Physics of a glacial 'slushy' reveal granular forces on a massive scale

The ridge in the right center of the photo shows where icebergs have broken off from Jakobshavn Glacier and tumbled into the water to form a slushy ice mélange — the world's largest granular material. Photo by Ryan Cassotto.

By Carol Clark

The laws for how granular materials flow apply even at the giant, geophysical scale of icebergs piling up in the ocean at the outlet of a glacier, scientists have shown.

The Proceedings of the National Academy of Sciences (PNAS) published the findings, describing the dynamics of the clog of icebergs — known as an ice mélange — in front of Greenland’s Jakobshavn Glacier. The fast-moving glacier is considered a bellwether for the effects of climate change.

“We’ve connected microscopic theories for the mechanics of granular flowing with the world’s largest granular material — a glacial ice mélange,” says Justin Burton, a physicist at Emory University and lead author of the paper. “Our results could help researchers who are trying to understand the future evolution of the Greenland and Antarctica ice sheets. We’ve showed that an ice mélange could potentially have a large and measurable effect on the production of large icebergs by a glacier.”

The National Science Foundation funded the research, which brought together physicists who study the fundamental mechanics of granular materials in laboratories and glaciologists who spend their summers exploring polar ice sheets.

“Glaciologists generally deal with slow, steady deformation of glacial ice, which behaves like thick molasses — a viscous material creeping towards the sea,” says co-author Jason Amundson, a glaciologist at the University of Alaska Southeast, Juneau. “Ice mélange, on the other hand, is fundamentally a granular material — essentially a giant slushy — that is governed by different physics. We wanted to understand the behavior of ice mélange and its effects on glaciers.”



For thousands of years, the massive glaciers of Earth’s polar regions have remained relatively stable, the ice locked into mountainous shapes that ebbed in warmer months but gained back their bulk in winter. In recent decades, however, warmer temperatures have started rapidly thawing these frozen giants. It’s becoming more common for sheets of ice — some one kilometer tall — to shift, crack and tumble into the sea, splitting from their mother glaciers in an explosive process known as calving.

Jakobshavn Glacier is advancing as fast as 50 meters per day until it reaches the ocean edge, a point known as the glacier terminus. About 35 billion tons of icebergs calve off of Jakobshavn Glacier each year, spilling out into Greenland’s Ilulissat fjord, a rocky channel that is about five kilometers wide. The calving process creates a tumbling mix of icebergs which are slowly pushed through the fjord by the motion of the glacier. The ice mélange can extend hundreds of meters deep into the water but on the surface it resembles a lumpy field of snow which inhibits, but cannot stop, the motion of the glacier.

“An ice mélange is kind of like purgatory for icebergs, because they’ve broken off into the water but they haven’t yet made it out to open ocean,” Burton says.

While scientists have long studied how ice forms, breaks and flows within a glacier, no one had quantified the granular flow of an ice mélange. It was an irresistible challenge to Burton. His lab creates experimental models of glacial processes to try to quantify their physical forces. It also uses microscopic particles as a model to understand the fundamental mechanics of granular, amorphous materials, and the boundary between a free-flowing state and a rigid, jammed-up one.

“Granular material is everywhere, from the powders that make up pharmaceuticals to the sand, dirt and rocks that shape our Earth,” Burton says. And yet, he adds, the properties of these amorphous materials are not as well understood as those of liquids or crystals.

In addition to Amundson, Burton’s co-authors on the PNAS paper include glaciologist Ryan Cassotto — formerly with the University of New Hampshire and now with the University of Colorado Boulder — and physicists Chin-Chang Kuo and Michael Dennin, from the University of California, Irvine.

The researchers characterized both the flow and mechanical stress of the Jacobshavn ice mélange using field measurements, satellite data, lab experiments and numerical modeling. The results quantitatively describe the flow of the ice mélange as it jams and unjams during its journey through the fjord.

The paper also showed how the ice mélange can act as a “granular ice shelf” in its jammed state, buttressing even the largest icebergs calved into the ocean.

“We’ve shown that glaciologists modeling the behavior of ice shelves with ice mélanges should factor in the forces of those mélanges,” Burton says. “We’ve provided them with the quantitative tools to do so.”

