The extreme wet and dry periods Mongolia has experienced in the late 20th and early 21st centuries are rare but not unprecedented and future droughts may be no worse, according to an international research team that includes a University of Arizona scientist.

Kevin Anchukaitis (plaid shirt) and Oyunsanaa Byambasuren (orange chainsaw chaps) taking pieces of wood from dead trees on Mongolia's Uurgat lava field. The researchers use tree rings to create a record of Mongolia's droughts stretching two centuries into the past [Credit: Neil Pederson © 2013]

The research team developed a climate record stretching 2,060 years into Mongolia's past by using the natural archive of weather conditions stored in the annual rings of Siberian pines. The 10 researchers then combined that information on past climate with computer models that can project future regional climate.

The most recent extended drought in Mongolia lasted from 2000 to 2010 and resulted in major livestock die-offs and a massive migration of nomadic herders to the capital city.

"We were able to quantify how unusual this drought was," said co-author Kevin J. Anchukaitis, a University of Arizona associate professor of geography and development. "The drought was not unprecedented, but it has a 900-year return interval. It's a once-in-a-millennium drought."

Finding that future droughts would likely be no worse than those of the past was a surprise, said Anchukaitis, who led the modeling team. In other semi-arid regions of the world that he has studied such as California and the Mediterranean, global warming has already changed precipitation and temperature patterns and thereby increased the risk of long-term drought.

Mongolia, a landlocked country in central Asia, has long, cold winters and short summers. Much of the country is cold, semi-arid grasslands that resemble eastern Montana.

Lead author Amy Hessl of West Virginia University said, "You would expect, based on everything we've been thinking about and reading as climate scientists, that elevated temperatures are going to lead to more severe droughts in semi-arid regions. But the models did not project increased frequency or severity of droughts."

Researchers Kevin Anchukaitis and Amy Hessl walk across the Khorgo lava field in central Mongolia to collect cross-sections of dead trees. The researchers use tree rings to create a record of Mongolia's droughts stretching two centuries into the past [Credit: Neil Pederson © 2012]

The timing of the rainy season is the likely cause, the researchers said. Mongolia's rainy season is in the summer, the warmer time of the year, whereas California and the Mediterranean have winter rains and dry summers. As global temperatures increase, continental regions with summer rains may get more precipitation, offsetting the effects on plants of higher temperatures.

The team's research paper, "Past and Future Drought in Mongolia," has been published in Science Advances. A complete list of the authors is at the bottom of this release. National Geographic and the National Science Foundation funded the research.

Anchukaitis, who also has appointments in geosciences and in the UA Laboratory of Tree-Ring Research, is interested in how past and current civilizations dealt with drought and climate variability. This new research is an outgrowth of previous research he, Hessl and their colleagues conducted to figure out how past climate influenced the Mongol civilization.

Anchukaitis and his colleagues used their tree-ring record of past climate in Mongolia to reconstruct what the annual Palmer Drought Severity Index, or PDSI, would have been going back in time 2,060 years. The PDSI combines both temperature and precipitation to get a measure of soil moisture, one measure of how water-stressed a plant would be.

He and his colleagues combined the reconstruction of past annual PDSI measures with a set of climate model simulations called the Community Earth System Model to understand what influenced the Mongolian droughts for the period from 850 to 2100.

The Uurgat lava field with the Khangai Mountains in the background and the seasonal homes of nomadic herders in the lower right. An international team of researchers took wood samples of the Siberian pines growing on the lava field to construct a drought chronology reaching two centuries into the past [Credit: Scott Nichols]

The model incorporates information about past solar variability, volcanic eruptions, land use changes and carbon dioxide emissions. For projections to the end of the 21st century, the model uses the future emissions scenario called RCP 8.5, in which the rate of emissions of greenhouse gases continues to increase.

Even with the highest level of greenhouse gas emissions and rising global temperatures, the model simulations indicate that future droughts in Mongolia would be no more severe than those of the past.

"There's a tug of war between trends toward increased rainfall and more evaporative demand because of hotter temperatures. There's uncertainty about which will win this tug of war," Anchukaitis said.

"The simulations say that Mongolia dries between now and about 2050 because of higher temperatures, but then it turns around because of the increase in precipitation," he said.

Many people in Mongolia are nomadic pastoralists. They are particularly affected by the vagaries of weather and climate, because the combination of winter and summer temperatures plus rainfall controls the number of cattle the grassland can support.

"What to me stands out is this deep uncertainty about the future, particularly when you have a society that is so vulnerable to climate variability," he said, adding that uncertainty makes it hard to plan for coping with future climate change.

Anchukaitis said one of his next steps is translating the team's estimates of future soil moisture into estimates of the future productivity of Mongolia's grasslands.

Author: Mari N. Jensen | Source: University of Arizona [March 14, 2018]

It may not rank among the all-time greatest dramas, but the history of ice on Greenland has been a source of scientific controversy for more than a decade.

Iceberg off the coast of Greenland [Credit: Drew Avery/WikiCommons]

A study led by UCLA climate scientist Aradhna Tripati appears to put the debate to rest, with major implications for future research across a range of disciplines, from climate science to geology. The paper, which is published today in the journal Nature Communications, also sheds light on how global climate may change as people continue emitting greenhouse gases, revealing a potential tipping point: atmospheric carbon dioxide concentrations of 500 parts per million or more. Beyond that threshold, major ice sheets at both poles could melt significantly. Current levels are near 400 parts per million.

For years, the prevailing belief was that glaciers first appeared on Greenland between 5 million and 11 million years ago. Then, in 2005, Tripati authored a study suggesting the ice had been present there much earlier: about 35 to 40 million years ago.

Though Tripati's paper was published in Nature—one of the most-respected scientific journals—it was considered controversial. At the heart of the conflict was a simple question: Why weren't similar observations made by other studies? Because the findings were not in line with previous knowledge, the paper was regarded as an outlier.

Tripati, who was then a postdoctoral fellow, admits that her research, which was based on the chemistry of Pacific Ocean samples and what they implied about ancient seawater, was "a pretty indirect indicator." Still, she had confidence in the results. She, her students and other researchers conducted a series of studies using different climate indicators, and they kept reaching the same conclusion.

"Understanding the history of ice at both poles and how they respond to changing carbon dioxide levels is so important that, as we published these papers, controversy built up," said Tripati, who is a member of the UCLA Institute of the Environment and Sustainability. "We dug in and continued to try to understand what the history, in fact, was."

In 2014, Tripati sent Dennis Darby, an Arctic paleoclimate specialist at Old Dominion University who became her co-author on the new paper, promising samples taken from a site in the Greenland Sea where icebergs that broke off—a process known as "calving"—from glaciers on the island would have drifted by.

"As glaciers move across land, they incorporate pieces of sediment," Tripati said. "As glaciers produce icebergs and those icebergs drift through the ocean, those little fragments of rock get released as the ice melts. Each rock fragment has a unique chemistry. That chemistry is a fingerprint—each grain tells you something about where the ice came from."

