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]

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]

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 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]

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]

Have you ever wished you could travel inside a rock? It may sound more like magic than science, but Princeton scientists have found a way to make it (almost) true.

With an industrial grinder, a super-high-resolution camera usually used for wedding photography, and high-speed neural networks, Princeton geoscientists Adam Maloof and Akshay Mehra can deconstruct rock samples and create three- dimensional digital versions, which they have used to analyze specimens of Cloudina fossils gathered by Mehra (left) and undergraduates Will Van Cleve and Christian Gray (right) of the Class of 2017 from the Byng Formation, a fossil reef formation in a glacier-carved valley on Salient Mountain in the Canadian Rockies [Credit: Adam Maloof and Akshay Mehra, Princeton University Department of Geosciences]

With an industrial grinder and a super-high-resolution camera, Princeton geoscientists Adam Maloof and Akshay Mehra can deconstruct rock samples and create three-dimensional digital versions that scientists can look at from any angle. In addition, they have developed software that allows the computer to segment images and isolate objects without human bias.

Using this technology in conjunction with detailed field observations, they examined a thin-shelled creature that lived over much of the world about 545 million years ago, Cloudina, generally agreed to be the first-ever "biomineralizer," an organism that can create a shell or bones in addition to soft tissue.

While previous researchers had argued that Cloudina were reef builders, Maloof and Mehra were able to use their 3-D reconstruction of the creatures' delicate tube-like structures to conclude that the fossils had been transported from other areas, suggesting that Cloudina played only a minor role in the earliest reef systems. Their work appears in the current issue of the Proceedings of the National Academy of Sciences.

"I thought going in we would learn all sorts about this amazing first biomineralizer and first reef builder, but Cloudina turned out to be more like a reef dweller," said Maloof, an associate professor of geosciences. He has now turned his focus to the next-oldest potential reef builder, a sponge called Archaeocyathid that lived about 520 million years ago.

Cloudina had proven resistant to detailed study because its delicate casing is too fragile to extract physically from the surrounding limestone, and it could not be imaged remotely with traditional X-ray tomography techniques, which require density differences between the object of interest and the surrounding material. Because Cloudina is chemically identical to limestone, the fossils were effectively invisible to X-rays.

Meet GIRI

Almost five years ago, Maloof a nd Situ Studio collaborator Brad Samuels assembled the technology to create what he now calls "flipbooks," digital renderings that move through more than a thousand wafer-thin slices through a rock. Known as "GIRI" or "the grinder," the Princeton Grinding Imaging and Reconstruction Instrument is an answer to geologists' long-standing desire to know what rocks look like on the inside.

Princeton University geoscientist Adam Maloof has spent five years perfecting a combination grinder and imaging system that can create a three-dimensional 'virtual tour' through the inside of any solid object, from rocks to batteries. Here, a diamond wheel grinds a sample in the Princeton Grinding Imaging and Reconstruction Instrument (GIRI) in the Grinder Lab behind Guyot Hall, Princeton University [Credit: Adam Maloof and Akshay Mehra, Princeton University Department of Geosciences]

"Forever -- since Darwin -- people have tried to figure out how fossils look in 3-D, when they're embedded in rock and it's hard to get them out," Maloof said. "People did serial sections just like this way back then -- but perhaps not at this scale -- where they would grind away a little rock, draw it, grind a little more, draw it. ... It can be incredibly time-consuming."

Enter GIRI, which can cut slices as thin as a few microns (less than 1 percent of a millimeter) and can run 24 hours a day for weeks on end. As each slice takes about 90 seconds to cut and image, researchers have to choose between speed and scale. Most of the specimens Maloof and Mehra have imaged are cut into 30-micron slices, about a third the thickness of a human hair. A typical inch-thick, 1,500-slice sample takes about a day and a half to grind and image; during this time, the operator needs to replace machine fluids and clean the wipers (which clear the surface after each cut) only once.

