Thursday, June 25, 2015

Calving icebergs fall back, spring forward, causing glacial earthquakes

"We've provided an unprecedented understanding of how a glacial earthquake evolves," says Emory physicist Justin Burton. The research focused on Helheim Glacier in Greenland, above. Photo by NASA/Jim Yungel.

By Carol Clark

When a massive iceberg breaks off from the front of a glacier it can fall backwards, slamming into the glacier with such force that it reverses the ice flow for several minutes and causes it to drop, producing an earthquake that can be measured across the globe.

The journal Science is publishing the discovery, including detailed documentation of the forces involved in these iceberg calving events and an explanation for the causes of glacial earthquakes. The research marks a major step toward the ability to measure the size of iceberg calving events in near real-time and from anywhere in the world.

“Glaciers are extremely sensitive indicators of climate change,” says co-author Justin Burton, a physicist at Emory University who specializes in laboratory modeling of glacial forces. “Having a quantitative understanding of how our polar regions are losing ice is crucial to any forecasting related to climate change, in particular sea-level rise and its environmental and economic impacts.”

Placing a GPS sensor. (Swansea)
The study, which focused on Helheim Glacier in the Greenland Ice Sheet, also included scientists from the universities of Swansea, Newcastle and Sheffield in the UK and the universities of Columbia and Michigan in the U.S.

The Greenland Ice Sheet is disappearing at a faster rate than Antarctica, and shows no sign of slowing down. As much as half of that loss is due not to melting, but to icebergs breaking off and discharging into the sea, a process known as calving. As sheets of ice taller than a New York skyscraper fall over and collapse into the water they release energy equivalent to several nuclear bombs.

In 2003, scientists discovered the existence of glacial earthquakes. They knew that iceberg calving caused these quakes, but it was unclear why. A regular earthquake originates from stress building up from deep within the Earth, which then gets released suddenly. A glacial earthquake, however, originates on the surface and happens in relative slow motion, during the 10 to 15 minutes it takes an iceberg to flip 90 degrees, collapse into the sea and generate waves of energy.

The study authors wanted to gain a better understanding of the processes involved in collapsing icebergs and how they cause glacial earthquakes.

Tavi Murray, a glaciologist from Swansea University, led the field portion of the study. During the summer of 2013, researchers from Swansea, Newcastle and Sheffield universities flew over Helheim Glacier in helicopters. They installed a sophisticated network of Global Positioning System (GPS) devices on the glacier’s surface to record movements of the glacier in the minutes surrounding calving events.

The Greenland Ice Sheet is getting smaller. If it melts entirely, scientists estimate that sea level will rise about 6 meters (20 feet). Photo of Helheim Glacier by Nick Selmes, Swansea University.

One of the surprises revealed by the resulting data was that some of the calving events actually reversed the flow of the glacier during a glacial earthquake.

“That’s really strange,” Burton says, “because a glacier is an enormous mass that is always moving towards the sea. What could possibly reverse that?”

Burton led a laboratory modeling portion of the study, along with Mac Cathles, who is now at the University of Michigan. They built a rectangular, Plexiglas water tank as a scaled-down version of a fjord. Rectangular plastic blocks that have the same density as icebergs are tipped in the water tank and the resulting hydrodynamics are recorded.

The analysis phase also drew from the expertise of co-author Meredith Nettles, a seismologist at Columbia’s Lamont-Doherty Earth Observatory, and data in the Global Seismographic Network. The collaborative analyses and experimental modeling allowed the researchers to tease apart all the forces responsible for the motion of the glacier, recreate them in the lab, and solve the mystery of how glacial earthquakes work.

Watch a video of the Burton lab's model of a backwards falling iceberg, based on the data from Helheim Glacier:


“We were able to explain the motion of the GPS sensors by tracking all the forces that affect the glacier during iceberg calving, providing an unprecedented understanding of how a glacial earthquake evolves,” Burton says.

They found that many of the calving icebergs are falling backwards, slamming into the face of the glacier before they collapse into the sea. The front of the glacier gets compressed like a spring, temporarily reversing the motion of the glacier and generating the horizontal force of a glacial earthquake.

As the iceberg hits the water, it rapidly reduces pressure behind the rotating iceberg. This dramatic drop in water pressure draws the glacier down about 10 centimeters, while pulling the Earth upwards, creating the vertical force seen in the seismic signature of a glacier earthquake.

