NSIDC: Greenland’s summer: The pressure is on, and off

NSIDC, August 20, 2014

Melting on the surface of the Greenland Ice Sheet in June and July 2014 has been well above the 1981 to 2010 average in most areas, but after a fast start in May, the southern region and the southeastern coast have seen lower-than-average melt. Mid-summer surface melting did not reach higher elevations (above 2,000 meters) as often as in the reference period 1981 to 2010. Short bursts of extensive melting were related to periods of high air pressure over the ice sheet favoring sunny conditions, and promoting increased melting in darker areas of the ice sheet (wet snow, bare ice, or dirty snow).

Overview of conditions

Figure 1. Cumulative days of surface melting (top pair) and anomalies in the number of melt days (bottom pair) for June and July, 2014 (left side and right side, respectively). Anomalies are compared to the period 1981 to 2010. Data are from theGreenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data. Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Daily melt extent in June surged to nearly 40% of the ice surface area by mid-month and remained above the average extent for the 30-year reference period (1981 to 2010) for almost the entire month. Positive melt day anomalies were present in all areas except for the southeastern ice sheet. In July, melting was intense along the northwestern coast (more than 15 days above the average in some areas) and unusually low along the southeastern coast, especially near Helheim Glacier where July melt days were 3 to 8 days less than average. Overall, melting was less frequent than average in the high interior and southeastern areas of the ice sheet.

Conditions in context

Figure 2. Melt extent time-series for 2014 (top) and average air temperature anomaly at a level about 800 meters (2,500 feet, 925 hPa) above the sea level for June 1 to August 14, 2014. Melt extent data are from the Greenland Daily Surface Melt 25-km EASE-Grid 2.0 Climate Data Record. Air temperature data are from the National Center for Environmental Prediction (NCEP) Reanalysis. Top image credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
Bottom image credit: NOAA Earth System Research Laboratory, Physical Sciences Division
High-resolution image

Thus far, the maximum daily melt extent for summer 2014 was near 40% of the ice sheet surface on June 13. This was the first in a series of four warm periods followed by four periods of near-average conditions spanning the rest of June and July. Since August began, daily melt extent declined to near-average values for late summer. Summer air temperatures for June, July, and the first half of August mirrored the overall pattern of melt intensity, with cooler-than-average conditions about 1degree Celsius (1.8 degrees Fahrenheit) below normal in the high ice sheet plateau, and warmer-than-average conditions along the western coast, especially the southwestern coastal area at 1.5 degrees Celsius (2.7 degrees Fahrenheit) above average.

Models of the Greenland 2014 summer season produced by the MAR version 3.4 model of Xavier Fettweis from Liège University show that the overall snowfall-melt balance for Greenland  (the surface mass balance, or SMB) is very close to the 1981 to 2010 average. While 2013 total autumn snowfall was slightly higher than average, melting in the 2014 summer has now reduced the initial winter 2013 to 2014 snow accumulation surplus. However, despite the high total snow amount, northwestern Greenland had lower-than-normal winter snowfall accumulation. With the onset of a vigorous melt season in that area, the bright white snow cover was quickly removed, exposing darker ice below, and increasing the amount of melting as well as decreasing the ice sheet meltwater retention capacity in this area. This has produced a strong and statistically significant negative mass balance for this summer along Greenland’s northwestern coast.

Melting under pressure

Figure 3. Three 6-day periods in the Greenland surface melt extent daily time-series plot outline periods of high and low melting during June and July. Below, surface air pressure anomaly plots for the same periods (A, B, and C) are shown. A and C are high-melt-extent periods, and show greater-than-average air pressure (2 to 6 millibars); the opposite is true for the low-melt period, B. The two other high-melt periods, June 15 to 20 and July 19 to 25, also show higher-than-average air pressure. Melt extent data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. Air pressure data are from the National Center for Environmental Prediction (NCEP) Reanalysis.
Image credit: National Snow and Ice Data Center. High-resolution image

