From the microstructure of snow to the massiveness of ice sheets, from fundamental science to practical applications, from Thayer's ice lab to the earth's polar regions, Thayer researchers are uncovering what snow and ice reveal about the world.
By Elizabeth Kelsey, Lee Michaelides, and Karen Endicott
COLD TRUTH: Ice Creeps and Fractures
RESEARCHER: Professor Erland Schulson
Professor Erland Schulson opened his ice lab in the basement of Cummings Hall 29 years ago to study the basic physics and mechanics of ice. “The object is to understand the physical processes that lead to creep and fracture,” says Schulson. “But this is not done in isolation of the world’s issues. Issues are driving the work.”
Shortly after arriving at Dartmouth, Schulson, who has a doctorate in metallurgical engineering, was intrigued by the work being done a few miles north at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) and decided he wanted an ice lab at Thayer to do complementary research. Funding from Mobil Oil and the Army helped establish Dartmouth’s Ice Research Laboratory (IRL), and a $7.2-million grant from the Navy funded a major upgrade in 1987.
Schulson still directs the IRL, which is currently outfitted with eight custom cold rooms, various presses, a cold-room machine shop, an electron microscope, cameras, an X-ray micro-CT scanner, and a multi-axial loading system that remains unique in the world.
What changed over the years are the issues driving the work. Originally the IRL worked on problems related to oil exploration and national defense. “The Navy was very concerned about submarines surfacing through the ice,” says Schulson. Research related to the oil industry, dormant for a while, is back in the forefront. The Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) recently awarded the lab $500,000 to study how Arctic sea ice breaks as it flows and pushes against engineered structures. Through micromechanical modeling and experimentation, the IRL will identify physical characteristics of ice conditions and quantify the rate at which ice becomes fractured and weakened. “The U.S. Geological Survey estimates that about 13 percent of the world’s undiscovered oil and about 30 percent of the world’s undiscovered gas are located above the Arctic Circle—most of which is beneath the Arctic Ocean. The ice forms a thick 1–3-meter mobile cover on the ocean, and therein lies the challenge to recovery,” says Schulson.
Part of his research focuses on climate change. Given that polar regions are canaries in the global climate coal mine, scientists want to know what will happen as polar ice sheets melt and crack. Climate-change questions also circle back to the work done for BOEMRE: as ice fractures, what will be the impact on the industrial infrastructure?
Schulson’s ice expertise has interested NASA over the years. After the 2003 Space Shuttle Columbia disaster, NASA consulted Schulson about ways to prevent ice from building up on the external fuel tanks. Now the space agency is funding Schulson to study the icy surfaces of Europa, Jupiter’s largest moon, and Enceladus, the second moon in the Saturn system.
It seems amazing that research done on ice blocks at Thayer applies to the ice crust of Europa some 367 million miles from earth. But comparing photos of ice in his lab, Landsat satellite photos of Arctic ice, and photos of Europa, Schulson sees similar fracture patterns. His conclusion: “Patterns of fracture are independent of scale.”
As with many emerging areas of knowledge, not everyone agrees with Schulson. “Some geophysicists are skeptics,” he says.
But NASA wants to learn more about the ice on Europa because “the conditions are there for a form of life,” says Schulson. “NASA has engaged the IRL to get more information about the creeping, fracturing, and frictional sliding of ice because underneath the ice there may be an ocean. And where there is an ocean, the potential exists for a form of life.”
Schulson, coauthor with Paul Duval of Creep and Fracture of Ice (Cambridge University Press 2009), the first complete account of these mechanical properties, brings his appreciation for ice into the classroom. “Ice is a wonderful teacher,” he says. “Ice is a transparent material, and you can see cracks in ice, whereas you can’t see cracks in other brittle materials. We can understand ice and relate it to other materials, like rock.” (In fact, the National Science Foundation is funding Schulson and Dartmouth earth sciences professor Carl Renshaw to study faulting in ice for insight into how faults form and earthquakes develop in the earth’s crust.)
“For someone learning about materials science, the clarity of ice allows students to see inside ice as it deforms under pressure,” says Schulson. “This has been one of the most intellectually satisfying parts of this whole thing—to be able to relate what we see in ice to other materials and then what we see in ice in the lab to what we see in ice in the field.”
