Paleotempestology and 2011’s Hurricane Irene

Hurricane Irene made landfall in Onslow Bay, N.C., USA, on Aug. 27, 2011. Satellite image courtesy NASA. -  NASA
Hurricane Irene made landfall in Onslow Bay, N.C., USA, on Aug. 27, 2011. Satellite image courtesy NASA. – NASA

A new study published in the December issue of GSA Today examines the geological legacy of Hurricane Irene, not only in terms of its impact on current coastal conditions but also in what it can tell geoscientists about the past. Hurricane Irene made landfall in Onslow Bay, North Carolina, USA, on 27 August 2011, at which time it had been downgraded to a Category 1 hurricane after hitting the Bahamas at Category 3 strength.

In their GSA Today article, geoscientists Scott P. Hippensteel, Matthew D. Eastin, and William J. Garcia of the University of North Carolina at Charlotte call for a better understanding of the long-term record of storm frequency and impact, not only because of the increase in the strength of storms hitting coastal areas but also because of the high population density in vulnerable areas along the U.S. East Coast and Gulf Coast.

Those who study the paleo-storm record explain that gaining understanding of past events provides the context for future coastal vulnerability. Hippensteel and colleagues apply evidence of what they call the “lack of a definitive signature” from Hurricane Irene to a 1500-year paleostorm record at Onslow Bay. They write that fewer hurricanes could be found in the fossil and sedimentary records (through bioturbation or foraminiferal dissolution) than had actually made landfall there.

The authors infer that the lack of storm records in the marsh sediments from Onslow Bay means that only hurricane strikes of higher magnitude can provide proxies for understanding the paleostorm record, because only the most robust storm deposits are archived. The lack of definitive signs of Hurricane Irene in the area raises their concerns about the current understanding of hurricane deposition and preservation.

Rain as acidic as lemon juice may have contributed to ancient mass extinction

Rain as acidic as undiluted lemon juice may have played a part in killing off plants and organisms around the world during the most severe mass extinction in Earth’s history.

About 252 million years ago, the end of the Permian period brought about a worldwide collapse known as the Great Dying, during which a vast majority of species went extinct.

The cause of such a massive extinction is a matter of scientific debate, centering on several potential causes, including an asteroid collision, similar to what likely killed off the dinosaurs 186 million years later; a gradual, global loss of oxygen in the oceans; and a cascade of environmental events triggered by massive volcanic eruptions in a region known today as the Siberian Traps.

Now scientists at MIT and elsewhere have simulated this last possibility, creating global climate models of scenarios in which repeated bursts of volcanism spew gases, including sulfur, into the atmosphere. From their simulations, they found that sulfur emissions were significant enough to create widespread acid rain throughout the Northern Hemisphere, with pH levels reaching 2 – as acidic as undiluted lemon juice. They say such acidity may have been sufficient to disfigure plants and stunt their growth, contributing to their ultimate extinction.

“Imagine you’re a plant that’s growing happily in the latest Permian,” says Benjamin Black, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “It’s been getting hotter and hotter, but perhaps your species has had time to adjust to that. But then quite suddenly, over the course of a few months, the rain begins to sizzle with sulfuric acid. It would be quite a shock if you were that plant.”

Black is lead author of a paper reporting the group’s results, which appears in the journal Geology. Co-authors include Jean-Fran├žois Lamarque, Christine Shields, and Jeffrey Kiehl from the National Center for Atmospheric Research and Linda Elkins-Tanton of the Carnegie Institution for Science.

Lemon juice spike

Geologists who have examined the rock record in Siberia have observed evidence of immense volcanism that came in short bursts beginning near the end of the Permian period and continuing for another million years. The volume of magma totaled several million cubic kilometers – enough to completely blanket the continental United States. This boiling stew of magma likely released carbon dioxide and other gases into the atmosphere, leading to gradual but powerful global warming.

The eruptions may also have released large clouds of sulfur, which ultimately returned to Earth’s surface as acid rain. Black, who has spent several summers in Siberia collecting samples to measure sulfur and other chemicals preserved in igneous rocks, used these measurements, along with other evidence, to develop simulations of magmatic activity in the end-Permian world.

