Do dust particles curb climate change?

Every cloud is different from the next. It is therefore important to study the types of cloud systems in which aerosols have the greatest influence. -  Max Planck Institute for Meteorology / Stevens
Every cloud is different from the next. It is therefore important to study the types of cloud systems in which aerosols have the greatest influence. – Max Planck Institute for Meteorology / Stevens

A knowledge gap exists in the area of climate research: for decades, scientists have been asking themselves whether, and to what extent man-made aerosols, that is, dust particles suspended in the atmosphere, enlarge the cloud cover and thus curb climate warming. Research has made little or no progress on this issue. Two scientists from the Max Planck Institute for Meteorology in Hamburg (MPI-M) and the American National Oceanic and Atmospheric Administration (NOAA) report in the journal Nature that the interaction between aerosols, clouds and precipitation is strongly dependent on factors that have not been adequately researched up to now. They urge the adoption of a research concept that will close this gap in the knowledge. (Nature, October 1st, 2009)

Greenhouse gases that heat up the earth’s atmosphere have their adversaries: dust particles suspended in the atmosphere which are known as aerosols. They arise naturally, for example when wind blows up desert dust, and through human activities. A large proportion of the man-made aerosols arise from sulfur dioxides that are generated, in turn, by the combustion of fossil fuels.

The aerosols are viewed as climate coolers, which compensate in part for the heating up of the earth by greenhouse gases. Climate researchers imagine the workings of this cooling mechanism in very simple terms: when aerosols penetrate clouds, they attract water molecules and therefore act as condensation seeds for drops of water. The more aerosol particles suspended in the cloud, the more drops of water are formed. When man-made dust particles join the natural ones, the number of drops increases. As a result, the average size of the drops decreases. Because smaller drops do not fall to the ground, the aerosols prevent the cloud from raining out and extend its lifetime. Consequently, the cloud cover over the earth’s surface increases. Because clouds reflect the solar radiation and throw it back into space, less heat collects in the atmosphere than when the sky is clear. Climate researchers refer to this mechanism as the “cloud lifetime effect”.

To date, however, it has not been possible to quantify the influence of the cloud lifetime effect on climate. The estimates vary hugely and range from no influence whatsoever to a cooling effect that is sufficient to more than compensate for the heating effect of carbon dioxide.

According to Bjorn Stevens from the MPI-M and Graham Feingold from the Earth System Research Laboratory at NOAA in Washington D.C the enormous uncertainty surrounding this phenomenon is indicative of the fact that the explanation of the cooling mechanism generated by aerosols is oversimplified. The two cloud researchers have analyzed the specialist literature published on this topic since the 1970s. In their survey of the literature they encountered observations that disagree with the cloud lifetime effect: for example, a field study carried out a few years ago found that clouds in the Trade Wind region rain out more quickly rather than more slowly in the presence of virtually opaque aerosols.

On the completion of their analysis of the literature, Stevens and Feingold came to the following conclusion: “Clouds react to aerosols in a very complex way and the reaction is strongly dependent on the type and state of the cloud,” says Stevens. Therefore the aerosol problem is a cloud problem. “We climate researchers must focus more on cloud systems and understand them better,” he stresses.

As the researchers write, processes in the clouds that counteract or even negate the influence of the aerosol particles have not been taken into account up to now. One example: when a cumulus cloud comes into contact with aerosols, it does not rain out. However, this has certain consequences: the fluid rises and evaporates above the cloud. The air that lies above the cloud cools down and becomes susceptible to the upward extension of the cumulus cloud. Higher cumulus clouds rain out more easily than lower ones. This is what causes precipitation. Therefore, in such situations the aerosol does not prevent the cloud from raining out.

Stevens and Feingold believe that due to such buffer mechanisms the cooling effect of the aerosols is likely to be minimal. They admit, however, that the cloud lifetime effect is not unsuitable per se as a way of explaining the processes triggered by aerosols in the clouds. “All cloud types and states cannot, however, be lumped together,” says Stevens. He calls for rethinking aerosol research and makes a comparison with cancer research: “People used to think that cancer was based on a single mechanism. Today, it is known that each type of cancer must be researched individually,” says the scientist.

According to Stevens and Feingold, research must first identify the cloud systems on which aerosols have the greatest influence. They suggest starting with particularly common types of cloud, for example flat cumulus clouds over the oceans (Trade Wind cumuli), which cover 40 percent of the global seas.

A research project to be undertaken jointly by the Max Planck Institute for Meteorology and the Caribbean Institute for Meteorology and Hydrology in Miami will make a start on this. The two-year empirical field study will commence on the Caribbean island of Barbados, which is located in the Trade Wind region, in 2010. The researchers will install remote sensing instruments on the island’s windward side that will focus on the clouds coming from the open ocean. The land measurements will be complemented by measurements taken in the clouds themselves by HALO, the German research aircraft. The data from this measurement campaign should help the scientists to reach a better understanding of the relationships between cloud cover, precipitation, local meteorological conditions and aerosols.

