Glacier beds can get slipperier at higher sliding speeds

Neal Iverson developed the Iowa State University Sliding Simulator to test how glaciers slide over their beds. -  Bob Elbert/Iowa State University
Neal Iverson developed the Iowa State University Sliding Simulator to test how glaciers slide over their beds. – Bob Elbert/Iowa State University

As a glacier’s sliding speed increases, the bed beneath the glacier can grow slipperier, according to laboratory experiments conducted by Iowa State University glaciologists.

They say including this effect in efforts to calculate future increases in glacier speeds could improve predictions of ice volume lost to the oceans and the rate of sea-level rise.

The glaciologists – Lucas Zoet, a postdoctoral research associate, and Neal Iverson, a professor of geological and atmospheric sciences – describe the results of their experiments in the Journal of Glaciology. The paper uses data collected from a newly constructed laboratory tool, the Iowa State University Sliding Simulator, to investigate glacier sliding. The device was used to explore the relationship between drag and sliding speed for comparison with the predictions of theoretical models.

“We really have a unique opportunity to study the base of glaciers with these experiments,” said Zoet, the lead author of the paper. “The other tactic you might take is studying these relationships with field observations, but with field data so many different processes are mixed together that it becomes hard to untangle the relevant data from the noise.”

Data collected by the researchers show that resistance to glacier sliding – the drag that the bed exerts on the ice – can decrease in response to increasing sliding speed. This decrease in drag with increasing speed, although predicted by some theoreticians a long as 45 years ago, is the opposite of what is usually assumed in mathematical models of the flow of ice sheets.

These are the first empirical results demonstrating that as ice slides at an increasing speed – perhaps in response to changing weather or climate – the bed can become slipperier, which could promote still faster glacier flow.

The response of glaciers to changing climate is one of the largest potential contributors to sea-level rise. Predicting glacier response to climate change depends on properly characterizing the way a glacier slides over its bed. There has been a half-century debate among theoreticians as to how to do that.

The simulator features a ring of ice about 8 inches thick and about 3 feet across that is rotated over a model glacier bed. Below the ice is a hydraulic press that can simulate the weight of a glacier several hundred yards thick. Above are motors that can rotate the ice ring over the bed at either a constant speed or a constant stress. A circulating, temperature-regulated fluid keeps the ice at its melting temperature – a necessary condition for significant sliding.

“About six years were required to design, construct, and work the bugs out of the new apparatus,” Iverson said, “but it is performing well now and allowing hypothesis tests that were formerly not possible.”

NASA study finds 1934 had worst drought of last thousand years

A new study using a reconstruction of North American drought history over the last 1,000 years found that the drought of 1934 was the driest and most widespread of the last millennium.

Using a tree-ring-based drought record from the years 1000 to 2005 and modern records, scientists from NASA and Lamont-Doherty Earth Observatory found the 1934 drought was 30 percent more severe than the runner-up drought (in 1580) and extended across 71.6 percent of western North America. For comparison, the average extent of the 2012 drought was 59.7 percent.

“It was the worst by a large margin, falling pretty far outside the normal range of variability that we see in the record,” said climate scientist Ben Cook at NASA’s Goddard Institute for Space Studies in New York. Cook is lead author of the study, which will publish in the Oct. 17 edition of Geophysical Research Letters.

Two sets of conditions led to the severity and extent of the 1934 drought. First, a high-pressure system in winter sat over the west coast of the United States and turned away wet weather – a pattern similar to that which occurred in the winter of 2013-14. Second, the spring of 1934 saw dust storms, caused by poor land management practices, suppress rainfall.

“In combination then, these two different phenomena managed to bring almost the entire nation into a drought at that time,” said co-author Richard Seager, professor at the Lamont-Doherty Earth Observatory of Columbia University in New York. “The fact that it was the worst of the millennium was probably in part because of the human role.”

According to the recent Fifth Assessment Report of the Intergovernmental Panel on Climate Change, or IPCC, climate change is likely to make droughts in North America worse, and the southwest in particular is expected to become significantly drier as are summers in the central plains. Looking back one thousand years in time is one way to get a handle on the natural variability of droughts so that scientists can tease out anthropogenic effects – such as the dust storms of 1934.

“We want to understand droughts of the past to understand to what extent climate change might make it more or less likely that those events occur in the future,” Cook said.

The abnormal high-pressure system is one lesson from the past that informs scientists’ understanding of the current severe drought in California and the western United States.

“What you saw during this last winter and during 1934, because of this high pressure in the atmosphere, is that all the wintertime storms that would normally come into places like California instead got steered much, much farther north,” Cook said. “It’s these wintertime storms that provide most of the moisture in California. So without getting that rainfall it led to a pretty severe drought.”

This type of high-pressure system is part of normal variation in the atmosphere, and whether or not it will appear in a given year is difficult to predict in computer models of the climate. Models are more attuned to droughts caused by La Niña’s colder sea surface temperatures in the Pacific Ocean, which likely triggered the multi-year Dust Bowl drought throughout the 1930s. In a normal La Niña year, the Pacific Northwest receives more rain than usual and the southwestern states typically dry out.

But a comparison of weather data to models looking at La Niña effects showed that the rain-blocking high-pressure system in the winter of 1933-34 overrode the effects of La Niña for the western states. This dried out areas from northern California to the Rockies that otherwise might have been wetter.

As winter ended, the high-pressure system shifted eastward, interfering with spring and summer rains that typically fall on the central plains. The dry conditions were exacerbated and spread even farther east by dust storms.

“We found that a lot of the drying that occurred in the spring time occurred downwind from where the dust storms originated,” Cook said, “suggesting that it’s actually the dust in the atmosphere that’s driving at least some of the drying in the spring and really allowing this drought event to spread upwards into the central plains.”

