Higher wetland methane emissions caused by climate warming 40,000 years ago

40,000 years ago rapid warming led to an increase in methane concentration. The culprit for this increase has now been identified. Mainly wetlands in high northern latitudes caused the methane increase, as discovered by a research team from the University of Bern and the German Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association. This result refutes an alternative theory discussed amongst experts, the so-called “clathrate gun hypothesis”. The latter assumed that large amounts of methane were released from the ocean sediment and led to higher atmospheric methane concentrations and thus to rapid climate warming.

Earlier measurements on ice cores showed that the atmospheric methane concentration changed drastically in parallel to rapid climate changes occurring during the last ice age. Those climate changes – so-called Dansgaard-Oeschger events – were characterized by a sudden warming and an increase in methane concentration. However, it was not yet clear to what extent the climate changes 40,000 years ago led to the methane increase or vice versa. Climate researchers from the Universities in Bern and Copenhagen and from the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven now conclude that the methane increase at that time was largely due to higher methane emissions from wetlands. As published by the researchers in the current issue of the magazine “Science“, these natural methane sources produced more methane especially in high northern latitudes in response to the warming. Through their study the researchers also refute another controversial hypothesis, which claimed that large amounts of methane stored as clathrate in the ocean sediment along the continental margins was released and triggered the rapid warming.

The scientists stress, however, that the climate conditions 40,000 years ago are not comparable to the current climate evolution. “Our results do not imply that methane or other greenhouse gases play no role for climate change. Our study reflects natural climate conditions during the last ice age, long before mankind affected global climate by emitting greenhouse gases. At that time climate warming caused an increase in methane concentration, generating in turn a more substantial greenhouse effect. Nowadays, additional methane and carbon dioxide are artificially emitted into the atmosphere by human activities and are the main driver of the observed climate warming.”

Ongoing studies of the Alfred Wegener Institute in Arctic permafrost regions take on greater importance in view of these research results.

Novel analytical method: Clear isotopic “fingerprints”

In nature a few methane molecules (CH4) have one more neutron in the carbon and hydrogen atoms they are made of and are therefore a little heavier. Methane from wetland sources has fewer molecules with the heavier hydrogen atom than methane produced in the ocean. Accordingly, the marine and terrestrial methane sources have unique “isotopic fingerprints”. Using these fingerprints, it is possible to quantify the emission of both sources. Developing a novel analytical method at the University of Bern and the Alfred Wegener Institute to take these “fingerprints” allowed the international team of scientists to come up with the unambiguous results now published in “Science“.

Tiny clays curb big earthquakes

California’s San Andreas fault is notorious for repeatedly generating major earthquakes and for being on the brink of producing the next “big one” in a heavily populated area. But the famously violent fault also has quieter sections, where rocks easily slide against each other without giving rise to damaging quakes.

The relatively smooth movement, called creep, happens because the fault creates its own lubricants—slippery clays that form ultra-thin coatings on rock fragments, geologist Ben van der Pluijm and colleagues at the University of Michigan and Germany’s Ernst-Moritz-Arndt Universität Institut für Geographie und Geologie report in the July issue of Geology.

The question of why some fault zones creep slowly and steadily while others lock for a time and then shift suddenly and violently, spawning earthquakes, has long puzzled scientists. Some have speculated that fluids facilitate slippage, while others have focused on serpentine—a greenish material that can alter to slippery talc.

But when van der Pluijm and colleagues analyzed samples of rock from an actively creeping segment that was brought up from a depth of two miles below the surface as part of the San Andreas Fault Observatory at Depth (SAFOD) project, they found very little talc. Instead, they found that fractured rock surfaces were coated with a thin layer of smectitic clay, less than 100 nanometers thick, that acts something like grease on ball bearings.

“For a long time, people thought you needed a lot of lubricant for creep to occur,” said van der Pluijm, who is the Bruce R. Clark Collegiate Professor of Geology and Professor of the Environment. “What we can show is that you don’t really need a lot; it just needs to be in the right place. It’s a bit like real estate: location, location, location.” The nanocoatings occur on the interfaces of broken-up bits of rock in exactly the places where they affect the fault’s “weakness”—how easily it moves.

The technique of argon dating provided key evidence, when the researchers determined that these clays, found only in fault rock, formed relatively recently.

“The clays are growing in the fault zone, and the fault is coating its own pieces of fragmented rock,” van der Pluijm said. “At some point there’s enough coating that it begins to drive the behavior of the fault, and creeping kicks in.”