The four higher-melting periods of mid-June to late July and the intervening periods of more average melt extent appear to be associated with periods of high and low air pressure, respectively. Examining 6-day intervals in air pressure reveals higher-than-average pressure dominates during the peaks in surface melt extent, and low pressure during the low-melt periods. High pressure is associated with clear skies, and therefore greater solar energy input to the surface snow, impacting mainly the low albedo zones (in particular the ablation zone). This explains why the melt extent has been abnormally high in the ablation zone and abnormally low in the higher-elevation snow accumulation zone. The melt rate in the accumulation zone is more sensitive to warm but cloudy days and the associated increase in long-wave radiation, due the high surface albedo in this zone. Moderate Resolution Imaging Spectroradiometer (MODIS) images of Greenland on June 13 and July 3 indeed show a mostly cloudless Greenland, whereas more cloud cover is present on June 30 and July 1 during the lower-melt-extent periods.

Sky selfie

Figure 4. Images of the Greenland Ice Sheet near Kangerlugssuaq in west-central Greenland taken by a drone (UAV) used to evaluate the evolving albedo of the ice sheet surface during the summer melt season. At top left, Prof. Jason Box and Johnny Ryan, a Ph.D. student at Aberystwyth University, hold the drone they used. Top left, the drone takes a picture of the surface (and the operator, J. Ryan) on August 9, 2014 from low altitude, showing numerous cryoconite holes filled with black dust, grit, and soot that had accumulated in the winter snowpack, and melted out of the older ice below. Bottom, a higher-altitude image of the same area reveals sinuous melt streams and linear fractures, as well as small speckles of cryoconite holes on the ice sheet. Tents from the camp are also visible as colorful dots against the ice surface.  Credit: Photos courtesy of Johnny Ryan, Aberystwyth University, Jason Box, GEUS, and Dark Snow Project.
High-resolution image

Our colleague Jason Box of the Geological Survey of Denmark and Greenland (GEUS), and graduate student Johnny Ryan of Aberystwyth University spent much of the summer on the western ice sheet at Camp Dark Snow, near Kangerlugssuaq on the Arctic Circle (67 degrees north latitude at 1,010 meters above sea level). The team was investigating the Greenland surface albedo, climate, and surface melting, and how these evolve during summer. As part of the research, they have been using drones (Unmanned Aerial Vehicles, or UAVs) to photograph the surface from low altitude to examine the development of surface structures associated with melting. Strips of images and albedo measurements from the UAV are compared with simultaneous satellite images from the NASA MODIS sensor as an intermediate state to relate ground albedo measurements with that of the entire ice sheet. UAV photos reveal a surface riven with fractures, and drained by ephemeral rivers of melt water. The mid-summer melt surface in this area is pocked with 0.5 to 1 meter-wide (1.5 to 3 feet-wide) potholes with black grit and dust collected at the bottom. This black material is called cryoconite, and is comprised of dust and soot deposited on the surface, and melted out from the older ice exposed by melting. The dark patches are often glued together by tiny microbes.

Further reading

Fettweis, X., et al. 2014 Greenland ice sheet SMB simulated by MARv3.4 in real time.

Ryan, J.C., A.L. Hubbard, J. Todd, J.R. Carr, J.E. Box, P. Christoffersen, T.O. Holt, and N. Snooke, 2014, in review. Repeat UAV photogrammetry to assess calving front dynamics at a large outlet glacier draining the Greenland Ice Sheet. The Cryosphere Discussions 8, 2243-2275, doi:10.5194/tcd-8-2243-2014.

http://nsidc.org/greenland-today/

NASA data shed new light on changing Greenland ice

by George Hale, phys.org, March 10, 2014

This is the calving front of Greenland's Jakobshavn Glacier seen during an IceBridge survey flight in 2012. Credit: NASA / Jefferson Beck

Research using NASA data is giving new insight into one of the processes causing Greenland's ice sheet to lose mass. A team of scientists used satellite observations and ice thickness measurements gathered by NASA's Operation IceBridge to calculate the rate at which ice flows through Greenland's glaciers into the ocean. The findings of this research give a clearer picture of how glacier flow affects the Greenland Ice Sheet and shows that this dynamic process is dominated by a small number of glaciers.

