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Whales in the desert: Fossil bonanza poses mystery

More than 2 million years ago, scores of whales congregating off the Pacific Coast of South America mysteriously met their end.

A paleontologist from the museum prepares a whale fossil at the site where many prehistoric whale fossils were discovered in the Atacama desert near Copiapo, Chile. The fossil is enclosed in a plaster jacket to protect it during transport back to the museum. More than 2 million years ago, scores of whales congregating off the Pacific Coast of South America mysteriously met their end. Maybe they became disoriented and beached themselves. Maybe they were trapped in a lagoon by a landslide or a ferocious storm. Maybe they died there over a period of a few millennia. But somehow, they ended up right next to one another, many just several yards (meters) apart, entombed over the ages as the shallow sea floor was driven upward by geologic forces and transformed into the driest place on the planet. Today, the whales have emerged again atop a desert hill more than half a mile (a kilometer) from the surf, where researchers have begun to unearth one of the world's best-preserved graveyards of prehistoric whales [Credit: AP Photo/Museo Paleontologico de Caldera]

Maybe they became disoriented and beached themselves. Maybe they were trapped in a lagoon by a landslide or a storm. Maybe they died there over a period of a few millennia. But somehow, they ended up right next to one another, many just meters (yards) apart, entombed as the shallow sea floor was driven upward by geological forces and transformed into the driest place on the planet.

Today, they have emerged again atop a desert hill more than a kilometer (half a mile) from the surf, where researchers have begun to unearth one of the world's best-preserved graveyards of prehistoric whales.

Chilean scientists together with researchers from the Smithsonian Institution are studying how these whales, many of the them the size of buses, wound up in the same corner of the Atacama Desert.

"That's the top question," said Mario Suarez, director of the Paleontological Museum in the nearby town of Caldera, about 700 kilometers (440 miles) north of Santiago, the Chilean capital.

Experts say other groups of prehistoric whales have been found together in Peru and Egypt, but the Chilean fossils stand out for their staggering number and beautifully preserved bones. More than 75 whales have been discovered so far — including more than 20 perfectly intact skeletons.

They provide a snapshot of sea life at the time, and even include what might have been a family group: two adult whales with a juvenile between them.

"I think they died more or less at the same time," said Nicholas Pyenson, curator of fossil marine mammals at the Smithsonian's National Museum of Natural History. Pyenson and Suarez are jointly leading the research.

As for why such a great number perished in the same place, Pyenson said: "There are many ways that whales could die, and we're still testing all those different hypotheses."

A prehistoric whale fossil lies in the Atacama desert near Copiapo, Chile. More than 2 million years ago, scores of whales congregating off the Pacific Coast of South America mysteriously met their end. Maybe they became disoriented and beached themselves. Maybe they were trapped in a lagoon by a landslide or a ferocious storm. Maybe they died there over a period of a few millennia. But somehow, they ended up right next to one another, many just several yards (meters) apart, entombed over the ages as the shallow sea floor was driven upward by geologic forces and transformed into the driest place on the planet. Today, the whales have emerged again atop a desert hill more than half a mile (a kilometer) from the surf, where researchers have begun to unearth one of the world's best-preserved graveyards of prehistoric whales [Credit: AP Photo/Museo Paleontologico de Caldera]

The scientists have yet to publish their findings about the fossil bed and the extensive remains, which began to emerge in June last year during a highway-widening project that is now on hold.

So far, the fossils have been found in a roadside strip the length of two football fields — about 240 meters (260 yards) long and 20 meters (yards) wide.

Pyenson said the spot was once a "lagoon-like environment" and that the whales probably died between 2 million and 7 million years ago.

Most of the fossils are baleen whales that measured about 8 meters (25 feet) long, Pyenson said.

The researchers also discovered a sperm whale skeleton and remains of a now-extinct dolphin that had two walrus-like tusks and previously had only turned up in Peru, he said.

