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.”

Geologists dig into science around the globe, on land and at sea

University of Cincinnati geologists will be well represented among geoscientists from around the world at The Geological Society of America’s Annual Meeting and Exposition. The meeting takes place Oct. 19-22, in Vancouver, Canada, and will feature geoscientists representing more than 40 different disciplines. The meeting will feature highlights of UC’s geological research that is taking place globally, from Chile to Costa Rica, Belize, Bulgaria, Scotland, Trinidad and a new project under development in the Canary Islands.

UC faculty and graduate students are lead or supporting authors on more than two dozen Earth Sciences-related research papers and/or PowerPoint and poster exhibitions at the GSA meeting.

The presentations also cover UC’s longtime and extensive exploration and findings in the Cincinnati Arch of the Ohio Valley, world-renowned for its treasure trove of paleontology – plant and animal fossils that were preserved when a shallow sea covered the region 450 million years ago during the Paleozoic Era.

Furthermore, in an effort to diversify the field of researchers in the Earth Sciences, a UC assistant professor of science education and geology, Christopher Atchison, was awarded funding from the National Science Foundation and the Society of Exploration Geophysics to lead a research field trip in Vancouver for students with disabilities. Graduate and undergraduate student participants will conduct the research on Oct. 18 and then join events at the GSA meeting. They’ll be guided by geoscience researchers representing the United Kingdom, New Zealand, Canada and the U.S. Those guides include Atchison and Julie Hendricks, a UC special education major from Batavia, Ohio, who will be using her expertise in American Sign Language (ASL) to assist student researchers representing Deaf and Hard of Hearing communities.

The meeting will also formally introduce Arnold Miller, UC professor of geology, as the new president-elect of the national Paleontological Society Thomas Lowell, professor of geology, is a recently elected Fellow of the Geological Society of America – a recognition for producing a substantial body of research. Lowell joins colleagues Warren Huff, professor of geology, and Lewis Owen, professor and head of the Department of Geology, as GSA Fellows.

Here are highlights of the UC research to be presented at the GSA meeting Oct. 19-22:

Staying Put or Moving On? Researchers Develop Model to Identify Migrating Patterns of Different Species

Are plant and animal species what you might call lifelong residents – they never budge from the same place? That’s a relatively common belief in ecology and paleoecology – that classes of organisms tend to stay put over millions of years and either evolve or go extinct as the environment changes. UC researchers developed a series of numerical models simulating shifting habitats in fossil regions to compare whether species changed environments when factoring geological and other changes in the fossil record. They found that geologically driven changes in the quality of the fossil record did not distort the real ecological signal, and that most species maintained their particular habitat preferences through time. They did not evolve to adapt to changing environments, but rather, they migrated, following their preferred environments. That is to say, they did not stay in place geographically but by moving, they were able to track their favored habitats. Field research for the project was conducted in New York state as well as the paleontological-rich region of Cincinnati; Dayton, Ohio, Lexington, Ky.; and Indiana. Funding for the project was supported by The Paleontological Society; The Geological Society of America; The American Museum of Natural History and the UC Geology Department’s Kenneth E. Caster Memorial Fund.

Presenter: Andrew Zaffos, UC geology doctoral student

Co-authors: Arnold Miller, Carlton Brett

Pioneering Study Provides a Better Understanding of What Southern Ohio and Central Kentucky Looked Like Hundreds of Millions of Years Ago

The end of the Ordovician period resulted in one of the largest mass extinction events in the Earth’s history. T.J. Malgieri, a UC master’s student in geology, led this study examining the limestone and shales of the Upper Ordovician Period – the geologic Grant Lake Formation covering southern Ohio and central Kentucky – to recreate how the shoreline looked some 445 million years ago. In this pioneering study of mud cracks and deposits in the rocks, the researchers discovered that the shoreline existed to the south and that the water became deeper toward the north. By determining these ecological parameters, the ramp study provides a better understanding of environments during a time of significant ecological change. Malgieri says the approach can be applied to other basins throughout the world to create depth indicators in paeloenvironments.

Presenter: T.J. Malgieri, UC geology master’s student

Co-authors: Carlton Brett, Cameron Schalbach, Christopher Aucoin, UC; James Thomka (UC, University of Akron); Benjamin Dattilo, Indiana University Purdue University Ft. Wayne

UC Researchers Take a Unique Approach to Monitoring Groundwater Supplies Near Ohio Fracking Sites

A collaborative research project out of UC is examining effects of fracking on groundwater in the Utica Shale region of eastern Ohio. First launched in Carroll County in 2012, the team of researchers is examining methane levels and origins of methane in private wells and springs before, during and after the onset of fracking. The team travels to the region to take water samples four times a year.

