Slowly slip-sliding faults don’t cause earthquakes

This is an antenna for receiving GPS signals in a geodesy network located in northern Italy. -  Copyright 2006 Sigrun Hreinsdottir
This is an antenna for receiving GPS signals in a geodesy network located in northern Italy. – Copyright 2006 Sigrun Hreinsdottir

Some slow-moving faults may help protect some regions of Italy and other parts of the world against destructive earthquakes, suggests new research from The University of Arizona in Tucson.

Until now, geologists thought when the crack between two pieces of the Earth’s crust was at a very gentle slope, there was no movement along that particular fault line.

“This study is the first to show that low-angle normal faults are definitely active,” said Sigrún Hreinsdóttir, UA geosciences research associate.

Richard A. Bennett, a UA assistant professor of geosciences, wrote in an e-mail. “We can show that the Alto Tiberina fault beneath Perugia is steadily slipping as we speak–fortunately, for Perugia, without producing large earthquakes.”

Perugia is the capital city of Italy’s Umbria region.

Creeping slowly is unusual, Bennett said. Most faults stick, causing strain to build up, and then become unstuck with a big jerk. Big jerks are big earthquakes.

For decades, researchers have known about the Alto Tiberina and similar faults and debated whether such features in the Earth’s crust were faults at all, because they didn’t seem to produce earthquakes.

Hreinsdóttir and Bennett have now shown that the gently sloping fault beneath Perugia is moving steadily at the rate of approximately one-tenth of an inch (2.4 mm) a year.

Perugia has not experienced a damaging earthquake in about 2,000 years, Hreinsdóttir said. Because the fault is actively slipping, it might not be collecting strain, she said. “To have an earthquake, you have to have strain.”

Other towns in the region that lie near steeply sloping faults, including L’Aquila and Assisi, have experienced large earthquakes within the last 20 years.

The team published their paper, “Active aseismic creep on the Alto Tiberina low-angle normal fault, Italy,” in the August issue of Geology. The National Science Foundation funded the research.

In the same issue of Geology, Geoffrey A. Abers terms the UA team’s work “a fascinating new discovery.” Abers, of Lamont-Doherty Earth Observatory of Columbia University in Palisades, N.Y., was not involved in the research.

The UA team became interested in the Alto Tiberina fault because previous research suggested the fault might be moving.

To check on the fault, the UA team measured rock movements in and around Perugia using a technique called geodesy.

Geodesy works much like the GPS system in a car. Geoscientists put GPS units on rocks, Bennett said. Just as the car’s GPS uses global positioning satellites to tell where the car is relative to a desired destination, the geodesy network can tell where one antenna and its rock are relative to another antenna.

Taking repeated measurements over time shows whether the rocks moved relative to one another.

In some cases, the GPS sites are too far apart to attribute very small movements of the Earth to an individual fault such as the Alto Tiberina, Hreinsdóttir said. However, the University of Perugia established a dense network of GPS stations in the region in 2005.

The UA team analyzed data from 19 GPS stations within approximately a 30-mile (50 km) radius around Perugia. Having such closely spaced stations and several years of data were key for detecting the fault’s tiny motions, she said.

“This study is one more piece in the puzzle to understand seismic hazards in the region and can apply to other regions of the world that have low-angle normal faults,” Hreinsdóttir said.

Bennett said there are numerous examples of such faults that are thought to be inactive, including the western U.S., Italy, Greece and Tibet.

He and UA geosciences doctoral candidate Austin Holland are now investigating similar faults in Arizona. One such fault, the Catalina Detachment, was involved in the formation of the Santa Catalina and Rincon Mountains that surround Tucson to the north and the east.

“No large earthquakes are known to have occurred on the Catalina detachment in historic times, so we don’t really know if that fault is active or not,” Bennett said. “Based on the results from the Alto Tiberina, it’s possible the Catalina Detachment fault just slides very slowly and doesn’t produce earthquakes.”

The motion would be so slow as to be undetectable until the most recent technological advances in geodesy, he said. “The technology has evolved so far that we are now confident we can see little motions.”