Those samples are dated based on what fossils are present and their magnetic properties, allowing researchers to reconstruct where and when there was ice present on Greenland and other land masses in the Arctic, as well as when there was sea ice in the ocean.

Data visualization showing changes in Greenland’s ice sheet from 2003 to 2012. Rapidly thinning coastal regions are shown in green, blue and purple [Credit: NASA]

Tripati chose to send those new samples to Darby because he had published a study that corroborated her 2005 findings. Using a method he pioneered, Darby analyzed them without knowing what he was looking at, where it came from or how old it was—sort of like a blind taste test.

He found that the samples contained "very high matches" to east Greenland source sites, again confirming Tripati's earlier research. In fact, his analysis showed that large glaciers were present on Greenland even earlier: up to 47.1 million years ago. That was right at the beginning of the middle Eocene epoch, about 20 million years after dinosaurs went extinct.

Darby was also able to match ice from the samples to other locations across the Arctic region.

"That's important," Darby said. "It shows this was not just a local or regional effect in Greenland. It was something climatically induced on a much larger scale, a polar event."

With their new study, Tripati and Darby think the mystery is solved. Darby's technique was rigorously tested in a 2012 study and found to be accurate 98.5 percent of the time. They examined 100 sediment samples and fingerprinted the chemistry of more than 2,000 rock fragments.

Today's paper also contains revelations about how atmospheric conditions relate to the presence or absence of ice. In the years since that first freeze, ice formed and retreated from Greenland several times. The researchers found that ice was usually present when carbon dioxide levels were lower than 500 parts per million.

"What happens if carbon dioxide levels get sustained at 800 parts per million, where some carbon emissions scenarios have us going?" Tripati asked. "Greenland has a lot of ice. If it all melted, it could raise sea level globally by about 20 feet."

Ice comes and goes at both poles under those conditions, the study found. Tripati's research from 2016 that suggested massive ice shelves on Antarctica are also at risk of melting supports this.

Understanding tipping points is important because Earth's climate can change quickly, Darby said. He pointed to 10,000 years ago in Greenland, when temperatures rose 10 degrees Celsius in 10 years.

"Those thresholds need to be researched," Darby said. "They are largely ignored by climate scientists because these things happened way in the past. Many of them are sort of stuck in the past 50 years. And in that time, we don't see any big changes except in the past two decades, when we see very rapid changes that are concerning."

Tripati said that controversies are good for science in general, she said—it shows the scientific process is healthy. She recalled cat-sitting for renowned scientist Sir Nicholas Shackleton around the time she was conducting the early study.

"He said to me 'When you discover something surprising, remember that it's OK to be wrong, but ideally you should be the person to find out. Always try to prove yourself wrong instead of trying to prove yourself right,' " Tripati recalled.

"I think that's excellent advice. With this study, I didn't know what we were going to find. If it didn't work out, fine—we could have written a paper that definitively said 'no evidence for this.' And then we're on the right side of science."

The process also underscored the importance of including diverse perspectives in science, Tripati said. Last summer she launched the UCLA Center for Diverse Leadership in Science—the first initiative of its kind devoted to including people of all backgrounds in environmental science. Dogma that endured for decades can shift dramatically if the scientific community is inclusive and welcomes new perspectives, she said. Inclusion and social belonging will foster diversity, and research shows that leads to more creative approaches and ideas, fueling innovation and scientific breakthroughs.

Tripati and Darby both hope today's findings inspire future research to better understand what will happen to Earth's climate, species and human communities if we continue on our current carbon emissions trajectory.

They also hope it will inform policies aimed at preventing a climate catastrophe—particularly efforts to reduce carbon emissions, Darby said.

"We need to start looking at what we're doing," Darby said. "Some people stick their heads in the sand because they think we'll come up with technology to save us at the last minute. But that's provided we don't hit one of these thresholds first."

Author: David Colgan | Source: University of California, Los Angeles [March 13, 2018]

Imagine a year in Africa that summer never arrives. The sky takes on a gray hue during the day and glows red at night. Flowers do not bloom. Trees die in the winter. Large mammals like antelope become thin, starve and provide little fat to the predators (carnivores and human hunters) that depend on them. Then, this same disheartening cycle repeats itself, year after year. This is a picture of life on earth after the eruption of the super-volcano, Mount Toba in Indonesia, about 74,000 years ago. In a paper published this week in Nature, scientists show that early modern humans on the coast of South Africa thrived through this event.

The glass shards at Pinnacle Point were carried nearly 9000 km from the source in Indonesia [Credit: Erich Fisher]

An eruption a hundred times smaller than Mount Toba - that of Mount Tambora, also in Indonesia, in 1815 - is thought to have been responsible for a year without summer in 1816. The impact on the human population was dire - crop failures in Eurasia and North America, famine and mass migrations. The effect of Mount Toba, a super-volcano that dwarfs even the massive Yellowstone eruptions of the deeper past, would have had a much larger, and longer-felt, impact on people around the globe.

The scale of the ash-fall alone attests to the magnitude of the environmental disaster. Huge quantities of aerosols injected high into the atmosphere would have severely diminished sunlight - with estimates ranging from a 25 to 90 percent reduction in light. Under these conditions, plant die-off is predictable, and there is evidence of significant drying, wildfires and plant community change in East Africa just after the Toba eruption.

If Mount Tambora created such devastation over a full year - and Tambora was a hiccup compared to Toba - we can imagine a worldwide catastrophe with the Toba eruption, an event lasting several years and pushing life to the brink of extinctions.

In Indonesia, the source of the destruction would have been evident to terrified witnesses - just before they died. However, as a family of hunter-gatherers in Africa 74,000 years ago, you would have had no clue as to the reason for the sudden and devastating change in the weather. Famine sets in and the very young and old die. Your social groups are devastated, and your society is on the brink of collapse.

The effect of the Toba eruption would have certainly impacted some ecosystems more than others, possibly creating areas - called refugia - in which some human groups did better than others throughout the event. Whether or not your group lived in such a refuge would have largely depended on the type of resources available. Coastal resources, like shellfish, are highly nutritious and less susceptible to the eruption than the plants and animals of inland areas.

The research team has been excavating caves at Pinnacle Point, South Africa, for nearly 20 years. Glass shards from Mount Toba were discovered at the PP5-6 location [Credit: Erich Fisher]

When the column of fire, smoke and debris blasted out the top of Mount Toba, it spewed rock, gas and tiny microscopic pieces (cryptotephra) of glass that, under a microscope, have a characteristic hook shape produced when the glass fractures across a bubble. Pumped into the atmosphere, these invisible fragments spread across the world.

Panagiotis (Takis) Karkanas, director of the Malcolm H. Wiener Laboratory for Archaeological Science, American School of Classical Studies, Greece, saw a single shard of this explosion under a microscope in a slice of archaeological sediment encased in resin.

"It was one shard particle out of millions of other mineral particles that I was investigating. But it was there, and it couldn't be anything else," says Karkanas.