If the fault is greasing itself, then why do earthquakes still occur?

“The problem is that the fault doesn’t always move at strands where the coating sits,” van der Pluijm said. The San Andreas fault is actually a network of faults, with new strands being added all the time. Because it takes some time for the slick nanocoatings to develop in a new strand, the unlubricated, new strand “gets stuck” for a time and then shifts in a violent spasm.

Although the samples obtained through SAFOD are from a depth of only about two miles, van der Pluijm and colleagues think it’s likely the clay nanocoatings also are forming and driving fault behavior at greater depths. What’s more, analyses of older, inactive strands suggest that the coatings have been facilitating creep for the millions of years of fault activity.

The SAFOD project, which is establishing the world’s first underground earthquake observatory, is a major research component of EarthScope, an ambitious, $197-million federal program to investigate the forces that shaped the North American continent and the processes controlling earthquakes, volcanoes and other geological activity.

New areas prone to moderate earthquakes identified in Iberian Peninsula

The map indicates the nodes (circles) with the potential to generate moderate earthquakes in the Iberian Peninsula and earthquakes historically (blue dots) of this magnitude. -  A. I. Gorshkov  et al.
The map indicates the nodes (circles) with the potential to generate moderate earthquakes in the Iberian Peninsula and earthquakes historically (blue dots) of this magnitude. – A. I. Gorshkov et al.

Some areas of the Iberian Peninsula, where earthquakes of moderate magnitude have never yet been recorded, such as certain parts of the Cordillera Cantábrica mountain range, the far west of the Cordilleras Béticas mountains and the north of Valencia, could have the potential to generate such quakes, according to a study produced by Spanish, Russian and Italian scientists and published this month in the journal Rendiconti Lincei.

“The methodology we have used confirms the most seismically significant areas of the Iberian Peninsula, but also identifies possible sources of earthquakes with magnitudes of over five in some areas where, to date, none have been recorded” Mariano García-Fernández, co-author of the study and a researcher at the Spanish National Museum of Natural Sciences (CSIC), tells SINC.

According to the study, which has been published in the latest issue of the journal Rendiconti Lincei, these areas are located in some parts of the Cordillera Cantábrica mountain range, the northern coast of Portugal, the far west of the Cordilleras Béticas mountains and the north of Valencia. The remaining areas with the potential for moderate seismic activity are the same as those shown on seismic maps – around the edges of the Peninsula, above all the south east and the Pyrenees.

“The important thing about this study is that it identifies zones prone to moderate earthquakes at regional level, although this does not mean they will ever happen”, points out García-Fernández.

The researcher explains that the magnitude 5 was chosen as the threshold for potential earthquakes “since it is above this level that you start to see significant damage to structures”.

In search of nodes

The research, which is the fruit of collaboration between scientists at the Russian Academy of Sciences, the International Centre for Theoretical Physics and the University of Trieste (Italy) and the CSIC, is based on the morphostructural zoning method. The technique uses topographic, geological and geophysical information, along with satellite imagery, to identify the nodes or intersection points of morphostructural lines.

These nodes are classified as likely to cause earthquakes of a specific threshold size by combining the seismicity data from seismic catalogs with mathematical recognition methods, similar to those used in voice or fingerprint identification.

García-Fernández insists that the resulting classification does not necessarily mean that the potentially seismic nodes identified will produce earthquakes of this size, “but rather that their features make them more susceptible than those classified as having lower potential”.

The authors of the study are confident that the results will make it possible to better identify the continental seismogenic sources affecting the Iberian Peninsula. This will allow progress to be made in studies into danger levels and seismic risk at regional scale and in specific places, such as metropolitan areas or special structures such as nuclear power plants and large dams.

Like fireflies, earthquakes may fire in synchrony

A magnitude 7.3 quake in Landers, Calif., in 1992 killed one person. -  Southern California Earthquake Data Center.
A magnitude 7.3 quake in Landers, Calif., in 1992 killed one person. – Southern California Earthquake Data Center.

In nature, random signals often fall mysteriously in step. Fireflies flashing sporadically in early evening soon flash together, and the same harmonic behavior can be seen in chirping crickets, firing neurons, swinging clock pendulums and now, it turns out, rupturing earthquake faults.

