Climate change was not to blame for the collapse of the Bronze Age

Scientists will have to find alternative explanations for a huge population collapse in Europe at the end of the Bronze Age as researchers prove definitively that climate change – commonly assumed to be responsible – could not have been the culprit.

Archaeologists and environmental scientists from the University of Bradford, University of Leeds, University College Cork, Ireland (UCC), and Queen’s University Belfast have shown that the changes in climate that scientists believed to coincide with the fall in population in fact occurred at least two generations later.

Their results, published this week in Proceedings of the National Academy of Sciences, show that human activity starts to decline after 900BC, and falls rapidly after 800BC, indicating a population collapse. But the climate records show that colder, wetter conditions didn’t occur until around two generations later.

Fluctuations in levels of human activity through time are reflected by the numbers of radiocarbon dates for a given period. The team used new statistical techniques to analyse more than 2000 radiocarbon dates, taken from hundreds of archaeological sites in Ireland, to pinpoint the precise dates that Europe’s Bronze Age population collapse occurred.

The team then analysed past climate records from peat bogs in Ireland and compared the archaeological data to these climate records to see if the dates tallied. That information was then compared with evidence of climate change across NW Europe between 1200 and 500 BC.

“Our evidence shows definitively that the population decline in this period cannot have been caused by climate change,” says Ian Armit, Professor of Archaeology at the University of Bradford, and lead author of the study.

Graeme Swindles, Associate Professor of Earth System Dynamics at the University of Leeds, added, “We found clear evidence for a rapid change in climate to much wetter conditions, which we were able to precisely pinpoint to 750BC using statistical methods.”

According to Professor Armit, social and economic stress is more likely to be the cause of the sudden and widespread fall in numbers. Communities producing bronze needed to trade over very large distances to obtain copper and tin. Control of these networks enabled the growth of complex, hierarchical societies dominated by a warrior elite. As iron production took over, these networks collapsed, leading to widespread conflict and social collapse. It may be these unstable social conditions, rather than climate change, that led to the population collapse at the end of the Bronze Age.

According to Katharina Becker, Lecturer in the Department of Archaeology at UCC, the Late Bronze Age is usually seen as a time of plenty, in contrast to an impoverished Early Iron Age. “Our results show that the rich Bronze Age artefact record does not provide the full picture and that crisis began earlier than previously thought,” she says.

“Although climate change was not directly responsible for the collapse it is likely that the poor climatic conditions would have affected farming,” adds Professor Armit. “This would have been particularly difficult for vulnerable communities, preventing population recovery for several centuries.”

The findings have significance for modern day climate change debates which, argues Professor Armit, are often too quick to link historical climate events with changes in population.

“The impact of climate change on humans is a huge concern today as we monitor rising temperatures globally,” says Professor Armit.

“Often, in examining the past, we are inclined to link evidence of climate change with evidence of population change. Actually, if you have high quality data and apply modern analytical techniques, you get a much clearer picture and start to see the real complexity of human/environment relationships in the past.”

Massive geographic change may have triggered explosion of animal life

A new analysis from The University of Texas at Austin's Institute for Geophysics suggests a deep oceanic gateway, shown in blue, developed between the Pacific and Iapetus oceans immediately before the Cambrian sea level rise and explosion of life in the fossil record, isolating Laurentia from the supercontinent Gondwanaland. -  Ian Dalziel
A new analysis from The University of Texas at Austin’s Institute for Geophysics suggests a deep oceanic gateway, shown in blue, developed between the Pacific and Iapetus oceans immediately before the Cambrian sea level rise and explosion of life in the fossil record, isolating Laurentia from the supercontinent Gondwanaland. – Ian Dalziel

A new analysis of geologic history may help solve the riddle of the “Cambrian explosion,” the rapid diversification of animal life in the fossil record 530 million years ago that has puzzled scientists since the time of Charles Darwin.

A paper by Ian Dalziel of The University of Texas at Austin’s Jackson School of Geosciences, published in the November issue of Geology, a journal of the Geological Society of America, suggests a major tectonic event may have triggered the rise in sea level and other environmental changes that accompanied the apparent burst of life.

The Cambrian explosion is one of the most significant events in Earth’s 4.5-billion-year history. The surge of evolution led to the sudden appearance of almost all modern animal groups. Fossils from the Cambrian explosion document the rapid evolution of life on Earth, but its cause has been a mystery.

The sudden burst of new life is also called “Darwin’s dilemma” because it appears to contradict Charles Darwin’s hypothesis of gradual evolution by natural selection.

“At the boundary between the Precambrian and Cambrian periods, something big happened tectonically that triggered the spreading of shallow ocean water across the continents, which is clearly tied in time and space to the sudden explosion of multicellular, hard-shelled life on the planet,” said Dalziel, a research professor at the Institute for Geophysics and a professor in the Department of Geological Sciences.

Beyond the sea level rise itself, the ancient geologic and geographic changes probably led to a buildup of oxygen in the atmosphere and a change in ocean chemistry, allowing more complex life-forms to evolve, he said.

The paper is the first to integrate geological evidence from five present-day continents — North America, South America, Africa, Australia and Antarctica — in addressing paleogeography at that critical time.

Dalziel proposes that present-day North America was still attached to the southern continents until sometime into the Cambrian period. Current reconstructions of the globe’s geography during the early Cambrian show the ancient continent of Laurentia — the ancestral core of North America — as already having separated from the supercontinent Gondwanaland.

In contrast, Dalziel suggests the development of a deep oceanic gateway between the Pacific and Iapetus (ancestral Atlantic) oceans isolated Laurentia in the early Cambrian, a geographic makeover that immediately preceded the global sea level rise and apparent explosion of life.

“The reason people didn’t make this connection before was because they hadn’t looked at all the rock records on the different present-day continents,” he said.

The rock record in Antarctica, for example, comes from the very remote Ellsworth Mountains.

