A seismograph for ancient earthquakes

This is professor Shmuel Marco of Tel Aviv University. -  AFTAU
This is professor Shmuel Marco of Tel Aviv University. – AFTAU

Earthquakes are one of the world’s biggest enigmas – impossible to predict and able to wreak untold damage within seconds. Now, a new tool from Tel Aviv University may be able to learn from earthquakes of the ancient past to better predict earthquakes of the future.

Prof. Shmuel Marco of Tel Aviv University’s Department of Geophysics and Planetary Sciences in the Raymond and Beverly Sackler Faculty of Exact Sciences and his colleagues have invented a new tool which he describes as a “fossil seismograph,” to help geophysicists and other researchers understand patterns of seismic activity in the past.

Inspired by a strange “wave” phenomenon he studied in disturbed sediment in the Dead Sea region, Prof. Marco says the new tool, developed with input from geologists and physicists, is relevant to areas where earthquakes affect bodies of water, like the West Coast of the United States. It also can help engineers understand what’s at risk when they plan new hydroelectric power plants. The new research was published in the journal Geology.

A geophysical yardstick for centuries past


“Current seismographical data on earthquakes only reaches back a century or so,” says Prof. Marco. “Our new approach investigates wave patterns of heavy sediment that penetrates into the light sediments that lie directly on top of them. This helps us to understand the intensity of earthquakes in bygone eras – it’s a yardstick for measuring the impact factor of earthquakes from the past.”

Prof. Marco, his departmental colleague Prof. Eyal Hefetz, and doctoral student Nadav Wetzer took a highly technical look at layers of mud at the Dead Sea. The layers were originally stratified in a very stable manner, but now heavier sediment appears to have been pulled up into the lighter sediment.

The researchers propose that the physics governing the sediment patterns is similar to a phenomenon found in clouds and sea waves but in the case of rocks it was the earthquake shaking (rather than wind) that triggered the formation of waves. The scientists call it the “Kelvin-Helmholtz Instability,” which describes a theory of turbulence in fluids. The Tel Aviv University team applied this theory to analyze the deformation of sediment caused by past earthquakes.

Earthquakes cause deformation in rocks and sediment. Using the basic principles of friction, the researchers considered the geometry of the shapes they found in the Dead Sea sediment and combined it with a number of other parameters found in physical science to calculate how earthquakes from the past were distributed in scale, time and place.

The bigger geological picture


Prof. Marco and his colleagues found that the deformation begins as moderate wave-like folds, evolves into complex recumbent folds, and finally exhibit instability and fragmentation. The deformation process advances depending on the earthquake size – the stronger the earthquake, the more intense the deformation.

The seismological record for fault lines like those near Jerusalem and Los Angeles simply isn’t old enough to predict when the next quake might strike. “We’ve expanded the window of observation beyond 100 years, to create, if you will, a ‘fossil seismograph,'” says Prof. Marco. He adds that the tool is only relevant in earthquake zones that intersect with bodies of water such as lakes or the sea.

But it could be very relevant to geologists studying earthquake patterns in areas like the Salton Sea in Colorado. The Salton Sea, only 100 years old, is located directly on the San Andreas Fault in California’s Border Region.

Geoscientists meet in Pittsburgh to discuss ‘the shield to the sea’

Over 1500 geoscientists, including 500 students, will gather in Pittsburgh, Pennsylvania, USA, on 20-22 March, to present their earth-science research in a program themed “from the Shield to the Sea,” at the 46th/45th (respectively) joint annual meeting of the Northeastern and North-Central Sections of The Geological Society of America. Members of the media are invited to attend and cover technical sessions with complimentary registration (see below).

Issues of local importance such as the Devonian Marcellus Shale development and carbon sequestration will be discussed. The geosciences departments at Slippery Rock University, Kent State University and The University of Pittsburgh are hosting the meeting at the Omni William Penn Hotel, 530 William Penn Place, Pittsburgh, PA 15219.