Over the past few years, Operation IceBridge measured the thickness of many of Greenland's glaciers, which allowed researchers to make a more accurate calculation of ice discharge rates. In a new study published in the journal Geophysical Research Letters, researchers calculated ice discharge rates for 178 Greenland glaciers more than one kilometer (0.62 miles) wide.

Ice sheets grow when snow accumulates and is compacted into ice. They lose mass when ice and snow at the surface melts and runs off and when glaciers at the coast discharge ice into the ocean. The difference between yearly snowfall on an ice sheet and the sum of melting and discharge is called a mass budget. When these factors are equal, the mass budget is balanced, but for years the Greenland Ice Sheet has had a negative mass budget, meaning the ice sheet is losing mass overall.

For years the processes of surface melt and glacier discharge were roughly equal in size, but around 2006 surface melt increased and now exceeds iceberg production. In recent years, computer model projections have shown an increasing dominance of surface melt, but a limited amount of glacier thickness data made pinpointing a figure for ice discharge difficult.

Ice discharge is controlled by three major factors: ice thickness, glacier valley shape and ice velocity. Researchers used data from IceBridge's ice-penetrating radar – the Multichannel Coherent Radar Depth Sounder, or MCoRDS, which is operated by the Center for Remote Sensing of Ice Sheets at the University of Kansas, Lawrence, Kan. – to determine ice thickness and sub-glacial terrain, and images from satellite sources such as Landsat and Terra to calculate velocity. The team used several years of observations to ensure accuracy. "Glacier discharge may vary considerably between years," said Ellyn Enderlin, glaciologist at the University of Maine, Orono, Maine and the study's lead author. "Annual changes in speed and thickness must be taken into account."

Being able to study Greenland in such a large and detailed scale is one of IceBridge's strengths. "IceBridge has collected so much data on elevation and thickness that we can now do analysis down to the individual glacier level and do it for the entire ice sheet," said Michael Studinger, IceBridge project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "We can now quantify contributions from the different processes that contribute to ice loss."

With data on glacier size, shape and speed, researchers could calculate each glacier's contribution to Greenland's mass loss and the total volume of ice being discharged from the Greenland Ice Sheet. Of the 178 glaciers studied, 15 accounted for more than three-quarters of ice discharged since 2000, and four accounted for roughly half. Considering the large size of some of Greenland's glacier basins, such as the areas drained by the Jakobshavn, Helheim and Kangerdlugssuaq glaciers, this was not exactly surprising.

What they also found was that the size of these basins did not necessarily correlate with glacier discharge rate, shuffling the order of Greenland's largest glaciers. Previously Helheim Glacier was thought to be Greenland's third largest glacier, but this study puts it in fifth place and adds two southeast Greenland glaciers, Koge Bugt and Ikertivaq South to the list of big ice-movers.

Glacier thickness measurements and this study's calculation methods have the potential to improve future computer model projections of the Greenland Ice Sheet. And with a new picture of which glaciers contribute most to mass loss, IceBridge will be able to more effectively target areas in future campaigns, promising more and better data to add to the research community's body of knowledge.

 Explore further: Mathematician uses skills to study Greenland's retreating glaciers (w/ Video)

Journal reference: Geophysical Research Letters  

Provided by NASA's Goddard Space Flight Center

http://phys.org/news/2014-03-nasa-greenland-ice.html

Glaciologists measure outflow of the Kangerdlugssuaq Glacier

Dear Readers, I've seen a lot of these videos, but this one is particularly interesting and well worth viewing.
 

On the Kangerdlugssuaq Glacier -- one of Greenland's largest ice fields -- scientists measure the movement of the ice sheet as it transports frozen water to the ocean. They discover that the speed of the glacier's march to the sea has tripled in just ten years. Alarm bells sound because at the current melt rate, within a few decades rising seas will have a profound effect on the low-lying countries of the world.

Once considered an inexhaustible source of food, the oceans are now in danger of being significantly depleted. Matt Damon hosts "The State of the Planet's Oceans" as award-winning filmmakers Hal and Marilyn Weiner investigate the health and sustainability of the world's oceans and the issues affecting marine preserves, fisheries, and coastal ecosystems worldwide.

