The Arctic is changing with a rapidity that has amazed scientists. The Greenland ice sheet is shrinking, sending over 48 cubic miles a year of ice streaming into the oceans, while Arctic sea ice cover continues to track below average. These changes will have significant effects regionally and globally. Scientists from Columbia University's Lamont-Doherty Earth Observatory are flying over the region on a NASA-led mission called Operation IceBridge to understand what is happening on and below the ice.
Location: Greenland Ice Sheet
Team: Jim Cochran, Tim Creyts, Indrani Das
Purpose: Glacier and Climate Research
Start Date: March 30, 2010
A new project will study Greenland’s Helheim Glacier in unprecedented detail, using drones, laser scanners, and high-resolution models to untangle the processes that are driving ice loss in this region.
The research will be carried out by scientist Marco Tedesco from Columbia University’s Lamont-Doherty Earth Observatory and colleagues at partner institutions. It is supported by a multimillion dollar grant from the California-based Heising-Simons Foundation.
The Greenland Ice Sheet plays an important role in global sea level change in a warming world by releasing increasing amounts of freshwater into the ocean. Rapid mass loss from the Greenland Ice Sheet is now responsible for 25 percent of present-day sea level rise, making Greenland the largest single contributor to sea level rise. The majority of ice loss is due to acceleration, retreat, and thinning of glaciers at the ice-ocean interface, through processes that remain poorly understood. The Helheim, on the eastern coast of Greenland, is one of the ice sheet’s largest outlet glaciers and has been rapidly shrinking since 2001. The accelerated retreat of glaciers can exert effects worldwide, from causing sea level rise to adding freshwater to oceans, both of which can affect weather and ocean cycles in the North Atlantic.
The overarching goal of the new project is to improve understanding of the processes occurring at the marine margin of Helheim Glacier, using innovative data-gathering and modeling techniques.
“The project is allowing us to study the Helheim system in its glaciology, atmospheric, and ocean aspects and link them together to provide a picture that will help us understand the mechanisms that drive mass loss and the relative role of atmosphere and ocean on this,” explained Tedesco.
The team will use drones, both above and below water, as well as lasers scanning the ice flow to gather information at a very precise scale.
“We will be running models at ultra-high spatial resolution and combine those outputs with remote sensing to capture what we do well and we don’t. It will be unprecedented and amazing,” said Tedesco.
The high-resolution models will include snowfall, runoff, light reflected off of snow and ice, and other factors responsible for mass loss or gain. “We will also study how the atmospheric changes recently observed in the Arctic and strongly driven by jet stream disruption have been affecting Helheim,” said Tedesco.
The team will spend three to four years collecting comprehensive and parallel measurements of multiple systems to gain an understanding of what drives changes to the Helheim. Additionally, the research will provide an open source database for continued study.
Whereas most federally funded system-based research in the Arctic focuses on the entire Arctic system, this project represents a first in that private donations are supporting a system-based analysis concentrated on a specific region or subsystem.
The team — which includes colleagues from the Woods Hole Oceanographic Institution in San Diego, California; Woods Hole Institute in Woods Hole, Massachusetts; University of California, Irvine; Cold Region Research and Engineering Laboratory, Kansas University; Penn State University; and Oregon State University — performed the first research campaign during the past summer, and is in the planning stages to coordinate next steps.
Rainy weather is becoming increasingly common over parts of the Greenland ice sheet, triggering sudden melting events that are eating at the ice and priming the surface for more widespread future melting, says a new study. Some parts of the ice sheet are even receiving rain in winter—a phenomenon that will spread as climate continues to warm, say the researchers. The study appears this week in the European scientific journal The Cryosphere.
Greenland has been losing ice in recent decades due to progressive warming. Since about 1990, average temperatures over the ice sheet have increased by as much as 1.8 degrees C (3.2F) in summer, and up to 3 degrees C (5.4F) in winter. The 660,000-square-mile sheet is now believed to be losing about 270 billion tons of ice each year. For much of this time, half of this was thought to come from icebergs calving into the ocean, and the other half from melting. But since 2011, direct meltwater runoff has come to dominate, accounting for about 70 percent of the loss. Rainy weather, say the study authors, is increasingly becoming the trigger for that runoff.
The researchers combined satellite imagery with on-the-ground weather observations from 1979 to 2012 in order to pinpoint what was triggering melting in specific places. Satellites are used to map melting in real time because their imagery can distinguish snow from liquid water. Automated weather stations spread across the ice offer concurrent data on temperature, wind and precipitation. Combining the two sets of data, the researchers zeroed in on more than 300 events in which they found the initial trigger for melting was weather that brought rain. “That was a surprise to see,” said the study’s lead author, Marilena Oltmanns of Germany’s GEOMAR Centre for Ocean Research. She said that over the study period, melting associated with rain and its subsequent effects doubled during summer, and tripled in winter. Total precipitation over the ice sheet did not change; what did change was the form of precipitation. All told, the researchers estimate that nearly a third of total runoff they observed was initiated by rainfall.
Melting can be driven by a complex of factors, but the introduction of liquid water is one of the most powerful, said Marco Tedesco, a glaciologist at Columbia University’s Lamont-Doherty Earth Observatory and coauthor of the study. Warm air, of course, can melt ice directly, but is not very efficient by itself, he said. However, warmer air can produce cascading effects. For one, it makes it more likely that atmospheric conditions will pass the threshold where precipitation comes down as rain, not snow. Liquid water carries a great deal of heat, and when it soaks into a snowy surface, it melts the snow around it, releasing more energy. Meanwhile, the warm air that brought the rain often forms clouds, which hem in the heat.
