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-François 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.”

‘Highway from hell’ fueled Costa Rican volcano

Volcanologist Philipp Ruprecht analyzed crystals formed as Irazú's magma cooled to establish how fast it traveled. -  Kim Martineau
Volcanologist Philipp Ruprecht analyzed crystals formed as Irazú’s magma cooled to establish how fast it traveled. – Kim Martineau

If some volcanoes operate on geologic timescales, Costa Rica’s Irazú had something of a short fuse. In a new study in the journal Nature, scientists suggest that the 1960s eruption of Costa Rica’s largest stratovolcano was triggered by magma rising from the mantle over a few short months, rather than thousands of years or more, as many scientists have thought. The study is the latest to suggest that deep, hot magma can set off an eruption fairly quickly, potentially providing an extra tool for detecting an oncoming volcanic disaster.

“If we had had seismic instruments in the area at the time we could have seen these deep magmas coming,” said the study’s lead author, Philipp Ruprecht, a volcanologist at Columbia University’s Lamont-Doherty Earth Observatory. “We could have had an early warning of months, instead of days or weeks.”

Towering more than 10,000 feet and covering almost 200 square miles, Irazú erupts about every 20 years or less, with varying degrees of damage. When it awakened in 1963, it erupted for two years, killing at least 20 people and burying hundreds of homes in mud and ash. Its last eruption, in 1994, did little damage.

Irazú sits on the Pacific Ring of Fire, where oceanic crust is slowly sinking beneath the continents, producing some of earth’s most spectacular fireworks. Conventional wisdom holds that the mantle magma feeding those eruptions rises and lingers for long periods of time in a mixing chamber several miles below the volcano. But ash from Irazú’s prolonged explosion is the latest to suggest that some magma may travel directly from the upper mantle, covering more than 20 miles in a few months.

“There has to be a conduit from the mantle to the magma chamber,” said study co-author Terry Plank, a geochemist at Lamont-Doherty. “We like to call it the highway from hell.”

Their evidence comes from crystals of the mineral olivine separated from the ashes of Irazú’s 1963-1965 eruption, collected on a 2010 expedition to the volcano. As magma rising from the mantle cools, it forms crystals that preserve the conditions in which they formed. Unexpectedly, Irazú’s crystals revealed spikes of nickel, a trace element found in the mantle. The spikes told the researchers that some of Irazú’s erupted magma was so fresh the nickel had not had a chance to diffuse.

“The study provides one more piece of evidence that it’s possible to get magma from the mantle to the surface in very short order,” said John Pallister, who heads the U.S. Geological Survey (USGS) Volcano Disaster Assistance Program in Vancouver, Wash. “It tells us there’s a potentially shorter time span we need to worry about.”

Deep, fast-rising magma has been linked to other big events. In 1991, Mount Pinatubo in the Philippines spewed so much gas and ash into the atmosphere that it cooled Earth’s climate. In the weeks before the eruption, seismographs recorded hundreds of deep earthquakes that USGS geologist Randall White later attributed to magma rising from the mantle-crust boundary. In 2010, a chain of eruptions at Iceland’s Eyjafjallajökull volcano that caused widespread flight cancellations also indicated that some magma was coming from down deep. Small earthquakes set off by the eruptions suggested that the magma in Eyjafjallajökull’s last two explosions originated 12 miles and 15 miles below the surface, according to a 2012 study by University of Cambridge researcher Jon Tarasewicz in Geophysical Research Letters.

Volcanoes give off many warning signs before a blow-up. Their cones bulge with magma. They vent carbon dioxide and sulfur into the air, and throw off enough heat that satellites can detect their changing temperature. Below ground, tremors and other rumblings can be detected by seismographs. When Indonesia’s Mount Merapi roared to life in late October 2010, officials led a mass evacuation later credited with saving as many as 20,000 lives.

Still, the forecasting of volcanic eruptions is not an exact science. Even if more seismographs could be placed along the flanks of volcanoes to detect deep earthquakes, it is unclear if scientists would be able to translate the rumblings into a projected eruption date. Most problematically, many apparent warning signs do not lead to an eruption, putting officials in a bind over whether to evacuate nearby residents.

“[Several months] leaves a lot of room for error,” said Erik Klemetti, a volcanologist at Denison University who writes the “Eruptions” blog for Wired magazine. “In volcanic hazards you have very few shots to get people to leave.”

Scientists may be able to narrow the window by continuing to look for patterns between eruptions and the earthquakes that precede them. The Nature study also provides a real-world constraint for modeling how fast magma travels to the surface.

“If this interpretation is correct, you start having a speed limit that your models of magma transport have to catch,” said Tom Sisson, a USGS volcanologist based at Menlo Park, Calif.

Olivine minerals with nickel spikes similar to Irazú’s have been found in the ashes of arc volcanoes in Mexico, Siberia and the Cascades of the U.S. Pacific Northwest, said Lamont geochemist Susanne Straub, whose ideas inspired the study. “It’s clearly not a local phenomenon,” she said. The researchers are currently analyzing crystals from past volcanic eruptions in Alaska’s Aleutian Islands, Chile and Tonga, but are unsure how many will bear Irazú’s fast-rising magma signature. “Some may be capable of producing highways from hell and some may not,” said Ruprecht.

