Rare 2.5-billion-year-old rocks reveal hot spot of sulfur-breathing bacteria

Gold miners prospecting in a mountainous region of Brazil drilled this 590-foot cylinder of bedrock from the Neoarchaean Eon, which provides rare evidence of conditions on Earth 2.5 billion years ago. -  Alan J. Kaufman
Gold miners prospecting in a mountainous region of Brazil drilled this 590-foot cylinder of bedrock from the Neoarchaean Eon, which provides rare evidence of conditions on Earth 2.5 billion years ago. – Alan J. Kaufman

Wriggle your toes in a marsh’s mucky bottom sediment and you’ll probably inhale a rotten egg smell, the distinctive odor of hydrogen sulfide gas. That’s the biochemical signature of sulfur-using bacteria, one of Earth’s most ancient and widespread life forms.

Among scientists who study the early history of our 4.5 billion-year-old planet, there is a vigorous debate about the evolution of sulfur-dependent bacteria. These simple organisms arose at a time when oxygen levels in the atmosphere were less than one-thousandth of what they are now. Living in ocean waters, they respired (or breathed in) sulfate, a form of sulfur, instead of oxygen. But how did that sulfate reach the ocean, and when did it become abundant enough for living things to use it?

New research by University of Maryland geology doctoral student Iadviga Zhelezinskaia offers a surprising answer. Zhelezinskaia is the first researcher to analyze the biochemical signals of sulfur compounds found in 2.5 billion-year-old carbonate rocks from Brazil. The rocks were formed on the ocean floor in a geologic time known as the Neoarchaean Eon. They surfaced when prospectors drilling for gold in Brazil punched a hole into bedrock and pulled out a 590-foot-long core of ancient rocks.

In research published Nov. 7, 2014 in the journal Science, Zhelezinskaia and three co-authors–physicist John Cliff of the University of Western Australia and geologists Alan Kaufman and James Farquhar of UMD–show that bacteria dependent on sulfate were plentiful in some parts of the Neoarchaean ocean, even though sea water typically contained about 1,000 times less sulfate than it does today.

“The samples Iadviga measured carry a very strong signal that sulfur compounds were consumed and altered by living organisms, which was surprising,” says Farquhar. “She also used basic geochemical models to give an idea of how much sulfate was in the oceans, and finds the sulfate concentrations are very low, much lower than previously thought.”

Geologists study sulfur because it is abundant and combines readily with other elements, forming compounds stable enough to be preserved in the geologic record. Sulfur has four naturally occurring stable isotopes–atomic signatures left in the rock record that scientists can use to identify the elements’ different forms. Researchers measuring sulfur isotope ratios in a rock sample can learn whether the sulfur came from the atmosphere, weathering rocks or biological processes. From that information about the sulfur sources, they can deduce important information about the state of the atmosphere, oceans, continents and biosphere when those rocks formed.

Farquhar and other researchers have used sulfur isotope ratios in Neoarchaean rocks to show that soon after this period, Earth’s atmosphere changed. Oxygen levels soared from just a few parts per million to almost their current level, which is around 21 percent of all the gases in the atmosphere. The Brazilian rocks Zhelezinskaia sampled show only trace amounts of oxygen, a sign they were formed before this atmospheric change.

With very little oxygen, the Neoarchaean Earth was a forbidding place for most modern life forms. The continents were probably much drier and dominated by volcanoes that released sulfur dioxide, carbon dioxide, methane and other greenhouse gases. Temperatures probably ranged between 0 and 100 degrees Celsius (32 to 212 degrees Fahrenheit), warm enough for liquid oceans to form and microbes to grow in them.

Rocks 2.5 billion years old or older are extremely rare, so geologists’ understanding of the Neoarchaean are based on a handful of samples from a few small areas, such as Western Australia, South Africa and Brazil. Geologists theorize that Western Australia and South Africa were once part of an ancient supercontinent called Vaalbara. The Brazilian rock samples are comparable in age, but they may not be from the same supercontinent, Zhelezinskaia says.

