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Ozone may be heating the planet more than we realize

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31/03/2022

Ozone may be heating the planet more than we realize

Ozone may be weakening one of the Earth’s most important cooling mechanisms, making it a more significant greenhouse gas than previously thought, research has found.

A new study has revealed that changes to ozone levels in the upper and lower atmosphere were responsible for almost a third of the warming seen in ocean waters bordering Antarctica in the second half of the 20th century.

The deep and rapid warming in the Southern Ocean affects its role as one of the main regions for soaking up excess heat as the planet warms.

The majority of this warming was the result of ozone increases in the lower atmosphere. Ozone—one of the main components of smog—is already hazardous as a pollutant, but the research shows it may also play a significant role in driving climate change in the coming years.

Dr. Michaela Hegglin, an Associate Professor in atmospheric chemistry and one of the study’s authors, said: “Ozone close to Earth’s surface is harmful to people and the environment, but this study reveals it also has a big impact on the ocean’s ability to absorb excess heat from the atmosphere.

“These findings are an eye-opener and hammer home the importance of regulating air pollution to prevent increased ozone levels and global temperatures rising further still.”

The new research by an international team of scientists, and led by the University of California Riverside, is published in Nature Climate Change.

The team used models to simulate changes in ozone levels in the upper and lower atmosphere between 1955 and 2000, to isolate them from other influences and increase the currently poor understanding of their impact on the Southern Ocean heat uptake.

These simulations showed that a decrease in ozone in the upper atmosphere and increase in the lower atmosphere both contributed to warming seen in the upper 2km of the ocean waters in the high latitudes by overall greenhouse gas increases.

They revealed that the increased ozone in the lower atmosphere caused 60% of the overall ozone-induced warming seen in the Southern Ocean over the period studied—far more than previously thought. This was surprising because tropospheric ozone increases are mainly thought of as a climate forcing in the Northern hemisphere since that is where the main pollution occurs.

Ozone hit the headlines in the 1980s when a hole was discovered in the ozone layer high in the atmosphere over the South Pole, due to damage caused by chlorofluorocarbons (CFCs), a gas used in industry and consumer products.

The ozone layer is vital as it filters dangerous ultraviolet radiation from reaching Earth’s surface. This discovery led to the Montreal Protocol, an international agreement to halt the production of CFCs.

Dr. Hegglin said: “We have known for a while that ozone depletion high in the atmosphere has affected surface climate in the Southern Hemisphere. Our research has shown that ozone increases in the lower atmosphere due to air pollution, which occurs primarily in the Northern Hemisphere and ‘leaks’ into the Southern Hemisphere, is a serious problem as well.

“There is hope to find solutions, and the success of the Montreal Protocol at cutting CFC use shows that international action is possible to prevent damage to the planet.”

Ozone is created in the upper atmosphere by interaction between oxygen molecules and UV radiation from the sun. In the lower atmosphere, it forms due to chemical reactions between pollutants like vehicle exhaust fumes and other emissions.

Changes in ozone concentrations in the atmosphere affect westerly winds in the Southern Hemisphere as well as causing contrasting levels of salt and temperature close to the surface in the Southern Ocean. Both affect ocean currents in distinct ways, thereby affecting ocean heat uptake.

More information: Wei Liu, Stratospheric ozone depletion and tropospheric ozone increases drive Southern Ocean interior warming, Nature Climate Change (2022). DOI: 10.1038/s41558-022-01320-w. www.nature.com/articles/s41558-022-01320-w

Journal information: Nature Climate Change

Provided by University of Reading.

A billion-year history of Earth’s interior shows it’s more mobile than we thought

EARTH

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31/03/2022

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A billion-year history of Earth’s interior shows it’s more mobile than we thought

Deep in the Earth beneath us lie two blobs the size of continents. One is under Africa, the other under the Pacific Ocean.

The blobs have their roots 2,900km below the surface, almost halfway to the center of the Earth. They are thought to be the birthplace of rising columns of hot rock called “deep mantle plumes” that reach Earth’s surface.

