Climate capers of the past 600,000 years

The researchers remove samples from a core segment taken from Lake Van at the center for Marine environmental sciences MARUM in Bremen, where all of the cores from the PALEOVAN project are stored. -  Photo: Nadine Pickarski/Uni Bonn
The researchers remove samples from a core segment taken from Lake Van at the center for Marine environmental sciences MARUM in Bremen, where all of the cores from the PALEOVAN project are stored. – Photo: Nadine Pickarski/Uni Bonn

If you want to see into the future, you have to understand the past. An international consortium of researchers under the auspices of the University of Bonn has drilled deposits on the bed of Lake Van (Eastern Turkey) which provide unique insights into the last 600,000 years. The samples reveal that the climate has done its fair share of mischief-making in the past. Furthermore, there have been numerous earthquakes and volcanic eruptions. The results of the drilling project also provide a basis for assessing the risk of how dangerous natural hazards are for today’s population. In a special edition of the highly regarded publication Quaternary Science Reviews, the scientists have now published their findings in a number of journal articles.

In the sediments of Lake Van, the lighter-colored, lime-containing summer layers are clearly distinguishable from the darker, clay-rich winter layers — also called varves. In 2010, from a floating platform an international consortium of researchers drilled a 220 m deep sediment profile from the lake floor at a water depth of 360 m and analyzed the varves. The samples they recovered are a unique scientific treasure because the climate conditions, earthquakes and volcanic eruptions of the past 600,000 years can be read in outstanding quality from the cores.

The team of scientists under the auspices of the University of Bonn has analyzed some 5,000 samples in total. “The results show that the climate over the past hundred thousand years has been a roller coaster. Within just a few decades, the climate could tip from an ice age into a warm period,” says Doctor Thomas Litt of the University of Bonn’s Steinmann Institute and spokesman for the PALEOVAN international consortium of researchers. Unbroken continental climate archives from the ice age which encompass several hundred thousand years are extremely rare on a global scale. “There has never before in all of the Middle East and Central Asia been a continental drilling operation going so far back into the past,” says Doctor Litt. In the northern hemisphere, climate data from ice-cores drilled in Greenland encompass the last 120,000 years. The Lake Van project closes a gap in the scientific climate record.

The sediments reveal six cycles of cold and warm periods

Scientists found evidence for a total of six cycles of warm and cold periods in the sediments of Lake Van. The University of Bonn paleoecologist and his colleagues analyzed the pollen preserved in the sediments. Under a microscope they were able to determine which plants around the eastern Anatolian Lake the pollen came from. “Pollen is amazingly durable and is preserved over very long periods when protected in the sediments,” Doctor Litt explained. Insight into the age of the individual layers was gleaned through radiometric age measurements that use the decay of radioactive elements as a geologic clock. Based on the type of pollen and the age, the scientists were able to determine when oak forests typical of warm periods grew around Lake Van and when ice-age steppe made up of grasses, mugwort and goosefoot surrounded the lake.

Once they determine the composition of the vegetation present and the requirements of the plants, the scientists can reconstruct with a high degree of accuracy the temperature and amount of rainfall during different epochs. These analyses enable the team of researchers to read the varves of Lake Van like thousands of pages of an archive. With these data, the team was able to demonstrate that fluctuations in climate were due in large part to periodic changes in the Earth’s orbit parameters and the commensurate changes in solar insolation levels. However, the influence of North Atlantic currents was also evident. “The analysis of the Lake Van sediments has presented us with an image of how an ecosystem reacts to abrupt changes in climate. This fundamental data will help us to develop potential scenarios of future climate effects,” says Doctor Litt.

Risks of earthquakes and volcanic eruptions in the region of Van

Such risk assessments can also be made for other natural forces. “Deposits of volcanic ash with thicknesses of up to 10 m in the Lake Van sediments show us that approximately 270,000 years ago there was a massive eruption,” the University of Bonn paleoecologist said. The team struck some 300 different volcanic events in its drillings. Statistically, that corresponds to one explosive volcanic eruption in the region every 2000 years. Deformations in the sediment layers show that the area is subject to frequent, strong earthquakes. “The area around Lake Van is very densely populated. The data from the core samples show that volcanic activity and earthquakes present a relatively high risk for the region,” Doctor Litt says. According to media reports, in 2011 a 7.2 magnitude earthquake in the Van province claimed the lives of more than 500 people and injured more than 2,500.