Dust clouds reflect sunlight and block solar energy from reaching the surface. That prevents evaporation that would otherwise help form rain clouds, meaning that the presence of the dust clouds themselves leads to less rain, Cook said.

“Previous work and this work offers some evidence that you need this dust feedback to explain the real anomalous nature of the Dust Bowl drought in 1934,” Cook said.

Dust storms like the ones in the 1930s aren’t a problem in North America today. The agricultural practices that gave rise to the Dust Bowl were replaced by those that minimize erosion. Still, agricultural producers need to pay attention to the changing climate and adapt accordingly, not forgetting the lessons of the past, said Seager. “The risk of severe mid-continental droughts is expected to go up over time, not down,” he said.

First eyewitness accounts of mystery volcanic eruption

This eruption occurred just before the 1815 Tambora volcanic eruption which is famous for its impact on climate worldwide, with 1816 given memorable names such as ‘Eighteen-Hundred-and-Froze-to-Death’, the ‘Year of the Beggar’ and the ‘Year Without a Summer’ because of unseasonal frosts, crop failure and famine across Europe and North America. The extraordinary conditions are considered to have inspired literary works such as Byron’s ‘Darkness’ and Mary Shelley’s Frankenstein.

However, the global deterioration of the 1810s into the coldest decade in the last 500 years started six years earlier, with another large eruption. In contrast to Tambora, this so-called ‘Unknown’ eruption seemingly occurred unnoticed, with both its location and date a mystery. In fact the ‘Unknown’ eruption was only recognised in the 1990s, from tell-tale markers in Greenland and Antarctic ice that record the rare events when volcanic aerosols are so violently erupted that they reach the Earth’s stratosphere.

Working in collaboration with colleagues from the School of Earth Sciences and PhD student Alvaro Guevara-Murua, Dr Caroline Williams, from the Department of Hispanic, Portuguese and Latin American Studies, began searching historical archives for references to the event.

Dr Williams said: “I spent months combing through the vast Spanish colonial archive, but it was a fruitless search – clearly the volcano wasn’t in Latin America. I then turned to the writings of Colombian scientist Francisco José de Caldas, who served as Director of the Astronomical Observatory of Bogotá between 1805 and 1810. Finding his precise description of the effects of an eruption was a ‘Eureka’ moment.”

In February 1809 Caldas wrote about a “mystery” that included a constant, stratospheric “transparent cloud that obstructs the sun’s brilliance” over Bogotá, starting on the 11 December 1808 and seen across Colombia. He gave detailed observations, for example that the “natural fiery colour [of the sun] has changed to that of silver, so much so that many have mistaken it for the moon”; and that the weather was unusually cold, the fields covered with ice and the crops damaged by frost.

Unearthing a short account written by physician José Hipólito Unanue in Lima, Peru, describing sunset after-glows (a common atmospheric effect caused by volcanic aerosols in the stratosphere) at the same time as Caldas’ “vapours above the horizon”, enabled the researchers to verify that the atmospheric effects of the eruption were seen at the same time on both sides of the equator.

These two 19th century Latin American scientists provide the first direct observations that can be linked to the ‘Unknown’ eruption. More importantly, the accounts date the eruption to within a fortnight of 4 December 1808.

Dr Erica Hendy said: “There have to be more observations hidden away, for example in ship logs. Having a date for the eruption will now make it much easier to track these down, and maybe even pinpoint the volcano. Climate modelling of this fascinating decade will also now be more accurate because the season of the eruption determines how the aerosols disperse around the globe and where climatic effects are felt.”

Alvaro Guevara-Murua added: “This study has meant delving into many fields of research – obviously paleoclimatology and volcanology, but also 19th century meteorology and Spanish colonial history – and has also needed rigorous precision to correctly translate the words of two scientists writing 200 years ago. Giving them a voice in modern science has been a big responsibility.”

One further question remains: why are there so few historical accounts of what was clearly a significant event with wide-reaching consequences? Perhaps, Dr Williams suggests, the political environment on both sides of the Atlantic at the beginning of the nineteenth century played a part.

“The eruption coincided with the Napoleonic Wars in Europe, the Peninsular War in Spain, and with political developments in Latin America that would soon lead to the independence of almost all of Spain’s American colonies. It’s possible that, in Europe and Latin America at least, the attention of individuals who might otherwise have provided us with a record of unusual meteorological or atmospheric effects simply turned to military and political matters instead,” she said.

Mystery solved: ‘Sailing stones’ of Death Valley seen in action for the first time

Racetrack Playa is home to an enduring Death Valley mystery. Littered across the surface of this dry lake, also called a “playa,” are hundreds of rocks – some weighing as much as 320 kilograms (700 pounds) – that seem to have been dragged across the ground, leaving synchronized trails that can stretch for hundreds of meters.

What powerful force could be moving them? Researchers have investigated this question since the 1940s, but no one has seen the process in action – until now.

In a paper published in the journal PLOS ONE on Aug. 27, a team led by Scripps Institution of Oceanography, UC San Diego, paleobiologist Richard Norris reports on first-hand observations of the phenomenon.

Because the stones can sit for a decade or more without moving, the researchers did not originally expect to see motion in person. Instead, they decided to monitor the rocks remotely by installing a high-resolution weather station capable of measuring gusts to one-second intervals and fitting 15 rocks with custom-built, motion-activated GPS units. (The National Park Service would not let them use native rocks, so they brought in similar rocks from an outside source.) The experiment was set up in winter 2011 with permission of the Park Service. Then – in what Ralph Lorenz of the Applied Physics Laboratory at the Johns Hopkins University, one of the paper’s authors, suspected would be “the most boring experiment ever” – they waited for something to happen.