A meeting highlight is the conference banquet program on Mon., 21 March, 8 p.m., in the Urban Room at the Omni William Penn Hotel.

Why Geologists Aren’t Meteorologists: Deep Time Perspectives on Global Warming

Lee Kump, Pennsylvania State University, author of The Earth System and Dire Predictions-A Layperson’s Guide to Global Warming and the IPCC Report.

Charles Darwin’s Advice to Students: Conjectures upon the Likely

Patrick Burkhart, Slippery Rock University

Technical sessions begin at 8 a.m. on Sunday, 20 March, and end at 5:35 p.m. on Tuesday, 22 March.

Pre-, concurrent, and post-meeting field trips will explore regional sites of geological significance, from glaciers to gristmills, shales to slides, and even Pittsburgh’s building stones.
http://www.geosociety.org/Sections/ne/2011mtg/fieldTrips.htm.

The meeting field guide volume, From the Shield to the Sea, is available now, and features eight of the geological field trips offered during the Joint Meeting. Timely and topical trips highlight the region’s geology from eastern Ohio to the Central Appalachian Valley and Ridge and show how it has shaped the region-topographically, structurally, historically, industrially, and evolutionarily.
http://www.geosociety.org/bookstore/default.asp?oID=0&catID=18&pID=FLD020.

View the session schedule by day or search the program by keywords at http://gsa.confex.com/gsa/2011NE/finalprogram/. Click on session titles for a list of presentations, and click on presentations for the individual abstracts.

Find complete meeting information at http://www.geosociety.org/Sections/ne/2011mtg/.

SELECTED HIGHLIGHTS FROM THE SCIENTIFIC PROGRAM

Marcellus-Exploration and Production

8:00 AM󈝸:00 PM, Sunday, 20 March, Omni William Penn Hotel, Conference A

http://gsa.confex.com/gsa/2011NE/finalprogram/session_27367.htm

Marcellus-Production and Disposal of Produced Water

1:30 PM-5:30 PM, Sunday, 20 March, Omni William Penn Hotel: Conference A

http://gsa.confex.com/gsa/2011NE/finalprogram/session_27388.htm

CO2 Sequestration

8:00 AM-12:00 PM, Monday, 21 March, Omni William Penn Hotel: Conference A

http://gsa.confex.com/gsa/2011NE/finalprogram/session_27368.htm

Cultural Geology: Building Stones, Archaeological Materials, Terrain, and More

1:30 PM-5:30 PM, Tuesday, 22 March, Omni William Penn Hotel: Conference B

http://gsa.confex.com/gsa/2011NE/finalprogram/session_27397.htm

MEDIA REGISTRATION

Eligibility for media registration is as follows:
Working press representing bona fide, recognized news media with a press card, letter or business card from the publication.
Freelance science writers, presenting a current membership card from NASW, ISWA, regional affiliates of NASW, ISWA, CSWA, ACS, ABSW, EUSJA, or evidence of work pertaining to science published in 2010 or 2011.
PIOs of scientific societies, educational institutions, and government agencies.

Present media credentials to William Cox onsite at the GSA registration desk to obtain a badge for media access. Complimentary meeting registration covers attendance at all technical sessions and access to the exhibit hall. Journalists and PIOs must pay regular fees for paid luncheons and any short courses or field trips in which they participate. Representatives of the business side of news media, publishing houses, and for-profit corporations must register at the main registration desk and pay the appropriate fees.

Northern peatlands a misunderstood player in climate change

University of Alberta researchers have determined that the influence of northern peatlands on the prehistorical record of climate change has been over estimated, but the vast northern wetlands must still be watched closely as the planet grapples with its current global warming trend.

Northern peatlands, which are a boggy mixture of dead organic material and water, cover more than four million square kilometers. The largest northern peatlands occur in the subarctic regions of Canada and Russia. As peatlands grow they sequester carbon (in the form of carbon dioxide from the atmosphere. However, as old peat is buried and begins to decompose it emits large amounts of methane, a potent greenhouse gas.