"The process is destructive," Maloof said. "Dinosaur bones, lunar samples -- there are certain specimens that people are less likely to give us. It hasn't really stopped us, because most samples are not precious. Cloudina, there are zillions of them -- we could never grind them all."

GIRI can produce a 3-D rendering of any solid object, whether or not it has the density differences needed for effective X-ray computed microtomography (usually known as X-ray CT or Micro CT). In addition, because you're taking a super-high-resolution photograph with every slice, you're always seeing the rock itself, not just the density model that remote sensing can provide.

"It's destructive of course, that's the disadvantage, but what's so nice is that you get to see photographs and make direct observations," Maloof. "That's what's been so life-changing to me: I love that it's not a model. You can just see it. On any given slice, if you find something great, you can just find the slice and say, 'What did it look like?' ...We're on a virtual tour inside, rather than looking at waveforms and trying to interpret them."


And while GIRI does pulverize the sample, it preserves every detail in its high-resolution images, Maloof said, which arguably makes it less destructive than other approaches. It also preserves the structural information that reveals how the rocks formed. "When people have attempted to get 3-D information from rocks like this that are opaque to X-rays, they've always tried to dissolve the material out. But then you lose all the in-situ information. You don't know how they grew. They have no relationship to each other. And you don't know how they are related to perhaps smaller or less resilient parts. You may preferentially dissolve the ornamentation or other key details. So this is a way to keep them in their habitat while still trying to figure out what they looked like."

In the years since Maloof assembled GIRI, he and his research team have made physical improvements. These include redesigning and replacing the camera housing as well as the mechanism for wiping and preparing the rock surface for photographing after each grind. They've also installed monitors for temperature and humidity to record conditions during every photograph. The researchers also cut down the grind time per slice from seven minutes to 90 seconds. The biggest changes, though, have been improving software to run the machine and analyze the output.

Using a collection of interactive MATLAB scripts and Applescript functions, the control computer can now send and receive signals from the grinder, trigger the shutter, and verify image capture, all while GIRI is in operation, Mehra said.

"From the ground up, Akshay has designed machine-learning solutions to make the process of image segmentation -- differentiating fossils from matrix, cement, etc., in every slice -- automated and reliable," said Maloof. "He has developed techniques that ultimately will be important for any tomographic applications, including X-ray CT. Akshay also has developed ways to make quantitative measurements in the reconstructed 3-D volumes. You'd be surprised how much 3-D modeling out there only leads to visualization and qualitative interpretation, whereas Akshay actually measures the size, shape and 3-D orientation of these critters."

Using the software that he has developed, "We can directly measure these Cloudina specimens," said Mehra. "We can directly measure what directions the tubes are bending, what their diameters are, what their curvatures are -- none of them are actually straight -- and based on that information, we can determine whether they are in situ or not in situ."

Mehra has also designed neural networks to identify rock types by only their visual properties: color and texture. After the user defines which "classes" are present in a handful of images from the stack -- fossil versus matrix, for example, or the key minerals in a metamorphic rock -- the network can then predict whether a pixel belongs to a given class with greater than 90 percent accuracy.

And with all of that, he said, undergraduate and graduate students can typically be trained to run GIRI in about a day.

Scientists from around the world have reached out to Maloof and Mehra to ask for virtual, visual tours inside their own specimens. Paleontologists are hoping to examine the delicate structures from the earliest life on Earth, the huge range of early shelled creatures, the first fish, the first land creatures, the internal structure of ammonites and other organisms with internal buoyancy systems, and even dinosaur bones. Planetary scientists have begun examining meteorites with GIRI to look at tiny grains called chondrules that contain hints to how the planets formed. Engineers are testing possible reservoir rocks for carbon sequestration and grinding graphite batteries to examine the 3-D structure of porosity within the carbon.

There's really no limit to the contributions GIRI can make, said Maloof. "This represents five years of work. It's the only instrument in the world like it."

