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News Article | November 8, 2016
Site: www.sciencedaily.com

A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by inserting dark matter in the theory. Prof. Erik Verlinde, an expert in string theory at the University of Amsterdam and the Delta Institute for Theoretical Physics, just published a new research paper in which he expands his groundbreaking views on the nature of gravity. In 2010, Erik Verlinde surprised the world with a completely new theory of gravity. According to Verlinde, gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime. In his 2010 article, Verlinde showed how Newton's famous second law, which describes how apples fall from trees and satellites stay in orbit, can be derived from these underlying microscopic building blocks. Extending his previous work and work done by others, Verlinde now shows how to understand the curious behaviour of stars in galaxies without adding the puzzling dark matter. The outer regions of galaxies, like our own Milky Way, rotate much faster around the centre than can be accounted for by the quantity of ordinary matter like stars, planets and interstellar gasses. Something else has to produce the required amount of gravitational force, and so dark matter entered the scene. Dark matter seems to dominate our universe: more than 80% of all matter must have a dark nature. Hitherto, the alleged dark matter particles have never been observed, despite many efforts to detect them. No need for dark matter According to Erik Verlinde, there is no need to add a mysterious dark matter particle to the theory. In a new paper, which appeared today on ArXiv.org, Verlinde shows how his theory of gravity accurately predicts the velocities by which the stars rotate around the center of the Milky Way, as well as the motion of stars inside other galaxies. 'We have evidence that this new view of gravity actually agrees with the observations,' says Verlinde. 'At large scales, it seems, gravity just doesn't behave the way Einstein's theory predicts.' At first glance, Verlinde's theory has features similar to modified theories of gravity like MOND (modified Newtonian Dynamics, Mordehai Milgrom (1983)). However, where MOND tunes the theory to match the observations, Verlinde's theory starts from first principles. "A totally different starting point," according to Verlinde. One of the ingredients in Verlinde's theory is an adaptation of the holographic principle, introduced by his tutor Gerard 't Hooft (Nobel Prize 1999, Utrecht University) and Leonard Susskind (Stanford University). According to the holographic principle, all the information in the entire universe can be described on a giant imaginary sphere around it. Verlinde now shows that this idea is not quite correct: part of the information in our universe is contained in space itself. This extra information is required to describe that other dark component of the universe: the dark energy, which is held responsible for the accelerated expansion of the universe. Investigating the effects of this additional information on ordinary matter, Verlinde comes to a stunning conclusion. Whereas ordinary gravity can be encoded using the information on the imaginary sphere around the universe only -- as he showed in his 2010 work -- the result of the additional information in the bulk of space is a force that nicely matches the one so far attributed to dark matter. On the brink of a scientific revolution Gravity is in dire need of new approaches like the one by Verlinde, since it doesn't combine well with quantum physics. Both theories, the crown jewels of 20th century physics, cannot be true at the same time. The problems arise in extreme conditions: near black holes, or during the Big Bang. Verlinde: 'Many theoretical physicists like me are working on a revision of the theory, and some major advancements have been made. We might be standing on the brink of a new scientific revolution that will radically change our views on the very nature of space, time and gravity'. See the article at: http://www.uva.nl/en/news-events/news/uva-news/content/press-releases/2016/11/new-theory-of-gravity-might-explain-dark-matter.html