Publication: “Results from the PALEOVAN drilling project: A 600,000 year long continental archive in the Near East”, Quaternary Science Reviews, Volume 104, online publication: (

Asian monsoon much older than previously thought

University of Arizona geoscientist Alexis Licht (bottom left) and his colleagues from the French-Burmese Paleontological Team led by Jean-Jacques Jaeger of the University of Poitiers, France (center with hiking staff) used fossils they collected in Myanmar to figure out that the Asian monsoon started at least 40 million years ago. -  French-Burmese Paleontological Team 2012
University of Arizona geoscientist Alexis Licht (bottom left) and his colleagues from the French-Burmese Paleontological Team led by Jean-Jacques Jaeger of the University of Poitiers, France (center with hiking staff) used fossils they collected in Myanmar to figure out that the Asian monsoon started at least 40 million years ago. – French-Burmese Paleontological Team 2012

The Asian monsoon already existed 40 million years ago during a period of high atmospheric carbon dioxide and warmer temperatures, reports an international research team led by a University of Arizona geoscientist.

Scientists thought the climate pattern known as the Asian monsoon began 22-25 million years ago as a result of the uplift of the Tibetan Plateau and the Himalaya Mountains.

“It is surprising,” said lead author Alexis Licht, now a research associate in the UA department of geosciences. “People thought the monsoon started much later.”

The monsoon, the largest climate system in the world, governs the climate in much of mainland Asia, bringing torrential summer rains and dry winters.

Co-author Jay Quade, a UA professor of geosciences, said, “This research compellingly shows that a strong Asian monsoon system was in place at least by 35-40 million years ago.”

The research by Licht and his colleagues shows the earlier start of the monsoon occurred at a time when atmospheric CO2 was three to four times greater than it is now. The monsoon then weakened 34 million years ago when atmospheric CO2 then decreased by 50 percent and an ice age occurred.

Licht said the study is the first to show the rise of the monsoon is as much a result of global climate as it is a result of topography. The team’s paper is scheduled for early online publication in the journal Nature on Sept. 14.

“This finding has major consequences for the ongoing global warming,” he said. “It suggests increasing the atmospheric CO2 will increase the monsoonal precipitation significantly.”

Unraveling the monsoon’s origins required contributions from three different teams of scientists that were independently studying the environment of 40 million years ago.

All three investigations showed the monsoon climate pattern occurred 15 million years earlier than previously thought. Combining different lines of evidence from different places strengthened the group’s confidence in the finding, Licht said. The climate modeling team also linked the development of the monsoon to the increased CO2 of the time.

Licht and his colleagues at Poitiers and Nancy universities in France examined snail and mammal fossils in Myanmar. The group led by G. Dupont-Nivet and colleagues at Utrecht University in the Netherlands studied lake deposits in Xining Basin in central China. J.-B. Ladant and Y. Donnadieu of the Laboratory of Sciences of the Climate and Environment (LSCE) in Gif-sur-Yvette, France, created climate simulations of the Asian climate 40 million years ago.

A complete list of authors of the group’s publication, “Asian monsoons in a late Eocene greenhouse world,” is at the bottom of this release, as is a list of funding sources.

Licht didn’t set out to study the origin of the monsoon.

He chose his study site in Myanmar because the area was rich in mammal fossils, including some of the earliest ancestors of modern monkeys and apes. The research, part of his doctoral work at the University of Poitiers, focused on understanding the environments those early primates inhabited. Scientists thought those primates had a habitat like the current evergreen tropical rain forests of Borneo, which do not have pronounced differences between wet and dry seasons.

To learn about the past environment, Licht analyzed 40-million-year-old freshwater snail shells and teeth of mammals to see what types of oxygen they contained. The ratio of two different forms of oxygen, oxygen-18 and oxygen-16, shows whether the animal lived in a relatively wet climate or an arid one.

“One of the goals of the study was to document the pre-monsoonal conditions, but what we found were monsoonal conditions,” he said.

To his surprise, the oxygen ratios told an unexpected story: The region had a seasonal pattern very much like the current monsoon – dry winters and very rainy summers.

“The early primates of Myanmar lived under intense seasonal stress – aridity and then monsoons,” he said. “That was completely unexpected.”

The team of researchers working in China found another line of evidence pointing to the existence of the monsoon about 40 million years ago. The monsoon climate pattern generates winter winds that blow dust from central Asia and deposits it in thick piles in China. The researchers found deposits of such dust dating back 41 million years ago, indicating the monsoon had occurred that long ago.

The third team’s climate simulations indicated strong Asian monsoons 40 million years ago. The simulations showed the level of atmospheric CO2 was connected to the strength of the monsoon, which was stronger 40 million years ago when CO2 levels were higher and weakened 34 million years ago when CO2 levels dropped.

Licht’s next step is to investigate how geologically short-term increases of atmospheric CO2 known as hyperthermals affected the monsoon’s behavior 40 million years ago.

“The response of the monsoon to those hyperthermals could provide interesting analogs to the ongoing global warming,” he said.