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DNA analysis adds twists to ancient story of a Native American group

"I want to help Native American tribes to reclaim knowledge of their very ancient evolutionary histories — histories that have been largely wiped away because of colonialism," says Emory geneticist John Lindo. Photo by Kay Hinton, Emory Photo/Video.

By Carol Clark

The ancient genomes of the Tsimshian indigenous people left tell-tale markers on the trail of their past, revealing that at least 6,000 years ago their population size was on a slow but steady decline.

The American Journal of Human Genetics published the findings, which draw from the first population-level nuclear DNA analysis of a Native American group from ancient to modern times.

“The finding contradicts a popular notion,” says John Lindo, a geneticist in Emory University’s Department of Anthropology and first author on the paper. “There is this idea that after Native Americans came in through the Bering Strait that they were all expanding in population size until Europeans showed up. At least for this one population, we’ve shown that was not the case.”

A boon in next-generation DNA sequencing technology has opened the possibility to explore the evolutionary history of different populations. “Ancient nuclear DNA analysis is a relatively new field,” Lindo says. “Not until recently have we had methods to sequence an entire genome quickly and inexpensively.”

Nuclear DNA provides information on an individual’s lineages going back hundreds of thousands of years. Lindo is one of the few geneticists looking at ancient whole genomes of Native Americans. He is especially interested in understanding how the genomes of their different populations evolved over time.

“Their evolutionary histories are radically different,” Lindo says. “Over thousands of years, various Native American populations have adapted to living in every ecology throughout North and South America, from the Arctic to the Amazon. That’s about as an extreme as you can get for differences in environments.”

The Tsimshian people historically lived in longhouses in coastal British Columbia and southern Alaska where they harvested the abundant sea life. Lindo and his colleagues sequenced the genomes of 25 living Tsimshian people and 25 ancient individuals who lived in the same region between 6,000 and 500 years ago, and confirmed that they were a continuous population through time.

Members of the Tsimshian Native American tribe hold a tea party near Fort Simpson, British Columbia, in 1889. Image from the Library and Archives Canada.

In a previous paper, drawing from the same data set, they found a dramatic shift between the two time periods in a class of genes associated with the immune system, suggesting a strong evolutionary pressure on the population to adapt to pathogens. A demographic model indicated a crash in the Tsimshian population size of about 57 percent during the early-to-mid 19th century. That finding fitted with historical accounts for how smallpox, introduced by European colonization, devastated the Tsimshian population during two epidemics within that time-frame.

The current paper looked at broader genetic variations between the ancient and modern DNA. An analysis showed both how the variation declined slowly in the ancient population before the collapse, but has since recovered.

“After a population collapse, only a subset of the genetic diversity remains,” Lindo says. “We find a more nuanced story, that despite the population collapse, the genetic diversity of modern Tsimshian people varies significantly.”

Intermarriage with other Native American groups and non-native populations increased the genetic diversity of some of the modern-day Tsimshian people so that it is near the levels prior to their population collapse, the analysis showed.

“A population with relatively high genetic diversity has a greater potential to fight off pathogens and avoid recessive traits,” Lindo says. “It exemplifies the benefits of gene flow between populations, especially following catastrophic events such as the small pox epidemics that the Tsimshian endured.”

Senior authors on the paper are Michael DeGiorgio from Pennsylvania State University and Ripan Malhi from the University of Illinois. The paper’s coauthors include Tsimshian representatives Joycelynn Mitchell and Barbara Petzelt from the Metlakatla Treaty Office in Prince Rupert, Canada.

Malhi, a leader in forging trusting relationships between genetic researchers and indigenous people, was a mentor to Lindo, who earned his PhD at the University of Illinois at Champaign-Urbana.

Lindo is continuing that tradition of building trust and working closely with indigenous populations. His ancient DNA research at Emory integrates the approaches of ancient whole genomes, statistical modeling and functional methods.

One of his projects is focused on genetic fluctuations to help understand ancient adaptions in various Native American populations. He is currently working with 10 different tribes from throughout North America.