News Article | February 15, 2017
Site: www.eurekalert.org

For the 100 million people who live within 3 feet of sea level in East and Southeast Asia, the news that sea level in their region fluctuated wildly more than 6,000 years ago is important, according to research published by a team of ocean scientists and statisticians, including Rutgers professors Benjamin Horton and Robert Kopp and Rutgers Ph.D. student Erica Ashe. That's because those fluctuations occurred without the assistance of human-influenced climate change. In a paper published in Nature Communications, Horton, Kopp, Ashe, lead author Aron Meltzner and others report that the relative sea level around Belitung Island in Indonesia rose twice just under 2 feet in the period from 6,850 years ago to 6,500 years ago. That this oscillation took place without any human-assisted climate change suggests to Kopp, Horton and their co-authors that such a change in sea level could happen again now, on top of the rise in sea level that is already projected to result from climate change. This could be catastrophic for people living so close to the sea. "This research is a very important piece of work that illustrates the potential rates of sea-level rise that can happen from natural variability alone," says Horton, professor of marine and coastal sciences in the School of Environmental and Biological Sciences. "If a similar oscillation were to occur in East and Southeast Asia in the next two centuries, it could impact tens of millions of people and associated ecosystems." Meltzner, a senior research fellow at the Earth Observatory of Singapore at Nanyang Technological University, along with Horton, Kopp and their co-authors, used coral microatolls to understand when, and by how much, the sea level had risen and fallen near the Indonesian island of Belitung, which lies between Sumatra and Borneo. A microatoll is a circular coral colony, typically no more than about 20 feet across, in which the topmost coral is dead and the bottom part living and growing. By taking samples from microatolls in different places, scientists can date rises and falls of sea level. The microatolls are what scientists call a "proxy" - a natural process that provides a reliable record of past events. "In any region, you try to find the proxy controlled by sea level," Horton says. "In New Jersey, we have no corals, so we use salt marshes. In the tropics, corals are the go-to proxy." The scientists studied microatolls at two sites on opposite sides of the island. Meltzner says they didn't expect the fluctuations they found because those changes in sea level contradicted what they knew about sea level in Southeast Asia. "Our conventional understanding of ocean circulation and ice-melting history told us that such fluctuations should not occur, so we were a bit mystified at the results from our first site," Meltzner says. "But after finding a similar pattern at a second site 80 kilometers to the southeast, and ruling out other plausible explanations, it was clear that the coral growth patterns must reflect regional changes in sea level. There would be way too many coincidences otherwise." The paper comes out of a long-running research project aimed at understanding the physical processes involved in sea-level rise. Such understanding, Kopp says, is necessary to help scientists understand the present and likely future state of the ocean. "This is a basic science problem," Kopp says. "It's about understanding past changes. Understanding what drove those changes is what allows us to test the climate models we use to predict future changes." In addition to Meltzner, Horton, Kopp, and Ashe, the authors are Adam Switzer, Qiang Qiu, Emma Hill, and Jedrzej Majewski, also of Nanyang Technological University in Singapore; David Hill of Oregon State University, Sarah Bradley of Utrecht University and Delft University of Technology in the Netherlands; and Danny Natawidjaja and Bambang Suwargadi of the Indonesian Institute of Sciences.


News Article | February 24, 2017
Site: phys.org

A photonic crystal chip is illuminated with violet laser light that is patterned by a spatial light modulator. The patterned laser light effectively cancels atomic-scale disorder. Credit: Utrecht University Nanophotonic circuits, tiny chips which filter and steer light, suffer from small random variations which degrade the transmission of light. Researchers have now found a way to compensate those variations, which may lead to energy savings in datacenters and computer equipment. The researchers from Utrecht University (Debye Institute), University of Twente (MESA+ Institute for Nanotechnology) and Thales Research & Technology France published their results in the leading optical journal Optics Express on 21 February. Optical communication is adopted worldwide: basically every high-speed internet connection nowadays is provided by optical fibers. Today, an active area of development is the use of optical communication on the scale of a single chip, to reduce power consumption in computers and data centers. One of the promising ways to steer the light propagation on such a chip is to use coupled photonic crystal nanoresonators, where light is transmitted between resonators that are tuned to the exact same resonance frequency. These frequencies are determined by the shape and structure of each resonator. However, even the best nanofabrication possible today, in which the holes are placed with a precision of ten times the diameter of an atom, small random variations induce changes in the resonance frequencies, which degrade the transmission of light. The researchers have now proposed and experimentally demonstrated an optical method to control photonic crystal nanoresonators. They employ digital holography techniques to focus several spots of laser light at definite positions. The laser light locally heats the nanophotonic chip and undoes the random variations. Moreover, this method enables the researchers to program photonic circuits by switching them into and out of resonance. The results, published in the open access journal Optics Express, will contribute to the ongoing development of low-power high-performance communication and computer equipment. Explore further: Warm regards for confined light in nanophotonic circuits More information: Sergei Sokolov et al. Tuning out disorder-induced localization in nanophotonic cavity arrays, Optics Express (2017). DOI: 10.1364/OE.25.004598