When these plumes first reach the surface, giant volcanic eruptions occur—the kind that contributed to the extinction of the dinosaurs 65.5 million years ago. The blobs may also control the eruption of a kind of rock called kimberlite, which brings diamonds from depths 120–150km (and in some cases up to around 800km) to Earth’s surface.

Scientists have known the blobs existed for a long time, but how they have behaved over Earth’s history has been an open question. In new research, we modeled a billion years of geological history and discovered the blobs gather together and break apart much like continents and supercontinents.

A model for Earth blob evolution

The blobs are in the mantle, the thick layer of hot rock between Earth’s crust and its core. The mantle is solid but slowly flows over long timescales. We know the blobs are there because they slow down waves caused by earthquakes, which suggests the blobs are hotter than their surroundings.

Scientists generally agree the blobs are linked to the movement of tectonic plates at Earth’s surface. However, how the blobs have changed over the course of Earth’s history has puzzled them.

One school of thought has been that the present blobs have acted as anchors, locked in place for hundreds of millions of years while other rock moves around them. However, we know tectonic plates and mantle plumes move over time, and research suggests the shape of the blobs is changing.

Volcanoes, diamonds, and blobs: a billion-year history of Earth’s interior shows it’s more mobile than we thought — Earth’s blobs as imaged from seismic data. The African blob is at the top and the Pacific blob at the bottom. Credit: Ömer Bodur

Our new research shows Earth’s blobs have changed shape and location far more than previously thought. In fact, over history they have assembled and broken up in the same way that continents and supercontinents have at Earth’s surface.

We used Australia’s National Computational Infrastructure to run advanced computer simulations of how Earth’s mantle has flowed over a billion years.

These models are based on reconstructing the movements of tectonic plates. When plates push into one another, the ocean floor is pushed down between them in a process known as subduction. The cold rock from the ocean floor sinks deeper and deeper into the mantle, and once it reaches a depth of about 2,000km it pushes the hot blobs aside.

We found that just like continents, the blobs can assemble—forming “superblobs” as in the current configuration—and break up over time.

A key aspect of our models is that although the blobs change position and shape over time, they still fit the pattern of volcanic and kimberlite eruptions recorded at Earth’s surface. This pattern was previously a key argument for the blobs as unmoving “anchors.”

Strikingly, our models reveal the African blob assembled as recently as 60 million years ago—in stark contrast to previous suggestions the blob could have existed in roughly its present form for nearly ten times as long.

Remaining questions about the blobs

How did the blobs originate? What exactly are they made of? We still don’t know.

The past 200 million years of Earth’s interior. Hot structures are in yellow to red (darker is shallower) and cold structures in blue (darker is deeper).

The blobs may be denser than the surrounding mantle, and as such they could consist of material separated out from the rest of the mantle early in Earth’s history. This could explain why the mineral composition of the Earth is different from that expected from models based on the composition of meteorites.

Alternatively, the density of the blobs could be explained by the accumulation of dense oceanic material from slabs of rock pushed down by tectonic plate movement.

Regardless of this debate, our work shows sinking slabs are more likely to transport fragments of continents to the African blob than to the Pacific blob. Interestingly, this result is consistent with recent work suggesting the source of mantle plumes rising from the African blob contains continental material, whereas plumes rising from the Pacific blob do not.

Tracking the blobs to find minerals and diamonds

While our work addresses fundamental questions about the evolution of our planet, it also has practical applications.

Our models provide a framework to more accurately target the location of minerals associated with mantle upwelling. This includes diamonds brought up to the surface by kimberlites that seem to be associated with the blobs.

Magmatic sulfide deposits, which are the world’s primary reserve of nickel, are also associated with mantle plumes. By helping target minerals such as nickel (an essential ingredient of lithium-ion batteries and other renewable energy technologies) our models can contribute to the transition to a low-emission economy.

More information: Nicolas Flament et al, Assembly of the basal mantle structure beneath Africa, Nature (2022). DOI: 10.1038/s41586-022-04538-y

Journal information: Nature

Provided by The Conversation.

Research team proves Mercury has magnetic storms

ASTRONOMY

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31/03/2022

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Research team proves Mercury has magnetic storms

An international team of scientists has proved that Mercury, our solar system’s smallest planet, has geomagnetic storms similar to those on Earth.