The shard came from an archaeological site in a rockshelter called Pinnacle Point 5-6, on the south coast of South Africa near the town of Mossel Bay. The sediments dated to about 74,000 years ago.

"Takis and I had discussed the potential of finding the Toba shards in the sediments of our archaeological site, and with his eagle eye, he found one," explains Curtis W. Marean, project director of the Pinnacle Point excavations. Marean is the associate director of the Institute of Human Origins at Arizona State University and honorary professor at the Centre for Coastal Palaeoscience at Nelson Mandela University, South Africa.

Marean showed the shard image to Eugene Smith, a volcanologist with the University of Nevada at Las Vegas, and Smith confirmed it was a volcanic shard.

"The Pinnacle Point study brought me back to the study of glass shards from my master's thesis 40 years earlier," says Smith.

Students excavating the site at Vleesbaai [Credit: Dr. Jayne Wilkins]

Early in the study, the team brought in expert cryptotephra scientist Christine Lane who trained graduate student Amber Ciravolo in the needed techniques. Racheal Johnsen later joined Ciravalo as lab manager and developed new techniques.

From scratch, with National Science Foundation support, they developed the Cryptotephra Laboratory for Archaeological and Geological Research, which is now involved in projects not only in Africa, but in Italy, Nevada and Utah.

Encased in that shard of volcanic glass is a distinct chemical signature, a fingerprint that scientists can use to trace to the killer eruption. In their paper in Nature, the team describes finding these shards in two archaeological sites in coastal South Africa, tracing those shards to Toba through chemical fingerprinting and documenting a continuous human occupation across the volcanic event.

"Many previous studies have tried to test the hypothesis that Toba devastated human populations," Marean notes. "But they have failed because they have been unable to present definitive evidence linking a human occupation to the exact moment of the event."

Most studies have looked at whether or not Toba caused environmental change. It did, but such studies lack the archaeological data needed to show how Toba affected humans.

The Pinnacle Point team has been at the forefront of development and application of highly advanced archaeological techniques. They measure everything on site to millimetric accuracy with a "total station," a laser-measurement device integrated to handheld computers for precise and error-free recording.

Naomi Cleghorn with the University of Texas at Arlington, recorded the Pinnacle Point samples as they were removed.

Cleghorn explains, "We collected a long column of samples - digging out a small amount of sediment from the wall of our previous excavation. Each time we collected a sample, we shot its position with the total station."

Sampling of Cryptotephra at Vleesbaai, South Africa [Credit: Dr. Jayne Wilkins]

The sample locations from the total station and thousands of other points representing stone artifacts, bone, and other cultural remains of the ancient inhabitants were used to build digital models of the site.

"These models tell us a lot about how people lived at the site and how their activities changed through time," say Erich Fisher, associate research scientist with the Institute of Human Origins, who built the detailed photorealistic 3D models from the data. "What we found was that during and after the time of the Toba eruption people lived at the site continuously, and there was no evidence that it impacted their daily lives."

In addition to understanding how Toba affected humans in this region, the study has other important implications for archaeological dating techniques. Archaeological dates at these age ranges are imprecise - 10 percent (or 1000s of years) error is typical. Toba ash-fall, however, was a very quick event that has been precisely dated. The time of shard deposition was likely about two weeks in duration - instantaneous in geological terms.

"We found the shards at two sites," explains Marean. "The Pinnacle Point rockshelter (where people lived, ate, worked and slept) and an open air site about 10 kilometers away called Vleesbaai. This latter site is where a group of people, possibly members of the same group as those at Pinnacle Point, sat in a small circle and made stone tools. Finding the shards at both sites allows us to link these two records at almost the same moment in time."

Not only that, but the shard location allows the scientists to provide an independent test of the age of the site estimated by other techniques. People lived at the Pinnacle Point 5-6 site from 90,000 to 50,000 years ago. Zenobia Jacobs with the University of Wollongong, Australia, used optically stimulated luminescence (OSL) to date 90 samples and develop a model of the age of all the layers. OSL dates the last time individual sand grains were exposed to light.

The photo shows a volcanic glass shard erupted 74,000 years ago from the Toba volcano in Indonesia found at an archaeological site nearly 9000 km away at Vleesbaai, South Africa [Credit: Racheal Johnsen]

"There has been some debate over the accuracy of OSL dating, but Jacobs' age model dated the layers where we found the Toba shards to about 74,000 years ago - right on the money," says Marean. This lends very strong support to Jacobs' cutting-edge approach to OSL dating, which she has applied to sites across southern Africa and the world.

"OSL dating is the workhorse method for construction of timelines for a large part of our own history. Testing whether the clock ticks at the correct rate is important. So getting this degree of confirmation is pleasing," says Jacobs.

In the 1990s, scientists began arguing that this eruption of Mount Toba, the most powerful in the last two million years, caused a long-lived volcanic winter that may have devastated the ecosystems of the world and caused widespread population crashes, perhaps even a near-extinction event in our own lineage, a so-called bottleneck.

This study shows that along the food-rich coastline of southern Africa, people thrived through this mega-eruption, perhaps because of the uniquely rich food regime on this coastline. Now other research teams can take the new and advanced methods developed in this study and apply them to their sites elsewhere in Africa so researchers can see if this was the only population that made it through these devastating times.

Source: Arizona State University [March 12, 2018]

A new experiment by Iowa State University's Elizabeth Swanner that evaluates the reduction of iron in prehistoric oceans may reinterpret the conditions under which iron-rich sedimentary rock is formed.

Graduated cylinder model of the ocean. The green shows cyanobacteria and the brown shows the oxidized iron [Credit: Iowa State University's College of Liberal Arts and Sciences]

Swanner, an assistant professor of geological and atmospheric sciences, was part of an international research team including researchers from the University of Tuebingen in Germany and the Chinese Academy of Sciences in Beijing. The team modeled the prehistoric ocean, similar to that of the Archean Era 2.5 billion years ago within a graduated cylinder.

"We really only wanted to simulate it in the vertical dimension, so we used a graduated cylinder and modified it," Swanner said.

In a previous experiment, the researchers had modified the cylinder to simulate an Archean ocean with large amounts of iron and no oxygen except for what was made by cyanobacteria. Ports along the cylinder's side allowed for sampling at various levels.

"We were studying cyanobacteria because these are the organisms which we think put all of the oxygen in the atmosphere originally," she said.

The research, recently published by Scientific Reports, showed that despite the oxygenation by the cyanobacteria, much of the iron did not remain oxidized but was reduced again into its dissolved form.

This unexpected result may be explained by an enzyme on cyanobacteria which reduces iron. In the modern ocean, which contains at least 1,000 times less iron, cyanobacteria reduce a small amount of iron, but the experiment showed a larger amount of iron reduction than the researchers anticipated. Another possible explanation is that the iron is reduced by a photochemical reaction occurring when the iron is hit by light.

The implications of this finding could change the conditions under which iron-rich sedimentary rocks are thought to be formed from the ancient oceans.