The group simulated 27 scenarios, each approximating the release of gases from a plausible volcanic episode, including medium eruptions, large eruptions, and magma erupted through explosive pipes in the Earth’s crust. The researchers included a wide range of gases in their simulations, based on estimates from chemical analyses and thermal modeling. They then tracked water in the atmosphere, and the interactions among various gases and aerosols, to calculate the pH of rain.

The results showed that both carbon dioxide and volcanic sulfur could have significantly affected the acidity of rain at the end of the Permian. Levels of carbon dioxide and other greenhouse gases may have risen rapidly at the time, in part because of Siberian volcanism. According to their simulations, the researchers found that this elevated carbon dioxide could have increased rain’s acidity by an order of magnitude.

Adding sulfur emissions to the mix, they found that acidity further spiked to a pH of 2 – as acidic as undiluted lemon juice – and that such acidic rain may have fallen over most of the Northern Hemisphere. After an eruption ended, the researchers found that pH levels in rain bounced back, becoming less acidic within one year. However, with repeated bursts of volcanic activity, Black says the resulting swings in acid rain could have greatly stressed terrestrial species.

“Plants and animals wouldn’t have much time to adapt to these changes in the pH of rain,” Black says. “I think it certainly contributed to the environmental stress which was making it difficult for plants and animals to survive. At a certain point you have to ask, ‘How much can a plant take?'”

Life as an end-Permian organism

In addition to acid rain, the researchers modeled ozone depletion resulting from volcanic activity. While ozone depletion is more difficult to model than acid rain, their results suggest that a mix of gases released into the atmosphere may have destroyed 5 to 65 percent of the ozone layer, substantially increasing species’ exposure to ultraviolet radiation. The greatest ozone depletion occurred near the poles.

Going forward, Black hopes paleontologists and geochemists will consider the results as a point of comparison for their own observations of the end-Permian mass extinction. In the meantime, he says he now has a much more vivid picture of that catastrophic time.

“It’s not just one thing that was unpleasant,” Black says. “It’s this whole host of really nasty atmospheric and environmental effects. These results really made me feel sorry for end-Permian organisms.”

Ancient minerals: Which gave rise to life?

The magnesium silicate forsterite was one of the most abundant minerals in the Hadean Eon, and it played a major role in Earth's near-surface processes. The green color of this mineral (which is also known as the semi-precious gemstone peridot, the birthstone of August) is caused by small amounts iron. The iron can react with seawater to promote chemical reactions that may have played a role in life's origins. -  Robert Downs, University of Arizona, Ruff Project
The magnesium silicate forsterite was one of the most abundant minerals in the Hadean Eon, and it played a major role in Earth’s near-surface processes. The green color of this mineral (which is also known as the semi-precious gemstone peridot, the birthstone of August) is caused by small amounts iron. The iron can react with seawater to promote chemical reactions that may have played a role in life’s origins. – Robert Downs, University of Arizona, Ruff Project

Life originated as a result of natural processes that exploited early Earth’s raw materials. Scientific models of life’s origins almost always look to minerals for such essential tasks as the synthesis of life’s molecular building blocks or the supply of metabolic energy. But this assumes that the mineral species found on Earth today are much the same as they were during Earth’s first 550 million years-the Hadean Eon-when life emerged. A new analysis of Hadean mineralogy challenges that assumption. It is published in American Journal of Science.

Carnegie’s Robert Hazen compiled a list of every plausible mineral species on the Hadean Earth and concludes that no more than 420 different minerals-about 8 percent of the nearly 5,000 species found on Earth today-would have been present at or near Earth’s surface.

“This is a consequence of the limited ways that minerals might have formed prior to 4 billion years ago,” Hazen explained. “Most of the 420 minerals of the Hadean Eon formed from magma-molten rock that slowly crystallized at or near Earth’s surface-as well as the alteration of those minerals when exposed to hot water.”

By contrast, thousands of mineral species known today are the direct result of growth by living organisms, such as shells and bones, as well as life’s chemical byproducts, such as oxygen from photosynthesis. In addition, hundreds of other minerals that incorporate relatively rare elements such as lithium, beryllium, and molybdenum appear to have taken a billion years or more to first appear because it is difficult to concentrate these elements sufficiently to form new minerals. So those slow-forming minerals are also excluded from the time of life’s origins.