This combination of factors produces a pulse of melting that feeds on itself, and well outlasts the rain itself, often by several days. Moreover, the scientists found that the length of these pulses increased over the decades they analyzed, in cold weather from two days to three, and in the brief summer, from two days to five.
There are longer-term effects, say the study authors. They believe that part of the meltwater runs off, but the rest refreezes in place, morphing normally fluffy, reflective snow on or near the surface into darker, denser masses of ice. This ice absorbs solar radiation more easily than snow, so when the sun comes out, it melts more easily, producing more liquid water, which feeds more melting, in a vicious feedback loop. This, said Tedesco, has led to more and earlier melting in the summer. And because the surface has been hardened into ice, much of that meltwater can more easily flow off the ice sheet toward the sea.
“If it rains in the winter, that preconditions the ice to be more vulnerable in the summer,” said Tedesco. “We are starting to realize, you have to look at all the seasons.”
While rain is hitting increasingly far-flung parts of the ice in summer, winter rainfall so far appears mostly confined to lower elevations in south and southwest Greenland. It is brought in by moist, relatively warm ocean winds from the south, which some communities in other areas call neqqajaaq. These winds may be getting more common due to climate-induced shifts in the jet stream. The elevation of the ice sheet increases further inland and it is thus colder and snowier there; but if average temperatures continue to increase as expected, the line where the moisture comes down as rain instead of snow will rapidly move inward, upward and northward. “The ice should be gaining mass in winter when it snows, but an increasing part of the mass gain from precipitation is lost by melt,” said Oltmanns.
Greenland is not the only place in the far north affected by increasing rain. In recent years, anomalous winter rains have hit the northern Canadian tundra, then refrozen over the surface, sealing in plants that caribou and musk oxen normally forage through the loose snow; in some years, this has decimated herds. And a just-published study from near Fairbanks, Alaska, shows that increasing spring rains are percolating down through the permafrost, thawing it and releasing large amounts of methane, a highly efficient greenhouse gas.
Between 1993 and 2014, global sea-level rise accelerated from about 2.2 millimeters a year to 3.3 millimeters, and much of that acceleration is thought to be due to melting in Greenland. Projections of sea-level rise for the end of this century generally range from two to four feet, but most projections do not yet account for what may happen to the ice in Greenland, nor with the much larger mass in Antarctica, because understanding of the physics is still not advanced enough.
Richard Alley, a prominent glaciologist at Pennsylvania State University, said that the new paper adds to the understanding. “The big picture is clear and unchanged,” he said. “Warming melts ice,” But, he added, the specific processes that will carry this “need to be quantified, understood and incorporated into models. This new paper does important work understanding and quantifying.”
Fiammetta Straneo of Scripps Institution of Oceanography was involved in conceiving the research, and is coauthor on the paper.
Just north of the Arctic Circle in southwest Greenland is a spot at the end of a rugged tundra road where one can step directly off the edge of the earth as most of us know it, and onto the Greenland ice sheet. In summer, hike out a few miles into the jagged, rising surface, and you will hear only wind, the gurgle of running meltwater, and the occasional boom of an ice mass fracturing underfoot somewhere nearby. Amid the 24-hour daylight and seasonal warmth, the ice is rotting. Water ripples in pools and flows through ephemeral streams. In places, the water may plunge and disappear into a moulin–a potentially deadly hole that resonates with the deep-throated thrum of an invisible under-ice river.
Glaciologist Marco Tedesco and a few colleagues walked here this July to study how warming climate is fueling the accelerating decline of the Greenland sheet–the second-largest ice mass on earth. Specifically, he was investigating cryoconites–curious little cylindrical melt holes filled with microorganisms and dust. Often no bigger than a fist, they are part of a much larger natural system that may be magnifying the human forces tearing at the ice.
Tedesco works at Columbia University’s Lamont-Doherty Earth Observatory, home to many ice and snow scientists. A dedicated student of all things frozen, he has a series of snowflakes tattooed on his right bicep, each dedicated to a different person, including his mom. One morning near the start of this latest expedition, he was standing next to a vigorous meltwater stream cutting the ice. “To build an ice sheet is a very long, elaborate process. But it could take really a very short time to melt it all,” he said. “This water flowing here, it has a long memory–it probably froze before Rome was born. What boggles me is the power we humans have to squeeze changes into such a small amount of time. This blanket of ice, it’s like an elephant’s skin. It’s a very powerful dormant animal. But when we wake it up, it has the power to destroy everything it runs through.”
Behind him loomed 660,000 square miles of frozen water. At the edge, it might be only tens of feet thick; in the faraway interior, nearly two miles. If all of it were to melt, it would raise global sea levels about 20 feet. Most scientists think that if this comes to pass due to human-induced climate change, it will take centuries or millennia. But no one really knows. Some of Tedesco’s colleagues recently published geologic evidence that Greenland’s ice did in fact largely disappear some time in the last million years, during one or more past warm periods quite similar to our own.
