Insects offer clues to climate variability 10,000 years ago

University of Illinois plant biology and geology professor Feng Sheng Hu collected core samples from Alaskan lakes. The abundance and diversity of midges buried in sediments offers a reliable record of temperature fluctuations over time. -  Feng Sheng Hu
University of Illinois plant biology and geology professor Feng Sheng Hu collected core samples from Alaskan lakes. The abundance and diversity of midges buried in sediments offers a reliable record of temperature fluctuations over time. – Feng Sheng Hu

An analysis of the remains of ancient midges – tiny non-biting insects closely related to mosquitoes – opens a new window on the past with a detailed view of the surprising regional variability that accompanied climate warming during the early Holocene epoch, 10,000 to 5,500 years ago.

Researchers at the University of Illinois and the University of British Columbia looked at the abundance and variety of midge larvae buried in lake sediments in Alaska. Midges are highly sensitive to summer temperatures, so changes in the abundance of different species over time gave the scientists a reliable marker of temperature fluctuations over the last 10,000 years.

Northern high latitudes are thought to have been warmer than today during the early Holocene, a time of heightened solar irradiation as a result of Earth’s axial tilt and orbit around the sun. The period is often referred to as the Holocene Thermal Maximum. Scientists hope to understand the ecological impacts of climate warming during that time to make better predictions about the effects of future warming. But several decades of research have yielded only ambiguous evidence of climate conditions in Alaska at that time.

The new analysis, conducted by University of Illinois doctoral student Benjamin Clegg with U. of I. plant biology and geology professor Feng Sheng Hu, who led the study, offers the first detailed record of temperature variation over the last 10,000 years in Alaska. The analysis reveals that the region was significantly cooler than expected during the early Holocene.

“This study shows that early Holocene warming did not occur everywhere in high latitudes, and exhibited important regional exceptions, even though the driving force behind it – solar input, in this case – was geographically uniform,” said Clegg, who is now a postdoctoral researcher in Hu’s lab.

The drivers of climate change during the early Holocene “were different than the greenhouse gases responsible for global warming today,” Clegg said. “So we should not expect to see exactly the same spatial patterns of temperature anomalies in the next few decades as during the early Holocene.”

The researchers hypothesize that solar warming during the early Holocene spurred atmospheric circulation patterns that contributed to extensive sea-ice off the Alaskan coast. That, and a treeless tundra over more of the land area than at present would have increased surface reflectivity, potentially contributing to the observed cooling, Clegg said.

“This study has important ecological and societal implications,” Hu said. “Nonlinear responses such as those identified here constitute a major source of potential climate ‘surprises’ that make it more difficult to anticipate and prepare for future regional climate scenarios.”

New sources found for accumulated dust on Chinese Loess Plateau

Geologists have long thought the loess-or fine silt-that accumulated on the Chinese Loess Plateau was carried on winds from desert regions to the northwest over the past 2.6 million years. New research indicates the loess may actually have come from due west, which would change conventional thinking about wind patterns during that period.

A team of geologists from the U.S. and China-led by the University of Rochester-compared the composition of uranium and lead in zircon crystals excavated from the Chinese Loess Plateau and potential source sites. The scientists found that the ages of the crystals from the Chinese Loess Plateau matched with samples from the northern Tibetan Plateau and the Qaidam Basin, both of which are due west.

The results have been published in a recent issue of the journal Geology.

“The data suggest a dramatic shift in atmospheric winds,” said lead author Alex Pullen.

By testing for the ages of the embedded zircon crystals, the researchers determined that the loess came from the west during recent glacial periods, which suggests that the atmospheric jet streams shifted equatorward during those periods. That would mean there have been alternating northwesterly and westerly sources for the loess during warm interglacial and cold glacial periods, respectively. The geological team says additional studies of ancient soil (paleosol) layers of the Chinese Loess Plateau are needed to test that theory.

“The research should help us better understand how the earth behaves as a system,” said Pullen. “With that knowledge, we’ll be able to improve our climate models.”

Evidence emerges of ancient lake in California’s Eel River

A catastrophic landslide 22,500 years ago dammed the upper reaches of northern California’s Eel River, forming a 30-mile-long lake which has since disappeared. It left a living legacy found today in the genes of the region’s steelhead trout.

Using remote-sensing technology known as airborne Light Detection and Ranging (LiDAR) and hand-held global-positioning-systems (GPS) units, scientists recently found evidence for a late Pleistocene, landslide-dammed lake along the river.

Today the Eel river is 200 miles long, carved into the ground from high in the California Coast Ranges to the river’s mouth in the Pacific Ocean in Humboldt County.