"Traditionally if you see iron enriched in sediments from the ocean you tend to think it was deposited under anoxic conditions," Swanner said. "But potentially we have a way to still deposit a lot of iron but have it be deposited under fully oxygenated conditions."

The initial results in the laboratory prompt new questions for Swanner, including whether she will find evidence of this process in the Midwestern lakes that her research group is now studying. These lakes have iron at the bottom and oxygen only in the top of the water column, and also contain cyanobacteria.

Source: Iowa State University [March 09, 2018]

Core samples taken during an international ocean drilling expedition are yielding the most high-resolution, extended record of continental rifting ever obtained.

IODP Expedition 381 collected 1.6 kilometers of sediment core from the Corinth Rift in Greece [Credit: University of Southampton]

A team of researchers from around the world, working as part of the Corinth Active Rift Development expedition, collected 1.6 kilometers (one mile) of sediment core and data from boreholes at three different locations in the Gulf of Corinth in Central Greece. The samples provide a continuous, high resolution record of complex changes in past environment and rift-faulting rates over at least the last one million years.

The Corinth Rift is one of the most seismically active areas in Europe where one of the Earth's tectonic plates is being ripped apart causing geological hazards including earthquakes, tsunamis and landslides. This rifting process is the focus of the International Ocean Discovery Program (IODP) Expedition 381 led by Co-Chief Scientists Professor Lisa McNeill from the University of Southampton and Professor Donna Shillington of the Lamont-Doherty Earth Observatory of Columbia University in the USA.

The Expedition team collected the core samples whilst aboard the drilling vessel Fugro Synergy between October and December 2017. The cores were then opened, analysed and sampled by the scientific team in February 2018 during a month of intensive work at the University of Bremen in Germany.

Analysis of the cores recovered from deep below the seafloor reveals a series of very complex changes in the chemical and biological conditions within the waters of the basin over the last approximately 0.5 million years. These changes are driven by the global growth and shrinkage of the Earth's ice sheets, which in turn control the height of global sea level.

Fluctuations in sea level cause the Gulf of Corinth basin to switch between a normal marine environment, when the Gulf was connected to the world's oceans, and a wide range of more complex conditions when sea level is low. The rift's sediments show that an unusual range of organisms lived within the basin under these complex conditions.

The data collected will be used to calculate how quickly the active earthquake-generating faults are slipping within the rift. This can be used to assess the earthquake hazard potential of the region, which has a populated coastal zone around the Gulf and the city of Athens nearby that can be impacted by future earthquakes.

"The new cores are revealing exactly what we hoped: The potential to accurately calculate the activity of important faults that regularly generate earthquakes with magnitudes 6 to 7 in the area," said Professor McNeill. "Researchers have been working in the Corinth Rift region for many decades, examining sediments and active fault traces exposed on land and using marine geophysics to image the basin and its structure below the seafloor. The missing piece of the jigsaw puzzle has been the age of the basin sediments that record the history of rifting. We know now that the core samples will enable us to complete this piece of the puzzle. This in turn can be used to calculate fault earthquake potential, and, on a longer timescale, unravel the sequence of events as the rift has evolved."

Professor Shillington added: "The new discoveries resulting from this expedition will help us to understand other active and ancient rift zones around the world, including others with high hazard potential. The complex story from the microfossils preserved in the sediments and their implications for the living conditions in the basin was unexpected and will significantly widen the impact of the project. Analysis of these results will take many months and we are excited to see what they reveal."

Continental rifting is fundamental for the formation of new ocean basins, and active rift zones are dynamic regions of high hazard potential. The Corinth Rift is one such location and serves as a unique laboratory in an area of Europe with some of the highest levels of earthquake activity. Geologically the Corinth Rift is very young (only a few million years old) and provides a unique chance to study the very first stages of the splitting apart of a continent and changing climate in the eastern Mediterranean. Young rift basins fill with eroded sediments that are also sensitive recorders of past changes in climate and sea level and of the chemical and biological conditions of the rift basin.

Source: University of Southampton [March 09, 2018]

Researchers from Cardiff University have revealed how sea ice has been contributing to the waxing and waning of ice sheets over the last million years.

Credit: Cardiff University

In a new study published in the journal Nature Communications, the team have shown for the first time that ice ages, occurring every 100,000 years, are accompanied by a rapid build-up of sea ice in the Earth's oceans.

Our planet's ice ages used to occur at intervals of every 40,000 years, which made sense to scientists as the Earth's seasons vary in a predictable way, with colder summers occurring at these intervals. However there was a point, about a million years ago, called the 'Mid-Pleistocene transition', in which the ice age intervals changed from every 40,000 years to every 100,000 years.

The reason why ice ages occur at these timescales has been a mystery to scientists for a long time.

By tracking molecules produced by tiny marine algae preserved in ocean sediments, the team have been able to reconstruct sea-ice conditions during the Mid-Pleistocene transition.

Their results showed that at the same time as the cycles of ice ages changed from 40,000 years to 100,000 years there was a distinct increase in sea ice extent and a change in the rhythm of sea ice build-up across climate cycles.

"Prior to the Mid-Pleistocene transition, sea ice build-up and decay during ice ages was more gradual, whereas in the late Pleistocene, when the cyclicity of ice ages changed, we observed conditions characterised by a prominent short-lived peak in sea ice extent during late ice ages," said Henrieka Detlef, a postgraduate researcher at Cardiff University School of Earth and Ocean Sciences who led the study.

With less water evaporating into the atmosphere, there would be less moisture being transported to continental glaciers which, in turn, would cause them to retreat and help in the transition from an ice age to a warm period.

"It's clear that sea ice plays a fundamental role in the transition from an ice age into a warm stage every 100,000 years," Detlef continued.

"Understanding the interactions of sea ice with the regional ecosystem and oceanography is particularly important with respect to anthropogenic climate change and a rapidly shrinking sea ice cover in the Arctic Ocean. Our study is an important step forward in understanding the role of sea ice for long-term climate change."

Source: Cardiff University [March 09, 2018]

A scientific team has discovered the geological footprint of earthquakes and tsunamis that affected the Aysen region (southern Chile) up to 9,000 years ago. This new study improves the assessment of seismic hazard in a wide area of the American continent prone to large earthquakes.

The new study is a first step forward to improve the evaluation of the seismic hazard in Andean regions [Credit: Universidad de Barcelona]

The study, published in Journal of Geophysical Research: Solid Earth, enabled the researchers to establish the first paleoseismological record of the Liquine-Ofqui Fault Zone (LOFZ), a large geological structure that crosses southern Chile and is partially responsible for the seismic activity of the Andean country.

The LOFZ fracture area, which stretches over more than 1,000 kilometres north-south in Chile, is a geological structure associated with volcanism and that has an impact on the relief of the Andean country. This seismically hazardous area has some active volcanoes –such as Maca, Hudson and Mentolat- and steep reliefs that can enlarge the effects of the most violent geological phenomena.