COLD TRUTH: Ice Resembles Metals
RESEARCHER: Professor Ian Baker
Professor Ian Baker doesn’t mind admitting that he fell into ice work at Thayer. “I started reading about dislocations in ice really because of Erland Schulson’s work here, and then I got interested in this question about how ice deforms on a fundamental level,” he says. “Nobody has answered it yet. Nobody knows for sure.”
Baker applied what he did know—the physics of various metals and intermetallic compounds—to ice.
He began by using transmission electron microscopy to study how ice changes over time. Despite using liquid nitrogen (a frigid -346°F) to keep the ice from melting, Baker encountered a technical problem. “Ice suffers tremendous beam damage in the electron microscope,” he says. “Ionization damage breaks the bonds in the ice, and the bonds reorient themselves. You end up with voids that form very rapidly in the ice and change the defect structure.”
Next he tried synchrotron X-ray topography. “The X-ray technique images the defects like the electron microscopy, but it doesn’t use electrons, so it’s less of a problem. You do need a synchrotron, so I used the Brookhaven National Laboratory’s synchrotron,” he says. “We could do real-time experiments, deforming the ice and looking at how the defects moved in the ice. That led me to look at the effect of impurities on the dislocations’ motion. We added dopants, like hydrofluoric acid and hydrochloric acid, to pure ice to see how they affected the velocity at which these defects moved.”
He moved on to studying the effects of an impurity that abounds in nature: sulfuric acid from decomposition, volcanic eruptions, and other phenomena. “It turns out that sulfuric acid has a really dramatic effect. It makes ice softer and more ductile, which means you can deform it more before it cracks,” Baker says. “Then the question was: We can show this in the lab, but does this have any relevance to ice out in nature?”
For answers he looked at ice cores. “Natural ice consists of individual crystals that make up a big block of ice. A lot of people think that the impurities end up in the interfaces between the crystals. We found that the impurities are both in the interfaces and in the crystal itself,” he says, giving credit to Daniel Cullen ’86 Th’02, who was then his graduate student and is now a lab manager at Thayer.
The work necessitated creative lab techniques, including new ways of preparing ice specimens for scanning electron microscopy and using a confocal scanning optical microscope. “Instead of shining a light over something, you scan a beam over the surface. At each point you can get a signal; you can get the Raman spectrum from it so you can determine the impurities in the ice,” Baker says. “Later we were able to get the electron backscatter patterns from ice. We were the first people to do that.”
The work put Baker’s ice lab on the map. “We’ve got a lab that can characterize ice microstructurally in the same way that people can do metals. We’re pretty much the only lab in the world that does that,” he says. “We’ve had a lot of collaborators in the last couple of years who come along because we can do things that nobody else has got that setup for.”
A member of the ice core advisory group for the National Ice Core Laboratory in Denver, Baker is now studying ice from Greenland to learn more about the microstructural changes that occur when ice sheets flow. He’s also collaborating with Professor Mary Albert on gases in firn, old snow that hasn’t become ice. “People look at trapped gases to determine past climate. One question is: When were those gases actually trapped?” he says. “Pores are open to the atmosphere to quite a depth, so as the wind blows over the top of the ice sheet, the air goes into these pores and exchanges with what’s in there, so the pores generally are much younger than the ice surrounding them. The pores are not all closed off at the same time. Some are probably closed off close to the surface and some are closed off 70 meters down, so we’re trying to figure that out by relating permeability measurements to the microstructure.”
Meanwhile, Baker works on metals as well, including iron oxide nanoparticles for use in cancer treatments and magnetic materials for energy applications.
There’s no disconnect for him. “When I work on ice or snow I come at it from a materials scientist point of view,” he says. “I look at things at the microscopic level to understand what’s going on. The metallurgical literature feeds into a lot of the behavior. The details are different, but the overall concepts are similar.”
COLD TRUTH: Ice Records Climates
RESEARCHER: Professor Mary Albert
To understand climate conditions today, scientists can measure carbon dioxide, methane, and other gases in the atmosphere. To know what the earth’s climate was like thousands of years ago, researchers can consult a natural archive: air bubbles trapped in polar ice sheets.