Alberto Reyes and Colin Cooke were PhD students in the U of A’s Department of Earth and Atmospheric Sciences when they began their research into the response of northern peatlands to climate change.

They began their research by studying radiocarbon dates of ancient peatlands to examine how peatlands first colonized northern regions at the end of the last ice age, a period of rapid global warming. Using this technique, they compared the expansion of northern peatlands to ice-core records of past climate, including carbon dioxide and methane.

Atmospheric carbon dioxide and methane rose dramatically 10,000 years ago at the end of the last ice age. In the past, scientists had suggested that northern peatlands were a large, if not the principle, source of the dramatic increase in atmospheric methane.

But the U of A team revealed that the peatlands did not colonize the north until 500-1000 years after the abrupt increases in atmospheric methane. These results show that other methane sources, such as tropical wetlands, were the likely drivers of the initial rises in methane levels at the end of the last ice age.

The research by Reyes and Cooke points to the miscalculation of the role of northern peatlands and wetlands in the methane rise 10,000 years ago as an example of how complex and easily these huge areas of the planet can be misunderstood. The researchers say future work will focus on the northern peatlands as nature’s own carbon-capture mechanism and on their flip-side role an emitter of carbon in the form of methane.

EARTH: Still in a haze: Black carbon

Black carbon – fine particles of soot in the atmosphere produced from the burning of fossil fuels or biomass – a major contributor to the thick hazes of pollution hovering over cities around the world, has been known to be a health hazard for decades. But over the last decade, scientists have been examining in increasing detail the various ways in which these particles contribute to another hazard: heating up the planet.

Black carbon’s impact on climate is not cut-and-dried, however, as EARTH explores in “Still in a Haze: What We Don’t Know About Black Carbon” in the April issue. Does black carbon decrease the albedo in snow-covered areas, thus warming the planet? Or does it increase cloud cover, thus cooling the planet?

Learn more about black carbon’s mysterious effects on climate, and read other stories on topics such as how microbes survive for tens of thousands of years in salt crystals, how Earth is becoming dustier, and whether invasive species have caused mass extinctions in the past in the April issue of EARTH. Plus, don’t miss the surprising story about discovering dinosaur tracks in a New Jersey housing development.

March GSA Today: The case for a neoproterozoic oxygenation event

The Cambrian “explosion” of multicellular animal life is one of the most significant evolutionary events in Earth’s history. But what was it that jolted the Earth system enough to prompt the evolution of animals? While we take the presence of oxygen in our atmosphere for granted, it was not always this way.

The Neoproterozoic era that preceded the Cambrian explosion of life was witness to a dramatic rise in oxygen levels. It has been widely assumed that the rise in atmospheric oxygen was the essential precursor to the evolution of animals. But the work of Graham Shields-Zhou and Lawrence Och of University College London shows that the rise of oxygen was chaotic and nonlinear. Tectonically, the Neoproterozoic Earth was in the throes of the breakup of a supercontinent, Rodinia, and climatically, it had plunged into a snowball state, with ice-covered oceans extending from pole to pole.

In their March GSA Today article, Shields-Zhou and Och summarize geochemical and biological data that suggests that oxygen-depleted waters characterized the scattered seas that lay trapped beneath this global ice sheet. It may well have been the ability to survive in this harsh and variable climate that constituted the vital first step in the evolution of animals.

Shrinking tundra, advancing forests: how the Arctic will look by century’s end

Imagine the vast, empty tundra in Alaska and Canada giving way to trees, shrubs and plants typical of more southerly climates. Imagine similar changes in large parts of Eastern Europe, northern Asia and Scandinavia, as needle-leaf and broadleaf forests push northward into areas once unable to support them. Imagine part of Greenland’s ice cover, once thought permanent, receding and leaving new tundra in its wake.

Those changes are part of a reorganization of Arctic climates anticipated to occur by the end of the 21st century, as projected by a team of University of Nebraska-Lincoln and South Korean climatologists.