"We're very excited about that," Pyenson said in a telephone interview. "It is a very bizarre animal."

Other unusual creatures found elsewhere in the fossil-rich Atacama Desert include an extinct aquatic sloth and a seabird with a 5-meter (17-foot) wingspan, bigger than a condor's.

Erich Fitzgerald, a vertebrate paleontologist at Museum Victoria in Melbourne, Australia, emailed that the latest find is very significant.

"The fossils are exceptionally well preserved and quite complete — a rare combination in paleontology and one that will likely shed light on many facets of the ... ecology and evolution of these extinct species," Fitzgerald said.

He said it's possible "these fossilized remains may have accumulated over a relatively long period of time."

Hans Thewissen, an expert on early whales, agreed. Another scenario, he said, is that the whales might have gathered in a lagoon and then an earthquake or storm could have closed off the outlet to the ocean.

Researchers from the museum work at the site where prehistoric whale fossils were discovered in the Atacama desert near Copiapo, Chile. More than 2 million years ago, scores of whales congregating off the Pacific Coast of South America mysteriously met their end. Maybe they became disoriented and beached themselves. Maybe they were trapped in a lagoon by a landslide or a ferocious storm. Maybe they died there over a period of a few millennia. But somehow, they ended up right next to one another, many just several yards (meters) apart, entombed over the ages as the shallow sea floor was driven upward by geologic forces and transformed into the driest place on the planet. Today, the whales have emerged again atop a desert hill more than half a mile (a kilometer) from the surf, where researchers have begun to unearth one of the world's best-preserved graveyards of prehistoric whales [Credit: AP Photo/Museo Paleontologico de Caldera]

"Subsequently the lagoon dries up and the whales die," said Thewissen, a professor of anatomy at Northeast Ohio Medical University. He said the accumulation of so many complete skeletons is "a very unusual situation."

"If this were a lagoon that dried up, you might see signs that ocean water evaporated," such as crystallized salt and gypsum in the rock, said Thewissen, who is not involved in the research. "On the other hand, if a giant wave or storm flung the whales onto shore, it would also have pushed the ocean floor around, and you would see scour marks in the rocks."

Dating fossils is complicated, experts said, and it will be very hard to distinguish dates precisely enough to determine whether the whales all died simultaneously.

The researchers have been told to finish their onsite studies so that fossils can be moved out of the path of the widened Pan American Highway, or Route 5, which is Chile's main north-south road.

Many of the fossils have been transported in plaster coverings to the museum in Caldera. Researchers from Chile's National Museum of Natural History are also studying the fossils.

Pyenson and his team are working quickly under tents to document the intact skeletons. With funding from the National Geographic Society, the Smithsonian team is using sophisticated photography and laser scanners to capture 3D images of the whales that can later be used to make life-sized models of them.

Suarez, the paleontologist, had long known about the whale bones just north of Caldera — they could be seen jutting out of the sandstone ridge alongside the highway at the spot known as Cerro Ballena, or Whale Hill. When the road work began last year, the construction company asked him to monitor the job to avoid destroying fossils.

"In the first week, about six or seven whales appeared," Suarez said. "We realized that it was a truly extraordinary site."

The Chilean government has declared the site a protected zone, and Pyenson said he hopes a museum will be built to showcase the intact skeletons where they lie, in the same way fossils are displayed at Dinosaur National Monument in Utah and Colorado.

Suarez thinks there are probably fossils of hundreds of whales waiting to be uncovered — enough to keep him working at this one spot for the rest of his life.

"We have a unique opportunity to develop a great scientific project and make a great contribution to science," he said.

Author: Eva Vergara | Source: Associated Press [November 19, 2011]

Antarctica's ghost mountains give up their secrets

The birth of the Gamburtsev Subglacial Mountains buried beneath the vast East Antarctic Ice Sheet – a puzzle mystifying scientists since their first discovery in 1958 – is finally solved. The remarkably long geological history explains the formation of the mountain range in the least explored frontier on Earth and where the Antarctic Ice Sheet first formed. The findings are published this week in the journal Nature.