Presenter: Claire Botner, a UC geology master’s student

Co-author: Amy Townsend-Small, UC assistant professor of geology

Sawing Through Seagrass to Reveal Clues to the Past

Kelsy Feser, a UC doctoral student in geology, is working at several sites around St. Croix in the Virgin Islands to see if human developments impact marine life. The research focuses on shells of snails and clams that have piled up on the sea floor for thousands of years. Digging through layers of thick seagrass beds on the ocean floor, Feser can examine deeper shells that were abundant thousands of years ago and compare them to shallower layers that include living clams and snails. Early analysis indicates a greater population of potentially pollution-tolerant mussels in an area near a landfill on the island, compared with shells from much earlier time periods. Feser is doing this sea grass analysis around additional sites including tourist resorts, an oil refinery, a power plant and a marina. Funding for the research is provided by the Paleontological Society, the GSA, the American Museum of Natural History and the UC Geology Department.

Presenter: Kelsy Feser, UC geology doctoral student

Co-authors: Arnold Miller

Turning to the Present to Understand the Past

In order to properly interpret changes in climate, vegetation, or animal populations over time, it is necessary to establish a comparative baseline. Stella Mosher, a UC geology master’s student, is studying stable carbon, nitrogen, sulfur and strontium isotopes in modern vegetation from the Canary Islands in order to quantify modern climatic and environmental patterns. Her findings will provide a crucial foundation for future UC research on regional paleoclimatic and paleoenvironmental shifts.

Presenter: Stella Mosher, graduate student in geology

Co-authors: Brooke Crowley, assistant professor of geology; Yurena Yanes, research assistant professor of geology

A Study on the Impact of Sea Spray

Sulfur is an element of interest in both geology and archaeology, because it can reveal information about the diets of ancient cultures. This study takes a novel approach to studying how sea spray can affect the sulfur isotope values in plants on a small island, focusing on the island of Trinidad. Researchers collected leaves from different plant species to get their sulfur isotope value, exploring whether wind direction played a role in how plants were influenced by the marine water from sea spray. Vegetation was collected from the edges of the island to the deeply forested areas. The study found that sulfur isotope values deeper inland and on the calmer west coast were dramatically lower in indicating marine water than vegetation along the edges and the east coast. The findings can help indicate the foraging activities of humans and animals. Funding for the study was supported by the Geological Society of America, the UC Graduate Student Association and the UC Department of Geology.

Presenter: Janine Sparks, UC geology doctoral student

Co-authors: Brooke Crowley, UC assistant professor, geology/anthropology; William Gilhooly III, assistant professor, Earth Sciences, Indiana University-Purdue University Indianapolis

Proxy Wars – The Paleobiology Data Debate

For the past several decades, paleobiologists have built large databases containing information on fossil plants and animals of all geological ages to investigate the timing and extent of major changes in biodiversity – changes such as mass extinctions that have taken place throughout the history of life. Biodiversity researcher Arnold Miller says that in building these databases, it can be a challenge to accurately identify species in the geological record, so it has been common for researchers to instead study biodiversity trends using data compiled at broader levels of biological classification, including the genus level, under the assumption that these patterns are effective proxies for what would be observed among species if the data were available. Miller has been involved in construction of The Paleobiology Database, an extensive public online resource that contains global genus- and species-level data, now permitting a direct, novel look at the similarities and differences between patterns at these two levels. Miller’s discussion aims to set the record straight as to when researchers can effectively use a genus as a proxy for a species and also when it’s inappropriate. This research is funded by the NASA Astrobiology Program.

Presenter: Arnold Miller, UC professor of geology

A Novel New Method for Examining the Distribution of Pores in Rocks

Oil and gas companies take an interest in the porosity of sedimentary rocks because those open spaces can be filled with fuel resources. Companies involved with hydraulic fracturing (“fracking”) are also interested in porosity because it could be a source for storing wastewater as a result of fracking. In this unique study, UC researchers made pore-size measurements similar to those used in crystal size distribution (CSD) theory to determine distribution of pores as a function of their sizes, using thin sections of rock. In addition to providing accurate porosity distribution at a given depth, their approach can be extended to evaluate variation of pore spaces as a function of depth in a drill core, percent of pores in each size range, and pore types and pore geometry. The Texas Bureau of Economic Geology provided the rock samples used in the study. Funding for the study was supported by the Turkish Petroleum Corporation.

Presenter: Ugurlu Ibrahim, master’s student in geology

Co-author: Attila Kilinc, professor of geology

Researchers Turn to 3-D Technology to Examine the Formation of Cliffband Landscapes

A blend of photos and technology takes a new twist on studying cliff landscapes and how they were formed. The method called Structure-From-Motion Photogrammetry – computational photo image processing techniques – is used to study the formation of cliff landscapes in Colorado and Utah and to understand how the layered rock formations in the cliffs are affected by erosion.