In any case, sea-level rise is already gnawing at coastal areas and islands around the world, and Greenland is partly responsible. Seasonal melting there has increased by about a third since 1970, in tandem with a 2.2-degree Fahrenheit increase in summer temperatures. It is now losing about 270 billion tons of ice each year. About 70 percent of this loss comes from meltwater runoff; the rest is caused by icebergs discharging directly into the ocean. In 2016, parts of Greenland saw a melt season 20 to 40 days longer than the 1979-2015 average. Largely as a result of this, between 1993 and 2014, yearly global sea-level rise accelerated from 2.2 millimeters to 3.3 millimeters.
Most projections of 21st-century sea-level rise range around two to four feet–but these projections generally do not take into account the melting of Greenland, nor the even bigger mass of Antarctica, because the processes there are still too poorly understood. Considering those factors, some scientists say the rise could be up to 10 feet. That is why it is important to try and figure this out now, says Tedesco.
Climate-related darkening of the ice may be one major factor helping drive the accelerating melt. Windblown dust from natural erosion and human pollution lands on the snowy, naturally reflective surface. In winter, snow covers this up. But because summers are hotter now, come each summer, the surface melts more quickly and extensively, exposing and distilling residue from previous years. Thus the summer surface is becoming progressively darkening. Darker surfaces absorb more solar radiation, so this leads to faster melting. This leads to more darkening. And so on. “It’s a vicious circle,” says Tedesco.
And, it is only part of the circle. Hardy photosynthetic algae and other tiny organisms that specialize in growing within ice and meltwater are basking in the increased warmth, and also building up. To protect themselves from the sun, they develop dark pigments–and this darkens the ice even more. This may be adding greatly to the melting; in fact recent research suggests that such organisms may have now become the primary source of ice darkening. Scientists are only just beginning to appreciate this interplay of ice physics and ice biology. Cryoconites are hot spots of such activity.
Tedesco’s trip began at Kangerlussuaq, a speck of a settlement built around an airstrip that links it to the outside world. In summer the town becomes a staging area for scientists, and for tourists willing to pay the steep cost of getting there for a glimpse of the far north.
Here Tedesco hooked up with Matthew Cooper, a PhD. student at the University of California, Los Angeles, who studies the hydrology of the ice; Dan Bennett, a member of Lamont’s advisory board who had volunteered to come along; and myself. After a couple of days spent sorting out equipment and supplies, we headed out in a rented four-wheel drive pickup along Greenland’s longest road–a rough, 16-mile dirt ribbon following the Akuliarusiarsuup Kuua River, which drains a tongue of the ice sheet.
On the way, Cooper told me that studies by his group have shown the river grows as summer progresses, and melting gathers speed; it also waxes and wanes daily as the sun rises higher in the sky during day and drops lower at night. Near Kangerlussuaq–in Greenlandic, the name means Big Fjord–the river joins other melt streams, and the water flows out said big fjord to the ocean. In recent particularly warm weeks, it has washed out the few crude bridges around town–a real-time, hyperlocal effect of climate change.
Before we even reached the ice, there were reminders that the climate is changing. The road wound through green tundra hills punctuated by raw rock outcrops. In one protected spot we passed a small patch scraggly spruce trees–unremarkable anywhere else, but practically unknown this far north, because it is, or was, too cold. Rumor had it that someone planted these as an experiment some years back. Now they were reaching skyward–not the only place in the Arctic where trees are poised to invade the tundra ecosystem. Tedesco and Cooper’s more immediate concern: polar bears. Normally they live on sea ice, hunting seals, but now the sea ice is melting too, and the 1,000-pound predators are moving onto land–even into the largely lifeless ice sheet, where they have never before been seen. Two had been spotted just weeks before at research stations deep in the ice. One menaced scientists for a day and half before it was shot and killed. We came armed only with pepper spray and air horns.
At first, what appeared to be a low-lying cloud bank loomed on the horizon. This, Tedesco told me, was the Russell Glacier, an outlier of the ice. As we approached, the landscape became ever bigger and grander. Towering, heavily crevassed ice tongues lapped into the river valley’s sides. Creeks gushed out of them and into the river, which raged over rapids and waterfalls.
The road dead-ended at a series of bare hills made of loose dirt and giant boulders–the Russell’s terminal moraine, where advancing ice had previously pushed on the earth like a giant plow. Now, with the glacier in retreat, the ice edge sat low on the other side of the moraine. We made camp nearby. Harried by mosquitoes and distracted by caribou galloping by, the scientists readied instruments and equipment to carry in.
Next day, we hiked over the moraine and descended onto the ice. Here at the edge, it looked more like a dirt sheet than an ice sheet; mud and pebbles coated the crunchy, fast-melting surface. Much of this debris was probably blown off the moraine onto the ice. Jumping the first of dozens of shallow meltwater streams, we walked inward. The ice sloped up in fits and starts. The topography roughened, devolving into hummocks, gullies, hills, pinnacles, cracks, rivulets, puddles, pools and waterfalls. As we ascended, the surface became progressively whiter. It was cold, but the sun was blinding; without sunglasses and sunblock, we would have fried.
After an hour or so, the land behind us was no longer visible. Cracks and meltwater ponds revealed ice that gleamed bright blue–a sign that it had been once deeply buried and heavily compressed, probably over thousands of years. Now the blue ice was exposed to the sun. At one crack, a modest meltwater stream suddenly disappeared into a hole, producing a distant low-frequency gargle. It was a small moulin. “Oooh, that’s creepy,” said Tedesco. “Stay away from that, guys.” Up ahead somewhere, we could hear the distant roar of a much larger one.