“People have wondered for a long time what rifted off there, and I think it was probably North America, opening up this deep seaway,” Dalziel said. “It appears ancient North America was initially attached to Antarctica and part of South America, not to Europe and Africa, as has been widely believed.”

Although the new analysis adds to evidence suggesting a massive tectonic shift caused the seas to rise more than half a billion years ago, Dalziel said more research is needed to determine whether this new chain of paleogeographic events can truly explain the sudden rise of multicellular life in the fossil record.

“I’m not claiming this is the ultimate explanation of the Cambrian explosion,” Dalziel said. “But it may help to explain what was happening at that time.”


To read the paper go to

Scientists discover carbonate rocks are unrecognized methane sink

Since the first undersea methane seep was discovered 30 years ago, scientists have meticulously analyzed and measured how microbes in the seafloor sediments consume the greenhouse gas methane as part of understanding how the Earth works.

The sediment-based microbes form an important methane “sink,” preventing much of the chemical from reaching the atmosphere and contributing to greenhouse gas accumulation. As a byproduct of this process, the microbes create a type of rock known as authigenic carbonate, which while interesting to scientists was not thought to be involved in the processing of methane.

That is no longer the case. A team of scientists has discovered that these authigenic carbonate rocks also contain vast amounts of active microbes that take up methane. The results of their study, which was funded by the National Science Foundation, were reported today in the journal Nature Communications.

“No one had really examined these rocks as living habitats before,” noted Andrew Thurber, an Oregon State University marine ecologist and co-author on the paper. “It was just assumed that they were inactive. In previous studies, we had seen remnants of microbes in the rocks – DNA and lipids – but we thought they were relics of past activity. We didn’t know they were active.

“This goes to show how the global methane process is still rather poorly understood,” Thurber added.

Lead author Jeffrey Marlow of the California Institute of Technology and his colleagues studied samples from authigenic compounds off the coasts of the Pacific Northwest (Hydrate Ridge), northern California (Eel River Basin) and central America (the Costa Rica margin). The rocks range in size and distribution from small pebbles to carbonate “pavement” stretching dozens of square miles.

“Methane-derived carbonates represent a large volume within many seep systems and finding active methane-consuming archaea and bacteria in the interior of these carbonate rocks extends the known habitat for methane-consuming microorganisms beyond the relatively thin layer of sediment that may overlay a carbonate mound,” said Marlow, a geobiology graduate student in the lab of Victoria Orphan of Caltech.

These assemblages are also found in the Gulf of Mexico as well as off Chile, New Zealand, Africa, Europe – “and pretty much every ocean basin in the world,” noted Thurber, an assistant professor (senior research) in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences.

The study is important, scientists say, because the rock-based microbes potentially may consume a huge amount of methane. The microbes were less active than those found in the sediment, but were more abundant – and the areas they inhabit are extensive, making their importance potential enormous. Studies have found that approximately 3-6 percent of the methane in the atmosphere is from marine sources – and this number is so low due to microbes in the ocean sediments consuming some 60-90 percent of the methane that would otherwise escape.

Now those ratios will have to be re-examined to determine how much of the methane sink can be attributed to microbes in rocks versus those in sediments. The distinction is important, the researchers say, because it is an unrecognized sink for a potentially very important greenhouse gas.

“We found that these carbonate rocks located in areas of active methane seeps are themselves more active,” Thurber said. “Rocks located in comparatively inactive regions had little microbial activity. However, they can quickly activate when methane becomes available.

“In some ways, these rocks are like armies waiting in the wings to be called upon when needed to absorb methane.”

The ocean contains vast amounts of methane, which has long been a concern to scientists. Marine reservoirs of methane are estimated to total more than 455 gigatons and may be as much as 10,000 gigatons carbon in methane. A gigaton is approximate 1.1 billion tons.

By contrast, all of the planet’s gas and oil deposits are thought to total about 200-300 gigatons of carbon.

2015 DOE JGI’s science portfolio delves deeper into the Earth’s data mine

The U.S. Department of Energy Joint Genome Institute (DOE JGI), a DOE Office of Science user facility, has announced that 32 new projects have been selected for the 2015 Community Science Program (CSP). From sampling Antarctic lakes to Caribbean waters, and from plant root micro-ecosystems, to the subsurface underneath the water table in forested watersheds, the CSP 2015 projects portfolio highlights diverse environments where DOE mission-relevant science can be extracted.

“These projects catalyze JGI’s strategic shift in emphasis from solving an organism’s genome sequence to enabling an understanding of what this information enables organisms to do,” said Jim Bristow, DOE JGI Science Deputy who oversees the CSP. “To accomplish this, the projects selected combine DNA sequencing with large-scale experimental and computational capabilities, and in some cases include JGI’s new capability to write DNA in addition to reading it. These projects will expand research communities, and help to meet the DOE JGI imperative to translate sequence to function and ultimately into solutions for major energy and environmental problems.”

The CSP 2015 projects were selected by an external review panel from 76 full proposals received that resulted from 85 letters of intent submitted. The total allocation for the CSP 2015 portfolio is expected to exceed 60 trillion bases (terabases or Tb)-or the equivalent of 20,000 human genomes of plant, fungal and microbial genome sequences. The full list of projects may be found at The DOE JGI Community Science Program also accepts proposals for smaller-scale microbial, resequencing and DNA synthesis projects and reviews them twice a year. The CSP advances projects that harness DOE JGI’s capability in massive-scale DNA sequencing, analysis and synthesis in support of the DOE missions in alternative energy, global carbon cycling, and biogeochemistry.

Among the CSP 2015 projects selected is one from Regina Lamendella of Juniata College, who will investigate how microbial communities in Marcellus shale, the country’s largest shale gas field, respond to hydraulic fracturing and natural gas extraction. For example, as fracking uses chemicals, researchers are interested in how the microbial communities can break down environmental contaminants, and how they respond to the release of methane during oil extraction operations.