Presenter: Dylan Ward, UC assistant professor of geology

Testing the Links Between Climate and Sedimentation in the Atacama Desert, Northern Chile

The Atacama Desert is used as an analog for understanding the surface of Mars. In some localities, there has been no activity for millions of years. UC researchers have been working along the flank of the Andes Mountains in northern Chile, and this particular examination focuses on the large deposits of sediment that are transported down the plateau and gather at the base. The researchers are finding that their samples are not reflecting the million-year-old relics previously found on such expeditions, but may indicate more youthful activity possibly resulting from climatic events. The research is supported by a $273,634 grant from the National Science Foundation to explore glacio-geomorphic constraints on the climate history of subtropical northern Chile.

Presenter: Jason Cesta, UC geology master’s student

Co-author: Dylan Ward, UC assistant professor of geology

Uncovering the Explosive Mysteries Surrounding the Manganese of Northeast Bulgaria

UC’s geology collections hold minerals from field expeditions around the world, including manganese from the Obrochishte mines of northeastern Bulgaria. Found in the region’s sedimentary rock, manganese can be added to metals such as steel to improve strength. It’s widely believed that these manganese formations were the result of ocean water composition at the time the sediments were deposited in the ocean. In this presentation, UC researchers present new information on why they believe the manganese formations resulted from volcanic eruptions, perhaps during the Rupelian stage of the geologic time scale, when bentonite clay minerals were formed. The presentation evolved from an advance class project last spring under the direction of Warren Huff, a UC professor of geology.

Presenter: Jason Cesta, UC geology master’s student

Co-authors: Warren Huff, UC professor of geology; Christopher Aucoin; Michael Harrell; Thomas Malgieri; Barry Maynard; Cameron Schwalbach; Ibrahim Ugurlu; Antony Winrod

Two UC researchers will chair sessions at the GSA meeting: Doctoral student Gary Motz will chair the session, “Topics in Paleoecology: Modern Analogues and Ancient Systems,” on Oct. 19. Matt Vrazo, also a doctoral student in geology, is chairing “Paleontology: Trace Fossils, Taphonomy and Exceptional Preservation” on Oct. 21, and will present, “Taphonomic and Ecological Controls on Eurypterid Lagerstäten: A Model for Preservation in the Mid-Paleozoic.”


UC’s nationally ranked Department of Geology conducts field research around the world in areas spanning paleontology, quaternary geology, geomorphology, sedimentology, stratigraphy, tectonics, environmental geology and biogeochemistry.

The Geological Society of America, founded in 1888, is a scientific society with more than 26,500 members from academia, government, and industry in more than 100 countries. Through its meetings, publications, and programs, GSA enhances the professional growth of its members and promotes the geosciences in the service of humankind.

Trinity geologists re-write Earth’s evolutionary history books

The study site landscape is shown with boulders of the paleosol in the foreground. -  Quentin Crowley
The study site landscape is shown with boulders of the paleosol in the foreground. – Quentin Crowley

Geologists from Trinity College Dublin have rewritten the evolutionary history books by finding that oxygen-producing life forms were present on Earth some 3 billion years ago – a full 60 million years earlier than previously thought. These life forms were responsible for adding oxygen (O2) to our atmosphere, which laid the foundations for more complex life to evolve and proliferate.

Working with Professors Joydip Mukhopadhyay and Gautam Ghosh and other colleagues from the Presidency University in Kolkata, India, the geologists found evidence for chemical weathering of rocks leading to soil formation that occurred in the presence of O2. Using the naturally occurring uranium-lead isotope decay system, which is used for age determinations on geological time-scales, the authors deduced that these events took place at least 3.02 billion years ago. The ancient soil (or paleosol) came from the Singhbhum Craton of Odisha, and was named the ‘Keonjhar Paleosol’ after the nearest local town.

The pattern of chemical weathering preserved in the paleosol is compatible with elevated atmospheric O2 levels at that time. Such substantial levels of oxygen could only have been produced by organisms converting light energy and carbon dioxide to O2 and water. This process, known as photosynthesis, is used by millions of different plant and bacteria species today. It was the proliferation of such oxygen-producing species throughout Earth’s evolutionary trajectory that changed the composition of our atmosphere – adding much more O2 – which was as important for the development of ancient multi-cellular life as it is for us today.

Quentin Crowley, Ussher Assistant Professor in Isotope Analysis and the Environment in the School of Natural Sciences at Trinity, is senior author of the journal article that describes this research which has just been published online in the world’s top-ranked Geology journal, Geology. He said: “This is a very exciting finding, which helps to fill a gap in our knowledge about the evolution of the early Earth. This paleosol from India is telling us that there was a short-lived pulse of atmospheric oxygenation and this occurred considerably earlier than previously envisaged.”

