Supra-glacial Rivers Are Draining Greenland Quickly: NASA-UCLA

from the Jet Propulsion Laboratory, NASA, January 12, 2015



A river of meltwater flowing across Greenland's ice sheet. Image credit: UCLA/Laurence C. Smith

Rivers of glacial meltwater flowing over Greenland's frozen surface may be contributing as much to global sea level rise as all other processes that drain water from the melting ice sheet combined, according to researchers at the University of California, Los Angeles, and NASA.

The new finding is published today in the journal Proceedings of the National Academy of Sciences. The research is dedicated to the memory of coauthor Alberto Behar of NASA's Jet Propulsion Laboratory, Pasadena, California, who died in a small-plane crash in Los Angeles on Jan. 9.

Eighty percent of Greenland, which is about the size of the United States west of the Rocky Mountains, is covered by ice, which has the potential to make a significant contribution to sea level rise as it melts.

Because Greenland's ice sheet is vast and difficult to study from ground level, scientists are still learning about the many processes by which its melting water reaches the ocean. This is the first study of the drainage system of rivers and streams that forms atop the ice sheet in summer.

The new paper is based on research that took place on the ice sheet itself, carried out by lead author Laurence Smith of UCLA, JPL's Behar and nine other researchers in July 2012, and on remote sensing data from the same period. The researchers traveled by helicopter to map the network of rivers and streams over about 2,000 square miles (5,600 square kilometers) of Greenland. They were especially interested in learning how much of the meltwater remained within the ice sheet and how much drained to the ocean.

Virtually all of the flowing water drains directly to the ocean through sinkholes, the researchers found.

Behar designed two types of remotely controlled boats to collect data from the surface water. One was a drone boat that measured the depth of the water and how much light it reflected, allowing the researchers to create a scale with which to calibrate the depth of the surface water from satellite images. This boat was used on lakes and slow-flowing rivers. For dangerous, swift-flowing rivers, Behar developed disposable robotic river drifters that measured streamflow velocity, depth and temperature as they swept downstream.

"The measurements we collected would not have been possible without the truly innovative instruments designed by Alberto Behar, and his steady hand during some very trying conditions in the field. The scientific outcomes of this study can be traced directly to him," said lead author Smith, professor and chair of the geography department at UCLA.

Behar, who was also a research professor at Arizona State University in Tempe, produced many other innovative technologies in a 23-year career at JPL that specialized in robotics for exploring extreme environments in our solar system. To measure ice sheets in Antarctica as well as Greenland, he also developed robotic submarines and ice rovers. Behar was an investigation scientist for instruments on NASA's Mars Curiosity rover and Mars Odyssey orbiter.

The full paper is available online at:

http://www.pnas.org/content/early/2015/01/07/1413024112.full.pdf+html

For more information on the research, see:

http://newsroom.ucla.edu/releases/ucla-study-shows-rivers-meltwater-on-greenlands-ice-sheet-contribute-rising-sea-levels

Additional information and quotes about Alberto Behar and his career can be found at:

http://www.jpl.nasa.gov/news/news.php?feature=4438

http://www.jpl.nasa.gov/news/news.php?feature=4439

IceSat data confirm that Greenland's ice sheet melting has been underestimated, and it is accelerating

The most detailed study yet of the Greenland ice sheet illustrates the complex process that is causing billions of tonnes to melt every year

by Tim Radford, Climate News Network, December 27, 2014

LONDON − Greenland’s ice sheet shrank by an average of 243 billion tonnes a year between 2003 and 2009 – a rate of melting that is enough to raise the world’s sea levels by 0.68 mm per year.

In what is claimed as the first detailed study, geologist Beata Csatho, of the University of Buffalo in the US, and colleagues report in the Proceedings of the National Academy of Sciences that they used satellite and aerial data to reconstruct changes in the ice sheet at 100,000 places, and to confirm that the process of losing 277 cubic kilometres of ice a year is more complex than anyone had predicted.