Some 1,500 miles south from those gas extraction sites, Monica Medina-Munoz of Penn State University will study the effect of thermal stress on the Caribbean coral Orbicella faveolata and the metabolic contribution of its coral host Symbiodinium. The calcium carbonate in coral reefs acts as carbon sinks, but reef health depends on microbial communities. If the photosynthetic symbionts are removed from the coral host, for example, the corals can die and calcification rates decrease. Understanding how to maintain stability in the coral-microbiome community can provide information on the coral’s contribution to the global ocean carbon cycle.

Longtime DOE JGI collaborator Jill Banfield of the University of California (UC), Berkeley is profiling the diversity of microbial communities found in the subsurface from the Rifle aquifer adjacent to the Colorado River. The subsurface is a massive, yet poorly understood, repository of organic carbon as well as greenhouse gases. Another research question, based on having the microbial populations close to both the water table and the river, is how they impact carbon, nitrogen and sulfur cycles. Her project is part of the first coordinated attempt to quantify the metabolic potential of an entire subsurface ecosystem under the aegis of the Lawrence Berkeley National Laboratory’s Subsurface Biogeochemistry Scientific Focus Area.

Banfield also successfully competed for a second CSP project to characterize the tree-root microbial interactions that occur below the soil mantle in the unsaturated zone or vadose zone, which extends into unweathered bedrock. The project’s goal is to understand how microbial communities this deep underground influence tree-based carbon fixation in forested watersheds by the Eel River in northwestern California.

Several fungal projects were selected for the 2015 CSP portfolio, including one led by Kabir Peay of Stanford University. He and his colleagues will study how fungal communities in animal feces decompose organic matter. His project has a stated end goal of developing a model system that emulates the ecosystem at Point Reyes National Seashore, where Tule elk are the largest native herbivores.

Another selected fungal project comes from Timothy James of University of Michigan, who will explore the so-called “dark matter fungi” – those not represented in culture collections. By sequencing several dozen species of unculturable zoosporic fungi from freshwater, soils and animal feces, he and his colleagues hope to develop a kingdom-wide fungal phylogenetic framework.

Christian Wurzbacher of Germany’s the Leibniz Institute of Freshwater Ecology and Inland Fisheries, IGB, will characterize fungi from the deep sea to peatlands to freshwater streams to understand the potentially novel adaptations that are necessary to thrive in their aquatic environments. The genomic information would provide information on their metabolic capabilities for breaking down cellulose, lignin and other plant cell wall components, and animal polymers such as keratin and chitin.

Many of the selected projects focus on DOE JGI Flagship Plant Genomes, with most centered on the poplar (Populus trichocarpa.) For example, longtime DOE JGI collaborator Steve DiFazio of West Virginia University is interested in poplar but will study its reproductive development with the help of a close relative, the willow (Salix purpurea). With its shorter generation time, the plant is a good model system and comparator for understanding sex determination, which can help bioenergy crop breeders by, for example, either accelerating or preventing flowering.

Another project comes from Posy Busby of the University of Washington, who will study the interactions between the poplar tree and its fungal, non-pathogenic symbionts or endophytes. As disease-causing pathogens interact with endophytes in leaves, he noted in his proposal, understanding the roles and functions of endophytes could prove useful to meeting future fuel and food requirements.

Along the lines of poplar endophytes, Carolin Frank at UC Merced will investigate the nitrogen-fixing endophytes in poplar, willow, and pine, with the aim of improving growth in grasses and agricultural crops under nutrient-poor conditions.

Rotem Sorek from the Weizmann Institute of Science in Israel takes a different approach starting from the hypothesis that poplar trees have an adaptive immunity system rooted in genome-encoded immune memory. Through deep sequencing of tissues from single poplar trees (some over a century old, others younger) his team hopes to gain insights into the tree genome’s short-term evolution and how its gene expression profiles change over time, as well as to predict how trees might respond under various climate change scenarios.

Tackling a different DOE JGI Flagship Plant Genome, Debbie Laudencia-Chingcuangco of the USDA-ARS will develop a genome-wide collection of several thousand mutants of the model grass Brachypodium distachyon to help domesticate the grasses that are being considered as candidate bioenergy feedstocks. This work is being done in collaboration with researchers at the Great Lakes Bioenergy Research Center, as the team there considers Brachypodium “critical to achieving its mission of developing productive energy crops that can be easily processed into fuels.”

Continuing the theme of candidate bioenergy grasses, Kankshita Swaminathan from the University of Illinois will study gene expression in polyploidy grasses Miscanthus and sugarcane, comparing them against the closely related diploid grass sorghum to understand how these plants recycle nutrients.

Baohong Zhang of East Carolina University also focused on a bioenergy grass, and his project will look at the microRNAs in switchgrass. These regulatory molecules are each just a couple dozen nucleotides in length and can downregulate (decrease the quantity of) a cellular component. With a library of these small transcripts, he and his team hope to identify the gene expression variation associated with desirable biofuel traits in switchgrass such as increased biomass and responses to drought and salinity stressors.

Nitin Baliga of the Institute of Systems Biology will use DOE JGI genome sequences to build a working model of the networks that regulate lipid accumulation in Chlamydomonas reinhardtii, still another DOE JGI Plant Flagship Genome and a model for characterizing biofuel production by algae.

Other accepted projects include:

The study of the genomes of 32 fungi of the Agaricales order, including 16 fungi to be sequenced for the first time, will be carried out by Jose Maria Barrasa of Spain’s University of Alcala. While many of the basidiomycete fungi involved in wood degradation that have been sequenced are from the Polyporales, he noted in his proposal, many of the fungi involved in breaking down leaf litter and buried wood are from the order Agaricales.

Now at the University of Connecticut, Jonathan Klassen conducted postdoctoral studies at GLBRC researcher Cameron Currie’s lab at University of Wisconsin-Madison. His project will study interactions in ant-microbial community fungus gardens in three states to learn more about how the associated bacterial metagenomes contribute to carbon and nitrogen cycling.

