郑少群博客: 四月 2015

2015年4月30日星期四

Eagle Nebula: The Pillars of Creation revealed in 3-D -- ScienceDaily

The original NASA/ESA Hubble Space Telescope image of the famous Pillars of Creation was taken two decades ago and immediately became one of its most famous and evocative pictures. Since then, these billowing clouds, which extend over a few light-years,* have awed scientists and the public alike.

The jutting structures, along with the nearby star cluster, NGC 6611, are parts of a star formation region called the Eagle Nebula, also known as Messier 16 or M16. The nebula and its associated objects are located about 7000 light-years away in the constellation of Serpens (The Serpent).

The Pillars of Creation are a classic example of the column-like shapes that develop in the giant clouds of gas and dust that are the birthplaces of new stars. The columns arise when immense, freshly formed blue-white O and B stars give off intense ultraviolet radiation and stellar winds that blow away less dense materials from their vicinity.

Denser pockets of gas and dust, however, can resist this erosion for longer. Behind such thicker dust pockets, material is shielded from the harsh, withering glare of O and B stars. This shielding creates dark "tails" or "elephant trunks," which we see as the dusky body of a pillar, that point away from the brilliant stars.

ESO's MUSE instrument on the Very Large Telescope has now helped illustrate the ongoing evaporation of the Pillars of Creation in unprecedented detail, revealing their orientation.

MUSE has shown that the tip of the left pillar is facing us, atop a pillar that is is actually situated behind NGC 6611, unlike the other pillars. This tip is bearing the brunt of the radiation from NGC 6611's stars, and as a result looks brighter to our eyes than the bottom left, middle and right pillars, whose tips are all pointed away from our view.

Astronomers hope to better understand how young O and B stars like those in NGC 6611 influence the formation of subsequent stars. Numerous studies have identified protostars forming in these clouds -- they are indeed Pillars of Creation. The new study also reports fresh evidence for two gestating stars in the left and middle pillars as well as a jet from a young star that had escaped attention up to now.

For more stars to form in environments like the Pillars of Creation, it is a race against time as intense radiation from the powerful stars that are already shining continues to grind away at the pillars.

By measuring the Pillars of Creation's rate of evaporation, MUSE has given astronomers a time frame for when the pillars will be no more. They shed about 70 times the mass of the Sun every million years or so. Based on the their present mass of about 200 times that of the Sun, the Pillars of Creation have an expected lifetime of perhaps three million more years -- an eyeblink in cosmic time. It seems that an equally apt name for these iconic cosmic columns might be the Pillars of Destruction.

* The left pillar, considered as a complete object from top to bottom, is estimated to be about four light-years in length. It is the longest pillar and about twice the height of the right pillar.

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Challenging work tasks may have an upside for the brain -- ScienceDaily

"Our study is important because it suggests that the type of work you do throughout your career may have even more significance on your brain health than your education does," said study author Francisca S. Then, PhD, with the University of Leipzig in Germany. "Education is a well-known factor that influences dementia risk."

For the study, 1,054 people over the age of 75 were given tests that measured their memory and thinking abilities every one-and-a-half years for eight years.

The researchers also asked the participants about their work history and categorized the tasks they completed into three groups: executive, verbal and fluid. Examples of executive tasks are scheduling work and activities, developing strategies and resolving conflicts. Examples of verbal tasks are evaluating and interpreting information and fluid tasks were considered to be those which included selective attention and analyzing data.

Memory and thinking abilities were examined through a clinical test, the Mini-Mental State Examination (MMSE). In this clinical test, a small decline in points can indicate a clinically relevant deficit.

The study found that people whose careers included the highest level of all three types of tasks scored highest on the thinking and memory tests by two MMSE points over people with the lowest level.

People with the highest level of all three types of tasks also had the slowest rate of cognitive decline. Over eight years, their rate of decline was half the rate of participants with a low level of mentally demanding work tasks. Among the three types of work tasks, high levels of executive and verbal tasks were distinctively associated with slower rates of memory and thinking decline.

Participants with a high level of executive tasks scored two MMSE points higher on memory and thinking tests at the beginning of the study and five MMSE points higher after eight years in the study compared to participants with a low level of these tasks. Participants with a high level of verbal tasks declined an average two MMSE points less than those with a low level.

"Challenges at work may indeed be a positive element, if they build up a person's mental reserve in the long-term," said Then.

The study was supported by the Interdisciplinary Center for Clinical Research of the University of Leipzig and the LIFE Leipzig Research Center for Civilization Diseases at the Leipzig University, Germany, which is funded by means of the European Social Fund and the Free State of Saxony.