“Fortunately for most origin-of-life models, the most commonly invoked minerals were present on early Earth,” Hazen said.

For example, clay minerals-sometimes theorized by chemists to trigger interesting reactions-were certainly available. Sulfide minerals, including reactive iron and nickel varieties, were also widely available to catalyze organic reactions. However, borate and molybdate minerals, which are relatively rare even today, are unlikely to have occurred on the Hadean Earth and call into question origin models that rely on those mineral groups.

Several questions remain unanswered and offer opportunities for further study of the paleomineralogy of the Hadean Eon. For example, the Hadean Eon differs from today in the frequent large impacts of asteroids and comets-thousands of collisions by objects with diameters from a mile up to 100 miles. Such impacts would have caused massive disruption of Earth’s crust, with extensive fracture zones that were filled with hot circulating water. Such hydrothermal areas could have created complex zones with many exotic minerals.

This study also raises the question of how other planets and moons evolved mineralogically. Hazen suggests that Mars today may have progressed only as far as Earth’s Hadean Eon. As such, Mars may be limited to a similar suite of no more than about 400 different mineral species. Thanks to the Curiosity rover, we may soon know if that’s the case.

Acid raid, ozone depletion contributed to ancient extinction

This photo taken along Kotuy River in Arctic Siberia shows the base of the Siberian Traps volcanic sequence. -  Benjamin Black
This photo taken along Kotuy River in Arctic Siberia shows the base of the Siberian Traps volcanic sequence. – Benjamin Black

Around 250 million years ago, at the end of the Permian period, there was a mass extinction so severe that it remains the most traumatic known species die-off in Earth’s history. Some researchers have suggested that this extinction was triggered by contemporaneous volcanic eruptions in Siberia. New results from a team including Director of Carnegie’s Department of Terrestrial Magnetism Linda Elkins-Tanton show that the atmospheric effects of these eruptions could have been devastating. Their work is published in Geology.

The mass extinction included the sudden loss of more than 90 percent of marine species and more than 70 percent of terrestrial species and set the stage for the rise of the dinosaurs. The fossil record suggests that ecological diversity did not fully recover until several million years after the main pulse of the extinction.One leading candidate for the cause of this event is gas released from a large swath of volcanic rock in Russia called the Siberian Traps. Using advanced 3-D modeling techniques, the team, led by Benjamin Black of the Massachusetts Institute of Technology, was able to predict the impacts of gas released from the Siberian Traps on the end-Permian atmosphere.

Their results indicate that volcanic releases of both carbon dioxide (CO2) and sulfur dioxide (SO2) could have created highly acidic rain, potentially leaching the soil of nutrients and damaging plants and other vulnerable terrestrial organisms. Releases of halogen-bearing compounds such as methyl chloride could also have resulted in global ozone collapse.

The volcanic activity was likely episodic, producing pulses of acid rain and ozone depletion. The team concluded that the resulting drastic fluctuations in pH and ultraviolet radiation, combined with an overall temperature increase from greenhouse gas emissions, could have contributed to the end-Permian mass extinction on land.

The team also included Jean-Fran├žois Lamarque, Christine Shields, and Jeffrey Kiehl of the National Center for Atmospheric Research.

Early-career investigator discovers current volcanic activity under West Antarctica

This image shows a researcher digging out a seismographic instrument in Antarctica. -  Douglas Wiens, Washington University in St. Louis
This image shows a researcher digging out a seismographic instrument in Antarctica. – Douglas Wiens, Washington University in St. Louis

Scientists funded by the National Science Foundation (NSF) have observed “swarms” of seismic activity–thousands of events in the same locations, sometimes dozens in a single day–between January 2010 and March 2011, indicating current volcanic activity under the massive West Antarctic Ice Sheet (WAIS).

Previous studies using aerial radar and magnetic data detected the presence of subglacial volcanoes in West Antarctica, but without visible eruptions or seismic instruments recording data, the activity status of those systems ranged from extinct to unknown. However, as Amanda Lough, a doctoral candidate at Washington University in St. Louis, points out, “Just because we can’t see …below the ice, doesn’t mean there’s not something going on there.”

