From greenhouse to icehouse — reconstructing the environment of the Voring Plateau

<IMG SRC="/Images/335517525.jpg" WIDTH="350" HEIGHT="325" BORDER="0" ALT="This is a scanning electron micrograph of one of the characteristic brackish water species of the genus Wezteliella. – NOCS”>
This is a scanning electron micrograph of one of the characteristic brackish water species of the genus Wezteliella. – NOCS

The analysis of microfossils found in ocean sediment cores is illuminating the environmental conditions that prevailed at high latitudes during a critical period of Earth history.

Around 55 million years ago at the beginning of the Eocene epoch, the Earth’s poles are believed to have been free of ice. But by the early Oligocene around 25 million years later, ice sheets covered Antarctica and continental ice had developed on Greenland.

“This change from greenhouse to icehouse conditions resulted from decreasing greenhouse gas concentrations and changes in Earth’s orbit,” said Dr Ian Harding of the University of Southampton’s School of Ocean and Earth Science (SOES) at the National Oceanography Centre, Southampton (NOCS): “However, the opening or closing of various marine gateways and shifts in ocean currents may also have influenced regional climate in polar high-latitudes.”

The separation of Eurasia and Greenland due to shifting tectonic plates led to the partial or complete submergence of former land barriers such as the Vøring Plateau of the Norwegian continental margin. For the first time, waters could exchange between the Norwegian-Greenland Sea, the Arctic Ocean and the North Atlantic.

Dr Harding and his former PhD student Dr James Eldrett have reconstructed the environmental conditions over the Vøring Plateau over this time period by carefully analyzing the fossilized remains of organic debris and cysts of tiny aquatic organisms called dinoflagellates from sediment cores.

“Because different dinoflagellate species are adapted to different surface water conditions, their fossilized remains help us reconstruct past environments,” said Dr Harding.

The evidence from the sediments cores suggests the development of shallow marine environments across parts of the Vøring Plateau during the early Eocene. However, the presence of fossilized species that lived in fresh or brackish water indicates that northerly parts of the plateau as well as the crest of the Vøring Escarpment were still above water.

In the late Eocene sediments (around 44 million years old) only marine plankton species were found, indicating that the entire Vøring Plateau had by then subsided and become submerged. This demonstrates that marine connections were established between the various Nordic sea basins much earlier than had previously been thought. These surface water connections may have promoted the increased surface water productivity evidenced by the abundance of planktonic fossils preserved in the sediment cores of this age.

“Increased productivity would have drawn carbon dioxide down from the atmosphere,” said Dr Harding: “Because carbon dioxide is a greenhouse gas, this may have contributed to declining global temperatures and led to the early development of continental ice on Greenland in the latest Eocene.

Pre-eruption earthquakes offer clues to volcano forecasters

The Alaska Volcano Observatory monitors earthquake activity at Augustine volcano (above), which erupted most recently in 2006. Photo by Cyrus Read, image courtesy of AVO/USGS.
The Alaska Volcano Observatory monitors earthquake activity at Augustine volcano (above), which erupted most recently in 2006. Photo by Cyrus Read, image courtesy of AVO/USGS.

Like an angry dog, a volcano growls before it bites, shaking the ground and getting “noisy” before erupting. This activity gives scientists an opportunity to study the tumult beneath a volcano and may help them improve the accuracy of eruption forecasts, according to Emily Brodsky, an associate professor of Earth and planetary sciences at the University of California, Santa Cruz.

Brodsky will present recent findings on pre-eruption earthquakes on Wednesday, December 16, at the fall meeting of the American Geophysical Union in San Francisco.

Each volcano has its own personality. Some rumble consistently, while others stop and start. Some rumble and erupt the same day, while others take months, and some never do erupt. Brodsky is trying to find the rules behind these personalities.

“Volcanoes almost always make some noise before they erupt, but they don’t erupt every time they make noise,” she said. “One of the big challenges of a volcano observatory is how to handle all the false alarms.”

Brodsky and Luigi Passarelli, a visiting graduate student from the University of Bologna, compiled data on the length of pre-eruption earthquakes, time between eruptions, and the silica content of lava from 54 volcanic eruptions over a 60-year span. They found that the length of a volcano’s “run-up”–the time between the onset of earthquakes and an eruption–increases the longer a volcano has been dormant or “in repose.” Furthermore, the underlying magma is more viscous or gummy in volcanoes with long run-up and repose times.

Scientists can use these relationships to estimate how soon a rumbling volcano might erupt. A volcano with frequent eruptions over time, for instance, provides little warning before it blows. The findings can also help scientists decide how long they should stay on alert after a volcano starts rumbling.

“You can say, ‘My volcano is acting up today, so I’d better issue an alert and keep that alert open for 100 days or 10 days, based on what I think the chemistry of the system is,’ ” Brodsky said.

Volcano observers are well-versed in the peculiarities of their systems and often issue alerts to match, according to Brodsky. But this study is the first to take those observations and stretch them across all volcanoes, she said.