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How babies' lives were saved by 3-D printing -- ScienceDaily

Three babies all had the same life-threatening condition: a terminal form of tracheobronchomalacia, which causes the windpipe to periodically collapse and prevents normal breathing. There was no cure and life-expectancies were grim.

The three boys became the first in the world to benefit from groundbreaking 3D printed devices that helped keep their airways open, restored their breathing and saved their lives at the University of Michigan's C.S. Mott Children's Hospital. Researchers have closely followed their cases to see how well the bioresorable splints implanted in all three patients have worked, publishing the promising results in today's issue of Science Translational Medicine.

"These cases broke new ground for us because we were able to use 3D printing to design a device that successfully restored patients' breathing through a procedure that had never been done before," says senior author Glenn Green, M.D., associate professor of pediatric otolaryngology at C.S. Mott Children's Hospital.

"Before this procedure, babies with severe tracheobronchomalacia had little chance of surviving. Today, our first patient Kaiba is an active, healthy 3-year-old in preschool with a bright future. The device worked better than we could have ever imagined. We have been able to successfully replicate this procedure and have been watching patients closely to see whether the device is doing what it was intended to do. We found that this treatment continues to prove to be a promising option for children facing this life-threatening condition that has no cure."

The findings reported today suggest that early treatment of tracheobronchomalacia may prevent complications of conventional treatment such as a tracheostomy, prolonged hospitalization, mechanical ventilation, cardiac and respiratory arrest, food malabsorption and discomfort. None of the devices, which were implanted in then 3-month-old Kaiba, 5-month-old Ian and 16-month-old Garrett have caused any complications.

The findings also show that the patients were able to come off of ventilators and no longer needed paralytics, narcotics and sedation. Researchers noted improvements in multiple organ systems. Patients were relieved of immunodeficiency-causing proteins that prevented them from absorbing food so that they no longer needed intravenous therapy.

Kaiba Gionfriddo made national headlines after he became the first patient to benefit from the procedure in 2012, and the procedure was repeated with Garrett Peterson and Ian Orbich. Using 3D printing, Green and his colleague Scott Hollister, Ph.D., professor of biomedical engineering and mechanical engineering and associate professor of surgery at U-M, were able to create and implant customized tracheal splints for each patient. The device was created directly from CT scans of their tracheas, integrating an image-based computer model with laser-based 3D printing to produce the splint.

The specially- designed splints were placed in the three patients at C.S. Mott Children's Hospital. The splint was sewn around their airways to expand the trachea and bronchus and give it a skeleton to aid proper growth. The splint is designed to be reabsorbed by the body over time. The growth of the airways were followed with CT and MRI scans, and the device was shown to open up to allow airway growth for all three patients.

Doctors received emergency clearance from the FDA to do the procedures.

"We were pleased to find that all of our cases so far have proven to improve these patients' lives," Green says. "The potential of 3D-printed medical devices to improve outcomes for patients is clear, but we need more data to implement this procedure in medical practice."

Authors say the recent report was not designed for device safety and that rare potential complications of the therapy may not yet be evident. However, Richard G. Ohye, M.D., head of pediatric cardiovascular surgery at C.S. Mott who performed the surgeries, says the cases provide the groundwork to potentially explore a clinical trial that could help other children with less-severe forms of tracheobronchomalacia in the future.

Kaiba, now a curious, active 3-year-old who loves playing with his siblings and who recently saw his favorite character Mickey Mouse at Disney World thanks to the Make-a-Wish Foundation, was back at Mott in April for a follow-up appointment.

The splint is dissolving just how it's supposed to and doctors expect that eventually, his trachea will reflect that of his peers with no signs of the tracheobronchomalacia that nearly killed him as a newborn.

"The first time he was hospitalized, doctors told us he may not make it out," Kaiba's mom April Gionfriddo remembers. "It was scary knowing he was the first child to ever have this procedure, but it was our only choice and it saved his life."

Now an energetic 2-and-a-half-year-old with a contagious laugh, Garrett is able to breathe on his own and spend his days ventilator-free. Ian, now 17 months old, is known for his huge grins, enthusiastic high fives and love for playing with his big brother, Owen. Ian had the splint procedure done at Mott exactly one year ago this month.

"We were honestly terrified, just hoping that we were making the right decision," his mother Meghan Orbich remembers. "I am thankful every single day that this splint was developed. It has meant our son's life. I am certain that if we hadn't had the opportunity to bring Ian to Mott, he would not be here with us today."