The cause of Earth’s largest environmental catastrophe

The eruption of giant masses of magma in Siberia 250 million years ago led to the Permo-Triassic mass extinction when more than 90 % of all species became extinct. An international team including geodynamic modelers from the GFZ German Research Centre for Geosciences together with geochemists from the J. Fourier University of Grenoble, the Max Plank Institute in Mainz, and Vernadsky-, Schmidt- and Sobolev-Institutes of the Russian Academy of Sciences report on a new idea with respect to the origin of the Siberian eruptions and their relation to the mass extinction in the recent issue of Nature (15.09.2011, vol. 477, p. 312-316).

Large Igneous Provinces (LIPs) are huge accumulations of volcanic rock at the Earth’s surface. Within short geological time spans of often less than one million years their eruptions cover areas of several hundred thousand square kilometers with up to 4 kilometers thick lava flows. The Siberian Traps are considered the largest continental LI

A widely accepted idea is that LIPs originate through melting within thermal mantle plumes, a term applied to giant mushroom-shaped volumes of plastic mantle material that rise from the base of the mantle to the lithosphere, the Earth’s rigid outer shell. The high buoyancy of purely thermal mantle plumes, however, should cause kilometer-scale uplift of the lithosphere above the plume head, but such uplift is not always present. Moreover, estimates of magmatic degassing from many LIPs are considered insufficient to trigger climatic crises. The team of scientists presents a numerical model and new geochemical data with which unresolved questions can now be answered.

They suggest that the Siberian mantle plume contained a large fraction of about 15 percent of recycled oceanic crust; i.e. the crust that had long before been subducted into the deep mantle and then, through the hot mantle plume, brought back to the Earth’s lithosphere. This recycled oceanic crust was present in the plume as eclogite, a very dense rock which made the hot mantle plume less buoyant. For this reason the impingement of the plume caused negligible uplift of the lithosphere. The recycled crustal material melts at much lower temperatures than the normal mantle material peridotite, and therefore the plume generated exceptionally large amounts of magmas and was able to destroy the thick Siberian lithosphere thermally, chemically and mechanically during a very short period of only a few hundred thousand years. During this process, the recycled crust, being exceptionally rich in volatiles such as CO2 and halogens, degassed and liberated gases that passed through the Earth crust into the atmosphere to trigger the mass extinction. The model predicts that the mass extinction should have occurred before the main magmatic eruptions. Though based on sparse available data, this prediction seems to be valid for many LIPs.

Scientists return from expedition to drill beneath frozen Russian lake

The project site was near the center of Lake E'gygytgyn; the lake's eastern rim is visible. -  Julie Brigham-Grette, University of Massachusetts
The project site was near the center of Lake E’gygytgyn; the lake’s eastern rim is visible. – Julie Brigham-Grette, University of Massachusetts

A team of scientists from the United States, Germany, Russia and Austria has just returned from a six-month drilling expedition to a frozen lake in Siberia: Lake El’gygytgyn, “Lake E” for short.

Lake E was created 3.6 million years ago when a meteor more than a half-mile wide hit Earth and formed an 11-mile wide crater.

There, the researchers collected the longest sediment core samples retrieved in the Arctic region. Information contained in the cores, say the scientists, is of unprecedented significance for understanding climate change in the Arctic.

Cores collected from three holes drilled under the frozen Lake E are more than 30 times longer than cores from the Greenland Ice Sheet, according to geoscientist Julie Brigham-Grette of the University of Massachusetts at Amherst, the lead U.S. scientist on the project.

The research team will compare this Arctic record with oceanic and land-based records from lower latitudes to better understand global climate change.

Nearly 3.5 tons of temperature-controlled sediment cores are being flown by special cargo plane from Siberia to St. Petersburg in early June, then on to a lab in Germany to begin analysis by paleoclimatologists.

Archived core halves will arrive later at the University of Minnesota’s LacCore facility, where they will be preserved in cold storage.

Brigham-Grette says the team recovered a total of 1,165 feet of sediments; the sediment record collected extends back roughly two million years.

“Studying high-latitude systems is of great importance to an understanding of Earth’s climate at all latitudes,” says Paul Filmer, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which co-funded the expedition to Lake E with NSF’s Office of Polar Programs. “Of primary interest is determining why and how the Arctic evolved from a warm forested ecosystem to a cold permafrost ecosystem between two and three million years ago.”

The continuous record collected in this unique lake “offers us a way to look at the glacial/interglacial climate change of the past,” Brigham-Grette says.

“Earth’s warm and cold cycles over the past one million years varied every 100,000 years at times. Before that, however, climate change, especially in high latitudes, varied over 41,000- and 23,000-year cycles. The record from Lake E will show the ramp up to that type of change in the Earth’s climate.”

Below the lake’s sediments, cores drilled into bedrock will offer geologists a rare opportunity to study meteor impact melt rocks from one of the best preserved large meteor impact craters on Earth, and the only one formed in silicon-rich volcanic rock.

The team recovered roughly 40 meters (131 feet) of the earliest history of the lake in the warm middle Pliocene. This geologic time interval is fascinating, says Brigham-Grette, as a possible analog for future climate.

Initial results from the drilling are still limited.

The sediment cores could not opened in the field because of the remoteness of the drilling site, and rough transportation overland.

During pilot coring in November, the scientists recovered 141 meters (462 feet) of sediments showing alluvial fan and lake deposits in permafrost at the western edge of the lake outside the talik (unfrozen ground in an area of permafrost).

After drilling, the borehole was permanently instrumented for future ground temperature monitoring as part of the Global Terrestrial Network for Permafrost.