Source: Princeton University [February 27, 2018]

The island chain of Hawaii consists of several volcanoes, which are fed by a "hotspot." In geosciences a "hotspot" refers to a phenomenon of columnar shaped streams, which transport hot material from the deep mantle to the surface. Like a blow torch, the material burns through the Earth's crust and forms volcanoes. For a long time, it was assumed that these hotspots are stationary. If the tectonic plate moves across it, a chain of volcanoes evolves, with the youngest volcano at one end, the oldest at the other.

The graph shows the dates of volcanoes of the three volcanic chains in the Pacific and their relative movement over time (left). The location of the three volcanic chains shown in the map (right). The stars mark the youngest end or the active volcanoes today [Credit: Nature Communications, Kevin Konrad et al.]

This concept was initially proposed for the Hawaiian Islands. They are the youngest end of the Hawaiian-Emperor chain that lies beneath the Northwest Pacific. But soon there was doubt over whether hotspots are truly stationary. The biggest contradiction was a striking bend of about 60 degrees in this volcanic chain, which originated 47 million years ago.

"If you try to explain this bend with just a sudden change in the movement of the Pacific Plate, you would expect a significantly different direction of motion at that time relative to adjacent tectonic plates," says Bernhard Steinberger of the GFZ German Research Center for Geosciences. "But we have not found any evidence for that."

Recent studies have suggested that apparently two processes were effective: On the one hand, the Pacific Plate has changed its direction of motion. On the other hand, the Hawaiian hotspot moved relatively quickly southward in the period from 60 to about 50 million years ago -- and then stopped. If this hotspot motion is considered, only a smaller change of Pacific plate motions is needed to explain the volcano chain.

This hypothesis is now supported by work in which Steinberger is also involved. First author Kevin Konrad, Oregon State University in Corvallis, Oregon, and his team have evaluated new rock dating of volcanoes in the Rurutu volcanic chain, including, for example, the Tuvalu volcanic islands in the Western Pacific. Furthermore, they added similar data from the Hawaiian-Emperor chain and the Louisville chain in the Southern Pacific. Based on the geography and the age of volcanoes in these three chains, researchers can look into the geological past and see how the three hotspots have moved relative to each other over millions of years.

The new data published in the journal Nature Communications shows that the relative motion of hotspots under the Rurutu and Louisville is small while the Hawaiian-Emperor hotspot displays strong motion between 60 and 48 million years ago relative to the other two hotspots.

"This makes it very likely that mainly the Hawaii hotspot has moved," says Steinberger. According to his geodynamic modelling the Hawaiian hotspot moved at a rate of several tens of kilometers per million years. Paleomagnetic data support this interpretation, says Steinberger.

"Our models for the motion of the Pacific Plate and the hotspots therein still have some inaccuracies. With more field data and information about the processes deep in the mantle, we hope to explain in more detail how the bend in the Hawaiian-Emperor chain has evolved."

Source: GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre [February 27, 2018]

The vestiges of lakes long extinct dot the landscape of the American desert west. These fossilized landforms provide clues of how dynamic climate has been over the past few million years.

Erosional Pleistocene shorelines in Surprise Valley, California, USA [Credit: Anne Egger]

Identification of ancient lake shoreline features began with early explorers of the continent. The first detailed studies were conducted by pioneering American geologists such as G.K. Gilbert and I.C. Russell in the late 1800s, who studied Lake Bonneville, now the remnant Great Salt Lake in Utah, and Lake Lahonton, located in northwestern Nevada.

Through this long history of studying fossil shorelines and lake sediments, we know that these lakes existed during two periods with distinct environmental conditions during the geologically recent past. The first was during ice age maxima, such as the last ice age, 14 to 30 thousand years ago, when global temperatures were 4 to 6 degrees colder and continental ice sheets expanded into the continental United States.

The second time period was about three million years ago during the middle of the Pliocene epoch--a global climate characterized by warmer temperatures and atmospheric CO2 levels roughly equivalent to today's values, which has led many scientists to view the Pliocene as a potential analogue for future climate change.