“The innovation of this study is trying to stitch together those empirical rules with the underlying physics and find some sort of generality,” Brodsky said.

The underlying physics all lead back to magma, she said. When the pressure in a chamber builds high enough, the magma pushes its way to the volcano’s mouth and erupts. The speed of this ascent depends on how viscous the magma is, which depends in turn on the amount of silica in the magma. The less silica, the runnier the magma. The runnier the magma, the quicker the volcanic chamber fills and the quicker it will spew, according to Brodsky.

The path from chamber to surface isn’t easy for magma as it forces its way up through the crust. The jostling of subsurface rock causes pre-eruption tremors, which oscillate in length and severity based on how freely the magma can move.

“If the magma’s very sticky, then it takes a long time both to recharge the chamber and to push its way to the surface,” Brodsky said. “It extends the length of precursory activity.”

Thick magma is the culprit behind the world’s most explosive eruptions, because it traps gas and builds pressure like a keg, she said. Mount St. Helens is an example of a volcano fed by viscous magma.

Brodsky and Passarelli diagrammed the dynamics of magma flow using a simple analytical model of fluids moving through channels. The next step, Brodsky said, is to test the accuracy of their predictions on future eruptions.

Volcanoes are messy systems, however, with wildly varying structures and mineral ingredients. Observatories will likely have to tweak their predictions based on the unique characteristics of each system, she said.

Low-cost temperature sensors, tennis balls to monitor mountain snowpack

UW assistant professor Jessica Lundquist (left) and graduate student Eset Alemu flake nylon rope into a bag so it will unravel smoothly when a sensor is catapulted into the canopy. -  University of Washington
UW assistant professor Jessica Lundquist (left) and graduate student Eset Alemu flake nylon rope into a bag so it will unravel smoothly when a sensor is catapulted into the canopy. – University of Washington

Fictional secret agent Angus MacGyver knew that tough situations demand ingenuity. Jessica Lundquist takes a similar approach to studying snowfall. The University of Washington assistant professor of civil and environmental engineering uses dime-sized temperature sensors, first developed for the refrigerated food industry, and tennis balls. In summer months she attaches the sensors to tennis balls that are weighted with gravel, and uses a dog-ball launcher to propel the devices high into alpine trees where they will record winter temperatures.

This isn’t TV spy work – it’s science. Lundquist studies mountain precipitation to learn how changes in snowfall and snowmelt will affect the communities and environments at lower elevations. If the air temperature is above 32 degrees Fahrenheit the precipitation will fall as rain, but if it’s below freezing, it will be snow.

“It’s fun, like backyard science,” Lundquist said of her sensors, which were originally designed to record temperature of frozen foods in transit. She began adapting the devices for environmental science while a postdoctoral researcher in Colorado and has refined them over the years. “It turns out they work phenomenally well.”

Last year the American Geophysical Union awarded Lundquist its Cryosphere Young Investigators Award for her fieldwork. This week at the AGU’s fall meeting in San Francisco she will present her low-cost temperature-sensing technology and some current applications.

Scientific weather stations typically cost about $10,000. Lundquist’s system measures and records the temperature every hour for up to 11 months in remote locations for just $30 apiece. Another advantage is that they are easily deployed in rough terrain.

Her temperature sensors are a fun approach to studying a serious problem. One quarter of the Earth’s continents have mountainous terrain, Lundquist said, and mountain rivers provide water for 40 percent of the world’s population. Those mountain rivers are largely fed by snowmelt. But if winters become warmer due to climate change, the snow line is expected to inch up the mountainside, and snow is expected to melt earlier in the springtime.

“Mountains are the water towers of the world,” Lundquist said. “We essentially use the snow as an extra reservoir. And you want that reservoir to hold the snow for as long as possible

Her sensors are being used to improve computer models in areas where water managers want to know exactly where snow is accumulating and on what date it starts to melt.

“People typically assume that temperature decreases with elevation,” Lundquist says. But actual mountain temperatures depend on the vegetation, slope and variable weather. “If you have a management decision, there’s a specific place you have to make a decision for.”

If more rain falls instead of snow, it will increase the risk of flooding during storms. Lundquist’s sensors are currently being used by the California-Nevada River Forecasting Center as part of a project pinpointing at what elevation snow turns to rain, to improve storm flooding forecasts. As part of that project, UW graduate students are placing her sensors in river canyons that are too steep for traditional weather stations.

She is also deploying sensors in Yosemite National Park to see if earlier snowmelt may cause earlier drying of streambeds and affect vegetation growth in the Tuolumne Meadows. Her sensors there provide ground verification of satellite measurements.

The City of Seattle is also using Lundquist’s sensors to study how different restoration approaches for trees in the Cedar River watershed, which supplies water to the city, affect snow retention.

“I have a lot of fun deploying my sensors because I love being in the mountains,” Lundquist said. “They also sense conditions in these remote environments that we can’t know about any other way.

New discoveries could improve climate projections

New discoveries about the deep ocean’s temperature variability and circulation system could help improve projections of future climate conditions.