To better assess the earthquake risk in the Tucson region, his team is using geodesy throughout southern Arizona to recheck the markers that the National Geodetic Survey measured in the late 1990s.

“Now we can go out and repeat measurements to see how the positions have changed in ten years,” he said.

Bennett will soon be able to say how fast the Tucson area’s mountains are moving — his team took measurements earlier this year and is analyzing the data now.

Cognitive scientists use eye-tracking technology to learn what makes a great geologist

Cognitive scientists, geologists, and vision scientists are teaming up to learn how expert geologists unconsciously view landscapes for clues that point the way to important discoveries. The National Science Foundation has awarded the team, led by the University of Rochester and including the Rochester Institute of Technology, $2 million over the next five years to find the answers.

Not only might the findings shed light on how a seasoned geologist’s brain teases out information from a terrain full of complex features, but the results might be applicable to scientists in other fields. Crucially, the findings could help reduce the costs of training young scientists by giving them useful simulated field training without the high costs of travel and equipment.

“This is a new way to look at how experience changes how we see,” says Robert Jacobs, professor of brain and cognitive sciences at the University of Rochester, and lead investigator of the project. “In the past, there had been some attempts to understand how radiologists read an X-ray image, but no one has ever done something like this-where we monitor people out in the natural environment and try to understand how experienced and inexperienced scientists see the same scene differently.”

John Tarduno, professor of earth and environmental sciences at the University, will take 10 undergraduate students to various areas of geologic interest, such as the San Andreas Fault, the snowy Sierra Nevada near Yosemite National Park, and the deserts of eastern California including Death Valley. As he and the students walk through different landscapes over the course of 10 days, each will wear a small head-mounted eye-tracking system that will monitor precisely where he or she is looking at any given time.

Back at the University, Jacobs and Tarduno will analyze the data, noting the way each student takes in the geological formations around them, and comparing that to the way Tarduno and his seasoned assistants view the same formations.

“An expert geologist scanning a landscape might notice where a stream is offset from its normal course and deduce that motion on a fault had caused the stream diversion,” says Tarduno. “Streams and patterns of erosion in general provide clues to processes shaping landscapes. But we want to know more about how experts make the connections visually. The data could be invaluable in letting us know how a student sees the landscape and how we can teach them to see it through more experienced eyes.”

In addition to the eye-tracking data, Tarduno and the project team will bring back high-resolution images of the areas he and his students visit. These images will be projected onto giant 180-degree wrap-around screens, and students’ direction of gaze will be monitored as they look around the projected landscapes. If there is a clear correlation between the way student geologists in the field and student geologists in the laboratory take note of the formations around them, then it may be possible to use the simulation to train students without incurring the costs of an actual field trip.

In addition, says Tarduno, it might be possible to give prospective geologists far more “field” experience than they could normally expect to receive. Instead of a single trip to geological sites each year, students could take dozens of simulated trips and perhaps hone their observational abilities earlier and be ready to make better use of actual trips.

Along with the scientists from the University of Rochester, two scientists from the Rochester Institute of Technology’s Center for Imaging Science, Jeff Pelz and Mitchell Rosen, are part of the project. Pelz is an expert in small, wearable eye trackers, and will not only outfit the team, but will help analyze the data the trackers collect. Rosen will help with the image processing, especially taking ultra-large, high-resolution photographs of the landscapes, which will be used in the simulations.

Has northern-hemisphere pollution affected Australian rainfall?

New research announced at the International Water in a Changing Climate Science Conference in Melbourne 24-28 August, implicates pollution from Asia, Europe and North America as a contributor to recent Australian rainfall changes. Australian scientists using a climate model that includes a treatment of tiny particles – or aerosols – report that the build up of these particles in the northern hemisphere affects their simulation of recent climate change in the southern hemisphere, including rainfall in Australia.

The CSIRO climate model, which can include the effects of aerosols caused by humans, suggests that aerosols – whose major sources are in the northern hemisphere – can drive changes in atmospheric and oceanic circulation in the southern hemisphere. Their model results suggest that human-generated aerosols from the northern hemisphere may have contributed to increased rainfall in north-western and central Australia, and decreased rainfall in parts of southern Australia.