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Making robots more human: Wearable sensors read human facial expressions -- ScienceDaily

Nae-Eung Lee and colleagues note that one way to make interactions between people and robots more intuitive would be to endow machines with the ability to read their users' emotions and respond with a computer version of empathy. Most current efforts toward this goal analyze a person's feelings using visual sensors that can tell a smile from a frown, for example. But these systems are expensive, highly complex and don't pick up on subtle eye movements, which are important in human expression. Lee's team wanted to make simple, low-cost sensors to detect facial movements, including slight changes in gaze.

The researchers created a stretchable and transparent sensor by layering a carbon nanotube film on two different kinds of electrically conductive elastomers. They found it could tell whether subjects were laughing or crying and where they were looking. In addition to applications in robotics, the sensors could be used to monitor heartbeats, breathing, dysphagia (difficulty swallowing) and other health-related cues.

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Artificial photosynthesis could help make fuels, plastics and medicine -- ScienceDaily

Peidong Yang, Michelle C. Y. Chang, Christopher J. Chang and colleagues note that plants use photosynthesis to convert sunlight, water and carbon dioxide to make their own fuel in the form of carbohydrates. Globally, this natural process harvests 130 Terawatts of solar energy. If scientists could figure out how to harness just a fraction of that amount to make fuels and power industrial processes, they could dramatically cut our reliance on fossil fuels. So, Yang, Michelle Chang and Christopher Chang's teams wanted to contribute to these efforts.

The groups developed a stand-alone, nanowire array that captures light and with the help of bacteria, converts carbon dioxide into acetate. The bacteria directly interact with light-absorbing materials, which the researchers say is the first example of "microbial photoelectrosynthesis." Another kind of bacteria then transforms the acetate into chemical precursors that can be used to make a wide range of everyday products from antibiotics to paints.

The authors acknowledge funding from the U.S. Department of Energy, the Lawrence Berkeley National Laboratory, Howard Hughes Medical Institute, the National Science Foundation and the National Institutes of Health.

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A smartphone with ultimate macro feature: DNA-scanning fluorescent microscope -- ScienceDaily

"A single DNA molecule, once stretched, is about two nanometers in width," said Aydogan Ozcan, HHMI Chancellor Professor, UCLA. "For perspective, that makes DNA about 50,000 times thinner than a human hair. Currently, imaging single DNA molecules requires bulky, expensive optical microscopy tools, which are mostly confined to advanced laboratory settings. In comparison, the components for my device are significantly less expensive."

Enter Ozcan's smartphone attachment -- an external lens, thin-film interference filter, miniature dovetail stage mount for making fine alignments, and a laser diode, all enclosed in a small, 3D-printed case and integrated to act just like a fluorescence microscope.

Although other smart-phone-turned-microscopes can image larger scale objects such as cells, Ozcan's group's latest mobile-phone optical attachment is the first to image and size the slim strand of a single DNA molecule.

The device is intended for use in remote laboratory settings to diagnose various types of cancers and nervous system disorders, such as Alzheimer's, as well as detect drug resistance in infectious diseases. To use the camera it is necessary to first isolate and label the desired DNA with fluorescent tags. Ozcan says such laboratory procedures are possible even in remote locations and resource-limited settings.

To scan the DNA, the group developed a computational interface and Windows smart application running on the same smart phone. The scanned information is then sent to a remote server in Ozcan's laboratory, which measures the length of the DNA molecules. Assuming you have a reliable data connection, the entire data processing takes less than 10 seconds.

In their lab, Ozcan's group tested the device's accuracy by imaging fluorescently labeled and stretched DNA segments. It reliably sized DNA segments of 10,000 base pairs or longer. (A base pair is the basic structural unit of DNA.) Many important genes fall in this size range, including a bacterial gene notorious for giving Staphylococcus aureus and other bacteria antibiotic resistance that is about 14,000 base pairs long.

The smartphone microscope demonstrated a significant drop in accuracy for 5,000 base-pair or shorter segments, however, due to the reduced detection signal-to-noise ratio and contrast for such short fragments. The problem could easily be remedied by replacing the device's current lens with one of a higher numerical aperture, Ozcan said.

In addition to its use in point-of-care diagnostics, Ozcan proposes that his platform could also be useful for differentiating high molecular weight DNA fragments, which are problematic for conventional gel electrophoresis, a frequently used technique in biochemistry and molecular biology to size DNA and RNA fragments. Ozcan's group next plans to test their device in the field to detect the presence of malaria-related drug resistance.