The Greenland ice sheet is the second biggest body of ice on Earth − second only to Antarctica − and its role in the machinery of the northern hemisphere climate is profound.

Careful measurements

It has been closely studied for decades, but such are the conditions in the high Arctic that researchers have tended to make careful measurements of ice melt and glacier calving in fixed locations – in particular, at four glaciers − and then try to estimate what that might mean for the island as a whole.

“The great importance of our data is that, for the first time, we have a comprehensive picture of how all of Greenland’s glaciers have changed over the past decade,” Dr Csatho said.

The study looked at readings from NASA’s ice, cloud and land elevation satellite ICESat, and from aerial surveys of 242 glaciers wider than 1.5 km at their outlets, to get a more complete picture of melting, loss and – in some cases – thickening of the ice sheet as a whole.

Previous studies have focused on the four glaciers. One of them, Jakobshavn, has doubled its speed of flow since 2003, and closer studies have begun to reveal more about the dynamics of individual flows.

But the real strength of the study is that it establishes the pattern of ice melt in more detail, and suggests that climate models may not give a clear enough picture of the future of the ice cap. To put it crudely, Greenland could lose ice faster in the future than any of today’s predictions suggest.

Meanwhile, a team from the UK has been trying to work out what is happening on the surface of the ice sheet. Each summer, of course, some of the ice melts. Some of this gets to the sea, but some freezes again in the natural seasonal order of things.

But glaciology researcher Amber Leeson, of the University of Leeds, and colleagues report in Nature Climate Change that the “supraglacial” lakes that form each summer could also affect ice flow.

Their computer simulations suggest that these lakes will migrate further inland as the century wears on and the world continues to warm. Ice reflects heat, water absorbs it. So the process could trigger further melting. Some of this extra meltwater could slide or drain to the base of the glacier, lubricating its flow and accelerating the process yet again.

Thin pancake

“Our research shows that, by 2060, the area of Greenland covered by them will double,” Dr Leeson said. “When you pour pancake batter into a pan, if it rushes quickly to the edge of the pan, you end up with a thin pancake. It’s similar to what happens with ice sheets. The faster it flows, the thinner it will be.

“When the ice sheet is thinner, it is at a slightly lower elevation and at the mercy of warmer air temperatures than it would be if it were thicker, increasing the size of the melt zone around the edge of the ice sheet.”

In the last 40 years, the band in which such supraglacial lakes can form has crept 56 km inland. By 2060, the simulations now suggest, it could reach 110 km inland, doubling the area of coverage and delivering yet more meltwater to fuel further warming.

Once again, the research suggests that current models underestimate the rate of ice loss. 

Hundreds of melt ponds already forming on the edge of the Greenland Ice Sheet, some of which have already drained. Good view of Jakobshavn Isbrae, June 19, 2012

OK, we used to see this in August. Fifteen years ago, it was pretty rare.  I am providing the link because in this way you will have a better view:

http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_143.A2012171151500-2012171152000.250m.jpg

M. Tedesco et al., Year 2011 Greenland melting remains well above the (1979–2010) average; close-to-record mass loss

Year 2011 Greenland melting remains well above the (1979–2010) average; close-to-record mass loss

M. Tedesco¹, X. Fettweis², T. Mote³ , N. Steiner¹ and  J. E. Box⁴

1) City College of New York, NYC, NY, USA

2) University of Liege, Liege, Belgium

3) University of Athens, Athens, Georgia, USA

4) Byrd Polar Research Center, Ohio State University, Columbus, Ohio, USA

Summary: Melting in Greenland in 2011 was still above the average (1979–2010 baseline period), exceptionally high over the west coast and reaching close-to-record simulated surface mass balance, bare ice exposure, albedo and runoff anomalies.