Scientists have well established that big earthquakes can trigger other big quakes by transferring stress along a single fault, as successive earthquakes in Turkey and Indonesia have shown. But some powerful quakes can set off other big quakes on faults tens of kilometers away, with just a tiny nudge, says a new paper. Christopher Scholz, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory, explains how: the faults are already synchronized, he says.

Scholz argues in the most recent issue of the Bulletin of the Seismological Society of America that when a fault breaks, it may sometimes gently prod a neighboring fault also on the verge of fracturing. The paper finds evidence for synchronized, or “phase locked,” faults in southern California’s Mojave Desert, the mountains of central Nevada, and the south of Iceland. Drawing on earthquake patterns as far back as 15,000 years, the paper identifies strings of related earthquakes, and explains the physics of how faults separated by up to 50 kilometers, and rupturing every few thousand years, might align themselves to rupture almost simultaneously.

“All of a sudden bang, bang, bang, a whole bunch of faults break at the same time,” says Scholz. “Now that we know that some faults may act in consort, our basic concept of seismic hazard changes. When a large earthquake happens, it may no longer mean that the immediate future risk is lower, but higher.”

The idea of independent events synchronizing themselves goes back to the Age of Discovery and the pendulum clock, invented as scientists and navigators were searching for a device to measure longitude at sea. In 1665, Christiaan Huygens, the Dutch mathematician who invented the pendulum clock (a dead end, it turned out, in solving the longitude problem) first described how the pendulums of two clocks hanging from the same wall became synchronized. Known as entrainment, or coupled oscillation, this phenomenon is caused by the motion of the two pendulums communicating through the beam supporting the clocks.

Entrainment can also happen when faults lie relatively close, between 10 and 50 kilometers apart, and are moving at comparable speeds, Scholz says. As faults break successively over time, their cycles may eventually fall in sync, a process described in the paper by the mathematical “Kuramoto Model.”

The paper provides real-world examples from places where geologists and seismologists have compiled a long record of past quakes. In the Mojave Desert, the Camp Rock fault, a secondary fault off the San Andreas, ruptured in 1992, causing a magnitude 7.3 quake in the town of Landers, killing one child. Seven years later, the Pisgah fault, 24 kilometers away, broke, causing a magnitude 7.1 quake at Hector Mine, inside the Twentynine Palms Marine Corps Base.

When a fault ruptures in a large earthquake, the movement releases stresses that may have built up over millennia. But the movement also transfers a small amount of that stress, usually a fraction of a percent, to nearby faults. In order for that tiny added stress to trigger a large earthquake on a nearby fault, that fault had to already be very near its breaking point, says Scholz. For the two faults to have been simultaneously near their breaking points requires them to be synchronized in their seismic cycles.

Paleoseismology-that is, studies of the physical signs left by past earthquakes– show that the Mojave faults rupture every 5,000 years or so, so the relatively short seven-year lag between the Landers and Hector Mine quakes suggested to Scholz the timing could not be random. When he looked at the paleoseismological record, he saw that both faults had ruptured together before, at about 5,500 years ago and 10,000 years ago. He noticed a similar trend with the nearby Lenwood and Helendale faults, which had ruptured together 1,000 years ago and 9,000 years ago. And, the two fault pairs happened to be moving at virtually the same pace, 1 millimeter and .8 millimeter, respectively.

He noticed a similar trend in Nevada. In the summer of 1954, the Rainbow Mountain fault system was hit by five earthquakes ranging in magnitude from 5.5 to 6.8. The action culminated on Dec. 16 with a 7.1 quake on Fairview Peak and a 6.8 quake four minutes later on the Dixie Valley fault, 40 kilometers away. Again, the triggering stress was a small fraction of a percent. Paleoseismic evidence showed that similar groups of faults nearby had produced clusters of earthquakes every 3,000 years or so over the last 12,000 years.

The same pattern emerged in Iceland. In June 2000, two quakes–magnitudes 6.5 and 6.4– struck within four days of each other on parallel faults 14 kilometers apart. In 1896, five large quakes struck on different neighboring faults within 11 days of each other, with similar clusters occurring in 1784, and from 1732 to 1734.

Scholz says his hypothesis of synchronized faults could make it easier to assess some earthquake hazards by showing that faults moving at similar speeds, and within roughly 50 kilometers of each other, may break at similar times, while faults moving at greatly different speeds, and located relatively far apart, will not.

However, seismologists have yet to come up with a reliable method for predicting imminent earthquakes; the best they can do so far is to identify dangerous areas, and roughly estimate how often quakes of certain sizes may strike.