* Learn more at: http://www.pbs.org/journeytoplanetearth -- OR --http://www.screenscope.com

The Greenland Ice Sheet in a Changing Climate
http://climateforce.net/2012/01/19/the-greenland-ice-sheet-in-a-changing-clim...

I.M. Howat et al., GRL 38, Mass balance of Greenland's three largest outlet glaciers, 2000–2010

Geophysical Research Letters, 38 (2011) L12501; doi: 10.1029/2011GL047565.


Mass balance of Greenland's three largest outlet glaciers, 2000–2010


Ian M. Howat (School of Earth Sciences, and the Byrd Polar Research Center, Ohio State University, Columbus, OH, USA), Yushin Ahn (Byrd Polar Research Center, Ohio State University, Columbus, OH, USA), Ian Joughin (Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA, USA), Michiel R. van den Broeke (Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Netherlands), Jan T. M. Lenaerts (Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Netherlands) and Ben Smith (Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA, USA)


Abstract

Acceleration of Greenland's three largest outlet glaciers, Helheim, Kangerdlugssuaq and Jakobshavn Isbræ, accounted for a substantial portion of the ice sheet's mass loss over the past decade. Rapid changes in their discharge, however, make their cumulative mass-change uncertain. We derive monthly mass balance rates and cumulative balance from discharge and surface mass balance (SMB) rates for these glaciers from 2000 through 2010. Despite the dramatic changes observed at Helheim, the glacier gained mass over the period, due primarily to the short-duration of acceleration and a likely longer-term positive balance. In contrast, Jakobshavn Isbræ lost an equivalent of over 11 times the average annual SMB and loss continues to accelerate. Kangerdlugssuaq lost over 7 times its annual average SMB, but loss has returned to the 2000 rate. These differences point to contrasts in the long-term evolution of these glaciers and the danger in basing predictions on extrapolations of recent changes.

Received 24 March 2011; accepted 7 May 2011; published 18 June 2011


Howat, I. M., Y. Ahn, I. Joughin, M. R. van den Broeke, J. T. M. Lenaerts, and B. Smith. 2011. Mass balance of Greenland's three largest outlet glaciers, 2000–2010. Geophys. Res. Lett. 38, L12501, doi: 10.1029/2011GL047565.


http://www.agu.org/pubs/crossref/2011/2011GL047565.shtml

Ian Howat: 2 Greenland glaciers (Jakobshavn Isbrae and Kangerdlugssuaq) lose enough ice to fill Lake Erie

2 Greenland glaciers lose enough ice to fill Lake Erie

esciencenews, published May 24, 2011, in Earth & Climate

A new study aimed at refining the way scientists measure ice loss in Greenland is providing a "high-definition picture" of climate-caused changes on the island. And the picture isn't pretty.

In the last decade, two of the largest three glaciers draining that frozen landscape have lost enough ice that, if melted, could have filled Lake Erie.

The three glaciers – Helheim, Kangerdlugssuaq and Jakobshavn Isbrae – are responsible for as much as one-fifth of the ice flowing out from Greenland into the ocean.

"Jakobshavn alone drains somewhere between 15 and 20 percent of all the ice flowing outward from inland to the sea," explained Ian Howat, an assistant professor of earth sciences at Ohio State University. His study appears in the current issue of the journal Geophysical Research Letters.

As the second largest holder of ice on the planet, and the site of hundreds of glaciers, Greenland is a natural laboratory for studying how climate change has affected these ice fields.

Researchers focus on the "mass balance" of glaciers, the rate of new ice being formed as snow falls versus the flow of ice out into the sea.

The new study suggests that, in the last decade, Jakobshavn Isbrae has lost enough ice to equal 11 years' worth of normal snow accumulation, approximately 300 gigatons (300 billion tons) of ice.

"Kangerdlugssuaq would have to stop flowing and accumulate snowfall for seven years to regain the ice it has lost," said Howat, also a member of the Byrd Polar Research Center at Ohio State.