Hinsby Cadillo-Quiroz, at Arizona State University, will conduct a study of the microbial communities in the Amazon peatlands to understand their roles in both emitting greenhouse gases and in storing and cycling carbon. The peatlands are hotspots of soil organic carbon accumulation, and in the tropical regions, they are estimated to hold between 11 percent and 14 percent, or nearly 90 gigatons, of the global carbon stored in soils.

Barbara Campbell, Clemson University will study carbon cycling mechanisms of active bacteria and associated viruses in the freshwater to marine transition zone of the Delaware Bay. Understanding the microbes’ metabolism would help researchers understand they capabilities with regard to dealing with contaminants, and their roles in the nitrogen, sulfur and carbon cycles.

Jim Fredrickson of Pacific Northwest National Laboratory will characterize functional profiles of microbial mats in California, Washington and Yellowstone National Park to understand various functions such as how they produce hydrogen and methane, and break down cellulose.

Joyce Loper of USDA-ARS will carry out a comparative analysis of all Pseudomonas bacteria getting from DOE JGI the sequences of just over 100 type strains to infer a evolutionary history of the this genus — a phylogeny — to characterize the genomic diversity, and determine the distribution of genes linked to key observable traits in this non-uniform group of bacteria.

Holly Simon of Oregon Health & Science University is studying microbial populations in the Columbia River estuary, in part to learn how they enhance greenhouse gas CO2 methane and nitrous oxide production.

Michael Thon from Spain’s University of Salamanca will explore sequences of strains of the Colletotrichum species complex, which include fungal pathogens that infect many crops. One of the questions he and his team will ask is how these fungal strains have adapted to break down the range of plant cell wall compositions.

Kathleen Treseder of UC Irvine will study genes involved in sensitivity to higher temperatures in fungi from a warming experiment in an Alaskan boreal forest. The team’s plan is to fold the genomic information gained into a trait-based ecosystem model called DEMENT to predict carbon dioxide emissions under global warming.

Mary Wildermuth of UC Berkeley will study nearly a dozen genomes of powdery mildew fungi, including three that infect designated bioenergy crops. The project will identify the mechanisms by which the fungi successfully infect plants, information that could lead to the development of crops with improved resistance to fungal infection and limiting fungicide use to allow more sustainable agricultural practices.

Several researchers who have previously collaborated with the DOE JGI have new projects:

Ludmila Chistoserdova from the University of Washington had a pioneering collaboration with the DOE JGI to study microbial communities in Lake Washington. In her new project, she and her team will look at the microbes in the Lake Washington sediment to understand their role in metabolizing the potent greenhouse gas methane.

Rick Cavicchioli of Australia’s University of New South Wales will track how microbial communities change throughout a complete annual cycle in three millennia-old Antarctic lakes and a near-shore marine site. By establishing what the microbes do in different seasons, he noted in his proposal, he and his colleagues hope to learn which microbial processes change and about the factors that control the evolution and speciation of marine-derived communities in cold environments.

With samples collected from surface waters down to the deep ocean, Steve Hallam from Canada’s University of British Columbia will explore metabolic pathways and compounds involved in marine carbon cycling processes to understand how carbon is regulated in the oceans.

The project of Hans-Peter Klenk, of DSMZ in Germany, will generate sequences of 1,000 strains of Actinobacteria, which represent the third most populated bacterial phylum and look for genes that encode cellulose-degrading enzymes or enzymes involved in synthesizing novel, natural products.

Han Wosten of the Netherlands’ Utrecht University will carry out a functional genomics approach to wood degradation by looking at Agaricomycetes, in particular the model white rot fungus Schizophyllum commune and the more potent wood-degrading white rots Phanaerochaete chrysosporium and Pleurotus ostreatus that the DOE JGI has previously sequenced.

Wen-Tso Liu of the University of Illinois and his colleagues want to understand the microbial ecology in anaerobic digesters, key components of the wastewater treatment process. They will study microbial communities in anaerobic digesters from the United States, East Asia and Europe to understand the composition and function of the microbes as they are harnessed for this low-cost municipal wastewater strategy efficiently removes waster and produces methane as a sustainable energy source.

Another project that involves wastewater, albeit indirectly, comes from Erica Young of the University of Wisconsin. She has been studying algae grown in wastewater to track how they use nitrogen and phosphorus, and how cellulose and lipids are produced. Her CSP project will characterize the relationship between the algae and the bacteria that help stabilize these algal communities, particularly the diversity of the bacterial community and the pathways and interactions involved in nutrient uptake and carbon sequestration.

Previous CSP projects and other DOE JGI collaborations are highlighted in some of the DOE JGI Annual User Meeting talks that can be seen here: The 10th Annual Genomics of Energy and Environment Meeting will be held March 24-26, 2015 in Walnut Creek, Calif. A preliminary speakers list is posted here ( and registration will be opened in the first week of November.

First eyewitness accounts of mystery volcanic eruption

This eruption occurred just before the 1815 Tambora volcanic eruption which is famous for its impact on climate worldwide, with 1816 given memorable names such as ‘Eighteen-Hundred-and-Froze-to-Death’, the ‘Year of the Beggar’ and the ‘Year Without a Summer’ because of unseasonal frosts, crop failure and famine across Europe and North America. The extraordinary conditions are considered to have inspired literary works such as Byron’s ‘Darkness’ and Mary Shelley’s Frankenstein.

However, the global deterioration of the 1810s into the coldest decade in the last 500 years started six years earlier, with another large eruption. In contrast to Tambora, this so-called ‘Unknown’ eruption seemingly occurred unnoticed, with both its location and date a mystery. In fact the ‘Unknown’ eruption was only recognised in the 1990s, from tell-tale markers in Greenland and Antarctic ice that record the rare events when volcanic aerosols are so violently erupted that they reach the Earth’s stratosphere.