Most of the Neoarchaean rocks studied are from Western Australia and South Africa and are black shale, which forms when fine dust settles on the sea floor. The Brazilian prospector’s core contains plenty of black shale and a band of carbonate rock, formed below the surface of shallow seas, in a setting that probably resembled today’s Bahama Islands. Black shale usually contains sulfur-bearing pyrite, but carbonate rock typically does not, so geologists have not focused on sulfur signals in Neoarchaean carbonate rocks until now.

Zhelezinskaia “chose to look at a type of rock that others generally avoided, and what she saw was spectacularly different,” said Kaufman. “It really opened our eyes to the implications of this study.”

The Brazilian carbonate rocks’ isotopic ratios showed they formed in ancient seabed containing sulfate from atmospheric sources, not continental rock. And the isotopic ratios also showed that Neoarchaean bacteria were plentiful in the sediment, respiring sulfate and emitted hydrogen sulfide–the same process that goes on today as bacteria recycle decaying organic matter into minerals and gases.

How could the sulfur-dependent bacteria have thrived during a geologic time when sulfur levels were so low? “It seems that they were in shallow water, where evaporation may have been high enough to concentrate the sulfate, and that would make it abundant enough to support the bacteria,” says Zhelezinskaia.

Zhelezinskaia is now analyzing carbonate rocks of the same age from Western Australia and South Africa, to see if the pattern holds true for rocks formed in other shallow water environments. If it does, the results may change scientists’ understanding of one of Earth’s earliest biological processes.

“There is an ongoing debate about when sulfate-reducing bacteria arose and how that fits into the evolution of life on our planet,” says Farquhar. “These rocks are telling us the bacteria were there 2.5 billion years ago, and they were doing something significant enough that we can see them today.”

###

This research was supported by the Fulbright Program (Grantee ID 15110620), the NASA Astrobiology Institute (Grant No. NNA09DA81A) and the National Science Foundation Frontiers in Earth-System Dynamics program (Grant No. 432129). The content of this article does not necessarily reflect the views of these organizations.

“Large sulfur isotope fractionations associated with Neoarchaean microbial sulfate reductions,” Iadviga Zhelezinskaia, Alan J. Kaufman, James Farquhar and John Cliff, was published Nov. 7, 2014 in Science. Download the abstract after 2 p.m. U.S. Eastern time, Nov. 6, 2014: http://www.sciencemag.org/lookup/doi/10.1126/science.1256211

James Farquhar home page

http://www.geol.umd.edu/directory.php?id=13

Alan J. Kaufman home page

http://www.geol.umd.edu/directory.php?id=15

Iadviga Zhelezinskaia home page

http://www.geol.umd.edu/directory.php?id=66

Media Relations Contact: Abby Robinson, 301-405-5845, abbyr@umd.edu

Writer: Heather Dewar

Scientists find ancient mountains that fed early life

This image shows the ancient mountain site, Brazil. -  Carlos Ganade de Araujo
This image shows the ancient mountain site, Brazil. – Carlos Ganade de Araujo

Scientists have found evidence for a huge mountain range that sustained an explosion of life on Earth 600 million years ago.

The mountain range was similar in scale to the Himalayas and spanned at least 2,500 kilometres of modern west Africa and northeast Brazil, which at that time were part of the supercontinent Gondwana.

“Just like the Himalayas, this range was eroded intensely because it was so huge. As the sediments washed into the oceans they provided the perfect nutrients for life to flourish,” said Professor Daniela Rubatto of the Research School of Earth Sciences at The Australian National University (ANU).

“Scientists have speculated that such a large mountain range must have been feeding the oceans because of the way life thrived and ocean chemistry changed at this time, and finally we have found it.”

The discovery is earliest evidence of Himalayan-scale mountains on Earth.

“Although the mountains have long since washed away, rocks from their roots told the story of the ancient mountain range’s grandeur,” said co-researcher Professor Joerg Hermann.

“The range was formed by two continents colliding. During this collision, rocks from the crust were pushed around 100 kilometres deep into the mantle, where the high temperatures and pressures formed new minerals.”