Surprisingly, the researchers found that the third glacier, Helheim, had actually gained a small amount of mass over the same period. It gained approximately one-fifteenth of what Jakobshavn had lost, Howat said.

The real value of the research, however, is the confirmation that the new techniques Howat and his colleagues developed will provide scientists a more accurate idea of exactly how much ice is being lost.

"These glaciers change pretty quickly. They speed up and then slow down. There's a pulsing in the flow of ice," Howat said. "There's variability, a seasonal cycle and lots of different changes in the rate that ice is flowing through these glaciers."

Past estimates, he said, have been merely snapshots of what was going on at these glaciers in terms of mass loss. "We really need to sample them very frequently or else we won't really know how much change has occurred.

"This new research pumps up the resolution and gives us a kind of high-definition picture of ice loss," he said.

To get this longer-timeframe image, Howat and colleagues drew on data sets provided by at least seven orbiting satellites and airplanes, as well as other sources.

"To get a good picture of what's going on, we need different tools and each one of these satellites plays an important role and adds more information," Howat said.

The next step is to look at the next-largest glaciers in Greenland and work their way down through smaller and smaller ice flows.

"Currently, the missing piece is ice thickness data for all of the glaciers, but a NASA aircraft is up there getting it. When that's available, we'll be able to apply this technique to the entire Greenland ice sheet and get a monthly total mass balance for the last 10 years or so," he said.

http://esciencenews.com/articles/2011/05/24/2.greenland.glaciers.lose.enough.ice.fill.lake.erie

"Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade" by S. F. Price, A. J. Payne, I. M. Howat & B. E. Smith, PNAS, May 16, 2011

Proceedings of the National Academy of Sciences, published online before print May 16, 2011; doi: 10.1073/pnas.1017313108

Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade

1. Stephen F. Price^a,*, 
2. Antony J. Payne^b, 
3. Ian M. Howat^c, and 
4. Benjamin E. Smith^d

+Author Affiliations

1. ^aFluid Dynamics and Solid Mechanics Group, Los Alamos National Laboratory, T3 MS B216, Los Alamos, NM 87545;
2. ^bBristol Glaciology Centre, University of Bristol, University Road, Clifton, Bristol BS8 1SS, United Kingdom;
3. ^cSchool of Earth Sciences, Ohio State University, 125 South Oval Mall, Columbus, OH 43210; and
4. ^dPolar Science Center, Applied Physics Laboratory, University of Washington, Box 35560, Seattle, WA 98105

1. Edited by Hans-Joachim Schellnhuber, Potsdam Institute for Climate Impact Research, Potsdam, Germany, and approved April 19, 2011 (received for review November 22, 2010)

Abstract

We use a three-dimensional, higher-order ice flow model and a realistic initial condition to simulate dynamic perturbations to the Greenland ice sheet during the last decade and to assess their contribution to sea level by 2100. Starting from our initial condition, we apply a time series of observationally constrained dynamic perturbations at the marine termini of Greenland’s three largest outlet glaciers, Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier. The initial and long-term diffusive thinning within each glacier catchment is then integrated spatially and temporally to calculate a minimum sea-level contribution of approximately 1 ± 0.4 mm from these three glaciers by 2100. Based on scaling arguments, we extend our modeling to all of Greenland and estimate a minimum dynamic sea-level contribution of approximately 6 ± 2 mm by 2100. This estimate of committed sea-level rise is a minimum because it ignores mass loss due to future changes in ice sheet dynamics or surface mass balance. Importantly, > 75% of this value is from the long-term, diffusive response of the ice sheet, suggesting that the majority of sea-level rise from Greenland dynamics during the past decade is yet to come. Assuming similar and recurring forcing in future decades and a self-similar ice dynamical response, we estimate an upper bound of 45 mm of sea-level rise from Greenland dynamics by 2100. These estimates are constrained by recent observations of dynamic mass loss in Greenland and by realistic model behavior that accounts for both the long-term cumulative mass loss and its decay following episodic boundary forcing.

• ice sheet modeling
 
• climate change

• *Correspondence e-mail: sprice@lanl.gov
• http://www.pnas.org/content/early/2011/05/09/1017313108.abstract