The evidence for the ancient landslide, which, scientists say, blocked the river with a 400-foot-wall of loose rock and debris, is detailed this week in a paper appearing on-line in the journal Proceedings of the National Academy of Sciences.


The research provides a rare glimpse into the geological history of this rapidly evolving mountainous region.

“This study reminds us that there are still significant surprises to be unearthed about past landscape dynamics and their broad impacts,” said Paul Cutler, program director in the National Science Foundation’s Division of Earth Sciences, which funded the research. “For example, it provides valuable information for assessing modern landslide hazard potential in this region.”

It also helps to explain emerging evidence from other studies that show a dramatic decrease in the amount of sediment deposited from the river in the ocean just offshore at about the same time period, says lead author of the paper Benjamin Mackey of the California Institute of Technology.

“Perhaps of most interest, the presence of this landslide dam also provides an explanation for the results of previous research on the genetics of steelhead trout in the Eel River,” Mackey said.

In that study, scientists found a striking relationship between two types of ocean-going steelhead in the river–a genetic similarity not seen among summer-run and winter-run steelhead in other nearby waterways.

An interbreeding of the two fish, in a process known as genetic introgression, may have occurred among the fish brought together while the river was dammed, Mackey said.

“The dam likely would have been impassable to the fish migrating upstream, meaning both ecotypes would have been forced to spawn and inadvertently breed downstream of the dam. This period of gene flow between the two types of steelhead can explain the genetic similarity observed today.”

Once the dam burst, the fish would have reoccupied their preferred spawning grounds and resumed different genetic trajectories.

“The damming of the river was a dramatic, punctuated event that greatly altered the landscape,” said co-author Joshua Roering, a geologist at the University of Oregon.

“Although current physical evidence for the landslide dam and ancient lake is subtle, its effects are recorded in the Pacific Ocean and persist in the genetic make-up of today’s Eel River steelhead,” said Roering. “It’s rare for scientists to be able to connect the dots between such diverse phenomena.”

The lake formed by the landslide, the researchers theorize, covered about 18 square miles.

After the dam was breached, the flow of water would have generated one of North America’s largest landslide-dam outburst floods.

Landslide activity and erosion have erased much of the evidence for the now-gone lake. Without the acquisition of LiDAR mapping, the lake’s existence may have never been discovered, the scientists said.

The area affected by the landslide-caused dam accounts for about 58 percent of the modern Eel River watershed. Based on today’s general erosion rates, the geologists believe that the lake could have filled in with sediment within about 600 years.

“The presence of a dam of this size was unexpected in the Eel River, given the abundance of easily eroded sandstone and mudstone, which are generally not considered strong enough to form long-lived dams,” Mackey said.

He and colleagues were drawn to the Eel River–among the most-studied erosion systems in the world–to study large, slow-moving landslides.

“While analyzing the elevation of terraces along the river, we discovered they clustered at a common elevation rather than decreased in elevation downstream paralleling the river profile, as would be expected for river terraces,” said Mackey.

“That was the first sign of something unusual, and it clued us into the possibility of an ancient lake.”

Exploring the last white spot on Earth

This computer-generated image shows the different layers of the Earth: The outer solid crust, the viscous upper and lower mantle, the liquid outer core, and the solid inner core. -  ESRF
This computer-generated image shows the different layers of the Earth: The outer solid crust, the viscous upper and lower mantle, the liquid outer core, and the solid inner core. – ESRF

Scientists will soon be exploring matter at temperatures and pressures so extreme it can only be produced for microseconds using powerful pulsed lasers. Matter in such states is present in the Earth’s liquid iron core, 2500 kilometers beneath the surface, and also in elusive “warm dense matter” inside large planets like Jupiter. A new X-ray beamline ID24 at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, allows a new quality of exploration of the last white spot on our globe: the center of the Earth.

We know surprisingly little about the interior of the Earth. The pressure at the center can be calculated accurately from the propagation of Earthquake waves, and it is about three and a half million times atmospheric pressure. The temperature at the center of the Earth, however, is unknown, but it is thought to be roughly as hot as the surface of the sun.

ID24, which was inaugurated today, opens new fields of science, being able to observe like in a time-lapse film sequence many rapid processes, whether laser-heating of iron to 10.000 degrees, charge reactions in new batteries or catalysts cleaning pollutants. It is the first of eight new beamlines built within the ESRF Upgrade Programme, a 180 million Euros investment over eight years to maintain the world-leading role of the ESRF. ID24 extends the existing capabilities at the ESRF in X-ray absorption spectroscopy to sample volumes twenty times smaller and time resolutions one thousand times better than in the past.