In an article to be published in a forthcoming issue of the scientific journal Climate Dynamics, the research team analyzed 16 global climate models from 1950 to 2099 and combined it with more than 100 years of observational data to evaluate what climate change might mean to the Arctic’s sensitive ecosystems by the dawn of the 22nd century.

The study is one of the first to apply a specific climate classification system to a comprehensive examination of climate changes throughout the Arctic by using both observations and a collection of projected future climate changes, said Song Feng, research assistant professor in UNL’s School of Natural Resources and the study’s lead author.

Based on the climate projections, the new study shows that the areas of the Arctic now dominated by polar and sub-polar climate types will decline and will be replaced by more temperate climates – changes that could affect a quarter to nearly half of the Arctic, depending on future greenhouse gas emission scenarios, by the year 2099.

Changes to Arctic vegetation will naturally follow shifts in the region’s climates: Tundra coverage would shrink by 33 to 44 percent by the end of the century, while temperate climate types that support coniferous forests and needle-leaf trees would push northward into the breach, the study shows.

“The expansion of forest may amplify global warming, because the newly forested areas can reduce the surface reflectivity, thereby further warming the Arctic,” Feng said. “The shrinkage of tundra and expansion of forest may also impact the habitat for wildlife and local residents.”

Also according to the study:

  • By the end of the century, the annual average surface temperature in Arctic regions is projected to increase by 5.6 to 9.5 degrees Fahrenheit, depending on the greenhouse gas emission scenarios.

  • The warming, however, is not evenly distributed across the Arctic. The strongest warming in the winter (by 13 degrees Fahrenheit) will occur along the Arctic coast regions, with moderate warming (by 4 to 6 degrees Fahrenheit) along the North Atlantic rim.

  • The projected redistributions of climate types differ regionally; in northern Europe and Alaska, the warming may cause more rapid expansion of temperate climate types than in other places.

  • Tundra in Alaska and northern Canada would be reduced and replaced by boreal forests and shrubs by 2059. Within another 40 years, the tundra would be restricted to the northern coast and islands of the Arctic Ocean.

  • The melting of snow and ice in Greenland following the warming will reduce the permanent ice cover, giving its territory up to tundra.

“The response of vegetation usually lags changes in climate. The plants don’t have legs, so it takes time for plant seed dispersal, germination and establishment of seedlings,” Feng said. Still, the shrub density in tundra regions has seen a rapid increase on decadal and shorter time scales, while the boreal forest expansion has seen a much slower response on century time scales.

Also, increasing drought conditions may help offset any potential benefits of warmer temperatures and reduce the overall vegetation growth in the Arctic regions, Feng said.

Non-climate factors – human activity, land use changes, permafrost thawing, pest outbreaks and wildfires, for example – may also locally affect the response of vegetation to temperature warming in the Arctic.

UF Pine lsland pollen study leads to revision of state’s ancient geography

A new University of Florida study of 45-million-year-old pollen from Pine Island west of Fort Myers has led to a new understanding of the state’s geologic history, showing Florida could be 10 million to 15 million years older than previously believed.

The discovery of land in Florida during the early Eocene opens the possibility for researchers to explore the existence of land animals at that time, including their adaptation, evolution and dispersal until the present.

Florida Museum of Natural History vertebrate paleontologist Jonathan Bloch, who was not involved in the current study, said he is especially interested in the finding and future related research.

“As a paleontologist who studies the evolution of mammals, my first question is ‘OK, if there was land here at that time, what kinds of animals lived here?’ ” Bloch said. “Most of our current understanding of the evolution of early mammals comes from fossils discovered out west.”

The study in the current issue of the journal Palynology by David Jarzen, a research scientist at the Florida Museum of Natural History on the UF campus, determined sediment collected from a deep injection well contained local, land-based pollen, disproving the popular belief Florida was underwater 45 million years ago during the early Eocene.

“When I got the sample, I could actually break it apart with my fingers,” Jarzen said. “It wasn’t just land, it was low-lying land with boggy conditions and near shore because it showed marine influence.”