The deep ocean is affected more by surface warming than previously thought, and this understanding allows for more accurate predictions of factors such as sea level rise and ice volume changes.

High ocean surface temperatures have also been found to result in a more vigorous deep ocean circulation system. This increase results in a faster transport of large quantities of warm water, with possible impacts including reduction of sea ice extent and overall warming of the Arctic.

“The deep ocean is relatively unexplored, and we need a true understanding of its many complex processes,” said U.S. Geological Survey Director Marcia McNutt. “An understanding of climate change and its impacts based on sound, objective data is a keystone to the type of long-term strategies and solutions that are being discussed now at the United Nations conference in Copenhagen.”

USGS scientists created the first ever 3-D reconstruction of an ocean during a past warm period, focusing on the mid-Pliocene warm period 3.3 to 3 million years ago.

“Our findings are significant because they improve our previous understanding that the deep ocean stayed at relatively constant, cold temperatures and that the deep ocean circulation system would slow down as surface temperatures increased,” said USGS scientist Harry Dowsett. “By looking at conditions in the past, we acquire real data that allow us to see the global climate system as it actually functioned.”

“The average temperature of the entire ocean during the mid-Pliocene was approximately one degree warmer than current conditions, showing that warming wasn’t just at the surface but occurred at all depths” said USGS scientist Marci Robinson. “Temperatures were determined by analyzing marine plankton fossils, which are organisms that inhabited the water’s surface, as well as fossils of bottom-dwelling organisms, known as ostracodes.”

Global average surface temperatures during the mid-Pliocene were about 3°C (5.5°F) greater than today and within the range projected for the 21st century by the Intergovernmental Panel on Climate Change. Therefore it may be one of the closest analogs in helping to understand Earth’s current and future conditions. USGS research on the mid-Pliocene is also the most comprehensive global reconstruction for any warm period.

Going vertical: Fleeing tsunamis by moving up, not out

Damaged mosque and surrounding area in Banda Aceh, Indonesia, after the 2004 tsunami.
Damaged mosque and surrounding area in Banda Aceh, Indonesia, after the 2004 tsunami.

In the minutes after a strong earthquake struck offshore of the Indonesian city of Padang on Sept. 30, fears of a tsunami prompted hundreds of thousands of residents to evacuate the coastal city. Or try to.

The traffic jam resulting from the mass exodus kept most of them squarely in the danger zone, had a tsunami followed the magnitude 7.6 temblor. Stanford researchers who’ve studied the city have concluded that fleeing residents would have a better chance of surviving a tsunami if instead of all attempting an evacuation, some could run to the nearest tall building to ride out the wave.

It’s called “vertical evacuation” and could save thousands of lives, but only if the city’s buildings are reinforced to withstand both earthquakes and tsunamis.

Residents of Padang are trained to immediately evacuate to higher ground when they feel an earthquake. About 600,000 of the people in Padang live less than 5 meters above sea level, in the “Red Zone” for tsunamis. They have only about 20 minutes to evacuate, but on Sept. 30, it took them several hours.

“In the event of a tsunami, hundreds of thousands of people would be at risk and could have been killed, all because they couldn’t evacuate fast enough,” said Greg Deierlein, professor of civil and environmental engineering. Indonesia is at high risk for a large tsunami, Deierlein said, and horizontal evacuation strategies alone – by motor vehicle or foot – are clearly not adequate.

Deierlein and some Stanford students are investigating how to build or retrofit buildings to withstand both the earthquake ground shaking and tsunami inundation waves of 15 to 25 feet. Deierlein led a reconnaissance team of engineers and scientists to Padang, in Western Sumatra, nine days after the September earthquake to examine how buildings fared.

“It was like a big living laboratory,” he said. “We were able to see how buildings performed and how the city reacted to the threat of a tsunami.” During his visit, he was surprised by how many modern buildings collapsed.

“Existing buildings can be strengthened to perform better under future earthquakes and tsunamis,” he said.

Deierlein, the John A. Blume Professor in the School of Engineering, will present this work Dec. 15 at the American Geophysical Union meeting in San Francisco. The reconnaissance team he led was organized through the multidisciplinary Earthquake Engineering Research Institute, a nonprofit society of technical professionals, and supported by a grant from the National Science Foundation.

Though designing a brand-new building to withstand a tsunami would provide optimal protection from the onslaught of waves, it is often more economical to retrofit.

To retrofit buildings, engineers turn to computer models that combine principles of geophysics and structural engineering. The models can predict how a building will perform, depending on how strong the ground shaking is, how tall the tsunami waves are, the speed and direction of the waves when they hit and whether the flow is carrying debris, such as floating cars. The models also factor in the structure of the building – construction materials, the placement and strength of beams, columns and walls.

To enhance strength and stiffness, Deierlein said, engineers could make concrete columns or beams stronger and more ductile by retrofitting them with fiber-reinforced polymer composite overlays or concrete and steel jackets. Workers might add steel braces to the frame or construct walls that are reinforced to resist horizontal forces.