We stopped at an irregular swale. Here, the scientists spotted hundreds of circular holes drilled into blue ice. Cryoconites. Ranging from finger- to soccer ball-size, many were filled with crystal-clear meltwater. At the bottoms, a few inches or a foot down, lay a coat of dark ooze. Cooper and Tedesco set up shop here.
Cryoconites exist in icy environments across the world. Biologists have shown the bottom ooze is an admixture of dust, soot and dozens of organisms. These may include photosynthetic algae, bacteria that feed off the dust itself, protozoa, yeasts, microscopic eight-legged rotifers, jellyfish-like tardigrades, and lots of viruses. In many of the cryoconites, small bubbles were forming at the bottoms and ballooning to the surface–methane and other gases produced by this metabolic stew, said Tedesco. He cautioned me not to fill my water bottle from the cryoconites.
No one is exactly sure how they evolve, but somehow, dust and organisms concentrate in one spot. The organisms deposit their byproducts and dead bodies, eventually in enough quantity to form a slime that binds themselves and the dust into a muck that becomes increasingly coherent and efficient at attracting solar energy, melting out a little hole. Little holes become bigger holes. Holes may grow into each other, forming a pond. Liquid in a ponds tends to melt out its sides, and if this progresses outward to a low spot, this spot may become the headwaters of an erosive melt stream.
Tedesco and Cooper had come equipped with sterile bottles, a big syringe and a long spoon to sample the cryoconites’ water and ooze for a biologist at Montana State University. Tedesco deposited a dollop of the ooze on the end of yardstick and offered it to me like a sample of fresh fudge. “Here, you have to feel it!” he said. I did, and it felt like fine, slippery swamp slime. From somewhere nearby came a muffled thunderclap within the ice–slight adjustment of a very large mass, though with no visible results, at least for the moment. Everyone looked at each other, then went back to work.
Tedesco had lugged up a heavy, breadbox-size spectrometer in a backpack. With Bennett holding a laptop to record data, he walked around pointing an attached sensor at the sky, then at the surface, to measure incoming light, and the amount and colors being reflected back. Such measurements are routinely made by satellites on a much larger scale. Comparing ground data with these should help researchers understand how to interpret the satellite imagery, and how small features like cryoconites feed into the overall picture. As a side project, Tedesco is in on a NASA effort to study Mars, where cryoconite-like features are thought to exist. Do they hold liquid water, like those on earth? Do they have living ecosystems? Comparing the light signatures of earthly cryoconites with Martian ones might help address these questions.
Cooper, for his part, had carried up a small drone equipped with a camera. With a portable joystick setup, he launched the helicopter-like machine. It flew a series of grids over the study area with a sound like a giant hummingbird. The images would later be stitched together to make a highly detailed map of the area.
As the evening sun dipped toward the horizon, we made our way back to camp, Tedesco lugging a now-loaded picnic cooler holding water and ooze samples. It was 8pm by the time we returned, and getting quite cold. A young caribou trotted by. After a quick dinner heated up on a portable stove, Tedesco and Cooper were up until midnight checking out their data and recharging batteries.
During the following few days, Cooper tested out an instrument to measure light penetration under the ice. One day, fog rolled in, and we did not venture out; too easy to get lost out there. Occasionally, a few hardy tourists showed up in rented vehicles. Most just stepped briefly onto the ice edge to take selfies, and turned around.
On the final day of fieldwork, we hiked back to the initial study site. This time, Cooper and Tedesco lugged in a 10-foot pole and tripod in order to mount the spectrometer well above the ice. The apparatus was unwieldy, and it took them several hours to wrestle it into position in several spots.
It was getting late, but we decided to do some extra scouting. Following the distant roar of water we had heard the first day, we hiked deeper into the ice. Past a series of ridges, we came upon a clear river running in a blue-ice canyon maybe a hundred feet deep. At one sharp bend, a whirlpool churned. Upstream, to our right, the river wended its way out of sight through a series of loops reminiscent of the Grand Canyon. To our left, it entered a snow-roofed tunnel and abruptly swirled down the lip of a giant, roaring hole. We knew enough not to get too close. It was time to stop doing science, and just stand back in fear, and awe.
As climate warms, the Greenland ice sheet is melting, helping to fuel global sea-level rise. Follow a small team of scientists as they hike onto the sheet to investigate the forces large and small that are demolishing the ice. (All photos: Kevin Krajick) READ THE FULL SCIENTIFIC STORY AND SEE A VIDEO
Earth Institute explorations have led to vitally important new discoveries. In 2017, Gisela Winckler and Joerg Schaefer from the Lamont-Doherty Earth Observatory developed findings about the history of Greenland’s ice sheet that have incited new questions around science’s understanding of the Arctic. Here is the story from Lamont-Doherty’s 2017 annual report. Meanwhile, our 2018 field work season is already in full swing.
A combination of processes determines future sea level rise: thermal expansion of the oceans (the seas swell when water warms); the melting of the ice sheets that cover Greenland in the extreme north and Antarctica in the extreme south; and mountain glacier retreat, the melting of glacial ice on Earth’s mountain ranges. Projections of sea-level rise by the end of this century hover between two and three feet, but many, including predictions compiled and synthesized by the Intergovernmental Panel on Climate Change, do not take Greenland into account. For decades, scientists believed that the Greenland Ice Sheet is relatively stable compared with the vulnerable West Antarctic Ice Sheet.
