
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.