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Sun's blistering heat: Strong evidence for coronal heating theory -- ScienceDaily

Clear evidence now suggests that the heating mechanism depends on regular, but intermittent explosive bursts of heat, rather than on continuous gradual heating. This solution to the coronal heating mystery was presented in a media briefing on April 28, 2015, at the Triennial Earth-Sun Summit, or TESS, meeting in Indianapolis, Indiana.

This is the inaugural meeting for TESS, which is a first of its kind: uniting the various research groups that study the sun-Earth connection from explosions on the sun to their effects near our home planet and all the way out to the edges of the solar system - a research field collectively known as heliophysics. The overarching goal is to share techniques across disciplines and encourage interdisciplinary collaboration on outstanding heliophysics questions.

The coronal heating mystery is one such outstanding question. Four scientists spoke at the media briefing.

Jim Klimchuk, a solar scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, explained that the new evidence supports a theory that the sun's corona is heated by tiny explosions called nanoflares. These are impulsive heating bursts that individually reach incredibly hot temperatures of some 10 million Kelvins or 18 million degrees Fahrenheit - even greater than the average temperature of the corona - and provide heat to the atmosphere. The research evidence presented by the panel spotted this super hot solar material, called plasma, representative of a nanoflare.

"The explosions are called nanoflares because they have one-billionth the energy of a regular flare," said Klimchuk. "Despite being tiny by solar standards, each packs the wallop of a 10 megaton hydrogen bomb. Millions of them are going off every second across the sun, and collectively they heat the corona."

The first evidence of the presence of this super hot plasma was presented by Adrian Daw, a solar scientist at Goddard and principal investigator of the Extreme Ultraviolet Normal Incidence Spectrograph, or EUNIS, sounding rocket mission. EUNIS flew on a 15-minute flight in December 2013 equipped with an instrument called a spectrograph, which can gather information about how much material is present at a given temperature. The EUNIS spectrograph was tuned into a range of wavelengths useful for spotting material at temperatures of 18 million F, the temperatures that signify nanoflares. The spectrograph unambiguously spotted this extremely hot material in active regions that visibly appeared to be quiet. In a quiet region, such hot temperatures clearly weren't due to a large explosive solar flare, and so are a smoking gun that something otherwise unobservable was heating up this area.

Daw also reported the results from another experiment launched on sounding rockets in 2012 and 2013 that imaged soft X-rays from the corona. These results, too, confirmed the presence of super hot plasma on the sun.

Iain Hannah, an astrophysicist at the University of Glasgow in Scotland, spoke about NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, which typically examines X-rays from distant stars and black holes. However, it is also capable of observing the much brighter light of the sun - something most astronomical observatories can't do.

"X-rays are a direct probe into the high-energy processes of the sun," said Hannah.

NuSTAR saw X-rays that are signatures of super hot plasma in non-flaring active regions. While the sounding rocket experiments observed the energy produced by these nanoflares, NuSTAR is also able to look for the X-ray signatures of energetic particles. Understanding what and how particles are accelerated out from these smaller nanoflare explosions can help scientists understand what processes create them.

Stephen Bradshaw, a solar astrophysicist at Rice University in Houston, Texas, was the last speaker. Bradshaw used a sophisticated computational model to demonstrate why spotting signatures of the nanoflares has been so difficult and how the new evidence will help researchers go forward to improve theories on the details of coronal heating - one day allowing heliophysics researchers to at last solve the coronal heating mystery.

The TESS meeting will occur every three years and is a joint meeting of the Space Physics and Aeronomy Section of the American Geophysical Union and the Solar Physics Division of the American Astronomical Society.

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Oil and gas development transforms landscapes -- ScienceDaily

But what are the ecological consequences of this accelerated drilling activity? Researchers at the University of Montana have conducted the first-ever broad-scale scientific assessment of how oil and gas development transforms landscapes across the U.S. and Canada.

Their work was published April 24 in an article titled "Ecosystem services lost to oil and gas in North America" in Science. The article concludes that oil and gas development creates significant vegetation loss of rangelands and croplands across broad swaths of central North America.

Lead author Brady Allred said, "There are two important things here: First, we examine all of central North America, from the south coast of Texas to northern Alberta. When we look at this continental scale picture, we see impacts and degradation that are missed when focusing only at a local scale. Second, we see how present policies may potentially compromise future ecosystem integrity over vast areas."