The melting index (e.g., the number of melting days times the area subject to melting) in 2011 estimated from spaceborne microwave observations using the approach in (Tedesco, 2007) did not break the previous record set in 2010 (e.g., Tedesco et al., 2011). However, 2011 is positioning itself 6th in terms of melting index, after 2010, 2007, 1998, 2002, 2005. An alternative approach using microwave data as well (Mote & Anderson, 2005) indicates that melt extent for the period June through August 2011 ranked third since 1979, following 2010 and 2007. Satellites data cannot produce estimates of runoff and liquid water content. However, these can be analyzed by means of models. The model used in this analysis (MAR, e.g., Tedesco et al., 2011) indicates that 2011 was comparable to the record season of 2010 with respect to runoff, surface mass balance, albedo and bare ice exposure. Strong negative surface mass balance anomalies occurred in 2011, according to MAR (e.g., the loss in 2011 and 2010 were much higher than the gained mass because of accumulation). Surface albedo simulated by MAR was consistently below or around 2 standard deviations below the mean for the period June–August (e.g., more solar radiation absorbed supporting more melting, see Figure 4 for a diagram). The bare ice area exposed during the summer of 2011 was also large with respect to the mean (close to up 3 standard deviations for the month of July), similarly to what happened in 2010.

Figure 1 Map of the 2011 anomaly for the number of melting days

Figure 2 illustrates the snowfall, runoff and surface mass balance for the period 1958 – 2011 obtained from the MAR model. MAR indicates that 2011 runoff and surface mass balance was comparable to the record setting year 2010, with strong negative surface mass balance anomalies. The loss in 2011 and 2010 was much higher than the mass gain from snow accumulation.

Figure 2. Snowfall, runoff and surface mass balance for the period 1958 - 2011 simulated by the MAR model.

Figure 3 illustrates the 2011 standardized anomalies for near surface air temperature, surface albedo, snowfall, melt water production, bare ice area, and melt area all obtained from MAR for the months of April through August.  Anomalies for the North Atlantic Oscillation (NAO) index are also reported.  The temperatures in 2011 were higher than normal from mid June to mid August, according to a constant negative NAO index during these months. The constant negative NAO index induced anticyclonic and then dry conditions over the ice sheet, allowing to maintain a large bare ice extent through the whole melt season compared to 2010, when two snowfall events reduced temporarily the bare ice extent.

Figure 3. 2011 standardized anomalies for the the 3m temperature, surface albedo, snowfall, meltwater, bare ice area, melt area obtained from MAR for the months of April through August.

According to MAR, 2011 was characterized by an anomalously cold spring. Year 2011 melt onset was relatively late, beginning in June. The melt area for 2011 simulated by MAR is above 1 and 2 standard deviations in June and August, respectively, but within the mean during July. Nevertheless, surface albedo was consistently below or around 2 standard deviations below the mean for the period June–August (e.g., more solar radiation absorbed enhancing melting). The bare ice area exposed during the summer of 2011 was also anomalous with respect to the mean (close to up 3 standard deviations for the month of July), similarly to 2010. Figure 4 illustrates the simulated melt water, runoff, melt extent for the period May through August, and the bare ice extent for the same period simulated by MAR for the years 1958 through 2011. Both runoff and bare ice extent in 2011 are close to the 2010 record.

Figure 4. Feedback mechanisms diagram.

As mentioned above, the exposure of bare ice plays a major role on the increase of runoff and mass loss, either because it promotes enhanced absorption of solar radiation, much more than snow and because ice can melt faster than snow (see Figure 4 for a diagram explaining some of the feedback mechanisms).

How can we explain the differences between the record simulated by MAR and the results from spaceborne microwave data ?

Strong positive melting anomalies occurred in 2010 mainly because melting started earlier and lasted longer than usual. This aspect was captured by spaceborne microwave data because melting anomalies were largely driven by the length of the melting season. Because of this, the surface mass balance and runoff simulated by MAR for 2010 were in agreement with the melting index record derived from spaceborne observations. In 2011, however, melting did not start until late in the season and it did not last as long as in 2010. The exposure of bare ice promoted strong melting with the 2011 season being characterized by relatively short but intense melting. This was not captured by spaceborne microwave data because of their limitation in estimating the amount of liquid water within the snowpack. In summary: the 2010 season was largely driven by a longer season and therefore captured by microwave data, where the 2011 season was characterized by a relatively short but intense melting season, with the albedo feedback mechanism playing a major role (as in 2010) and large bare ice areas subject to melting.

http://greenland2011.cryocity.org/

An increase in crevasse extent, West Greenland: Hydrologic implications, GRL 38, by William Colgan et al.