As the mountains eroded, the roots came back up to the surface, to be collected in Togo, Mali and northeast Brazil, by Brazilian co-researcher Carlos Ganade de Araujo, from the University of Sao Paolo.

Dr Ganade de Araujo recognised the samples were unique and brought the rocks to ANU where, using world-leading equipment, the research team accurately identified that the rocks were of similar age, and had been formed at similar, great depths.

The research team involved specialists from a range of different areas of Earth Science sharing their knowledge, said Professor Rubatto.

“With everyone cooperating to study tiny crystals, we have managed to discover a huge mountain range,” she said.




Video
Click on this image to view the .mp4 video
Scientists from Australian National University reveal how they found a mountain range that fed an explosion of life 600 million years ago. The range stretched 2,500 km across Gondwana from modern west Africa to Northeast Brazil. Tiny mineral crystals formed in the roots of these huge mountains were the key to reconstructing their age and size. – ANU Media

New map uncovers thousands of unseen seamounts on ocean floor

This is a gravity model of the North Atlantic; red dots are earthquakes. Quakes are often related to seamounts. -  David Sandwell, SIO
This is a gravity model of the North Atlantic; red dots are earthquakes. Quakes are often related to seamounts. – David Sandwell, SIO

Scientists have created a new map of the world’s seafloor, offering a more vivid picture of the structures that make up the deepest, least-explored parts of the ocean.

The feat was accomplished by accessing two untapped streams of satellite data.

Thousands of previously uncharted mountains rising from the seafloor, called seamounts, have emerged through the map, along with new clues about the formation of the continents.

Combined with existing data and improved remote sensing instruments, the map, described today in the journal Science, gives scientists new tools to investigate ocean spreading centers and little-studied remote ocean basins.

Earthquakes were also mapped. In addition, the researchers discovered that seamounts and earthquakes are often linked. Most seamounts were once active volcanoes, and so are usually found near tectonically active plate boundaries, mid-ocean ridges and subducting zones.

The new map is twice as accurate as the previous version produced nearly 20 years ago, say the researchers, who are affiliated with California’s Scripps Institution of Oceanography (SIO) and other institutions.

“The team has developed and proved a powerful new tool for high-resolution exploration of regional seafloor structure and geophysical processes,” says Don Rice, program director in the National Science Foundation’s Division of Ocean Sciences, which funded the research.

“This capability will allow us to revisit unsolved questions and to pinpoint where to focus future exploratory work.”

Developed using a scientific model that captures gravity measurements of the ocean seafloor, the map extracts data from the European Space Agency’s (ESA) CryoSat-2 satellite.

CryoSat-2 primarily captures polar ice data but also operates continuously over the oceans. Data also came from Jason-1, NASA’s satellite that was redirected to map gravity fields during the last year of its 12-year mission.

“The kinds of things you can see very clearly are the abyssal hills, the most common landform on the planet,” says David Sandwell, lead author of the paper and a geophysicist at SIO.

The paper’s co-authors say that the map provides a window into the tectonics of the deep oceans.

The map also provides a foundation for the upcoming new version of Google’s ocean maps; it will fill large voids between shipboard depth profiles.

Previously unseen features include newly exposed continental connections across South America and Africa and new evidence for seafloor spreading ridges in the Gulf of Mexico. The ridges were active 150 million years ago and are now buried by mile-thick layers of sediment.

“One of the most important uses will be to improve the estimates of seafloor depth in the 80 percent of the oceans that remain uncharted or [where the sea floor] is buried beneath thick sediment,” the authors state.

###

Co-authors of the paper include R. Dietmar Muller of the University of Sydney, Walter Smith of the NOAA Laboratory for Satellite Altimetry Emmanuel Garcia of SIO and Richard Francis of ESA.

The study also was supported by the U.S. Office of Naval Research, the National Geospatial-Intelligence Agency and ConocoPhillips.

Study shows air temperature influenced African glacial movements

Changes in air temperature, not precipitation, drove the expansion and contraction of glaciers in Africa’s Rwenzori Mountains at the height of the last ice age, according to a Dartmouth-led study funded by the National Geographic Society and the National Science Foundation.