“This research required the combined efforts of glaciology, seismology and physics,” Burton says. “It was great to work hand-in-hand with field researchers, while also showing that lab research is crucial to understanding what’s happening on the surface of the Earth.”

Glacial earthquakes are globally detectable seismic events. The researchers hope their detailed documentation of the forces at play will help interpret the remote sensing of calving events, which are increasingly occurring at tidewater-terminating glaciers in Greenland and Antarctica.

Related:
The physics of falling icebergs

Thursday, June 18, 2015

How flu viruses use transportation networks in the U.S.

Emory biologists analyzed transportation data and flu cases from across the United States. The graphic of the U.S. interstate commuter network shows the number of people traveling daily between states for work. Credit: Brooke Bozick.

By Carol Clark

To predict how a seasonal influenza epidemic will spread across the United States, one should focus more on the mobility of people than on their geographic proximity, a new study suggests.

PLOS Pathogens published the analysis of transportation data and flu cases conducted by Emory University biologists. Their results mark the first time genetic patterns for the spread of flu have been detected at the scale of the continental United States.

“We found that the spread of a flu epidemic is somewhat predictable by looking at transportation data, especially ground commuter networks and H1N1,” says Brooke Bozick, who led the study as a graduate student in Emory’s Population Biology, Ecology and Evolution program. “Finding these kinds of patterns is the first step in being able to develop targeted surveillance and control strategies.”

The co-author of the study is Leslie Real, Emory professor of biology and Bozick’s PhD adviser.

One of the fundamental ideas in ecology is isolation by distance: The further apart things are geographically, the more distant they tend to be genetically.

This idea applies to disease ecology in the cases of animals that do not travel far from where they are born. Rabies spread by raccoons, for instance, tends to generate a wave-like pattern of transmission across a geographic space.

People, however, are much more mobile, often traveling by rail, road and air. The human mobility effect of an epidemic stands out starkly on the global scale. For instance, during the 2003 outbreak of severe acute respiratory syndrome (SARS), airline travel clearly connected cases in people from Asia and Canada.

Map shows an example of how commuting communities can differ from state boundaries. Credit: Brooke Bozick.

The researchers wanted to see if they could detect a correlation to mobility and the genetic structure of seasonal flu cases on a national scale for the United States.

The study tapped Genbank, an online, public repository of genetic flu data, to analyze U.S. cases from 2003 to 2013 for two different subtypes of seasonal flu: H3N2 and H1N1. Transportation data for that decade was drawn from the U.S. Census Bureau and the Bureau of Transportation Statistics, to map out networks of air travel and ground commutes, and the number of people moving along them during the flu season.

The researchers compared genetic distance of the flu subtypes with their geographic distance and the measures of distance defined by airline and commuter transportation networks.

They found some correlations in both subtypes for all the distance metrics used. The correlations were seen a greater proportion of the time, however, when looking at commuter movements and the H1N1 subtype.

“H1N1 tends to be a milder subtype of flu that spreads slower, so that may make it easier to pick up the pattern across shorter-distance commutes,” Bozick says. “We think that a similar pattern for H3N2 may exist. The pattern may just be harder to detect, since H3N2 tends to be more virulent and spread faster, from coast-to-coast.”

The study shows that there are underlying spatial patterns in the genetic data, and that they are dependent on how the “distance” between locations is being measured, she adds.

“Humans can move long distances very rapidly so the idea that geographic proximity is key to determining disease spread doesn’t always hold,” Bozick says. “The patterns we found are likely influenced by states with many commuters, and the identification of these states, as well as network pathways that contribute substantially to influenza spread, is an important next step for epidemiological research.”

Related:
Dengue mosquitos hitch rides on Amazon river boats
Human mobility data may help curb epidemics

Tuesday, June 16, 2015

Dengue mosquitos hitch rides on Amazon river boats

Boats are the main means of transport in the Peruvian Amazon. Some of these boats are providing a first-class ride for disease-carrying mosquitos, helping them expand their range, a study found.

By Carol Clark

The urban mosquito that carries the dengue fever virus is hitching rides on river boats connecting the Amazonian town of Iquitos, Peru, with rural areas.

PLOS Neglected Tropical Diseases published a study by disease ecologists at Emory University, showing how the Aedes aegypti mosquito, which is normally associated with urban areas, is tapping human transportation networks to expand its range.