These observations lead to an important question, says the study's lead author, Daniel Ibarra, "Why are there lake systems under both colder and warmer climates, but not today?" Of particular interest, he says, is the presence of lakes under warmer conditions, which, under a "wet gets wetter, dry gets drier" paradigm, goes against projections of future warming.

Shorelines of Lake Bonneville along the Oquirrh Mountains, Utah, USA. (H.H. Nichols [artist] and G.K. Gilbert, in Gilbert, 1884) [Credit: H.H. Nichols [artist] and G.K. Gilbert, in Gilbert, 1884. Public domain]

To answer this question, Ibarra and colleagues looked at the competing influences of temperature and precipitation, and how they combine to allow for the existence of lakes under these dual climate states.

The authors compiled evidence for, and created models of, lakes during both colder and warmer than modern periods of the Pliocene-Pleistocene (the last 5 million years). During colder glacial periods, they found that increased precipitation and decreased evaporation combined to form large lakes that occupied the inward draining basins in the western United States, particularly in northern Nevada and Utah.

Increased precipitation also drove the formation of lakes, particularly in southern Nevada and southern California during the warmer middle Pliocene, outpacing higher temperatures and evaporation rates during that time. This increase in precipitation during the middle Pliocene and dominantly southwestern distribution of lake deposits is similar to the pattern of precipitation during modern El Niño years, corroborating previous hypotheses for mean "El Niño-like" conditions during the mid-Pliocene.

The team's interdisciplinary approach explains the conditions driving lake systems in mid-latitude regions today and over the geologic past. Further, notes Ibarra, "This work illustrates the importance of understanding how the El Niño Southern Oscillation drives precipitation patterns in arid regions, which is important for future water resources planning for the western United States."

The study appears in the Geological Society of America Bulletin.

Source: Geological Society of America [February 22, 2018]

The biggest landslides on Earth aren't on land, but on the seafloor. These mega-slides can move thousands of cubic kilometers of material, and sometimes trigger tsunamis. Yet, remarkably, they occur on nearly flat slopes of less than three degrees.

Seismic reflection data [Credit: Morelia Urlaub and colleagues, and Geology]

Morelia Urlaub, a marine geoscientist at the Geomar Helmholtz Center for Ocean Research in Kiel, Germany, voices the obvious question: "How can you fail on a slope that is so flat?" Now, Urlaub and colleagues may have discovered the answer. The smoking -- or in this case, oozing -- gun is a layer of siliceous microfossils called diatoms.

The study, published online ahead of print for the Geological Society of America's journal Geology, is the first to identify the weak layer responsible for a submarine mega-slide. Although the nature of these critical weak layers has been highly debated, studying them has been nearly impossible because they are typically destroyed along with the slides.

Urlaub was compiling ocean drilling data from 1980 when she realized that the core sampled the seafloor just outside the Cap Blanc slide, a 149,000 year-old mega-slide off the coast of northwest Africa. She correlated that data with high resolution seismic reflection data recorded in the same area in 2009. Together, these data revealed diatom-rich layers, up to ten meters thick, that traced directly from the core to the base of slide layers within the mega-slide complex.

What's more, each diatom layer was topped by a layer of clay-rich sediment. That clay is apparently key. "Diatom layers are very compressible and water rich," Urlaub says. As pressure builds, she explains, water would be squeezed from the diatom layer into the clay. Ultimately the clay or the interface between the clay and diatoms fails, sending the sediments above sliding.

At the Cap Blanc slide, the seafloor slopes at just 2.8 degrees. Yet when it broke loose, the slide transported over 30 cubic kilometers of material, and extended at least 35 kilometers. Another submarine mega-slide 8,500 years ago off Norway moved a staggering 3,000 cubic kilometers, causing a damaging tsunami. And some scientists speculate that the 2011 Tohoku tsunami in Japan may have been amplified by a submarine mega-slide.

Although such slides don't occur very often, says Urlaub, their size makes them quite significant. "One-fifth of all tsunamis may be caused by undersea mega-slides," she says. If diatom layers are a major factor, then understanding where paleoclimate conditions may have favored diatom growth might help reveal potential mega-slide sites.