“This [study] is saying that we have seismicity, which means [this system] is active right now,” according to Lough. “This is saying that the magmatic chamber is still alive; that there is magma that is moving around in the crust.”

Lough published her discovery in this week’s issue of Nature Geoscience along with her advisor Douglas Wiens, a professor of earth and planetary sciences at Washington University in St. Louis, and a team of co-authors.

NSF has a presidential mandate to manage the U.S. Antarctic Program, through which it coordinates all U.S. science on the Southernmost continent and in the Southern Ocean and the logistical support which makes the science possible.

The characteristics of the seismic events, including the 25- to 40-kilometer (15- to 25-mile) depth at which they occurred, the low frequency of the seismic waves, and the swarm-like behavior rule out glacial and tectonic sources, but are typical of deep long-period earthquakes. Deep long-period earthquakes indicate active magma moving within the Earth’s crust and are most often associated with volcanic activity.

The two swarms of seismic activity were detected by instruments deployed to obtain data on the behavior of the WAIS as part of the NSF-funded POLENET project, a global network of GPS and seismic stations. Wiens is a POLENET principal investigator.

Lough plotted the location of the swarms and realized their proximity to the Executive Committee Range, a cluster of volcanoes that were believed to be dormant, in Marie Byrd Land. She consulted with a volcanic seismologist to confirm that the frequency content and the waveforms of the seismic signals were indicative of a volcanic system.

The location of the current seismicity, about 55-60 kilometers (34-37 miles) south of Mt. Sidley, is where current volcanic activity would be predicted to occur based on the geographic locations and the ages of the lava of the known volcanoes in the Executive Committee Range. The seismic swarms were also located near a subglacial high-point of elevation and magnetic anomalies which are both indicative of a volcano.

In some volcanic systems, deep long period earthquakes can indicate an imminent eruption, but Lough sent samples of her data to volcano seismologists who “didn’t see seismic events that would occur during an eruption.” However, the elevation in bed topography did indicate to Lough and her colleagues that this newly discovered volcano had erupted in the past.

Radar data showed an ash layer trapped within the ice directly above the area of seismic and magmatic activity. Lough initially thought that the ash layer might have evidence of a past eruption from the volcano detected in this study, but based on the distribution of the materials and the prevailing winds, the ash most likely came from an eruption of nearby Mt. Waesche about 8000 years ago. The dating of the ash layer did confirm that Mt. Waesche, believed to have last been active around 100,000 years ago, erupted much more recently than previously thought.

Only an extremely powerful eruption from the active magmatic complex discovered in this study would break through the 1- to 1.5-kilometer (0.6-0.9 miles) thick ice sheet overlying the area, but this research extends the range of active volcanism deeper into the interior of the WAIS than previously known. Should an eruption occur at this location, the short-term increase in heat could cause additional melting of the bottom of the ice sheet, thereby increasing the bed lubrication and hastening ice loss from WAIS.

New study determines more accurate method to date tropical glacier moraines

The Quelccaya Ice Cap, the world's largest tropical ice sheet, is rapidly melting. -  Meredith Kelly
The Quelccaya Ice Cap, the world’s largest tropical ice sheet, is rapidly melting. – Meredith Kelly

A Dartmouth-led team has found a more accurate method to determine the ages of boulders deposited by tropical glaciers, findings that will likely influence previous research of how climate change has impacted ice masses around the equator.

The study appears in the journal Quaternary Geochronology. A PDF of the study is available on request.

Scientists use a variety of dating methods to determine the ages of glacial moraines around the world, from the poles where glaciers are at sea level to the tropics where glaciers are high in the mountains. Moraines are sedimentary deposits that mark the past extents of glaciers. Since glaciers respond sensitively to climate, especially at high latitudes and high altitudes, the timing of glacial fluctuations marked by moraines can help scientists to better understand past climatic variations and how glaciers may respond to future changes.