But in December 2013, Norris and co-author and cousin Jim Norris arrived in Death Valley to discover that the playa was covered with a pond of water seven centimeters (three inches) deep. Shortly after, the rocks began moving.

“Science sometimes has an element of luck,” Richard Norris said. “We expected to wait five or ten years without anything moving, but only two years into the project, we just happened to be there at the right time to see it happen in person.”

Their observations show that moving the rocks requires a rare combination of events. First, the playa fills with water, which must be deep enough to form floating ice during cold winter nights but shallow enough to expose the rocks. As nighttime temperatures plummet, the pond freezes to form thin sheets of “windowpane” ice, which must be thin enough to move freely but thick enough to maintain strength. On sunny days, the ice begins to melt and break up into large floating panels, which light winds drive across the playa, pushing rocks in front of them and leaving trails in the soft mud below the surface.

“On Dec. 21, 2013, ice breakup happened just around noon, with popping and cracking sounds coming from all over the frozen pond surface,” said Richard Norris. “I said to Jim, ‘This is it!'”

These observations upended previous theories that had proposed hurricane-force winds, dust devils, slick algal films, or thick sheets of ice as likely contributors to rock motion. Instead, rocks moved under light winds of about 3-5 meters per second (10 miles per hour) and were driven by ice less than 3-5 millimeters (0.25 inches) thick, a measure too thin to grip large rocks and lift them off the playa, which several papers had proposed as a mechanism to reduce friction. Further, the rocks moved only a few inches per second (2-6 meters per minute), a speed that is almost imperceptible at a distance and without stationary reference points.

“It’s possible that tourists have actually seen this happening without realizing it,” said Jim Norris of the engineering firm Interwoof in Santa Barbara. “It is really tough to gauge that a rock is in motion if all the rocks around it are also moving.”

Individual rocks remained in motion for anywhere from a few seconds to 16 minutes. In one event, the researchers observed rocks three football fields apart began moving simultaneously and traveled over 60 meters (200 feet) before stopping. Rocks often moved multiple times before reaching their final resting place. The researchers also observed rock-less trails formed by grounding ice panels – features that the Park Service had previously suspected were the result of tourists stealing rocks.

“The last suspected movement was in 2006, and so rocks may move only about one millionth of the time,” said Lorenz. “There is also evidence that the frequency of rock movement, which seems to require cold nights to form ice, may have declined since the 1970s due to climate change.”

Richard and Jim Norris, and co-author Jib Ray of Interwoof started studying the Racetrack’s moving rocks to solve the “public mystery” and set up the “Slithering Stones Research Initiative” to engage a wide circle of friends in the effort. They needed the help of volunteers who repeatedly visited the remote dry lake, quarried the rocks that were fitted with GPS, and maintained custom-made instruments. Lorenz and Brian Jackson of the Department of Physics at Boise State University started working on the phenomenon for their own reasons: They wanted to study dust devils and other desert weather features that might have analogs to processes happening on other planets.

“What is striking about prior research on the Racetrack is that almost everybody was doing the work not to gain fame or fortune, but because it is such a neat problem,” said Jim Norris.

So is the mystery of the sliding rocks finally solved?

“We documented five movement events in the two and a half months the pond existed and some involved hundreds of rocks”, says Richard Norris, “So we have seen that even in Death Valley, famous for its heat, floating ice is a powerful force in rock motion. But we have not seen the really big boys move out there?.Does that work the same way?”

Yellowstone supereruption would send ash across North America

An example of the possible distribution of ash from a month-long Yellowstone supereruption. The distribution map was generated by a new model developed by the US Geological Survey using wind information from January 2001. The improved computer model, detailed in a new study published in Geochemistry, Geophysics, Geosystems, finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America. Ash distribution will vary depending on cloud height, eruption duration, diameter of volcanic particles in the cloud, and wind conditions, according to the new study. -  Credit: USGS
An example of the possible distribution of ash from a month-long Yellowstone supereruption. The distribution map was generated by a new model developed by the US Geological Survey using wind information from January 2001. The improved computer model, detailed in a new study published in Geochemistry, Geophysics, Geosystems, finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America. Ash distribution will vary depending on cloud height, eruption duration, diameter of volcanic particles in the cloud, and wind conditions, according to the new study. – Credit: USGS

In the unlikely event of a volcanic supereruption at Yellowstone National Park, the northern Rocky Mountains would be blanketed in meters of ash, and millimeters would be deposited as far away as New York City, Los Angeles and Miami, according to a new study.

An improved computer model developed by the study’s authors finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America.

A supereruption is the largest class of volcanic eruption, during which more than 1,000 cubic kilometers (240 cubic miles) of material is ejected. If such a supereruption were to occur, which is extremely unlikely, it could shut down electronic communications and air travel throughout the continent, and alter the climate, the study notes.

A giant underground reservoir of hot and partly molten rock feeds the volcano at Yellowstone National Park. It has produced three huge eruptions about 2.1 million, 1.3 million and 640,000 years ago. Geological activity at Yellowstone shows no signs that volcanic eruptions, large or small, will occur in the near future. The most recent volcanic activity at Yellowstone-a relatively non-explosive lava flow at the Pitchstone Plateau in the southern section of the park-occurred 70,000 years ago.

Researchers at the U.S. Geological Survey used a hypothetical Yellowstone supereruption as a case study to run their new model that calculates ash distribution for eruptions of all sizes. The model, Ash3D, incorporates data on historical wind patterns to calculate the thickness of ash fall for a supereruption like the one that occurred at Yellowstone 640,000 years ago.