“Community engagement is essential when working with indigenous communities,” says Lindo, explaining that he first meets personally with a tribal community to talk about how a genetic study might add to their knowledge of their own history.

“I listen to their stories and how they are working to keep their cultures alive,” he says. “One elder from a southwestern tribe told me that his grandfather was taken away in the early 1900s because he was a shaman and Christianity was swelling through the area. Each tribe’s stories are different but they are all powerful, and sometimes difficult, stories to hear.”

Most ancient DNA analyses have come out of Europe, where more ancient DNA labs are based and cold temperatures have helped preserve specimens.

Lindo wants to bring some of the same insights that those of European ancestry are gaining about their past to Native Americans.

“I’d like to disentangle this idea that Native Americans are part of a singular race,” he says. “I want to help Native American tribes to reclaim knowledge of their very ancient evolutionary histories — histories that have been largely wiped away because of colonialism.”

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Science Art Wonder: Students team with labs to bring research to life

Art by Emory senior Pamela Romero, Science.Art.Wonder. founder and president, portrays how aphids can develop wings in response to environmental changes. The DNA painted along the edges of the canvases is the same, except that different genes are switched on. Photo by Ann Watson, Emory Photo/Video

By Carol Clark

A small crowd gathers in Emory’s White Hall before the menacing sight: Large rubber worms arrayed on triangular red spikes. The jagged spikes, from a few inches to more than a foot tall, lean crazily in all directions. Some of the worms — suspended on near-invisible fishing line — appear to rise off the spikes, escaping to a circular mirror hanging from above.

“This is how evolution works!” says Ethan Mock, a sophomore majoring in ancient history, who created the sculpture, titled "The Crucible." He looks dapper in a leather vest and tweed cap and speaks with theatrical flair to the crowd. “The spikes represent the trials and tribulations of the worms’ struggles. Most are trapped in the spikes but a few climb out, not realizing that they are simply climbing into a new trial, a new test.”

The onlookers include a mix of college students, children and their parents, brought together by campus events during the recent Atlanta Science Festival. Joining the regular attractions of Physics Live! and Chemistry Carnival is the debut of an art exhibit by a new, student-run program called Science.Art.Wonder., or S.A.W. Just over 100 artists — most of them untrained college students — teamed with scientists from Emory and Georgia Tech to translate their research into art.

Ethan Mock and his art, "The Crucible"

Mock worked with the lab of Levi Morran, an assistant professor in Emory’s Department of Biology who studies co-evolutionary dynamics by experimenting with a host (a microscopic worm called C. elegans) and a parasite (a bright red species of bacteria called Serratia marcescens that is lethal to C. elegans upon consumption).

“This is so cool!” says Pareena Sharma, a first-year biochemistry major at Emory, as she snaps a photo of the sculpture. “It’s so relatable to me. I’ve been doing this same experiment since the first of the semester in Biology 142.”

Two young boys draw near the spikes. “Look up into the mirror,” Mock encourages them. “Now tell me what you see.”

“The same thing,” one of the boys replies.

“That’s right!” Mock says. “The process of evolution keeps repeating, going in a loop.”

Morran, arriving with his eight-year-old daughter, Maggie, is impressed. “You could see the light come on in those boys’ eyes,” he says. “They understood what Ethan is trying to convey. And it’s not an easy concept to grasp — the continual evolutionary struggle.”

Both artists and researchers engage with visitors as they peruse more than 140 works of art, set up on the Quad, in White Hall, the Math and Science Center and the Atwood Chemistry Center during the festival.

“This artwork gives you a snapshot of how much research is being done in Atlanta. I’m taken aback by how cutting edge and varied it is,” says Pamela Romero, president of S.A.W. The program is the brainchild of Romero, a senior majoring in neuroscience and behavioral biology and minoring in computer science.

Young visitors to the Emory campus peruse science-inspired art on the Quad. Photo by Ann Watson, Emory Photo/Video

The Emory S.A.W. contributions span labs across the University and beyond. The artists picked their mediums, from acrylic to watercolor and everything in between.