Walls in lower stories can be designed to break away under intense pressure from waves to reduce the stress on the building. These “frangible” wall systems, also found in hurricane-resistant buildings, are similar to windows that are designed to pop out under pressure. “It’s like wind blowing on a building,” Deierlein said. “Once windows pop out, wind can go right through.”

Another important consideration is the foundation, which should be protected from water that scours around the building. A tsunami could actually scour out so much of the ground around the building that it could be destabilized and fall over. Diversionary walls and berms could reduce this risk.

There isn’t a single magic formula, Deierlein said; instead, buildings have to be treated on a case-by-case basis. Given the high cost of retrofitting, some buildings deserve more attention than others. “The design depends on the everyday function of the building,” he said. “It’s OK if a warehouse gets damaged, but an emergency response center, a large school or large hotel could be used as an effective refuge place during tsunamis and should be designed to a higher performance level.”

To implement the latest research findings in developing countries, Deierlein and Stanford’s Blume Earthquake Engineering Center are partnering with the Stanford chapter of Engineers for a Sustainable World, a national nonprofit organization linking students with professionals, and a Palo Alto nonprofit organization called GeoHazards International, which aims to prepare developing countries for natural disasters.

They are collaborating with Indonesian government agencies to suggest recommendations for building design and educate engineering students at Andalas University in Padang. “We’re stepping up our efforts after the latest earthquake,” Deierlein said. “Working with the Andalas University is a key way to transfer knowledge and technologies to the future generation of engineering professionals in Indonesia.”

One challenge is training people to think about vertical evacuation. “Their instinct is to flee inland,” Deierlein said. “So we have to figure out how to educate people to have faith in buildings.” Most people see at most one tsunami in their lifetime, so they must rely on training rather than personal experience to change their habits.

Another approach is to make the most of people’s instincts. “We’re trying to understand what type of structures people would feel safe going to,” said Veronica Cedillos, a structural engineer and project manager at GeoHazards International. “For example, we heard about a lot of people going to mosques after a tsunami, so that’s definitely one of the main types of building we’ve been exploring as potential evacuation sites.”

No matter the strategy, Deierlein has faith that people in Padang will rise to the challenge. “Developing countries have one advantage: They struggle all the time to survive,” he said. He recalls visiting a hospital while in Padang and asking if the emergency generator worked. The answer: “Of course. We use it several times a week.”

“I was impressed with the resiliency of the city,” Deierlein said.

Still, he knows it’s an uphill battle. “Developing countries have a long way to go to make the same improvements the U.S. has made in building design,” he said. “It’s important to reach out and look at problems facing developing countries, and to see how research and education can contribute to solving those problems.”

Understanding ocean climate

This image shows ocean temperature at the 100 m depth and sea ice thickness in Sept. 2006 from the 8 km resolution global model. -  NOCS
This image shows ocean temperature at the 100 m depth and sea ice thickness in Sept. 2006 from the 8 km resolution global model. – NOCS

High-resolution computer simulations performed by scientists at the National Oceanography Centre, Southampton (NOCS) are helping to understand the inflow of North Atlantic water to the Arctic Ocean and how this influences ocean climate.

The summer of 2007 saw a record retreat in Arctic sea ice, and in general Arctic climate has become steadily warmer since the early 1990s. This has changed both sea ice drift and upper ocean circulation.

The warm North Atlantic water intrudes into the central Arctic Ocean through Fram Strait, the deep channel between Greenland and Spitsbergen that connects the Nordic Seas to the Arctic Ocean, contributing to sea ice melting.

“We need to understand what is going on because changes in the Arctic Ocean can influence climate around the world,” said Dr Yevgeny Aksenov of NOCS: “The worry is that freshwater from melting ice and increased atmospheric precipitation in the Arctic could ultimately slow the overturning circulation of the North Atlantic, with serious consequences for global climate.”

The researchers used a high-resolution computer model of ocean and sea ice, taking into account the shape of the seabed, and the affects of ice melting, snow and rainfall, solar radiation, and winds. The simulations were verified using long-term measurements of ocean currents and other key climatological and oceanographical data.

“Computers are now powerful enough to run multi-decadal global simulations at high resolution,” said Dr Aksenov: “This helps to understand how the ocean is changing and to plan observational programmes so as to make measurements at sea more efficient.”

The researchers find that between 1989 and 2009, about half of the salty North Atlantic water entering the Arctic Ocean came through Fram Strait, and half through the Barents Sea, north of Norway and Russia. However, most of the heat entered the Arctic Ocean through Fram Strait.

Based on their simulations and available observations, they propose a new scheme for the inflow of North Atlantic water into the Arctic Ocean, involving three main routes.

The first delivers warm saline water to the Arctic Ocean through Fram Strait. The other two bring cooled and freshened North Atlantic water to the Arctic Ocean via the Barents Sea.