Working in collaboration with colleagues from the School of Earth Sciences and PhD student Alvaro Guevara-Murua, Dr Caroline Williams, from the Department of Hispanic, Portuguese and Latin American Studies, began searching historical archives for references to the event.

Dr Williams said: “I spent months combing through the vast Spanish colonial archive, but it was a fruitless search – clearly the volcano wasn’t in Latin America. I then turned to the writings of Colombian scientist Francisco José de Caldas, who served as Director of the Astronomical Observatory of Bogotá between 1805 and 1810. Finding his precise description of the effects of an eruption was a ‘Eureka’ moment.”

In February 1809 Caldas wrote about a “mystery” that included a constant, stratospheric “transparent cloud that obstructs the sun’s brilliance” over Bogotá, starting on the 11 December 1808 and seen across Colombia. He gave detailed observations, for example that the “natural fiery colour [of the sun] has changed to that of silver, so much so that many have mistaken it for the moon”; and that the weather was unusually cold, the fields covered with ice and the crops damaged by frost.

Unearthing a short account written by physician José Hipólito Unanue in Lima, Peru, describing sunset after-glows (a common atmospheric effect caused by volcanic aerosols in the stratosphere) at the same time as Caldas’ “vapours above the horizon”, enabled the researchers to verify that the atmospheric effects of the eruption were seen at the same time on both sides of the equator.

These two 19th century Latin American scientists provide the first direct observations that can be linked to the ‘Unknown’ eruption. More importantly, the accounts date the eruption to within a fortnight of 4 December 1808.

Dr Erica Hendy said: “There have to be more observations hidden away, for example in ship logs. Having a date for the eruption will now make it much easier to track these down, and maybe even pinpoint the volcano. Climate modelling of this fascinating decade will also now be more accurate because the season of the eruption determines how the aerosols disperse around the globe and where climatic effects are felt.”

Alvaro Guevara-Murua added: “This study has meant delving into many fields of research – obviously paleoclimatology and volcanology, but also 19th century meteorology and Spanish colonial history – and has also needed rigorous precision to correctly translate the words of two scientists writing 200 years ago. Giving them a voice in modern science has been a big responsibility.”

One further question remains: why are there so few historical accounts of what was clearly a significant event with wide-reaching consequences? Perhaps, Dr Williams suggests, the political environment on both sides of the Atlantic at the beginning of the nineteenth century played a part.

“The eruption coincided with the Napoleonic Wars in Europe, the Peninsular War in Spain, and with political developments in Latin America that would soon lead to the independence of almost all of Spain’s American colonies. It’s possible that, in Europe and Latin America at least, the attention of individuals who might otherwise have provided us with a record of unusual meteorological or atmospheric effects simply turned to military and political matters instead,” she said.

International team maps nearly 200,000 global glaciers in quest for sea rise answers

CU-Boulder Professor Tad Pfeffer, shown here on Alaska's Columbia Glacier, is part of a team that has mapped nearly 200,000 individual glaciers around the world as part of an effort to track ongoing contributions to global sea rise as the planet heats up. -  University of Colorado
CU-Boulder Professor Tad Pfeffer, shown here on Alaska’s Columbia Glacier, is part of a team that has mapped nearly 200,000 individual glaciers around the world as part of an effort to track ongoing contributions to global sea rise as the planet heats up. – University of Colorado

An international team led by glaciologists from the University of Colorado Boulder and Trent University in Ontario, Canada has completed the first mapping of virtually all of the world’s glaciers — including their locations and sizes — allowing for calculations of their volumes and ongoing contributions to global sea rise as the world warms.

The team mapped and catalogued some 198,000 glaciers around the world as part of the massive Randolph Glacier Inventory, or RGI, to better understand rising seas over the coming decades as anthropogenic greenhouse gases heat the planet. Led by CU-Boulder Professor Tad Pfeffer and Trent University Professor Graham Cogley, the team included 74 scientists from 18 countries, most working on an unpaid, volunteer basis.

The project was undertaken in large part to provide the best information possible for the recently released Fifth Assessment of the Intergovernmental Panel on Climate Change, or IPCC. While the Greenland and Antarctic ice sheets are both losing mass, it is the smaller glaciers that are contributing the most to rising seas now and that will continue to do so into the next century, said Pfeffer, a lead author on the new IPCC sea rise chapter and fellow at CU-Boulder’s Institute of Arctic and Alpine Research.

“I don’t think anyone could make meaningful progress on projecting glacier changes if the Randolph inventory was not available,” said Pfeffer, the first author on the RGI paper published online today in the Journal of Glaciology. Pfeffer said while funding for mountain glacier research has almost completely dried up in the United States in recent years with the exception of grants from NASA, there has been continuing funding by a number of European groups.

Since the world’s glaciers are expected to shrink drastically in the next century as the temperatures rise, the new RGI — named after one of the group’s meeting places in New Hampshire — is critical, said Pfeffer. In the RGI each individual glacier is represented by an accurate, computerized outline, making forecasts of glacier-climate interactions more precise.

“This means that people can now do research that they simply could not do before,” said Cogley, the corresponding author on the new Journal of Glaciology paper. “It’s now possible to conduct much more robust modeling for what might happen to these glaciers in the future.”

As part of the RGI effort, the team mapped intricate glacier complexes in places like Alaska, Patagonia, central Asia and the Himalayas, as well as the peripheral glaciers surrounding the two great ice sheets in Greenland and Antarctica, said Pfeffer. “In order to model these glaciers, we have to know their individual characteristics, not simply an average or aggregate picture. That was one of the most difficult parts of the project.”

The team used satellite images and maps to outline the area and location of each glacier. The researchers can combine that information with a digital elevation model, then use a technique known as “power law scaling” to determine volumes of various collections of glaciers.