“The majority of large barges we surveyed were heavily infested,” says Sarah Anne Guagliardo, who led the study as a PhD student in the lab of Uriel Kitron, chair of Emory’s Department of Environmental Sciences. “As the barges move across the Peruvian Amazon they are carrying large populations of these mosquitos, which can transmit many viral diseases, the most important of which is dengue fever.”

Like the housefly, Aedes aegypti is perfectly adapted to the domestic life of humans. It especially thrives in densely populated urban areas, since it feeds almost exclusively on human blood and has a limited flight range of about 100 meters.

“When Aedes aegpti mosquitos began popping up in rural areas around Iquitos, we knew that humans must somehow be involved in that transportation process,” Guagliardo says.

The research team boards a large cargo barge, on left, to survey for mosquitos. (Photo courtesy Sarah Anne Guagliardo.)

Iquitos, located deep in the Amazonian rainforest, is one of the most isolated cities in the world, accessible only by boat or plane, except for one two-lane road connecting it to a much smaller town. The population of 400,000 is surrounded by thick jungle that is difficult to clear, inhibiting urban expansion.

To learn how the mosquitos of Iquitos hitch rides with humans, the researchers investigated six different vehicle types, from large and medium-sized barges, water taxis and speedboats to buses and road taxis.

Large barges (71.9 percent infested) and medium barges (39 percent infested) accounted for most of the infestations. In contrast, buses had an overall infestation rate of 12.5 percent.

The cargo hold of large barges, where water often collects in puddles, was ground zero for the infestations. “We were collecting not just adult mosquitos, but also pupae, larvae and eggs,” Guagliardo says. “The mosquitoes are not just riding the boats, they are reproducing on the boats.”

These large barges, which can be about 60 meters long, may have as many as four floors in addition to the cargo hold. They carry human passengers along with livestock, plantains, fish, gasoline and other goods. The medium barges tend to be half the size and lack cargo holds.

Many of the cargo barges are old and not well-maintained.

The researchers surveyed for mosquitos using the Prokopack aspirator, a mosquito “vacuum” co-invented by Emory disease ecologist Gonzalo Vazquez-Prokopec.

“The cargo hold is in the bottom of the large barges and you have to crawl into really dark spaces to collect mosquitos,” Guagliardo says. “There’s often rotting organic matter from things like plantains and fish. And it’s moldy and damp. Many of the barges are really old and rust holes form on each floor and ceiling. Every time it rains, water drips down and collects in the cargo hold.”

It’s a first-class ride, however, for these disease-carrying mosquitos. The adults have a dark, cool resting place, while their eggs and larvae can incubate in standing puddles. If the mosquitoes get hungry, a captive group of human hosts is nearby for blood meals.

“I think it’s important that people are aware that this is a problem,” Guagliardo says. “Our study is the first of its kind, to my knowledge, comparing mosquito infestations across a range of vehicles. I’m curious how these mosquitos may use modes of transport in other parts of the world.”

Some of the large barges of Iquitos with infestations of adult and immature mosquitoes were surveyed repeatedly by the research team during different seasons of the year. “It turns out the barges that were infested were consistently infested, and that a small proportion of barges produce the vast majority of mosquitos,” Guagliardo says. “That suggests that some boats may act as super-transporters of mosquitos, just as individual human hosts may act as super-spreaders of pathogens.”

The researchers propose that governmental agencies invest in mosquito control programs for aquatic transport, and implement more stringent punitive policies and incentives to ensure the cooperation of boat owners. The programs could target those boats producing the greatest amount of mosquitoes.

During the last 50 years, the incidence of dengue, which causes debilitating pain and can be fatal, has increased 30-fold. The World Health Organization estimates that 50-100 million dengue infections occur each year.

Guagliardo, who received her PhD from Emory in May, currently works on HIV/AIDS programs for the Centers for Disease Control and Prevention.

In addition to Guagliardo, Kitron and Vazquez-Prokopec, the study’s authors include Amy Morrison, Jose Luis Barboza, Edwin Requena and Helvio Astete.

Related:
How the dengue virus makes a home in the city
Human mobility data may help curb epidemics 

Credit: Top and bottom photos from ThinkstockPhotos

Monday, June 15, 2015

A paleontologist explains why 'Jurassic World' stinks

That transport sphere will not look so crystal clear after it rolls across a steaming pile of triceratops dung. 

Emory palentologist Anthony Martin wrote about the new movie "Jurassic World" from a scientific perspective. Below is an excerpt of his article, which appeared in The New Republic, among other outlets:

"Like many moviegoers this summer, I plan to watch Jurassic World. And because I’m a paleontologist, I’ll cheer for the movie’s protagonists (the dinosaurs) and jeer at the villains (the humans).

