Scientists who study the melting of Greenland’s glaciers are discovering that water flowing beneath the ice plays a much more complex role than they previously imagined.
Researchers previously thought that meltwater simply lubricated ice against the bedrock, speeding the flow of glaciers out to sea.
Now, new studies have revealed that the effect of meltwater on acceleration and ice loss -- through fast-moving outlet glaciers that connect the inland ice sheet to the ocean -- is much more complex. This is because a kind of plumbing system evolves over time at the base of the ice, expanding and shrinking with the volume of meltwater.
Researchers are now developing new low-cost technologies to track the flow of glaciers and get a glimpse of what lies beneath the ice.
As ice melts, water trickles down into the glacier through crevices large and small, and eventually forms vast rivers and lakes under the ice, explained Ian Howat, assistant professor of earth sciences at Ohio State University. Researchers once thought that this sub-glacial water was to blame for sudden speed-ups of outlet glaciers along the Greenland coasts.
“We’ve come to realize that sub-glacial meltwater is not responsible for the big accelerations that we’ve seen for the last ten years,” Howat said. “Changes in the glacial fronts, where the ice meets the ocean, are the real key.”
“That doesn’t mean that meltwater is not important,” he continued. “It plays a role along these glacial fronts -- it’s just a very complex role, one that makes it hard for us to predict the future.”
In a press conference at the American Geophysical Union (AGU) meeting in San Francisco on Wednesday, December 16, 2009, Howat will join colleagues from the University of Colorado-Boulder/NOAA Cooperative Institute for Research in Environmental Sciences (CIRES) and NASA’s Jet Propulsion Laboratory (JPL) to discuss three related projects -- all of which aim to uncover how this meltwater interacts with ice and the ocean.
Their work has implications for ice loss elsewhere in the world -- including Antarctica -- and could ultimately lead to better estimates of future sea level rise due to climate change.
Howat leads a team of researchers who are planting inexpensive global positioning system (GPS) devices on the ice in Greenland and Alaska to track glacial flow. Designed to transmit their data off the ice, these systems have to be inexpensive, because there’s a high likelihood that they will never be recovered from the highly crevassed glaciers.
Howat will describe the team’s early results at the AGU meeting, and give an overview of what researchers have learned about meltwater so far.
John Adler, a doctoral student at CIRES, works to calculate the volume of water in lakes on the top of the ice sheet. These lakes periodically drain, and the entire water volume disappears into the ice. He uses small unmanned aerial vehicles to measure the ice’s surface roughness -- an indication of where cracks may form to enable this drainage to happen. Other members of his team are releasing GPS-tagged autonomous probes into the meltwater itself, to follow the water all the way down to the base of the ice sheet and out to sea.
“My tenet is pushing the miniaturization of technology, so that small autonomous platforms -- in the sea, on the surface, or in the air -- can reliably gather scientific information in remote regions,” Adler said.
All these efforts require cutting-edge technology, and that’s where Alberto Behar of JPL comes in. An Investigation Scientist on the upcoming Mars rover project, Behar designs the GPS units that will give researchers the data they need.
Howat’s team placed six units on outlet glaciers in Greenland last year, and this year they placed three in Greenland and three in Alaska. The units offer centimeter-scale measurements of ice speed, and Behar designed the power and communications systems to keep the overall cost per unit as inexpensive as possible.
Howat has found that glacial meltwater at the base of the ice sheet has little influence on ice loss along the coast -- most of the time.
All over Greenland, meltwater collects beneath the ice, gradually carving out an intricate network of passageways called moulins. The moulins form an ever-changing plumbing system that regulate where water collects between the ice and bedrock at different times of the year. According to Howat, meltwater increases as ice melts in the summer, and decreases as water re-freezes in winter.
In the early summer, the sudden influx of water overwhelms the subglacial drainage system, causing the water pressure to increase and the ice to lift off its bed and flow faster, to the tune of 100 meters per year, he said. The water passageways quickly expand, however, and reduce the water pressure so that by mid-summer the glaciers are flowing slowly again.
Inland, this summertime boost in speed is very noticeable, since the glaciers are moving so slowly in general.
But outlet glaciers along the coast are already flowing out to sea at rates as high as 10 kilometers per year -- a rate too high to be caused by the meltwater.
“So you have this inland ice moving slowly, and you have these outlet glaciers moving 100 times faster. Those outlet glaciers are feeling a small acceleration from the meltwater, but overall the contribution is negligible,” Howat said.
His team looked for correlations between times of peak meltwater in the summer and times of sudden acceleration in outlet glaciers, and found none. “Some of these outlet glaciers accelerated in the wintertime, and some of accelerated over long periods of time. The changes didn’t correlate with any time that you would expect there to be more melt,” he added.
So if meltwater is not responsible for rapidly moving outlet glaciers, then what is responsible? Howat suspects that the ocean is the cause.
Through computer modeling, he and his colleagues have determined that friction between the glacial walls and the fjords that surround them is probably what holds outlet glaciers in place, and sudden increases in ocean water temperature cause the outlet glaciers to speed up.
Howat did point out two cases in which meltwater can have a dramatic effect on ice loss along the coast: it can expand within cracks to form stress fractures, or it can bubble out from under the base of the ice sheet and stir up the warmer ocean water. Both circumstances can cause large pieces of the glacier to break off.
At one point, he and his colleagues witnessed the latter effect first hand. They detected a sudden decrease of sub-glacial meltwater inland, only to see a giant plume of dirty water burst out from under the ice at the nearby water’s edge.
The dirty water was freshwater -- glacial meltwater. It sprayed out from between the glacier and the bedrock “like a fire hose,” Howat said. Since saltwater is more dense than freshwater, the freshwater bubbled straight up to the surface. “This was the equivalent of the pipes bursting on all that plumbing beneath the ice, releasing the pressure.”
That kind of turbulence stirs up the warm ocean water, and can cause more ice to melt, he said. “So you can’t just say, ‘if you increase melting, you increase glacial speed.’ The relationship is much more complex than that, and since the plumbing system evolves over time, it’s especially hard to pin down.”
This research was funded by Ohio State’s Climate, Water, and Carbon Program; NASA; and the National Science Foundation.Contact: Ian Howat, (614) 292-6641; Howat.firstname.lastname@example.org
Ian Howat | EurekAlert!
Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute
Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
07.12.2016 | Health and Medicine
07.12.2016 | Life Sciences
07.12.2016 | Health and Medicine