International team maps nearly 200,000 global glaciers in quest for sea rise answers

CU-Boulder Professor Tad Pfeffer, shown here on Alaska's Columbia Glacier, is part of a team that has mapped nearly 200,000 individual glaciers around the world as part of an effort to track ongoing contributions to global sea rise as the planet heats up. -  University of Colorado
CU-Boulder Professor Tad Pfeffer, shown here on Alaska’s Columbia Glacier, is part of a team that has mapped nearly 200,000 individual glaciers around the world as part of an effort to track ongoing contributions to global sea rise as the planet heats up. – University of Colorado

An international team led by glaciologists from the University of Colorado Boulder and Trent University in Ontario, Canada has completed the first mapping of virtually all of the world’s glaciers — including their locations and sizes — allowing for calculations of their volumes and ongoing contributions to global sea rise as the world warms.

The team mapped and catalogued some 198,000 glaciers around the world as part of the massive Randolph Glacier Inventory, or RGI, to better understand rising seas over the coming decades as anthropogenic greenhouse gases heat the planet. Led by CU-Boulder Professor Tad Pfeffer and Trent University Professor Graham Cogley, the team included 74 scientists from 18 countries, most working on an unpaid, volunteer basis.

The project was undertaken in large part to provide the best information possible for the recently released Fifth Assessment of the Intergovernmental Panel on Climate Change, or IPCC. While the Greenland and Antarctic ice sheets are both losing mass, it is the smaller glaciers that are contributing the most to rising seas now and that will continue to do so into the next century, said Pfeffer, a lead author on the new IPCC sea rise chapter and fellow at CU-Boulder’s Institute of Arctic and Alpine Research.

“I don’t think anyone could make meaningful progress on projecting glacier changes if the Randolph inventory was not available,” said Pfeffer, the first author on the RGI paper published online today in the Journal of Glaciology. Pfeffer said while funding for mountain glacier research has almost completely dried up in the United States in recent years with the exception of grants from NASA, there has been continuing funding by a number of European groups.

Since the world’s glaciers are expected to shrink drastically in the next century as the temperatures rise, the new RGI — named after one of the group’s meeting places in New Hampshire — is critical, said Pfeffer. In the RGI each individual glacier is represented by an accurate, computerized outline, making forecasts of glacier-climate interactions more precise.

“This means that people can now do research that they simply could not do before,” said Cogley, the corresponding author on the new Journal of Glaciology paper. “It’s now possible to conduct much more robust modeling for what might happen to these glaciers in the future.”

As part of the RGI effort, the team mapped intricate glacier complexes in places like Alaska, Patagonia, central Asia and the Himalayas, as well as the peripheral glaciers surrounding the two great ice sheets in Greenland and Antarctica, said Pfeffer. “In order to model these glaciers, we have to know their individual characteristics, not simply an average or aggregate picture. That was one of the most difficult parts of the project.”

The team used satellite images and maps to outline the area and location of each glacier. The researchers can combine that information with a digital elevation model, then use a technique known as “power law scaling” to determine volumes of various collections of glaciers.

In addition to impacting global sea rise, the melting of the world’s glaciers over the next 100 years will severely affect regional water resources for uses like irrigation and hydropower, said Pfeffer. The melting also has implications for natural hazards like “glacier outburst” floods that may occur as the glaciers shrink, he said.

The total extent of glaciers in the RGI is roughly 280,000 square miles or 727,000 square kilometers — an area slightly larger than Texas or about the size of Germany, Denmark and Poland combined. The team estimated that the corresponding total volume of sea rise collectively held by the glaciers is 14 to 18 inches, or 350 to 470 millimeters.

The new estimates are less than some previous estimates, and in total they are less than 1 percent of the amount of water stored in the Greenland and Antarctic ice sheets, which collectively contain slightly more than 200 feet, or 63 meters, of sea rise.

“A lot of people think that the contribution of glaciers to sea rise is insignificant when compared with the big ice sheets,” said Pfeffer, also a professor in CU-Boulder’s civil, environmental and architectural engineering department. “But in the first several decades of the present century it is going to be this glacier reservoir that will be the primary contributor to sea rise. The real concern for city planners and coastal engineers will be in the coming decades, because 2100 is pretty far off to have to make meaningful decisions.”

Part of the RGI was based on the Global Land Ice Measurements from Space Initiative, or GLIMS, which involved more than 60 institutions from around the world and which contributed the baseline dataset for the RGI. Another important research data tool for the RGI was the European-funded program “Ice2Sea,” which brings together scientific and operational expertise from 24 leading institutions across Europe and beyond.

The GLIMS glacier database and website are maintained by CU-Boulder’s National Snow and Ice Data Center, or NSIDC. The GLIMS research team at NSIDC includes principal investigator Richard Armstrong, technical lead Bruce Raup and remote-sensing specialist Siri Jodha Singh Khalsa.

NSIDC is part of the Cooperative Institute for Research in Environmental Sciences, or CIRES, a joint venture between CU-Boulder and the National Oceanic and Atmospheric Administration.