A northern branch delivers water from the western Barents Sea, mixed to some extent with the Fram Strait branch. Here, North Atlantic water interacts with Arctic waters, resulting in fresh, cold water overlying saltier water below the mixed layer at a depth of around 50-170 metres.

The southern branch supplies the Arctic Ocean with warmer and more saline bottom water formed in the southeastern Barents Sea via full-depth convection and mixing.

Both the northern and southern branches of the Barents Sea flow deliver North Atlantic water to the Arctic Ocean via the 620 metre deep St Anna’s Trough, located east of the Franz Josef archipelago in the far north of Russia. Together they transport around one and a half million cubic metres of water a second.

“Our research is leading to a physically based picture, our eventual goal being a comprehensive understanding of the mechanisms driving ocean climate change,” said Dr Aksenov.

Tremors between slip events: More evidence of great quake danger to Seattle

Scientists have discovered more small seismic tremor events lasting one to 70 hours that occur in somewhat regular patterns in a megathrust earthquake zone in Washington state and British Columbia.
Scientists have discovered more small seismic tremor events lasting one to 70 hours that occur in somewhat regular patterns in a megathrust earthquake zone in Washington state and British Columbia.

For most of a decade, scientists have documented unfelt and slow-moving seismic events, called episodic tremor and slip, showing up in regular cycles under the Olympic Peninsula of Washington state and Vancouver Island in British Columbia. They last three weeks on average and release as much energy as a magnitude 6.5 earthquake.

Now scientists have discovered more small events, lasting one to 70 hours, which occur in somewhat regular patterns during the 15-month intervals between episodic tremor and slip events.

“There appear to be tremor swarms that repeat, both in terms of their duration and in where they are. We haven’t seen enough yet to say whether they repeat in regular time intervals,” said Kenneth Creager, a University of Washington professor of Earth and space sciences.

“This continues to paint the picture of the possibility that a megathrust earthquake can occur closer to the Puget Sound region than was thought just a few years ago,” he said.

The phenomenon, which Creager will discuss today (Dec. 15) during a presentation at the annual meeting of the American Geophysical Union, is the latest piece of evidence as scientists puzzle out exactly what is happening deep below the surface near Washington state’s populous Interstate 5 corridor. He noted that the work shows that tremor swarms follow a size distribution similar to earthquakes, with larger events occurring much less frequently than small events.

The Cascadia subduction zone, where the Juan de Fuca tectonic plate dips beneath the North American plate, runs just off the Pacific coast from northern California to the northern edge of Vancouver Island in British Columbia. It can be the source of massive megathrust earthquakes on the order of magnitude 9 about every 500 years. The last one occurred in 1700.

The fault along the central Washington coast, where the Pacific and Juan de Fuca plates are locked together most of the time but break apart from each other during a powerful megathrust earthquake, was believed to lie 80 miles or more from the Seattle area. But research has shown that the locked zone extends deeper and farther east than previously thought, bringing the edge of the rupture zone beneath the Olympic Mountains, perhaps 40 miles closer to the Seattle area. It is this locked area that can rupture to produce a megathrust earthquake that causes widespread heavy damage, comparable to the 2004 Indian Ocean earthquake or the great Alaska quake of 1964.

Episodic tremor and slip events appear to occur at the interface of the plates as they gradually descend beneath the surface, at depths of about 19 to 28 miles. The smaller tremors between slip episodes, what Creager refers to as inter-episodic tremor and slip events, appear to occur at the interface of the plates a little farther east and a few miles deeper.

“There’s a whole range of events that take place on or near the plate interface. Each improvement in data collection and processing reveals new discoveries,” Creager said.

Episodic tremor and slip events often begin in the area of Olympia, Wash., and move northward to southern Vancouver Island over a three-week period, but scientists have yet to pin down such patterns among the smaller tremors that occur between the slip events.

Because the two tectonic plates are locked together, stress builds at their interface as they collide with each other at a rate of about 4 centimeters (1.6 inches) a year. The slip events and smaller tremors ease some of that stress locally, Creager said, but they don’t appear to account for all of it.

“Each one of these slip events puts more stress on the area of the plate boundary where megathrust earthquakes occur, which is shallower and farther to the west, bringing you closer to the next big event,” he said. “There’s nothing to tell you which one will be the trigger.”

Since the slip events and intervening small tremors don’t accommodate all of the stress built up on the fault, scientists are getting a better idea of just what the hazard from a megathrust earthquake is in the Seattle area. One benefit from that is the ability to revise building codes so structures will be better able to withstand the immense shaking from a great quake, particularly if the source is substantially closer to the city than it was previously expected to be.

“We’d like to go back and see how much slip has occurred in these slip events, compared to how much should have occurred,” Creager said. “Then we’ll know how much of that slip will have to be accommodated in a megathrust earthquake, or through other processes.”