While these ridges poke through Antarctica's frosty surface, the Gamburtsev mountains are completely hidden beneath three kilometres of ice [Credit: Mark Baker/Reuters]

A seven-nation team of scientists explored the Gamburtsev Subglacial Mountains - buried beneath up to 3km of ice – during the International Polar Year (2007- 09) by using two twin-engine aircraft equipped with ice penetrating radars, gravity meters and magnetometers.

By analyzing the new data, the researchers describe the extraordinary processes – which took place over the last billion years – that created and preserved a root beneath the mountains and the East Antarctic rift system – a 3,000km long fracture in the earth's surface that extends from East Antarctica across the ocean to India.

One billion years ago, before animals and plants evolved on Earth, several continents (or micro-continents) collided, crushing the oldest rocks of the mountain range together. This event formed a thick crustal root extending deep beneath the mountain range. Over time these ancient mountains were eroded but the cold dense root was left behind.

Three dimensional perspective of the Gamburtsev Subglacial Mountains, including a view of the deep root imaged beneath the range and of the thinner crust of the East Antarctic Rift System that surrounds the mountains [Credit: British Antarctic Survey]

Around 250-100 million years ago – when dinosaurs walked the Earth – rifting paved the way for the supercontinent Gondwana to break apart, which included Antarctica, causing the old crustal root to warm. This rejuvenated crustal root, together with the East Antarctic Rift forced the land upwards again reforming the mountains. Rivers and glaciers carved deep valleys and this helped uplift the peaks to create the spectacular landscape of the Gamburtsevs, which resemble the European Alps. The East Antarctic Ice Sheet, which formed 34 million years ago and covers 10 million km² of our planet (an area the size of Canada), protected the mountains from erosion.

Lead author, Dr Fausto Ferraccioli from British Antarctic Survey says:

"Understanding the origin of the Gamburtsevs was a primary goal of our International Polar Year expedition. It was fascinating to find that the East Antarctic rift system resembles one of the geological wonders of the world – the East African rift system – and that it provides the missing piece of the puzzle that helps explain the Gamburtsev Subglacial Mountains. The rift system was also found to contain the largest subglacial lakes in Antarctica."

Co-author, Dr Carol Finn from US Geological Survey says:

"Resolving the contradiction of the Gamburtsev high elevation and youthful Alpine topography but location on the East Antarctic craton by piecing together the billion year history of the region was exciting and challenging. We are accustomed to thinking that mountain building relates to a single tectonic event, rather than sequences of events. The lesson we learned about multiple events forming the Gamburtsevs may inform studies of the history of other mountain belts."

Co-author, Dr Robin Bell of Columbia University's Lamont-Doherty Earth Observatory says:

"The next steps will be to assemble a team to drill through the ice into the mountains to obtain the first rock samples from the Gamburtsevs. Amazingly, we have samples of the moon but none of the Gamburtsevs. With these rock samples we will be able to constrain when this ancient piece of crust was rejuvenated and grew to a magnificent mountain range."

"It is very fitting that the initial results of Antarctica's Gamburtsev Province (AGAP) project are coming out 100 years after the great explorers raced to the South Pole," said Alexandra Isern, Programme Director at the National Science Foundation. "The scientific explorers of the AGAP project worked in harsh conditions to collect the data and detailed images of this major mountain range under the East Antarctic Ice Sheet. The results of their work will guide research in this region for many years to come."

These discoveries in central East Antarctica have significant implications for understanding mountain building and ice sheet evolution within continental interiors.

Source: British Antarctic Survey [November 16, 2011]

Evidence of ancient lake in California's Eel River emerges

A catastrophic landslide 22,500 years ago dammed the upper reaches of northern California's Eel River, forming a 30-mile-long lake, which has since disappeared, and leaving a living legacy found today in the genes of the region's steelhead trout, report scientists at two West Coast universities.