“Scientists can use several other synchrotrons notably in Japan and the U.S for fast X-ray absorption spectroscopy, but it is the microsecond time resolution for single shot acquisition (or experiments) coupled to the micron sized spot that makes ID24 unique worldwide,” says Sakura Pascarelli, beamline responsible scientist for ID24. “The rebuilt ID24 sets the ESRF apart, and even before the first users have arrived, I am asked to share our technology.”

The Earth’s interior is literally inaccessible and today it is easier to reach Mars than to visit even the base of the Earth’s thin crust. Scientists can however reproduce the extreme pressure and temperature of a planet’s interior in the laboratory, using diamond anvil cells to squeeze a material and once under pressure, heat it with short, intense laser pulses. However, these samples are not bigger than the size of a speck of dust and remain stable under high temperatures only for very short time, measured in microseconds.

Thanks to new technologies employed at ID24, scientists can now study what happens at extreme conditions, for example when materials undergo a fast chemical reaction or at what temperature a mineral will melt in the interior of a planet. Germanium micro strip detectors enable measurements to be made sequentially and very rapidly (a million in one second) in order not to miss any detail. A stable, microscopic X-ray beam means they can also be made in two dimensions by scanning across a sample to obtain a map instead of a measurement only at a single point. A powerful infrared spectrometer complements the X-ray detectors for the study of chemical reactions under industrial processing conditions.

Today, geologists want to know whether a chemical reaction exists between the Earth’s mostly liquid core and the rocky mantle surrounding it. They would like to know the melting temperature of materials other than iron that might be present in the Earth’s core in order to make better models for how the core — which produces the Earth’s magnetic field — works and to understand why the magnetic field changes over time and periodically in Earth’s history, has disappeared and reversed.

We know even less about warm dense matter believed to exist in the core of larger planets, for example Jupiter, which should be even hotter and denser. It can be produced in the laboratory using extremely powerful laser shock pulses compressing and heating a sample. The dream of revealing the secrets of the electronic and local structure in this state of matter with X-rays is now becoming reality, as ID24 allows to look at sample volumes 10000 times smaller than those at the high power laser facilities, making these experiments possible at the synchrotron using table top lasers.

The ID24 beamline works like an active probe rather than a passive detector, firing an intense beam of X-rays at a sample. It uses a technique called X-ray absorption spectroscopy where the way how atoms of a given chemical element absorb X-rays is studied in fine detail. From this data not only the abundance of an element can be deducted but also its chemical states and which other atoms, or elements, are in their immediate neighborhood, and how distant they are. In short, a complete picture at the atomic scale of the sample studied is obtained.

In the past weeks, ID24 has been tested with X-ray beams, and it will be open for users from across the world as of May 2012, after the ESRF winter shutdown 2011/12. The date for its inauguration was chosen to coincide with the autumn meeting of the ESRF’s Science Advisory Committee of external experts who played a key role in selecting the science case for ID24 and the other Upgrade Beamlines.

“ID24 opens unchartered territories of scientific exploration, as will the seven other beamlines of the ESRF Upgrade Programme. The economic crisis has hit our budgets hard, and it is not obvious to deliver new opportunities for research and industrial innovation under these circumstances”, says Harald Reichert, ESRF Director of Research. “I wish to congratulate the project team for extraordinary achievements, and I look forward to seeing some extraordinary new science.”

Trees on tundra’s border are growing faster in a hotter climate

Trees in Alaska's far north are growing faster than they were a hundred years ago says a study led by Lamont-Doherty scientist Laia Andreu-Hayles. -  Lamont-Doherty Earth Observatory
Trees in Alaska’s far north are growing faster than they were a hundred years ago says a study led by Lamont-Doherty scientist Laia Andreu-Hayles. – Lamont-Doherty Earth Observatory

Evergreen trees at the edge of Alaska’s tundra are growing faster, suggesting that at least some forests may be adapting to a rapidly warming climate, says a new study.

While forests elsewhere are thinning from wildfires, insect damage and droughts partially attributed to global warming, some white spruce trees in the far north of Alaska have grown more vigorously in the last hundred years, especially since 1950, the study has found. The health of forests globally is gaining attention, because trees are thought to absorb a third of all industrial carbon emissions, transferring carbon dioxide into soil and wood. The study, in the journal Environmental Research Letters, spans 1,000 years and bolsters the idea that far northern ecosystems may play a future role in the balance of planet-warming carbon dioxide that remains in the air. It also strengthens support for an alternative technique for teasing climate data from trees in the far north, sidestepping recent methodological objections from climate skeptics.