Source: Geological Society of America [February 12, 2018]

Geophysicists have obtained detailed three-dimensional images of a dangerous megathrust fault west of Costa Rica where two plates of the Earth's crust collide. The images reveal features of the fault surface, including long grooves or corrugations, that may determine how the fault will slip in an earthquake.

Perspective view of the shallow megathrust looking seaward towards the trench; the frontal prism has been cut away. The color scales indicate depth below seafloor, and grey denotes the seafloor [Credit: Edwards et al., 2018]

The study, published in Nature Geoscience, focused on the Costa Rica subduction zone where the Cocos plate slowly dives beneath the overriding Caribbean plate. Variations in texture seen in different portions of the fault surface may explain why Costa Rica has complex, patchy earthquakes that do not seem to slip to shallow depths, unlike some other megathrust faults, said first author Joel Edwards, a Ph.D. candidate in Earth and planetary sciences at UC Santa Cruz.

"Our new imagery shows large variability in the conditions along the megathrust, which may be linked to a number of earthquake phenomena we observe in the region," Edwards said.

Megathrusts, the huge continuous faults found in subduction zones, are responsible for Earth's largest earthquakes. Megathrust earthquakes can generate destructive tsunamis and are a serious hazard facing communities located near subduction zones. Understanding the mechanisms at work along these faults is vital for disaster management around the globe.

Edwards worked with a team of geophysicists at UC Santa Cruz, the U.S. Geological Survey, the University of Texas-Austin, and McGill University to obtain 3-dimensional imagery of the fault interface using cutting-edge acoustic imaging technology. The long grooves, or corrugations, they observed along the interface are similar in size to those found along the base of fast-flowing glaciers and along some ocean ridges. The images also showed varying amounts of smoothness and corrugations on different portions of the fault.

"This study produced an unprecedented view of the megathrust. Such 3-D information is critical to our ability to better understand megathrust faults and associated hazards worldwide," said coauthor Jared Kluesner, a geophysicist at the USGS in Santa Cruz.

The acoustic dataset was collected in spring 2011 on the academic research vessel Marcus G. Langseth. The ship towed an array of underwater microphones and sound sources behind it as it made a series of overlapping loops over the area of the fault. The data were processed over the next 2 years and have since been used in a number of studies looking at different aspects of the subduction zone process. This particular study focused on the interface between the sliding plates, which serves as a record of slip and slip processes.

"The 3-D site selection was really good and the resulting acoustic dataset showed extraordinary detail," said Edwards, noting that coauthor Emily Brodsky, professor of Earth and planetary sciences, was the first to recognize the corrugations. Such features had been observed in exposed faults on land, but never before in a fault deep beneath the surface.

"I had an early rendition of the interface that vaguely showed long grooves, and during my qualifying exam, Brodsky saw them and asked, 'are those corrugations!?' I didn't know, but I knew they were real features. Slip-derived corrugations was a really neat hypothesis, and we dug into it after that," he said.

The area in this study had long been a target for drilling into the megathrust by the Costa Rica Seismic Project (CRISP). Coauthor Eli Silver, professor emeritus of Earth and planetary sciences at UC Santa Cruz, and others in the CRISP program decided to pursue a 3-D seismic study, which must precede any deep drilling, and the project was funded by the National Science Foundation in 2009. "At present, two drilling expeditions have been accomplished with shallower targets, and, though not yet scheduled, we are hopeful that the deep drilling will occur," Silver said.

Researchers hope to use similar imaging techniques on other subduction zones, such as the Cascadia margin along the northern U.S. west coast, where there is a long history of large megathrust earthquakes and related tsunamis. "Conducting this type of 3-D study along the Cascadia margin could provide us with key information along the megathrust, a plate boundary that poses a substantial hazard risk to the U.S. west coast," Kluesner said.