Two Lamont scientists questioned this assumption about Greenland’s ice and wanted to take a much closer look.
To find answers, geochemists and climate scientists Joerg Schaefer and Gisela Winckler needed to obtain a portion of what is one of Earth’s rarest geologic samples, the only bit of bedrock yet retrieved from the base of the Greenland Ice Sheet, drilled from nearly two miles below the summit of the ice sheet and into the bedrock more than two decades ago.
“It is the most expensive piece of rock ever retrieved on Earth,” said Schaefer. The National Ice Core Laboratory in Lakewood, Colorado, where the core is archived granted the scientists a small portion to subject to geochemical analysis.
Both Schaefer and Winckler specialize in an analytical process that dates samples with cosmogenic nuclides, isotopes produced by tiny particles from outer space that constantly bombard the planet. Specific isotopes are characteristic of exposure to the open sky. Winckler and Schaefer posited that if they could access the surface of Greenland that lies beneath the ice sheet, they could test for the presence of these isotopes and thereby illuminate the history of Greenland’s ice cover, giving scientists a clearer picture of its stability. What they discovered upends aspects of the world’s understanding of polar ice and its impact on the future of the planet.
“The two nuclides we analyzed clearly told us the bedrock that sits underneath the summit of Greenland was exposed for a substantial amount of time,” Schaefer explained. “This simple measurement gets rid of the idea that Greenland is a stable ice cube,” said Schaefer.
“The fact that we measured a certain amount of these cosmogenic nuclides means this whole thing was open to the sky. All of the ice was gone,” said Winckler.
Their analysis shows that Greenland was deglaciated for extended periods during the Pleistocene epoch (from 2.6 million years ago to 11,700 years ago), on the basis of their measurements of cosmic-ray produced beryllium and aluminum isotopes in the bedrock core. Within the rock, the scientists found traces of radioactive beryllium-10 and aluminum-26. The isotopes decay at known rates, and since they cannot be created if the rock is covered with ice, their abundance can be tied to the time when the rocks were exposed. Modelers agree that the region where the core was taken would be one of the last to melt were the ice sheet to disappear. The authors thus concluded that the ice sheet must have been down to less than 10 percent of its current mass when this site was ice-free.
“Unfortunately, this makes the Greenland ice sheet look highly unstable,” said Schaefer. “If we lost it during periods of natural forcing, we may lose it again.” With human-induced warming now well underway, loss of Greenland ice has approximately doubled since the 1990s; during the last four years, by some estimates, it shed more than a trillion tons. Jeff Severinghaus, a paleoclimatologist at the Scripps Institution of Oceanography who was not involved in the study, called the evidence “very direct and incontrovertible.” The study “challenges some prevailing thought on the stability of the ice sheet in the face of anthropogenic warming,” he said. “We can now reject some of the lowest sea-level projections, because the models underpinning them assume continuous ice cover during the last million years.”
Scientists disagree about which potential forces might tip the Greenland ice into quick decline.
These could include water percolating from the surface to lubricate the ice sheet’s base, or massive ice streams discharging icebergs into the ocean.
“That’s the big worry, not today or tomorrow, but that there could be something in the system that is catastrophic. All of a sudden, not gradual, and then the ice is breaking up,” said Winckler.
“Our study steered the entire research field away from the idea that Greenland is a stable ice cube to, ‘oh, my God, Greenland is not stable,’” said Schaefer. “We are missing something big.”
These findings will inform new models of Greenland’s ice. Winckler and Schaefer say their next step is to obtain funding to do a more comprehensive study of the bedrock beneath the ice, to develop a more detailed picture of the past, present, and future of the Greenland Ice Sheet.
Nicolás Young (LDEO), Jason Briner (UB) and an assortment of fellow scientists and graduate students are gearing up to spend a third summer camping along the Greenland ice margin. As part of an ambitious multi-institutional and cross-disciplinary project, NSF-funded Snow on Ice, Young and Briner are collecting lake sediment, rock, water and plant samples that will be used to tease apart linkages between reductions in sea ice on the Arctic Ocean, atmospheric uptake through increased evaporation from the exposed ocean surface and changes in snowfall on the Greenland Ice Sheet. The fieldwork will be centered in southwest Greenland where climate sensitivity during past interglacials was the greatest. The resulting data will be combined with new isotopic ice core work (UW) and updated subglacial topography (UCI), for delivery to two sets of modelers on the project team (UM and NASA JPL) to feed into a set of nested models. Canada’s Geotop and Denmark’s GEUS fill out the partner list.
Explore the photo essay below and read more below to learn about the exciting work of the Snow on Ice Project.
The project goal is to look at the last 8000 years in Western Greenland, spanning back into the last Thermal Maximum when temperatures were approximated at 1-2°C warmer than today and the ice sheet was smaller. It is difficult to constrain the dimensions of an ice sheet that is smaller than present as the traditional markers that are used for evidence are covered over but we will tackle it with the multiple instrument approach described above. The data will be used as a proxy for what might happen in Greenland’s future, addressing with increased certainty whether reductions in Arctic sea ice in the past triggered a feedback loop that caused increased precipitation falling as snow, and resulted in stabilizing the Greenland ice Sheet even in a warming climate.