News Article | February 15, 2017
Site: www.scientificamerican.com

A dark plume leapt into the sky over southern Mexico. Below, waves of hot gas and rock screamed down volcanic slopes, stripping the mountain and surrounding area of vegetation, killing any living thing in their path. It mixed with rivers to create torrents of water, mud and other material as thick as wet concrete. For days afterward the air was choked with ash—microscopic shards of glass—that sickened survivors who inhaled it. It fell like snow onto the surrounding landscape, jamming rivers to create massive floods that wreaked havoc on agriculture. It was A.D. 540, and El Chichón—a small and previously unremarkable volcano—had plunged Maya civilization into darkness and chaos. At least that is the story according to a new paper published in the February Geology, jumping into the long-running archaeological debate about what drove Maya civilization—one of the most sophisticated of its time—into a century-long “dark age.” The Maya, who thrived from A.D. 250 to 900, are widely considered the most advanced civilization in the pre-Columbian Americas. They developed a writing system, precise calendars, new mathematics and magnificent cities with pyramids that still cast their shadows today. But a major mystery remains. In 1938 an archaeologist noticed a strange gap in dated Maya monuments. For more than 100 years the Maya inexplicably halted construction projects, seemingly deserted some areas and engaged in warfare. And in the 75 years since the discovery archaeologists have failed to find an explanation—although they have come up with a lot of hypotheses. Some have speculated an earthquake or hurricane struck the area. Others think trade routes might have collapsed. An early hint that an ancient volcanic eruption might be the culprit came far from the Maya lowlands, in Greenland and Antarctica. A volcano can send a large amount of sulfur particles rocketing into the stratosphere, where they can easily spread across the globe. Once they reach the area over the poles they fasten to snow crystals and eventually become trapped in the ice sheets below, leaving a precise record for scientists to uncover centuries later. That is how Michael Sigl, a chemist from the Paul Scherrer Institute in Switzerland, deduced that a massive eruption must have happened somewhere in the world in A.D. 540—right at the start of the mysterious Maya “dark age.” Tree ring records indicate that sunlight-reflecting sulfur particles high in the atmosphere caused the global temperature to plummet by 1.5 to 2 degrees Celsius at the same time. A volcanic eruption had clearly rocked the world. But could scientists pinpoint its location? The answer came at a chance meeting. Sigl encountered Kees Nooren, a PhD student from Utrecht University in the Netherlands, when the two were presenting side-by-side research posters at a conference. Nooren had been studying lake sediments in a delta just west of the Términos Lagoon along the Gulf of Mexico near the Yucatan Peninsula, when he unearthed a few shiny layers of volcanic ash. He analyzed individual shards of volcanic glass in the sediment and traced them back to El Chichón, then used carbon dating to pin the layers to A.D. 540, give or take 16 years. So when Nooren saw the sulfur spike at 540 on Sigl’s poster, he turned to him and said: “Hey, I might have a candidate for that.” The resulting study clearly shows El Chichón erupted around the same time that sulfur particles got into the ice sheets, and that the Maya “dark age” began. Still, scientists disagree on what the eruption’s exact effect on the Maya might have been. If this eruption was the major event that lofted sulfur particles halfway across the world, it would not have only caused harsher winters (as seen from tree ring records), but also regional droughts. This is what Payson Sheets, an archaeologist at the University of Colorado Boulder who was not involved in the study, thinks interrupted Maya civilization. When Tikal—a powerful Maya city that dominated much of the region—was especially devastated by the ensuing drought, it was attacked by other Maya cities that fared better, causing a temporary collapse, Sheets believes. He also thinks drought affected other civilizations across the world, from the Wei Dynasty in northern China to the pre-Columbian city of Teotihuacán in the Mexican highlands (both civilizations are believed to have revolted against their rulers after poor harvests in the mid-6th century A.D.). But it is also possible that El Chichón did not cause these global changes and that the true culprit has yet to be detected. “The equatorial Pacific is really a hotspot for these big eruptions,” says Matthew Toohey, a climate scientist from the Helmholtz Center for Ocean Research Kiel in Germany, who was not involved in the latest study. “But it’s also a blind spot, and there could be a different eruption there that we just don’t have any records of at the moment.” A number of studies have tried to link other tropical volcanoes to the sulfur spike, albeit with dates that are less certain. Discovering ash in the ice cores (along with the previously detected sulfur) would give scientists a smoking gun, allowing them to trace that ash to a specific volcano. But none has been discovered yet. Nor can researchers be sure El Chichón’s A.D. 540 eruption was massive enough for its effects to span the entire globe. Nooren’s team assumes it was as large as the devastating event that occurred in 1982, when the mountain released huge amounts of sulfur dioxide gas, buried nine villages and killed 2,000 people. Juan Espindola, a volcanologist at the National Autonomous University of Mexico who was not involved in the study, agrees with this assessment given the large distance between the deposited ash that Nooren’s team studied in the Mexican Delta and El Chichón itself. Only a massive eruption would blow ash more than 100 kilometers, he thinks. Volcanologists will have to search for other ash deposits in order to really measure the event’s magnitude. However, even if the eruption was too small to have global effects, its proximity could have helped it play a role in the Maya “dark age.” Nooren and his colleagues think ash and pyroclastic flows from El Chichón could have easily thrown nearby cities into chaos. Other archaeologists who were not part of this research agree the Maya hiatus was likely caused by the volcano—but they think it is because the eruption was beneficial, not disastrous. “Human societies are amazingly resilient and adaptable to natural disasters,” says Robin Torrence, an archaeologist from the Australian Museum. “People can often pick themselves up, dust themselves off and in many cases take advantage of new opportunities.” Those opportunities could have included the volcanic ash itself; in small amounts it can be a great fertilizer. Kenneth Tankersley, an archaeologist from the University of Cincinnati, thinks the Maya might have deserted some areas after the eruption to move closer to the beneficial ash. He goes so far as to suggest they depended on the fertilizing ash so much that a dearth of major volcanism at the end of the eighth century might have led to their civilization’s ultimate collapse—another mystery waiting to be solved. Large or small, El Chichón likely played a role in the Maya’s mysterious dark age. It is no wonder that Sheets thinks this era could easily be turned into a screenplay. “This is great drama,” he says, “and it’s based in reality.”