In the tropics, glacial scientists commonly use beryllium-10 surface exposure dating. Beryllium-10 is an isotope of beryllium produced when cosmic rays strike bedrock that is exposed to air. Predictable rates of decay tell scientists how long ago the isotope was generated and suggest that the rock was covered in ice before then. Elevation, latitude and other factors affect the rate at which beryllium-10 is produced, but researchers typically use rates taken from calibration sites scattered around the globe rather than rates locally calibrated at the sites being studied.

The Dartmouth-led team looked at beryllium-10 concentrations in moraine boulders deposited by the Quelccaya Ice Cap, the largest ice mass in the tropics. Quelccaya, which sits 18,000 feet above sea level in the Peruvian Andes, has retreated significantly in recent decades. The researchers determined a new locally calibrated production rate that is at least 11 percent to 15 percent lower than the traditional global production rate.

“The use of our locally calibrated beryllium-10 production rate will change the surface exposure ages reported in previously published studies at low latitude, high altitude sites and may alter prior paleoclimate interpretations,” said Assistant Professor Meredith Kelly, the study’s lead author and a glacial geomorphologist at Dartmouth.

The new production rate yields beryllium-10 ages that are older than previously reported, which means the boulders were exposed for longer than previously estimated. Prior studies suggested glaciers in the Peruvian Andes advanced during early Holocene time 8,000 -10,000 years ago, a period thought to have been warm but perhaps wet in the Andes. But the new production rate pushes back the beryllium-10 ages to 11,000 -12,000 years ago when the tropics were cooler and drier. Also during this time, glaciers expanded in the northern hemisphere, which indicates a relationship between the climate mechanisms that caused cooling in the northern hemisphere and southern tropics.

The findings suggest the new production rate should be used to deliver more precise ages of moraines in low-latitude, high-altitude locations, particularly in the tropical Andes. Such precision can help scientists to more accurately reconstruct past glacial and climatic variations, Kelly said.

Volcano discovered smoldering under a kilometer of ice in West Antarctica

Mount Sidley, at the leading edge of the Executive Committee Range in Marie Byrd Land is the last volcano in the chain that rises above the surface of the ice. But a group of seismologists has detected new volcanic activity under the ice about 30 miles ahead of Mount Sidley in the direction of the range's migration. The new finding suggests that the source of magma is moving beyond the chain beneath the crust and the Antarctic Ice Sheet. -  Doug Wiens
Mount Sidley, at the leading edge of the Executive Committee Range in Marie Byrd Land is the last volcano in the chain that rises above the surface of the ice. But a group of seismologists has detected new volcanic activity under the ice about 30 miles ahead of Mount Sidley in the direction of the range’s migration. The new finding suggests that the source of magma is moving beyond the chain beneath the crust and the Antarctic Ice Sheet. – Doug Wiens

It wasn’t what they were looking for but that only made the discovery all the more exciting.

In January 2010 a team of scientists had set up two crossing lines of seismographs across Marie Byrd Land in West Antarctica. It was the first time the scientists had deployed many instruments in the interior of the continent that could operate year-round even in the coldest parts of Antarctica.

Like a giant CT machine, the seismograph array used disturbances created by distant earthquakes to make images of the ice and rock deep within West Antarctica.

There were big questions to be asked and answered. The goal, says Doug Wiens, professor of earth and planetary science at Washington University in St. Louis and one of the project’s principle investigators, was essentially to weigh the ice sheet to help reconstruct Antarctica’s climate history. But to do this accurately the scientists had to know how the earth’s mantle would respond to an ice burden, and that depended on whether it was hot and fluid or cool and viscous. The seismic data would allow them to map the mantle’s properties.

In the meantime, automated-event-detection software was put to work to comb the data for anything unusual.

When it found two bursts of seismic events between January 2010 and March 2011, Wiens’ PhD student Amanda Lough looked more closely to see what was rattling the continent’s bones.

Was it rock grinding on rock, ice groaning over ice, or, perhaps, hot gases and liquid rock forcing their way through cracks in a volcanic complex?

Uncertain at first, the more Lough and her colleagues looked, the more convinced they became that a new volcano was forming a kilometer beneath the ice.

The discovery of the new as yet unnamed volcano is announced in the Nov. 17 advanced online issue of Nature Geoscience.