Lead researcher, Dr Leon Rotstayn, Principal Research Scientist at the Centre for Australian Weather and Climate Research, a partnership between CSIRO and the Bureau of Meteorology, said: “Perhaps surprisingly, inclusion of northern hemisphere aerosols may be important for accurate modelling of Australian climate change.”

Aerosols come from many different sources. Sulphur is released when we burn coal and oil. More dust, also an aerosol, circulates in the atmosphere when land is cleared, burned or overgrazed. Some aerosols occur naturally like sea spray and volcanic emissions, but NASA estimates ten percent of the total aerosols in the atmosphere are caused by people. Most of this ten percent is in the northern hemisphere.

European researchers also attending the conference will discuss a new forecasting service that will identify in unprecedented detail where these aerosols are coming from and where they are going.

The new service, part of Europe’s Global Monitoring for Environment and Security (GMES) initiative, will give global information on how pollutants move around the world across oceans and continents, and will refine estimates of their sources and sinks.

Dr Adrian Simmons from the European Centre for Medium-Range Weather Forecasts, which is coordinating the multi-institution initiative, says: “The service will give much more detailed forecast information on air quality over Europe and provide the basis for better health advice across Europe and beyond”. The service has clear implications for environmental policy and legislation.

The five-day conference, organised by the Global Energy and Water Cycle Experiment (GEWEX) and the Integrated Land Ecosystem-Atmosphere Processes Study (iLEAPS) and locally hosted by Monash University, brings together many of the world’s leading experts to discuss the important processes that govern water availability and drought and their role in present and future climate and global change.

Professor Christian Jakob, who holds the Chair for Climate Modelling at Monash University and who chairs the local organising committee for the conference says: “It is fantastic to have attracted more than 350 researchers from more than 15 countries to come to Australia to discuss these very timely issues with us here in Melbourne.”

“The exchanges of energy, carbon and water between the land, ocean and atmosphere are of utmost importance to current and future climate. The fundamental role of the land surface, clouds, aerosols and of course rainfall for climate has been highlighted many times in the reports of the Intergovernmental Panel on Climate Change (IPCC). This conference will advance our knowledge in all these important areas by bringing world-leading experts together for a week of discussions. It has been a great privilege for me and Monash University to host this event,” he added.

The conference brings together the work of two major international research projects: GEWEX and iLEAPS. These projects complement each other and collaborate in a variety of global-change and climate-change research.

The mysterious glaciers that grew when Asia heated up

BYU professor Summer Rupper doing field work with Switzerland's Gornergrat glacier. Her newest study details how a group of Himalayan glaciers grew despite a significant rise in temperatures.
BYU professor Summer Rupper doing field work with Switzerland’s Gornergrat glacier. Her newest study details how a group of Himalayan glaciers grew despite a significant rise in temperatures.

Ice, when heated, is supposed to melt.

That’s why a collection of glaciers in the Southeast Himalayas stymies those who know what they did 9,000 years ago. While most other Central Asian glaciers retreated under hotter summer temperatures, this group of glaciers advanced from one to six kilometers.

A new study by BYU geologist Summer Rupper pieces together the chain of events surrounding the unexpected glacial growth.

“Stronger monsoons were thought to be responsible,” said Rupper, who reports her findings in the September issue of the journal Quaternary Research. “Our research indicates the extra snowfall from monsoonal effects can only take credit for up to 30 percent of the glacial advance.”

As Central Asia’s summer climate warmed as much as 6 degrees Celsius, shifting weather patterns brought more clouds to the Southeast Himalayas. The additional shade created a pocket of cooler temperatures.

Temperatures also dropped when higher winds spurred more evaporation in this typically humid area, the same process behind household swamp coolers.

The story of these seemingly anomalous glaciers underscores the important distinction between the terms “climate change” and “global warming.”

“Even when average temperatures are clearly rising regionally or globally, what happens in any given location depends on the exact dynamics of that place,” Rupper said.

The findings come from a framework Rupper developed as an alternative to the notion that glaciers form and melt in direct proportion to temperature. Her method is based on the balance of energy between a glacier and a wide range of climate factors, including wind, humidity, precipitation, evaporation and cloudiness.