Geophysical Research Letters, 38 (2011) L18502;
doi: 10.1029/2011GL048491 

An increase in crevasse extent, West Greenland: Hydrologic implications

 

Key points:

• There has been a significant increase in crevassed area extent
• Crevasse drainage is less efficient in enhancing sliding than moulin drainage
• Increased crevasse extent could also potentially enhance mass loss

William Colgan, Konrad Steffen, W. Scott McLamb, Waleed Abdalati (Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, CO, U.S.A.), Harihar Rajaram (Department of Civil, Environmental, and Architectural Engineering, University of Colorado at Boulder, Boulder, CO, U.S.A.), Roman Motyka (Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA), Thomas Phillips (Department of Aerospace Engineering Sciences, University of Colorado at Boulder, Boulder, CO, U.S.A.), and Robert Anderson (Institute of Arctic and Alpine Research, University of Colorado at Boulder, Boulder, CO, U.S.A.)

Abstract

We compare high-resolution 1985 and 2009 imagery to assess changes in crevasse extent in the Sermeq Avannarleq ablation zone, West Greenland. The area occupied by crevasses >2 m wide significantly increased (13 ± 4%) over the 24-year period. This increase consists of an expansion of existing crevasse fields, and is accompanied by widespread changes in crevasse orientation (up to 45°). We suggest that a combination of ice sheet thinning and steepening are responsible for the increase in crevasse extent. We examine the potential impact of this change on the hydrology of the ice sheet. We provide a first-order demonstration that moulin-type drainage is more efficient in transferring meltwater fluctuations to the subglacial system than crevasse-type drainage. As enhanced basal sliding is associated with meltwater “pulses,” an increase in crevasse extent can therefore be expected to result in a net decrease in basal sliding sensitivity. An increase in crevasse extent may also accelerate cryo-hydrologic warming and enhance surface ablation.

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http://www.agu.org/pubs/crossref/2011/2011GL048491.shtml

Citation: Colgan, W., K. 

Increased crevasse extent in Greenland may dampen ice sheet sliding

Increased crevasse extent in Greenland may dampen ice sheet sliding

The area covered by crevasses northeast of Ilulissat, West Greenland, has expanded by 13% over the last 24 years, according to scientists at the Cooperative Institute for Research in Environmental Sciences (CIRES)—a change that may impact the sliding of the Greenland Ice Sheet and subsequent sea level rise. 

“The area covered by crevasses is increasing,” said CIRES research associate William Colgan, lead author of the study published online today in Geophysical Research Letters. 

“Theoretically, this change may cause the ice sheet to slide more slowly toward the coast or into the ocean.” 

Colgan and his coworkers, a team led by CIRES Director Konrad Steffen at the University of Colorado Boulder, investigate the slide of the Greenland Ice Sheet, the second largest ice sheet on Earth. “People typically think of a block of ice as something really solid and inflexible,” Colgan said. 

“But when a block of ice is as big as the Greenland Ice Sheet, there is sufficient pressure from its weight to cause it to flow like a really, really slow river into the ocean.”

The weight of the ice causes the sheet to flow like a viscous fluid, and water between the ice sheet and its bed means the sheet slides as well as flows, Colgan said. The flow and sliding of the ice sheet can cause more ice than normal to flow into the ocean, which can lead to sea level rise, he said. “It is really important to understand how the Greenland Ice Sheet flows, slides and melts today, in order to be able to predict how it will contribute to sea level rise in the future.”

To investigate the impact of crevasses on ice sheet flow, the team first analyzed crevasse extent at Sermeq Avannarleq, northeast of Ilulissat, West Greenland. The scientists detected crevasses in high-resolution digital images taken in 1985 and 2009 and what they found surprised them. “We initially weren't looking for changes in crevasse area, we had thought it was stationary in time,” Colgan said. “But we found that the change in crevasse area was significant.”