Until recently, Florida was believed to have been submerged until the Oligocene epoch, 23 million to 34 million years ago, Jarzen said. The 2010 study of the Pine Island sample from the Oldsmar Formation dates Florida’s land from the early Eocene, about 10 million to 15 million years earlier than determined in a 2006 study of pollen and invertebrate fossils from the Avon Park Formation in west central Florida by Jarzen and former Florida Museum scientist David Dilcher.

“What we thought we knew was an incomplete body of information,” said Fredrick Rich, a professor of geology in the department of geology and geography at Georgia Southern University. “Those terrestrial trees, shrubs and herbs didn’t live out there all by themselves. I envision a small key, or maybe several small keys just like the islands in Florida Bay.

The study appears in the December 2010 edition of the bi-annual journal, which was distributed in January.

The sample of dark gray lignitic clay and limestone contained pollen from 17 different flowering plants, representing the earliest report of land vegetation to date. It was collected in 2004 by study co-author Curtis Klug, a hydrogeologist with Cardno Entrix, a Fort Myers-based natural resource management and environmental consulting company.

“As we’re drilling through the rock and the cuttings come to the surface, we collect them, examine them, and determine the type of rock and its estimated age,” Klug said. “As we were drilling, we did go through several lignites, but this was one of the thickest ones we found in this particular well.”

The company was digging a 767-meter well for the Greater Pine Island Water Association, a company that uses reverse osmosis to produce drinking water. In this case, the well was used to dispose of excess saline brine, Klug said.

Lignite, also known as brown coal, is geologically younger than higher-grade coals and contains decomposed organic matter, largely plant material from wetlands. Along with the 17 land-based pollens, which included species of trees, palms and possibly ferns representing a climate similar to the panhandle today, the sample also contained at least four examples of marine phytoplankton. The presence of limestone and foraminiferas, single-celled organisms found in all marine environments, indicates the rise and fall of the area’s sea level.

“Depending upon the anticipated uses of future injection wells, the developers might find it very interesting to know that what they will drill into is not likely to be simple and homogeneous,” Rich said. “There is a buried landscape down there and the engineers need to know that is the case.”Klug said the age of the sample was determined by analyzing the foraminiferas’ carbonate shells and comparing the layer to sediments recovered from the same depth. “I think it’s really very interesting,” Klug said. “It’s a preliminary study but what it shows I think is that the information is available for anybody who’s willing to spend the time looking into it.”

Pine Island was the site of a Calusa Indian village for more than 1,500 years and is important for research in archaeology and ecology. The Florida Museum maintains the Randell Research Center at Pineland, an archaeological site on the northwest part of the island.

“Our studies of environmental change at Pineland show that while sea level is rising very quickly today, water levels fluctuated up and down when the Calusa inhabited the area from AD 1 to 1700,” said William Marquardt, Randell Center director and curator of archaeology at the Florida Museum. “Jarzen and Klug’s new findings from the Eocene epoch may be suggesting something similar 35 million years ago – that there were fluctuations during the Eocene that periodically exposed land in Florida.”

Some Antarctic ice is forming from bottom

Scientists flew geophysical instruments over a California-size part of the East Antarctic ice sheet in order to image what lies below. -  Michael Studinger/Lamont-Doherty Earth Observatory
Scientists flew geophysical instruments over a California-size part of the East Antarctic ice sheet in order to image what lies below. – Michael Studinger/Lamont-Doherty Earth Observatory

Scientists working in the remotest part of Antarctica have discovered that liquid water locked deep under the continent’s coat of ice regularly thaws and refreezes to the bottom, creating as much as half the thickness of the ice in places, and actively modifying its structure. The finding, which turns common perceptions of glacial formation upside down, could reshape scientists’ understanding of how the ice sheet expands and moves, and how it might react to warming climate, they say. The study appears in this week’s early online edition of the leading journal Science; it is part of a six-nation study of the invisible Gamburtsev Mountains, which lie buried under as much as two miles of ice.