This is how the ancient lake likely appeared after being formed by a landslide, based on LiDAR technology [Credit: Benjamin Mackey]

Using remote-sensing technology known as airborne Light Detection and Ranging (LiDAR) and hand-held global-positioning-systems (GPS) units, a three-member research team found evidence for a late Pleistocene, landslide-dammed lake along the river, about 60 miles southeast of Eureka.

The river today is 200 miles long, carved into the ground from high in the California Coast Ranges to its mouth in the Pacific Ocean in Humboldt County.

The evidence for the ancient landslide, which, scientists say, blocked the river with a 400-foot wall of loose rock and debris, is detailed this week in a paper appearing online ahead of print in the Proceedings of the National Academy of Sciences.

The National Science Foundation-funded study provides a rare glimpse into the geological history of this rapidly evolving mountainous region.

It helps to explain emerging evidence from other studies that show a dramatic decrease in the amount of sediment deposited from the river in the ocean just off shore at about the same time period, says lead author Benjamin H. Mackey, who began the research while pursuing a doctorate earned in 2009 from the University of Oregon. He is now a postdoctoral researcher at the California Institute of Technology.

This graphic shows the Eel River system in northern California, where researchers found evidence for an ancient lake [Credit: Benjamin Mackey]

"Perhaps of most interest, the presence of this landslide dam also provides an explanation for the results of previous research on the genetics of steelhead trout in the Eel River," Mackey said, referring to a 1999 study by U.S. Forest Service researchers J.L. Nielson and M.C. Fountain. In their study, published in the journal Ecology of Freshwater Fish, they found a striking relationship between two types of ocean-going steelhead in the river -- a genetic similarity not seen among summer-run and winter-run steelhead in other nearby rivers.

An interbreeding of the two fish, in a process known as genetic introgression, may have occurred among the fish brought together while the river was dammed, Mackey said. "The dam likely would have been impassable to the fish migrating upstream, meaning both ecotypes would have been forced to spawn and inadvertently breed downstream of the dam. This period of gene flow between the two types of steelhead can explain the genetic similarity observed today."

Once the dam burst, the fish would have reoccupied their preferred spawning grounds and resumed different genetic trajectories, he added.

"The damming of the river was a dramatic, punctuated affair that greatly altered the landscape," said co-author Joshua J. Roering, a professor of geological sciences at the University of Oregon. "Although current physical evidence for the landslide dam and paleo-lake is subtle, its effects are recorded in the Pacific Ocean and persist in the genetic make-up of today's Eel River steelhead. It's rare for scientists to be able to connect the dots between such diverse and widely-felt phenomena."

Sediment from ancient lakebed [Credit: Benjamin Mackey]

The lake's surface formed by the landslide, researchers theorize, covered about 12 square miles. After the damn was breached, the flow of water would have generated one of North America's largest landslide-dam outburst floods. Landslide activity and erosion have erased much of the evidence for the now-gone lake. Without the acquisition of LiDAR mapping, the lake's existence may have never been discovered, researchers say.

The area affected by the landslide-caused dam accounts for about 58 percent of the modern Eel River watershed. Based on today's general erosion rates, researchers theorize the lake could have been filled in with sediment within about 600 years.

"The presence of a dam of this size was highly unexpected in the Eel River environment given the abundance of easily eroded sandstone and mudstone, which are generally not considered strong enough to form long-lived dams," Mackey said.

He and his colleagues were drawn to the Eel River -- among the most-studied erosion systems in the world -- to study large, slow-moving landslides. "While analyzing the elevation of terraces along the river, we discovered they clustered at a common elevation rather than decrease in elevation downstream, paralleling the river profile, as would be expected for river terraces. This was the first sign of something unusual, and it clued us into the possibility of an ancient lake."