“I was expecting to see trees stressed from the warmer temperatures,” said study lead author Laia Andreu-Hayles, a tree ring scientist at Columbia University’s Lamont-Doherty Earth Observatory. “What we found was a surprise.”

Members of the Lamont Tree-Ring Lab have traveled repeatedly to Alaska, including the Arctic National Wildlife Refuge this past summer. In an area where the northern treeline gives way to open tundra, the scientists removed cores from living white spruces, as well as long-dead partially fossilized trees preserved under the cold conditions. In warm years, trees tend to produce wider, denser rings and in cool years, the rings are typically narrower and less dense. Using this basic idea and samples from a 2002 trip to the refuge, Andreu-Hayles and her colleagues assembled a climate timeline for Alaska’s Firth River region going back to the year 1067. They discovered that both tree-ring width and density shot up starting a hundred years ago, and rose even more after 1950. Their findings match a separate team’s study earlier this year that used satellite imagery and tree rings to also show that trees in this region are growing faster, but that survey extended only to 1982.

The added growth is happening as the arctic faces rapid warming. While global temperatures since the 1950s rose 1.6 degrees F, parts of the northern latitudes warmed 4 to 5 degrees F. “For the moment, warmer temperatures are helping the trees along the tundra,” said study coauthor Kevin Anchukaitis, a tree-ring scientist at Lamont. “It’s a fairly wet, fairly cool, site overall, so those longer growing seasons allow the trees to grow more.”

The outlook may be less favorable for the vast interior forests that ring the Arctic Circle. Satellite images have revealed swaths of brown, dying vegetation and a growing number of catastrophic wildfires in the last decade across parts of interior Alaska, Canada and Russia. Evidence suggests forests elsewhere are struggling, too. In the American West, bark beetles benefitting from milder winters have devastated millions of acres of trees weakened by lack of water. A 2009 study in the journal Science found that mortality rates in once healthy old-growth conifer forests have doubled in the past few decades. Heat and water stress are also affecting some tropical forests already threatened by clear-cutting for farming and development.

Another paper in Science recently estimated that the world’s 10 billion acres of forest are now absorbing about a third of carbon emissions, helping to limit carbon dioxide levels and keep the planet cooler than it would be otherwise.

There are already signs that the treeline is pushing north, and if this continues, northern ecosystems will change. Warming temperatures have benefitted not only white spruce, the dominant treeline species in northwestern North America, but also woody deciduous shrubs on the tundra, which have begun shading out other plants as they expand their range. As habitats change, scientists are asking whether insects, migratory songbirds, caribou and other animals that have evolved to exploit the tundra environment will adapt. “Some of these changes will be ecologically beneficial, but others may not,” said Natalie Boelman, an ecologist at Lamont-Doherty who is studying the effects of climate change in the Alaskan tundra.

In another finding, the study strengthens scientists’ ability to use tree rings to measure past climate. Since about 1950, tree ring widths in some northern locations have stopped varying in tandem with temperature, even though modern instruments confirm that temperatures are on a steady rise. As scientists looked for ways to get around the problem, critics of modern climate science dismissed the tree ring data as unreliable and accused scientists of cooking up tricks to support the theory of global warming. The accusations came to a head when stolen mails discussing the discrepancy between tree-ring records and actual temperatures came to light during the so-called “Climategate” episode of 2009-10.

The fact that temperatures were rising was never really in dispute among scientists, who had thermometers as well as tree rings to confirm the trend. But still scientists struggled with how to correct for the so-called “divergence problem.” The present study adds support for another proxy for tree growth: ring density. Trees tend to produce cells with thicker walls at the end of the growing season, forming a dark band of dense wood. While tree-ring width in some places stops correlating with temperature after 1950, possibly due to moisture stress or changes in seasonality due to warming, tree ring density at the site studied continues to track temperature.

“This is methodologically a big leap forward that will allow scientists to go back to sites sampled in the past and fill in the gaps,” said Glenn Juday, a forest ecologist at University of Alaska, Fairbanks, who was not involved in the study. The researchers plan to return to Alaska and other northern forest locations to improve geographical coverage and get more recent records from some sites. They are also investigating the use of stable isotopes to extract climate information from tree rings.