Ice sheets are well known to grow from the top as snow falls and builds up annual layers over thousands of years, but scientists until recently have known little about the processes going on far below. In 2006, researchers in the current study showed that lakes of liquid water underlie widespread parts of Antarctica. In 2008-2009, they mounted an expedition using geophysical instruments to create 3-D images of the Gamburtsevs, a range larger than the European Alps. The expedition also made detailed images of the overlying ice, and subglacial water.

“We usually think of ice sheets like cakes–one layer at a time added from the top. This is like someone injected a layer of frosting at the bottom–a really thick layer,” said Robin Bell, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory and a project co-leader. “Water has always been known to be important to ice sheet dynamics, but mostly as a lubricant. As ice sheets change, we want to predict how they will change. Our results show that models must include water beneath.” The Antarctic ice sheet holds enough fresh water to raise ocean levels 200 feet; if even a small part of it were to melt into the ocean, it could put major coastal cities under water.

The scientists found that refrozen ice makes up 24% of the ice sheet base around Dome A, a 13,800-foot-high plateau that forms the high point of the East Antarctic ice sheet, at 3.8 million square miles roughly the size of the continental United States. In places, slightly more than half the ice thickness appears to have originated from the bottom, not the top. Here, rates of refreezing are greater than surface accumulation rates. The researchers suggest that such refreezing has been going on since East Antarctica became encased in a large ice sheet some 32 million years ago. They may never know for sure: the ice is always moving from the deep interior toward the coast, so ice formed millions of years ago, and the evidence it would carry, is long gone.

Deeply buried ice may melt because overlying layers insulate the base, hemming in heat created there by friction, or radiating naturally from underlying rock. When the ice melts, refreezing may take place in multiple ways, the researchers say. If it collects along mountain ridges and heads of valleys, where the ice is thinner, low temperatures penetrating from the surface may refreeze it. In other cases, water gets squeezed up valley walls, and changes pressure rapidly. In the depths, water remains liquid even when it is below the normal freezing point, due to pressure exerted on it. But once moved up to an area of less pressure, such supercooled water can freeze almost instantly. Images produced by the researchers show that the refreezing deforms the ice sheet upward.

“When we first saw these structures in the field, we thought they looked like beehives and were worried they were an error in the data,” Bell said. “As they were seen on many lines, it became clear that they were real. We did not think that water moving through ancient river valleys beneath more than one mile of ice would change the basic structure of the ice sheet.”

Because the ice is in motion, understanding how it forms and deforms at the base is critical to understanding how the sheets will move, particularly in response to climate changes, researchers say. “It’s an extremely important observation for us because this is potentially lifting the very oldest ice off the bed,” said Jeff Severinghaus, a geologist at Scripps Institution of Oceanography in San Diego who was not involved in the study. He said it could either mean older ice is better preserved – or, it could “make it harder to interpret the record, if it’s shuffled like a deck of cards.”

From November 2008 to January 2009, the researchers did fieldwork around a California-size part of Dome A. Using aircraft equipped with ice penetrating radars, laser ranging systems, gravity meters and magnetometers, they flew low-altitude transects back and forth over the ice to draw 3-D images of what lay beneath. The aim was to understand how the mountains arose, and to study the connections between the peaks, the ice sheet, and subglacial lakes. They were also hunting for likely spots where future coring may retrieve the oldest ice. The work took place near the Southern Pole of Inaccessibility, the point farthest away from any ocean, and much harder to reach than the South Pole itself. They lived in isolated field camps, enduring high winds and temperatures ranging down to minus 40 degrees C.

“Understanding these interactions is critical for the search for the oldest ice and also to better comprehend subglacial environments and ice sheet dynamics,” said Fausto Ferraccioli, a scientist with the British Antarctic Survey who also helped lead the project. “Incorporating these processes into models will enable more accurate predictions of ice sheet response to global warming and its impact on future sea-level rise.”