In this area, Aysen fjord is a model to study geological processes –earthquakes, tsunamis, etc.— that can be a threat to the local population. According to Galderic Lastras, "the Aysen fjord is cross-cut by the strike-slip fault system (LOFZ) that causes local earthquakes, such as the crisis in 2007. The main earthquake of this crisis —magnitude 6.2— caused dozens of landslides and a local tsunami, with some casualties and important damage to fish farms."

"Moreover, this fjord is quite close to the plate boundary between the South American and the Nazca Plates, an active subduction zone that causes large magnitude earthquakes," says Lastras, expert on submarine cartography and head of the oceanographic survey DETSUFA that worked on the cartography of the geological footprint of submarine landslides in Aysen.

Aysen fjord: earthquakes and tsunamis in a natural laboratory

When an earthquake occurs –moderate or strong-, it can destabilize the mountain slopes that surround the fjord. Rock masses can slide and fall until reaching the fjord bottom, causing local tsunamis. This forms an increased risk for the population since there is an extremely short warning time. The geological footprint of these landslides -piled up at the bottom of the fjord and separated by sediments- is then visible in the sedimentary record.

The geological footprints of the last seismic crisis ─April 21, 2007─ are still visible in the Aysén fjord [Credit: G. Lastras]

According to Maarten Van Daele, postdoctoral researcher and expert on sedimentary deposits created by earthquakes, "strong seismic shaking triggers both onshore and subaquatic landslides. These are buried in the fjord and we can image and map them using geophysical methods. In this study, we also retrieved sediment cores, which allowed us to determine ages for the landslide events using radiocarbon dating of organic material in the sediment."

Combining different geophysical techniques —reflection seismics, geochemistry of volcanic ashes, etc.— the scientific team constructed the first paleoseismic record of the Liquine-Ofqui Fault Zone. "For the first time —adds Van Daele— we have a rough idea of earthquake recurrence rates along this fault. Other similar studies are needed along the fault trace, but this is an important first step to improve the assessment of the seismic hazard in the region."

Looking for the most violent seismic episodes

Earthquakes can destabilize fjord slopes and cause landslides, but other factors such as heavy rainfall can also be involved and enhance slope instability. As a result, the experts could identify evidence of ten earthquakes in Aysen fjord –including the most recent one in 2007— but the amount of such earthquake events is probably even higher since not every earthquake will cause a significant landslide.

The study presents the first paleoseismological record of the Liquiñe-Ofqui Fault Zone (LOFZ), a geological structure that crosses southern Chile [Credit: University of Barcelona]

According to Katleen Wils, predoctoral researcher at Ghent University and first author of the study, "we know these landslides occurred due to a common trigger: an earthquake. In the Aysen region, the main source of seismic hazard comes from the LOFZ fault rather than the subduction zone. Those earthquakes had intensities similar to those occurring during the 2007 main episode, which was up to IX, corresponding to violent shaking and considerable damage."

"According to the data, six of the analysed earthquake events took place in the fjord during the last 9,000 years, while the other four occurred before that. This shows that there is an important seismic hazard in the region, mainly originating from the LOFZ, but also from the subduction zone," notes Wils, expert on geophysics and the study of earthquakes and seismic hazard.

The number of earthquakes recorded in Aysen fjord may be clear, but "it is more difficult to have a clear idea of their magnitude," warns Galderic Lastras. "One of the identified events has a similar age (about 2,000 years before present) to a tsunami deposit described in the coastal Lake Huelde, in Chiloe Island, and with a turbidite in Lake Rinihue. Identifying signs of an earthquake in different locations far away from each other is a sign of a large magnitude earthquake, which has likely originated in the subduction zone."

According to the authors, their study reveals that LOFZ is an active fault system that should be characterized in more detail in future studies in order to have more knowledge on the complete seismic system.

Paleoseismology: the unwritten history of great earthquakes

The paleoseismological record of Aysen fjord is an important part of the geological history of the region as a written record of past earthquakes in the area is non-existent. Understanding the rate at which earthquakes took place in the past is essential to infer the occurrence of future earthquakes.

Because of this uncertainty, "geological research is an essential tool to explain the unwritten history of the most violent earthquake events that affected a certain area. It is important to know as much as possible about past seismic activity of a region. This means that technology and scientific knowledge are the key to improve the assessment of seismic hazard, mitigate the effects of natural disasters and help society directly," the authors write.

Source: University of Barcelona [March 07, 2018]

The East Asian summer monsoon and desertification in Eurasia is driven by fluctuating Northern Hemisphere ice volume and global sea level during the Ice Age, as shown in a study published in Nature Communications. Today, two thirds of the world's population is dependent on agriculture sustained by rains of the East Asian summer monsoon, and future climate change in this region can therefore have a major impact on global food production.

The East Asian summer monsoon and desertification in Eurasia is driven by fluctuating Northern Hemisphere ice volume and global sea level during the Ice Age, as shown in a study published in Nature Communications. Today, two thirds of the world's population is dependent on agriculture sustained by rains of the East Asian summer monsoon, and future climate change in this region can therefore have a major impact on global food production [Credit: Thomas Stevens]

Huge areas of central China is covered by a plateau consisting of a fine grained soil type called loess - a sediment deposited here by winds during the Ice Age. The soils formed on loess are very fertile and have been one of the key factors driving cultural development and population growth in China for thousands of years. Additionally, the loess plateau also contains a geological archive that can be used to decipher past climate changes.

Through detailed examination of the loess sediments, a group led by researchers at Uppsala Univirsity together with colleagues from Denmark has identified how changes in climatological phenomena such as ice volume and sea level also affected the extent of deserts in China, as well as the behavior of the East Asian summer monsoon.

"We have conducted the most detailed dating of the loess to date, which has enabled us to identify changes in the monsoon and desertification processes in more detail and with much greater accuracy than previously possible. We can now compare these changes to other known climate changes such as variation in ice volume, sea level and even the Earth's orbit during the Ice Age", says Dr. Thomas Stevens, first author and researcher at Uppsala University.

"We can now show that when ice volume decreased and sea level rose, the summer monsoon rainfalls in East Asia intensified and spread further inland, while sandy deserts in China retreated", says Dr. Stevens.

With today's shrinking ice caps and rising sea levels, this has implications for how the Eurasian continent will once again experience changes in the summer monsoon rainfall and desertification.

Source: Uppsala University [March 07, 2018]

A new NASA study has, for the first time, cut a clear path through a nettlesome problem: accurately measuring a powerful effect on global sea level that lingers from the last ice age.

Glacial isostatic adjustment is the ongoing movement of land once burdened by ice-age glaciers [Credit: NASA/John Sonntag]

Just how quickly Earth's deep, rocky mantle is rebounding from the heavy burden of ancient ice sheets and oceans remains somewhat uncertain. But this rebound effect, known as glacial isostatic adjustment (GIA), is critical to properly understanding the causes of sea level change.

Even getting a solid handle on the level of uncertainty associated with estimates of GIA has proven elusive. The new study offers a more rigorous way out of this thicket – establishing a formal system for assessing this uncertainty. That should lead to more realistic estimates of sea level change, and greater precision in projections of future sea level rise, according to the study's authors.

