29 August MODIS image

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.

click here for a higher resolution version of the above graphic

This area is more than three times that of Manhattan Is, New York.

The glacier effectively retreated 15 km (9 miles).

We have been measuring Petermann glacier area changes in a survey spanning 2000-2009. Consulting other publications and imagery, we conclude that this is a retreat to a new minimum in available satellite observations since 1962. Eric Rignot observed that “Petermann was not that far back when first visited by the Lauge Koch expedition in the 1920s”.

Petermann glacier disintegration has been progressing since year 2000, with a pause in 2009. Petermann has retreated 21 km (13 mi) since year 2000. The 2010 disintegration is 3 times larger than any previous ice area loss in Greenland, or the Northern Hemisphere for that matter, since at least year 2000.

click here for a higher resolution version of the above graphic

Is it possible to link this event to climate change?

While it is unreasonable to pin an individual cracking event of a glacier on Global Warming, even if enormous, the retreat of Petermann glacier is most certainly part of a pattern of global warming.

It is safe to say that glaciers retreat in a warming climate.

Warming is stronger in the polar regions because melting removes reflective snow and ice cover, allowing more sunlight to be absorbed by the underlying dark ocean or land, further increasing melt rates in a ‘feedback loop’.

Record Setting Warmth
2009/2010 winter and the month of May were the warmest on record since 1873 at Nuuk, southwest Greenland. At Upernavik, northwest Greenland, air temperatures are well above normal in 2010.

Those who may think that winter warming is irrelevant to increased melting need recognize that a warmed ice or snow volume requires less heat during summer to bring it to the melting point.

Abnormally warm air temperatures observed around Greenland this year are linked with observations of reduced sea ice concentration and warming sea surface temperatures.

What does this mean for the greater Greenland ice-sheet?
When ice is lost from the glacier front, there is less flow resistance and acceleration follows. While there is relatively little friction between Petermann glacier and the adjacent fjord walls, some acceleration is now expected. It is ominous because Petermann is among a handful of Greenland glaciers that flow through bedrock trenches extending inland to the thickest parts of the ice sheet. There is no mechanism expected to keep the retreat from moving further and further inland, hastening the demise of the ice sheet, adding to an accelerating global sea level rise.

It has yet to be shown that Petermann glacier has accelerated. GPS left on the surface in year 2009 by Alun Hubbard, if recovered this year, should document how much Petermann may have accelerated owing to the loss of the lowest 15 km of the glacier front.

Greenland glaciers have been losing ice area steadily since at least year 2000.  3/4 of the area loss has been in northern Greenland. Humboldt Glacier, immediately south of Petermann, has lost 120 square km since 2000. It too has a sub-marine trench leading into the heart of the ice sheet.

The NASA gravity-sensing satellite GRACE has detected that the Greenland ice sheet has been losing ice at an accelerating rate (reference 1). Greenland glaciers are discharging more ice than accumulates each year by snowfall. This mass imbalance has spread to northwest Greenland (reference 2).

The important link with the ocean
Greenland ice sheet volume loss has increased since the mid-1990s when a warm ocean current impinged on the sub-marine parts of marine-terminating glaciers (reference 3).

The Earth is 7/10 covered by oceans. The global oceans have uptaken an enormous amount of heat (reference 4), far more heat than the atmosphere has during the past century-plus of human loading of the atmosphere with heat-trapping greenhouse gasses. The ultimate de-stabilization of the Greenland and Antarctic ice sheets will likely be triggered by ocean warming. Increased surface melting is a smaller part of the story.

Time Lapse Cameras

During a July-August 2009 field campaign, Jason Box, Byrd Polar Research Center, left behind two time lapse cameras viewing the part of Petermann Glacier that has disintegrated. Jason obviously is keen to return to the site to recover the photos to produce a movie of the ice disintegration to share with the world. Insufficient resources are currently in hand to finance the helicopter charter to return to Petermann glacier to gather the images. Partnership is sought to bridge the funding gap. Contact: Jason Box

Two Extreme Ice Survey (EIS) time lapse cameras have been photographing every half-hour of daylight at Petermann Glacier for the last 13 months. The photographs will be recovered in early September, enabling the EIS team to assemble time-lapse videos. Jason Box will use these data to measure speed changes and analyze the dynamics and processes of the Petermann breakup.

This blog entry was composed by Jason Box. David Decker and Russ Benson at Byrd Polar Research Center assisted with satellite image area analysis and graphics, respectively.

References

1. Velicogna I, and J. John Wahr, 2006, Acceleration of Greenland ice mass loss in spring 2004, Nature, Vol 443|21 September 2006|doi:10.1038/nature05168 [a more recent study has been published]

2. Khan, S. A., J. Wahr, M. Bevis, I. Velicogna and E. Kendrick. 2010. Spread of ice mass loss into northwest Greenland observed by GRACE and GPS, Geophys. Res. Lett., 37, L06501, doi:10.1029/2010GL042460.

3. Holland, D.M., R.H. Thomas, B. de Young, M.H. Ribergaard and B. Lyberth.  2008. Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters, Nature Geoscience, 1, 659–664, (10.1038/ngeo316.

4. Levitus, S., J. Antonov, and T. Boyer (2005), Warming of the world ocean, 1955–2003, Geophys. Res. Lett., 32, L02604, doi:10.1029/2004GL021592

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.

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.

]]> http://bprc.osu.edu/MODIS/?feed=rss2&p=57 3 http://bprc.osu.edu/MODIS/?p=28 http://bprc.osu.edu/MODIS/?p=28#comments Sat, 07 Feb 2009 00:16:15 +0000 David Decker http://bprc.osu.edu/MODIS/?p=28 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.

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

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)