The research by scientists in the United States, Canada and China includes work by Hui Zhang, a space physics professor at the University of Alaska Fairbanks Geophysical Institute.

Their finding, a first, answers the question of whether other planets, including those outside our solar system, can have geomagnetic storms regardless of the size of their magnetosphere or whether they have an Earth-like ionosphere.

The research was published in two papers in February. Zhang is among the co-authors of each paper.

The first of those papers proves the planet has a ring current, a doughnut-shaped field of charged particles flowing laterally around the planet and excluding the poles. The second proves the existence of geomagnetic storms triggered by the ring current.

A geomagnetic storm is a major disturbance in a planet’s magnetosphere caused by the transfer of energy from the solar wind. Such storms in Earth’s magnetosphere produce the aurora and can disrupt radio communications.

The geomagnetic storms finding was published Feb. 18 in the journal Science China Technological Sciences. QiuGang Zong of the Institute of Space Physics and Applied Technology at Peking University and the Polar Research Institute of China is the author.

That paper built on a finding published one day earlier that verified through data observation earlier suggestions that Mercury has a ring current. Earth also has a ring current.

The ring current paper, published in Nature Communications, is authored by Jiutong Zhao, also of the Institute of Space Physics and Applied Technology at Peking University.

Seven of the 14 scientists involved worked on both papers.

“The processes are quite similar to here on Earth,’ Zhang said of Mercury’s magnetic storms. “The main differences are the size of the planet and Mercury has a weak magnetic field and virtually no atmosphere.”

Confirmation about geomagnetic storms on Mercury results from research made possible by a fortuitous coincidence: a series of coronal mass ejections from the sun on April 8-18, 2015, and the end of NASA’s Messenger space probe, which launched in 2004 and crashed into the planet’s surface on April 30, 2015, at the expected end of its mission.

A coronal mass ejection, or CME, is an ejected cloud of the sun’s plasma—a gas made of charged particles. That cloud includes the plasma’s embedded magnetic field.

The coronal mass ejection of April 14 proved to be the key for scientists. It compressed Mercury’s ring current on the sun-facing side and increased the current’s energy.

New analysis of data from Messenger, which had dropped closer to the planet, shows “the presence of a ring current intensification that is essential for triggering magnetic storms,” the second of the two papers reads.

“The sudden intensification of a ring current causes the main phase of a magnetic storm,” Zhang said.

But this doesn’t mean Mercury has auroral displays like those on Earth.

On Earth, the storms produce aurora displays when solar wind particles interact with the particles of the atmosphere. On Mercury, however, solar wind particles don’t encounter an atmosphere. Instead, they reach the surface unimpeded and may therefore be visible only through X-ray and gamma ray examination.

The results of the two papers show that magnetic storms are “potentially a common feature of magnetized planets,” the second of the papers reads.

“The results obtained from Messenger provide a further fascinating insight into Mercury’s place in the evolution of the solar system following the discovery of its intrinsic planetary magnetic field,” it concludes.

Other institutions involved in the research include the University of Alberta, Edmonton; University of Michigan and the Heliophysics Science Division at NASA’s Goddard Space Flight Center.

More information: QiuGang Zong et al, Magnetic storms in Mercury’s magnetosphere, Science China Technological Sciences (2022). DOI: 10.1007/s11431-022-2009-8
Journal information: Nature Communications, Provided by University of Alaska Fairbanks

How carbonates behave in the Earth’s interior

EARTH

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31/03/2022

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How carbonates behave in the Earth’s interior

Carbonates are the most important carbon reservoirs on the planet. But what role do they play in the Earth’s interior? How do they react to conditions in the Earth’s mantle? These are the questions being asked by a group of scientific researchers from Frankfurt, Bayreuth, Berlin/Potsdam, Freiberg and Hamburg, in a project funded by the DFG. The Research Unit brings together experts from various geoscience disciplines and cutting edge technology.