"Knowing how much we don't know is the first step," said Lambert Caron, a post-doctoral researcher at NASA's Jet Propulsion Laboratory in Pasadena, California and lead author of the new study published today in Geophysical Research Letters, a journal of the American Geophysical Union,

Try out a NASA simulation of GIA from JPL’s Virtual Earth Systems Laboratory here.

While new findings based on strong data get most of the headlines, gauging levels of uncertainty also is important to scientific investigations. It's an especially thorny problem in the study of sea level change.

Interpreting data from NASA's twin GRACE (Gravity Recovery and Climate Experiment) satellites offers one example. By measuring subtle shifts in gravity across Earth's surface, the GRACE satellites gathered an important 15-year-long data set, now being used to help determine how much sea level rise is caused by additional water mass. GRACE also can be used to track varying quantities of ocean water, changes in polar ice and the movement of water between oceans and land.

GIA looms in the background of such measurements. Pinning down the uncertainty connected with it more precisely helps scientists separate ice age and present-day processes, including how much of sea-level rise is driven by expansion of ocean water as it warms. Knowledge of GIA also helps clarify trends in water storage on land, measured by satellite as well as ground-based instruments. Another question it can help clear up: how alterations in the shape of ocean basins caused by GIA contributes to apparent sea level changes.

Measurement and uncertainty

Previous studies attempted to put a fence around uncertainty using various methods, Caron said. These included running repeated computer models and culling out all but a handful that seemed to provide the best match, or "fit," to what the data gathered by GRACE and other observation platforms show.

Differences among the "best fit" models then can be used to reveal likely levels of uncertainty in interpreting the data.

"People started comparing a handful of models, some of them relying on similar assumptions and setups, and concluding that the differences between them were essentially how much uncertainty we had over GIA," Caron said. "That's fine, but it doesn't allow us to explore the entire range of possible scenarios. We need a more formal approach."

The new study relies on technological improvements, which have only become possible within the past decade, to carry out a high number of computer simulations – in this case, more than 100,000. By more systematically exploring the range of GIA scenarios, Caron's team seeks to turn discrepancies among different models into a virtue. They framed the question in a new way: How different can models be while still matching the data? From this spread of models and a method called the Bayesian approach, better statistics on uncertainty can be retrieved.

The new assessment also is based on GPS time series measurements from 459 sites in Europe, North America and Antarctica, and more than 11,000 records of relative sea level – that is, sea level in relation to coastal elevation. This allows the parameters controlling the GIA rebound to be more thoroughly scrutinized.

The new framework translates into what Caron calls the first formal uncertainties for GIA on a global scale.

The study reveals an underestimate of uncertainty levels for GIA estimates, he said – from a typical 20 percent uncertainty in previous studies to a median value of 44 percent. In polar regions, GIA has a large impact on the interpretation of gravity data.

That leads to refinements in uncertainty levels for sea level rise in specific locations around the world. In the New Orleans region, for example, applying the new method yields a prediction of a 1 millimeter rise in relative sea level per year, with an uncertainty of 0.4 millimeters per year.

Caron said he hopes the new formal uncertainties will be a useful tool not only for researchers, but for city planners as well.

"We want to give them a measure of confidence for the average scenario, and what is the worst-case scenario they would have to plan for – how much the country has to invest in modernizing infrastructure, reconstructing piers, or to mitigate flooding," he said.

Author: Pat Brennan | Source: American Geophysical Union [March 07, 2018]

This story is republished courtesy of AGU Blogs, hosted by the American Geophysical Union. Read the original story here.

For decades, the world's leading scientists have observed the phenomena known as El Nino and La Nina. Both significantly impact the global climate and both pose a puzzle to scientists since they're not completely understood. Now, a new study helps clear up some of the obscurity surrounding El Nino and La Nina, which together are called the El Nino Southern Oscillation (ENSO). This new study examines ENSO frequency asymmetry during different phases of the Pacific Decadal Oscillation (PDO), a climate pattern in the North Pacific.

This is an artistic representation of the observed Pacific Decadal Oscillation spatial pattern in the North Pacific and its significant association with El Nino/La Nina occurrence, which is also evident in most CMIP5 models [Credit: Advances in Atmospheric Sciences]

Previous studies have investigated the relationship between ENSO and PDO but none have examined if the warm (positive) and cool (negative) phases of PDO in the North Pacific influence the frequency of ENSO events in the tropical Pacific. "For the first time," said Prof. ZHENG Fei from the Institute of Atmospheric Physics, Chinese Academy of Sciences, and coauthor on the study, "we quantitatively demonstrated that El Nino is 300 percent more (58 percent less) frequent than La Nina in positive (negative) PDO phases."

To arrive at their findings, the researchers used observational data and the output of 19 models from the Coupled Model Intercomparison Project Phase 5 (CMIP5). "By adopting the observations and CMIP5 climate model simulations," said Zheng, "we had an opportunity to explore how PDO modulates the occurrence of ENSO." This type of exploration meets an increasing need today, which is for scientists to better understand the mechanisms that affect the occurrence of ENSO.

While all the answers surrounding these events aren't known, the effects of ENSO are well understood. When sea surface temperatures are warmer or cooler than normal in the equatorial Pacific Ocean, weather patterns around the world are impacted. Everything from pressure systems to wind and precipitation can be influenced by ENSO, including the supply of water in a region since it can cause moisture extremes.

ZHENG and his group at the Chinese Academy of Sciences have been focusing on ENSO for more than 10 years now. The results from their own recent studies showing that ENSO prediction highly relies on off-equatorial physical processes motivated this latest study exploring the effects of PDO, according to Zheng, who believes that this approach is necessary to understand ENSO better. "Our study suggests that more attention should be paid to the processes outside the equator when attempting ENSO predictions to provide reliable warning of climate extreme events and avoid potential economic loss," he said.

The findings were published in Advances of Atmospheric Sciences.

Source: Institute of Atmosperic Physics, Chinese Academy of Sciences [March 07, 2018]

The simple story says that during the last ice age, temperatures were colder and ice sheets expanded around the planet. That may hold true for most of Europe and North America, but new research from the University of Washington tells a different story in the high-altitude, desert climates of Mongolia.

The Gobi-Altai mountain range in western Mongolia is in a very dry region but ice can accumulate on mountaintops, such  as Sutai Mountain, the tallest peak in the range. In the picture, friends of Jigjidsurengiin Batbaatar descend this mountain after helping to install a weather station [Credit: Jigjidsurengiin Batbaatar/University of Washington]

The recent paper in Quaternary Science Reviews is the first to date ancient glaciers in the high mountains of Mongolia's Gobi Desert. It compares them with glacial records from nearby mountains to reveal how glaciers behave in extreme climates.

On some of the Gobi mountain ranges included in the study, glaciers started growing thousands of years after the last ice age ended. In contrast, in slightly wetter parts of Mongolia the largest glaciers did date from the ice age but reached their maximum lengths tens of thousands of years earlier in the glacial period rather than at its culmination, around 20,000 years ago, when glaciers around most of the planet peaked.