The new study provides the first quantitative estimates of the thickness and distribution of ash in cities around the U.S. if the Yellowstone volcanic system were to experience this type of huge, yet unlikely, eruption.

Cities close to the modeled Yellowstone supereruption could be covered by more than a meter (a few feet) of ash. There would be centimeters (a few inches) of ash in the Midwest, while cities on both coasts would see millimeters (a fraction of an inch) of accumulation, according to the new study that was published online today in Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union. The paper has been made available at no charge at http://onlinelibrary.wiley.com/doi/10.1002/2014GC005469/abstract.

The model results help scientists understand the extremely widespread distribution of ash deposits from previous large eruptions at Yellowstone. Other USGS scientists are using the Ash3D model to forecast possible ash hazards at currently restless volcanoes in Alaska.

Unlike smaller eruptions, whose ash deposition looks roughly like a fan when viewed from above, the spreading umbrella cloud from a supereruption deposits ash in a pattern more like a bull’s eye – heavy in the center and diminishing in all directions – and is less affected by prevailing winds, according to the new model.

“In essence, the eruption makes its own winds that can overcome the prevailing westerlies, which normally dominate weather patterns in the United States,” said Larry Mastin, a geologist at the USGS Cascades Volcano Observatory in Vancouver, Washington, and the lead author of the new paper. Westerly winds blow from the west.

“This helps explain the distribution from large Yellowstone eruptions of the past, where considerable amounts of ash reached the west coast,” he added.

The three large past eruptions at Yellowstone sent ash over many tens of thousands of square kilometers (thousands of square miles). Ash deposits from these eruptions have been found throughout the central and western United States and Canada.

Erosion has made it difficult for scientists to accurately estimate ash distribution from these deposits. Previous computer models also lacked the ability to accurately determine how the ash would be transported.

Using their new model, the study’s authors found that during very large volcanic eruptions, the expansion rate of the ash cloud’s leading edge can exceed the average ambient wind speed for hours or days depending on the length of the eruption. This outward expansion is capable of driving ash more than 1,500 kilometers (932 miles) upwind – westward — and crosswind – north to south — producing a bull’s eye-like pattern centered on the eruption site.

In the simulated modern-day eruption scenario, cities within 500 kilometers (311 miles) of Yellowstone like Billings, Montana, and Casper, Wyoming, would be covered by centimeters (inches) to more than a meter (more than three feet) of ash. Upper Midwestern cities, like Minneapolis, Minnesota, and Des Moines, Iowa, would receive centimeters (inches), and those on the East and Gulf coasts, like New York and Washington, D.C. would receive millimeters or less (fractions of an inch). California cities would receive millimeters to centimeters (less than an inch to less than two inches) of ash while Pacific Northwest cities like Portland, Oregon, and Seattle, Washington, would receive up to a few centimeters (more than an inch).

Even small accumulations only millimeters or centimeters (less than an inch to an inch) thick could cause major effects around the country, including reduced traction on roads, shorted-out electrical transformers and respiratory problems, according to previous research cited in the new study. Prior research has also found that multiple inches of ash can damage buildings, block sewer and water lines, and disrupt livestock and crop production, the study notes.

The study also found that other eruptions – powerful but much smaller than a Yellowstone supereruption — might also generate an umbrella cloud.

“These model developments have greatly enhanced our ability to anticipate possible effects from both large and small eruptions, wherever they occur,” said Jacob Lowenstern, USGS Scientist-in-Charge of the Yellowstone Volcano Observatory in Menlo Park, California, and a co-author on the new paper.

Yellowstone geyser eruptions influenced more by internal processes

<IMG SRC="/Images/994664490.jpg" WIDTH="350" HEIGHT="396" BORDER="0" ALT="This is a map showing the location of Daisy and Old Faithful geysers in Yellowstone's Upper Geyser Basin. Inset map of Yellowstone National Park shows the weather station at Yellowstone Lake, seismic stations LKWY and H17A, and strainmeter B944. – Images taken from: Shaul Hurwitz, Robert A. Sohn, Karen Luttrell, Michael Manga, "Triggering and modulation of geyser eruptions in Yellowstone National Park by earthquakes, earth tides, and weather", Journal of Geophysical Research: Solid Earth, DOI:10.1002/2013JB010803″>
This is a map showing the location of Daisy and Old Faithful geysers in Yellowstone’s Upper Geyser Basin. Inset map of Yellowstone National Park shows the weather station at Yellowstone Lake, seismic stations LKWY and H17A, and strainmeter B944. – Images taken from: Shaul Hurwitz, Robert A. Sohn, Karen Luttrell, Michael Manga, “Triggering and modulation of geyser eruptions in Yellowstone National Park by earthquakes, earth tides, and weather”, Journal of Geophysical Research: Solid Earth, DOI:10.1002/2013JB010803

The intervals between geyser eruptions depend on a delicate balance of underground factors, such as heat and water supply, and interactions with surrounding geysers. Some geysers are highly predictable, with intervals between eruptions (IBEs) varying only slightly. The predictability of these geysers offer earth scientists a unique opportunity to investigate what may influence their eruptive activity, and to apply that information to rare and unpredictable types of eruptions, such as those from volcanoes.

Dr. Shaul Hurwitz took advantage of a decade of eruption data-spanning from 2001 to 2011-for two of Yellowstone’s most predictable geysers, the cone geyser Old Faithful and the pool geyser, Daisy.