Black carbon deposits on Himalayan ice threaten Earth’s ‘Third Pole’

To better understand the role that black soot has on glaciers, researchers trekked high into the Himalayas to collect ice cores that contain a record of soot deposition that spans back to the 1950s. -  Institute of Tibetan Plateau Research, Chinese Academy of Sciences
To better understand the role that black soot has on glaciers, researchers trekked high into the Himalayas to collect ice cores that contain a record of soot deposition that spans back to the 1950s. – Institute of Tibetan Plateau Research, Chinese Academy of Sciences

Black soot deposited on Tibetan glaciers has contributed significantly to the retreat of the world’s largest non-polar ice masses, according to new research by scientists from NASA and the Chinese Academy of Sciences. Soot absorbs incoming solar radiation and can speed glacial melting when deposited on snow in sufficient quantities.

Temperatures on the Tibetan Plateau — sometimes called Earth’s “third pole” — have warmed by 0.3°C (0.5°F) per decade over the past 30 years, about twice the rate of observed global temperature increases. New field research and ongoing quantitative modeling suggests that soot’s warming influence on Tibetan glaciers could rival that of greenhouse gases.

“Tibet’s glaciers are retreating at an alarming rate,” said James Hansen, coauthor of the study and director of NASA’s Goddard Institute for Space Studies (GISS) in New York City. “Black soot is probably responsible for as much as half of the glacial melt, and greenhouse gases are responsible for the rest.”

“During the last 20 years, the black soot concentration has increased two- to three-fold relative to its concentration in 1975,” said Junji Cao, a researcher from the Chinese Academy of Sciences in Beijing and a coauthor of the paper.

The study was published December 7th in the Proceedings of the National Academy of Sciences.

“Fifty percent of the glaciers were retreating from 1950 to 1980 in the Tibetan region; that rose to 95 percent in the early 21st century,” said Tandong Yao, director of the Chinese Academy’s Institute of Tibetan Plateau Research. Some glaciers are retreating so quickly that they could disappear by mid-century if current trends continue, the researchers suggest.

Since melt water from Tibetan glaciers replenishes many of Asia’s major rivers-including the Indus, Ganges, Yellow, and Brahmaputra-such losses could have a profound impact on the billion people who rely on the rivers for fresh water. While rain and snow would still help replenish Asian rivers in the absence of glaciers, the change could hamper efforts to manage seasonal water resources by altering when fresh water supplies are available in areas already prone to water shortages.

Researchers led by Baiqing Xu of the Chinese Academy drilled and analyzed five ice cores from various locations across the Tibetan Plateau, looking for black carbon (a key component of soot) as well as organic carbon. The cores support the hypothesis that black soot amounts in the Himalayan glaciers correlate with black carbon emissions in Europe and South Asia.

At Zuoqiupu glacier — a bellwether site on the southern edge of the plateau and downwind from the Indian subcontinent — black soot deposition increased by 30 percent between 1990 and 2003. The rise in soot levels at Zuoqiupu follows a dip that followed the enacting of clean air regulations in Europe in the 1970s.

Most soot in the region comes from diesel engines, coal-fired power plants, and outdoor cooking stoves. Many industrial processes produce both black carbon and organic carbon, but often in different proportions. Burning diesel fuel produces mainly black carbon, for example, while burning wood produces mainly organic carbon. Since black carbon is darker and absorbs more radiation, it’s thought to have a stronger warming effect than organic carbon.

To refine this emerging understanding of soot’s impact on glaciers, scientists are striving to gather even more robust measurements. “We can’t expect this study to clarify the effect of black soot on the melting of Tibetan snow and glaciers entirely,” said Cao. “Additional work that looks at albedo measurements, melting rate, and other types of reconnaissance is also needed.”

For example, scientists are using satellite instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the NASA satellites Terra and Aqua to enhance understanding of the region’s albedo. And a new NASA climate satellite called Glory, which will launch late in 2010, will carry a new type of aerosol sensor that should be able to distinguish between aerosol types more accurately than previous instruments.

“Reduced black soot emissions, in addition to reduced greenhouse gases, may be required to avoid demise of Himalayan glaciers and retain the benefits of glaciers for seasonal fresh water supplies,” Hansen said.

Greenland glaciers: What lies beneath

A member of the research team installs GPS equipment in Greenland. -  Photo courtesy of Alberto Behar, Jet Propulsion Laboratory.
A member of the research team installs GPS equipment in Greenland. – Photo courtesy of Alberto Behar, Jet Propulsion Laboratory.

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.”