Gerard Roe and Alan Gillespie of the University of Washington are co-authors of the new study.

Knowing how glaciers responded in past periods of climate change will help Rupper forecast the region’s water supply in the coming decades. She and collaborators are in the process of determining how much of the Indus River comes from the vast network of glaciers far upstream from the agricultural valleys of India and Pakistan.

“Their study can be used to help assess future glaciological and hydrological changes in the most populated part of our planet, which is a region that is now beginning to experience the profound effects of human-induced climate change,” said Lewis Owen, a geologist at the University of Cincinnati who was not affiliated with this study.

New temperature reconstruction from Indo-Pacific warm pool

A map of the Indo-Pacific region indicates the locations of sediment cores used for the study. Station BJ8 marks the cores taken by Oppo and her colleagues. MD60 marks the site of published data. -  Jack Cook, Woods Hole Oceanographic Institution
A map of the Indo-Pacific region indicates the locations of sediment cores used for the study. Station BJ8 marks the cores taken by Oppo and her colleagues. MD60 marks the site of published data. – Jack Cook, Woods Hole Oceanographic Institution

A new 2,000-year-long reconstruction of sea surface temperatures (SST) from the Indo-Pacific warm pool (IPWP) suggests that temperatures in the region may have been as warm during the Medieval Warm Period as they are today.

The IPWP is the largest body of warm water in the world, and, as a result, it is the largest source of heat and moisture to the global atmosphere, and an important component of the planet’s climate. Climate models suggest that global mean temperatures are particularly sensitive to sea surface temperatures in the IPWP. Understanding the past history of the region is of great importance for placing current warming trends in a global context.

The study is published in the journal Nature.

In a joint project with the Indonesian Ministry of Science and Technology (BPPT), the study’s authors, Delia Oppo, a paleo-oceanographer with the Woods Hole Oceanographic Institution, and her colleagues Yair Rosenthal of Rutgers State University and Braddock K. Linsley of the University at Albany-State University of New York, collected sediment cores along the continental margin of the Indonesian Seas and used chemical analyses to estimate water past temperatures and date the sediment. The cruise included 13 US and 14 Indonesian scientists.

“This is the first record from the region that has really modern sediments and a record of the last two millennia, allowing us to place recent trends in a larger framework,” notes Oppo.

Global temperature records are predominantly reconstructed from tree rings and ice cores. Very little ocean data are used to generate temperature reconstructions, and very little data from the tropics. “As palaeoclimatologists, we work to generate information from multiple sources to improve confidence in the global temperature reconstructions, and our study contributes to scientists’ efforts towards that goal,” adds Oppo.

Temperature reconstructions suggest that the Northern Hemisphere may have been slightly cooler (by about 0.5 degrees Celsius) during the ‘Medieval Warm Period’ (~AD 800-1300) than during the late-20th century. However, these temperature reconstructions are based on, in large part, data compiled from high latitude or high altitude terrestrial proxy records, such as tree rings and ice cores, from the Northern Hemisphere (NH). Little pre-historical temperature data from tropical regions like the IPWP has been incorporated into these analyses, and the global extent of warm temperatures during this interval is unclear. As a result, conclusions regarding past global temperatures still have some uncertainties.

Oppo comments, “Although there are significant uncertainties with our own reconstruction, our work raises the idea that perhaps even the Northern Hemisphere temperature reconstructions need to be looked at more closely.”

Comparisons

The marine-based IPWP temperature reconstruction is in many ways similar to land temperature reconstructions from the Northern Hemisphere (NH). Major trends observed in NH temperature reconstructions, including the cooling during the Little Ice Age (~1500-1850 AD) and the marked warming during the late twentieth century, are also observed in the IPWP.

“The more interesting and potentially controversial result is that our data indicate surface water temperatures during a part of the Medieval Warm Period that are similar to today’s,” says Oppo. NH temperature reconstructions also suggest that temperatures warmed during this time period between A.D. 1000 and A.D. 1250, but they were not as warm as modern temperatures. Oppo emphasizes, “Our results for this time period are really in stark contrast to the Northern Hemisphere reconstructions.”