For more on this project see the Snow On Ice website.
As climate warms, the surface of the Greenland ice sheet is melting, and all that meltwater ends up in seasonal rivers that flow to the sea. At least that is what scientists have assumed until now. Now, a new study has shown that some of the meltwater is actually being soaked into porous subsurface ice and held there, at least temporarily. The finding is part of the first comprehensive on-the-ground study of such a river system. The research could alter calculations of how ongoing melting might fuel global sea-level rise.
Declining ice sheets have been playing an growing role in sea-level rise in recent years. Satellite measurements show that Greenland is losing an average of 260 billion tons of ice a year to the ocean. Something less than half of that appears to come from icebergs falling off the end of the sheet into the sea; the rest is presumably meltwater. But it is not clear exactly how much meltwater actually reaches the sea and where it comes from, because most of the plumbing system is hidden under ice. Lacking direct measurements, computer models have generally used the assumption that meltwater just flows directly out. “It’s always treated as a parking lot, water runs straight off,” said Laurence Smith, a geographer at the University of California, Los Angeles who led the new study.
The study indicates that instead, “the ice acts as a sort of sponge, in which part of the water is trapped,” said Marco Tedesco, a glaciologist at Columbia University’s Lamont-Doherty Earth Observatory and coauthor of the paper. “Instead of behaving like a rigid slab, the ice can rot, creating pores and interstices that are filled with water.” Writing in the Italian newspaper La Repubblica, Tedesco said, “The inclusion of this phenomenon reduces discrepancies between satellite data and model outcomes and may alter Greenland’s projected contributions to sea-level rise.” Tedesco said that meltwater sponged up by various parts of the sheet will eventually make its way to the sea, but the timetable is unknown.
The scientists gathered their data in summer 2015 from a 27-square mile watershed on the ice surface, consisting of a complex system of lakes, tributary creeks and a substantial river. The river culminated at a moulin—a giant hole where the water plunged down, presumably all the way to the rocky bed of the ice. The team mapped the watershed with a drone. Then, anchored to icy stream banks to avoid a fatal fall in, team members took turns lowering instruments down to take hourly readings of the water’s volume, velocity, temperature and depth. They also dropped free-floating sacrificial instruments into the current that took continuous readings until they were swept into the depths of the moulin. The work was documented in a multimedia package by The New York Times.
The scientists determined that up to 430,000 gallons per minute flowed into the moulin. But this did not account for all the water being fed by the watershed. The rest, they concluded, was being soaked into cracks and pore spaces of so-called rotten ice along the route, and probably stored there. Previous models have assumed that there was about 20 to 60 percent more runoff than what the scientists actually measured.
“After eliminating all the other possibilities, we deduced that the disagreement in our data could be attributed to subsurface melting and meltwater storage,” said coauthor Dirk van As, a researcher at the Geological Survey of Denmark and Greenland.
“If there’s a mismatch between observation and model, that means the model is moving the mass in one way or another and not respecting the way things happen in the real world,” said Tedesco.
Tedesco and colleagues plan to return to Greenland this summer to investigate other phenomena, including the widespread growth of algae within the ice that is darkening the near-surface and apparently increasing the ice’s uptake of solar energy. This in turn may be accelerating melting in many areas.
When summer temperatures rise in Greenland and the melt season begins, water pools on the surface, and sometimes disappears down holes in the ice. That water may eventually reach bedrock, creating a slipperier, faster slide for glaciers. But where does it go once it gets there, and what happens to it in the winter? A new study helps answer these questions.
Scientists have been able to observe liquid water at single points by drilling holes, but those observations are limited. An improved technique developed by a graduate student at Lamont-Doherty Earth Observatory and her colleagues is now expanding that view across entire regions, and across seasons for the first time, by making it possible to use airborne ice-penetrating radar to reveal meltwater’s life under the ice throughout the year.
The first results, just published in the journal Geophysical Research Letters, reveal extensive winter water storage beneath the ice. They suggest that glaciers’ response to melting depends not only on the rate at which meltwater flows down, but also on the amount of water stored beneath the ice through the winter, and on the topography and permeability of the land below, said the study’s lead author, Columbia University graduate student Winnie Chu.
“The distribution of meltwater evolves constantly, switching from one location to another,” said Chu. “By knowing how this distribution changes seasonally, we can better understand the spatial linkage between ice and water flow.” Chu said that more meltwater is produced as temperatures rise, and the study suggests that Greenland has the potential to store some of it at the base of the ice. This could potentially mediate the impact of meltwater on summer ice flow by maintaining stable subglacial water pressures through the year, she said.
Greenland’s ice sheet has a wide range of temperatures and impurities that cause the ice to freeze in different ways, and those variations have made it difficult for ice-penetrating radar to identify pockets of water beneath the ice. Chu and her colleagues developed a way to correct for those variations by using 3D thermomechanical ice-sheet models and knowledge of the ice sheet’s chemistry to bring out the reflectivity that indicates water in radar data.
In the study, the researchers describe where water was prevalent inside the ice at the start of the melt season and where it was present at the end of winter in Russell Glacier and neighboring Isunnguata Sermia, in western Greenland. They showed that early in the melt season, most of the meltwater reaching bedrock was along sediment-filled troughs beneath the glaciers. In contrast, during the winter, the bulk of the region’s subglacial water could be seen pooling in higher bedrock ridges, while the lower-elevation troughs were mostly dry.