The results – along with a recent Dartmouth-led study that found air temperature also likely influenced the fluctuating size of South America’s Quelccaya Ice Cap over the past millennium — support many scientists’ suspicions that today’s tropical glaciers are rapidly shrinking primarily because of a warming climate rather than declining snowfall or other factors. The two studies will help scientists to understand the natural variability of past climate and to predict tropical glaciers’ response to future global warming.

The most recent study, which marks the first time that scientists have used the beryllium-10 surface exposure dating method to chronicle the advance and retreat of Africa’s glaciers, appears in the journal Geology. A PDF is available on request.

Africa’s glaciers, which occur atop the world’s highest tropical mountains, are among the most sensitive components of the world’s frozen regions, but the climatic controls that influence their fluctuations are not fully understood. Dartmouth glacial geomorphologist Meredith Kelly and her team used the beryllium-10 method to determine the ages of quartz-rich boulders atop moraines in the Rwenzori Mountains on the border of Uganda and the Democratic Republic of Congo. These mountains have the most extensive glacial and moraine systems in Africa. Moraines are ridges of sediments that mark the past positions of glaciers.

The results indicate that glaciers in equatorial East Africa advanced between 24,000 and 20,000 years ago at the coldest time of the world’s last ice age. A comparison of the moraine ages with nearby climate records indicates that Rwenzori glaciers expanded contemporaneously with regionally dry, cold conditions and retreated when air temperature increased. The results suggest that, on millennial time scales, past fluctuations of Rwenzori glaciers were strongly influenced by air temperature.

Magnetic anomaly deep within Earth’s crust reveals Africa in North America

Boulder, Colo., USA – The repeated cycles of plate tectonics that have led to collision and assembly of large supercontinents and their breakup and formation of new ocean basins have produced continents that are collages of bits and pieces of other continents. Figuring out the origin and make-up of continental crust formed and modified by these tectonic events is a vital to understanding Earth’s geology and is important for many applied fields, such as oil, gas, and gold exploration.

In many cases, the rocks involved in these collision and pull-apart episodes are still buried deep beneath the Earth’s surface, so geologists must use geophysical measurements to study these features.

This new study by Elias Parker Jr. of the University of Georgia examines a prominent swath of lower-than-normal magnetism — known as the Brunswick Magnetic Anomaly — that stretches from Alabama through Georgia and off shore to the North Carolina coast.

The cause of this magnetic anomaly has been under some debate. Many geologists attribute the Brunswick Magnetic Anomaly to a belt of 200 million year old volcanic rocks that intruded around the time the Atlantic Ocean. In this case, the location of this magnetic anomaly would then mark the initial location where North America split from the rest of Pangea as that ancient supercontinent broke apart. Parker proposes a different source for this anomalous magnetic zone.

Drawing upon other studies that have demonstrated deeply buried metamorphic rocks can also have a coherent magnetic signal, Parker has analyzed the detailed characteristics of the magnetic anomalies from data collected across zones in Georgia and concludes that the Brunswick Magnetic Anomaly has a similar, deeply buried source. The anomalous magnetic signal is consistent with an older tectonic event — the Alleghanian orogeny that formed the Alleghany-Appalachian Mountains when the supercontinent of Pangea was assembled.

Parker’s main conclusion is that the rocks responsible for the Brunswick Magnetic Anomaly mark a major fault-zone that formed as portions of Africa and North America were sheared together roughly 300 million years ago — and that more extensive evidence for this collision are preserved along this zone. One interesting implication is that perhaps a larger portion of what is now Africa was left behind in the American southeast when Pangea later broke up.</P