The early Earth was very different to what we see today. Our planet’s early atmosphere was rich in methane and carbon dioxide and had only very low levels of O2. The widely accepted model for evolution of the atmosphere states that O2 levels did not appreciably rise until about 2.4 billion years ago. This ‘Great Oxidation Event’ event enriched the atmosphere and oceans with O2, and heralded one of the biggest shifts in evolutionary history.

Micro-organisms were certainly present before 3.0 billion years ago but they were not likely capable of producing O2 by photosynthesis. Up until very recently however, it has been unclear if any oxygenation events occurred prior to the Great Oxidation Event and the argument for an evolutionary capability of photosynthesis has largely been based on the first signs of an oxygen build-up in the atmosphere and oceans.

“It is the rare examples from the rock record that provide glimpses of how rocks weathered,” added Professor Crowley. “The chemical changes which occur during this weathering tell us something about the composition of the atmosphere at that time. Very few of these ‘paleosols’ have been documented from a period of Earth’s history prior to 2.5 billion years ago. The one we worked on is at least 3.02 billion years old, and it shows chemical evidence that weathering took place in an atmosphere with elevated O2 levels.”

There was virtually no atmospheric O2 present 3.4 billion years ago, but recent work from South African paleosols suggested that by about 2.96 billion years ago O2 levels may have begun to increase. Professor Crowley’s finding therefore moves the goalposts back at least 60 million years, which, given humans have only been on the planet for around a tenth of that time, is not an insignificant drop in the evolutionary ocean.

Professor Crowley concluded: “Our research gives further credence to the notion of early and short-lived atmospheric oxygenation.

This particular example is the oldest known example of oxidative weathering from a terrestrial environment, occurring about 600 million years before the Great Oxidation Event that laid the foundations for the evolution of complex life.”

Mantle plumes crack continents

In some parts of the Earth, material rises upwards like a column from the boundary layer of the Earth’s core and the lower mantel to just below the Earth’s crust hundreds of kilometres above. Halted by the resistance of the hard crust and lithospheric mantle, the flow of material becomes wider, taking on a mushroom-like shape. Specialists call these magma columns “mantle plumes” or simply “plumes”.

Are mantel plumes responsible for the African rift system?

Geologists believe that plumes are not just responsible for creating volcanoes outside of tectonically active areas – they can also break up continents. The scientists offer the Danakil Depression (the lowlands in the Ethiopia-Eritrea-Djibouti triangle) as an example of this. This “triple junction” is extremely tectonically and volcanically active. Geologists believe that the so-called Afar plume is rising up below it and has created a rift system that forks into the Red Sea, the Gulf of Aden and Africa’s Great Rift Valley. However, the sheer length of time required, geologically speaking, for this process to take place, means that nobody is able to confirm or disprove with absolute certainty that the force of a plume causes continental breakup.

Simulations becoming more realistic

Evgueni Burov, a Professor at the University of Paris VI, and Taras Gerya, Professor of Geophysics at ETH Zurich, have now taken a step closer to solving this geological mystery with a new computer model. Their paper has recently been published in the journal Nature. The two researchers conducted numerical experiments to reproduce the Earth’s surface in high-resolution 3D.

These simulations show that the rising flow of material is strong enough to cause continental breakup if the tectonic plate is under (weak) tensile stress. “The force exerted by a plume on a plate is actually too weak to break it up,” says Gerya. In experiments using simple models, the researchers allowed the plumes to hit an unstressed plate, which did not cause it to break, but merely formed a round hump. However, when the geophysicists modelled the same process with a plate under weak tensile stress, it broke apart, forming a crevice and rift system like the ones found around the world.

“The process can be compared to a taut piece of plastic film. Weak, pointed force is enough to tear the film, but if the film is not pulled taut, it is extremely difficult to tear.” This mechanism has already been proposed in the past as a possible model for explaining continental breakup, but had never been outlined in plausible terms before now.

First high-resolution simulations

“We are the first to create such a high-resolution model which demonstrates how a plume interacts with a plate under tensile stress,” says Gerya. Fast and powerful computers and stable algorithms programmed by the scientists themselves were required for the simulations. The researchers benefited from technical advances made and experience accumulated by the ETH professor in this field over the past ten years.

In the model, the deformations are created quickly from a geological point of view. Rift systems several kilometres deep and more than a thousand kilometres long can form after “just” two million years. The processes are therefore up to ten times faster than tectonic processes such as subduction and 50 times faster than the Alpine orogeny, for example.