In addition to impacting global sea rise, the melting of the world’s glaciers over the next 100 years will severely affect regional water resources for uses like irrigation and hydropower, said Pfeffer. The melting also has implications for natural hazards like “glacier outburst” floods that may occur as the glaciers shrink, he said.

The total extent of glaciers in the RGI is roughly 280,000 square miles or 727,000 square kilometers — an area slightly larger than Texas or about the size of Germany, Denmark and Poland combined. The team estimated that the corresponding total volume of sea rise collectively held by the glaciers is 14 to 18 inches, or 350 to 470 millimeters.

The new estimates are less than some previous estimates, and in total they are less than 1 percent of the amount of water stored in the Greenland and Antarctic ice sheets, which collectively contain slightly more than 200 feet, or 63 meters, of sea rise.

“A lot of people think that the contribution of glaciers to sea rise is insignificant when compared with the big ice sheets,” said Pfeffer, also a professor in CU-Boulder’s civil, environmental and architectural engineering department. “But in the first several decades of the present century it is going to be this glacier reservoir that will be the primary contributor to sea rise. The real concern for city planners and coastal engineers will be in the coming decades, because 2100 is pretty far off to have to make meaningful decisions.”

Part of the RGI was based on the Global Land Ice Measurements from Space Initiative, or GLIMS, which involved more than 60 institutions from around the world and which contributed the baseline dataset for the RGI. Another important research data tool for the RGI was the European-funded program “Ice2Sea,” which brings together scientific and operational expertise from 24 leading institutions across Europe and beyond.

The GLIMS glacier database and website are maintained by CU-Boulder’s National Snow and Ice Data Center, or NSIDC. The GLIMS research team at NSIDC includes principal investigator Richard Armstrong, technical lead Bruce Raup and remote-sensing specialist Siri Jodha Singh Khalsa.

NSIDC is part of the Cooperative Institute for Research in Environmental Sciences, or CIRES, a joint venture between CU-Boulder and the National Oceanic and Atmospheric Administration.

The Atlantic Ocean dances with the sun and volcanoes

Imagine a ballroom in which two dancers apparently keep in time to their own individual rhythm. The two partners suddenly find themselves moving to the same rhythm and, after a closer look, it is clear to see which one is leading.

It was an image like this that researchers at Aarhus University were able to see when they compared studies of solar energy release and volcanic activity during the last 450 years, with reconstructions of ocean temperature fluctuations during the same period.

The results actually showed that during the last approximately 250 years – since the period known as the Little Ice Age – a clear correlation can be seen where the external forces, i.e. the Sun’s energy cycle and the impact of volcanic eruptions, are accompanied by a corresponding temperature fluctuation with a time lag of about five years.

In the previous two centuries, i.e. during the Little Ice Age, the link was not as strong, and the temperature of the Atlantic Ocean appears to have followed its own rhythm to a greater extent.

The results were recently published in the scientific journal Nature Communications.

In addition to filling in yet another piece of the puzzle associated with understanding the complex interaction of the natural forces that control the climate, the Danish researchers paved the way for linking the two competing interpretations of the origin of the oscillation phenomenon.

Temperature fluctuations discovered around the turn of the millennium

The climate is defined on the basis of data including mean temperature values recorded over a period of thirty years. Northern Europe thus has a warm and humid climate compared with other regions on the same latitudes. This is due to the North Atlantic Drift (often referred to as the Gulf Stream), an ocean current that transports relatively warm water from the south-west part of the North Atlantic to the sea off the coast of Northern Europe.

Around the turn of the millennium, however, climate researchers became aware that the average temperature of the Atlantic Ocean was not entirely stable, but actually fluctuated at the same rate throughout the North Atlantic. This phenomenon is called the Atlantic Multidecadal Oscillation (AMO), which consists of relatively warm periods lasting thirty to forty years being replaced by cool periods of the same duration.

The researchers were able to read small systematic variations in the water temperature in the North Atlantic in measurements taken by ships during the last 140 years.

Although the temperature fluctuations are small – less than 1°C – there is a general consensus among climate researchers that the AMO phenomenon has had a major impact on the climate in the area around the North Atlantic for thousands of years, but until now there has been doubt about what could cause this slow rhythm in the temperature of the Atlantic Ocean. One model explains the phenomenon as internal variability in the ocean circulation – somewhat like a bathtub sloshing water around in its own rhythm. Another model explains the AMO as being driven by fluctuations in the amount of solar energy received by the Earth, and as being affected by small changes in the energy radiated by the Sun itself and the after-effects of volcanic eruptions. Both these factors are also known as ‘external forces’ that have an impact on the Earth’s radiation balance.

However, there has been considerable scepticism towards the idea that a phenomenon such as an AMO could be driven by external forces at all – a scepticism that the Aarhus researchers now demonstrate as unfounded.

“Our new investigations clearly show that, since the Little Ice Age, there has been a correlation between the known external forces and the temperature fluctuations in the ocean that help control our climate. At the same time, however, the results also show that this can’t be the only driving force behind the AMO, and the explanation must therefore be found in a complex interaction between a number of mechanisms. It should also be pointed out that these fluctuations occur on the basis of evenly increasing ocean temperatures during the last approximately fifty years – an increase connected with global warming,” says Associate Professor Mads Faurschou Knudsen, Department of Geoscience, Aarhus University, who is the main author of the article.

Convincing data from the Earth’s own archives

Researchers have attempted to make computer simulations of the phenomenon ever since the discovery of the AMO, partly to enable a better understanding of the underlying mechanism. However, it is difficult for the computer models to reproduce the actual AMO signal that can be read in the temperature data from the last 140 years.

Associate Professor Knudsen and his colleagues instead combined all available data from the Earth’s own archives, i.e. previous studies of items such as radioactive isotopes and volcanic ash in ice cores. This provides information about solar energy release and volcanic activity during the last 450 years, and the researchers compared the data with reconstructions of the AMO’s temperature rhythm during the same period.