The Earth has an average radius of around 6,400 kilometers. However, the deepest borehole thus far drilled has only reached a depth of twelve kilometers. And even with huge technical advances, it is unthinkable that we will ever be able to carry out empirical research on the deepest layers, according to Björn Winkler, Professor of Crystallography at the Goethe University Frankfurt and coordinator of the new Research Unit. “We can only get an idea of the conditions in the Earth’s interior by combining experiments and model calculations”, he explains. While we already have detailed knowledge of silicates, which are a key component of the earth’s mantle, very little research on carbonates has been done to date. “The composition of the earth can be explained without carbonates – but the question is, how well?”, continues Winkler.

“Structures, Properties and Reactions of Carbonates at High Temperatures and Pressures” is the title of the project being funded by the DFG as of mid-February. “We want to understand how the Earth works,” is the way Winkler describes the primary research goal of the approximately 30 scientists and their teams. What possibilities our planet has for storing carbon, how much carbon there actually is on the earth – the entire carbon cycle is still a complete mystery.

The research group, which combines seven individual projects, is focusing its attention on the Earth’s mantle: the 2,850 kilometer thick middle layer in the internal structure of the earth. The aim is to come to a better understanding of the phase relationships, crystal chemistry and physical properties of carbonates. To that end, the plan is to simulate the conditions of the mantle transition zone and the lower earth mantle below it – namely very high temperatures and very high pressure. Each of the seven projects examines a different aspect; for example the carbonate calcite, or the combination of carbonates with iron or silicates, or the behavior of carbonates under shock.

Winkler and his team have been dealing with this issue for six years already. His colleague, Dr. Lkhamsuren Bayarjargal has already been awarded the Max-von-Laue Prize from the German Association of Crystallography for his work with high-power lasers, and has received funding from the Focus Program of the Goethe University. The nationwide collaboration among the researchers is not an entirely new phenomenon either. The DFG funding will enable them to build special equipment to simulate the conditions in the Earth’s mantle. This research apparatus includes diamond anvil cells, capable of producing pressures a million times greater than atmospheric pressure, and high-power lasers that can generate temperatures of up to 5,000 degrees Celsius. Calculations have shown that these are the conditions that prevail in the Earth’s mantle.

The tiniest amounts of a carbonate are enough for an experiment. During the experiment, the substance is exposed to the respective conditions while the researchers examine it for any changes. A variety of techniques are used for this, such as Raman spectroscopy in Frankfurt, and infrared spectroscopy in Potsdam. “If we come to the same conclusions using different methods, we will know that we have got it right,” says Prof. Winkler.

The above story is based on materials provided by Goethe University.

Traces of life in the Earth’s deep mantle

EARTH

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31/03/2022

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Traces of life in the Earth’s deep mantle

The rapid development of fauna 540 million years ago has permanently changed the Earth — deep into its lower mantle. A team led by ETH researcher Andrea Giuliani found traces of this development in rocks from this zone.

It is easy to see that the processes in the Earth’s interior influence what happens on the surface. For example, volcanoes unearth magmatic rocks and emit gases into the atmosphere, and thus influence the biogeochemical cycles on our planet.

What is less obvious, however, is that the reverse is also true: what happens on the Earth’s surface effect the Earth’s interior — even down to great depths. This is the conclusion reached by an international group of researchers led by Andrea Giuliani, SNSF Ambizione Fellow in the Department of Earth Sciences at ETH Zurich, in a new study published in the journal Science Advances. According to this study, the development of life on our planet affects parts of Earth’s lower mantle.

Carbon as a messenger

In their study, the researchers examined rare diamond-bearing volcanic rocks called kimberlites from different epochs of the Earth’s history. These special rocks are messengers from the lowest regions of the Earth’s mantle. Scientists measured the isotopic composition of carbon in about 150 samples of these special rocks. They found that the composition of younger kimberlites, which are less than 250 million years old, varies considerably from that of older rocks. In many of the younger samples, the composition of the carbon isotopes is outside the range that would be expected for rocks from the mantle.

The researchers see a decisive trigger for this change in composition of younger kimberlites in the Cambrian Explosion. This relatively short phase — geologically speaking — took place over a period of few tens of million years at the beginning of the Cambrian Epoch, about 540 million years ago. During this drastic transition, almost all of today’s existing animal tribes appeared on Earth for the first time. “The enormous increase in life forms in the oceans decisively changed what was happening on the Earth’s surface,” Giuliani explains. “And this in turn affected the composition of sediments at the bottom of the ocean.”