Disputed idea

The idea of mantel plumes is widely disputed, with some researchers denying that they even exist. “I think it is much more likely that they do exist,” says Gerya. As is often the case in geology, especially when researching the Earth’s interior, such processes and phenomena like the existence of plumes cannot be observed directly. Furthermore, the periods over which geological processes take place are far too long for humans to experience first-hand. “So far, we have only been able to observe the effects that plumes have on the Earth’s surface and on the propagation of seismic waves in the Earth’s interior.”

The scientists are therefore reliant on good, realistic models that show the processes in a geological time lapse. How realistic the calculated simulations are depends on the parameters used. The plume-plate interaction model incorporated physical laws, the characteristics of materials in the Earth’s crust and mantle, and temperature and pressure conditions. “We know the rules, but humans generally lack the intuition to identify how they interact on geological timescales.”

Composition of Earth’s mantle revisited

Research published recently in Science suggested that the makeup of the Earth’s lower mantle, which makes up the largest part of the Earth by volume, is significantly different than previously thought.

Understanding the composition of the mantle is essential to seismology, the study of earthquakes and movement below the Earth’s surface, and should shed light on unexplained seismic phenomena observed there.

Though humans haven’t yet managed to drill further than seven and a half miles into the Earth, we’ve built a comprehensive picture of what’s beneath our feet through calculations and limited observation. We all live atop the crust, the thin outer layer; just beneath is the mantle, outer core and finally inner core. The lower portion of the mantle is the largest layer – stretching from 400 to 1,800 miles below the surface – and gives off the most heat. Until now, the entire lower mantle was thought to be composed of the same mineral throughout: ferromagnesian silicate, arranged in a type of structure called perovskite.

The pressure and heat of the lower mantle is intense – more than 3,500° Fahrenheit. Materials may have very different properties at these conditions; structures may exist there that would collapse at the surface.

To simulate these conditions, researchers use special facilities at the Advanced Photon Source, where they shine high-powered lasers to heat up the sample inside a pressure cell made of a pair of diamonds. Then they aim powerful beams of X-rays at the sample, which hit and scatter in all directions. By gathering the scatter data, scientists can reconstruct how the atoms in the sample were arranged.

The team found that at conditions that exist below about 1,200 miles underground, the ferromagnesian silicate perovskite actually breaks into two separate phases. One contains nearly no iron, while the other is full of iron. The iron-rich phase, called the H-phase, is much more stable under these conditions.

“We still don’t fully understand the chemistry of the H-phase,” said lead author and Carnegie Institution of Washington scientist Li Zhang. “But this finding indicates that all geodynamic models need to be reconsidered to take the H-phase into account. And there could be even more unidentified phases down there in the lower mantle as well, waiting to be identified.”

The facilities at Argonne’s Advanced Photon Source were key to the findings, said Carnegie scientist Yue Meng, also an author on the paper. “Recent technological advances at our beamline allowed us to create the conditions to simulate these intense temperatures and pressures and probe the changes in chemistry and structure of the sample in situ,” she said.

“What distinguished this work was the exceptional attention to detail in every aspect of the research – it demonstrates a new level for high-pressure research,” Meng added.

From ‘Finding Nemo’ to minerals — what riches lie in the deep sea?

Left: The first species ever recovered from the deep sea. Center: Rockfish use deep-sea carbonate formations at Hydrate Ridge, US, as a refuge. Right: Deep-sea corals such as the one pictured are a source of jewelery and other riches. -  SERPENT Project/D.O.B. Jones, L. Levin, UK's BIS Department
Left: The first species ever recovered from the deep sea. Center: Rockfish use deep-sea carbonate formations at Hydrate Ridge, US, as a refuge. Right: Deep-sea corals such as the one pictured are a source of jewelery and other riches. – SERPENT Project/D.O.B. Jones, L. Levin, UK’s BIS Department

As fishing and the harvesting of metals, gas and oil have expanded deeper and deeper into the ocean, scientists are drawing attention to the services provided by the deep sea, the world’s largest environment. “This is the time to discuss deep-sea stewardship before exploitation is too much farther underway,” says lead-author Andrew Thurber. In a review published today in Biogeosciences, a journal of the European Geosciences Union (EGU), Thurber and colleagues summarise what this habitat provides to humans, and emphasise the need to protect it.

“The deep sea realm is so distant, but affects us in so many ways. That’s where the passion lies: to tell everyone what’s down there and that we still have a lot to explore,” says co-author Jeroen Ingels of Plymouth Marine Laboratory in the UK.

“What we know highlights that it provides much directly to society,” says Thurber, a researcher at the College of Earth, Ocean and Atmospheric Sciences at Oregon State University in the US. Yet, the deep sea is facing impacts from climate change and, as resources are depleted elsewhere, is being increasingly exploited by humans for food, energy and metals like gold and silver.

“We felt we had to do something,” says Ingels. “We all felt passionate about placing the deep sea in a relevant context and found that there was little out there aimed at explaining what the deep sea does for us to a broad audience that includes scientists, the non-specialists and ultimately the policy makers. There was a gap to be filled. So we said: ‘Let’s just make this happen’.”