Yellowstone’s plumbing exposed

Seismic imaging was used by University of Utah scientists to construct this 3-D picture of the Yellowstone hotspot plume of hot and molten rock that feeds the shallower magma chamber (not shown) beneath Yellowstone National Park, outlined in green at the surface, or top of the illustration. The Yellowstone caldera, or giant volcanic crater, is outlined in red. State boundaries are shown in black. The park, caldera and state boundaries also are projected to the bottom of the picture to better illustrate the plume's tilt. Researchers believe 'blobs' of hot rock float off the top of the plume, then rise to recharge the magma chamber located 3.7 miles to 10 miles beneath the surface at Yellowstone. The illustration also shows a region of warm rock extending southwest from near the top of the plume. It represents the eastern Snake River Plain, where the Yellowstone hotspot triggered numerous cataclysmic caldera eruptions before the plume started feeding Yellowstone 2.05 million years ago. -  University of Utah
Seismic imaging was used by University of Utah scientists to construct this 3-D picture of the Yellowstone hotspot plume of hot and molten rock that feeds the shallower magma chamber (not shown) beneath Yellowstone National Park, outlined in green at the surface, or top of the illustration. The Yellowstone caldera, or giant volcanic crater, is outlined in red. State boundaries are shown in black. The park, caldera and state boundaries also are projected to the bottom of the picture to better illustrate the plume’s tilt. Researchers believe ‘blobs’ of hot rock float off the top of the plume, then rise to recharge the magma chamber located 3.7 miles to 10 miles beneath the surface at Yellowstone. The illustration also shows a region of warm rock extending southwest from near the top of the plume. It represents the eastern Snake River Plain, where the Yellowstone hotspot triggered numerous cataclysmic caldera eruptions before the plume started feeding Yellowstone 2.05 million years ago. – University of Utah

The most detailed seismic images yet published of the plumbing that feeds the Yellowstone supervolcano shows a plume of hot and molten rock rising at an angle from the northwest at a depth of at least 410 miles, contradicting claims that there is no deep plume, only shallow hot rock moving like slowly boiling soup.

A related University of Utah study used gravity measurements to indicate the banana-shaped magma chamber of hot and molten rock a few miles beneath Yellowstone is 20 percent larger than previously believed, so a future cataclysmic eruption could be even larger than thought.

The study’s of Yellowstone’s plume also suggests the same “hotspot” that feeds Yellowstone volcanism also triggered the Columbia River “flood basalts” that buried parts of Oregon, Washington state and Idaho with lava starting 17 million years ago.

Those are key findings in four National Science Foundation-funded studies in the latest issue of the Journal of Volcanology and Geothermal Research. The studies were led by Robert B. Smith, research professor and professor emeritus of geophysics at the University of Utah and coordinating scientist for the Yellowstone Volcano Observatory.

“We have a clear image, using seismic waves from earthquakes, showing a mantle plume that extends from beneath Yellowstone,” Smith says.

The plume angles downward 150 miles to the west-northwest of Yellowstone and reaches a depth of at least 410 miles, Smith says. The study estimates the plume is mostly hot rock, with 1 percent to 2 percent molten rock in sponge-like voids within the hot rock.

Some researchers have doubted the existence of a mantle plume feeding Yellowstone, arguing instead that the area’s volcanic and hydrothermal features are fed by convection – the boiling-like rising of hot rock and sinking of cooler rock – from relatively shallow depths of only 185 miles to 250 miles.

The Hotspot: A Deep Plume, Blobs and Shallow Magma

Some 17 million years ago, the Yellowstone hotspot was located beneath the Oregon-Idaho-Nevada border region, feeding a plume of hot and molten rock that produced “caldera” eruptions – the biggest kind of volcanic eruption on Earth.

As North America slid southwest over the hotspot, the plume generated more than 140 huge eruptions that produced a chain of giant craters – calderas – extending from the Oregon-Idaho-Nevada border northeast to the current site of Yellowstone National Park, where huge caldera eruptions happened 2.05 million, 1.3 million and 642,000 years ago.

These eruptions were 2,500, 280 and 1,000 times bigger, respectively, than the 1980 eruption of Mount St. Helens. The eruptions covered as much as half the continental United States with inches to feet of volcanic ash. The Yellowstone caldera, 40 miles by 25 miles, is the remnant of that last giant eruption.

The new study reinforces the view that the hot and partly molten rock feeding volcanic and geothermal activity at Yellowstone isn’t vertical, but has three components:

  • The 45-mile-wide plume that rises through Earth’s upper mantle from at least 410 miles beneath the surface. The plume angles upward to the east-southeast until it reaches the colder rock of the North American crustal plate, and flattens out like a 300-mile-wide pancake about 50 miles beneath Yellowstone. The plume includes several wider “blobs” at depths of 355 miles, 310 miles and 265 miles.

    “This conduit is not one tube of constant thickness,” says Smith. “It varies in width at various depths, and we call those things blobs.”

  • A little-understood zone, between 50 miles and 10 miles deep, in which blobs of hot and partly molten rock break off of the flattened top of the plume and slowly rise to feed the magma reservoir directly beneath Yellowstone National Park.

  • A magma reservoir 3.7 miles to 10 miles beneath the Yellowstone caldera. The reservoir is mostly sponge-like hot rock with spaces filled with molten rock.

    “It looks like it’s up to 8 percent or 15 percent melt,” says Smith. “That’s a lot.”

Researchers previously believed the magma chamber measured roughly 6 to 15 miles from southeast to northwest, and 20 or 25 miles from southwest to northeast, but new measurements indicate the reservoir extends at least another 13 miles outside the caldera’s northeast boundary, Smith says.