Both trends differ from the typical chronology of glacier growth during an ice age.

"In some of the Gobi mountains, the largest glaciers didn't happen during the last ice age," said first author Jigjidsurengiin Batbaatar, a UW doctoral student in Earth and Space Sciences. "Some of these glaciers were starving for precipitation then. Our measurements show that they actually shrank as cold, dry conditions of the ice age became more intense. Then they grew when the warming climate of the Holocene brought more moist air, feeding the glaciers with more snow."

Batbaatar and co-author Alan Gillespie, a UW research professor emeritus in Earth and Space Sciences, collected samples from moraines, which are long ridges of rocky debris dropped at a glacier's edge. They used a dating technique perfected in the last 20 years that measures elemental changes in the rock that occur when the rock gets bombarded by cosmic rays after the glacier's retreat.

"We were expecting to find rocks exposed for 20,000 years, the date of the peak of the last ice age, but these moraines were much younger. That means that these glaciers were smaller when the climate was the coldest," Batbaatar said. "The results were so surprising that we went back to double check."

At a moraine, a band of boulders left by a retreating glacier, co-author Ari Matmon collects rock samples with his son. This site is in the Khangai Mountains in Mongolia [Credit: Jigjidsurengiin Batbaatar/University of Washington]

The study was possible both because of advances in the cosmic-ray dating method, and political changes that allow more access to Central Asia.

"After the fall of the Soviet Union, Russia opened up, China opened up, and Mongolia opened up to Western researchers with these novel dating techniques. And we see a very different pattern of glacial advances compared to North America and Europe," Batbaatar said.

The data collected in 2007 and 2010 confirm a theoretical study by Summer Rupper, a former UW doctoral student now at the University of Utah, and UW faculty member Gerard Roe. In very cold and dry environments, where rain and snow are scarce, it predicted that temperature would not always be the main factor driving a glacier's growth.

"Because the melting is so dominant a process, and the melting is mostly controlled by temperature, people think of glaciers as thermometers. But we all know that precipitation plays a role," Batbaatar said.

The new study confirms that so-called "starving glaciers" in dry, high-altitude environments are indeed controlled by precipitation. They grow so slowly that they seldom reach the lower altitudes where melting is possible. Instead, they shrink when sunlight hits the surface and transforms ice into water vapor, a process called sublimation. These glaciers are thus less sensitive to temperature shifts, but very sensitive to precipitation amounts.

"Generally, people have assumed from well-documented North American and European records that the largest glaciers should have come in the peak of the last ice age," Batbaatar said. "But in Mongolia, our results show that this was not the case. Glacier behavior there was different from the better-studied areas of the Alps or the Sierra Nevada in the U.S. Even within Mongolia we observe very different behavior from range to range."

Jigjidsurengiin Batbaatar chisels rock from the surface of a boulder dropped by a glacier in the Gobi-Altai range in  Mongolia. The elemental traces of exposure to cosmic rays show that this glacier reached its maximum size 7,500 years ago, much later than the last ice age [Credit: Alan Gillespie/University of Washington]

The conditions at the Gobi-Altai mountain range are extreme, with precipitation at the five research sites Batbaatar established there ranging from roughly 50 to 300 millimeters (2 inches to 1 foot) per year. Nearby mountains in Mongolia with more precipitation have more typically behaving glaciers. But other extreme climates, for example the driest parts of Tibet or the Andes, can produce glaciers with similar paradoxical trends.

"Even in this current warming climate, some mountains are so high that the temperatures are still below freezing, and the warming ocean may provide more precipitation to drive some of the glaciers to advance," Batbaatar said.

He is now working to interpret more measurements collected from a wider geographic area in Central Asia.

"Batbaatar has shown that glaciers growing in cold, arid, desert mountains may be out of sync with those in wetter, warmer environments such as the Alps," Gillespie said. "His findings move us toward a more complete understanding of how glaciers advance and retreat in response to climatic fluctuations."

Source: University of Washington [March 06, 2018]

New research, published in Scientific Reports, has outlined a new methodology for estimating ancient atmospheric water content based on fossil plant leaf waxes.

This is the Calatayud-Daroca Basin in Central Spain [Credit: Michael Hren]

As the Earth's surface and atmosphere warm, the amount of moisture - water vapour - in the atmosphere will increase. Understanding the size of this increase is important for predicting future climates as water vapour is a significant greenhouse gas. Atmospheric moisture content also influences the patterns and intensity of rainfall events.

The relationship between temperature and moisture content can be explored by the study of intervals in Earth's history when climates where significantly warmer than those seen in modern times, which necessitates a method for estimating ancient atmospheric moisture content.

Dr Yvette Eley, from the University of Birmingham, explained, "If we want to understand how the Earth would work with a climate substantially warmer than today, we have to study intervals millions of years in the past - made difficult because these warm climates are much older than our oldest climate records from Antarctic ice cores (less than one million years old)."

To try and understand climate properties related to the atmosphere - like rainfall and atmospheric moisture content - in such ancient times is very challenging. Existing methods, using calcium carbonate concretions that form in soils, or the chemistry of fossilised mammal teeth, are both hampered by their relative rarity in ancient sediments.

Dr Eley added, "Our new approach to quantifying ancient atmospheric moisture content relies on the fundamental properties of plant leaves, and how they alter their protective waxy coverings in response to water stress. These leaf waxes are tough and resistant, and are regularly found as what we call biomarker compounds in ancient river, lake and even marine sediments."

A method of estimating ancient moisture content based on these plant wax compounds overcomes the limitations of other methods because plant waxes are commonly found in soils and sediments stretching back tens or even hundreds of millions of years and across many environments.

The validity of this new tool was proven in studies of modern soils across the US and Central America, carried out by the research team of Associate Professor Michael Hren in the Center for Integrative Geosciences at the University of Connecticut. These studies showed a clear relationship between the chemistry of these waxy compounds and the amount of moisture in the atmosphere.

"What we see is that the distribution of organic compounds preserved in soils seems to be strongly related to the difference between how much water is in an air mass, and how much the air mass can hold, or what is known as the vapour pressure deficit," says Dr Hren.

Eley and Hren then applied their new proxy to reconstruct atmospheric moisture content in Central Spain during an interval 15 to 17 million years ago.

Although consistently much warmer than pre-industrial conditions, this interval marks one of the cooling steps that led to the development of the modern world. The new data confirms the expectations of climate models, that atmospheric cooling is coupled to less atmospheric moisture. The reconstructed changes in atmospheric moisture also align with results from other independent proxies used to investigate changes in temperature and rainfall in the region.

Dr Eley said, "This gives us the confidence that our proxy works, and we have every reason to believe that it will do so for future exploration into the even deeper past. We hope the results of this exploration will provide direct data to test our understanding of the relationship between global warming, atmospheric moisture content and rainfall systems."