Author: Tim Stephens | Source: University of California - Santa Cruz [February 12, 2018]

Methane hydrates, also known as 'burning ice', occur at all ocean margins. The compound of gas and water occurs in the seafloor and it is only stable under relatively high pressures and low temperatures. If the pressure is too low or the temperature too high, the hydrates dissociate (break down), the methane is released and the gas can seep from the seafloor into the ocean. Thus, scientists fear that warming of global water temperatures could destabilize gas hydrates on a large scale. At the same time, it has not been fully understood which other factors influence the stability of gas hydrates.

Bathymetric map of the Nyegga region off the coast of Central Norway [Credit: Jens Karstens/GEOMAR]

A team of researchers from the GEOMAR Helmholtz Centre for Ocean Research Kiel together with colleagues from Bergen, Oslo and Tromso (Norway), have now discovered that large-scale sedimentation caused by melting of glaciers in a region off Norway has played a greater role in gas hydrate dissociation than warming ocean waters.

For their study, the team had investigated the history of gas hydrates in the Nyegga area. "This region off middle Norway is quite interesting if you want to study the dynamics of gases and liquids in the seafloor. There are large gas hydrate deposits, and many crater-like structures, so-called 'pockmarks', on the seabed. They are generally associated with gas leaks from deeper gas reservoirs, but their exact origin in this area is still unclear."

Map of the Northern Atlantic Ocean with the largest extent of the northern ice shield during the last ice age [Credit: Jens Karstens/GEOMAR]

Numerous bathymetric maps, sediment cores and seismic surveys already exist in the Nyegga area, which the researchers used as a basis for the new study. "So we knew that in the final period of the recent Ice Age, between 30,000 and 15,000 years ago, large amounts of sediment were deposited in the region in a relatively short period of time," explains Dr. Karstens. In a computer model, the team used the available data to simulate the evolution of the seabed and the response of the gas hydrates during this period.

Despite the rising sea level and therefore increasing pressure, the simulation showed that towards the end of the ice age large amounts of gas hydrate became unstable and the released gas escaped through the sediment to the seawater. "Gas hydrates are only stable at a certain depth below the actual seafloor. When dozens of meters of new sediment settle on the seafloor, the solid compounds dissociate at the base of the hydrate stability zone, while new hydrates can form at the upper end of the stability zone. However, if the seafloor is already saturated with gas and the process takes place very quickly, the released gases make their way to the seafloor, without forming new hydrates," says Dr. Karstens.

Structure of gas hydrate [Credit: J. Greinert/GEOMAR]

The numerical simulations of the seafloor also showed that the pockmarks in Nyegga are likely associated with this phenomenon because they are located right in the area of the largest gas hydrate dissociation event at the end of the Ice Age. Samples from the seafloor confirm this assumption. Mussel shells of the species Isorropodon nyeggaensis were found in the pockmarks. The species is known from its symbiosis with bacteria that feed on methane. The researchers were able to date the shells precisely to the time when, according to the model calculations, the largest gas hydrate dissociation event occurred.

"We show that rapid changes in sedimentation can have a pronounced impact on the gas hydrate system and thus the entire carbon cycle", Dr. Karstens concludes. To date, this aspect has hardly been considered. However, further studies on other ocean margins are needed to obtain a more global picture, emphasizes the Kiel geophysicist.

The findings are published in Nature Communications.

Source: GEOMAR [February 12, 2018]

A record of volcanism preserved along ancient mid-ocean ridges provides evidence for heightened worldwide magmatic activity 66 million years ago just after the Chicxulub meteor struck Earth, according to University of Oregon scientists.

Coloured and black points mark the global distribution of mid-ocean ridges, with ages of 66 million years ago created at spreading rates above and below 35 millimeters a year, respectively. Colours indicate the maximum gravity anomaly within 2 degrees [Credit: Joseph Byrnes]

The research, published in Science Advances, points to changes in the strength of gravity above the seafloor, which indicate a transient period of increased volumes of magma being released along ridges that mark the oceanic boundaries of tectonic plates.

Lead author Joseph Byrnes, a former UO doctoral student, says that this global volcanic activity was likely triggered by strong seismic waves radiated from the meteorite impact site. Subsequently accelerated volcanism, he said, likely would have been active during the mass extinction of the world's non-avian dinosaurs.