Professor Mary Albert studies those ancient gases in ice cores from the Antarctic and Greenland ice sheets. “I’m really interested in how we can decode the climate record that is in ice sheets to learn about atmospheric gases and their role of abrupt climate change from the past,” she says. “We can better understand the present if we know what happened naturally in the past.”
Albert, executive director of the U.S. Ice Drilling Program Office, does a lot of her work on firn, accumulations of old snow. She focuses on how the physical aspects of firn affect gas trapping. “The entrapment process affects what gases get trapped. How air mixes depends on the structure of firn,” she says. “Understanding the snow physics and the mass transfer and the chemical transport allows us to figure out how the gases were trapped and what the gas concentrations mean.”
When Albert and her students drill an ice core, they look for a site that is so cold that it is dry, has a lot of snow accumulation, and has the atmospheric circulation patterns to answer the problems they are trying to solve. “The atmospheric pattern from North America goes over Greenland,” she explains, “so the Greenland ice sheet is a good indicator of chemical pollution from North America and from China. For gases that are globally mixed, we might go to Antarctica for carbon dioxide, for example, for records we know are in the atmosphere.”
The depth of the drilling also depends on the question being asked. If the questions are associated with industry, Albert and her team only need to drill 100 to 200 meters. If they want to know what happened at the end of the last ice age, they must drill down two miles. “The oldest ice we’ve had in an ice core so far is 800,000 years,” she says. “But we think there are other sites in Antarctica that go back a million years.”
After Albert and her team drill ice cores—samples one meter long and 10–20 centimeters across—they bring them back to CRREL’s cold rooms for analysis. (Albert previously worked at CRREL on snow physics and modeling of snow for army applications.) They view the cores on a light table to detect annual layering. They also measure the layers’ density and permeability, assessing the interconnected pore space in the snow and firn, which is related to the transport of gases. Her group also does gas diffusion experiments and microstructure analysis at Thayer. Albert’s partners at other universities measure the content of the bubbles for carbon dioxide and mercury levels. Interpreting ice cores “is a team effort because it’s a complicated problem,” Albert says.
“It’s really amazing that snow and ice that falls in the polar regions in Greenland and Antarctica can serve as an archive of climate for over hundreds of thousands of years,” Albert says. “The snow and ice on the polar ice sheets give us the highest-resolution climate record that exists.”
COLD TRUTH: Ice Amplifies Climate Change
RESEARCHER: Professor Donald Perovich
Donald Perovich’s 32 years of Arctic ice study have taken him cruising on U.S. Coast Guard icebreaker ships for weeks on end in the Beaufort Sea, diving under sea ice, and walking on ice floes.
Perovich, a glaciologist who works at CRREL and has been a longtime visiting professor at Thayer, studies sea ice as both an indicator and a potential amplifier of climate change.
Sea ice cover is a strong proxy indicator of climate change, Perovich says, “because it covers millions of square kilometers—but it’s thin. In a warming climate we’d expect the ice to retreat. In a cooling climate we’d expect it to advance. By keeping track of how much area is covered by sea ice, month by month, year by year, we can get an idea if there’s a net warming or net cooling in the Arctic.”
For the past 30 years, satellites have monitored the sea and can show which areas are composed of ice or water. Predictably, Arctic ice expands in the winter, covering around 15-million square kilometers and retreats in the summer, shrinking to 5–8-million square kilometers.
But Perovich and his colleagues aren’t interested in the change of seasons; instead, they want to know how the amount of ice has changed over time.
“The satellite data tell a really great story,” he says. “If we look at the overall trend, there’s been a decline. And what makes it really interesting is that the decline is accelerating.”
The acceleration doesn’t mean that the ice reliably decreases each year; just like harsh New England winters, Perovich points out, there can be variations from year to year. In 1980, Arctic sea ice covered 7.8-million square kilometers, roughly the size of the continental United States. In 2007 Arctic sea ice was at a record low of 4.2-million square kilometers. “In 2007 it was as though the entire U.S. east of the Mississippi had melted away along with all the states from Minnesota south to Louisiana, plus North Dakota and part of South Dakota,” says Perovich. “That’s a really strong signal that the area covered by ice is decreasing.”