Pine Island Glacier: A scientific quest in Antarctica to determine what’s causing ice loss

This shows the convoy at Pine Island Glacier in Antarctica. -  National Science Foundation
This shows the convoy at Pine Island Glacier in Antarctica. – National Science Foundation

An international team of researchers, funded by the National Science Foundation (NSF) and NASA, will helicopter onto the Pine Island Glacier ice shelf, one of Antarctica’s most active, remote and harsh spots, in mid-December 2011 — weather permitting.

The project’s mission is to determine how much heat ocean currents deliver to the underside of the Pine Island Glacier as it discharges into the sea. Quantifying this heat and understanding how much melting it causes is key to developing reliable models to predict glacier acceleration and therefore predict how much ice will be delivered from land into the ocean thus contributing to sea level rise.

“Pine Island Glacier has begun to flow more rapidly, discharging more ice into the ocean, which could have a significant impact on global sea-level rise over the coming century,” said Scott Borg, director of the Division of Antarctic Sciences at the NSF. “This project, which aims to determine the underlying causes of this phenomenon, illustrates the fact that research conducted in Antarctica contributes to knowledge that benefits society in general.”

As manager of the United States Antarctic Program, NSF coordinates all U.S. research on the southernmost continent and the surrounding ocean.

The multidisciplinary group of scientists will use a combination of traditional tools and sophisticated new oceanographic instruments to measure the ocean cavity shape underneath the ice shelf and determine how streams of relatively warmer ocean water enter this cavity, move toward the very bottom of the glacier and melt its underbelly, causing it to release more than 19 cubic miles of ice into the ocean each year. If all goes as planned, the 13-person team will depart from McMurdo Station, the National Science Foundation’s logistics hub on Ross Island, in mid-December and spend six weeks on the ice shelf.

Facilitating this work is difficult–Pine Island Glacier is almost 1,400 miles (2,200 kilometers) from McMurdo Station–about the distance from Washington, D.C. to Bismarck, North Dakota. Everything needed to support the research and the scientists at this remote site has to be airlifted to the camp or transported by an overland traverse.

Extreme hazards–cold, harsh, stormy climate, as well as crevasses in the region present even further challenges. Transporting supplies and personnel to the site is a major undertaking and one that has taken several years to master.

Assessing and mitigating these hazards and obstacles has been a significant undertaking for NSF. The Pine Island Glacier research was initially supported as a centerpiece of NSF’s 2007-2009 International Polar Year (IPY) suite of projects.

NSF served as the lead agency for IPY, a coordinated deployment of researchers from more than 60 nations to the Arctic and Antarctic.

“The scale of a project required to comprehend the dynamics of something as large and complex as the forces acting on the Pine Island Glacier also emphasizes the increasing need for agencies such as NASA and NSF to collectively bring their expertise to bear on common goals. It also highlights the important work done by the nation’s colleges and universities with NSF support,” said Borg. “This is a major undertaking but it promises very interesting and very important results.”

International team to drill beneath massive Antarctic ice shelf

Robert Bindschadler, an emeritus glaciologist with NASA Goddard Space Flight Center, was the first person to ever walk on the Pine Island Glacier ice shelf, in January 2008. -  NASA
Robert Bindschadler, an emeritus glaciologist with NASA Goddard Space Flight Center, was the first person to ever walk on the Pine Island Glacier ice shelf, in January 2008. – NASA

An international team of researchers funded by NASA and the National Science Foundation (NSF) will travel next month to one of Antarctica’s most active, remote and harsh spots to determine how changes in the waters circulating under an active ice sheet are causing a glacier to accelerate and drain into the sea.

The science expedition will be the most extensive ever deployed to Pine Island Glacier. It is the area of the ice-covered continent that concerns scientists most because of its potential to cause a rapid rise in sea level. Satellite measurements have shown this area is losing ice and surrounding glaciers are thinning, raising the possibility the ice could flow rapidly out to sea.

The multidisciplinary group of 13 scientists, led by Robert Bindschadler, emeritus glaciologist of NASA’s Goddard Space Flight Center in Greenbelt, Md., will depart from the McMurdo Station in Antarctica in mid-December and spend six weeks on the ice shelf. During their stay, they will use a combination of traditional tools and sophisticated new oceanographic instruments to measure the shape of the cavity underneath the ice shelf and determine how streams of warm ocean water enter it, move toward the very bottom of the glacier and melt its underbelly.

“The project aims to determine the underlying causes behind why Pine Island Glacier has begun to flow more rapidly and discharge more ice into the ocean,” said Scott Borg, director of NSF’s Division of Antarctic Sciences, the group that coordinates all U.S. research in Antarctica. “This could have a significant impact on global sea-level rise over the coming century.”