Several factors influence the extent of crevasses, Colgan said. The weight of ice surrounding the crevasse acts as a “closing” force on crevasses whereas tensile stress, caused by local variations in surface slope, acts as an “opening” force. Warmer temperatures, however, result in increased surface melt and a thinning ice sheet reducing the closing force. Conversely, the subsequent change in ice flow speed steepens the ice sheet, which strengthens the tensile stress. As the ice sheet melts, a third factor also contributes to the crevasses expanding, Colgan said. “Twenty years ago crevasses might have been sitting open exposed to air, but now they are filled with water which forces them open.”

The team then went on to investigate how the crevasse area increase might impact ice sheet sliding. In this study, and a companion study published online September 13 in the Journal of Glaciology, the scientists compared the drainage of water by crevasses and moulins—near-vertical chutes in the ice—and found moulin drainage to be more efficient in moving water to the bed of the ice sheet and promoting sliding. But with the increase in crevasse area, the number of moulins had decreased, Colgan said. “The crevasse fields seem to be absorbing the moulins.”

Previously, scientists had believed that as more ice melts and water accumulates on the surface of the ice sheet, more water drains though the moulin network to the underside of the ice sheet enhancing its slide into the ocean. “For the last ten years popular opinion has been more melt equals more slide into the ocean,” he said. “Some recent papers have speculated that more melt might equal no change in sliding, but ours might be the first paper that says that despite more melt, changes in the way that the water is routed to the bed might equal less slide.”

The team now intends to investigate whether crevasse area has increased Greenland-wide and, if so, determine the impact on ice-sheet sliding. While the study may have identified one previously unrecognized influence on ice-sheet dynamics, Colgan cautions it is just one of many factors which determine the iceberg calving rate. “The recent trend of increasing iceberg calving rates is unlikely to be reversed by a potential decrease in sliding, as the majority of ice movement comes from flow rather than sliding,” he said.

The study “An increase in crevasse extent, West Greenland: Hydrologic implications” was funded by the National Aeronautics and Space Administration and the National Science Foundation. Coauthors include CIRES Director Konrad Steffen, CIRES student W. Scott McLamb and CIRES Fellow Waleed Abdalati. Collaborators on the project include the Aerospace Engineering and Sciences and Civil, Environmental, and Architectural Engineering departments at the University of Colorado Boulder, the Institute of Arctic and Alpine Research at the University of Colorado Boulder and the Geophysical Institute of the University of Alaska Fairbanks. 

CIRES graduate student, Daniel McGrath led the study published in the Journal of Glaciology “Assessing the summer water budget of a moulin basin in the Sermeq Avannarleq ablation region, Greenland Ice Sheet.” Coauthors of this study include William Colgan and Konrad Steffen. 

Collaborators on the project include the Aerospace Engineering Sciences Department at the University of Colorado Boulder and the Extreme Ice Survey, Boulder. 

William Colgan, CIRES, 303-735-3681, william.colgan@colorado.edu

Konrad Steffen, CIRES, 303-492-8773, konrad.steffen@colorado.edu

Jane Palmer, CIRES media communications, 303-492-6289, Jane.Palmer@colorado.edu

http://cires.colorado.edu/news/press/2011/crevasse.html 

Powerful images of Greenland melting like mad in 2010 by Marco Tedesco

Link:  http://www.youtube.com/watch?v=QbuFphwJn4c

2010 Greenland Record over the Greenland Ice Sheet

2010 Greenland Record over the Greenland Ice Sheet

by Cryospheric Processes Laboratory, The City College of New York 

Remote sensing data, surface observations and models indicate new records in 2010 for surface melt and albedo, runoff, the number of days when bare ice is exposed and surface mass balance of the Greenland ice sheet. This  was especially true over over its west and southwest regions.