Satellite data look behind the scenes of deadly earthquake

An ALOS Phased Array type L-band Synthetic Aperture Radar (PALSAR) interferogram that shows the surface deformation associated with the 2008 Wenchuan earthquake. The white curves depict traces of fault surface breaks. ESA is supporting ALOS (Advanced Land Observing Satellite) as a 'Third Party Mission', which means ESA utilizes its multi-mission European ground infrastructure and expertise to acquire, process and distribute data from the satellite to its wide user community. - Credits: Jianbao Sun; ALOS data: JAXA
An ALOS Phased Array type L-band Synthetic Aperture Radar (PALSAR) interferogram that shows the surface deformation associated with the 2008 Wenchuan earthquake. The white curves depict traces of fault surface breaks. ESA is supporting ALOS (Advanced Land Observing Satellite) as a ‘Third Party Mission’, which means ESA utilizes its multi-mission European ground infrastructure and expertise to acquire, process and distribute data from the satellite to its wide user community. – Credits: Jianbao Sun; ALOS data: JAXA

Using satellite radar data and GPS measurements, Chinese researchers have explained the exceptional geological events leading to the 2008 Wenchuan Earthquake that killed nearly 90 000 people in China’s Sichuan Province.

“One of the very fundamental issues for understanding an earthquake is to know how the rupture is distributed on the fault plane, which is directly related to the amount of ground shaking and the damage it could cause at the surface,” said Dr Jianbao Sun of the Institute of Geology, China Earthquake Administration (IGCEA).

To learn this, Sun and Prof. Zhengkang Shen of IGCEA and Peking University’s Department of Geophysics, and collaborators acquired two kinds of satellite radar data: Advanced Synthetic Aperture Radar (ASAR) data in C-band from ESA’s Envisat satellite and Phased Array type L-band Synthetic Aperture Radar (PALSAR) data from Japan’s ALOS satellite.

Applying a technique called SAR Interferometry (InSAR) on the data, the researchers produced a set of ‘interferogram’ images covering the entire coseismic rupture region and its vicinity. This interferometric map revealed the amount and scope of surface deformation produced by the earthquake.

“This is perhaps the very first time people have seen the complete deformation field produced by an earthquake on such a large scale,” Sun said.

InSAR involves combining two or more radar images of the same ground location in such a way that very precise measurements – down to a scale of a few centimetres – can be made of any ground motion taking place between image acquisitions. Coloured interferograms usually appear as rainbow fringe patterns.

The researchers combined these SAR satellite data with GPS measurements and developed a model that shows fault geometry and rupture distribution of the Longmen Shan fault zone, a series of parallel faults that run for about 400 km from southwest to northeast in the region. The earthquake that struck on 12 May last year produced a 240-km-long rupture along the Beichuan fault and a 72-km-long rupture along part of the Pengguan fault.

Studying the model, they were able to determine that the fault plane dips considerably to the northwest in the zone’s southwest area and then rises up to a nearly vertical position in the zone’s northeast.

They also learned that the direction of the motion along the fault changed, going from a thrust where upper layer rocks were pushed up and lower layer rocks pulled down, to a ‘dextral faulting’, where two parts of Earth’s plates slide past each other. About a 7-metre slip, the greatest along the rupture, was detected on the Beichuan fault near Beichuan City, which was destroyed completely by the quake and suffered the highest number of casualties.

Another major finding was that the fault junctions (solid rock barriers that stop a quake from propagating from one segment to another), beneath the hardest-hit cities of Yingxiu, Beichuan and Nanba, failed to withstand the extraordinary energy released along the fault.

“These fault junctions are barriers, whose failures in a single event allowed the rupture to cascade through several fault segments, resulting in a major 7.9-earthquake,” Shen explained. “Earthquakes across fault segments like this are estimated to happen about every 4000 years.”

These new results were published this month in the journal Nature Geoscience, part of Nature magazine.

Following the quake, Sun and Shen worked closely with the ‘Dragon 2′ programme to coordinate SAR coverage of the seismic area. Dragon 2 is a joint undertaking between ESA and China’s Ministry of Science and Technology that encourages scientists to use satellite data to monitor and understand environmental phenomena in China.

“The resulting Envisat SAR data acquired along an important track close to the epicentre turned out to be vital in constraining the southern part of the deformation field and helping explain the fault geometry and rupture distribution of the Pengguan fault, which would be difficult to resolve otherwise,” Shen said.

The scientists also hope the data will help to assess earthquake potential in the future.

“Under the coordination of Dragon 2, the SAR data acquired during this period will be used, along with GPS measurements, to reveal geophysical processes within the Longmen Shan fault zone and the lower crust and upper mantle, which will help us understand the earthquake and faulting mechanisms and hopefully shed light on future seismic risks in this area.”