Rising mountains dried out Central Asia, scientists say

A record of ancient rainfall teased from long-buried sediments in Mongolia is challenging the popular idea that the arid conditions prevalent in Central Asia today were caused by the ancient uplift of the Himalayas and the Tibetan Plateau.

Instead, Stanford scientists say the formation of two lesser mountain ranges, the Hangay and the Altai, may have been the dominant drivers of climate in the region, leading to the expansion of Asia’s largest desert, the Gobi. The findings will be presented on Thursday, Dec. 12, at the annual meeting of the American Geophysical Union (AGU) in San Francisco.

“These results have major implications for understanding the dominant factors behind modern-day Central Asia’s extremely arid climate and the role of mountain ranges in altering regional climate,” said Page Chamberlain, a professor of environmental Earth system science at Stanford.

Scientists previously thought that the formation of the Himalayan mountain range and the Tibetan plateau around 45 million years ago shaped Asia’s driest environments.

“The traditional explanation has been that the uplift of the Himalayas blocked air from the Indian Ocean from reaching central Asia,” said Jeremy Caves, a doctoral student in Chamberlain’s terrestrial paleoclimate research group who was involved in the study.

This process was thought to have created a distinct rain shadow that led to wetter climates in India and Nepal and drier climates in Central Asia. Similarly, the elevation of the Tibetan Plateau was thought to have triggered an atmospheric process called subsidence, in which a mass of air heated by a high elevation slowly sinks into Central Asia.

“The falling air suppresses convective systems such as thunderstorms, and the result is you get really dry environments,” Caves said.

This long-accepted model of how Central Asia’s arid environments were created mostly ignores, however, the existence of the Altai and Hangay, two northern mountain ranges.

Searching for answers

To investigate the effects of the smaller ranges on the regional climate, Caves and his colleagues from Stanford and Rocky Mountain College in Montana traveled to Mongolia in 2011 and 2012 and collected samples of ancient soil, as well as stream and lake sediments from remote sites in the central, southwestern and western parts of the country.

The team carefully chose its sites by scouring the scientific literature for studies of the region conducted by pioneering researchers in past decades.

“A lot of the papers were by Polish and Russian scientists who went there to look for dinosaur fossils,” said Hari Mix, a doctoral student at Stanford who also participated in the research. “Indeed, at many of the sites we visited, there were dinosaur fossils just lying around.”

The earlier researchers recorded the ages and locations of the rocks they excavated as part of their own investigations; Caves and his team used those age estimates to select the most promising sites for their own study.

At each site, the team bagged sediment samples that were later analyzed to determine their carbon isotope content. The relative level of carbon isotopes present in a soil sample is related to the productivity of plants growing in the soil, which is itself dependent on the annual rainfall. Thus, by measuring carbon isotope amounts from different sediment samples of different ages, the team was able to reconstruct past precipitation levels.

An ancient wet period

The new data suggest that rainfall in central and southwestern Mongolia had decreased by 50 to 90 percent in the last several tens of million of years.

“Right now, precipitation in Mongolia is about 5 inches annually,” Caves said. “To explain our data, rainfall had to decrease from 10 inches a year or more to its current value over the last 10 to 30 million years.”

That means that much of Mongolia and Central Asia were still relatively wet even after the formation of the Himalayas and the Tibetan Plateau 45 million years ago. The data show that it wasn’t until about 30 million years ago, when the Hangay Mountains first formed, that rainfall started to decrease. The region began drying out even faster about 5 million to 10 million years ago, when the Altai Mountains began to rise.

The scientists hypothesize that once they formed, the Hangay and Altai ranges created rain shadows of their own that blocked moisture from entering Central Asia.

“As a result, the northern and western sides of these ranges are wet, while the southern and eastern sides are dry,” Caves said.

The team is not discounting the effect of the Himalayas and the Tibetan Plateau entirely, because portions of the Gobi Desert likely already existed before the Hangay or Altai began forming.

“What these smaller mountains did was expand the Gobi north and west into Mongolia,” Caves said.

The uplift of the Hangay and Altai may have had other, more far-reaching implications as well, Caves said. For example, westerly winds in Asia slam up against the Altai today, creating strong cyclonic winds in the process. Under the right conditions, the cyclones pick up large amounts of dust as they snake across the Gobi Desert. That dust can be lofted across the Pacific Ocean and even reach California, where it serves as microscopic seeds for developing raindrops.

The origins of these cyclonic winds, as well as substantial dust storms in China today, may correlate with uplift of the Altai, Caves said. His team plans to return to Mongolia and Kazakhstan next summer to collect more samples and to use climate models to test whether the Altai are responsible for the start of the large dust storms.

“If the Altai are a key part of regulating Central Asia’s climate, we can go and look for evidence of it in the past,” Caves said.