Reconstructing Historical Temperatures


Records of water temperature from instruments like thermometers are only available back to the 1850s. In order to reconstruct temperatures over the last 2,000 years, Oppo and her colleagues used a proxy for temperature collected from the skeletons of marine plankton in sediments in the Indo-Pacific Ocean. The ratio of magnesium to calcium in the hard outer shells of the planktonic foraminifera Globigerinoides ruber varies depending on the surface temperature of the water in which it grows. When the phytoplankton dies, it falls to the bottom of the ocean and accumulates in sediments, recording the sea surface temperature in which it lived.

“Marine sediments accumulate slowly in general — approximately 3 cm/yr — which makes it hard to overlap sediment record with instrumental record and compare that record to modern temperature records,” says Oppo. “That’s what is different about this study. The sediment accumulates fast enough in this region to give us enough material to sample and date to modern times.”

The team generated a composite 2000-year record by combining published data from a piston core in the area with the data they collected using a gravity corer and a multi-corer. Tubes on the bottom of the multi-corer collected the most recently deposited sediment, therefore enabling the comparison of sea surface temperature information recorded in the plankton shells to direct measurements from thermometers.

Oppo cautions that the reconstruction contains some uncertainties. Information from three different cores was compiled in order to reconstruct a 2,000-year-long record. In addition sediment data have an inherent uncertainty associated with accurately dating samples. The SST variations they have reconstructed are very small, near the limit of the Mg/Ca dating method. Even in light of these issues, the results from the reconstruction are of fundamental importance to the scientific community.

More Questions to Answer


The overall similarity in trend between the Northern Hemisphere and the IPWP reconstructions suggests that that Indonesian SST is well correlated to global SST and air temperature. On the other hand, the finding that IPWP SSTs seem to have been approximately the same as today in the past, at a time when average Northern Hemisphere temperature appear to have been cooler than today, suggests changes in the coupling between IPWP and Northern Hemisphere or global temperatures have occurred in the past, for reasons that are not yet understood. “This work points in the direction of questions that we have to ask,” Oppo says. “This is only the first word, not the last word.”

Water scarcity started 15 years ago

The long-term trend in total water availability in soil and groundwater between 1980 and 2008 (red areas have experienced declines over this period, blue areas increases). The dry state of the catchments show that a return of rainfall does not automatically mean streamflows will return to previous rates. -  CSIRO
The long-term trend in total water availability in soil and groundwater between 1980 and 2008 (red areas have experienced declines over this period, blue areas increases). The dry state of the catchments show that a return of rainfall does not automatically mean streamflows will return to previous rates. – CSIRO

New analysis shows that the water scarcity being experienced in southeast Australia started up to 15 years ago.

While the results from the work by senior CSIRO researcher, Dr Albert van Dijk, may not surprise many people, it provides scientific evidence of the shift.

The finding follows the first ever national and comprehensive analysis of 30 years of on-ground and satellite observations of Australia’s water resources.

Dr Albert van Dijk told the the Sixth International Scientific Conference on the Global Energy and Water Cycle in Melbourne today (Wednesday August 26) that the analysis provides a valuable, new insight into the country’s water balance.

“The data shows the first signs of diminishing water availability in Australia appeared somewhere between 1993 and 1996 when the rate of water resource capture and use started to exceed the rate of streamflow supply,” Dr van Dijk said.

Dr van Dijk’s work is part of the water information research and development alliance between the CSIRO’s Water for a Healthy Country Flagship and Bureau of Meteorology in which scientists are building an observation and modelling system that will provide water balance estimates across Australia.

Long-term on-ground records and 30 years of satellite observations are combined with models that integrate and analyze the data within a powerful computer system that provides comprehensive, detailed and reliable information about the nation’s water resources.

“If this technology had been available to us in the mid-1990s, the onset of dry conditions could have been detected earlier,” Dr van Dijk said.

“The results of the study underscore the importance of good water information for water resource planning.”

The data also reveals that the impact of the drought on Australia’s current water resources is broadly consistent with both the historical trend and climate change predictions.