Ross Stein, a geophysicist at the U.S. Geological Survey, who was not involved in the study, questioned the paper’s wider significance. There is “good” evidence for historic earthquake sequences, and “possible” evidence for prehistoric sequences, he said, but those quakes make up a minority of earthquake events.

Geologist investigates canyon carved in just 3 days in Texas flood

This is an aerial photograph taken near the time of the 2002 flood event at Canyon Lake, Texas. Floodwaters overflowed Canyon Lake reservoir and carved the gorge downstream. -  Comal County, Texas.
This is an aerial photograph taken near the time of the 2002 flood event at Canyon Lake, Texas. Floodwaters overflowed Canyon Lake reservoir and carved the gorge downstream. – Comal County, Texas.

In the summer of 2002, a week of heavy rains in Central Texas caused Canyon Lake-the reservoir of the Canyon Dam-to flood over its spillway and down the Guadalupe River Valley in a planned diversion to save the dam from catastrophic failure. The flood, which continued for six weeks, stripped the valley of mesquite, oak trees, and soil; destroyed a bridge; and plucked meter-wide boulders from the ground. And, in a remarkable demonstration of the power of raging waters, the flood excavated a 2.2-kilometer-long, 7-meter-deep canyon in the bedrock.

According to a new analysis of the flood and its aftermath-performed by Michael Lamb, assistant professor of geology at the California Institute of Technology (Caltech), and Mark Fonstad of Texas State University-the canyon formed in just three days.

A paper about the research appears in the June 20 advance online edition of the journal Nature Geoscience.

Our traditional view of deep river canyons, such as the Grand Canyon, is that they are carved slowly, as the regular flow and occasionally moderate rushing of rivers erodes rock over periods of millions of years.

Such is not always the case, however. “We know that some big canyons have been cut by large catastrophic flood events during Earth’s history,” Lamb says.

Unfortunately, these catastrophic megafloods-which also may have chiseled out spectacular canyons on Mars-generally leave few telltale signs to distinguish them from slower events. “There are very few modern examples of megafloods,” Lamb says, “and these events are not normally witnessed, so the process by which such erosion happens is not well understood.” Nevertheless, he adds, “the evidence that is left behind, like boulders and streamlined sediment islands, suggests the presence of fast water”-although it reveals nothing about the time frame over which the water flowed.

This is why the Canyon Lake flood is so significant. “Here, we know that all of the erosion occurred during the flood,” Lamb says. “Flood waters flowed for several weeks, but the highest discharge-during which the bulk of the erosion took place-was over a period of just three days.”

Lamb and Fonstad reached this conclusion using aerial photographs of the region taken both before and after the flood, along with field measurements of the topography of the region and measurements of the flood discharge. Then they applied an empirical model of the sediment-carrying capacity of the flood-that is, the amount of soil, rocks, boulders, and other debris carried by the flood to produce the canyon.

The analysis revealed that the rate of the canyon erosion was so rapid that it was limited only by the amount of sediment the floodwaters could carry. This is in contrast to models normally applied to rivers where the erosion is limited by the rate at which the underlying rock breaks and is abraded.

The researchers argue that the rate of erosion was rapid because the flood was able to pop out and cart away massive boulders (a process called “plucking”)-producing several 10- to 12-meter-high waterfalls that propagated upstream toward the dam, along with channels and terraces. The flood was able to pluck these boulders because the bedrock below the soil surface of the valley was already fractured and broken.

The abrasion of rock by sediment-loaded waters-while less significant in terms of the overall formation of the canyon-produced other features, like sculpted walls, plunge pools at the bases of the waterfalls, and teardrop-shaped sediment islands. The sediment islands are particularly significant, Lamb says, because “these are features we see on Earth and on Mars in areas where we think large flow events have occurred. It’s nice that here we’re seeing some of the same features that we’ve interpreted elsewhere as evidence of large flow events.”

The results, Lamb says, offer useful insight into ancient megafloods, both on Earth and on Mars, and the deep canyons they left behind. “We’re trying to build models of erosion rates so we can go to places like Mars and make quantitative reconstructions of how much water was there, how long it lasted, and how quickly it moved,” Lamb says. In addition, he says, “this is one of a few places where models for canyon formation can be tested because we know the flood conditions under which this canyon formed.”