Warmer climate not the cause of oxygen deficiency in the Baltic Sea

This is Daniel Hansson, Ph.D., from the Department of Earth Sciences at the University of Gothenburg. -  University of Gothenburg
This is Daniel Hansson, Ph.D., from the Department of Earth Sciences at the University of Gothenburg. – University of Gothenburg

Oxygen deficiency in the Baltic Sea has never been greater than it is now. But it is not an effect of climate change but rather of increased inputs of nutrients and fertilizers. This is the finding of researchers at the University of Gothenburg, Sweden, who have analyzed the ocean climate of the Baltic Sea since the 16th century.

85 million people live in the drainage basin of the Baltic Sea. This population has a great impact on the marine environment of the Baltic. This is shown by the researcher Daniel Hansson at the Department of Earth Sciences, who has analyzed the ocean climate of the Baltic Sea since the 16th century using new methods.

Human activity

In his thesis, Hansson notes that oxygen deficiency and spread of dead seabeds in the Baltic Sea are essentially due to human activity.
“Climate change to date has only had a negligible effect on oxygen deficiency in the Baltic Sea. The principal cause of oxygen deficiency and large areas of dead seabed is that inputs from agriculture and untreated wastewater increased sharply, in particular in conjunction with increased use of commercial fertilizer in the mid-20th century,” says Hansson.

New methods

By combining new methods to reconstruct the historical climate and modern computer models, Hansson has been able to study in detail changes in water temperature, ice extent, river runoff, salinity and oxygen concentrations in the Baltic Sea over 500 years. The studies show clearly that the oxygen condition today cannot be compared with any other period since the 16th century, and that the present-day raised water temperature and limited ice extent are similar to situations that have occurred only twice previously.

Changes can come

“But if the trend towards continued warming persists, we may soon see climate change outside the variation that has occurred in the past 500 years,” says Hansson.

The technique used in the thesis provides very high time resolution. Hansson has, for example, been able to reconstruct how the ice thickened during the turbulent days of January and February 1658, when King Charles X Gustav marched with the Swedish Army across the Little and Great Belt, leading to the annexation of Blekinge, Skåne, Halland and Bohuslän by Sweden.

Giant impact near India – not Mexico – may have doomed dinosaurs

This diagram shows a three-dimensional reconstruction of the submerged Shiva crater (~500 km diameter) at the Mumbai Offshore Basin, western shelf of India from different cross-sectional and geophysical data. The overlying 4.3-mile-thick Cenozoic strata and water column were removed to show the morphology of the crater. -  Sankar Chatterjee, Texas Tech University
This diagram shows a three-dimensional reconstruction of the submerged Shiva crater (~500 km diameter) at the Mumbai Offshore Basin, western shelf of India from different cross-sectional and geophysical data. The overlying 4.3-mile-thick Cenozoic strata and water column were removed to show the morphology of the crater. – Sankar Chatterjee, Texas Tech University

A mysterious basin off the coast of India could be the largest, multi-ringed impact crater the world has ever seen. And if a new study is right, it may have been responsible for killing the dinosaurs off 65 million years ago.

Sankar Chatterjee of Texas Tech University and a team of researchers took a close look at the massive Shiva basin, a submerged depression west of India that is intensely mined for its oil and gas resources. Some complex craters are among the most productive hydrocarbon sites on the planet. Chatterjee will present his research at this month’s Annual Meeting of the Geological Society of America in Portland, Oregon.

“If we are right, this is the largest crater known on our planet,” Chatterjee said. “A bolide of this size, perhaps 40 kilometers (25 miles) in diameter creates its own tectonics.”

By contrast, the object that struck the Yucatan Peninsula, and is commonly thought to have killed the dinosaurs was between 8 and 10 kilometers (5 and 6.2 miles) wide.

It’s hard to imagine such a cataclysm. But if the team is right, the Shiva impact vaporized Earth’s crust at the point of collision, leaving nothing but ultra-hot mantle material to well up in its place. It is likely that the impact enhanced the nearby Deccan Traps volcanic eruptions that covered much of western India. What’s more, the impact broke the Seychelles islands off of the Indian tectonic plate, and sent them drifting toward Africa.

The geological evidence is dramatic. Shiva’s outer rim forms a rough, faulted ring some 500 kilometers in diameter, encircling the central peak, known as the Bombay High, which would be 3 miles tall from the ocean floor (about the height of Mount McKinley). Most of the crater lies submerged on India’s continental shelf, but where it does come ashore it is marked by tall cliffs, active faults and hot springs. The impact appears to have sheared or destroyed much of the 30-mile-thick granite layer in the western coast of India.

The team hopes to go India later this year to examine rocks drill from the center of the putative crater for clues that would prove the strange basin was formed by a gigantic impact.

“Rocks from the bottom of the crater will tell us the telltale sign of the impact event from shattered and melted target rocks. And we want to see if there are breccias, shocked quartz, and an iridium anomaly,” Chatterjee said. Asteroids are rich in iridium, and such anomalies are thought of as the fingerprint of an impact.