Dust in the wind drove iron fertilization during ice age

Nitrogen is a critical building block for marine algae, yet the plankton in the Southern Ocean north of Antarctica leave much of it unused partly because they lack another needed nutrient, iron. The late John Martin hypothesized that dust-borne iron carried to the region by winds during ice ages may have fertilized the marine algae, allowing more of the Southern Ocean nitrogen to be used for growth and thus drawing CO2 into the ocean.  
To confirm Martin's hypothesis, the researchers measured isotopes of nitrogen in a sediment sample collected from a site that lies within the path of the winds that deposit iron-laden dust in the Subantarctic zone of the Southern Ocean (labeled ODP Site 1090). They found that the ratios of the types of nitrogen in the sample coincided with the predictions of Martin's hypothesis. The colors indicate simulated ice-age dust deposition from low to high (blue to red). The black contour lines show the concentrations of nitrate (a form of nitrogen) in modern surface waters. -  Image courtesy of Alfredo Martínez-García of ETH Zurich and Science/American Association for the Advancement of Science
Nitrogen is a critical building block for marine algae, yet the plankton in the Southern Ocean north of Antarctica leave much of it unused partly because they lack another needed nutrient, iron. The late John Martin hypothesized that dust-borne iron carried to the region by winds during ice ages may have fertilized the marine algae, allowing more of the Southern Ocean nitrogen to be used for growth and thus drawing CO2 into the ocean.
To confirm Martin’s hypothesis, the researchers measured isotopes of nitrogen in a sediment sample collected from a site that lies within the path of the winds that deposit iron-laden dust in the Subantarctic zone of the Southern Ocean (labeled ODP Site 1090). They found that the ratios of the types of nitrogen in the sample coincided with the predictions of Martin’s hypothesis. The colors indicate simulated ice-age dust deposition from low to high (blue to red). The black contour lines show the concentrations of nitrate (a form of nitrogen) in modern surface waters. – Image courtesy of Alfredo Martínez-García of ETH Zurich and Science/American Association for the Advancement of Science

Researchers from Princeton University and the Swiss Federal Institute of Technology in Zurich have confirmed that during the last ice age iron fertilization caused plankton to thrive in a region of the Southern Ocean.

The study published in Science confirms a longstanding hypothesis that wind-borne dust carried iron to the region of the globe north of Antarctica, driving plankton growth and eventually leading to the removal of carbon dioxide from the atmosphere.

Plankton remove the greenhouse gas carbon dioxide (CO2) from the atmosphere during growth and transfer it to the deep ocean when their remains sink to the bottom. Iron fertilization has previously been suggested as a possible cause of the lower CO2 levels that occur during ice ages. These decreases in atmospheric CO2 are believed to have “amplified” the ice ages, making them much colder, with some scientists believing that there would have been no ice ages at all without the CO2 depletion.

Iron fertilization has also been suggested as one way to draw down the rising levels of CO2 associated with the burning of fossil fuels. Improved understanding of the drivers of ocean carbon storage could lead to better predictions of how the rise in manmade carbon dioxide will affect climate in the coming years.

The role of iron in storing carbon dioxide during ice ages was first proposed in 1990 by the late John Martin, an oceanographer at Moss Landing Marine Laboratories in California who made the landmark discovery that iron limits plankton growth in large regions of the modern ocean.

Based on evidence that there was more dust in the atmosphere during the ice ages, Martin hypothesized that this increased dust supply to the Southern Ocean allowed plankton to grow more rapidly, sending more of their biomass into the deep ocean and removing CO2 from the atmosphere. Martin focused on the Southern Ocean because its surface waters contain the nutrients nitrogen and phosphorus in abundance, allowing plankton to be fertilized by iron without running low on these necessary nutrients.

The research confirms Martin’s hypothesis, said Daniel Sigman, Princeton’s Dusenbury Professor of Geological and Geophysical Sciences, and a co-leader of the study. “I was an undergraduate when Martin published his ‘ice age iron hypothesis,'” he said. “I remember being captivated by it, as was everyone else at the time. But I also remember thinking that Martin would have to be the luckiest person in the world to pose such a simple, beautiful explanation for the ice age CO2 paradox and then turn out to be right about it.”

Previous efforts to test Martin’s hypothesis established a strong correlation of cold climate, high dust and productivity in the Subantarctic region, a band of ocean encircling the globe between roughly 40 and 50 degrees south latitude that lies in the path of the winds that blow off South America, South Africa and Australia. However, it was not clear whether the productivity was due to iron fertilization or the northward shift of a zone of naturally occurring productivity that today lies to the south of the Subantarctic. This uncertainty was made more acute by the finding that ice age productivity was lower in the Antarctic Ocean, which lies south of the Subantarctic region.