Earthquakes and tectonics in Pamir Tien Shan

Earthquake damage to buildings is mainly due to the existing shear waves which transfer their energy during an earthquake to the houses. These shear waves are significantly influenced by the underground and the topography of the surrounding area. Detailed knowledge of the landform and the near-surface underground structure is, therefore, an important prerequisite for a local seismic hazard assessment and for the evaluation of the ground-effect, which can strongly modify and increase local ground motion.

As described in the latest issue of Geophysical Journal International, a team of scientists from the GFZ German Research Center for Geosciences could show that it is possible to map complex shear wave velocity structures almost in real time by means of a newly developed tomgraphic approach.

The method is based on ambient seismic noise recordings and analyses. “We use small, hardly noticeable amplitude ground motions as well as anthropogenic ground vibrations”, Marco Pilz, a scientist at GFZ, explains. “With the help of these small signals we can obtain detailed images of the shallow seismic velocity structure”. In particular, images and velocity changes in the underground due to earthquakes and landslides can be obtained in almost real time.

“What is new about our method is the direct calculation of the shear wave velocity. Moreover, we are working on a local, small-scale level — compared to many other studies”, Marco Pilz continues.

This method has already been successfully applied: Many regions of Central Asia are threatened by landslides. Since the shear wave velocity usually drops significantly before a landslide slip this technique offers the chance to monitor changes in landslide prone areas almost in real time.

Further application can be used in earthquake research. The authors were able to map the detailed structure of a section of the Issyk-Ata fault, Kyrgyzstan, which runs along the southern border of the capital city, Bishkek, with a population of approx. 900.000 inhabitants. They showed that close to the surface of the mapped section a splitting into two different small fault branches can be observed. This can influence the pace of expansion or also an eventual halting of the propagation on the main fault.

Central Asia is extensively seismically endangered; the accompanying processes and risks are investigated by the Central-Asian Institute of Applied Geosciences (CAIAG) in Bishkek, a joint institution established by the GFZ and the Kyrgyz government.

Why do these earthquakes occur?

The Pamir and Tien Shan are the result of the crash of two continental plates: the collision of India and Eurasia causes the high mountain ranges. This process is still ongoing today and causes breaking of the Earths crust, of which earthquakes are the consequence.

A second group of GFZ-scientists has investigated together with colleagues from Tajikistan and CAIAG the tectonic process of collision in this region. They were, for the first time, able to image continental crust descending into the Earth’s mantle. In the scientific journal Earth and Planetary Sciences Letters the scientists report that this subduction of continental crust has, to date, never been directly observed. To make their images, the scientists applied a special seismological method (so-called receiver function-analysis) on seismograms that had been collected in a two years long field experiment in the Tien Shan-Pamir-Hindu Kush area. Here, the collision of the Indian and Eurasian plates presents an extreme dimension.

“These extreme conditions cause the Eurasian lower crust to subduct into the Earth’s mantle”, explains Felix Schneider from the GFZ German Research Centre for Geosciences.” Such a subduction can normally be observed during the collision of ocean crust with continental crust, as the ocean floors are heavier than continental rock.”

Findings at the surface of metamorphic rocks that must have arisen from ultra-high pressures deep in the Earth’s mantle also provide evidence for subduction of continental crust in the Pamir region. Furthermore, the question arises, how the occurrence of numerous earthquakes at unusual depths of down to 300 km in the upper mantel can be explained. Through the observation of the subducting part of the Eurasian lower crust, this puzzle could, however, be solved.

Can China’s future earthquakes be predicted?

Ji ShaoCheng of the Universit้ de Montr้al’s affiliated engineering school ษcole Polytechnique is part of a team studying last May’s devastating earthquake in China.

On May 12, 2008, at 2:28 p.m., China’s Szechwan province changed forever. In the space of 90 seconds, an earthquake equivalent to 1,200 H-bombs pulverized the earth’s crust for more than 280 kilometers. Entire cities disappeared and eight million homes were swallowed up. This resulted in 70,000 deaths and 20,000 missing.

Two months later, ShaoCheng arrived in Szechwan province to study the damage first hand. The extent of the damage was unimaginable: roads and bridges collapsed, schools turned into rubble, and bodies of men and women everywhere.

According to ShaoCheng this tragedy could have been avoided. “There hasn’t been on earthquake in Szechwan province for 300 years. Chinese authorities thought the fault was dead,” he says.

The problem is that China relied on GPS data, which showed movements of 2 mm per year in certain areas when in reality the shifts were much bigger. “GPS is high-tech, but do we really know how to interpret its data?,” he questions.

ShaoCheng was recruited by one of his ex-colleagues with whom he completed his PhD in Montpellier and who now works for the Chinese Academy of Geological Sciences. His mission is to dig three narrow wells, 3-kilometers deep, into the earth’s crust for a whopping $75 million.

“The drilling will allow us to see the characteristics of the rocks before and after the earthquake. We will also measure their thermal properties and fluid pressure,” says ShaoCheng. “One of these wells will have a seismometer and another will be equipped with a device similar to a stethoscope designed to listen to the earth’s heartbeat.”