“We’ve only got direct measurements of the Atlantic Ocean temperature for the last 140 years, where it was measured by ships. But how do you measure the water temperature further back in time? Studies of growth rings in trees from the entire North Atlantic region come into the picture here, where ‘good’ and ‘bad’ growth conditions are calibrated to the actual measurements, and the growth rings from trees along the coasts further back in time can therefore act as reserve thermometers,” explains Associate Professor Knudsen.

The results provide a new and very important perspective on the AMO phenomenon because they are based on data and not computer models, which are inherently incomplete. The problem is that the models do not completely describe all the physical correlations and feedbacks in the system, partly because these are not fully understood. And when the models are thus unable to reproduce the actual AMO signal, it is hard to know whether they have captured the essence of the AMO phenomenon.

Impact of the sun and volcanoes

An attempt to simply explain how external forces such as the Sun and volcanoes can control the climate could sound like this: a stronger Sun heats up the ocean, while the ash from volcanic eruptions shields the Sun and cools down the ocean. However, it is hardly as simple as that.

“Fluctuations in ocean temperature have a time lag of about five years in relation to the peaks we can read in the external forces. However, the direct effect of major volcanic eruptions is clearly seen as early as the same year in the mean global atmospheric temperature, i.e. a much shorter delay. The effect we studied is more complex, and it takes time for this effect to spread to the ocean currents,” explains Associate Professor Knudsen.

“An interesting new theory among solar researchers and meteorologists is that the Sun can control climate variations via the very large variations in UV radiation, which are partly seen in connection with changes in sunspot activity during the Sun’s eleven-year cycle. UV radiation heats the stratosphere in particular via increased production of ozone, which can have an impact on wind systems and thereby indirectly on the global ocean currents as well,” says Associate Professor Knudsen. However, he emphasises that researchers have not yet completely understood how a development in the stratosphere can affect the ocean currents on Earth.

Towards a better understanding of the climate

“In our previous study of the climate in the North Atlantic region during the last 8,000 years, we were able to show that the temperature of the Atlantic Ocean was presumably not controlled by the Sun’s activity. Here the temperature fluctuated in its own rhythm for long intervals, with warm and cold periods lasting 25 years. The prevailing pattern was that this climate fluctuation in the ocean was approximately 30󈞔% faster than the fluctuation we’d previously observed in solar activity, which lasted about ninety years. What we can now see is that the Atlantic Ocean would like to – or possibly even prefer to – dance alone. However, under certain circumstances, the external forces interrupt the ocean’s own rhythm and take over the lead, which has been the case during the last 250 years,” says Associate Professor Bo Holm Jacobsen, Department of Geoscience, Aarhus University, who is the co-author of the article.

“It’ll be interesting to see how long the Atlantic Ocean allows itself to be led in this dance. The scientific challenge partly lies in understanding the overall conditions under which the AMO phenomenon is sensitive to fluctuations in solar activity and volcanic eruptions,” he continues.

“During the last century, the AMO has had a strong bearing on significant weather phenomena such as hurricane frequency and droughts – with considerable economic and human consequences. A better understanding of this phenomenon is therefore an important step for efforts to deal with and mitigate the impact of climate variations,” Associate Professor Knudsen concludes.

Going deep to study long-term climate evolution

A Rice University-based team of geoscientists is going to great lengths -- from Earth's core to its atmosphere -- to investigate the role that deep-Earth processes play in climate evolution over million-year timescales. -  Rice University
A Rice University-based team of geoscientists is going to great lengths — from Earth’s core to its atmosphere — to investigate the role that deep-Earth processes play in climate evolution over million-year timescales. – Rice University

A Rice University-based team of geoscientists is going to great lengths — from Earth’s core to its atmosphere — to get to the bottom of a long-standing mystery about the planet’s climate.

“We want to know what controls long-term climate change on Earth, the oscillations between greenhouse and icehouse cycles that can last as long as tens of million years,” said Cin-Ty Lee, professor of Earth science at Rice and the principal investigator (PI) on a new $4.3 million, five-year federal grant from the National Science Foundation’s Frontiers in Earth-System Dynamics (FESD) Program.

“There are long periods where Earth is relatively cool, like today, where you have ice caps on the North and South poles, and there are also long periods where there are no ice caps,” Lee said. “Earth’s climate has oscillated between these two patterns for at least half a billion years. We want to understand what controls these oscillations, and we have people at universities across the country who are going to attack this problem from many angles.”

For starters, Lee distinguished between the type of climate change that he and his co-investigators are studying and the anthropogenic climate change that often makes headlines.

“We’re working on much longer timescales than what’s involved in anthropogenic climate change,” Lee said. “We’re interested in explaining processes that cycle over tens of millions of years.”

Lee described the research team as “a patchwork of free spirits” that includes bikers, birdwatchers and skateboarders who are drawn together by a common interest in studying the whole Earth dynamics of carbon exchange. The group has specialists in oceanography, petrology, geodynamics, biogeochemistry and other fields, and it includes more than a dozen faculty and students from the U.S., Europe and Asia. Rice co-PIs include Rajdeep Dasgupta, Gerald Dickens and Adrian Lenardic.

The team will focus on how carbon moves between Earth’s external and internal systems. On the external side, carbon is known to cycle between oceans, atmosphere, biosphere and soils on timescales ranging from a few days to a few hundred thousand years. On million-year to billion-year timescales, carbon in these external reservoirs interacts with reservoirs inside Earth, ranging from crustal carbon stored in ancient sediments preserved on the continents to carbon deep in Earth’s mantle.

“Because of these differences in timescales, carbon cycling at Earth’s surface is typically modeled independently from deep-Earth cycling,” Lee said. “We need to bring the two together if we are to understand long-term greenhouse-icehouse cycling.”