Following the trail of clues

The teams that install seismographs in Antarctica are given first crack at the data. Lough had done her bit as part of the WUSTL team, traveling to East Antarctica three times to install or remove stations in East Antarctica.

In 2010 many of the instruments were moved to West Antarctica and Wiens asked Lough to look at the seismic data coming in, the first large-scale dataset from this part of the continent.

“I started seeing events that kept occurring at the same location, which was odd, “Lough said. “Then I realized they were close to some mountains-but not right on top of them.”

“My first thought was, ‘Okay, maybe its just coincidence.’ But then I looked more closely and realized that the mountains were actually volcanoes and there was an age progression to the range. The volcanoes closest to the seismic events were the youngest ones.”

The events were weak and very low frequency, which strongly suggested they weren’t tectonic in origin. While low-magnitude seismic events of tectonic origin typically have frequencies of 10 to 20 cycles per second, this shaking was dominated by frequencies of 2 to 4 cycles per second.

Ruling out ice

But glacial processes can generate low-frequency events. If the events weren’t tectonic could they be glacial?

To probe farther, Lough used a global computer model of seismic velocities to “relocate” the hypocenters of the events to account for the known seismic velocities along different paths through the Earth. This procedure collapsed the swarm clusters to a third their original size.

It also showed that almost all of the events had occurred at depths of 25 to 40 kilometers (15 to 25 miles below the surface). This is extraordinarily deep-deep enough to be near the boundary between the earth’s crust and mantle, called the Moho, and more or less rules out a glacial origin.

It also casts doubt on a tectonic one. “A tectonic event might have a hypocenter 10 to 15 kilometers (6 to 9 miles) deep, but at 25 to 40 kilometers, these were way too deep,” Lough says.

A colleague suggested that the event waveforms looked like Deep Long Period earthquakes, or DPLs, which occur in volcanic areas, have the same frequency characteristics and are as deep. “Everything matches up,” Lough says.

An ash layer encased in ice

The seismologists also talked to Duncan Young and Don Blankenship of the University of Texas who fly airborne radar over Antarctica to produce topographic maps of the bedrock. “In these maps, you can see that there’s elevation in the bed topography at the same location as the seismic events,” Lough says.

The radar images also showed a layer of ash buried under the ice. “They see this layer all around our group of earthquakes and only in this area,” Lough says.

“Their best guess is that it came from Mount Waesche, an existing volcano near Mt Sidley. But that is also interesting because scientists had no idea when Mount Waesche was last active, and the ash layer is sets the age of the eruption at 8,000 years ago. “

What’s up down there?

The case for volcanic origin has been made. But what exactly is causing the seismic activity?

“Most mountains in Antarctica are not volcanic,” Wiens says, “but most in this area are. Is it because East and West Antarctica are slowly rifting apart? We don’t know exactly. But we think there is probably a hot spot in the mantle here producing magma far beneath the surface.”

“People aren’t really sure what causes DPLs,” Lough says. “It seems to vary by volcanic complex, but most people think it’s the movement of magma and other fluids that leads to pressure-induced vibrations in cracks within volcanic and hydrothermal systems.”

Will the new volcano erupt?

“Definitely,” Lough says. “In fact because of the radar shows a mountain beneath the ice I think it has erupted in the past, before the rumblings we recorded.

Will the eruptions punch through a kilometer or more of ice above it?

The scientists calculated that an enormous eruption, one that released a thousand times more energy than the typical eruption, would be necessary to breach the ice above the volcano.

On the other hand a subglacial eruption and the accompanying heat flow will melt a lot of ice. “The volcano will create millions of gallons of water beneath the ice-many lakes full,” says Wiens. This water will rush beneath the ice towards the sea and feed into the hydrological catchment of the MacAyeal Ice Stream, one of several major ice streams draining ice from Marie Byrd Land into the Ross Ice Shelf.

By lubricating the bedrock, it will speed the flow of the overlying ice, perhaps increasing the rate of ice-mass loss in West Antarctica.