News Article | September 12, 2016
Site: phys.org

Fig. Visualisation of disorder-confined light in a photonic crystal. The green membrane is a photonic crystal with a waveguide; the patterns on top of it indicate the light signal that is stored. Credit: Utrecht University Faculty of Science Researchers at the Debye Institute for Nanomaterials Science, together with colleagues from the University of Twente and Thales Research and Technology (France), have found a non-invasive technique to measure the intensity profile of light that is confined by disorder in nano-sized photonic devices. This method may eventually lead to faster optical communications, and faster processing in quantum information technologies. The researchers published their results in the leading optical journal Optics Express on 12 September 2016. Every nanostructure suffers from unavoidable disorder: a disturbance of its function caused by unavoidable irregularities in nanofabrication. Contrary to what the name might suggest, disorder in a nanostructure is not necessarily a disadvantage. Disorder can cause light to be tightly confined, and if its intensity profile is measured accurately, the confined light might be used to make components for quantum information technology and high speed optical communication. One bottleneck in high-speed optical communication is that light signals have to be converted to electronic signals at nodes to switch data to different destinations. This conversion can be avoided with the help of optical buffers that store light signals temporarily. Right now, these buffers are usually implemented with optical fibres that are several centimeters long, which can store light for a few nanoseconds. However, with smart use of disorder-induced confinement, nanophotonic circuits 100 times smaller – only one-tenth of a millimeter long – can store light for a similar time. Photonic crystal waveguides are nanophotonic structures in which light confinement by disorder widely occurs. In order to make use of the confined light, the first essential step is to identify where the light is confined and what its spatial profile is. Compared to the previous measuring methods, which perturb the structure, Jin Lian (Debye Institute) and his colleagues have developed a new non-invasive method to precisely identify the spatial and spectral information, using local heating. The researchers used a blue laser to slightly heat a small spot on the crystal. The response of the optical system reveals how much light is confined there. Explore further: Unavoidable disorder used to build nanolaser More information: Measurement of the profiles of disorder-induced localized resonances in photonic crystal waveguides by local tuning, arxiv.org/abs/1606.01197