“Parts of Australia have had record low rainfall the last several years, but our records aren’t very long and the drought may still be within natural limits.”

“What makes the situation appear so much worse is that the sixties and seventies were quite wet. That’s also when we started capturing river flows in large reservoirs for our growing cities and irrigated agriculture. In retrospect it appears we have become over-reliant on what is now looking like ‘bonus’ rainfall during that time.”

The observation system that is developed will assist the Bureau in conducting regular water resource assessments and produce national water accounts.

Scientists propose Antarctic location for ‘missing’ ice sheet

Bruce Luyendyk and Douglas Wilson are researchers at University of California - Santa Barbara. -  George Foulsham, Office of Public Affairs, UCSB
Bruce Luyendyk and Douglas Wilson are researchers at University of California – Santa Barbara. – George Foulsham, Office of Public Affairs, UCSB

New research by scientists at UC Santa Barbara indicates a possible Antarctic location for ice that seemed to be missing at a key point in climate history 34 million years ago. The research, which has important implications for climate change, is described in a paper published today in Geophysical Research Letters, a journal of the American Geophysical Union.

“Using data from prior geological studies, we have constructed a model for the topography of West Antarctic bedrock at the time of the start of the global climate transition from warm ‘greenhouse’ earth to the current cool ‘icehouse’ earth some 34 million years ago,” explained Douglas S. Wilson, first author and an associate research geophysicist with UCSB’s Department of Earth Science and Marine Science Institute.

Wilson and his co-author, Bruce Luyendyk, a professor in the Department of Earth Science, discovered that, contrary to most current models for bedrock elevations of West Antarctica, the bedrock in the past was of much higher elevation and covered a much larger area than today. Current models assume that an archipelago of large islands existed under the ice at the start of the climate transition, similar to today, but Wilson and Luyendyk found that does not fit their new model. In fact, the authors state that the land area above sea level of West Antarctica was about 25 percent greater in the past.

The existing theory leaves West Antarctica in a minor role in terms of the ice accumulation beginning 34 million years ago. Ice sheet growth on earth is believed to have developed on the higher and larger East Antarctic subcontinent while West Antarctica joined the process later around 14 million years ago. “But a problem exists with leaving West Antarctica out of the early ice history,” said Wilson. “From other evidence, it is believed that the amount of ice that grew on earth at the 34 million year climate transition was too large to be accounted for by formation on East Antarctica alone, the most obvious location for ice sheet growth. Another site is needed to host the extra missing ice.”

Evidence for that large mass of ice comes from two sources: the chemical and isotopic composition in shell material of marine microfossils, which are sensitive to ocean temperatures and the amount of ice on land; and from geologic records of lowered sea level at the time that indicate how much ice formed on land to produce the sea level drop.

The new study, by showing that West Antarctica had a higher elevation 34 million years ago than previously thought, reveals a possible site for the accumulation of the early ice that is unaccounted for. “Preliminary climate modeling by researchers at Pennsylvania State University demonstrates that this new model of higher elevation West Antarctica bedrock topography can indeed host the missing ice,” said Luyendyk. “Our results, therefore, have opened up a new paradigm for the history of the growth of the great global ice sheets. Both East and West Antarctica hosted the growing ice.”

The new hypothesis may solve another conflict among climate scientists. Given that more ice grew than could be hosted on East Antarctica alone, some researchers have proposed that the missing ice formed in the northern hemisphere. This would have been many millions of years before the well-known documentation of ice growth there, which started about three million years ago; evidence for ice sheets in the northern hemisphere prior to that time is not established. The new bedrock model shows it is not necessary to have ice hosted in the northern polar regions at the start of global climate transition; West Antarctica could have accommodated the extra ice.

Searching for an interglacial on Greenland

This is an ice core drilled at NEEM ice camp. -  Anna Wegner, Alfred Wegener Institute
This is an ice core drilled at NEEM ice camp. – Anna Wegner, Alfred Wegener Institute

The first season of the international drilling project NEEM (North Greenland Eemian Ice Drilling) in north-western Greenland was completed at August 20th. A research team, with the participation of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association, has drilled an ice core of altogether 1757.87 m length on the Greenland inland ice within 110 days. It is expected to contain data on climate history of about 38.000 years.