And of the ice that does remain, he says, records show that it is getting thinner. “As an indicator, the sea ice is sending a pretty strong signal that there’s warming going on in the Arctic,” he says.
Perovich explains that sea ice is also an amplifier of climate change through a process known as albedo feedback: the amount of light reflected off its surface. He studies ice-albedo feedback through models, satellite data, and field experiments in the Arctic, where he walks on ice floes to take measurements. “You get a detector, you measure how much sunlight is coming in, you measure how much is reflected, and you divide. It’s important because the driving force of the earth’s climate is the sun, and how much of that sunlight is reflected by the surface, the albedo, is the key parameter in climate change.”
Snow-covered ice reflects 85 percent of the sunlight, Perovich explains, but melting ice results in open ocean that reflects only seven percent of the sunlight. “You go from a very good reflector to a very poor reflector,” he says. “The ocean absorbs more sunlight, more water gets heated, more ice is melted, the albedo lowers, and you get a feedback system that is really significant.”
Perovich, whose projects are funded by the National Science Foundation, NASA, and the National Oceanic and Atmospheric Administration, says, “The polar regions really give a lot of insight into climate change. They offer a prism to the past, present, and future. My ultimate goal is to understand climate feedback processes, because what happens in the Arctic doesn’t necessarily stay in the Arctic.”
COLD TRUTH: Robots Map Crevasses
RESEARCHER: Professor Laura Ray
Enabling technology. That’s the key to understanding why Professor Laura Ray started thinking about robots for polar environments in 2004. Previously she did pure research on artificial intelligence for robots. Then, she says, Thayer colleague Mark Lessard brought her an idea for “a solar-powered rover that could be on the ice sheet all summer under its own power and carry instruments for what others want to study.” Lessard, now a professor at the University of New Hampshire, wanted to gather data for studies of the ionosphere and the magnetosphere. Ray got interested in engineering a robot that could do the job.
“They do their work in Antarctica where the observation points are so few and far between it’s like having the biggest lake in the world and putting a thermometer in one place and saying what the temperature is,” says Ray. “You can’t just do that.”
You can, however, build a robot to do the job. She secured a National Science Foundation grant to develop a proof of concept for a robot that could rove the ice sheet 24/7. Ray and Thayer Adjunct Professor James Lever, a mechanical engineer at CRREL, concluded that they could build a prototype for about $15,000.
The result—known as the Cool Robot—looks like a box on wheels. “For the Cool Robot our ultimate goal is to demonstrate that it can go several hundred kilometers trouble-free and collect scientific data that are useful. The roving scientific platform would be a significant achievement,” says Ray.
Ray’s lab built a second robot, called Yeti, in conjunction with CRREL, to negotiate around crevasses, a danger to anyone working on ice sheets. Traveling in front of a convoy, Yeti takes the burden off human interpretation of ground penetrating radar (GPR) measurements. “GPR is almost like taking an X-ray of the ground. A radar operator working as long as 10 hours per shift must interpret the radar,” says Ray. If the operator detects danger ahead, “you have a couple of seconds to stop the vehicle.”
But a 10-hour shift is nothing for a robot. It never gets tired. Moreover, when Yeti spots a crevasse, its software can direct it to execute a series of turns to map the direction of the crevasse.
Lever wasn’t available to speak with Dartmouth Engineer about Yeti because he and the robot were busy surveying the old South Pole Station. The abandoned station is covered with 30 feet of snow and people now need to traverse it. Lever and Yeti are mapping the hollow spaces under the snow. The Dartmouth team was called after another survey team working with a PistenBully tractor found a void by falling into it. The situation then got worse. “They sent another vehicle out to rescue it, and that one fell in,” says Ray. “They said, ‘We need another way. Can we borrow your robot?’ ”
Yeti has also gained attention in Greenland. Last spring Popular Mechanics sent a writer to the Greenland Summit Station to watch the robot being tested. The magazine ran a story about Yeti in July and posted video of the robot to its website. In August Cool Robot and Yeti both made it into The New York Times.