Allred and co-authors estimated that from 2000 to 2012 oil and gas development removed large amounts of rangeland vegetation, culminating at a rate per year of more than half of the annual grazing on U.S. public lands. Vegetation removed by this development on croplands is equivalent to 120.2 million bushels of wheat, approximately 13 percent of all wheat exported by the U.S. in 2013.

Fragmentation and loss of habitat also disrupts wildlife migration routes, alters wildlife behavior and assists new disruptive invasive plant species. Co-author Dave Naugle highlights the complexity of the issue: "We've known about the impacts of oil and gas development for years, but we now have scientific data from a broad regional scale that tells us we need to act now to balance these competing land uses."

Furthermore, nearly half of wells drilled are in extreme- or high-water-stress regions. High-volume hydraulic fracturing uses 2 million to 13 million gallons of water per well, intensifying competition among agriculture, aquatic ecosystems and municipalities for water resources.

"We need a policy framework that quantifies and weighs major tradeoffs at large scales because current policy does not address both assessment and future mitigation adequately," said co-author Julia Haggerty of Montana State University.

"Satellite technologies now can provide annual acre-by-acre information for land managers on oil-and-gas-driven land-use changes," said Steve Running, a co-author and UM Regents Professor of Ecology. "We must have policies that ensure reclamation of this land after production has ended. Otherwise, by 2050, tens of millions of acres of land will be permanently degraded."

The authors assessed the ecosystem services lost by using high-resolution satellite measurements of vegetation growth based on methods developed by co-author W. Kolby Smith and previous groundbreaking research by Running. Terrestrial plant production is the foundation of the biospheric carbon cycle and the basis for a multitude of critical ecosystem services.

Allred is assistant professor of rangeland ecology at UM's College of Forestry and Conservation. Additional co-authors are W. Kolby Smith, a recent UM doctoral student now at the Institute on the Environment at the University of Minnesota; Dirac Twidwell from the University of Nebraska-Lincoln; and Samuel Fuhlendorf from Oklahoma State University.

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Brain circuitry for positive vs. negative memories discovered in mice -- ScienceDaily

"This study exemplifies the power of new molecular tools that can push and pull on the same circuit to see what drives behavior," explained Thomas R. Insel, M.D., director of NIH's National Institute of Mental Health (NIMH). "Improved understanding of how such emotional memory works holds promise for solving mysteries of brain circuit disorders in which these mechanisms are disrupted."

NIMH grantee Kay Tye, Ph.D., Praneeth Namburi and Anna Beyeler, Ph.D., of the Massachusetts Institute of Technology (MIT), Cambridge MA, and colleagues, report their findings April 29, 2015 in the journal Nature.

Prior to the new study, scientists suspected involvement of the circuits ultimately implicated, but were stumped by a seeming paradox. A crossroads of convergent circuits in an emotion hub deep in the brain, the basolateral amygdala, seem to be involved in both fear and reward learning, but how one brain region could orchestrate such opposing behaviors -- approach and avoidance -- remained an enigma. How might signals find the appropriate path to follow at this fork in the road?

To find out, Tye and colleagues explored whether two suspect circuit projections from the crossroads might hold clues. One projects to a reward center, the nucleus accumbens, and the other to a nearby fear center, the centromedial amygdala, the output station of the emotion hub.

Each circuit projection is composed of separate populations of intertwined neurons. The researchers first used telltale fluorescent bead tracers to sort out which neurons belonged to each circuit. They then measured an indicator of connectivity -- the strength of neural connections -- in the projections, after mice underwent fear or reward learning. Animals were trained to either fear a tone paired with a shock or to associate the tone with a sugar reward.

Strikingly, crossroads connectivity to reward center projections decreased after fear learning and increased with reward learning. By contrast, connectivity to fear center projections increased with fear learning and decreased after reward learning.

These converging mechanisms in anatomically intertwined circuits could hold clues to teasing apart how positive and negative emotional associations may influence each other, Tye suggested.

To prove a causal link between the projection-identified circuits and behavior, Tye's team turned to optogenetics, which enables light pulses to control brain circuitry in animals genetically engineered to be light-responsive. Optically stimulating the reward center projection enhanced positive reinforcement, while stimulating the fear center projection promoted negative reinforcement. Similarly, blocking the fear center projection impaired fear learning and enhanced reward learning.

Finally, the researchers pinpointed defining electrophysiological, anatomic and genetic features of the two circuits that help to explain the opposite connectivity responses.