The key role of the oceans’ subpolar regions in the climate control of the tropics is confirmed

An international team of researchers, led by the members of the Institut de Ciència i Tecnologia Ambientals (ICTA) at the Universitat Autònoma de Barcelona (UAB), has published the first registers of the evolution of Northern Pacific and Southern Atlantic sea-surface temperatures, dating from the Pliocene Era -some 3.65 million years ago- to the present. The data obtained in the reconstruction indicate that the regions closer to the poles of both oceans have played a fundamental role in climate evolution in the tropics.

This research solves another piece of the jigsaw puzzle that is the study of oceanic behavior and its influence on climate. The results are based on the doctoral thesis presented by Dr Alfredo Martínez-García (currently, a researcher with both the Swiss Federal Institute of Technology, ETH Zurich, and with the DFG-Leibniz Centre at the University of Postdam, Germany). The thesis was undertaken at the UAB and directed by Dr Antoni Rosell Melé, an ICTA ICREA researcher and adjunct professor with the Department of Geography. This work was carried out in collaboration with Dr Gerald H. Haug, of ETH and DFG-Leibniz Centre; Dr Erin L. McClymont of Newcastle University (UK); and Dr Rainer Gersonde, of the Alfred Wegener Institute (Germany).

The study of Pliocene climate has now been the object of intense research for several years, as this era represents-in the Earth’s history-the most recent climatic period in which, over a sustained period of time, average temperatures on the planet were significantly higher than those of the present. As a result, the Pliocene is thought of as a climatic period that might be representative of the Earth’s climate in future conditions of global warming.

In this study, the researchers analyzed marine sediment collected by the Integrated Ocean Drilling Program (an international initiative), and measured its composition of organic compounds termed alkenones.

Reconstruction of the surface temperature in the Northern Pacific and Southern Atlantic has enabled a simultaneous sea-surface cooling to be identified in the subpolar regions of the two hemispheres in the period between 1.8 and 1.2 million years ago. This finding coincides in time with the formation of the equatorial Pacific cold tongue-which currently almost disappears during the “El Niño” phenomenon.

Previous studies have shown that, during the warm conditions of the Pliocene, this cold tongue was not present; thus, conditions in the equatorial Pacific were similar to those of a permanent “El Niño” episode. Data obtained in this study indicate that the cooling and expansion of polar waters towards the tropics intensified atmospheric circulation. And this fact played a fundamental role in the equatorial Pacific, leading to the reduction in depth of the thermocline-the layer of ocean water in which the temperature fall rapidly-and therefore to the appearance of the equatorial cold tongue that we can currently observe.

The research undertaken provides empirical evidence, previously suggested by studies using climatic models, that the oceans in high latitudes may play a key role in the control of tropical climate and, most especially, in the thermocline depth in the equatorial Pacific.

The study contributes to the debate on which regions on the planet are those that, when their local climates change, give rise to processes of global change. It is often indicated that these regions are found in the tropics, since, when phenomena such as “El Niño” occur, they have global repercussions. This study provides evidence for the key role that may be played by the polar regions of the planet.

Currently, high latitudes are the ones that appear to be responding in the clearest way to global warming. Given the direct relationship established in this study between high-latitude climate variation and thermocline depth in the equatorial Pacific, it appears possible that the equatorial Pacific cold tongue will eventually respond to the current warming, giving rise to a climatic scenario similar to that of the Pliocene.

Retooling the ocean conveyor belt

For decades, oceanographers have embraced the idea that Earth’s ocean currents operate like a giant conveyor belt, overturning to continuously transport deep, cold polar waters toward the equator and warm equatorial surface waters back toward the poles along narrow boundary currents. The model held that the conveyor belt was driven by changes in the temperature and salinity of the surface waters at high latitudes.

In a paper in the June 18 issue of Science, a Duke University oceanographer reviews the growing body of evidence that suggests it’s time to rethink the conveyor belt model.

“The old model is no longer valid for the ocean’s overturning, not because it’s a gross simplification, but because it ignores crucial elements such as eddies and the wind field. The concept of a conveyor belt for the overturning was developed decades ago, before oceanographers had measured the eddy field of the ocean and before they understood how energy from the wind impacts the overturning,” says Susan Lozier, professor of physical oceanography and chair of the Division of Earth and Ocean Sciences at Duke University’s Nicholas School of the Environment.