Source: University of Oregon [November 14, 2011]

Welsh mudstones reveal ancient sponge ecosystem

A remarkably complete record of a prehistoric seabed ecosystem of a kind never discovered before has been revealed with X-ray scanning.

Fossilised nautiloid with a curved shell [Credit: Planet Earth]

A paper in Geology gives the first account of the plentiful and exceptionally well-preserved organisms from the Ordovician period that have been found in the Llanfawr Mudstones near Llandrindod Wells in central Wales. More than 20 species have turned up so far, and it's almost certain that many more remain to be uncovered.

The fossils include sponges, priapulid worms and arthropods, and shed new light on how living things colonised the deep oceans. Among the most exciting are beautiful specimens of a type of animals known as solitary hydroids – the earliest known examples of the group.

The rocks, which are about 460 million years old, provide a unique new perspective on life in the Ordovician, which stretched between about 488 and 444 million years ago and saw an explosion in the variety of living things on Earth. By the end of the period, the planet's total count of species is thought to have quadrupled, and whole new kinds of ecosystem had appeared, including the first coral reefs.

This area of mid-Wales is known for its fossils. But this particular assemblage of living things was only found in 2004; since then, the researchers have returned repeatedly to gather more specimens, using hi-tech scanning equipment to find out what's in the rocks without physically having to delve inside them.

The three palaeontologists who made the find – Dr Joe Botting, Dr Lucy Muir and Talfan Barnie - are among the paper's authors. Recent finds of fossil sponges made them suspect the area might have more to offer to fossil-hunters. 'We were on a field trip to the area, and decided to spend a day in the quarry looking for more sponges,' says Muir. 'Talfan hammered a large fresh block, found something, and said, "Is this interesting?" It was.'

X-ray scan of a nautiloid [Credit: Planet Earth]

The team took rock samples back to the Natural History Museum, where a colleague suggested X-raying them to find out what was inside. 'We tried one or two slabs, just to see if the technique worked, and this spectacular hydroid turned up in the very first slab,' Muir explains. 'It's not visible on the surface of the rock, so we had no idea that it was there.'

Unlike the few other exceptionally preserved Ordovician faunas we know of, this habitat was dominated by sponges, which account for three quarters of the inhabitants. There were few mobile animals – not unlike the sponge-based communities still common on modern deep ocean seabeds. Most of these animals had delicate skeletons or were completely soft-bodied, so it's very rare to find them preserved – creatures with hard skeletons are far more likely to become fossilised.
Ordovician ecologies

This means our knowledge of the Ordovician is skewed towards hard-bodied animals. 'We just don't know what the less well-preservable animals were doing,' says Muir. 'They may have been diversifying in the same way as the ones we know about, but they might have been doing something completely different. The significance of this particular community is that it's rather different from the others described from this age, even the ones that do preserve soft-bodied animals. The fact that all the sites with soft-bodied preservation have different communities from each other indicates that the Ordovician diversification of species and communities applied to soft-bodied animals as well as those that fossilised easily.'

This community is very unusual from an ecological perspective,' adds Dr Mark Sutton of Imperial College London, another of the paper's authors. 'It's dominated by fixed filter-feeders, with relatively few arthropods and other mobile organisms. If you found this in the modern world you'd certainly assume it came from the deep ocean beds, but we know that this was found in relatively shallow shelf-sea waters.'

X-ray scan of a hydroid - an animal with a mass of flexible tentacles, a small body, and a long stalk, which has split in two [Credit: Planet Earth]

These organisms' traces survive in the Welsh mudstones largely because of the unusual way they've been fossilised. Their shapes are preserved as patterns of iron pyrite, also known as fool's gold. The pyrite blocks X-rays much better than the rock around it does, so the fossil shapes show up well under scanning. But since they aren't usually visible from outside, it's a hit-and-miss process - the team brings blocks back for scanning; sometimes they contain a hitherto-undiscovered species, while at other times there's nothing at all.