The scientists suspect that during warmer weather, water pressure opens drainage systems in the ice, allowing meltwater from the surface to flow through to the troughs below. Those channels may close in the winter as less water pours in and water pressure decreases. In the troughs, the sediment-filled floor allows for better drainage. “Any remaining subglacial water then likely continues to seep through groundwater drainage, leaving little wintertime storage at the ice-bed interface,” the authors write. But the ridges are made up of less permeable material, so water can pool on them.
The effect of water is evident in the changing speed of the glaciers during the year. During the 2010 melt season, Russell Glacier flowed more than twice as fast as it did at the end of the following winter, the authors write. The glacier speeds up in early summer, suggesting water pressure rises rapidly there, Chu said. It decelerates quickly at the end of summer, suggesting that the formation of channels in the ice creates more efficient, faster drainage of the meltwater from the glacier bed, the scientists write.
Neighboring Isunnguata Sermia accelerates more slowly. That could be associated with its apparent widespread subglacial water storage capacity, which may be maintaining water pressures through the winter, Chu said. Russell Glacier, in contrast, has less winter water storage and would experience a greater increase in water pressure at the start of the melt season.
“Our findings suggest that the winter subglacial hydrological state could pre-condition the glacier response to additional meltwater in the following summer,” Chu said.
The technique used in the study provides a clearer view of how water moves beneath the ice than any other existing method, said Joseph MacGregor, a glaciologist and geophysicist at NASA-Goddard Space Flight Center who was not involved in the study.
“We have prevailing ideas of how water flows on the surface of ice sheets, through ice sheets, and under ice sheets. What we don’t have are great observations of where that water is beneath the ice most of the time,” MacGregor said. “This result changes that state of affairs. It also demonstrates the value of airborne remote sensing for testing fundamental glaciological hypotheses.”
The paper’s coauthors are Dustin Schroeder of Stanford University; Helene Seroussi of the Jet Propulsion Laboratory at the California Institute of Technology; Steven Palmer of the University of Exeter; and Timothy Creyts and Robin Bell of Lamont-Doherty Earth Observatory. The paper, “Extensive winter subglacial water storage
beneath the Greenland Ice Sheet,” is available online.
In southern Greenland in summer, rivers have been streaming off the ice sheet, pouring cold fresh water into the fjords. Attention has focused on the West Coast, where the majority of the meltwater has been entering the ocean in recent years, but a new study suggests that a greater risk to global climate may actually be coming from the east.
Along the West Coast, meltwater is kept close to shore by the winds that push it northward, the study shows. On the East Coast, however, as much as 60 percent of the meltwater is caught up by the East Greenland Current and ocean eddies that carry it to the Labrador Sea.
Once that cold freshwater is offshore, it can have a powerful effect on the ocean circulation that drives global climate. Recent studies have suggested that the Atlantic Meridional Overturning Circulation—the current that brings warm water up from the tropics toward Greenland and then turns south along North America’s Eastern Seaboard—is slowing and that cold Greenland meltwater may be to blame.
“It’s not like pouring water in a glass that stays where you pour it. It’s more like dumping water in a river—the freshwater will go where the river currents go. In this case, meltwater from the east is flowing toward the Labrador Sea, where it can have a great effect on the global climate,” said study co-author Marco Tedesco, a research professor at Columbia University’s Lamont-Doherty Earth Observatory and adjunct scientist at the NASA Goddard Institute of Space Studies.
Cold, salty water sinks, mixing with the warmer water brought up from the tropics and allowing heat to escape. Cold fresh water, on the other hand, is less dense than salt water and stays at the surface longer. In a 2015 paper, Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research highlighted an abnormally cold region of the North Atlantic and suggested it may be connected with cold Greenland meltwater that appeared to have contributed to the Atlantic Meridional Overturning Circulation slowing in recent decades.
In the new study, published this week in Nature Geoscience, the scientists followed the paths of Greenland’s meltwater using advanced computer modeling with maps of ice-sheet rivers and ocean-going tracers that can track currents. They found that only up to 15 percent of meltwater runoff from Southwest Greenland was being transported into the Labrador Sea, while as much as 50 to 60 percent of meltwater from Southeast Greenland reached the middle of the Labrador Sea.
“The large difference in fate between runoff coming from the West and East coasts of Greenland was quite surprising,” said co-author Renato Castelao of the University of Georgia. “While many studies have quantified nutrient fluxes in meltwater runoff from West Greenland, our results suggest that the northern Labrador Sea will be more influenced by chemical constituents introduced along the East Coast. Constraining fluxes from East Greenland glaciers will be important to quantify the potential impacts of increased runoff on stratification and biogeochemical processes in a region of the ocean that plays a critical role on global climate.”
Greenland’s melt rate is predicted to increase as the planet warms, also affecting sea level rise. On land, Tedesco has also shown how Greenland’s melting is triggering feedback loops, with the effects of melting reducing the ice sheet’s albedo, or reflectiveness, which increases melting. With that in mind, the authors also explored what would happen in the ocean if Greenland’s meltwater rate doubled. Doubling meltwater would more than double the impact on salinity offshore and would keep abnormally cold regions in the Labrador Sea later into winter, they write.
“This is something that needs absolutely to be monitored because of the impact on local ecosystems and the potential feedback of melting glaciers, but also because of the potential impact on a global scale,” Tedesco said.