Scientists have determined the interaction of winds, water and ice is driving ice loss from the floating glacier. Gusts of increasingly stronger westerly winds push cold surface waters away from the continent, allowing warmer waters that normally hover at depths below the continental shelf to rise. The upwelling warm waters spill over the border of the shelf and move along the sea floor, back to where the glacier rises from the bedrock and floats, causing it to melt.

The warm salty waters and fresh glacier melt water combine to make a lighter mixture that rises along the underside of the ice shelf and moves back to the open ocean, melting more ice on its way. How much more ice melts is what the team wants to find out, so it can improve projections of how the glacier will melt and contribute to sea-level rise.

In January 2008, Bindschadler was the first person to set foot on this isolated corner of Antarctica as part of initial reconnaissance for the expedition. Scientists had doubted it was even possible to reach the crevasse-ridden ice shelf. Bindschadler used satellite imagery to identify an area where helicopters could land safely to transport scientists and instrumentation to and from the ice shelf.

“The Pine Island Glacier ice shelf continues to be the place where the action is taking place in Antarctica,” Bindschadler said. “It only can be understood by making direct measurements, which is hard to do. We’re doing this hard science because it has to be done. The question of how and why it is melting is even more urgent than it was when we first proposed the project over five years ago.”

The team will use a hot water drill to make a hole through the ice shelf. After the drill hits the ocean, the scientists will send a camera down into the cavity to observe the underbelly of the ice shelf and analyze the seabed lying approximately 1,640 feet (500 meters) below the ice. Next the team will lower an instrument package provided by oceanographer Tim Stanton of the Naval Postgraduate School in Monterrey, Calif., into the hole. The primary instrument, called a profiler, will move up and down a cable attached to the seabed, measuring temperature, salinity and currents from approximately 10 feet (3 meters) below the ice to just above the seabed.

A second hole will support a similar instrument array fixed to a pole stuck to the underside of the ice shelf. This instrument will measure how ice and water exchange heat. The team also will insert a string of 16 temperature sensors in the lowermost ice to freeze inside and become part of the ice shelf. The sensors will measure how fast heat is transmitted upward through the ice when hot flushes of water enter the ocean cavity.

Sridhar Anandakrishnan, a geophysicist with Pennsylvania State University in University Park, Pa., will study the shape of the ocean cavity and the properties of the bedrock under the Pine Island Glacier ice shelf through a technique called reflective seismology, which involves generating waves of energy by detonating small explosions and banging the ice with instruments resembling sledgehammers. Measurements will be taken in about three dozen spots using helicopters to move from one place to another.



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Robert Bindschadler, an emeritus glaciologist with NASA Goddard Space Flight Center and leader of the Pine Island Glacier ice shelf project, describes the challenges and frustrations of trying to do science in Antarctica, in an interview filmed in 2009. – Credit: NASA/Goddard/Scientific Visualization Studio.

Methane may be answer to 56-million-year question

The release of massive amounts of carbon from methane hydrate frozen under the seafloor 56 million years ago has been linked to the greatest change in global climate since a dinosaur-killing asteroid presumably hit Earth 9 million years earlier. New calculations by researchers at Rice University show that this long-controversial scenario is quite possible.

Nobody knows for sure what started the incident, but there’s no doubt Earth’s temperature rose by as much as 6 degrees Celsius. That affected the planet for up to 150,000 years, until excess carbon in the oceans and atmosphere was reabsorbed into sediment.

Earth’s ecosystem changed and many species went extinct during the Paleocene-Eocene Thermal Maximum (PETM) 56 million years ago, when at least 2,500 gigatonnes of carbon, eventually in the form of carbon dioxide, were released into the ocean and atmosphere. (The era is described in great detail in a recent National Geographic feature.)

A new report by Rice scientists in Nature Geoscience suggests that at the time, even though methane-containing gas hydrates – the “ice that burns” – occupied only a small zone of sediment under the seabed before the PETM, there could have been as much stored then as there is now.

This is a concern to those who believe the continued burning of fossil fuels by humans could someday trigger another feedback loop that disturbs the stability of methane hydrate under the ocean and in permafrost; this change could warm the atmosphere and prompt the release of large amounts of methane, a more powerful greenhouse gas than carbon dioxide.

Some who study the PETM blame the worldwide burning of peat, volcanic activity or a massive asteroid strike as the source of the carbon, “but there’s no crater, or any soot or evidence of the burning of peat,” said Gerald Dickens, a Rice professor of Earth science and an author of the study, who thinks the new paper bolsters the argument for hydrates.