From the fossil record, scientists know that atmospheric carbon dioxide plays a vital role in determining Earth’s surface temperatures. Many studies have focused on how carbon moves between the atmosphere, oceans and biosphere. Lee said the FESD team will examine how carbon is removed from the surface and cycled back into the deep Earth, and it will also examine how volcanic eruptions bring carbon from the deep Earth to the surface. In addition, the team will examine the role that volcanic activity and plate tectonics may play in periodically releasing enormous volumes of carbon dioxide into the atmosphere. One of several hypotheses that will be tested is whether Earth’s subduction zones may at times be dominated by continental arcs, and if so, whether the passage of magmas through ancient carbonates stored in the continental upper plate can amplify the volcanic flux of carbon.

“Long-term climate variability is intimately linked to whole-Earth carbon cycling,” Lee said. “Our task is to build up a clearer picture of how the inputs and outputs change through time.”

In addition to the Rice team, the project’s primary investigators include Jaime Barnes of the University of Texas at Austin, Jade Star Lackey of Pomona College, Michael Tice of Texas A&M University and Richard Zeebe of the University of Hawaii. Research affiliates include Steve Bergman of Shell, Mark Jellinek of the University of British Columbia, Tapio Schneider of the Swiss Federal Institute of Technology and Yusuke Yokoyama of the University of Tokyo.

Harmful particles in Icelandic volcanic ash fell first, says new research

The type of particles which are most harmful to jet engines were the first to fall out of the Eyjafjallajökull ash plume following the volcano’s eruption in 2010, delegates at the Goldschmidt conference will be told today (Wednesday 28th August).

The research, led by Dr Bernard Grobety of the University of Fribourg in Switzerland, will help to mitigate the impact of future volcanic eruptions on air travel.

Dr Grobety’s team analysed samples of volcanic ash taken at different points in its journey from the volcano across Europe. They found that the two different forms of the ash particles – crystalline and glassy – behaved differently during transport. As the plume travelled through the air, the crystalline particles, which are denser and heavier, fell out of the cloud first compared to even-sized glassy particles.

“It’s already known that the larger, heavier particles in an ash cloud will be the first to fall out as the cloud travels away from a volcano,” explains Dr Grobety. “It is also clear that particles of equal size but higher density will fall out faster. Our research, however, is the first to evidence the faster loss of crystalline particles in a volcanic cloud and that the overall composition of the ash changes during transport. Since crystalline particles are harder and melt at higher temperatures, they are more harmful to jet engines than glassy particles. Understanding the behaviour of these different forms in the ash cloud will enable the authorities to fine tune their response should another volcanic eruption take place.

The 2010 eruption of Eyjafjallajökull caused air traffic in Europe to be grounded for six days, with widespread disruption in over 20 countries. There has been extensive research since 2010 to reduce the impact of future eruptions, but much of the research treats the ash cloud as homogenous, focusing on its concentration and the size of particles within it. Dr Grobety’s research adds another layer of detail which could reduce the impact of any eruption still further.

“We’re already at the point where we can say that if the ash is at a certain concentration and a certain particle size, it poses no threat to aircraft,” says Dr Grobety. “However, it’s possible that even at a higher concentration, if no crystalline particles are present, planes may still be safe to fly. By monitoring how quickly these particles are falling out of the cloud, it could reduce the area affected or help restrictions to be lifted sooner.

“However, there are a lot of factors which will determine the impact of any future eruptions – from the nature of the eruption itself, to the prevailing winds and the concentration of the ash. While the detail we’re able to provide may be only one of many factors to take into account, anything that can limit the disruption to air travel has to be worth looking at.

Simulating flow from volcanoes and oil spills

Some time around 37,000 BCE a massive volcano erupted in the Campanian region of Italy, blanketing much of Europe with ash, stunting plant growth and possibly dooming the Neanderthals. While our prehistoric relatives had no way to know the ash cloud was coming, a recent study provides a new tool that may have predicted what path volcanic debris would take.

“This paper provides a model for the pattern of the ash cloud if the wind is blowing past an eruption of a given size,” said Peter Baines, a scientist at the University of Melbourne in Australia who did the study. He published his work in the journal Physics of Fluids.

Volcanic eruptions are an example of what Baines calls an “intrusion.” Other examples include exhaust rising from a chimney, sewage flowing into the ocean, and the oil spilling underwater in the 2010 Deepwater Horizon disaster. In all these events, a fluid rises into a density-stratified environment like the atmosphere or the ocean. As the fluid rises, it is pushed by winds or currents, and this crossflow can cause the intruding fluid to disperse far from its origin.

Scientists have previously modeled intrusions into a completely calm environment, but before Baines nobody had ever attempted to introduce the effect of crosswinds, a necessary step toward making such models more realistic and useful.

Predicting Ash and Oil Flows

Baines thinks his work could be used to estimate how much ash is pouring out of a volcano, or how fast oil is gushing from a hole in the sea floor.

Baines is now working with volcanologists in Britain to apply his model to historic eruptions like the Campanian event and the catastrophic Toba supereruption that occurred around 73,000 years ago in Indonesia. The scientists are hoping to use ash deposits from these volcanoes to develop a sharper picture of the amount and speed of the ejected material.

“Most of what we know about prehistoric eruptions is from sedimentary records,” said Baines. “You then have to try to infer what the nature of the eruption was, when this is the only information you’ve got.”

Baines said his model can also help forecast the deposition patterns of future eruptions. And that should give us a big leg up on the poor Neanderthals.

How the Model Works

To understand how intrusions work in the presence of crossflows, Baines developed what he calls a semi-analytical model. He began with fluid dynamics equations, and then used numerical calculations to arrive at approximate solutions for specifics combinations of source flow and spread rates, and crosswind speed. He found that, under normal wind speeds, the intruding fluid reached a maximum thickness at a certain distance upstream from the source, and thinned in the downstream direction. The distance to the upstream stagnation point depended much more on the rate of source flow than the crossflow speed.