Source: University of Birmingham [March 01, 2018]

South Africa's history and economy has been built on its rich natural treasures of a number of precious metals, stones and minerals. The country's mineral deposits have been created over hundreds of millions of years through processes that are still not completely understood.

This is professor Rais Latypov in front of an example of the stratified chromite layers [Credit: Wits University]

One of these processes, that has troubled scientists and geologists for years, is the origin of chromitite layers hosted by layered intrusions -- a major source of chromium on our planet. This process has been a mystery for decades, as scientists tried to work out how layers of pure chromite form from magmas that are coming from Earth's mantle. These are supposed to be rich in a mineral called olivine -- not chromite.

"It has been widely believed that magmas sourced from the mantle cannot directly crystallise chromite, as the mantle rocks that are being melted are rich in olivine, and therefore these melts should crystallise olivine, not chromite," says Professor Rais Latypov from the School of Geosciences of the University of the Witwatersrand in South Africa, whose research team published a paper in Nature Communications.

"Together with a large group of my colleagues, I have been trying hard for several decades to find a mechanism that can explain the formation of these large chromite deposits in shallow crustal chambers but it turned out that we have been looking in the wrong place."

To find the answer to these questions, Latypov and his team have been studying layers of chromite in South Africa's Bushveld Complex, where over 80% of the global resources of platinum-bearing chromite deposits can be found.

They discovered that some basaltic magmas will form chromite after decompression as they rise up from the mantle through the crust towards the Earth's surface. The reduction in pressure, as the magma rises up from the mantle to the crust, is key to the crystallisation process of the chromite.


"When these magmas arrive into a shallow magma chamber, sitting only a few kilometres below the surface of the Earth, they are already saturated in pure chromite, and, on cooling, can crystallise layers of platinum-bearing massive chromitite.

Chromium is an important industrial element that substantially improves the physical and chemical properties of steels, increasing their strength and making them corrosion-resistant. The platinum that is associated with these rocks is used in catalytic converters within cars to break down toxic exhaust gases into relatively benign species.

These zebra-striped coloured layers of platinum-bearing chromite that are formed through this process can be seen clearly in the ridges at the top of the Bushveld Complex, near Steelpoort in Mpumalanga, which became exposed through erosion over the many millions of years since they formed. Some of these layers can be several meters thick and extend for hundreds of kilometres.

"The Bushveld Complex covers an area of 100s of square kilometres. It stretches from Steelpoort in Mpumalanga in the East, past Pretoria to the Pilanesberg in the West; and from Bethal, Mpumalanga in the South to north of Polokwane in Limpopo. We believe that the Bushveld chamber must have been operating as a flow-through system into which magmas were entering and depositing their chromite, before flowing out of the chamber and erupting as basalts via volcanoes, which have now been eroded away," says Latypov.

"It seems that the reduction of lithostatic pressure during the transfer of mantle-derived melts towards the surface plays a vital role in the formation of magmas that produce planetary resources, without which modern human society cannot develop in a sustainable manner."

Further research is being conducted on whether other magmatic deposits around the world, such as vanadium-bearing magnetite in layered intrusions, can also be related to lithostatic pressure reduction.

Source: University of the Witwatersrand [March 01, 2018]

Plumes of hot magma from the volcanic hotspot that formed Réunion Island in the Indian Ocean rise from an unusually primitive source deep beneath Earth's surface, according to new work in Nature from Carnegie's Bradley Peters, Richard Carlson, and Mary Horan along with James Day of the Scripps Institution of Oceanography.

A fieldwork photo from Réunion Island shows the flank of the Cirque de Cilaos, looking out towards the Indian Ocean [Credit: Bradley Peters]

Réunion marks the present-day location of the hotspot that 66 million years ago erupted the Deccan Traps flood basalts, which cover most of India and may have contributed to the extinction of the dinosaurs. Flood basalts and other hotspot lavas are thought to originate from different portions of Earth's deep interior than most volcanoes at Earth's surface and studying this material may help scientists understand our home planet's evolution.

The heat from Earth's formation process caused extensive melting of the planet, leading Earth to separate into two layers when the denser iron metal sank inward toward the center, creating the core and leaving the silicate-rich mantle floating above.

Over the subsequent 4.5 billion years of Earth's evolution, deep portions of the mantle would rise upwards, melt, and then separate once again by density, creating Earth's crust and changing the chemical composition of Earth's interior in the process. As crust sinks back into Earth's interior -- a phenomenon that's occurring today along the boundary of the Pacific Ocean -- the slow motion of Earth's mantle works to stir these materials, along with their distinct chemistry, back into the deep Earth.

Sunrise over the summit of Piton des Neiges, the extinct volcano on the Indian Ocean's Réunion Island [Credit: Bradley Peters]

But not all of the mantle is as well-blended as this process would indicate. Some older patches still exist -- like powdery pockets in a poorly mixed bowl of cake batter. Analysis of the chemical compositions of Réunion Island volcanic rocks indicate that their source material is different from other, better-mixed parts of the modern mantle.

Using new isotope data, the research team revealed that Réunion lavas originate from regions of the mantle that were isolated from the broader, well-blended mantle. These isolated pockets were formed within the first ten percent of Earth's history.

Isotopes are elements that have the same number of protons, but a different number of neutrons. Sometimes, the number of neutrons present in the nucleus make an isotope unstable; to gain stability, the isotope will release energetic particles in the process of radioactive decay. This process alters its number of protons and neutrons and transforms it into a different element. This new study harnesses this process to provide a fingerprint for the age and history of distinct mantle pockets.

Looking into down into a volcanic crater of Piton de la Fournaise on Réunion Island with dormant volcanic cones in the background [Credit: Bradley Peters]

Samarium-146 is one such unstable, or radioactive, isotope with a half-life of only 103 million years. It decays to the isotope neodymium-142. Although samarium-146 was present when Earth formed, it became extinct very early in Earth's infancy, meaning neodymium-142 provides a good record of Earth's earliest history, but no record of Earth from the period after all the samarium-146 transformed into neodymium-142. Differences in the abundances of neodymium-142 in comparison to other isotopes of neodymium could only have been generated by changes in the chemical composition of the mantle that occurred in the first 500 million years of Earth's 4.5 billion-year history.

The ratio of neodymium-142 to neodymium-144 in Réunion volcanic rocks, together with the results of lab-based mimicry and modeling studies, indicate that despite billions of years of mantle mixing, Réunion plume magma likely originates from a preserved pocket of the mantle that experienced a compositional change caused by large-scale melting of Earth's earliest mantle.

The team's findings could also help explain the origin of dense regions right at the boundary of the core and mantle called large low shear velocity provinces (LLSVPs) and ultralow velocity zones (ULVZs), reflecting the unusually slow speed of seismic waves as they travel through these regions of the deep mantle. Such regions may be relics of early melting events.

"The mantle differentiation event preserved in these hotspot plumes can both teach us about early Earth geochemical processes and explain the mysterious seismic signatures created by these dense deep-mantle zones," said lead author Peters.

Source: Carnegie Institution for Science [February 28, 2018]