Abstract: The Significance Of The Contemporaneous Shiva Impact Structure And Deccan Volcanism At The Kt Boundary

CHATTERJEE, Sankar, Geosciences, Texas Tech Univ, MS Box 41053, Lubbock, TX 79409-3191, and MEHROTRA, Naresh M., Paleobotany, Birbal Sahni Institute of Paleobotany, 53 University Road, Lucknow, 226007, India

India was ground zero for two catastrophic events, the Shiva impact and Deccan volcanism at the KT boundary that have been linked to the dinosaur extinction. The buried and multiringed Shiva crater (~500 km diameter) on the western shelf of India is the remnant of a giant meteorite impact that left high-resolution stratigraphic signals in the sedimentary and volcanic rocks such as shocked quartz, iridium anomaly, nickel-rich spinels, sanidine spherules, magnetic nanoparticles, high pressure fullerenes, megatsunami deposits, and melt lavas. The Shiva crater is the largest hydrocarbon reserve in India, where the central uplift, the Bombay High, and the associated brecciated bodies and peripheral strata form ideal structural traps for oil and gas. The Shiva bolide (~40 km diameter) would generate lethal amount of kinetic energy of 1.45 x 1025 joules. The impact was so powerful that it led to several geodynamic anomalies: it fragmented, sheared, and deformed the lithosphere mantle across the western Indian margin and contributed to major plate reorganization in the Indian Ocean. It initiated rifting between India and Seychelles in the west and created the Laxmi Ridge; it shattered the Indian plate easterly along the Narmada-Son Rift extending 1500 km across, dividing the Indian shield into a southern peninsular block and a northern foreland block. Because of topographic barrier of the Western Ghat Mountain range, the impact-triggered tsunami was restricted along the Narmada-Son Rift at the KT boundary. The relationships between large meteoritic impact, hotspot, flood basalt volcanism, plate tectonics, geodynamic anomalies, and sudden environmental catastrophe on Earth may open up a new field of unified investigation. Although the Reunion hotspot responsible for Deccan eruption was close to the Shiva crater in time and space, impact probably triggered a component of the Deccan Trap: the iridium-rich alkaline igneous complex rocks that were emplaced asymmetrically as a fluid ejecta at the KT boundary along the NE downrange direction of the bolide trajectory outside the crater ring. Two large impacts such as Shiva and Chicxulub in quick succession on the antipodal position, in concert with Deccan eruptions, would have devastating effects globally leading to climatic and environmental catastrophes that wiped out dinosaurs and many other organisms at the KT boundary.

Geological Society of America Abstracts with Programs, Vol. 41, No. 7, p. 160

What hit Earth in 1908 with the force of 3,000 atomic bombs?

Photograph from Kulik's 1927 expedition
Photograph from Kulik’s 1927 expedition

There have been numerous theories proposed about what struck the taiga in central Siberia, causing millions of trees to topple over and many still-standing trees to lose all their branches. Many expeditions have looked for traces of what hit Earth and have not found much. There is no telltale meteor crater, and no clear evidence of a nuclear blast. In fact, at the epicenter, the trees were found to be still standing. Whatever hit Earth did not reach the ground. It exploded in the air above the ground.

In The Tunguska Mystery by Vladimir Rubtsov, the efforts put forth by generations of Russian scientists, technicians, and others are documented. What did they find? Was it a meteorite, as had first been thought? Was it an asteroid? Was it a comet? Some support the idea that this was not a “natural” event at all but one caused by the explosion of an alien spaceship trying to land on Earth. Is there any evidence for this? How did the Russian scientific and world community react to this theory?

The mystery has been very difficult to solve, but it is important – perhaps even urgent – to solve it. We live in a very violent universe, and we are extremely vulnerable to its vagaries. How can we prevent another “Tunguska” if we don’t even know what it was? And next time, the event might not occur in a remote, barely inhabited region of Earth. It may take many thousands of lives and destroy whole cities.

Vladimir Rubtsov was born in 1948 in Kharkov, Ukraine. He received his Ph.D. degree in the philosophy of science from the Institute of Philosophy of the Academy of Sciences of the USSR, having defended in 1980 the doctoral thesis “Philosophical and Methodological Aspects of the Problem of Extraterrestrial Civilizations,” the first of its kind in the former USSR. Dr. Rubtsov has authored two monographs and some 120 scientific and popular science articles in the Soviet, post-Soviet and international press.

Acidic clouds nourish world’s oceans

Scientists at the University of Leeds have proved that acid in the atmosphere breaks down large particles of iron found in dust into small and extremely soluble iron nanoparticles, which are more readily used by plankton.

This is an important finding because lack of iron can be a limiting factor for plankton growth in the ocean – especially in the southern oceans and parts of the eastern Pacific. Addition of such iron nanoparticles would trigger increased absorption of carbon dioxide from the atmosphere.

“This could be a very important discovery because there’s only a very small amount of soluble iron in the ocean and if plankton use the iron nanoparticles formed in clouds then the whole flux of bioavailable iron to the oceans needs to be revised,” says Dr Zongbo Shi, lead author of the research from the School of Earth and Environment at the University of Leeds.