"But no matter how thrilling this movie may be, one question will plague me throughout: Where are the dung beetles?

"Dung beetles—which are beetles that eat and breed in dung—would be only one of many ecological necessities for an actual Jurassic World-style theme park.

"Yes, cloning long-extinct dinosaurs is impossible. But even if dinosaur genomes were available, the animals couldn’t simply be plopped anywhere.

"So for the sake of argument, let’s say an extremely wealthy corporation did manage to create a diverse bunch of dinosaurs in a laboratory. The next step in building a Mesozoic version of Busch Gardens would be figuring out how to recreate—and maintain—the dinosaurs' ecosystems."

Read the entire article in The New Republic.

Martin will present a "Dinosaurs After Dark" talk at the Fernbank Museum at 7 pm on June 26. He'll discuss both "Jurassic World" and the original "Jurassic Park," including answering questions about scientific fact and Hollywood fiction.

Check out the classic sick triceratops scene from the original "Jurassic Park":

Click here if video does not appear on screen.

Related:
Written in poo: The story of prehistoric life

Friday, June 12, 2015

Stone tools from Jordan point to dawn of division of labor

Two stone tool points made using a prismatic blade technique (left and center), and a bone point or needle (right). The finds "give us a new window onto a transitional time, on the cusp of modern human cultural behaviors," says anthropologist Aaron Stutz.

By Carol Clark

Thousands of stone tools from the early Upper Paleolithic, unearthed from a cave in Jordan, reveal clues about how humans may have started organizing into more complex social groups by planning tasks and specializing in different technical skills.

The Journal of Human Evolution published a study of the artifacts from Mughr el-Hamamah, or Cave of the Doves, led by Emory University anthropologists Liv Nilsson Stutz and Aaron Jonas Stutz.

“We have achieved remarkably accurate estimates of 40,000 to 45,000 years ago for the earliest Upper Paleolithic stone tools in the Near East,” says Aaron Stutz, an associate professor at Emory's Oxford College. “Our findings confirm that the Upper Paleolithic began in the region no later than 42,000 years ago, and likely at least 44,600 years ago.”

The rich array of artifacts shows a mix of techniques for making points, blades, scrapers and cutting flakes. “These toolmakers appear to have achieved a division of labor that may have been part of an emerging pattern of more organized social structures,” Stutz says.

The theory that greater social division of labor was important at this prehistoric juncture was first put forward by anthropologists Steven Kuhn and Mary Stiner.

“Our work really seems to support that idea,” Stutz says. “The finds from Mughr el-Hamamah give us a new window onto a transitional time, on the cusp of modern human cultural behaviors, bridging the Middle and Upper Paleolithic.”

Liv Nilsson Stutz and Aaron Stutz in the field, on the terrace of Mughr el-Hamamah.

This pivotal time also marked the ebbing of Neanderthals as a last wave of anatomically modern humans spread out from Africa and into the Near East. This region, also known as the Levant, comprises the eastern Mediterranean at the crossroads of western Asia and northeast Africa. As the final surge of modern humans passed through the Levant, they would likely have encountered human populations that arrived earlier, and they may also have interbred with Neanderthals.

“Our find sits right in the Levantine corridor, midway between the Dead Sea and the Sea of Galilee, where each generation expanding into Eurasia would have foraged for food and made campsites,” Stutz says. “We don’t know if these toolmakers were mainly Neanderthals or anatomically modern humans, but recent evidence from other studies now raises the possibility that they were a mix of different populations. What we see at the Mughr el-Hamamah site is that individuals were starting to live, work and form families in larger, more culturally structured social networks.”

Mughr el-Hamamah is located in a limestone outcrop 240 feet above sea level. It overlooks the Jordan Valley, opposite the Nablus Mountains in the West Bank. The Stutzes, a husband-and-wife team, led excavations of the cave in 2010, funded by a grant from the National Science Foundation.

The relatively undisturbed Upper Paleolithic layer included fireplaces stacked atop one another that yielded chunks of well-preserved charcoal from hearths associated with the tools. Co-authors Jeff Pigati of the U.S. Geological Survey and Jim Wilson of Aeon Laboratories derived radiocarbon dates for the charcoal specimens, using advanced techniques that minimized the chances of contamination.