To settle the matter, the research groups of Sigman at Princeton and Gerald Haug and Tim Eglinton at ETH Zurich teamed up to use a new method developed at Princeton. They analyzed fossils found in deep sea sediment -deposited during the last ice age in the Subantarctic region – with the goal of reconstructing past changes in the nitrogen concentration of surface waters and combining the results with side-by-side measurements of dust-borne iron and productivity. If the dust-borne iron fertilization hypothesis was correct, then nitrogen would have been more completely consumed by the plankton, leading to lower residual nitrogen concentrations in the surface waters. In contrast, if the productivity increases were in response to a northward shift in ocean conditions, then nitrogen concentrations would have risen.

The researchers measured the ratio of nitrogen isotopes, which have the same number of protons but differing numbers of neutrons, that were preserved within the carbonate shells of a group of marine microfossils called foraminifera. The investigators found that nitrogen concentrations indeed declined during the cold periods when iron deposition and productivity rose, in a manner consistent with the dust-borne iron fertilization theory. Ocean models as well as the strong correlation of the sediment core changes with the known changes in atmospheric CO2 suggest that this iron fertilization of Southern Ocean plankton can explain roughly half of the CO2 decline during peak ice ages.

Although Martin had proposed that purposeful iron addition to the Southern Ocean could reduce the rise in atmospheric CO2, Sigman noted that the amount of CO2 removed though iron fertilization is likely to be minor compared to the amount of CO2 that humans are now pushing into the atmosphere.

“The dramatic fertilization that we observed during ice ages should have caused a decline in atmospheric CO2 over hundreds of years, which was important for climate changes over ice age cycles,” Sigman said. “But for humans to duplicate it today would require unprecedented engineering of the global environment, and it would still only compensate for less than 20 years of fossil fuel burning.”

Edward Brook, a paleoclimatologist at Oregon State University who was not involved in the research, said, “This group has been doing a lot of important work in this area for quite a while and this an important advance. It will be interesting to see if the patterns they see in this one spot are consistent with variations in other places relevant to global changes in carbon dioxide.”

What sculpted Africa’s margin?

Break-up of the supercontinent Gondwana about 130 Million years ago could have lead to a completely different shape of the African and South American continent with an ocean south of today’s Sahara desert, as geoscientists from the University of Sydney and the GFZ German Research Centre for Geosciences have shown through the use of sophisticated plate tectonic and three-dimensional numerical modelling. The study highlights the importance of rift orientation relative to extension direction as key factor deciding whether an ocean basin opens or an aborted rift basin forms in the continental interior.

For hundreds of millions of years, the southern continents of South America, Africa, Antarctica, Australia, and India were united in the supercontinent Gondwana. While the causes for Gondwana’s fragmentation are still debated, it is clear that the supercontinent first split along along the East African coast in a western and eastern part before separation of South America from Africa took place. Today’s continental margins along the South Atlantic ocean and the subsurface graben structure of the West African Rift system in the African continent, extending from Nigeria northwards to Libya, provide key insights on the processes that shaped present-day Africa and South America. Christian Heine (University of Sydney) and Sascha Brune (GFZ) investigated why the South Atlantic part of this giant rift system evolved into an ocean basin, whereas its northern part along the West African Rift became stuck.

“Extension along the so-called South Atlantic and West African rift systems was about to split the African-South American part of Gondwana North-South into nearly equal halves, generating a South Atlantic and a Saharan Atlantic Ocean”, geoscientist Sascha Brune explains. “In a dramatic plate tectonic twist, however, a competing rift along the present-day Equatorial Atlantic margins, won over the West African rift, causing it to become extinct, avoiding the break-up of the African continent and the formation of a Saharan Atlantic ocean.” The complex numerical models provide a strikingly simple explanation: the larger the angle between rift trend and extensional direction, the more force is required to maintain a rift system. The West African rift featured a nearly orthogonal orientation with respect to westward extension which required distinctly more force than its ultimately successful Equatorial Atlantic opponent.