“We weren’t expecting to find anything like this,” Wiens says

Oxygen, phosphorous and early life on Earth

Two billion years ago the Earth system was recovering from perhaps the single-most profound modification of its surface environments: the oxygenation of the atmosphere and oceans. This led to a series of major changes in global biogeochemical cycles, as a team around Aivo Lepland of the Norwegian Geological Survey NGU reports in the latest online edition of “Nature Geoscience“.

This also resulted in the distribution of one of life’s key elements, phosphorous. Studies on the unique organic-rich Zaonega rock formation preserved in Carelia, NW Russia, with an age of around two billion years has revealed an astonishing result: “The formation of Earth’s earliest phosphorites was influenced strongly, if not controlled completely, by the activity of sulfur bacteria”, says co-author Richard Wirth of the GFZ German Research Centre for Geosciences, who analyzed the rock samples with an electron microscope. “This activity occurred in an oil field setting that had been influenced by active volcanism and associated venting and seeping.” In the modern world, sulfur bacteria inhabit upwelling vent and seep areas known as “Black Smokers” and mediate phosphorite formation. The authors therefore conclude that the formation of the earliest worldwide phosphorites 2 billion years ago can be linked to the establishment of sulfur bacteria habitats, triggered by the oxygenation of the Earth.

Amber provides new insights into the evolution of the Earth’s atmosphere

<IMG SRC="/Images/22324740.jpg" WIDTH="350" HEIGHT="233" BORDER="0" ALT="The team analyzed amber samples from almost all well-known amber deposits worldwide. This amber originates from the Cretaceous period, an inclusion of foilage of the extinct conifer tree Parataxodium sp. from the Foremost Formation at Grassy Lake, Alberta, Canada. It is approximately 77 million years old. – Ryan C. McKellar”>
The team analyzed amber samples from almost all well-known amber deposits worldwide. This amber originates from the Cretaceous period, an inclusion of foilage of the extinct conifer tree Parataxodium sp. from the Foremost Formation at Grassy Lake, Alberta, Canada. It is approximately 77 million years old. – Ryan C. McKellar

Scientists encounter big challenges when reconstructing atmospheric compositions in the Earth’s geological past because of the lack of useable sample material. One of the few organic materials that may preserve reliable data of the Earth’s geological history over millions of years are fossil resins (e.g. amber). “Compared to other organic matter, amber has the advantage that it remains chemically and isotopically almost unchanged over long periods of geological time,” explains Ralf Tappert from the Institute of Mineralogy and Petrography at the University of Innsbruck. The mineralogist and his colleagues from the University of Alberta in Canada and universities in the USA and Spain have produced a comprehensive study of the chemical composition of the Earth’s atmosphere since the Triassic period. The study has been published in the journal Geochimica et Cosmochimica Acta. The interdisciplinary team, consisting of mineralogists, paleontologists and geochemists, use the preserving properties of plant resins, caused by polymerization, for their study. “During photosynthesis plants bind atmospheric carbon, whose isotopic composition is preserved in resins over millions of years, and from this, we can infer atmospheric oxygen concentrations,” explains Ralf Tappert. The information about oxygen concentration comes from the isotopic composition of carbon or rather from the ratio between the stable carbon isotopes 12C and 13C.

Atmospheric oxygen between 10 and 15 percent

The research team analyzed a total of 538 amber samples from from well-known amber deposits worldwide, with the oldest samples being approximately 220 million years old and recovered from the Dolomites in Italy. The team also compared fossil amber with modern resins to test the validity of the data. The results of this comprehensive study suggest that atmospheric oxygen during most of the past 220 million years was considerably lower than today’s 21 percent. “We suggest numbers between 10 and 15 percent,” says Tappert. These oxygen concentrations are not only lower than today but also considerably lower than the majority of previous investigations propose for the same time period. For the Cretaceous period (65 – 145 million years ago), for example, up to 30 percent atmospheric oxygen has been suggested previously.