It is expected to take five years of hard labour to rebuild the devastated region.

U of Minnesota researchers uncover surprising effects of climate patterns in ancient China

Graph shows climate patterns in ancient China. -  University of Minnesota
Graph shows climate patterns in ancient China. – University of Minnesota

University of Minnesota geology and geophysics researchers, along with their colleagues from China, have uncovered surprising effects of climate patterns on social upheaval and the fall of dynasties in ancient China.

Their research identifies a natural phenomenon that may have been the last straw for some Chinese dynasties: a weakening of the summer Asian Monsoons. Such weakening accompanied the fall of three dynasties and now could be lessening precipitation in northern China.

The study, led researchers from the University of Minnesota and Lanzhou University in China, appears in the Nov. 7 issue of Science.

The work rests on climate records preserved in the layers of stone in a 118-millimeter-long stalagmite found in Wanxiang Cave in Gansu Province, China. By measuring amounts of the elements uranium and thorium throughout the stalagmite, the researchers could tell the date each layer was formed. And by analyzing the “signatures” of two forms of oxygen in the stalagmite, they could match amounts of rainfall–a measure of summer monsoon strength–to those dates.

The stalagmite was formed over 1,810 years; stone at its base dates from A.D. 190, and stone at its tip was laid down in A.D. 2003, the year the stalagmite was collected.

“It is not intuitive that a record of surface weather would be preserved in underground cave deposits. This research nicely illustrates the promise of paleoclimate science to look beyond the obvious and see new possibilities,” said David Verardo, director of the U.S. National Science Foundation’s Paleoclimatology Program, which funded the research.

“Summer monsoon winds originate in the Indian Ocean and sweep into China,” said Hai Cheng, corresponding author of the paper and a research scientist at the University of Minnesota. “When the summer monsoon is stronger, it pushes farther northwest into China.”

These moisture-laden winds bring rain necessary for cultivating rice. But when the monsoon is weak, the rains stall farther south and east, depriving northern and western parts of China of summer rains. A lack of rainfall could have contributed to social upheaval and the fall of dynasties.

The researchers discovered that periods of weak summer monsoons coincided with the last years of the Tang, Yuan, and Ming dynasties, which are known to have been times of popular unrest. Conversely, the research group found that a strong summer monsoon prevailed during one of China’s “golden ages,” the Northern Song Dynasty. The ample summer monsoon rains may have contributed to the rapid expansion of rice cultivation from southern China to the midsection of the country. During the Northern Song Dynasty, rice first became China’s main staple crop, and China’s population doubled.

“The waxing and waning of summer monsoon rains are just one piece of the puzzle of changing climate and culture around the world,” said Larry Edwards, Distinguished McKnight University Professor in Geology and Geophysics and a co-author on the paper. For example, the study showed that the dry period at the end of the Tang Dynasty coincided with a previously identified drought halfway around the world, in Meso-America, which has been linked to the fall of the Mayan civilization.

The study also showed that the ample summer rains of the Northern Song Dynasty coincided with the beginning of the well-known Medieval Warm Period in Europe and Greenland. During this time–the late 10th century–Vikings colonized southern Greenland. Centuries later, a series of weak monsoons prevailed as Europe and Greenland shivered through what geologists call the Little Ice Age. In the 14th and early 15th centuries, as the cold of the Little Ice Age settled into Greenland, the Vikings disappeared from there. At the same time, on the other side of the world, the weak monsoons of the 14th century coincided with the end of the Yuan Dynasty.

A second major finding concerns the relationship between temperature and the strength of the monsoons. For most of the last 1,810 years, as average temperatures rose, so, too, did the strength of the summer monsoon. That relationship flipped, however, around 1960, a sign that the late 20th century weakening of the monsoon and drying in northwestern China was caused by human activity.

If carbon dioxide is the culprit, as some have proposed, the drying trend may well continue in Inner Mongolia, northern China and neighboring areas on the fringes of the monsoon’s reach, as society is likely to continue adding carbon dioxide to the atmosphere for the foreseeable future. If, however, the culprit is man-made soot, as others have proposed, the trend could be reversed, the researchers said, by reduction of soot emissions.

May 2008 Earthquake in China Could Be Followed by Another Significant Rupture

Through computer modeling, researchers have calculated the shifting and changes in stress within earth's crust in the regions adjoining the May 2008 Wenchuan earthquake. (Toda, Lin, Meghraoui, and Stein, reprinted from Geophysical Research Letters)
Through computer modeling, researchers have calculated the shifting and changes in stress within earth’s crust in the regions adjoining the May 2008 Wenchuan earthquake. (Toda, Lin, Meghraoui, and Stein, reprinted from Geophysical Research Letters)

Researchers analyzing the May 2008 Wenchuan earthquake in China’s Sichuan province have found that geological stress has significantly increased on three major fault systems in the region. The magnitude 7.9 quake on May 12 has brought several nearby faults closer to failure and could trigger another major earthquake in the region.