News Article | December 6, 2016
Site: phys.org

Indeed, by some calculations, the so-called "break-even point" between dirty energy input and clean output may already have arrived, researchers in the Netherlands reported. "We show strong downward trends of environmental impact" of solar panel production, the team wrote in the journal Nature Communications. The study sought to address concerns that solar technology may be using fossil fuel energy in the panels' manufacture, and emitting greenhouse gases, faster than it was able to offset. The authors found that for every doubling in solar capacity installed, energy used to produce solar panels decreased by 12-13 percent, and greenhouse gas emissions dropped by 17-24 percent, depending on the material used. Solar panels, which convert sunlight into electricity, are a key player in the fast-growing renewable energy sector, which also includes water- and wind-generated electricity. Unlike energy from fossil fuels such as oil, coal and gas, the generation of electricity by so-called photovoltaic (PV) panels does not release planet-harming carbon dioxide. Solar panel capacity grew sharply, on average, by 45 percent per year from 1975 to reach 230 billion watts (Gigawatt or GW) in 2015. In 1975, there were fewer than 10,000 solar panels around the world, compared to about a billion today, study co-author Wilfried Van Sark of Utrecht University in the Netherlands told AFP. By the end of 2016, "we would have some 300 GW installed"—about 1-1.5 percent of global electricity demand. Over an average lifespan of 30-odd years, a PV system pays back the energy that was used in producing it "multiple times," said the study authors. Looking at data since 1976, the researchers calculated that on a global scale, solar energy's "debt was likely already repaid in 2011" for both energy input and greenhouse gases. Even on the least optimistic data, break-even point will be reached at the latest next year for net energy, and in 2018 for greenhouse gases, they said. The photovoltaic effect, by which certain materials convert the photon particles in sunlight into energy, was first identified by French physicist Edmund Bequerel in 1839. The first photovoltaic battery was built in 1954 but was too expensive for widespread use. The technology was used in the 1960s to generate power on spacecraft, and only started taking root on Earth in the 1970s. From 1975, costs decreased by about 20 percent for every doubling in capacity, the study found. In 1976, one would have paid about $80 (75 euros at today's rates) for one Watt-peak (Wp) unit, compared to about 64-67 US cents today.