Water droplets in clouds generally form around dust and other particles. When clouds evaporate, as they often do naturally, the surface of the particle can become very acidic. This is especially true where the air is polluted.

Paradoxically, scientists suggest that large scale industry in countries like China could be combating global warming to some extent by creating more bioavailable iron in the oceans, and therefore increasing carbon dioxide removal from the atmosphere.

“Man made pollution adds more acid to the atmosphere and therefore may encourage the formation of more iron nanoparticles,” says Dr Shi.

Scientists carried out the research by simulating clouds in the laboratory to which they added Saharan dust samples. They were then able to mimic natural conditions in order to monitor the chemical processes happening in the system. The laboratory experiments have been confirmed in natural samples where such cloud processing is known to have occurred.

The findings highlight the complexity of the pattern of natural iron delivery to the oceans, throwing new light on recent high profile plans to add iron to the southern oceans artificially to stimulate plankton growth.

“This process is happening in clouds all over the world, but there are particularly interesting consequences for the oceans. What we have uncovered is a previously unknown source of bioavailable iron that is being delivered to the Earth’s surface in precipitation,” says Professor Michael Krom, the principal investigator of the research, also at the University of Leeds.

Banded rocks reveal early Earth conditions, changes

Pictured in 2008, a banded iron formation about 2.5 billion years old near Soudan Underground Mine State Park in Minnesota shows alternating layers of silica-rich (red) and iron-rich (gray) minerals. This type of ancient rock formation dominated the global ocean floors for more than two billion years, but abruptly disappeared 1.7 billion years ago. A study by researchers at UW-Madison and elsewhere describes a new model of how these ancient rocks formed and what they reveal about the geology, oceans and atmosphere of the Earth’s early environment. - Photo: Huifang Xu
Pictured in 2008, a banded iron formation about 2.5 billion years old near Soudan Underground Mine State Park in Minnesota shows alternating layers of silica-rich (red) and iron-rich (gray) minerals. This type of ancient rock formation dominated the global ocean floors for more than two billion years, but abruptly disappeared 1.7 billion years ago. A study by researchers at UW-Madison and elsewhere describes a new model of how these ancient rocks formed and what they reveal about the geology, oceans and atmosphere of the Earth’s early environment. – Photo: Huifang Xu

The strikingly banded rocks scattered across the upper Midwest and elsewhere throughout the world are actually ambassadors from the past, offering clues to the environment of the early Earth more than 2 billion years ago.

Called banded iron formations or BIFs, these ancient rocks formed between 3.8 and 1.7 billion years ago at what was then the bottom of the ocean. The stripes represent alternating layers of silica-rich chert and iron-rich minerals like hematite and magnetite.

First mined as a major iron source for modern industrialization, BIFs are also a rich source of information about the geochemical conditions that existed on Earth when the rocks were made. However, interpreting their clues requires understanding how the bands formed, a topic that has been controversial for decades, says Huifang Xu, a geology professor at the University of Wisconsin-Madison.

A study appearing today (Oct. 11) as an advance online publication in Nature Geoscience offers a new picture of how these colorful bands developed and what they reveal about the composition of the early ocean floor, seawater, and atmosphere during the evolution of the Earth.

Previous hypotheses about band formation involved seasonal fluctuations, temperature shifts, or periodic blooms of microorganisms, all of which left many open questions about how BIFs dominated the global marine landscape for two billion years and why they abruptly disappeared 1.7 billion years ago.

With Yifeng Wang of Sandia National Laboratories, Enrique Merino of Indiana University and UW-Madison postdoc Hiromi Konishi, Xu developed a BIF formation model that offers a more complete picture of the environment at the time, including interactions between rocks, water, and air.

“They are all connected,” Xu explains. “The lithosphere affects the hydrosphere, the hydrosphere affects the atmosphere, and all those eventually affect the biosphere on the early Earth.”

Their model shows how BIFs could have formed when hydrothermal fluids, from interactions between seawater and hot oceanic crust from deep in the Earth’s mantle, mixed with surface seawater. This mixing triggered the oscillating production of iron- and silica-rich minerals, which were deposited in layers on the seafloor.

They used a series of thermodynamic calculations to determine that the source material for BIFs must have come from oceanic rocks with a very low aluminum content, unlike modern oceanic basalts that contain high levels of aluminum.

“The modern-day ocean floor is basalt, common black basalt like the Hawaiian islands. But during that time, there was also a strange kind of rock called komatiites,” says Xu. “When ocean water reacts with that kind of rock, it can produce about equal amounts of iron and silica” – a composition ideally suited to making BIFs.

Such a mixture can create distinct alternating layers – which range in thickness from 10 micrometers to about 1 centimeter – due to a constantly shifting state that, like a competition between two well-matched players, resists resolving to a single outcome and instead see-saws between two extremes.

BIFs dominated the global oceans 3.8 to 1.7 billion years ago, a time period known to geologists as the Archaean-Early Proterozoic, then abruptly disappeared from the geologic record. Their absence in more recent rocks indicates that the geochemical conditions changed around 1.7 billion years ago, Xu says.