From the oceans to the mantle and back

For the Earth’s lower mantle, this changeover is relevant because some of the sediments on the seafloor, in which material from dead living creatures is deposited, enter the mantle through plate tectonics. Along the subduction zones, these sediments — along with the underlying oceanic crust — are transported to great depths. In this way, the carbon that was stored as organic material in the sediments also reaches the Earth’s mantle. There the sediments mix with other rock material from the Earth’s mantle and after a certain time, estimated to at least 200-300 million years, rise to the Earth’s surface again in other places — for example in the form of kimberlite magmas.

It is remarkable that changes in marine sediments leave such profound traces, because overall, only small amounts of sediment are transported into the depths of the mantle along a subduction zone. “This confirms that the subducted rock material in the Earth’s mantle is not distributed homogeneously, but moves along specific trajectories,” Giuliani explains.

The Earth as a total system

In addition to carbon, the researchers also examined the isotopic composition of other chemical elements. For example, the two elements strontium and hafnium showed a similar pattern to carbon. “This means that the signature for carbon cannot be explained by other processes such as degassing, because otherwise the isotopes of strontium and hafnium would not be correlated with those of carbon,” Giuliani notes.

The new findings open the door for further studies. For example, elements such as phosphorus or zinc, which were significantly affected by the emergence of life, could also provide clues as to how processes at the Earth’s surface influence the Earth’s interior. “The Earth is really a complex overall system,” Giuliani says. “And we now want to understand this system in more detail.”

Reference: Andrea Giuliani, Russell N. Drysdale, Jon D. Woodhead, Noah J. Planavsky, David Phillips, Janet Hergt, William L. Griffin, Senan Oesch, Hayden Dalton, Gareth R. Davies. Perturbation of the deep-Earth carbon cycle in response to the Cambrian Explosion. Science Advances, 2022; 8 (9) DOI: 10.1126/sciadv.abj1325

Studying impact craters to uncover the secrets of the solar system

ASTRONOMY

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31/03/2022

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While for humans the constants might be death and taxes, for planets the constants are gravity and collisions.

Brandon Johnson studies the latter, using information about impacts to understand the history and the composition of planets, moons, asteroids and meteorites throughout the solar system.

“Impact cratering is the most ubiquitous surface process shaping planetary bodies,” Johnson said. “Craters are found on almost every solid body we’ve ever seen. They are a major driver of change in planetary bodies. They drive the evolution of planetary crusts. All the planets and asteroids were built from a series of impacts. Studying impacts can help us determine the composition and structure of planets.”

As an associate professor in the Department of Earth, Atmospheric, and Planetary Sciences in Purdue University’s College of Science, Johnson has studied almost every major planetary body in the solar system. And the time scale of his research ranges from relatively recent impacts to nearly the beginning of the solar system itself.

Collecting clues about collisions helps Johnson reconstruct the environment in which the collisions took place, offering deep insights into how and when bodies formed. His research is helping humans explore the planetary bodies in the solar system with only physics, math and a computer. Space missions and laboratory analyses provide a constant supply of new data and questions to work on.

“Most meteorites contain chondrules—small, previously molten, particles,” Johnson said. “Essentially, by studying the formation of chondrules by impacts, we can better understand what was going on in the nascent solar system. For example, based on one impact, we were able to determine that Jupiter had already formed right around 5 million years after the first solar system solids, changing the timeline of our understanding of the solar system.”

Johnson and his lab staff incorporate known factors about the composition and physics of planetary bodies into complex computer models, running the models through a range of conditions and comparing the results with observed phenomena. Analyzing movements and collisions can offer insights into the composition of asteroids and meteorites, helping scientists understand how elements like water and metal are distributed through a solar system. By studying impact craters and basins on places like Pluto, Venus and icy moons, and the mechanics of other processes occurring on Europa and asteroids like Psyche, his team can understand more about their interiors; whether they have molten cores and plate tectonics, for example, or whether they have liquid oceans.

His work doesn’t just span the solar system. He studies impacts closer to home, too, including on Earth’s own moon and terrestrial impacts that may have affected the way Earth’s crust, atmosphere and biosphere evolved.