Ironically, Ray herself hasn’t seen either robot in action in either Greenland or Antarctica. “I have four kids at home. It is a little hard to get away for three or four weeks. Someday maybe,” she says.
This spring Yeti heads to Greenland again with the National Science Foundation’s Greenland Inland Traverse team to ensure the team’s safety and map crevasses. You can follow Yeti’s progress at yetibot.blogspot.com.
COLD TRUTH: Electricity Flips Ice’s Grip
RESEARCHER: Professor Victor Petrenko
“I’m a semiconductor physicist, not an ice researcher,” says Professor Victor Petrenko. That statement is something of a surprise coming from the coauthor of Physics of Ice, the authoritative text on the subject.
Petrenko entered the field of ice research by coincidence 25 years ago. He was working at the University of Birmingham in England while on sabbatical from the Soviet Academy of Sciences. He saw a door marked “Ice Physics Lab” and opened it. Inside he met ice researcher John Glen. Glen told him three things about ice that changed Petrenko’s career. First, ice is a semiconductor. Second, ice is a protonic semiconductor—protons, not electrons, transport electrical current. Finally, and this was the game changer for Petrenko—the physics of ice, unlike the semiconductors he had been working on in Moscow, was still being discovered. Petrenko wanted in on the new discoveries.
Making the switch, however, wasn’t easy or quick under the Soviet system. When Petrenko returned from sabbatical he asked his lab director about shifting his focus to ice. “He suggested I apply ice to my head,” Petrenko recalls. “He said ‘Victor you are crazy. You want to trade the wonderful semiconductor physics for that dirty stuff—ice?’ ” Nevertheless, Petrenko spent 15 years working in both fields.
But that was then. Today the science of ice physics is a mature subject in part because of discoveries made by Petrenko and former Thayer researchers Valeri Kozlyuk, Michiya Higa, and Cheng Chen. Because of that, Petrenko has turned his research toward practical applications. He found that by applying short pulses of electricity across an ice-coated surface it is possible to break the bond between the ice and whatever material it covers. The process, which Petrenko calls pulse electrothermal de-icing (PETD), can be used to de-ice car windshields, airplanes, ships, power lines, bridges, and many other structures.
There’s a complementary aspect to Petrenko’s de-icing research. By reversing the polarity of the electrical current, the grip between ice and the material gets stronger. It is possible to make shoes that won’t slip on ice, skis with brakes, and car tires that can handle ice as if it were dry pavement.
Petrenko’s work has yielded 60 domestic and international patents, and 100 more are in the pipeline. Research funding has come from the military, the National Science Foundation, and Fortune 500 companies, such as BFGoodrich and GE.
Some of Petrenko’s inventions have moved out of his lab and into the field for trials. Tests for de-icing power lines are run in China because that country has two key elements: a problem with ice on power lines and a state-of-the-art power grid that enables PETD technology, something the older U.S. power grid can’t handle. Most recently, Petrenko’s work has been in refrigeration, a technology that has seen only incremental advancement in the last 100 years. Petrenko estimates that his de-icing technology can cut the electric bill of commercial users by 40 percent. Since Petrenko’s system provides uninterrupted cooling rather than cycling between warmth and cold, residential users would benefit from better food storage as well as lower electrical costs.
Petrenko sees a hot future for de-icing technology. “The applications based on ice physics have not been finished,” he says.
On the Antarctic Map
Two sites in Antarctica officially bear the names of members of the Thayer community.
Mount Arcone (81º43’S, 161º2’E), a horseshoe-shaped mountain in the Nash Range, honors Steven Arcone Th’77 for the ground-penetrating radar (GPR) and airborne radar surveys he conducted during six seasons on the ice. Having recorded and interpreted thousands of kilometers of GPR data, Arcone, a geophysicist at CRREL and former Thayer adjunct professor, has not only kept research convoys from falling into crevasses, but has also published numerous papers on the firn and ice stratigraphy GPR reveals.
Ackley Point (77º47’S, 166º55’E), an ice-covered point near McMurdo Sound, honors Stephen Ackley, an adjunct professor at Thayer from 1985 to 1999, for his extensive work on sea ice in McMurdo Sound and the Southern Ocean. The former CRREL researcher is a now a professor at the University of Texas at San Antonio.
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