The oldest ice comes from a period when the Greenland climate was characterized by strong temperature fluctuations: an average of 10° to 15° Celsius within a few centuries. The drilling is to be continued in the coming years to gain information on the last interglacial period, the Eemian of about 120.000 to 130.000 years ago.

Research institutes from fourteen nations are participating in the research project which is running since 2007: Denmark, the USA, France, Sweden, the Netherlands, Japan, Great Britain, Germany, South Korea, Switzerland, China, Belgium, Iceland and Canada. NEEM is one of the major projects of the International Polar Year 2007-2009. It is coordinated logistically by the Centre for Ice and Climate in Denmark.

The international team has been drilling an ice core in north-western Greenland (77°45’N – 51°06’W) since April this year. The ice cover at the location has a magnitude of 2.545 m and it is meant to be completely drilled in the coming years to make Eemian climate data of about 120.000 to 130.000 years ago accessible. The gases, trace elements and biological substances enclosed in the ice allow the reconstruction of climate conditions at that time.


“So far, we lack detailed information on the climate in Greenland during the last interglacial”, explains Prof. Frank Wilhelms, glaciologist at the Alfred Wegener Institute. “With the help of data gained from the ice core and particularly from the comparison with data from an ice core we drilled in the Antarctic Dronning Maud Land, we are for the first time able to draw conclusions on the interaction of the climate on the northern and southern hemisphere during that time”, Wilhelms continues. Because the drilling in this year could be conducted so successfully, researchers expect to obtain ice with the necessary information on this climate period in the summer of 2010.

Water in mantle may be associated with subduction

A team of scientists from Oregon State University has created the first global three-dimensional map of electrical conductivity in the Earth’s mantle and their model suggests that that enhanced conductivity in certain areas of the mantle may signal the presence of water.

What is most notable, the scientists say, is those areas of high conductivity coincide with subduction zones – where tectonic plates are being subducted beneath the Earth’s crust. Subducting plates are comparatively colder than surrounding mantle materials and thus should be less conductive. The answer, the researchers suggest, may be that conductivity in those areas is enhanced by water drawn downward during the subduction process.

Results of their study are being published this week in Nature.

“Many earth scientists have thought that tectonic plates are not likely to carry much if any water deep into the Earth’s mantle when they are being subducted,” said Adam Schultz, a professor in the College of Oceanic and Atmospheric Sciences at Oregon State and a co-author on the Nature study. “Most evidence suggests that subducting rocks initially hold water within their minerals, but that water is released as the rocks heat up.”

“There may be other explanations,” he added, “but the model clearly shows a close association between subduction zones and high conductivity and the simplest explanation is water.”

The study is important because it provides new insights into the fundamental ways in which the planet works. Despite all of the advances in technology, scientists are still unsure how much water lies beneath the ocean floor – and how much of it makes its way into the mantle.

The implications are myriad. Water interacts with minerals differently at different depths, and small amounts of water can change the physical properties of rocks, alter the viscosity of materials in the mantle, assist in the formation of rising plumes of melted rock and ultimately affect what comes out on the surface.

“In fact, we don’t really know how much water there is on Earth,” said Gary Egbert, also a professor of oceanography at OSU and co-author on the study. “There is some evidence that there is many times more water below the ocean floor than there is in all the oceans of the world combined. Our results may shed some light on this question.”

Egbert cautioned that there are other explanations for higher conductivity in the mantle, including elevated iron content or carbon.

There also may be different explanations for how the water – if indeed the conductivity is reflecting water – got there in the first place, the scientists point out.

“If it isn’t being subducted down with the plates,” Schultz said, “how did it get there? Is it primordial, down there for four billion years? Or did it indeed come down as the plates slowly subduct, suggesting that the planet may have been much wetter a long time ago? These are fascinating questions, for which we do not yet have answers.”

The scientists conducted their study using electromagnetic induction sounding of the Earth’s mantle. This electromagnetic imaging method is very sensitive to interconnecting pockets of fluid that may be found within rocks and minerals that enhance conductivity. Using magnetic observations from more than 100 observatories dating back to the 1980s, they were able to create a global three-dimensional map of mantle conductivity.