In the review of over 200 scientific papers, the international team of researchers points out how vital the deep sea is to support our current way of life. It nurtures fish stocks, serves as a dumping ground for our waste, and is a massive reserve of oil, gas, precious metals and the rare minerals we use in modern electronics, such as cell phones and hybrid-car batteries. Further, hydrothermal vents and other deep-sea environments host life forms, from bacteria to sponges, that are a source of new antibiotics and anti-cancer chemicals. It also has a cultural value, with its strange species and untouched habitats inspiring books and films from 20,000 Leagues Under the Sea to Finding Nemo.

“From jewellery to oil and gas and future potential energy reserves as well as novel pharmaceuticals, deep-sea’s worth should be recognised so that, as we decide how to use it more in the future, we do not inhibit or lose the services that it already provides,” says Thurber.

The deep sea (ocean areas deeper than 200m) represents 98.5% of the volume of our planet that is hospitable to animals. It has received less attention than other environments because it is vast, dark and remote, and much of it is inaccessible to humans. But it has important global functions. In the Biogeosciences review the team shows that deep-sea marine life plays a crucial role in absorbing carbon dioxide from the atmosphere, as well as methane that occasionally leaks from under the seafloor. In doing so, the deep ocean has limited much of the effects of climate change.

This type of process occurs over a vast area and at a slow rate. Thurber gives other examples: manganese nodules, deep-sea sources of nickel, copper, cobalt and rare earth minerals, take centuries or longer to form and are not renewable. Likewise, slow-growing and long-lived species of fish and coral in the deep sea are more susceptible to overfishing. “This means that a different approach needs to be taken as we start harvesting the resources within it.”

By highlighting the importance of the deep sea and identifying the traits that differentiate this environment from others, the researchers hope to provide the tools for effective and sustainable management of this habitat.

“This study is one of the steps in making sure that the benefits of the deep sea are understood by those who are trying to, or beginning to, regulate its resources,” concludes Thurber. “We ultimately hope that it will be a useful tool for policy makers.”

Modern ocean acidification is outpacing ancient upheaval, study suggests

<IMG SRC="/Images/964394569.jpg" WIDTH="350" HEIGHT="237" BORDER="0" ALT="The deep-sea benthic foram Aragonia velascoensis went extinct about 56 million years ago as the oceans rapidly acidified. – Ellen Thomas/Yale University”>
The deep-sea benthic foram Aragonia velascoensis went extinct about 56 million years ago as the oceans rapidly acidified. – Ellen Thomas/Yale University

Some 56 million years ago, a massive pulse of carbon dioxide into the atmosphere sent global temperatures soaring. In the oceans, carbonate sediments dissolved, some organisms went extinct and others evolved.

Scientists have long suspected that ocean acidification played a part in the crisis-similar to today, as manmade CO2 combines with seawater to change its chemistry. Now, for the first time, scientists have quantified the extent of surface acidification from those ancient days, and the news is not good: the oceans are on track to acidify at least as much as they did then, only at a much faster rate.

In a study published in the latest issue of Paleoceanography, the scientists estimate that surface ocean acidity increased by about 100 percent in a few thousand years or more, and stayed that way for the next 70,000 years. In this radically changed environment, some creatures died out while others adapted and evolved. The study is the first to use the chemical composition of fossils to reconstruct surface ocean acidity at the Paleocene-Eocene Thermal Maximum (PETM), a period of intense warming on land and throughout the oceans due to high CO2.

“This could be the closest geological analog to modern ocean acidification,” said study coauthor Bärbel Hönisch, a paleoceanographer at Columbia University’s Lamont-Doherty Earth Observatory. “As massive as it was, it still happened about 10 times more slowly than what we are doing today.”

The oceans have absorbed about a third of the carbon humans have pumped into the air since industrialization, helping to keep temperatures lower than they would be otherwise. But that uptake of carbon has come at a price. Chemical reactions caused by that excess CO2 have made seawater grow more acidic, depleting it of the carbonate ions that corals, mollusks and calcifying plankton need to build their shells and skeletons.

In the last 150 years or so, the pH of the oceans has dropped substantially, from 8.2 to 8.1–equivalent to a 25 percent increase in acidity. By the end of the century, ocean pH is projected to fall another 0.3 pH units, to 7.8. While the researchers found a comparable pH drop during the PETM–0.3 units–the shift happened over a few thousand years.

“We are dumping carbon in the atmosphere and ocean at a much higher rate today-within centuries,” said study coauthor Richard Zeebe, a paleoceanographer at the University of Hawaii. “If we continue on the emissions path we are on right now, acidification of the surface ocean will be way more dramatic than during the PETM.”