"Given that many mental health problems, including anxiety, addiction, and depression, may arise from perturbations in emotional processing, these findings could help to pave the way to a circuit-based approach to treating mental illness," said Tye.

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200-year lag between climate events in Greenland, Antarctica: Ocean involved -- ScienceDaily

Greenland climate during the last ice age was very unstable, the researchers say, characterized by a number of large, abrupt changes in mean annual temperature that each occurred within several decades. These so-called "Dansgaard-Oeschger events" took place every few thousand years during the last ice age. Temperature changes in Antarctica showed an opposite pattern, with Antarctica cooling when Greenland was warm, and vice versa.

In this study funded by the National Science Foundation and published this week in the journal Nature, the researchers discovered that the abrupt climates changes show up first in Greenland, with the response to the Antarctic climate delayed by about 200 years. The researchers documented 18 abrupt climate events during the past 68,000 years.

"The fact that temperature changes are opposite at the two poles suggests that there is a redistribution of heat going on between the hemispheres," said Christo Buizert, a post-doctoral research at Oregon State University and lead author on the study. "We still don't know what caused these past shifts, but understanding their timing gives us important clues about the underlying mechanisms.

"The 200-year lag that we observe certainly hints at an oceanic mechanism," Buizert added. "If the climatic changes were propagated by the atmosphere, the Antarctic response would have occurred in a matter of years or decades, not two centuries. The ocean is large and sluggish, thus the 200-year time lag is a pretty clear fingerprint of the ocean's involvement."

These past episodes of climate change differ in a major way from what is happening today, the researchers note. The abrupt events of the ice age were regional in scope -- and likely tied to large-scale changes in ocean circulation. Warming today is global and primarily from human carbon dioxide emissions in the Earth's atmosphere.

The key to the discovery was the analysis of a new ice core from West Antarctica, drilled to a depth of 3,405 meters in 2011 and spanning the last 68,000 years, according to Oregon State paleoclimatologist Edward Brook, a co-author on the Nature study and an internationally recognized ice core expert.

Because the area where the ice core was drilled gets high annual snowfall, Brook said, the new ice core provides one of the most detailed records of Antarctic temperatures at a very high resolution. Greenland temperatures were already well-established, the researchers say, because of high annual snowfall and more available ice core data.

"Past ice core studies did not reveal the temperature changes as clearly as this remarkable core," said Eric Steig, a professor in the Department of Earth and Space Sciences at the University of Washington, who co-wrote the paper. Steig's laboratory made one of the key measurements that provides past Antarctic temperatures.

"Previous work was not precise enough to determine the relative timing of abrupt climate change in Antarctica and Greenland, and so it was unclear which happened first," Steig noted. "Our new results show unambiguously that the Antarctic changes happen after the rapid temperature changes in Greenland. It is a major advance to know that the Earth behaves in this particular way."

Kendrick Taylor, chief scientist on the project, said the core enabled the research team to get the relative timing of Greenland and Antarctic temperatures down to several decades.

"We needed a climate record from the Southern Hemisphere that extended at least 60,000 years into the past and was able to resolve fast changes in climate," said Taylor, from the Desert Research Institute in Nevada. "We considered sites all over Antarctica before selecting the site with the best combination of thick ice, simple ice flow and the right amount of annual snowfall."

Taylor and colleagues formed a science and engineering team consisting of 28 laboratories from around the United States. "The resulting information provides unprecedented detail about many aspects of the Earth's past climate," Taylor said. "This will provide a generation of climate researchers a way to test and improve our understanding of how and why global climate changes."

OSU's Buizert said it is "very likely" that the Atlantic Meridional Overturning Circulation, or AMOC, is involved in these abrupt climate reversals.

"This ocean circulation brings warm surface waters from the tropics to the North Atlantic," said Buizert, who is in OSU's College of Earth, Ocean, and Atmospheric Sciences. "As these water masses cool, they sink to the bottom off the ocean. This happens right off the coast of Greenland, and therefore Greenland is located in a sweet spot where the climate is very sensitive to changes in the AMOC."

Brook said the AMOC seems to be critical, but was probably part of a combination of factors that ultimately controlled these past abrupt changes.

"Although ocean circulation may be the key, there are probably other feedbacks involved, such as the rise and fall of sea ice and changes in ice and snow cover on land," Brook said. "There is probably some kind of threshold in the system -- say, in the salinity of the surface ocean -- that triggers temperature reversals.

"It's not a problem to find potential mechanisms; it's just a question of figuring out which one is right. And the precise timing of these events, like we describe in this study, is an important part of the puzzle."

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