Melting is a crucial factor in both surface and subglacial processes. Here’s a video showing melting streams, supraglacial lakes and meltwater flowing through ice cracks that we recorded in 2009 and 2010.

If interested, here’s some B-roll used to create the video. Feel free to ask for a high-resolution version.

Broll 1: Meltwater from a stream of a supraglacial lake flowing into a large crack.

Broll 2: Supraglacial lake at the sunset

Broll 3: Rapids of meltwater in Greenland

In summer 2010, early melt onset in spring was triggered by above-normal near-surface air temperatures. This contributed to accelerated snowpack metamorphism (snow melts faster and in turns it gets ‘older’ sooner, with large grain sizes responsible for more solar radiation absorbed) and premature bare ice exposure, rapidly reducing the surface albedo. This implies that more solar energy is absorbed and hence more melting is occurring.  Warm conditions persisted through summer, with the positive albedo feedback mechanism being a major contributor to large negative surface mass balance anomalies (e.g., more melting than what was accumulated during the previous year). Summer snowfall was below average. This helped to maintain low albedo through the 2010 melting season, which also lasted longer than usual, until around mid September.

The figure on the left shows the anomaly map of melting days for 2010 derived from passive microwave data. Red areas indicate where melting lasted longer than average (up to 50 days).

The figure above shows the standardized melting index anomaly for the period 1979–2010. In simple words, each bar tells us by how many standard deviations melting in a particular year was above the average. For example, a value of ~2 for 2010 means that melting was above the average by two times the ‘variability’ of the melting signal along the period of observation. Previous record was set in 2007 and a new one was set in 2010. Negative values mean that melting was below the average. Note that highest anomaly values (high melting) occurred over the last 12 years, with the 8 highest values within the period 1998–2010. The increasing melting trend over Greenland can be observed from the figure. Over the past 30 years, the area subject to melting in Greenland has been increasing at a rate of ~17,000 km²/year.

This is equivalent to adding a melt-region the size of Washington State every ten years. Or, in alternative, this means that an area of the size of France melted in 2010 which was not melting in 1979.

The figure above shows the monthly standardized anomalies for 2010 (relative to 1979–2009) for near-surface temperature, albedo, snowfall, meltwater, bare ice area and melt area excluding bare ice simulated by the model described in the paper.

Here’s the link to the accepted version of the paper. ERL_Tedesco_et_al._2010_Greenland_record

The full paper will be available on Friday, January 21, at:  http://dx.doi.org/10.1088/1748-9326/6/1/014005.

All images should be referenced as M. Tedesco or M. Tedesco/WWF, as indicated in each photograph. Click on the pictures to see them in a new page or download them.

Supraglacial lakes view from the helicopter. these lakes from from meltwater that collects in areas of the ice sheet, mainly as a consequence of surface topography.

Detail of a supraglacial lake from the above picture. Note the streams feeding the lake and the darker area at the bottom. This could be cryoconite, a dark mixture of soot, sediments and organic matter.

View of the supraglacial lake ‘Olivia’, where we camped in 2010. The diameter of the lake is ~1 km.

Canyon over the ice sheet formed as a consequence of the flow of meltwater. The field of cracks is well visible. This is the consequence of the continuous sliding of the ice on the bedrock: as the ice at the bottom is slower than that at the surface, a ‘stress’ occurs at the surface, provoking cracks.

Fieldwork equipment and deployment of a remotely controlled boat to study supraglacial lakes from in-situ measurements.

Camp on the side of a supraglacial stream leaving a supraglacial lake.

Streamflow of meltwater draining into a crack in the ice. The water can reach the bedrock supporting the development of the subglacial hydrological system. Because of the flow of the water, the crack enlarges, becoming more and more tubular in shape

We searched for the crack for several hours at night, following the stream on the ice. It took us a long walk but we were extremely excited at the end! Note an old moulin on the back of the one that is forming from the flow.

Here’s a detail showing the crack propagating on the ice and meeting the streamflow, where it gets larger and accommodates the meltwater from the lake.

Link:  http://134.74.46.131/wordpress/?page_id=236