An online impact calculator tool developed by the late Jay Melosh, Johnson’s mentor and former Distinguished Professor of Earth, Atmospheric and Planetary Sciences, allows anyone to study the impacts of various rocks into the Earth. Johnson and his team are rebuilding the tool for a new generation of planetary students.

The research was published in Icarus.

More information: J.R. Elliott et al, The role of target strength on the ejection of martian meteorites, Icarus (2021). DOI: 10.1016/j.icarus.2021.114869

Gareth S. Collins et al, Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth, Meteoritics & Planetary Science (2010). DOI: 10.1111/j.1945-5100.2005.tb00157.x

Journal information: Icarus Provided by Purdue University

Solar energy explains fast yearly retreat of Antarctica’s sea ice

OCEANOGRAPHY

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31/03/2022

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Solar energy explains fast yearly retreat of Antarctica’s sea ice

In the Southern Hemisphere, the ice cover around Antarctica gradually expands from March to October each year. During this time the total ice area increases by 6 times to become larger than Russia. The sea ice then retreats at a faster pace, most dramatically around December, when Antarctica experiences constant daylight.

New research led by the University of Washington explains why the ice retreats so quickly: Unlike other aspects of its behavior, Antarctic sea ice is just following simple rules of physics.

The study was published March 28 in Nature Geoscience.

“In spite of the puzzling longer-term trends and the large year-to-year variations in Antarctic sea ice, the seasonal cycle is really consistent, always showing this fast retreat relative to slow growth,” said lead author Lettie Roach, who conducted the study as a postdoctoral researcher at the UW and is now research scientist at NASA and Columbia University. “Given how complex our climate system is, I was surprised that the rapid seasonal retreat of Antarctic sea ice could be explained with such a simple mechanism.”

Previous studies explored whether wind patterns or warm ocean waters might be responsible for the asymmetry in Antarctica’s seasonal sea ice cycle. But the new study shows that, just like a hot summer day reaches its maximum sizzling conditions in late afternoon, an Antarctic summer hits peak melting power in midsummer, accelerating warming and sea ice loss, with slower changes in temperature and sea ice when solar input is low during the rest of the year.

The researchers investigated global climate models and found they reproduced the quicker retreat of Antarctic sea ice. They then built a simple physics-based model to show that the reason is the seasonal pattern of incoming solar radiation.

At the North Pole, Arctic ice cover has gradually decreased since the 1970s with global warming. Antarctic ice cover, however, has seesawed over recent decades. Researchers are still working to understand sea ice around the South Pole and better represent it in climate models.

“I think because we usually expect Antarctic sea ice to be puzzling, previous studies assumed that the rapid seasonal retreat of Antarctic sea ice was also unexpected—in contrast to the Arctic, where the seasons of ice advance and retreat are more similar,” Roach said. “Our results show that the seasonal cycle in Antarctic sea ice can be explained using very simple physics. In terms of the seasonal cycle, Antarctic sea ice is behaving as we should expect, and it is the Arctic seasonal cycle that is more mysterious.”

The researchers are now exploring why Arctic sea ice doesn’t follow this pattern, instead each year growing slightly faster over the Arctic Ocean than it retreats. Because Antarctica’s geography is simple, with a polar continent surrounded by ocean, this aspect of its sea ice may be more straightforward, Roach said.

“We know the Southern Ocean plays an important role in Earth’s climate. Being able to explain this key feature of Antarctic sea ice that standard textbooks have had wrong, and showing that the models are reproducing it correctly, is a step toward understanding this system and predicting future changes,” said co-author Cecilia Bitz, a UW professor of atmospheric sciences.

Other co-authors are; Edward Blanchard-Wrigglesworth, a UW research assistant professor in atmospheric sciences; Ian Eisenman at Scripps Institution of Oceanography; and Till Wagner at the University of Wisconsin-Madison.

More information: Asymmetry in the seasonal cycle of Antarctic sea ice driven by insolation, Nature Geoscience (2022). DOI: 10.1038/s41561-022-00913-6

Journal information: Nature Geoscience

Provided by University of Washington

Where does all Earth’s gold come from?