Ocean acidification in the modern ocean may already be affecting some marine life, as shown by the partly dissolved shell of this planktic snail, or pteropod, caught off the Pacific Northwest.

The study confirms that the acidified conditions lasted for 70,000 years or more, consistent with previous model-based estimates.

“It didn’t bounce back right away,” said Timothy Bralower, a researcher at Penn State who was not involved in the study. “It took tens of thousands of years to recover.”

From seafloor sediments drilled off Japan, the researchers analyzed the shells of plankton that lived at the surface of the ocean during the PETM. Two different methods for measuring ocean chemistry at the time-the ratio of boron isotopes in their shells, and the amount of boron –arrived at similar estimates of acidification. “It’s really showing us clear evidence of a change in pH for the first time,” said Bralower.

What caused the burst of carbon at the PETM is still unclear. One popular explanation is that an overall warming trend may have sent a pulse of methane from the seafloor into the air, setting off events that released more earth-warming gases into the air and oceans. Up to half of the tiny animals that live in mud on the seafloor-benthic foraminifera-died out during the PETM, possibly along with life further up the food chain.

Other species thrived in this changed environment and new ones evolved. In the oceans, dinoflagellates extended their range from the tropics to the Arctic, while on land, hoofed animals and primates appeared for the first time. Eventually, the oceans and atmosphere recovered as elements from eroded rocks washed into the sea and neutralized the acid.

Today, signs are already emerging that some marine life may be in trouble. In a recent study led by Nina Bednarsek at the U.S. National Oceanic and Atmospheric Administration, more than half of the tiny planktic snails, or pteropods, that she and her team studied off the coast of Washington, Oregon and California showed badly dissolved shells. Ocean acidification has been linked to the widespread death of baby oysters off Washington and Oregon since 2005, and may also pose a threat to coral reefs, which are under additional pressure from pollution and warming ocean temperatures.

“Seawater carbonate chemistry is complex but the mechanism underlying ocean acidification is very simple,” said study lead author Donald Penman, a graduate student at University of California at Santa Cruz. “We can make accurate predictions about how carbonate chemistry will respond to increasing carbon dioxide levels. The real unknown is how individual organisms will respond and how that cascades through ecosystems.”

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.”

Forest emissions, wildfires explain why ancient Earth was so hot

This photo shows Nadine Unger with Yale University's omega supercomputer. -  Photo by Matthew Garrett/Yale School of Forestry & Environmental Studies
This photo shows Nadine Unger with Yale University’s omega supercomputer. – Photo by Matthew Garrett/Yale School of Forestry & Environmental Studies

The release of volatile organic compounds from Earth’s forests and smoke from wildfires 3 million years ago had a far greater impact on global warming than ancient atmospheric levels of carbon dioxide, a new Yale study finds.

The research provides evidence that dynamic atmospheric chemistry played an important role in past warm climates, underscoring the complexity of climate change and the relevance of natural components, according to the authors. They do not address or dispute the significant role in climate change of human-generated CO2 emissions.

Using sophisticated Earth system modeling, a team led by Nadine Unger of the Yale School of Forestry & Environmental Studies (F&ES) calculated that concentrations of tropospheric ozone, aerosol particles, and methane during the mid-Pliocene epoch were twice the levels observed in the pre-industrial era – largely because so much more of the planet was covered in forest.

Those reactive compounds altered Earth’s radiation balance, contributing a net global warming as much as two to three times greater than the effect of carbon dioxide, according to the study, published in the journal Geophysical Research Letters.

These findings help explain why the Pliocene was two to three degrees C warmer than the pre-industrial era despite atmospheric levels of carbon dioxide that were approximately the same as today, Unger said.

“The discovery is important for better understanding climate change throughout Earth’s history, and has enormous implications for the impacts of deforestation and the role of forests in climate protection strategies,” said Unger, an assistant professor of atmospheric chemistry at F&ES.

“The traditional view,” she said, “is that forests affect climate through carbon storage and by altering the color of the planet’s surface, thus influencing the albedo effect. But as we are learning, there are other ways that forest ecosystems can impact the climate.”

The albedo effect refers to the amount of radiation reflected by the surface of the planet. Light-colored snowy surfaces, for instance, reflect more light and heat back into space than darker forests.

Climate scientists have suggested that the Pliocene epoch might provide a glimpse of the planet’s future if humankind is unable to curb carbon dioxide emissions. During the Pliocene, the two main factors believed to influence the climate – atmospheric CO2 concentrations and the geographic position of the continents – were nearly identical to modern times. But scientists have long wondered why the Pliocene’s global surface air temperatures were so much warmer than Earth’s pre-industrial climate.