Dr. Hurwitz’s team focused their statistical analysis on possible correlations between the geysers’ IBEs and external forces such as weather, earth tides and earthquakes. The authors found no link between weather and Old Faithful’s IBEs, but they did find that Daisy’s IBEs correlated with cold temperatures and high winds. In addition, Daisy’s IBEs were significantly shortened following the 7.9 magnitude earthquake that hit Alaska in 2002.

The authors note that atmospheric processes exert a relatively small but statistically significant influence on pool geysers’ IBEs by modulating heat transfer rates from the pool to the atmosphere. Overall, internal processes and interactions with surrounding geysers dominate IBEs’ variability, especially in cone geysers.

Network for tracking earthquakes exposes glacier activity

Alaska’s seismic network records thousands of quakes produced by glaciers, capturing valuable data that scientists could use to better understand their behavior, but instead their seismic signals are set aside as oddities. The current earthquake monitoring system could be “tweaked” to target the dynamic movement of the state’s glaciers, suggests State Seismologist Michael West, who will present his research today at the annual meeting of the Seismological Society of America (SSA).

“In Alaska, these glacial events have been largely treated as a curiosity, a by-product of earthquake monitoring,” said West, director of the Alaska Earthquake Center, which is responsible for detecting and reporting seismic activity across Alaska.

The Alaska seismic network was upgraded in 2007-08, improving its ability to record and track glacial events. “As we look across Alaska’s glacial landscape and comb through the seismic record, there are thousands of these glacial events. We see patterns in the recorded data that raise some interesting questions about the glaciers,” said West.

As a glacier loses large pieces of ice on its leading edge, a process called calving, the Alaska Earthquake Center’s monitoring system automatically records the event as an earthquake. Analysts filter out these signals in order to have a clear record of earthquake activity for the region. In the discarded data, West sees opportunity.

“We have amassed a large record of glacial events by accident,” said West. “The seismic network can act as an objective tool for monitoring glaciers, operating 24/7 and creating a data flow that can alert us to dynamic changes in the glaciers as they are happening.” It’s when a glacier is perturbed or changing in some way, says West, that the scientific community can learn the most.

Since 2007, the Alaska Earthquake Center has recorded more than 2800 glacial events along 600 km of Alaska’s coastal mountains. The equivalent earthquake sizes for these events range from about 1 to 3 on the local magnitude scale. While calving accounts for a significant number of the recorded quakes, each glacier’s terminus – the end of any glacier where the ice meets the ocean – behaves differently. Seasonal variations in weather cause glaciers to move faster or slower, creating an expected seasonal cycle in seismic activity. But West and his colleagues have found surprises, too.

In mid-August 2010, the Columbia Glacier’s seismic activity changed radically from being relatively quiet to noisy, producing some 400 quakes to date. These types of signals from the Columbia Glacier have been documented every single month since August 2010, about the time when the Columbia terminus became grounded on sill, stalling its multi-year retreat.

That experience highlighted for West the value of the accidental data trove collected by the Alaska Earthquake Center. “The seismic network is blind to the cause of the seismic events, cataloguing observations that can then be validated,” said West, who suggests the data may add value to ongoing field studies in Alaska.

Many studies of Alaska’s glaciers have focused on single glacier analyses with dedicated field campaigns over short periods of time and have not tracked the entire glacier complex over the course of years. West suggests leveraging the data stream may help the scientific community observe the entire glacier complex in action or highlight in real time where scientists could look to catch changes in a glacier.

“This is low-hanging fruit,” said West of the scientific advances waiting to be gleaned from the data.

Warm US West, cold East: A 4,000-year pattern

<IMG SRC="/Images/485889256.jpg" WIDTH="350" HEIGHT="262" BORDER="0" ALT="University of Utah geochemist Gabe Bowen led a new study, published in Nature Communications, showing that the curvy jet stream pattern that brought mild weather to western North America and intense cold to the eastern states this past winter has become more dominant during the past 4,000 years than it was from 8,000 to 4,000 years ago. The study suggests global warming may aggravate the pattern, meaning such severe winter weather extremes may be worse in the future. – Lee J. Siegel, University of Utah.”>
University of Utah geochemist Gabe Bowen led a new study, published in Nature Communications, showing that the curvy jet stream pattern that brought mild weather to western North America and intense cold to the eastern states this past winter has become more dominant during the past 4,000 years than it was from 8,000 to 4,000 years ago. The study suggests global warming may aggravate the pattern, meaning such severe winter weather extremes may be worse in the future. – Lee J. Siegel, University of Utah.

Last winter’s curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, and suggests it may worsen as Earth’s climate warms.

“If this trend continues, it could contribute to more extreme winter weather events in North America, as experienced this year with warm conditions in California and Alaska and intrusion of cold Arctic air across the eastern USA,” says geochemist Gabe Bowen, senior author of the study.

The study was published online April 16 by the journal Nature Communications.

“A sinuous or curvy winter jet stream means unusual warmth in the West, drought conditions in part of the West, and abnormally cold winters in the East and Southeast,” adds Bowen, an associate professor of geology and geophysics at the University of Utah. “We saw a good example of extreme wintertime climate that largely fit that pattern this past winter,” although in the typical pattern California often is wetter.

It is not new for scientists to forecast that the current warming of Earth’s climate due to carbon dioxide, methane and other “greenhouse” gases already has led to increased weather extremes and will continue to do so.

The new study shows the jet stream pattern that brings North American wintertime weather extremes is millennia old – “a longstanding and persistent pattern of climate variability,” Bowen says. Yet it also suggests global warming may enhance the pattern so there will be more frequent or more severe winter weather extremes or both.

“This is one more reason why we may have more winter extremes in North America, as well as something of a model for what those extremes may look like,” Bowen says. Human-caused climate change is reducing equator-to-pole temperature differences; the atmosphere is warming more at the poles than at the equator. Based on what happened in past millennia, that could make a curvy jet stream even more frequent and-or intense than it is now, he says.