This change likely had wide-ranging effects on the physical and biological composition of the Earth. For example, the end of BIF deposition would have starved iron-dependent bacteria and shifted in favor of microbes with sulfur-based metabolisms. In addition, chemical and pH changes in the ocean and rising atmospheric oxygen may have allowed the emergence and spread of oxygen-dependent organisms.

The new study was partly funded by the NASA Astrobiology Institute, and Xu hopes to look for biosignatures trapped in the rock bands for additional clues to the changes that occurred 1.7 billion years ago and what may have triggered them.

Last time carbon dioxide levels were this high: 15 million years ago, scientists report

You would have to go back at least 15 million years to find carbon dioxide levels on Earth as high as they are today, a UCLA scientist and colleagues report Oct. 8 in the online edition of the journal Science.

“The last time carbon dioxide levels were apparently as high as they are today – and were sustained at those levels – global temperatures were 5 to 10 degrees Fahrenheit higher than they are today, the sea level was approximately 75 to 120 feet higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland,” said the paper’s lead author, Aradhna Tripati, a UCLA assistant professor in the department of Earth and space sciences and the department of atmospheric and oceanic sciences.

“Carbon dioxide is a potent greenhouse gas, and geological observations that we now have for the last 20 million years lend strong support to the idea that carbon dioxide is an important agent for driving climate change throughout Earth’s history,” she said.

By analyzing the chemistry of bubbles of ancient air trapped in Antarctic ice, scientists have been able to determine the composition of Earth’s atmosphere going back as far as 800,000 years, and they have developed a good understanding of how carbon dioxide levels have varied in the atmosphere since that time. But there has been little agreement before this study on how to reconstruct carbon dioxide levels prior to 800,000 years ago.

Tripati, before joining UCLA’s faculty, was part of a research team at England’s University of Cambridge that developed a new technique to assess carbon dioxide levels in the much more distant past – by studying the ratio of the chemical element boron to calcium in the shells of ancient single-celled marine algae. Tripati has now used this method to determine the amount of carbon dioxide in Earth’s atmosphere as far back as 20 million years ago.

“We are able, for the first time, to accurately reproduce the ice-core record for the last 800,000 years – the record of atmospheric C02 based on measurements of carbon dioxide in gas bubbles in ice,” Tripati said. “This suggests that the technique we are using is valid.

“We then applied this technique to study the history of carbon dioxide from 800,000 years ago to 20 million years ago,” she said. “We report evidence for a very close coupling between carbon dioxide levels and climate. When there is evidence for the growth of a large ice sheet on Antarctica or on Greenland or the growth of sea ice in the Arctic Ocean, we see evidence for a dramatic change in carbon dioxide levels over the last 20 million years.

“A slightly shocking finding,” Tripati said, “is that the only time in the last 20 million years that we find evidence for carbon dioxide levels similar to the modern level of 387 parts per million was 15 to 20 million years ago, when the planet was dramatically different.”

Levels of carbon dioxide have varied only between 180 and 300 parts per million over the last 800,000 years – until recent decades, said Tripati, who is also a member of UCLA’s Institute of Geophysics and Planetary Physics. It has been known that modern-day levels of carbon dioxide are unprecedented over the last 800,000 years, but the finding that modern levels have not been reached in the last 15 million years is new.

Prior to the Industrial Revolution of the late 19th and early 20th centuries, the carbon dioxide level was about 280 parts per million, Tripati said. That figure had changed very little over the previous 1,000 years. But since the Industrial Revolution, the carbon dioxide level has been rising and is likely to soar unless action is taken to reverse the trend, Tripati said.

“During the Middle Miocene (the time period approximately 14 to 20 million years ago), carbon dioxide levels were sustained at about 400 parts per million, which is about where we are today,” Tripati said. “Globally, temperatures were 5 to 10 degrees Fahrenheit warmer, a huge amount.”

Tripati’s new chemical technique has an average uncertainty rate of only 14 parts per million.

“We can now have confidence in making statements about how carbon dioxide has varied throughout history,” Tripati said.

In the last 20 million years, key features of the climate record include the sudden appearance of ice on Antarctica about 14 million years ago and a rise in sea level of approximately 75 to 120 feet.

“We have shown that this dramatic rise in sea level is associated with an increase in carbon dioxide levels of about 100 parts per million, a huge change,” Tripati said. “This record is the first evidence that carbon dioxide may be linked with environmental changes, such as changes in the terrestrial ecosystem, distribution of ice, sea level and monsoon intensity.”

Today, the Arctic Ocean is covered with frozen ice all year long, an ice cap that has been there for about 14 million years.

“Prior to that, there was no permanent sea ice cap in the Arctic,” Tripati said.

Some projections show carbon dioxide levels rising as high as 600 or even 900 parts per million in the next century if no action is taken to reduce carbon dioxide, Tripati said. Such levels may have been reached on Earth 50 million years ago or earlier, said Tripati, who is working to push her data back much farther than 20 million years and to study the last 20 million years in detail.