Geophysicists used computer models to calculate the changes in stress along the Xianshuihe, Kunlun, and Min Jiang faults-strike-slip faults like the San Andreas-which lie about 150 to 450 kilometers (90 to 280 miles) from the Longmen Shan rupture that caused the devastating quake. The research team also examined seismic activity in the region over the past decade.

They found that the May 12 event has doubled the probabilities of future earthquakes on these fault lines. Specifically, they estimated the probability of another earthquake of magnitude 6 or greater in the region is 57 to 71 percent over the next decade. There is an 8 to 12 percent chance of a quake larger than magnitude 7 in the next decade and 23-31 percent in the next 30 years.

The research team was led by Shinji Toda of the Geological Survey of Japan, and includes Jian Lin of the Woods Hole Oceanographic Institution (WHOI), Mustapha Meghraoui of the Institute of Geophysics in Strasbourg (France), and Ross Stein of the U.S. Geological Survey (USGS). Their findings were published September 9 in the online edition of the journal Geophysical Research Letters.

“One great earthquake seems to make the next one more likely, not less,” said Stein, who has been collaborating with Lin and Toda for nearly two decades. “We tend to think of earthquakes as relieving stress on a fault. That may be true for the one that ruptured, but not for the adjacent faults.”

In 1999, a 7.4 magnitude earthquake in Izmit, Turkey, was followed four months later by an M7.1 event in nearby Duzce. The devastating December 2004 Sumatra earthquake (M9.2) and tsunami were followed by an M8.7 quake three months later.

“Because the Tibetan Plateau is one of the most seismically active regions in the world, we believe there is credible evidence for a new major quake in this region,” said Lin, a senior scientist in WHOI’s Department of Geology and Geophysics. “The research community cannot forecast the timing of earthquakes, and there are still significant uncertainties in our models. But the Turkey and Sumatra events indicate that one major earthquake can indeed promote another.

Researchers see it as a domino-like effect, where the movement of one piece of Earth’s crust means that another piece must move up, down, or away. While the stress in the crust gets reduced in some locations, it is transferred to other faults nearby.

Large aftershocks that occurred on August 1 and 5 in the Sichuan region of China may fit with this predicted pattern.

“Earthquake prediction is a bit like the thundercloud and lightning,” Toda explained. “We can forecast that lightning will come from a thundercloud, but we cannot predict the exact time and place where the lightning will hit. With earthquakes, we can roughly forecast the probability of activity over broad ranges of time, magnitude, and location, but we cannot determine the exact value for any of these.”

On May 12, 2008, about 300 kilometers of the Longmen Shan fault zone ruptured in an earthquake that killed at least 69,000 people and left another 5 million homeless. It was the deadliest and strongest earthquake to hit China since the 1976 Tangshan earthquake, which killed at least 240,000.

As pieces of the Longman Shan fault slipped by as much as nine meters (28 feet) in the May quake, stress increased along the neighboring Xianshuihe, Kunlun, and Min Jiang faults, according to Toda and colleagues. All three faults have a history of large quakes, though portions of each have been quiet for most of the past century. All three faults were considered to be primed for an earthquake even before the recent events.

In addition to the broad prediction of earthquake triggering, the researchers have also forecasted the rate and distribution of seismic shocks greater than magnitude 6, a prediction that they plan to test from seismic stations over the next decade.

“Our paper predicts the change in the rate of small earthquakes for the faults in the region, and now we can test that prediction,” said Stein. “If the rate of shocks increases on the adjacent faults, then we can confirm at least part of our hypothesis that large shocks are also more likely. It may take time, but it is a testable hypothesis.”

In western China, the intrusion of the Indian sub-continent pushes the Tibetan Plateau up and over the older Sichuan Basin and other parts of the Eurasian continent. An estimated 33 percent of world’s continental earthquakes occur in China, even though it only occupies 7 percent of the planet’s land mass. Nearly 55 percent of all human loss to earthquakes occurs in China.

“Earthquakes do not kill people, buildings do,” said Lin, who was a high school student in China when the devastating Tangshan earthquake struck. “There needs to be widespread education in earthquake preparedness, as well as systematic inspection of buildings in these regions of heightened risk. Every new building inspection and evacuation plan could potentially save lives.”

“We hope the long-term forecasting allows the Chinese government to make it a priority to mitigate future damage,” Toda added. “We recommend that Chinese scientists carefully observe changes in seismicity by installing new seismometers in the region.”

Lin, Toda, and Stein were preparing to teach an earthquake modeling course to Meghraoui’s students and colleagues in France when the May 12 earthquake occurred. The researchers immediately went into action, working with an international group of scientists to analyze the new stresses on the system.