The answer might be found in highly reactive compounds that existed long before humans lived on the planet, Unger says. Terrestrial vegetation naturally emits vast quantities of volatile organic compounds, for instance. These are critical precursors for organic aerosols and ozone, a potent greenhouse gas. Wildfires, meanwhile, are a major source of black carbon and primary organic carbon.

Forest cover was vastly greater during the Pliocene, a period marked not just by warmer temperatures but also by greater precipitation. At the time, most of the arid and semi-arid regions of Africa, Australia, and the Arabian peninsula were covered with savanna and grassland. Even the Arctic had extensive forests. Notably, Unger says, there were no humans to cut the forests down.

Using the NASA Goddard Institute for Space Studies Model-E2 global Earth system model, the researchers were able to simulate the terrestrial ecosystem emissions and atmospheric chemical composition of the Pliocene and the pre-industrial era.

According to their findings, the increase in global vegetation was the dominant driver of emissions during the Pliocene – and the subsequent effects on climate.

Previous studies have dismissed such feedbacks, suggesting that these compounds would have had limited impact since they would have been washed from the atmosphere by frequent rainfall in the warmer climate. The new study argues otherwise, saying that the particles lingered about the same length of time – one to two weeks – in the Pliocene atmosphere compared to the pre-industrial.

Unger says her findings imply a higher climate sensitivity than if the system was simply affected by CO2 levels and the albedo effect.

“We might do a lot of work to reduce air pollution from road vehicle and industrial emissions, but in a warmer future world the natural ecosystems are just going to bring the ozone and aerosol particles right back,” she said. “Reducing and preventing the accumulation of fossil-fuel CO2 is the only way to ensure a safe climate future now.”

The modeling calculations were performed on Yale University’s omega supercomputer, a 704-node cluster capable of processing more than 52 trillion calculations per second.

Rainforests in Far East shaped by humans for the last 11,000 years

New research from Queen’s University Belfast shows that the tropical forests of South East Asia have been shaped by humans for the last 11,000 years.

The rain forests of Borneo, Sumatra, Java, Thailand and Vietnam were previously thought to have been largely unaffected by humans, but the latest research from Queen’s Palaeoecologist Dr Chris Hunt suggests otherwise.

A major analysis of vegetation histories across the three islands and the SE Asian mainland has revealed a pattern of repeated disturbance of vegetation since the end of the last ice age approximately 11,000 years ago.

The research, which was funded by the Arts and Humanities Research Council and the British Academy, is being published in the Journal of Archaeological Science. It is the culmination of almost 15 years of field work by Dr Hunt, involving the collection of pollen samples across the region, and a major review of existing palaeoecology research, which was completed in partnership with Dr Ryan Rabett from Cambridge University.

Evidence of human activity in rainforests is extremely difficult to find and traditional archaeological methods of locating and excavating sites are extremely difficult in the dense forests. Pollen samples, however, are now unlocking some of the region’s historical secrets.

Dr Hunt, who is Director of Research on Environmental Change at Queen’s School of Geography, Archaeology and Palaeoecology, said: “It has long been believed that the rainforests of the Far East were virgin wildernesses, where human impact has been minimal. Our findings, however, indicate a history of disturbances to vegetation. While it could be tempting to blame these disturbances on climate change, that is not the case as they do not coincide with any known periods of climate change. Rather, these vegetation changes have been brought about by the actions of people.

“There is evidence that humans in the Kelabit Highlands of Borneo burned fires to clear the land for planting food-bearing plants. Pollen samples from around 6,500 years ago contain abundant charcoal, indicating the occurrence of fire. However, while naturally occurring or accidental fires would usually be followed by specific weeds and trees that flourish in charred ground, we found evidence that this particular fire was followed by the growth of fruit trees. This indicates that the people who inhabited the land intentionally cleared it of forest vegetation and planted sources of food in its place.

“One of the major indicators of human action in the rainforest is the sheer prevalence of fast-growing ‘weed’ trees such as Macaranga, Celtis and Trema. Modern ecological studies show that they quickly follow burning and disturbance of forests in the region.

“Nearer to the Borneo coastline, the New Guinea Sago Palm first appeared over 10,000 years ago. This would have involved a voyage of more than 2,200km from its native New Guinea, and its arrival on the island is consistent with other known maritime voyages in the region at that time – evidence that people imported the Sago seeds and planted them.”

The findings have huge importance for ecological studies or rainforests as the historical role of people in managing the forest vegetation has rarely been considered. It could also have an impact on rainforest peoples fighting the advance of logging companies.

Dr Hunt continued: “Laws in several countries in South East Asia do not recognise the rights of indigenous forest dwellers on the grounds that they are nomads who leave no permanent mark on the landscape. Given that we can now demonstrate their active management of the forests for more than 11,000 years, these people have a new argument in their case against eviction.”