More than 50 million years ago, there were no ice sheets on Earth, and there were expanded deserts in the subtropics, Tripati noted. The planet was radically different.

Co-authors on the Science paper are Christopher Roberts, a Ph.D. student in the department of Earth sciences at the University of Cambridge, and Robert Eagle, a postdoctoral scholar in the division of geological and planetary sciences at the California Institute of Technology.

The research was funded by UCLA’s Division of Physical Sciences and the United Kingdom’s National Environmental Research Council.

Tripati’s research focuses on the development and application of chemical tools to study climate change throughout history. She studies the evolution of climate and seawater chemistry through time.

“I’m interested in understanding how the carbon cycle and climate have been coupled, and why they have been coupled, over a range of time-scales, from hundreds of years to tens of millions of years,” Tripati said.

Scientists obtain rocks moving into seismogenic zone

Scientists document and sample cores. -  JAMSTEC/IODP
Scientists document and sample cores. – JAMSTEC/IODP

An international group of scientists aboard the Deep-Sea Drilling Vessel CHIKYU, operated by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) for the Integrated Ocean Drilling Program (IODP), return from a 40-day scientific expedition off the shore of the Kii Peninsula, Japan on Oct. 10, 2009. Expedition 322, called “Subduction Inputs” in the multi-stage project, conducted drilling, logging and sampling beneath the ocean floor to investigate input material that will be transported to the seismogenic zone by the plate subduction system.

The drilling operations were carried out at two sites in the Shikoku Basin, the back-arc basin of the Izu-Bonin volcanic chain where the Philippine Sea Plate dives down into the Nankai Trough at a rate of about 4 cm per year. At the first site C0011, scientists began coring from a depth of 340 meters below the seafloor. The coring, however, had to be abandoned at a depth of 881 meters because of damage of the drill bit. At the second site C0012, coring was carried out from depths 60 meters to 576 meters below the seafloor, and successfully collected the targeted sedimentary and basement rock samples.

Dr. Michael Underwood, professor at University of Missouri, USA, and co-Chief Scientists of the expedition said, “We identified an interface of Miocene sediment and basement rock around 540 meters beneath the seafloor and successfully sampled basaltic pillow lava rocks that make up the basement.” He added “These sedimentary and volcanic rocks in the lower part of Shikoku Basin are key intervals for generating large earthquake slip after they are transported to the seismogenic zone. Studying their petrological, geotechnical, frictional and hydrogeological properties prior to subduction is expected to contribute significantly to the understanding of rupture dynamics in the seismogenic zone.”

The science party included 26 onboard research specialists from international member countries. “Scientists observed, measured and analyzed geological samples by day and night working shifts in the onboard laboratories,” said Dr. Saneatsu Saito from JAMSTEC who led research activities as another co-Chief Scientist. He explained the importance of the variety of data obtained, “The sand-rich volcanic sediments were confirmed in large quantity and may have been transported from the easterly located Izu-Bonin Arc about 5 to 11 million years ago. Other sandstones contain abundant minerals derived from land, implying the extensive supply of sand to the Shikoku Basin from the Japanese islands.” Prof. Underwood added, “Analysis of pore water and hydrocarbon gases retrieved from the sedimentary layers above the basement indicates multiple sources and migration paths of fluids. These results have important implications for understanding the properties of fluids within the seismogenic zone.”

Alfalfa sprouts key to discovering how meandering rivers form and maintain

Christian Braudrick, William Dietrich and colleagues at UC Berkeley are the first to build a scaled down meandering stream in the lab that successfully meandered through its flood plain for 130 hours, which represents 5 to 7 years of real time in the wild. The substrate is composed of sand to represent real-life gravel; white light-weight plastic for sand, and alfalfa sprouts for deep-rooting vegetation. -  Christian Braudrick/UC Berkeley
Christian Braudrick, William Dietrich and colleagues at UC Berkeley are the first to build a scaled down meandering stream in the lab that successfully meandered through its flood plain for 130 hours, which represents 5 to 7 years of real time in the wild. The substrate is composed of sand to represent real-life gravel; white light-weight plastic for sand, and alfalfa sprouts for deep-rooting vegetation. – Christian Braudrick/UC Berkeley

Sinuous, meandering streams produce diverse and wildlife-rich habitats and are the aim of many river restoration efforts, but until now, the bank, water flow and sediment conditions required to form and maintain meanders have been largely a matter of speculation.

No one has been able to experimentally create self-sustaining meanders in the lab, and numerous restored meanders have straightened out or turned into multi-channel “braided” rivers after the first flood.

Now, a University of California, Berkeley, study reports the first experimental creation of meanders in a flume – a scaled down representation of a natural channel using alfalfa sprouts to represent vegetated stream banks. These experiments reveal some of the necessary conditions for formation of meanders on Earth and throughout the solar system.