The lead author is graduate student Guangsheng Gu; co-authors are Walter Chapman, the William W. Akers Professor in Chemical Engineering; George Hirasaki, the A.J. Hartsook Professor in Chemical Engineering; and alumnus Gaurav Bhatnagar, all of Rice; and Frederick Colwell, a professor of ocean ecology and biogeochemistry at Oregon State University.

In the ocean, organisms die, sink into the sediment and decompose into methane. Under high pressure and low temperatures, methane molecules are trapped by water, which freezes into a slushy substance known as gas hydrate that stabilizes in a narrow band under the seafloor.

Warmer oceans before the PETM would have made the stability zone for gas hydrate thinner than today, and some scientists have argued this would allow for much less hydrate than exists under the seafloor now. “If the volume – the size of the box – was less than today, how could it have released so much carbon?” Dickens asked. “Gu’s solution is that the box contains a greater fraction of hydrate.”

“The critics said, ‘No, this can’t be. It’s warmer; there couldn’t have been more methane hydrate,'” Hirasaki said. “But we applied the numerical model and found that if the oceans were warmer, they would contain less dissolved oxygen and the kinetics for methane formation would have been faster.”

With less oxygen to consume organic matter on the way down, more sank to the ocean floor, Gu said, and there, with seafloor temperatures higher than they are today, microbes that turn organic matter into methane work faster. “Heat speeds things up,” Dickens said. “It’s true for almost all microbial reactions. That’s why we have refrigerators.”

The result is that a stability zone smaller than what exists now may have held a similar amount of methane hydrate. “You’re increasing the feedstock, processing it faster and packing it in over what could have been millions of years,” Dickens said.

While the event that began the carbon-discharge cycle remains a mystery, the implications are clear, Dickens said. “I’ve always thought of (the hydrate layer) as being like a capacitor in a circuit. It charges slowly and can release fast – and warming is the trigger. It’s possible that’s happening right now.”

That makes it important to understand what occurred in the PETM, he said. “The amount of carbon released then is on the magnitude of what humans will add to the cycle by the end of, say, 2500. Compared to the geological timescale, that’s almost instant.”

“We run the risk of reproducing that big carbon-discharge event, but faster, by burning fossil fuel, and it may be severe if hydrate dissociation is triggered again,” Gu said, adding that methane hydrate also offers the potential to become a valuable source of clean energy, as burning methane emits much less carbon dioxide than other fossil fuels.

The calculations should encourage geologists who discounted hydrates’ impact during the PETM to keep an open mind, Dickens said. “Instead of saying, ‘No, this cannot be,’ we’re saying, ‘Yes, it’s certainly possible.'”

Building a full-scale model of a trapped oil reservoir in a laboratory

Getting trapped oil out of porous layers of sandstone and limestone is a tricky and costly operation for energy exploration companies the world over. But now, University of Alberta researchers have developed a way to replicate oil-trapping rock layers in a laboratory and show energy producers the best way to recover every last bit of oil from these reservoirs.

Mechanical engineering professor Sushanta Mitra led a research team that uses core samples from oil drilling sites to make 3-D mathematical models of the porous rock formations that can trap huge quantities of valuable oil.

The process starts with a tiny chip of rock from a core sample where oil has become trapped, That slice of rock is scanned by a Focused Ion Beam-Scanning Electron Microscopy machine, which produces a 3-D copy of the porous rock. The replica is made of a thin layer of silicon and quartz at Nanofab, the U of A’s micro/nanofabrication facility.

The researchers call the finished product a “reservoir on a chip”, or ROC.

The hugely expensive process of recovering oil in the field is recreated right in our laboratory.. The researchers soak the ROC in oil and then water, which is under pressure, is forced into the chip to see how much oil can be pushed through the microscopic channels and recovered.

ROC replicas can be made from core samples from oil-trapping rock anywhere in the world. “Oil exploration companies will be able to use ROC technology to determine what concentration of water and chemicals they’ll need to pump into layers of sandstone or limestone to maximize oil recovery,” said Mitra.

UA scientists find evidence of Roman period megadrought

Dendrochronologists extract a small, pencil-shaped sample of wood from a tree with a tool called an increment borer. The tiny hole left in the tree's trunk quickly heals as the tree continues to grow. -  Daniel Griffin/Laboratory of Tree-Ring Research
Dendrochronologists extract a small, pencil-shaped sample of wood from a tree with a tool called an increment borer. The tiny hole left in the tree’s trunk quickly heals as the tree continues to grow. – Daniel Griffin/Laboratory of Tree-Ring Research

Almost nine hundred years ago, in the mid-12th century, the southwestern U.S. was in the middle of a multi-decade megadrought. It was the most recent extended period of severe drought known for this region. But it was not the first.