“It is important to understand that there is clear and convincing evidence that the ocean waters overturn and that this overturning impact’s the Earth’s climate,” she says. “Recent studies, however, have cast doubt on our ability to describe this overturning as a conveyor belt. From these studies we now understand that the overturning waters are not restricted to narrow boundary currents, that the overturning may vary from one ocean basin to the next and that the winds may create variability in the amount of water that overturns and in the pathways for the upper and lower limbs of the overturning.”

The Science article also reviews what remains unknown about the ocean’s overturning. As surface waters warm and/or freshen due to climate change, how might the overturning change? Though modeling studies have addressed this question, there has been no observational study.

A new international research program in the planning stages, led by Lozier, aims to address the question of climate effects. The initiative will bring together researchers from the United States, Germany, Canada, France and the United Kingdom to study overturning in the northern North Atlantic over a five-to-10-year period.

In her Science article, Lozier reviews the emerging view of the overturning circulation within a historical framework that chronicles significant scientific developments in the field, from the first reported measurement of ocean overturning in 1751 through the present.

“Basically, our ability to refine our understanding of the ocean’s overturning stems in large part from our ever increasing ability to measure the ocean at finer and finer scales and at depths previously unmeasured,” she says. “Because the ocean waters are corrosive, at high pressure and generally inaccessible, the ocean has historically been a sparsely observed system. Recent technological advances are rapidly expanding the ocean’s observational database and with it, our understanding of ocean circulation.”

New research sheds light on Antarctica’s melting Pine Island Glacier

Autosub - autonomous underwater vehicle
Autosub – autonomous underwater vehicle

New results from an investigation into Antarctica’s potential contribution to sea level rise are reported this week (Sunday 20 June) by scientists from the British Antarctic Survey (BAS), Lamont-Doherty Earth Observatory (LDEO) and the National Oceanography Centre in the journal Nature Geoscience.

Thinning ice in West Antarctica is currently contributing nearly 10 per cent of global sea level rise and scientists have identified Pine Island Glacier (PIG) as a major source. As part of a series of investigations to better understand the impact of melting ice on sea level an exciting new discovery has been made. Using Autosub (an autonomous underwater vehicle) to dive deep and travel far beneath the pine Island Glacier’s floating ice shelf, scientists captured ocean and sea-floor measurements, which revealed a 300m high ridge (mountain) on the sea floor.

Pine Island Glacier was once grounded on (sitting on top of) this underwater ridge, which slowed its flow into the sea. However, in recent decades it has thinned and disconnected from the ridge, allowing the glacier to move ice more rapidly from the land into the sea. This also permitted deep warm ocean water to flow over the ridge and into a widening cavity that now extends to an area of 1000 km² under the ice shelf. The warm water, trapped under the ice, is causing the bottom of the ice shelf to melt, resulting in continuous thinning and acceleration of the glacier.

Lead author Dr Adrian Jenkins of British Antarctic Survey said, “The discovery of the ridge has raised new questions about whether the current loss of ice from Pine Island Glacier is caused by recent climate change or is a continuation of a longer-term process that began when the glacier disconnected from the ridge.

“We do not know what kick-started the initial retreat from the ridge, but we do know that it started some time prior to 1970. Since detailed observations of Pine Island Glacier only began in the 1990s, we now need to use other techniques such as ice core analysis and computer modeling to look much further into the glacier’s history in order to understand if what we see now is part of a long term trend of ice sheet contraction. This work is vital for evaluating the risk of potential wide-spread collapse of West Antarctic glaciers.”

Co-author Stan Jacobs adds: “Since our first measurements in the Amundsen Sea, estimates of Antarctica’s recent contributions to sea level rise have changed from near-zero to significant and increasing. Now finding that the PIG’s grounding line has recently retreated more than 30 km from a shallow ridge into deeper water, where it is pursued by a warming ocean, only adds to our concern that this region is indeed the ‘weak underbelly’ of the West Antarctic Ice Sheet. Increased melting of continental ice also appears to be the primary cause of persistent ocean freshening and other impacts, both locally and downstream in the Ross Sea.”

New insights into volcanic activity on the ocean floor

The red zone indicates ancient eruptions that happened when North America split from Europe
The red zone indicates ancient eruptions that happened when North America split from Europe

New research reveals that when two parts of the Earth’s crust break apart, this does not always cause massive volcanic eruptions. The study, published today in the journal Nature, explains why some parts of the world saw massive volcanic eruptions millions of years ago and others did not.