Volcanism, particularly a massive outpouring of basalt recorded by the Deccan Traps in India, has been in and out of the extinction debate. Rare volcanic events at such a scale are known to cause catastrophic disturbances to Earth's climate and, when they occur, they are often linked to mass extinctions.

Since evidence of the meteor strike near present day Mexico surfaced in the 1980s, scientists have debated whether the impact or the Deccan Traps volcanic eruptions was the primary driver for extinction of the dinosaurs.

Progressively more accurate dating methods indicate that while the Deccan Traps eruptions were active during the mass extinction, they actually began significantly before the Chicxulub impact, said Leif Karlstrom, a professor in the UO's Department of Earth Sciences and co-author on the study with Byrnes.

The amount of seafloor exhibiting small structural anomalies is plotted as a function of the age of seafloor. Trends that  persist over 10 million years have been subtracted to highlight transient features, and only high spreading rates are plotted here. The highest peak, which indicates the production of 8 percent more anomalous seafloor than on average, occurs at 66 million years ago and is coincident with the age of the Chicxulub meteorite impact [Credit: Joseph Byrnes]

The meteor is closely aligned in time with the onset of mass extinction, seeming to indicate a dominant role, he said. Still, the near coincidence in time of such globally catastrophic events continues to spur debate.

In 2015, researchers at the University of California, Berkeley, proposed that the two events might be connected. They suggested that Chixculub may have modulated distant volcanism by sending seismic waves through the Earth and accelerating volcanic activity in the Deccan Traps. Similar to the impacts that normal tectonic earthquakes sometimes have on wells and streams, Karlstrom said, the study proposed that powerful shaking liberated magma stored in the mantle beneath the Deccan Traps and caused the largest eruptions there.

The new National Science Foundation-supported study at the UO adds another layer to the story, said Karlstrom, who also co-authored on the UC-Berkeley research. It suggests that other volcanic activity around the world was triggered by the meteor. Seismic waves moving through the Earth, he said, may have accelerated volcanism already occurring along mid-ocean ridges.

"Our work suggests a connection between these exceedingly rare and catastrophic events, distributed over the entire planet," Karlstrom said. "The meteorite's impact may have influenced volcanic eruptions that were already going on, making for a one-two punch."

The findings emerged as Byrnes, now a postdoctoral researcher at the University of Minnesota, discovered the evidence for volcanic activity by analyzing publicly available global datasets, including two updated in the last decade, on free-air gravity, ocean floor topography and tectonic spreading rates.


In his analyses, Byrnes divided the seafloor into one-million-year old groupings, constructing a record back to 100 million years ago. At about 66 million years, he found evidence for a "short-lived pulse of marine magmatism" along ancient ocean ridges. This pulse is suggested by a spike in the rate of the occurrence of free-air gravity anomalies seen in the dataset.

Free-air gravity anomalies, measured in milligals, account for variations in gravitational acceleration, found from satellite measurements of additional seawater collecting where the Earth's gravity is stronger.

Excess matter on the ocean floor, such as new magma, is a primary cause of elevated marine gravity anomalies. A gal reflects a change in the rate of motion of a centimeter, about 0.4 of an inch, per second squared. Byrnes and Karlstrom found changes in free-air gravity anomalies of between five and 20 milligals associated with seafloor created in the first million years after the meteor.

"We found evidence for a previously unknown period of globally heighted volcanic activity during the mass-extinction event," Byrnes said. "This study does not say precisely that this volcanic activity is what killed the dinosaurs. What we are adding to the conversation is global volcanic activity during the known environmental crisis."

The gravity data analyzed in the research came from the Scripps Institution of Oceanography at the University of California, San Diego, the seafloor ages from the EarthByte group at the University of Sydney, and seafloor elevation from the National Geophysical Data Center of the National Oceanic and Atmospheric Administration.

Source: University of Oregon [February 07, 2018]