The second century A.D. saw an extended dry period of more than 100 years characterized by a multi-decade drought lasting nearly 50 years, says a new study from scientists at the University of Arizona.

UA geoscientists Cody Routson, Connie Woodhouse and Jonathan Overpeck conducted a study of the southern San Juan Mountains in south-central Colorado. The region serves as a primary drainage site for the Rio Grande and San Juan rivers.

“These mountains are very important for both the San Juan River and the Rio Grande River,” said Routson, a doctoral candidate in the environmental studies laboratory of the UA’s department of geosciences and the primary author of the study, which is upcoming in Geophysical Research Letters.

The San Juan River is a tributary for the Colorado River, meaning any climate changes that affect the San Juan drainage also likely would affect the Colorado River and its watershed. Said Routson: “We wanted to develop as long a record as possible for that region.”

Dendrochronology is a precise science of using annual growth rings of trees to understand climate in the past. Because trees add a normally clearly defined growth ring around their trunk each year, counting the rings backwards from a tree’s bark allows scientists to determine not only the age of the tree, but which years were good for growth and which years were more difficult.

“If it’s a wet year, they grow a wide ring, and if it’s a dry year, they grow a narrow ring,” said Routson. “If you average that pattern across trees in a region you can develop a chronology that shows what years were drier or wetter for that particular region.”

Darker wood, referred to as latewood because it develops in the latter part of the year at the end of the growing season, forms a usually distinct boundary between one ring and the next. The latewood is darker because growth at the end of the growing season has slowed and the cells are more compact.

To develop their chronology, the researchers looked for indications of climate in the past in the growth rings of the oldest trees in the southern San Juan region. “We drove around and looked for old trees,” said Routson.

Literally nothing is older than a bristlecone pine tree: The oldest and longest-living species on the planet, these pine trees normally are found clinging to bare rocky landscapes of alpine or near-alpine mountain slopes. The trees, the oldest of which are more than 4,000 years old, are capable of withstanding extreme drought conditions.

“We did a lot of hiking and found a couple of sites of bristlecone pines, and one in particular that we honed in on,” said Routson.

To sample the trees without damaging them, the dendrochronologists used a tool like a metal screw that bores a tiny hole in the trunk of the tree and allows them to extract a sample, called a core. “We take a piece of wood about the size and shape of a pencil from the tree,” explained Routson.

“We also sampled dead wood that was lying about the land. We took our samples back to the lab where we used a visual, graphic technique to match where the annual growth patterns of the living trees overlap with the patterns in the dead wood. Once we have the pattern matched we measure the rings and average these values to generate a site chronology.”

“In our chronology for the south San Juan mountains we created a record that extends back 2,200 years,” said Routson. “It was pretty profound that we were able to get back that far.”

The chronology extends many years earlier than the medieval period, during which two major drought events in that region already were known from previous chronologies.

“The medieval period extends roughly from 800 to 1300 A.D.,” said Routson. “During that period there was a lot of evidence from previous studies for increased aridity, in particular two major droughts: one in the middle of the 12th century, and one at the end of the 13th century.”

“Very few records are long enough to assess the global conditions associated with these two periods of Southwestern aridity,” said Routson. “And the available records have uncertainties.”

But the chronology from the San Juan bristlecone pines showed something completely new:

“There was another period of increased aridity even earlier,” said Routson. “This new record shows that in addition to known droughts from the medieval period, there is also evidence for an earlier megadrought during the second century A.D.”

“What we can see from our record is that it was a period of basically 50 consecutive years of below-average growth,” said Routson. “And that’s within a much broader period that extends from around 124 A.D. to 210 A.D. – about a 100-year-long period of dry conditions.”

“We’re showing that there are multiple extreme drought events that happened during our past in this region,” said Routson. “These megadroughts lasted for decades, which is much longer than our current drought. And the climatic events behind these previous dry periods are really similar to what we’re experiencing today.”

The prolonged drought in the 12th century and the newly discovered event in the second century A.D. may both have been influenced by warmer-than-average Northern Hemisphere temperatures, Routson said: “The limited records indicate there may have been similar La Nina-like background conditions in the tropical Pacific Ocean, which are known to influence modern drought, during the two periods.”

Although natural climate variation has led to extended dry periods in the southwestern U.S. in the past, there is reason to believe that human-driven climate change will increase the frequency of extreme droughts in the future, said Routson. In other words, we should expect similar multi-decade droughts in a future predicted to be even warmer than the past.