Bowen and his co-authors analyzed previously published data on oxygen isotope ratios in lake sediment cores and cave deposits from sites in the eastern and western United States and Canada. Those isotopes were deposited in ancient rainfall and incorporated into calcium carbonate. They reveal jet stream directions during the past 8,000 years, a geological time known as middle and late stages of the Holocene Epoch.

Next, the researchers did computer modeling or simulations of jet stream patterns – both curvy and more direct west to east – to show how changes in those patterns can explain changes in the isotope ratios left by rainfall in the old lake and cave deposits.

They found that the jet stream pattern – known technically as the Pacific North American teleconnection – shifted to a generally more “positive phase” – meaning a curvy jet stream – over a 500-year period starting about 4,000 years ago. In addition to this millennial-scale change in jet stream patterns, they also noted a cycle in which increases in the sun’s intensity every 200 years make the jet stream flatter.

Bowen conducted the study with Zhongfang Liu of Tianjin Normal University in China, Kei Yoshimura of the University of Tokyo, Nikolaus Buenning of the University of Southern California, Camille Risi of the French National Center for Scientific Research, Jeffrey Welker of the University of Alaska at Anchorage, and Fasong Yuan of Cleveland State University.

The study was funded by the National Science Foundation, National Natural Science Foundation of China, Japan Society for the Promotion of Science and a joint program by the society and Japan’s Ministry of Education, Culture, Sports, Science and Technology: the Program for Risk Information on Climate Change.

Sinuous Jet Stream Brings Winter Weather Extremes

The Pacific North American teleconnection, or PNA, “is a pattern of climate variability” with positive and negative phases, Bowen says.

“In periods of positive PNA, the jet stream is very sinuous. As it comes in from Hawaii and the Pacific, it tends to rocket up past British Columbia to the Yukon and Alaska, and then it plunges down over the Canadian plains and into the eastern United States. The main effect in terms of weather is that we tend to have cold winter weather throughout most of the eastern U.S. You have a freight car of arctic air that pushes down there.”

Bowen says that when the jet stream is curvy, “the West tends to have mild, relatively warm winters, and Pacific storms tend to occur farther north. So in Northern California, the Pacific Northwest and parts of western interior, it tends to be relatively dry, but tends to be quite wet and unusually warm in northwest Canada and Alaska.”

This past winter, there were times of a strongly curving jet stream, and times when the Pacific North American teleconnection was in its negative phase, which means “the jet stream is flat, mostly west-to-east oriented,” and sometimes split, Bowen says. In years when the jet stream pattern is more flat than curvy, “we tend to have strong storms in Northern California and Oregon. That moisture makes it into the western interior. The eastern U.S. is not affected by arctic air, so it tends to have milder winter temperatures.”

The jet stream pattern – whether curvy or flat – has its greatest effects in winter and less impact on summer weather, Bowen says. The curvy pattern is enhanced by another climate phenomenon, the El Nino-Southern Oscillation, which sends a pool of warm water eastward to the eastern Pacific and affects climate worldwide.

Traces of Ancient Rains Reveal Which Way the Wind Blew

Over the millennia, oxygen in ancient rain water was incorporated into calcium carbonate deposited in cave and lake sediments. The ratio of rare, heavy oxygen-18 to the common isotope oxygen-16 in the calcium carbonate tells geochemists whether clouds that carried the rain were moving generally north or south during a given time.

Previous research determined the dates and oxygen isotope ratios for sediments in the new study, allowing Bowen and colleagues to use the ratios to tell if the jet stream was curvy or flat at various times during the past 8,000 years.

Bowen says air flowing over the Pacific picks up water from the ocean. As a curvy jet stream carries clouds north toward Alaska, the air cools and some of the water falls out as rain, with greater proportions of heavier oxygen-18 falling, thus raising the oxygen-18-to-16 ratio in rain and certain sediments in western North America. Then the jet stream curves south over the middle of the continent, and the water vapor, already depleted in oxygen-18, falls in the East as rain with lower oxygen-18-to-16 ratios.

When the jet stream is flat and moving east-to-west, oxygen-18 in rain is still elevated in the West and depleted in the East, but the difference is much less than when the jet stream is curvy.

By examining oxygen isotope ratios in lake and cave sediments in the West and East, Bowen and colleagues showed that a flatter jet stream pattern prevailed from about 8,000 to 4,000 years ago in North America, but then, over only 500 years, the pattern shifted so that curvy jet streams became more frequent or severe or both. The method can’t distinguish frequency from severity.

The new study is based mainly on isotope ratios at Buckeye Creek Cave, W. Va.; Lake Grinell, N.J.; Oregon Caves National Monument; and Lake Jellybean, Yukon.

Additional data supporting increasing curviness of the jet stream over recent millennia came from seven other sites: Crawford Lake, Ontario; Castor Lake, Wash.; Little Salt Spring, Fla.; Estancia Lake, N.M.; Crevice Lake, Mont.; and Dog and Felker lakes, British Columbia. Some sites provided oxygen isotope data; others showed changes in weather patterns based on tree ring growth or spring deposits.

Simulating the Jet Stream

As a test of what the cave and lake sediments revealed, Bowen’s team did computer simulations of climate using software that takes isotopes into account.

Simulations of climate and oxygen isotope changes in the Middle Holocene and today resemble, respectively, today’s flat and curvy jet stream patterns, supporting the switch toward increasing jet stream sinuosity 4,000 years ago.

Why did the trend start then?