An early version of the manuscript by Toda et al was circulated to several dozen Chinese scientists and government officials as they sought to assess the risk of aftershocks in the weeks after the earthquake. Chinese government organizations and scientists are now examining the paper in detail.

“The recent quake reminded us that Earth scientists have a tremendous responsibility to work on issues of societal relevance,” said Lin. “We don’t want to create panic, but there is legitimate cause for concern and we have a major role to play in educating the public about what we know.”

Funding for this research was provided by the Charles D. Hollister Endowed Fund for Support of Innovative Research at WHOI and the EOST-Institut de Physique du Globe de Strasbourg, France.

Major flooding risk could span decades after Chinese earthquake

Up to 20 million people are at increased risk of flooding and major power shortages in China’s massive Sichuan Basin.

Dr Alex Densmore, a geographer from Durham University, makes the observations on returning from carrying out investigative fieldwork in the China earthquake zone, where nearly 100,000 people were killed in May 2008.

Dr Densmore, who has been studying the active faults in Sichuan for the past eight years, says the risk from flooding and power shortages could occur over the next few decades or possibly centuries.

The biggest risk is posed by the ongoing landslides in Sichuan province, a common occurrence after major earthquakes such as these. Landslides cause rocks and sediment to be dumped in the river valleys, and this material then moves downstream to settle on river beds.

In some areas, river beds are already two to three metres higher due to the increased amounts of sediment after the earthquake. This means that during periods of heavy rains the rivers have greater potential to burst their banks — a risk that will last for decades to centuries.

There is also the potential for build up of sediment in the reservoirs behind the many dams in the area. These reservoirs then become useless for flood control or hydro-electric power generation.

These long term effects of the earthquake should be considered very carefully by the Chinese authorities, says Dr Densmore, who was “astounded and impressed” by the speed and efficiency of response to the earthquake’s short term effects.

Many mountain communities, who took the brunt of the disaster, have been relocated and re-housed into the 500 km-wide Sichuan Basin, which is perceived to be a safer area to live. Up to 20 million people live in the western part of the Basin, where the provincial capital, Chengdu, is also sited.

Thousands of those at risk have already been displaced from their homes due to May’s devastating earthquake.

Dr. Alex Densmore’s research in China is funded by The Natural Environment Research Council (NERC).

Dr Densmore, Director of Hazards Research at Durham University’s Institute of Hazard and Risk Research, said: “We were amazed at how fast the Chinese had responded to this disaster. Many of the people in the mountain areas have been resettled and there are big temporary housing communities with supplies of clean water, power, and access to food and transportation. It is a very impressive response and is a big contrast with how the US responded after Hurricane Katrina.

“However, while the short term response has been excellent, in the longer term they will need to have a well informed discussion about where to permanently move these communities.

“There is a significant risk of a major flooding disaster. At the moment it is very difficult to predict the exact nature of that risk but in ten years or so we may be in a better position. The enhanced risk due to the earthquake will persist for decades, possibly for up to 100 years.

“In the longer term, the authorities will need to look at issues such as moving people out of the flood plains and re-routing transportation links in areas where there are high risks of floods.”

Dr Densmore and his team have been studying the fault lines which caused the earthquake, and found that buildings which were directly on top of the fault line were almost always completely demolished, while others built near the fault were damaged but often remained standing.

He says that when or if it is time to rebuild the devastated towns, planners should consider establishing buffer zones around the fault lines, a practice followed in other places where there is high risk of earthquakes such as North America and Japan. Buildings of flexible materials such as wood and bamboo are preferable to rigid structures of bricks, concrete and mortar.

China’s first successful sampling of ice core in Mongolia

China's first successful sampling of ice core in Mongolia
China’s first successful sampling of ice core in Mongolia

In collaboration with their colleagues from the ROK and Mongolia, CAS scientists achieved their first success in obtaining a 40.18m. specimen of ice core in the drilling operation from 5 to 25 June in an expedition to the (Hovd) Tsambagarav glacier in Altay Mountains of Mongolia.

The glacier is a Quaternary glacial relic, with a total area of more than 15km² and a thickness of 90-100m. It is the headstream of the Hovd River, the largest river in the Central Asian endorheic basin. According to experts, the glacier and its vicinity are an ideal theatre for probing the interaction of the Arctic water vapor with westerly wind.

The joint expedition was first contrived in 2007 and related agreement was discussed and signed in Lanzhou, capital of northwest China’s Gansu Province in April 2008.

The ice core-drilling project was first proposed by Prof. QIN Dahe, director of the State Key Laboratory for Cryosphere Science under the CAS Cold & Arid Regions Environmental and Engineering Research Institute. Its enforcement was under the leadership of its Prof. HOU Shugui from the Lab. This is the first successful attempt for Chinese scientists to obtain ice core samples from a foreign site except the polar areas.