News Article | February 22, 2017
Site: phys.org

Landscapes with numerous waterbodies are inhabited by large numbers of mallards, who each visit their favourite feeding sites at night and share a common roost during the day. They connect wetlands by dispersing seeds over short distances. Landscapes with more sparse waterbodies are inhabited by fewer mallards, who fly between their more scattered feeding sites at night and connect wetlands by dispersing seeds over much longer distances. Credit: Utrecht University Plant populations in wetland areas face increasing isolation as wetlands are globally under threat from habitat loss and fragmentation. Erik Kleyheeg and Merel Soons of Utrecht University show that the daily movement behaviour of wintering mallards is highly predictable from the landscape they live in and that their daily flights contribute to maintaining the connections between wetland plant populations across increasingly fragmented landscapes. The researchers and co-authors are publishing their results today in the academic journal Journal of Ecology. Mallards are among the most numerous and widespread duck species in the world, their global population estimated at approximately 19 million individuals. They are strong flyers, able to cover long distances at great speed (about 80 km/h) and part of the population migrates over long distances from their breeding areas to their wintering areas. Mallards are omnivorous and in their non-breeding range, during autumn and winter, they feed largely on plant seeds. Many of these seeds are not digested and survive gut passage. In this way, the mallards play an important role in transporting the seeds between wetland feeding and resting areas. Effects of the landscape on mallard behaviour Analysis of the movement behaviour of individual mallards carrying a GPS data-logger revealed that the daily movement patterns of wintering mallards are remarkably predictable. Mallards typically spend the daytime resting on a common roost, usually a large open water body. At night, they leave the roost to forage in and around wetland areas and agricultural fields, visiting 2-4 of such areas per night. Surprisingly, they have very high site fidelity and return to the same sites almost every night. This foraging behaviour remains similar across a wide range of landscapes. As a result, mallards have small home ranges and travel short distances between foraging sites in landscapes with many wetlands, while they have larger home ranges and travel much longer distances per night in landscapes with few and sparse wetlands. Through these daily movements, mallards connect the wetlands in the landscapes they inhabit. Model calculations combining information on mallard movement behaviour, plant and seed traits and landscape configuration estimate that about 34% of seeds surviving digestion are dispersed towards roost areas, which may function as regional reservoir for plant biodiversity. About 7% of surviving seeds are dispersed between foraging areas. The seeds most likely to be dispersed are small, hard seeds, which are best able to withstand the mechanical digestion in the birds' gizzard. Given the large numbers of seeds mallards ingest on a daily basis, they are likely to greatly contribute to plant dispersal and the connection between otherwise isolated plant populations across a wide range of landscapes. Explore further: Plants actively direct their seeds via wind or water towards suitable sites More information: E. Kleyheeg, H.J. Treep, M. de Jager, B.A. Nolet and M.B. Soons (2017) Seed dispersal distributions resulting from landscape-dependent daily movement behaviour of a key vector species. Journal of Ecology, online early DOI: 10.1111/1365-2745.12738 E. Kleyheeg, J.B.G. van Dijk, D. Tsopoglou-Gkina, T. Woud, D. Boonstra, B.A. Nolet and M.B. Soons (2017) Movement patterns of a keystone waterbird species are highly predictable from landscape configuration. Movement Ecology, online early DOI: 10.1186/s40462-016-0092-7


News Article | February 22, 2017
Site: www.eurekalert.org

Plant populations in wetland areas face increasing isolation as wetlands are globally under threat from habitat loss and fragmentation. Erik Kleyheeg and Merel Soons of Utrecht University show that the daily movement behaviour of wintering mallards is highly predictable from the landscape they live in and that their daily flights contribute to maintaining the connections between wetland plant populations across increasingly fragmented landscapes. The researchers and co-authors are publishing their results today in the academic journal Journal of Ecology. Mallards are among the most numerous and widespread duck species in the world, their global population estimated at approximately 19 million individuals. They are strong flyers, able to cover long distances at great speed (about 80 km/h) and part of the population migrates over long distances from their breeding areas to their wintering areas. Mallards are omnivorous and in their non-breeding range, during autumn and winter, they feed largely on plant seeds. Many of these seeds are not digested and survive gut passage. In this way, the mallards play an important role in transporting the seeds between wetland feeding and resting areas. Analysis of the movement behaviour of individual mallards carrying a GPS data-logger revealed that the daily movement patterns of wintering mallards are remarkably predictable. Mallards typically spend the daytime resting on a common roost, usually a large open water body. At night, they leave the roost to forage in and around wetland areas and agricultural fields, visiting 2-4 of such areas per night. Surprisingly, they have very high site fidelity and return to the same sites almost every night. This foraging behaviour remains similar across a wide range of landscapes. As a result, mallards have small home ranges and travel short distances between foraging sites in landscapes with many wetlands, while they have larger home ranges and travel much longer distances per night in landscapes with few and sparse wetlands. Through these daily movements, mallards connect the wetlands in the landscapes they inhabit. Model calculations combining information on mallard movement behaviour, plant and seed traits and landscape configuration estimate that about 34% of seeds surviving digestion are dispersed towards roost areas, which may function as regional reservoir for plant biodiversity. About 7% of surviving seeds are dispersed between foraging areas. The seeds most likely to be dispersed are small, hard seeds, which are best able to withstand the mechanical digestion in the birds' gizzard. Given the large numbers of seeds mallards ingest on a daily basis, they are likely to greatly contribute to plant dispersal and the connection between otherwise isolated plant populations across a wide range of landscapes. E. Kleyheeg*, H.J. Treep*, M. de Jager*, B.A. Nolet and M.B. Soons* (2017) Seed dispersal distributions resulting from landscape-dependent daily movement behaviour of a key vector species. Journal of Ecology, online early DOI: 10.1111/1365-2745.12738. E. Kleyheeg*, J.B.G. van Dijk*, D. Tsopoglou-Gkina*, T. Woud*, D. Boonstra*, B.A. Nolet and M.B. Soons* (2017) Movement patterns of a keystone waterbird species are highly predictable from landscape configuration. Movement Ecology, online early DOI: 10.1186/s40462-016-0092-7.