The researchers now will look into how the refreezing process acts along the margins of ice sheets, where the most visible change is occurring in Antarctica. Based on their data, a Chinese team also hopes to drill deep into Dome A in the next two or three years to remove cores that would trace long-ago climate shifts. They hope to find ice more than a million years old.

New interpretation of Antarctic ice cores

Climate researchers at the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association (AWI) expand a prevalent theory regarding the development of ice ages. In the current issue of the journal Nature three physicists from AWI’s working group “Dynamics of the Palaeoclimate” present new calculations on the connection between natural insolation and long-term changes in global climate activity. Up to now the presumption was that temperature fluctuations in Antarctica, which have been reconstructed for the last million years on the basis of ice cores, were triggered by the global effect of climate changes in the northern hemisphere. The new study shows, however, that major portions of the temperature fluctuations can be explained equally well by local climate changes in the southern hemisphere.

The variations in the Earth’s orbit and the inclination of the Earth have given decisive impetus to the climate changes over the last million years. Serbian mathematician Milutin Milankovitch calculated their influence on the seasonal distribution of insolation back at the beginning of the 20th century and they have been a subject of debate as an astronomic theory of the ice ages since that time. Because land surfaces in particular react sensitively to changes in insolation, whereas the land masses on the Earth are unequally distributed, Milankovitch generally felt insolation changes in the northern hemisphere were of outstanding importance for climate change over long periods of time. His considerations became the prevailing working hypothesis in current climate research as numerous climate reconstructions based on ice cores, marine sediments and other climate archives appear to support it.

AWI scientists Thomas Laepple, Gerrit Lohmann and Martin Werner have analysed again the temperature reconstructions based on ice cores in depth for the now published study. For the first time they took into account that the winter temperature has a greater influence than the summer temperature in the recorded signal in the Antarctic ice cores. If this effect is included in the model calculations, the temperature fluctuations reconstructed from ice cores can also be explained by local climate changes in the southern hemisphere.

Thomas Laepple, who is currently conducting research at Harvard University in the US through a scholarship from the Alexander von Humboldt Foundation, explains the significance of the new findings: “Our results are also interesting because they may lead us out of a scientific dead end.” After all, the question of whether and how climate activity in the northern hemisphere is linked to that in the southern hemisphere is one of the most exciting scientific issues in connection with our understanding of climate change. Thus far many researchers have attempted to explain historical Earth climate data from Antarctica on the basis of Milankovitch’s classic hypothesis. “To date, it hasn’t been possible to plausibly substantiate all aspects of this hypothesis, however,” states Laepple. “Now the game is open again and we can try to gain a better understanding of the long-term physical mechanisms that influence the alternation of ice ages and warm periods.”

“Moreover, we were able to show that not only data from ice cores, but also data from marine sediments display similar shifts in certain seasons. That’s why there are still plenty of issues to discuss regarding further interpretation of palaeoclimate data,” adds Gerrit Lohmann. The AWI physicists emphasise that a combination of high-quality data and models can provide insights into climate change. “Knowledge about times in the distant past helps us to understand the dynamics of the climate. Only in this way will we learn how the Earth’s climate has changed and how sensitively it reacts to changes.”

To avoid misunderstandings, a final point is very important for the AWI scientists. The new study does not call into question that the currently observed climate change has, for the most part, anthropogenic causes. Cyclic changes, as those examined in the Nature publication, take place in phases lasting tens of thousand or hundreds of thousands of years. The drastic emission of anthropogenic climate gases within a few hundred years adds to the natural rise in greenhouse gases after the last ice age and is unique for the last million years. How the climate system, including the complex physical and biological feedbacks, will develop in the long run is the subject of current research at the Alfred Wegener Institute.

Press registration open for international seismology meeting

Hundreds of the world’s top seismologists will gather in Memphis, Tenn., April 13-15, at the annual meeting of the Seismological Society of America (SSA).

Press registration is now open and free for all holders of valid press identification or formal journalism credential

Highlights from the scientific program include special sessions on the New Madrid Seismic Zone, continental intraplate seismicity, earthquake triggering, induced seismicity, archeoseismology and much more.