MINERALS

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31/03/2022

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Ultra high precision analyses of some of the oldest rock samples on Earth by researchers at the University of Bristol provides clear evidence that the planet’s accessible reserves of precious metals are the result of a bombardment of meteorites more than 200 million years
The research is published in Nature.

During the formation of Earth, molten iron sank to its centre to make the core. This took with it the vast majority of the planet’s precious metals — such as gold and platinum. In fact, there are enough precious metals in the core to cover the entire surface of Earth with a four-metre thick layer.

The removal of gold to the core should leave the outer portion of Earth bereft of bling. However, precious metals are tens to thousands of times more abundant in Earth’s silicate mantle than anticipated. It has previously been argued that this serendipitous over-abundance results from a cataclysmic meteorite shower that hit Earth after the core formed. The full load of meteorite gold was thus added to the mantle alone and not lost to the deep interior.

To test this theory, Dr Matthias Willbold and Professor Tim Elliott of the Bristol Isotope Group in the School of Earth Sciences analysed rocks from Greenland that are nearly four billion years old, collected by Professor Stephen Moorbath of the University of Oxford. These ancient rocks provide a unique window into the composition of our planet shortly after the formation of the core but before the proposed meteorite bombardment.

The researchers determined the tungsten isotopic composition of these rocks. Tungsten (W) is a very rare element (one gram of rock contains only about one ten-millionth of a gram of tungsten) and, like gold and other precious elements, it should have entered the core when it formed. Like most elements, tungsten is composed of several isotopes, atoms with the same chemical characteristics but slightly different masses. Isotopes provide robust fingerprints of the origin of material and the addition of meteorites to Earth would leave a diagnostic mark on its W isotope composition.

Dr Willbold observed a 15 parts per million decrease in the relative abundance of the isotope 182W between the Greenland and modern day rocks. This small but significant change is in excellent agreement with that required to explain the excess of accessible gold on Earth as the fortunate by-product of meteorite bombardment.

Dr Willbold said: “Extracting tungsten from the rock samples and analysing its isotopic composition to the precision required was extremely demanding given the small amount of tungsten available in rocks. In fact, we are the first laboratory world-wide that has successfully made such high-quality measurements.”

The impacting meteorites were stirred into Earth’s mantle by gigantic convection processes. A tantalising target for future work is to study how long this process took. Subsequently, geological processes formed the continents and concentrated the precious metals (and tungsten) in ore deposits which are mined today.

Dr Willbold continued: “Our work shows that most of the precious metals on which our economies and many key industrial processes are based have been added to our planet by lucky coincidence when the Earth was hit by about 20 billion billion tonnes of asteroidal material.”

This research was funded by the Natural Environment Research Council (NERC), the Science and Technology Facilities Council (STFC) and the Deutsche Forschungsgemeinschaft (DFG).

Reference: Matthias Willbold, Tim Elliott, Stephen Moorbath. The tungsten isotopic composition of the Earth’s mantle before the terminal bombardment. Nature, 2011; 477 (7363): 195 DOI: 10.1038/nature10399

Hidden weaknesses within volcanoes may cause volcano collapse

VOLCANOES

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31/03/2022

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Hidden weaknesses within volcanoes may cause volcano collapse

Lava domes form at the top of many volcanoes when viscous lava erupts. When they become unstable, they can collapse and cause a hazard. An international team of researchers has analysed summit dome instabilities at Merapi Volcano, Indonesia. The researchers hope that by understanding the inner processes, volcano collapses can be better forecasted.

Catastrophic volcano collapses and associated explosions, like the famous collapse of Mt St Helens in 1980, are widely considered as unpredictable. This is because the physical properties, stress conditions, and internal structure of volcanoes and the lava domes on top of many volcanoes are not well understood and can change rapidly from one day to another.

A new study jointly led by Gadja Mata University in Yogyakarta Indonesia, Uppsala University in Sweden, and the German Research Center GFZ at Potsdam is now able to explain summit dome instabilities and associated pyroclastic flows at Merapi volcano, Indonesia. The study combines novel drone-based photogrammetry surveillance over several years with mineralogical, geochemical, and mechanical rock strength measurements.