“The money spent nationally on stream restoration is expanding exponentially, yet we’re fixing things faster than we can tell whether it’s doing any good,” said UC Berkeley graduate student Christian Braudrick, a former environmental consultant. “Our flume model will now let us do investigations that we can’t do in the field but, until now, haven’t been able to do in the lab, finally linking experiment with the geomorphology we see in nature.”

Braudrick and William Dietrich, UC Berkeley professor of earth and planetary science, along with colleagues at San Francisco State University and Berkeley-based Stillwater Sciences, reported their results last week in the online early edition of the journal Proceedings of the National Academy of Sciences.

Snaking meanders like those characteristic of the lower Mississippi River are common along rivers and streams on Earth, as well as along now-dry channels on Mars and even on the frozen surface of Saturn’s moon Titan. On Earth, they typically form in low-sloping valleys where, over the years, they wander across their floodplain, creating new floodplain deposits and leaving behind tree-lined sloughs, chutes and oxbow lakes that team with fish, birds, mammals and reptiles. The gravel bars, called point bars, at the inner bank of a meander also provide new surfaces that are critical for the establishment of riparian trees.

Yet, understanding how these channels form has relied until now on limited field measurements or theoretical analysis based on known physics and hydraulics – no one has been able to experimentally create meanders in a laboratory that don’t eventually turn into straight channels or braided streams, Braudrick said. An effort to restore Uvas Creek in Gilroy, Calif., for example, ended in failure when a five-year flood stripped away the sinuous meanders leaving a braided channel, similar to the channel prior to the restoration.

Braudrick created a successful laboratory model of a gravel-bed stream by finding the right material to reinforce the banks – alfalfa sprouts – and the right material to represent fine sediment – 0.25-0.42-millimeter lightweight plastic particles. He used sand to represent gravel. Working in a gently-sloping, 6.1×17-meter (20×56-foot) box filled with sand and planted with alfalfa sprouts, he carved a 40-cm (16-inch) wide channel with a single bend at the top, turned on the water, introduced plastic and sand and let the sproutscape rearrange itself over a total of 136 hours.

“We found that you need enough vegetation on the outer bank to slow down erosion and let the bars grow on the inner bank; otherwise, the stream cuts through the point bars and creates a braided river,” Braudrick said.

During the experiments, as the channel migrated into chutes or the sinuosity increased, individual bends cut off as the channel took a shorter path. Over the course of the experiment, which took a year to complete and was equivalent to about 5-7 years of high stream flow, the stream formed five new bends that moved downstream as they grew, cut off and re-formed, all the while migrating laterally across the flume’s floodplain.

One key to letting real-world bars grow, he said, is fine sediment, about the size of sand, that keeps point bars from being undermined or cut through before they can grow to the elevation of the floodplain, and that plugs holes in bars before the chutes becomes cutoffs. Sand and fine sediment are today considered detrimental when restoring streams for fish spawning because of fears the sediment will cover the gravel in which fish lay their eggs.

“Eliminating fine sediment is probably not a good idea if you want to maintain a single-thread, meandering river that migrates,” Braudrick said. A naturally migrating meander, however, constantly brings new sediment in from eroded banks upstream, while also providing wood and debris for animal habitat.

Interestingly, the researchers found that mixing high flows of various heights was not essential to creating meanders, as suggested by other studies. A steady flood flow was sufficient to provide the sediment needed to maintain and build bars and erode banks.

Key to their success was the use of alfalfa sprouts, which was suggested by related experiments at the University of Minnesota, headquarters of the National Center for Earth-Surface Dynamics, of which UC Berkeley is a member. As with trees and other vegetation along natural rivers, the roots of the alfalfa sprouts provide strength to the soil and, when exposed, protect the banks from the force of the water, preventing banks from washing away too quickly.

The downside of sprouts, Braudrick said, is that they rot when repeatedly wet and take time to grow. Every three days, the experiment had to be halted for more than a week to allow the sprouts to die and be replanted. The search is on for hardier plants or other materials that will allow longer trials that should more precisely reproduce natural, long-term processes.

Also key to the success was finding a way to scale-model the fine sediment common in rivers and streams. While sand adequately models gravel, the substances used previously to represent sand did not stay suspended in the water like sand and silt. Plastic materials like those used in sand-blasting were the right size and density to remain suspended and demonstrate the importance of fine sediment in stabilizing point bars.

“This work has taken extraordinary patience and considerable trial and error by Christian to perfect the methods, but now, for the first time, we know how to make dynamic, self-maintaining meanders in the lab, and this opens up many new areas of research,” Dietrich said.

Dietrich, Braudrick and their colleagues plan to investigate the role of various factors in determining the shape and migration rate of streams and how variables associated with climate change and land use might be expected to affect river form.

In addition, they hope to determine the conditions that allow meanders to form in permafrost absent vegetation, and on the lifeless surface of Mars.

“What’s cool is that meandering channels are all over Mars, and there’s no vegetation, so clearly the bank strength is coming from somewhere else, probably ice,” Braudrick said. “And the frozen surface of Titan has meanders. All these are vexing problems.”