Emily Isaac, a first-year Emory student majoring in environmental sciences and theater, stands on the Quad next to a large watercolor she painted. “Art can help scientists make a point without using any scientific jargon,” she says.

She teamed with Robert Wallace from Georgia Tech’s Agricultural Technology Research Program. One of Wallace’s projects gave plots of farmland to women in India who had been victims of an acid attack. Isaac did a portrait of a woman with a scarred face. The woman’s head is partially wrapped in strips of bandages that Isaac painted to look like rows of newly sprouting plants. “I wanted to show hope, and how connecting with the environment can help people,” Isaac says.

This year’s 36 Emory S.A.W. artists are mainly undergraduates — many of them science majors — but they also include a few graduate students, faculty and staff members. Georgia Tech makes up the bulk of other contributing artists and researchers in this year’s S.A.W., although 10 independent artists also got involved, along with Georgia State University undergraduates and the Atlanta campus of SCAD.

“S.A.W. is collaborative, not only across disciplines and institutions, but also across students, faculty, staff and members of the Atlanta community,” Romero says. “We even have one international artist, from Puerto Rico.”

A painting by Georgia Tech student Bianca Guerrero portrays a virtual reality game used to measure players' perception of time as well as eye movement. The art is based on research by Georgia Tech psychologist Malia Crane. Photo by Ann Watson, Emory Photo/Video.

As long as she can remember, everyone thought Romero would become an artist, or maybe an architect. She began taking art classes at the age of three in her home town of Tegucigalpa, Honduras. She continued making and studying art, developing a surrealist style.

In ninth grade, however, a psychology course sparked a fascination for neurobiology. Romero took online classes and started reading up on subjects like optogenetics and deep-brain stimulation.

By the time she was accepted to Emory, she had decided to forge a career as a scientist. “A lot of people told me that if I chose neuroscience I would have to forsake art, because I would be a bad scientist if I tried to do both,” she recalls. “I was determined to prove them wrong.”

Romero sought out kindred spirits like Nicole Gerardo, associate professor of biology, who also grew up with twin passions for science and art. Gerardo once had students create artwork using microbes in her lab under the direction of Nancy Lowe — a former lab technician at Emory who went on to create a retreat center in North Carolina called AS.IF: Art and Science in the Field.

Gerardo later paired students with labs to create ceramic representations of research under the direction of Diane Kempler, who formerly taught visual arts at Emory.

“Art provides a way to reach people who may be intimidated by science,” Gerardo says. “And working with an artist lets scientists see their own work in a different way. That could lead to new scientific approaches.”

When Romero first joined forces with Gerardo it was simply to produce art for her lab, which focuses on evolutionary ecology. “We were test subjects for S.A.W.,” Romero says.

Emory senior Maureen Ascona, a neuroscience and behavioral biology major, discusses her art with visitors to the Quad. Ascona teamed with Helen Mayberg, from the Emory School of Medicine, who uses deep-brain stimulation to help patients with treatment-resistant depression. Photo by Ann Watson, Emory Photo/Video.

One of the pieces Romero created consists of triangular canvases that can be shifted into different positions. The acrylic painting depicts how aphids develop wings in the presence of predators, like ladybugs, or if food becomes scarce. “When Dr. Gerardo explains her work to people, she can move the canvases to show how the aphids change in response to their environment,” Romero says.

Romero wanted to give other students the chance to enter research labs and experiment with art.

“Pamela is an amazing woman, a force of nature,” says Gerardo, who is the faculty mentor for S.A.W. “What she has done with the support of her fellow students is incredible. I had envisioned maybe 20 pairings of scientists and artists. I’m still surprised by how big it became.”

Connections from across the University helped S.A.W. grow. Wei Wei Chen and John Wang, student leaders of Emory Arts Underground, provided the platform for Romero to launch S.A.W. and encouraged her to form a charter, bylaws and an executive team. That team includes Emory undergraduates Alex Nazzari (vice-president), Aila Jiang, Veronica Paltaraskaya, Anne Pizzini, Deborah Seong and John Wang, along with Georgia Tech students Olivia Cox, Siyan Li and Iris Liu.