Effects on climate and environment

The researchers also relate this low atmospheric oxygen to climatic developments in the Earth’s history. “We found that particularly low oxygen levels coincided with intervals of elevated global temperatures and high carbon dioxide concentrations,” explains Tappert. The mineralogist suggests that oxygen may influence carbon dioxide levels and, under certain circumstances, might even accelerate the influx of carbon dioxide into the atmosphere. “Basically, we are dealing here with simple oxidation reactions that are amplified particularly during intervals of high temperatures such as during the Cretaceous period.” The researchers, thus, conclude that an increase in carbon dioxide levels caused by extremely strong vulcanism was accompanied by a decrease of atmospheric oxygen. This becomes particularly apparent when looking at the last 50 million years of geological history. Following the results of this study, the comparably low temperatures of the more recent past (i.e. the Ice Ages) may be attributed to the absence of large scale vulcanism events and an increase in atmospheric oxygen.

Oxygen may not be the cause of gigantism

According to the results of the study, oxygen may indirectly influence the climate. This in turn may also affect the evolution of life on Earth. A well-known example are dinosaurs: Many theories about animal gigantism offer high levels of atmospheric oxygen as an explanation. Tappert now suggests to reconsider these theories: “We do not want to negate the influence of oxygen for the evolution of life in general with our study, but the gigantism of dinosaurs cannot be explained by those theories.” The research team highly recommends conducting further studies and intends to analyze even older plant resins.

Underwater ‘tree rings’

This alga can be found in coastal regions of the North Atlantic, North Pacific and Arctic Ocean, where it can live for hundreds of years. -  Nick Caloyianus
This alga can be found in coastal regions of the North Atlantic, North Pacific and Arctic Ocean, where it can live for hundreds of years. – Nick Caloyianus

Almost 650 years of annual change in sea-ice cover can been seen in the calcite crust growth layers of seafloor algae, says a new study from the University of Toronto Mississauga (UTM).

“This is the first time coralline algae have been used to track changes in Arctic sea ice,” says Jochen Halfar, an associate professor in UTM’s Department of Chemical and Physical Sciences. “We found the algal record shows a dramatic decrease in ice cover over the last 150 years.”

With colleagues from the Smithsonian Institution, Germany and Newfoundland, Halfar collected and analyzed samples of the alga Clathromorphum compactum. This long-lived plant species forms thick rock-like calcite crusts on the seafloor in shallow waters 15 to 17 metres deep. It is widely distributed in the Arctic and sub-Arctic Oceans.

Divers retrieved the specimens from near-freezing seawater during several research cruises led by Walter Adey from the Smithsonian.

The algae’s growth rates depend on the temperature of the water and the light they receive. As snow-covered sea ice accumulates on the water over the algae, it turns the sea floor dark and cold, stopping the plants’ growth. When the sea ice melts in the warm months, the algae resume growing their calcified crusts.

This continuous cycle of dormancy and growth results in visible layers that can be used to determine the length of time the algae were able to grow each year during the ice-free season.

“It’s the same principle as using rings to determine a tree’s age and the levels of precipitation,” says Halfar. “In addition to ring counting, we used radiocarbon dating to confirm the age of the algal layers.”

After cutting and polishing the algae, Halfar used a specialized microscope to take thousands of images of each sample. The images were combined to give a complete overview of the fist-sized specimens.

Halfar corroborated the length of the algal growth periods through the magnesium levels preserved in each growth layer. The amount of magnesium is dependent on both the light reaching the algae and the temperature of the sea water. Longer periods of open and warm water result in a higher amount of algal magnesium.

During the Little Ice Age, a period of global cooling that lasted from the mid-1500s to the mid-1800s, the algae’s annual growth increments were as narrow as 30 microns due to the extensive sea-ice cover, Halfar says. However, since 1850, the thickness of the algae’s growth increments have more than doubled, bearing witness to an unprecedented decline in sea ice coverage that has accelerated in recent decades.

Halfar says the coralline algae represent not only a new method for climate reconstruction, but are vital to extending knowledge of the climate record back in time to permit more accurate modeling of future climate change.

Currently, observational information about annual changes in the Earth’s temperature and climate go back 150 years. Reliable information about sea-ice coverage comes from satellites and dates back only to the late 1970s.

“In the north, there is nothing in the shallow oceans that tells us about climate, water temperature or sea ice coverage on an annual basis,” says Halfar. “These algae, which live over a thousand years, can now provide us with that information.”