It wouldn't be practical to investigate these fossils using more traditional methods – they're so small – often only a few millimetres long - and so delicate that trying to dig them out of the mudstone using even very precise tools would be time-consuming and would probably still end up destroying many of the fossils' finer details.

So as well using X-ray imaging to find and categorise fossils within the stone, the researchers used a CT scanner to see them in partial 3D, rather than simply as flattened smears. This makes it far easier to reconstruct a living, functioning organism from its fossilised form.

The findings shed light on how living things colonised the deep oceans. 'There's been a school of thought for a long time that the ecosystems that are now found on the deep seabed were once found in shallower waters and moved out, perhaps because they were displaced by new organisms that evolved to live in the shelf seas,' Sutton explains. 'We have a good idea this happened with hard-bodied organisms, but our findings are some of the first evidence that it's true of soft-bodied organisms too.'

The finds suggest that even areas that have been extensively explored by fossil hunters may have much more to tell us, particularly now that affordable X-ray and CT scanning means that exciting new fossils can be found even in seemingly dull blocks of stone. The team are now preparing formal descriptions of some of the new organisms they've identified, while continuing to visit the site in search of more specimens.

The researchers also believe that collections of organisms like this may be much more common than previously thought. The reason the fossils were overlooked for so long is probably that the pyrite quickly decays to almost nothing in the Welsh weather. The fossils are only visible when you examine fresh rock surfaces – so other black mudstones may be hiding unexpected surprises as well.

Author: Tom Marshall | Source: Planet Earth [November 14, 2011]

Insects offer clues to climate variability 10,000 years ago

An analysis of the remains of ancient midges – tiny non-biting insects closely related to mosquitoes – opens a new window on the past with a detailed view of the surprising regional variability that accompanied climate warming during the early Holocene epoch, 10,000 to 5,500 years ago.

University of Illinois plant biology and geology professor Feng Sheng Hu collected core samples from Alaskan lakes. The abundance and diversity of midges buried in sediments offers a reliable record of temperature fluctuations over time [Credit: Feng Sheng Hu]

Researchers at the University of Illinois and the University of British Columbia looked at the abundance and variety of midge larvae buried in lake sediments in Alaska. Midges are highly sensitive to summer temperatures, so changes in the abundance of different species over time gave the scientists a reliable marker of temperature fluctuations over the last 10,000 years.

Northern high latitudes are thought to have been warmer than today during the early Holocene, a time of heightened solar irradiation as a result of Earth's axial tilt and orbit around the sun. The period is often referred to as the Holocene Thermal Maximum. Scientists hope to understand the ecological impacts of climate warming during that time to make better predictions about the effects of future warming. But several decades of research have yielded only ambiguous evidence of climate conditions in Alaska at that time.

The new analysis, conducted by University of Illinois doctoral student Benjamin Clegg with U. of I. plant biology and geology professor Feng Sheng Hu, who led the study, offers the first detailed record of temperature variation over the last 10,000 years in Alaska. The analysis reveals that the region was significantly cooler than expected during the early Holocene.

"This study shows that early Holocene warming did not occur everywhere in high latitudes, and exhibited important regional exceptions, even though the driving force behind it – solar input, in this case – was geographically uniform," said Clegg, who is now a postdoctoral researcher in Hu's lab.

The drivers of climate change during the early Holocene "were different than the greenhouse gases responsible for global warming today," Clegg said. "So we should not expect to see exactly the same spatial patterns of temperature anomalies in the next few decades as during the early Holocene."

The researchers hypothesize that solar warming during the early Holocene spurred atmospheric circulation patterns that contributed to extensive sea-ice off the Alaskan coast. That, and a treeless tundra over more of the land area than at present would have increased surface reflectivity, potentially contributing to the observed cooling, Clegg said.