The Earth’s crust is broken into plates that are in constant motion over timescales of millions of years. Plates occasionally collide and fuse, or they can break apart to form new ones. When the latter plates break apart, a plume of hot rock can rise from deep within the Earth’s interior, which can cause massive volcanic activity on the surface.

When the present-day continent of North America broke apart from what is now Europe, 54 million years ago, this caused massive volcanic activity along the rift between the two. Prior to today’s study, scientists had thought that such activity always occurred along the rifts that form when continents break apart.

However, today’s research shows that comparatively little volcanic activity occurred when the present-day sub-continent of India broke away from what is now the Seychelles, 63 million years ago.

Researchers had previously believed that the temperature of the mantle beneath a plate was the key to determining the level of volcanic activity where a rift occurred. The new study reveals that in addition, the prior history of a rift also strongly influences whether or not volcanic activity will occur along it.

In the case of the break-up of America from Europe, massive volcanic activity occurred along the rift because a previous geological event had thinned the plate, according to today’s study. This provided a focal point where the mantle underneath the plate could rapidly melt, forming magma that erupted easily through the thinned plate and onto the surface, in massive outbursts of volcanic activity.

In comparison, when India broke away from the Seychelles very little volcanic activity occurred along the North Indian Ocean floor, because the region had experienced volcanic activity in a neighboring area called the Gop Rift 6 million years earlier. This exhausted the supply of magma and cooled the mantle, so that when a rift occurred, very little magma was left to erupt.

Dr Jenny Collier, co-author from the Department of Earth Science and Engineering at Imperial College London, says: “Mass extinctions, the formation of new continents and global climate change are some of the effects that can happen when plates break apart and cause super volcanic eruptions. Excitingly, our study is helping us to see more clearly some of the factors that cause the events that have helped to shape the Earth over millions of years.”

The team reached their conclusions after carrying out deep sea surveys of the North Indian Ocean to determine the type of rock below the ocean floor. They discovered only small amounts of basalt rock, which is an indicator of earlier volcanic activity .The team also used new computer models that they had developed to simulate what had happened along the ocean floor in the lead up to India and the Seychelles splitting apart.

Dr John Armitage, lead author of the paper from the Department of Earth Science and Engineering at Imperial College London, adds: “Our study is helping us to see that the history of the rift is really important for determining the level of volcanic activity when plates break apart. We now know that this rift history is just as important as mantle temperature in controlling the level of volcanic activity on the Earth’s surface.”

In the future, the team hope to further explore the ocean floor off the coast of South America where that continent split from Africa millions of years ago to determine the level of ancient volcanic activity in the region.

Research is getting closer to understanding critical nucleus in haze formation, prof says

Renyi Zhang
Renyi Zhang

Haze, scientifically known as atmospheric aerosols – microscopic particles suspended in the Earth’s atmosphere – represents a major environmental problem because it degrades visibility, affects human health and influences the climate. Despite its profound impacts, how the haze is formed is not fully understood, says a Texas A&M University professor of atmospheric sciences and chemistry who has studied air chemistry for more than 20 years.

Professor Renyi Zhang published his work in the June 11 issue of Science magazine, summarizing recent findings and new research directions that could pave the way for a better understanding of aerosol formation.

“Aerosols, also referred to as haze, influence climate by absorbing and reflecting solar radiation and modifying cloud formation,” he explains. “A better understanding of how aerosols form in the atmosphere will greatly improve climate models.

“But, formation of aerosols in the atmosphere is not fully understood, particularly at the molecular level, creating one of the largest sources of uncertainty in climate predictions,” he adds.

For aerosols to form, the bonding particles must cross an energy threshold, which the scientists call nucleation barrier. Once the barrier is crossed, aerosol formation can happen spontaneously, he notes.

The interaction between organic acids and sulfuric acid can facilitate the crossing of the barrier by creating a critical nucleus, the Texas A&M professor says in the Science article.

Large amounts of organic gases are emitted to the atmosphere by plants, industry and automobiles and form organic acids; sulfur dioxide, on the other hand, are produced by human activities, such as burning coals, and then form sulfuric acid.

To better understand aerosol formation, scientists need to predict the nucleation rate based on knowledge of the composition of the critical nucleus, Zhang explains.

This knowledge can be obtained by combining theoretical approaches with “measurements of the size and chemical composition of freshly nucleated nanoparticles in the laboratory and in the field,” Zhang notes.

Understanding and eventually controlling aerosol formation may help the environment, benefit human health and improve climate prediction, he says.