Embarking on geoengineering, then stopping, would speed up global warming

Spraying reflective particles into the atmosphere to reflect sunlight and then stopping it could exacerbate the problem of climate change, according to new research by atmospheric scientists at the University of Washington.

Carrying out geoengineering for several decades and then stopping would cause warming at a rate that will greatly exceed that expected due to global warming, according to a study published Feb. 18 in Environmental Research Letters.

“The absolute temperature ends up being roughly the same as what it would have been, but the rate of change is so drastic, that ecosystems and organisms would have very little time to adapt to the changes,” said lead author Kelly McCusker, who did the work for her UW doctoral thesis.

The study looks at solar radiation management, a proposed method of geoengineering by spraying tiny sulfur-based particles into the upper atmosphere to reflect sunlight. This is similar to what happens after a major volcanic eruption, and many experts believe the technique is economically and technically feasible. But continuous implementation over years depends on technical functioning, continuous funding, bureaucratic agreement and lack of negative side effects.

The UW team used a global climate model to show that if an business-as-usual emissions pathway is followed up until 2035, allowing temperatures to rise 1°C above the 1970-1999 mean, and then geoengineering is implemented for 25 years and suddenly stopped, global temperatures could rise by 4°C in the following three decades, a rate more than double what it would have been otherwise, and one that exceeds historical temperature trends.

“The rate of standard projected global warming alone is going to be really detrimental to a lot of organisms, so if you increase that by a factor of 2 to 3, then those organisms are going to have an even harder time adapting or migrating,” said McCusker, now a postdoctoral researcher at the University of Victoria in Canada.

The results build on recent work led by British researchers pointing to the risk of implementing and then stopping geoengineering. That study compared several climate models, showing that the result is not specific to any one model. The UW researchers used a single model with a more realistic scenario, where instead of simply decreasing the strength of the sun they actually simulated sulfate particles to stabilize the temperature, allowing a more precise look at the spatial and seasonal pattern of the response.

“The changes that will be needed to adapt to a warmer climate are really profound,” said co-author David Battisti, a UW professor of atmospheric sciences. “The faster the climate changes, the less time farmers have to develop new agricultural practices, and the less time plants and animals have to move or evolve.”

The total amount of warming after stopping geoengineering would be largest in winter near the poles, but compared to typical historical rates of change they found that changes would be most extreme in the tropics in summertime, where there is usually very little temperature variation.

“According to our simulations, tropical regions like South Asia and sub-Saharan Africa will be hit particularly hard, the very same regions that are home to many of the world’s most food insecure populations,” McCusker said. “The potential temperature changes also pose a severe threat to biodiversity.”

The researchers looked at different variables and found that the rate of warming is largely determined by the length of time that geoengineering is deployed and the amount of greenhouse gases emitted during that time, rather than by how sensitive the climate is to changes in greenhouse-gas concentrations.

“If we must geoengineer, it does not give us an excuse to keep emitting greenhouse gases,” McCusker said. “On the contrary, our results demonstrate that if geoengineering is ever deployed, it’s imperative that greenhouse gases be reduced at the same time to reduce the risk of rapid warming.”

The research was funded by the Tamaki Foundation, the National Science Foundation and the James S. McDonnell Foundation. Other co-authors are Cecilia Bitz, a UW professor of atmospheric sciences, and Kyle Armour, a former UW doctoral student now at the Massachusetts Institute of Technology.

Researchers warn against abrupt stop to geoengineering method

As a range of climate change mitigation scenarios are discussed, University of Washington researchers have found that the injection of sulfate particles into the atmosphere to reflect sunlight and curb the effects of global warming could pose a severe threat if not maintained indefinitely and supported by strict reductions in greenhouse gas (GHG) emissions.

The new study, published today, 18 February, in IOP Publishing’s journal Environmental Research Letters, has highlighted the risks of large and spatially expansive temperature increases if solar radiation management (SRM) is abruptly stopped once it has been implemented.