He says the gravity and other data show the magma body “is an elongated structure that looks like a banana with the ends up. It is a lot larger than we thought – I would say about 20 percent [by volume]. This would argue there might be a larger magma source available for a future eruption.”

Images of the magma reservoir were made based on the strength of Earth’s gravity at various points in Yellowstone. Hot and molten rock is less dense than cold rock, so the tug of gravity is measurably lower above magma reservoirs.

The Yellowstone caldera, like other calderas on Earth, huffs upward and puffs downward repeatedly over the ages, usually without erupting. Since 2004, the caldera floor has risen 3 inches per year, suggesting recharge of the magma body beneath it.

How to View a Plume

Seismic imaging uses earthquake waves that travel through the Earth and are recorded by seismometers. Waves travel more slowly through hotter rock and more quickly in cooler rock. Just as X-rays are combined to make CT-scan images of features in the human body, seismic wave data are melded to produce images of Earth’s interior.

The study, the Yellowstone Geodynamics Project, was conducted during 1999-2005. It used an average of 160 temporary and permanent seismic stations – and as many as 200 – to detect waves from some 800 earthquakes, with the stations spaced 10 miles to 22 miles apart – closer than other networks and better able to “see” underground. Some 160 Global Positioning System stations measured crustal movements.

By integrating seismic and GPS data, “it’s like a lens that made the upper 125 miles much clearer and allowed us to see deeper, down to 410 miles,” Smith says.

The study also shows warm rock – not as hot as the plume – stretching from Yellowstone southwest under the Snake River Plain, at depths of 20 miles to 60 miles. The rock is still warm from eruptions before the hotspot reached Yellowstone.

A Plume Blowing in the 2-inch-per-year Mantle Wind

Seismic imaging shows a “slow” zone from the top of the plume, which is 50 miles deep, straight down to about 155 miles, but then as you travel down the plume, it tilts to the northwest as it dives to a depth of 410 miles, says Smith.

That is the base of the global transition zone – from 250 miles to 410 miles deep – that is the boundary between the upper and lower mantle – the layers below Earth’s crust.

At that depth, the plume is about 410 miles beneath the town of Wisdom, Mont., which is 150 miles west-northwest of Yellowstone, says Smith.

He says “it wouldn’t surprise me” if the plume extends even deeper, perhaps originating from the core-mantle boundary some 1,800 miles deep.

Why doesn’t the plume rise straight upward? “This plume material wants to come up vertically, it wants to buoyantly rise,” says Smith. “But it gets caught in the ‘wind’ of the upper mantle flow, like smoke rising in a breeze.” Except in this case, the “breeze” of slowly flowing upper mantle rock is moving horizontally 2 inches per year.

While the crustal plate moves southwest, the warm, underlying mantle slowly boils due to convection, with warm areas moving upward and cooler areas downward. Northwest of Yellowstone, this convection is such that the plume is “blown” east-southeast by mantle convection, so it angles upward toward Yellowstone.

Scientists have debated for years whether Yellowstone’s volcanism is fed by a plume rising from deep in the Earth or by shallow churning in the upper mantle caused by movements of the overlying crust. Smith says the new study has produced the most detailed image of the Yellowstone plume yet published.

But a preliminary study by other researchers suggests Yellowstone’s plume goes deeper than 410 miles, ballooning below that depth into a wider zone of hot rock that extends at least 620 miles deep.

The notion that a deep plume feeds Yellowstone got more support from a study published this month indicating that the Hawaiian hotspot – which created the Hawaiian Islands – is fed by a plume that extends downward at least 930 miles, tilting southeast.

A Common Source for Yellowstone and the Columbia River Basalts?

Based on how the Yellowstone plume slants now, Smith and colleagues projected on a map where the plume might have originated at depth when the hotspot was erupting at the Oregon-Idaho-Nevada border area from 17 million to almost 12 million years ago.

They saw overlap, between the zones within the Earth where eruptions originated near the Oregon-Idaho-Nevada border and where the famed Columbia River Basalt eruptions originated when they were most vigorous 17 million to 14 million years ago.

Their conclusion: the Yellowstone hotspot plume might have fed those gigantic lava eruptions, which covered much of eastern Oregon and eastern Washington state.

I argue it is the common source,” Smith says. “It’s neat stuff and it fits together.”

Smith conducted the seismic study with six University of Utah present or former geophysicists – former postdoctoral researchers Michael Jordan, of SINTEF Petroleum Research in Norway, and Stephan Husen, of the Swiss Federal Institute of Technology; postdoc Christine Puskas; Ph.D. student Jamie Farrell; and former Ph.D. students Gregory Waite, now at Michigan Technological University, and Wu-Lung Chang, of National Central University in Taiwan. Other co-authors were Bernhard Steinberger of the Geological Survey of Norway and Richard O’Connell of Harvard University.

Smith conducted the gravity study with former University of Utah graduate student Katrina DeNosaquo and Tony Lowry of Utah State University in Logan.