“It was a when seasonality becomes weaker,” Bowen says. The Northern Hemisphere was closer to the sun during the summer 8,000 years ago than it was 4,000 years ago or is now due to a 20,000-year cycle in Earth’s orbit. He envisions a tipping point 4,000 years ago when weakening summer sunlight reduced the equator-to-pole temperature difference and, along with an intensifying El Nino climate pattern, pushed the jet stream toward greater curviness.

The Atlantic Ocean dances with the sun and volcanoes

Imagine a ballroom in which two dancers apparently keep in time to their own individual rhythm. The two partners suddenly find themselves moving to the same rhythm and, after a closer look, it is clear to see which one is leading.

It was an image like this that researchers at Aarhus University were able to see when they compared studies of solar energy release and volcanic activity during the last 450 years, with reconstructions of ocean temperature fluctuations during the same period.

The results actually showed that during the last approximately 250 years – since the period known as the Little Ice Age – a clear correlation can be seen where the external forces, i.e. the Sun’s energy cycle and the impact of volcanic eruptions, are accompanied by a corresponding temperature fluctuation with a time lag of about five years.

In the previous two centuries, i.e. during the Little Ice Age, the link was not as strong, and the temperature of the Atlantic Ocean appears to have followed its own rhythm to a greater extent.

The results were recently published in the scientific journal Nature Communications.

In addition to filling in yet another piece of the puzzle associated with understanding the complex interaction of the natural forces that control the climate, the Danish researchers paved the way for linking the two competing interpretations of the origin of the oscillation phenomenon.

Temperature fluctuations discovered around the turn of the millennium

The climate is defined on the basis of data including mean temperature values recorded over a period of thirty years. Northern Europe thus has a warm and humid climate compared with other regions on the same latitudes. This is due to the North Atlantic Drift (often referred to as the Gulf Stream), an ocean current that transports relatively warm water from the south-west part of the North Atlantic to the sea off the coast of Northern Europe.

Around the turn of the millennium, however, climate researchers became aware that the average temperature of the Atlantic Ocean was not entirely stable, but actually fluctuated at the same rate throughout the North Atlantic. This phenomenon is called the Atlantic Multidecadal Oscillation (AMO), which consists of relatively warm periods lasting thirty to forty years being replaced by cool periods of the same duration.

The researchers were able to read small systematic variations in the water temperature in the North Atlantic in measurements taken by ships during the last 140 years.

Although the temperature fluctuations are small – less than 1°C – there is a general consensus among climate researchers that the AMO phenomenon has had a major impact on the climate in the area around the North Atlantic for thousands of years, but until now there has been doubt about what could cause this slow rhythm in the temperature of the Atlantic Ocean. One model explains the phenomenon as internal variability in the ocean circulation – somewhat like a bathtub sloshing water around in its own rhythm. Another model explains the AMO as being driven by fluctuations in the amount of solar energy received by the Earth, and as being affected by small changes in the energy radiated by the Sun itself and the after-effects of volcanic eruptions. Both these factors are also known as ‘external forces’ that have an impact on the Earth’s radiation balance.

However, there has been considerable scepticism towards the idea that a phenomenon such as an AMO could be driven by external forces at all – a scepticism that the Aarhus researchers now demonstrate as unfounded.

“Our new investigations clearly show that, since the Little Ice Age, there has been a correlation between the known external forces and the temperature fluctuations in the ocean that help control our climate. At the same time, however, the results also show that this can’t be the only driving force behind the AMO, and the explanation must therefore be found in a complex interaction between a number of mechanisms. It should also be pointed out that these fluctuations occur on the basis of evenly increasing ocean temperatures during the last approximately fifty years – an increase connected with global warming,” says Associate Professor Mads Faurschou Knudsen, Department of Geoscience, Aarhus University, who is the main author of the article.

Convincing data from the Earth’s own archives

Researchers have attempted to make computer simulations of the phenomenon ever since the discovery of the AMO, partly to enable a better understanding of the underlying mechanism. However, it is difficult for the computer models to reproduce the actual AMO signal that can be read in the temperature data from the last 140 years.

Associate Professor Knudsen and his colleagues instead combined all available data from the Earth’s own archives, i.e. previous studies of items such as radioactive isotopes and volcanic ash in ice cores. This provides information about solar energy release and volcanic activity during the last 450 years, and the researchers compared the data with reconstructions of the AMO’s temperature rhythm during the same period.

“We’ve only got direct measurements of the Atlantic Ocean temperature for the last 140 years, where it was measured by ships. But how do you measure the water temperature further back in time? Studies of growth rings in trees from the entire North Atlantic region come into the picture here, where ‘good’ and ‘bad’ growth conditions are calibrated to the actual measurements, and the growth rings from trees along the coasts further back in time can therefore act as reserve thermometers,” explains Associate Professor Knudsen.

The results provide a new and very important perspective on the AMO phenomenon because they are based on data and not computer models, which are inherently incomplete. The problem is that the models do not completely describe all the physical correlations and feedbacks in the system, partly because these are not fully understood. And when the models are thus unable to reproduce the actual AMO signal, it is hard to know whether they have captured the essence of the AMO phenomenon.

Impact of the sun and volcanoes

An attempt to simply explain how external forces such as the Sun and volcanoes can control the climate could sound like this: a stronger Sun heats up the ocean, while the ash from volcanic eruptions shields the Sun and cools down the ocean. However, it is hardly as simple as that.

“Fluctuations in ocean temperature have a time lag of about five years in relation to the peaks we can read in the external forces. However, the direct effect of major volcanic eruptions is clearly seen as early as the same year in the mean global atmospheric temperature, i.e. a much shorter delay. The effect we studied is more complex, and it takes time for this effect to spread to the ocean currents,” explains Associate Professor Knudsen.