The students’ efforts paid off with S.A.W.’s smash debut at the Atlanta Science Festival.

“One of my favorite parts was guiding artists through the process of disentangling the science, reassuring them that they could do it,” Romero says. “Many of them felt overwhelmed after first talking to a scientist. Some of them were first-year students who hadn’t even had introductory biology or chemistry.”

A piece by Alice Yang, a first-year Emory student majoring in neuroscience and behavioral biology who teamed with researchers of human genetics in the Emory 3q29 Project. Photo courtesy of S.A.W.

Exploring a lab through an art project allows students to develop a relationship with a researcher and often find a mentor, Romero says.

Alice Yang, a first-year Emory student majoring in neuroscience and behavioral biology, teamed with Jennifer Mulle, assistant professor at Rollins School of Public Health. Mulle is co-principal investigator of the Emory 3q29 Project, which seeks to understand a genetic deletion associated with an increased risk for schizophrenia.

“I’m so grateful for the experience,” Yang says of spending time with the 3q29 Project team. “I learned what it’s like to actually do science. And I caught their passion. People are just now realizing how genetics can be involved in mental illness. It’s a very new field.”

To create her art pieces, Yang ordered special scratch-off paper from her native China. “This paper’s easy to work with and it’s great for showing patterns and textures,” she says. She explains how she carefully cut slices from the black top layer of the paper to reveal the glowing, rainbow colors beneath. Her pictures portray the nanomapping of fluorescent-labeled alleles from the 3q29 lab while also paying tribute to Salvador Dali’s surrealism.

Even those who are not aspiring scientists can catch the science-art bug. Independent artist Aaron Artrip teamed with scientists Matthew Jackson and Dan Cook at Georgia Tech to demonstrate interaction with sound. A group of children buzzes around Artrip’s exhibit in White Hall. A piece of paper sprinkled with powdered black ink is taped to a wooden speaker, which is plugged into an electronic synthesizer. As Artrip taps a keyboard, the powder moves across the page, creating patterns.

“I’m making drawings with vibrations. Forcing sound through the ink causes it to move,” he explains.

“Would you like to try?” he asks a young girl watching him.

She doesn’t have to be asked twice.

A painting by Georgia Tech student Kate Bernart, "Connecting the Cycle," portrays Austin Ladshaw's research at Georgia Tech's School of Environmental Engineering on the nuclear fuel cycle and ways to prevent excessive accumulations of radioactive waste. Photo by Ann Watson, Emory Photo/Video

Ultimately, S.A.W. hopes to find ways to integrate its art-science model into grades K-12. “We would like to have artists and researchers go into K-12 classrooms to talk about the art and the research together,” Romero says.

She presented S.A.W. at the recent Georgia Tech STEAM Leadership Conference, which brought together educators and policymakers to explore new ways to teach science, technology, engineering, art and math, or STEAM. S.A.W. is now working to put together an anthology of its art into a booklet, to include descriptions of the science. The booklet will be aimed at high school students “to give them a glimpse of some of the possible fields available to them in college,” Romero says.

S.A.W. is also creating a web site where the art will be accessible in digital form, including videos of some of the interactive art pieces, along with other resources for K-12 teachers.

After graduating this spring, Romero plans to take a gap year, then go on to graduate school with the aim of becoming a professor with a research lab. “S.A.W. has an incredible executive team and I’m making sure that the program continues after I leave Emory,” she says. “I would also like to stay involved with it in some way.”

As she prepares for graduation, Romero is working on an art narrative piece funded by the Emory Center for Creativity and Arts. The work will combine acrylic painting and sculpture to represent the element Vanadium, discovered by Mexican mineralogist Andrews Manuel del Rio in 1801. A series of circular canvases will each represent an atom in Vanadium. Each canvas will also represent a country or group of countries in Latin America, on which Romero will depict the research of a scientist from that area.

“My main goal with this piece is to celebrate and encourage more Latin American science,” Romero says. She is calling the piece “Elementally Latino,” to describe how Latinos are an elemental, or basic, part of science and how they also embody an elemental force. “Latinos are such a passionate people that I can only adequately describe them as a force of nature,” she says.

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