The research demonstrated that a horseshoe-shaped fracture zone in the volcanoes summit region that formed in 2012 and which guided intense gas emission in the past was subsequently buried by renewed lava outpourings in 2018. The new lava dome that has been forming since 2018 started to show signs of instability in 2019 and the researchers were able to show that the summit dome of the volcano is currently collapsing along this now-hidden fracture zone. The research team then considered the changes that must have occurred along this now buried fracture zone from long term gas flux by measuring the composition and physical properties along similar fracture zones in the volcano’s summit region, and concludes that weakened rocks of the hidden fracture zone are likely the main cause for the location of the ongoing summit instabilities at Merapi.

Reference: Herlan Darmawan, Valentin R. Troll, Thomas R. Walter, Frances M. Deegan, Harri Geiger, Michael J. Heap, Nadhirah Seraphine, Chris Harris, Hanik Humaida, Daniel Müller. Hidden mechanical weaknesses within lava domes provided by buried high-porosity hydrothermal alteration zones. Scientific Reports, 2022; 12 (1) DOI: 10.1038/s41598-022-06765-9

Warmer summers and meltwater lakes are threatening the fringes of the world’s largest ice sheet

OCEANOGRAPHY

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31/03/2022

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Warmer summers and meltwater lakes are threatening the fringes of the world’s largest ice sheet

A first-of-its-kind study looking at surface meltwater lakes around the East Antarctic Ice Sheet across a seven-year period has found that the area and volume of these lakes is highly variable year-to-year, and offers new insights into the potential impact of recent climatic change on the ‘Frozen Continent’.

The research, led by Durham University (UK), used over 2000 satellite images from around the edge of the East Antarctic Ice Sheet to determine the size and volume of lakes on the ice surface, also known as supraglacial lakes, across seven consecutive years between 2014 and 2020.

The study, which involved Newcastle and Lancaster universities and the Georgia Institute of Technology, showed that lake volume varied year-to-year by as much as 200% on individual ice shelves (floating extensions of the main Antarctic ice sheet), and by around 72% overall.

Lakes were also found to be deeper and larger in warmer melt seasons and formed on some potentially vulnerable ice shelves.

This research, published today in Nature Communications, is the first time that meltwater lakes have been studied over consecutive melt seasons across the whole ice sheet, enabling the controls on their development to be explored. The study therefore provides vital insight into why and where lakes grow, and will help experts understand which ice shelves may be most at risk of breaking up as a consequence of surface melting.

Lead researcher, Ph.D. student Jennifer Arthur, Department of Geography, Durham University, said; “We knew that supraglacial lakes were more extensive than previously thought around the East Antarctic Ice Sheet, but until now only had snapshots of these in some years.

“Our study reveals these lakes change in scale far more than we originally suspected. We were surprised at how much lakes can change year-to-year between ice shelves.

“We explored the potential reasons for this and found that warmer summer air temperatures in Antarctica correlated with more extensive lakes.

“Due to climate change, air temperatures in Antarctica will continue to rise and our study suggests that this will lead to an increase in the number and volume of supraglacial lakes, which will in turn put some East Antarctic ice shelves at risk of meltwater-driven collapse.”

The East Antarctic Ice Sheet is the world’s largest ice mass and holds enough ice to raise global sea levels by around 52 meters.

The loss of ice shelves fringing an ice sheet allows ice further inland to flow faster into the ocean, contributing to global sea-level rise.

Until now, observations of supraglacial lakes on the East Antarctica Ice Sheet were relatively scarce and the year-to-year variability was largely unknown, making it difficult to assess whether some ice shelves are close to meltwater-driven break up under climate change.

This study will help experts understand supraglacial lake formation, climatic impacts on this and predict which ice shelves may be most at risk of collapse.

Understanding the climatic conditions controlling meltwater lake variability will also improve the accuracy of regional climate models used to replicate observations and predict future ice sheet change in Antarctica.

The study used images from the Landsat 8 satellite.

More information: Large interannual variability in supraglacial lakes around East Antarctica, Nature Communications (2022). DOI: 10.1038/s41467-022-29385-3

Journal information:Nature Communications

Provided by Durham University