“An interesting new theory among solar researchers and meteorologists is that the Sun can control climate variations via the very large variations in UV radiation, which are partly seen in connection with changes in sunspot activity during the Sun’s eleven-year cycle. UV radiation heats the stratosphere in particular via increased production of ozone, which can have an impact on wind systems and thereby indirectly on the global ocean currents as well,” says Associate Professor Knudsen. However, he emphasises that researchers have not yet completely understood how a development in the stratosphere can affect the ocean currents on Earth.

Towards a better understanding of the climate

“In our previous study of the climate in the North Atlantic region during the last 8,000 years, we were able to show that the temperature of the Atlantic Ocean was presumably not controlled by the Sun’s activity. Here the temperature fluctuated in its own rhythm for long intervals, with warm and cold periods lasting 25 years. The prevailing pattern was that this climate fluctuation in the ocean was approximately 30󈞔% faster than the fluctuation we’d previously observed in solar activity, which lasted about ninety years. What we can now see is that the Atlantic Ocean would like to – or possibly even prefer to – dance alone. However, under certain circumstances, the external forces interrupt the ocean’s own rhythm and take over the lead, which has been the case during the last 250 years,” says Associate Professor Bo Holm Jacobsen, Department of Geoscience, Aarhus University, who is the co-author of the article.

“It’ll be interesting to see how long the Atlantic Ocean allows itself to be led in this dance. The scientific challenge partly lies in understanding the overall conditions under which the AMO phenomenon is sensitive to fluctuations in solar activity and volcanic eruptions,” he continues.

“During the last century, the AMO has had a strong bearing on significant weather phenomena such as hurricane frequency and droughts – with considerable economic and human consequences. A better understanding of this phenomenon is therefore an important step for efforts to deal with and mitigate the impact of climate variations,” Associate Professor Knudsen concludes.

The complicated birth of a volcano

Snow storms, ice and glaciers – these are the usual images we associate with the Antarctic. But at the same time it is also a region of fire: the Antarctic continent and surrounding waters are dotted with volcanoes – some of them still active and others extinct for quite some time. The Marie Byrd Seamounts in the Amundsen Sea are in the latter group. Their summit plateaus are today at depths of 2400-1600 meters. Because they are very difficult to reach with conventional research vessels, they have hardly been explored, even though the Marie Byrd Seamounts are fascinating formations. They do not fit any of the usual models for the formation of volcanoes. Now geologists from GEOMAR Helmholtz Centre for Ocean Research Kiel were able to find a possible explanation for the existence of these seamounts on the basis of rare specimens. The study is published in the international journal “Gondwana Research“.

Classic volcanologists differentiate between two types of fire mountains. One type is generated where tectonic plates meet, so the earth’s crust is already cracked to begin with. The other type is formed within the earth’s plates. “The latter are called intraplate volcanoes. They are often found above a so-called mantle plume. Hot material rises from the deep mantle, collects under the earth’s crust, makes its way to the surface and forms a volcano,” said Dr. Reinhard Werner, one of the authors of the current paper. One example are the Hawaiian Islands. But neither of the above models fits the Marie Byrd Seamounts. “There are no plate boundary in the vicinity and no plume underground,” says graduate geologist Andrea Kipf from GEOMAR, first author of the study.

To clarify the origin of the Marie Byrd Seamounts, in 2006 the Kiel scientists participated in an expedition of the research vessel POLARSTEN in the Amundsen Sea. They salvaged rock samples from the seamounts and subjected these to thorough geological, volcanological and geochemical investigations after returning to the home labs. “Interestingly enough, we found chemical signatures that are typical of plume volcanoes. And they are very similar to volcanoes in New Zealand and the Antarctic continent,” says geochemist Dr. Folkmar Hauff, second author of the paper.

Based on this finding, the researchers sought an explanation. They found it in the history of tectonic plates in the southern hemisphere. Around 100 million years ago, remains of the former supercontinent Gondwana were located in the area of present Antarctica. A mantle plume melted through this continental plate and cracked it open. Two new continents were born: the Antarctic and “Zealandia”, with the islands of New Zealand still in evidence today. When the young continents drifted in different directions away from the mantle plume, large quantities of hot plume material were attached to their undersides. These formed reservoirs for future volcanic eruptions on the two continents. “This process explains why we find signatures of plume material at volcanoes that are not on top of plumes,” says Dr. Hauff.

But that still does not explain the Marie Byrd Seamounts because they are not located on the Antarctic continent, but on the adjacent oceanic crust instead. “Continental tectonic plates are thicker than the oceanic ones. This ensures, among other things, differences in temperature in the underground,” says volcanologist Dr. Werner. And just as air masses of different temperatures create winds, the temperature differences under the earth’s crust generate flows and movements as well. Thus the plume material, that once lay beneath the continent, was able to shift under the oceanic plate. With disruptions due to other tectonic processes, there were cracks and crevices which allowed the hot material to rise, turn into magma and then- about 60 million years ago – allowed the Marie Byrd Seamounts to grow. “This created islands are comparable to the Canary Islands today,” explains Andrea Kipf. “Some day the volcanoes became extinct again, wind and weather eroded the cone down to sea level, and other geological processes further eroded the seamounts. Finally, the summit plateaus arrived at the level that we know today,” the PhD student describes the last step of the development.

Based on the previously little investigated Marie Byrd Seamounts, the researchers were able to show another example of how diverse and complex the processes are, that can cause volcanism. “We are still far from understanding all of these processes. But with the current study, we can contribute a small piece to the overall picture,” says Dr. Werner.