Former NASA-GISS Director James Hansen, now director of the Climate Science, Awareness and Solutions program at Columbia University’s Earth Institute, waved a red flag last month about the risks that a melting Greenland Ice Sheet could be creating for ocean circulation, warning that increasing meltwater could shut down the Atlantic Meridional Overturning Circulation. If that happened, the North Atlantic would cool and the tropics would continue to warm as CO2 levels increased. The large temperature difference between sea surface and air temperature could drive severe storms along the U.S. East Coast, Hansen warned.
“What happens in Greenland is important, not just for the Arctic but for everything that happens on our planet,” Tedesco said. “You melt something on the East Coast of Greenland, that’s impacting the ocean at both local and global scales, which in turn impacts the climate and life of the Earth.”
The lead author of the new paper is Hao Luo of the University of Georgia. In addition to Tedesco and Castelao, the co-authors include Patricia Yager and Thomas Mote of the University of Georgia; Asa Rennermalm of Rutgers University; and Annalisa Bracco of Georgia Institute of Technology.
Leveraging Local Knowledge to Measure Greenland Fjords: Understanding the Community
Project Background: Changing conditions in Greenland’s northwest glaciers over the last decade have led to a range of questions about water temperature and circulation patterns in the fjords where ocean water meets the glacial fronts. We can use satellites to measure the loss of elevation, the acceleration of ice flow, or the retreat of ice from a glacier, but we can’t use satellite measurements to collect water column temperature profiles. Water column profiles would allow us to better determine how much melt is possible at the glacier connection to the ocean, and help us pinpoint why neighboring glaciers are behaving differently.
The Leveraging Local Knowledge project will work with members of local Greenlandic communities to collect water measurements in the fjords. This will assist in determining if warming Atlantic Ocean water is circulating up through Baffin Bay where it enters the fjords to lap against the frozen glacier footholds, causing them to loosen their hold on the rock below. Alison Glacier (74.37N and 56.08W) is selected as the project focus. Emptying into Melville Bay to the east of Kullorsuaq Island and has been undergoing dramatic change over the last decade.
Our Journey: Our research trip to the small village of Kullorsuaq is a journey that will start 200 kms to the south in the community of Upernavik, located 800 kms north of the Arctic Circle. Flying in on a small 37 seat Dash 7 airplane we overlook a coastline that is lined with glaciers flowing into a bay that is dotted with islands. Most are uninhabited, but Upernavik is home to a population of 1500 permanent residents. An island community, the main employment is fishing with the waterfront sporting a range of both commercial and smaller independent fishing boats.
Upernavik town was established by the Danes in the late 1700s but trade and a religious mission in the early 1800s cemented it as a permanent settlement. The southern end of the island is dotted with a cross covered graveyard representing the religion the Danish settlers brought and the practice of the current community. Christmas, Three Kings Day and other religious holidays are all causes for the community to celebrate. This week the priest will visit Upernavik to celebrate three weddings (Friday and Saturday) and the Confirmation (Sunday). With all such events scheduled for when the priest can preside the parties and celebrations will involve the whole community for days. Celebration and gatherings are a large part of this community’s practice.
The Setting: The icebergs being sloughed from the neighboring glaciers dominate the horizon, littering the waterfront with ice ranging from house-sized blocks to looming masses that appear as large as the neighboring islands. Looking around at the open water it is hard to imagine the origin of these large masses of ice. The closest blocks of ice move during the course of the day, shifting back and forth from north to south and back again. With the shifting and changing of the icebergs the sound of the settling and collapsing of ice is drilled into our consciousness – the sharp crack of the ice as if fractures and the larger canon-like rumble as sections break and fall into the water.
Our local host, a Dane who has lived in Upernavik for 40 years, has fully blended himself into the community where he and his family are well known and liked by both the Inuit and the Danish population. When he learns of our project he observes that in his time here ice cover has significantly changed. He recalls his early years here when the ice in May was so solid in the bay that visiting boats had to drop dynamite on the ice to open a pathway. He points to the open water and the line of haze that hangs on the horizon offering a cause, ‘global heating’.
Other changes have hit Upernavik. We meet a Danish couple who had spent 4 years living in the community, now returning after 30 years to ‘close out their memories’. They spoke with fondness of this lost time when they raised their small children as they worked as a teacher and a nurse. With a team of 10 dogs ‘Lars’ had hunted Greenlandic seal and still had a sharp eye picking a bobbing seal head out on the horizon. They spoke of the people numbering 900 while the Greenlandic dogs had numbered 3000, many times more than the dogs are now. Dogsleds were an important part of that older Upernavik when individual hunting and fishing were the mainstay of the community. While hunting and fishing are still important today Lars notes that things have changed becoming less rugged for an individual. Whether the changes in ice cover have played a part in this is hard to determine.
In our few days here in Upernavik we learn that residents are happy to help, they have networks that reach from one island community to another. Names and contacts are offered freely – “try this person for a place to stay”, “this teacher may be interested in helping you”. It is this networking of local people that we will rely on for the project. Their overall interest in what is happening to their community will be an important part of its long term success.
Leveraging Local Knowledge to Measure Greenland Fjords:
Dave Porter and Margie Turrin are in northwest Greenland working with local community members to collect water column temperature profiles. The project is funded by a Lamont Climate Center grant with support from the NASA Interdisciplinary Program and logistical support from NSF.