Anna Kelbert, a post-doctoral research associate at OSU and lead author on the paper, said the imaging doesn’t show the water itself, but the level of conductivity and interpreting levels of hydrogen, iron or carbon require additional constraints from mineral physics. She described the study of electrical conductivity as both computationally intensive and requiring years of careful measurements in the international observatories.

“The deeper you want to look into the mantle,” Kelbert said, “the longer periods you have to use. This study has required magnetic field recordings collected over decades.”

The scientists say the next step is to replicate the experiment with newly available data from both ground observatories and satellites, and then conduct more research to better understand the water cycle and how the interaction with deep-Earth minerals works. Their work is supported by the National Science Foundation and NASA to take the next steps in this research program.

Ultimately, they hope to produce a model quantifying how much water may be in the mantle, locked up within the mineral-bearing rocks.

The greenhouse gas that saved the world

When Planet Earth was just cooling down from its fiery creation, the sun was faint and young. So faint that it should not have been able to keep the oceans of earth from freezing. But fortunately for the creation of life, water was kept liquid on our young planet.

For years scientists have debated what could have kept earth warm enough to prevent the oceans from freezing solid. Now a team of researchers from Tokyo Institute of Technology and University of Copenhagen’s department of chemistry have coaxed an explanation out of ancient rocks, as reported in this week’s issue of PNAS

A perfect greenhouse gas


“The young sun was approximately 30 percent weaker than it is now, and the only way to prevent earth from turning into a massive snowball was a healthy helping of greenhouse gas,” Associate Professor Matthew S. Johnson of the Department of Chemistry at University of Copenhagen explains. And he has found the most likely candidate for an archean atmospheric blanket. Carbonyl Sulphide: A product of the sulphur disgorged during millennia of volcanic activity.

“Carbonyl Sulphide is and was the perfect greenhouse gas. Much better than Carbon Dioxide. We estimate that a blanket of Carbonyl Sulphate would have provided about 30 percent extra energy to the surface of the planet. And that would have compensated for what was lacking from the sun”, says Professor Johnson.

Strange distribution


To discover what could have helped the faint young sun warm early earth, Professor Johnson and his colleagues in Tokyo examined the ratio of sulphur isotopes in ancient rocks. And what they saw was a strange signal; A mix of isotopes that couldn’t very well have come from geological processes.

“There is really no process in the rocky mantle of earth that would explain this distribution of isotopes. You would need something happening in the atmosphere,” says Johnson


The question was: What.

Painstaking experimentation helped them find a likely atmospheric process. By irradiating sulphur dioxide with different wavelengths of sunlight, they observed that sunlight passing through Carbonyl Sulphide gave them the wavelengths that produced the weird isotope mix.

“Shielding by Carbonyl Sulphide is really a pretty obvious candidate once you think about it, but until we looked, everyone had missed it,” says Professor Johnson, and he continues. “What we found is really an archaic analogue to the current ozone layer. A layer that protects us from ultraviolet radiation. But unlike ozone, Carbonyl Sulphide would also have kept the planet warm. The only problem is: It didn’t stay warm”.

Life caused ice-age


As life emerged on earth it produced increasing amounts of oxygen. With an increasingly oxidizing atmosphere, the sulphur emitted by volcanoes was no longer converted to Carbonyl Sulphide. Instead it got converted to sulphate aerosols: A powerful climate coolant. Johnson and his co-workers created a Computer model of the ancient atmosphere. And the models in conjunction with laboratory experiments suggest that the fall in levels of Carbonyl Sulphide and rise of sulphate aerosols taken together would have been responsible for creating snowball earth, the planetwide ice-age hypothesised to have taken place near the end of the Archean eon 2500 million years ago. And the implications to Johnson are alarming.

“Our research indicates that the distribution and composition of atmospheric gasses swung the planet from a state of life supporting warmth to a planet-wide ice-age spanning millions of years. I can think of no better reason to be extremely cautious about the amounts of greenhouse gasses we are currently emitting to the atmosphere”.