Listen to Liv Nilsson Stutz, senior lecturer in Emory anthropology, describe the artifacts, in the slideshow below:


The cave is about 30-feet deep with an entrance about 20-feet wide. “We can speculate that several families shared the space and worked alongside one another,” Aaron Stutz says. “We found burned animal bones, so they were likely roasting meat, and perhaps boiling plants in hides suspended over their fires as they sat nearby making tools. From the mouth of the cave, they would have had a commanding view of what was likely wetlands and open-vegetation terrain. They could see approaching visitors and deer and gazelle wandering in the distance. If their kids were playing outside, they might also be watching for leopards or other predators.”

Toolmaking was a major activity of the group, as evidenced by their prolific output. Co-author John Shea, an anthropologist from Stony Brook University and an expert flint knapper himself, is continuing to analyze the thousands of implements they left behind.

Many discoveries of Near Eastern tool assemblages dating prior to the early Upper Paleolithic show that humans focused on just one technology. The tools tend to look similar and likely served many uses – the Stone Age version of a Swiss Army Knife. “It takes a good bit of cleverness to be able to devise a tool that helps you cover lots of different situations,” Stutz says. “And it makes sense in a context where you don’t necessarily know what you’re going to need your piece of flint for that day.”

The group of toolmakers at Mughr el-Hamamah, however, used different technologies to get different tools. “They were investing in the kinds of activities that require maintaining relationships and group planning,” Stutz says. “They were gearing up for a clearly defined division of labor, including firewood gathering, plant gathering, hunting and food foraging.”

They produced large quantities of blades for knives, and for hafting onto spears, using a prismatic blade technique that yields long, narrow points that are nearly identical. “This standardization minimizes waste of the rock while maximizing the end product,” Stutz says. “It’s the conceptual forerunner to assembly-line production.”

Through this method, the toolmakers could have efficiently produced the armature for multiple hunters going out on a lengthy foray, increasing the chances for finding and striking a target, he says.

“It would have been socially advantageous for individuals to give blades that they made to others, to entice them to stay together as a group,” he adds. “That kind of reciprocity builds relationships. And the stronger the connectivity of your social networks, the greater chance of increasing the number of calories and the quality of nutrients for the group.”

One of the tools made with the Levallois technique, used by Neanderthals and anatomically modern humans alike in earlier periods.

Artifacts from the cave also included scraping tools, made on thick blades for hafting onto a handle and likely used for working wood and animal hides. Other tools continued to be crafted with what is known as the Levallois technique, which was more often used to make the multi-use flakes and triangular points so common in earlier periods.

Even more surprising, Shea’s analysis identified hundreds of basic flakes made from the oldest, easiest Stone Age technology of striking a rock that the toolmaker balances on a stone anvil. These tiny, sharp flakes may have served almost like disposable cutlery – handy implements that could be grabbed for a variety of purposes and tossed aside when no longer needed, Stutz says.

It is not yet known if the few fragments of human bones found at Mughr el-Hamamah have left enough intact fragments of DNA for any genetic analysis. But the diverse tool technologies, in use throughout the occupation period of the cave, support the theory of hunter-gatherer populations starting to band together in larger, more interconnected social networks.

As humans began to dominate the landscape, the researchers theorize, they reached a population density threshold for living in larger groups and gained access to a range of technologies. That process may have helped tip the balance for the rise of modern human culture and the disappearance of the Neanderthals.

“Our findings positively show that the cultural changes associated with Neanderthal extinction in the Near East and wider western Eurasia really are more complex than many leading researchers have assumed,” Stutz says. “Instead of looking for a smoking-gun technology or climatic fluctuation or volcanic eruption, it’s clear we need to look at interconnected behavioral, population and ecological processes. That approach might reveal more clearly the similarities, as well as differences, between our mainly African, and slightly Neanderthal, biological inheritance.”

Additional co-authors of the study are: Jason Rech of the University of Miami; Miriam Belmaker of the University of Tulsa; Rosa Maria Alert and Dan Cabanes of the University of Barcelona; Trina Arpin, an independent researcher in Boston; Jaime Clark of the University of Alaska, Fairbanks; Gideon Hartman of the University of Connecticut; Fuad Hourani of the University of Jordan and Chantel White of the University of Notre Dame.

Credits: Tool photos by Aaron Stutz; field photo by Julie Margolis.

Related:
Complex cognition shaped the Stone Age hand axe
Modern population boom traced to pre-industrial roots