News Article | December 12, 2016
Site: news.yahoo.com

The main vulnerability of ice shelves to climate change remains warming ocean water that erodes their underbelly (AFP Photo/RYAN DOLAN) Paris (AFP) - East Antarctica’s massive ice sheet may be more exposed to global warming than long assumed, according to a study Monday that shows how strong winds can erode ice shelves that help hold it in place. There is enough frozen water sitting on top of the world's polar continent to raise sea level by dozens of metres and redraw the world map if it melts. But understanding the dynamics of the region -- which includes the much smaller West Antarctica ice sheet -- has proven difficult. Up to now, scientists have focused on the threat of West Antarctica. Recent studies have suggested that climate change may already have condemned large chunks of its ice sheet to disintegration, whether on a time scale of centuries or millennia. In contrast, ice covering East Antarctica was seen as far more stable, even gaining mass. The floating, cliff-like ice shelves straddling land and ocean that prevent inland ice from slipping into the sea, it was thought, were solidly anchored. That remains largely true. But a mysterious crater on the King Baudoin ice shelf, due south from the tip of Africa, prompted a team of researchers from the Netherlands, Belgium and Germany to challenge that assumption. "Our research has shown that East Antarctica is also vulnerable to climate change," said Jan Lenaerts, lead author of the study and a researcher at Utrecht University in the Netherlands. The findings were published in the journal Nature Climate Change. Some reports had attributed the crater to a meteorite impact, but when Lenaerts and his team arrived in January they realised the water-filled cavity had other origins. Combining climate models, satellite data and on-site measurements, they concluded that strong winds carrying warm air were blowing away reflective snow, allowing the Sun's rays to be absorbed into the darker ice rather than bounced back into space. The main vulnerability of ice shelves to climate change remains warming ocean water that erodes their underbelly. Normally, that erosion is compensated by the accumulation of fresh snow and ice from above. But oceans in recent decades have absorbed much of the excess heat generated by global warming, which has lifted average global air temperatures by one degree Celsius (1.8 degrees Fahrenheit). When combined with erosion from above, the impact on ice sheet stability may be larger than previously understood. "These processes -- previously unseen in East Antarctica -- indicate that further warming may amplify the risk of ice shelf collapse," said Martin Siegert of Imperial College London, commenting on the study. A dress rehearsal of what might happen more broadly occurred in 2002, when West Antarctica's Larsen B ice shelf underwent a "rapid and catastrophic mechanical failure," falling into the sea, he noted. There, too, meltwater had collected on the surface in hundreds of lakes, and when they quickly drained the buoyancy caused the shelf to rupture. "Larsen B tells us that surface melting can be critical to the structural integrity of ice shelves," Siegert wrote in a commentary, also in Nature Climate Change.


News Article | September 23, 2016
Site: phys.org

If we are to tame fungi and optimize their extremely important role in our ecosystem, we must gain a more complete view of their functional abilities. Researchers from TU Delft and Utrecht University have exposed a previously hidden layer of functional complexity in fungi. They publish their findings on Friday September 23th in Scientific Reports.

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