SRM is a proposed method of geoengineering whereby tiny sulfate-based aerosols are released into the upper atmosphere to reflect sunlight and cool the planet. The technique has been shown to be economically and technically feasible; however, its efficacy depends on its continued maintenance, without interruption from technical faults, global cooperation breakdown or funding running dry.

According to the study, global temperature increases could more than double if SRM is implemented for a multi-decadal period of time and then suddenly stopped, in relation to the temperature increases expected if SRM was not implemented at all.

The researchers used a global climate model to show that if an extreme emissions pathway-RCP8.5-is followed up until 2035, allowing temperatures to rise 1°C above the 1970-1999 mean, and then SRM is implemented for 25 years and suddenly stopped, global temperatures could increase by 4°C in the following decades.

This rate of increase, caused by the build-up of background greenhouse gas emissions, would be well beyond the bounds experienced in the last century and more than double the 2°C temperature increase that would occur in the same timeframe if SRM had not been implemented.

On a regional and seasonal scale, the temperature changes would be largest in an absolute sense in winter over high latitude land, but compared to historical fluctuations, temperature changes would be largest in the tropics in summertime, where there is usually very little variation.

Lead author of the research, Kelly McCusker, from the University of Washington, said: “According to our simulations, tropical regions like South Asia and Sub-Saharan Africa are hit particularly hard, the very same regions that are home to many of the world’s most food insecure populations. The potential temperature changes also pose a severe threat to biodiversity.”

Furthermore, the researchers used a simple climate model to study a variety of plausible greenhouse gas scenarios and SRM termination years over the 21st century. They showed that climate sensitivity-a measure of how much the climate will warm in response to the greenhouse effect-had a lesser impact on the rate of temperature changes.

Instead, they found that the rates of temperature change were determined by the amount of GHG emissions and the duration of time that SRM is deployed.

“The primary control over the magnitude of the large temperature increases after an SRM shutoff is the background greenhouse gas concentrations. Thus, the greater the future emissions of greenhouse gases, the larger the temperature increases would be, and, similarly, the later the termination occurs while GHG emissions continue, the larger the temperature increases,” continued McCusker.

“The only way to avoid creating the risk of substantial temperature increases through SRM, therefore, is concurrent strong reductions of GHG emissions.”

Ocean crust could store many centuries of industrial CO2

Researchers from the University of Southampton have identified regions beneath the oceans where the igneous rocks of the upper ocean crust could safely store very large volumes of carbon dioxide.

The burning of fossil fuels such as coal, oil, and natural gas has led to dramatically increasing concentrations of CO2 in the atmosphere causing climate change and ocean acidification. Although technologies are being developed to capture CO2 at major sources such as power stations, this will only avoid further warming if that CO2 is then safely locked away from the atmosphere for centuries.

PhD student Chiara Marieni, who is based at the National Oceanography Centre, Southampton, investigated the physical properties of CO2 to develop global maps of the ocean floor to estimate where CO2 can be safely stored.

At high pressures and low temperatures, such as those in the deep oceans, CO2 occurs as a liquid that is denser than seawater. By estimating temperatures in the upper ocean crust, Chiara and her colleagues identified regions where it may be possible to stably store large volumes of CO2 in the basalts. These fractured rocks have high proportions of open space, and over time may also react with the CO2 so that it is locked into solid calcium carbonate, permanently preventing its release into the oceans or atmosphere. As a precaution, Chiara refined her locations to areas that have the additional protection of thick blankets of impermeable sediments to prevent gas escape.

They identified five potential regions in off-shore Australia, Japan, Siberia, South Africa and Bermuda, ranging in size from ½ million square kilometres to almost four million square kilometres.

Postgraduate researcher Chiara says: “We have found regions that have the potential to store decades to hundreds of years of industrial carbon dioxide emissions although the largest regions are far off shore. However, further work is needed in these regions to accurately measure local sediment conditions and sample the basalt beneath before this potential can be confirmed.”

The new work, which is published in Geophysical Research Letters, shows that previous studies, which concentrated on the effect of pressure to liquefy the CO2 but ignored temperature, have pointed to the wrong locations, where high temperatures mean that the CO2 will have a low density, and thus be more likely to escape.