"This study has important ecological and societal implications," Hu said. "Nonlinear responses such as those identified here constitute a major source of potential climate 'surprises' that make it more difficult to anticipate and prepare for future regional climate scenarios."

The findings appear in the Proceedings of the National Academy of Sciences.

Source: University of Illinois at Urbana-Champaign [November 14, 2011]

Methane may be answer to 56-million-year question

The release of massive amounts of carbon from methane hydrate frozen under the seafloor 56 million years ago has been linked to the greatest change in global climate since a dinosaur-killing asteroid presumably hit Earth 9 million years earlier. New calculations by researchers at Rice University show that this long-controversial scenario is quite possible.

Research at Rice University bolstered a long-controversial theory that massive amounts of carbon from methane hydrate caused the Earth to warm 56 million years ago and drastically change the ecosystem. Rice scientists proposed in a new Nature Geoscience paper that hydrates collected in a narrower stability zone than today under the seafloor over millions of years were discharged rapidly as the planet warmed, much as an electrical capacitor gathers charge and releases it quickly [Credit: Guangsheng Gu/Rice University]

Nobody knows for sure what started the incident, but there's no doubt Earth's temperature rose by as much as 6 degrees Celsius. That affected the planet for up to 150,000 years, until excess carbon in the oceans and atmosphere was reabsorbed into sediment.

Earth's ecosystem changed and many species went extinct during the Paleocene-Eocene Thermal Maximum (PETM) 56 million years ago, when at least 2,500 gigatonnes of carbon, eventually in the form of carbon dioxide, were released into the ocean and atmosphere.

A new report by Rice scientists in Nature Geoscience suggests that at the time, even though methane-containing gas hydrates -- the "ice that burns" -- occupied only a small zone of sediment under the seabed before the PETM, there could have been as much stored then as there is now.

This is a concern to those who believe the continued burning of fossil fuels by humans could someday trigger another feedback loop that disturbs the stability of methane hydrate under the ocean and in permafrost; this change could warm the atmosphere and prompt the release of large amounts of methane, a more powerful greenhouse gas than carbon dioxide.

Some who study the PETM blame the worldwide burning of peat, volcanic activity or a massive asteroid strike as the source of the carbon, "but there's no crater, or any soot or evidence of the burning of peat," said Gerald Dickens, a Rice professor of Earth science and an author of the study, who thinks the new paper bolsters the argument for hydrates.

The lead author is graduate student Guangsheng Gu; co-authors are Walter Chapman, the William W. Akers Professor in Chemical Engineering; George Hirasaki, the A.J. Hartsook Professor in Chemical Engineering; and alumnus Gaurav Bhatnagar, all of Rice; and Frederick Colwell, a professor of ocean ecology and biogeochemistry at Oregon State University.

In the ocean, organisms die, sink into the sediment and decompose into methane. Under high pressure and low temperatures, methane molecules are trapped by water, which freezes into a slushy substance known as gas hydrate that stabilizes in a narrow band under the seafloor.

Warmer oceans before the PETM would have made the stability zone for gas hydrate thinner than today, and some scientists have argued this would allow for much less hydrate than exists under the seafloor now. "If the volume -- the size of the box -- was less than today, how could it have released so much carbon?" Dickens asked. "Gu's solution is that the box contains a greater fraction of hydrate."

"The critics said, 'No, this can't be. It's warmer; there couldn't have been more methane hydrate,'" Hirasaki said. "But we applied the numerical model and found that if the oceans were warmer, they would contain less dissolved oxygen and the kinetics for methane formation would have been faster."

With less oxygen to consume organic matter on the way down, more sank to the ocean floor, Gu said, and there, with seafloor temperatures higher than they are today, microbes that turn organic matter into methane work faster. "Heat speeds things up," Dickens said. "It's true for almost all microbial reactions. That's why we have refrigerators."

The result is that a stability zone smaller than what exists now may have held a similar amount of methane hydrate. "You're increasing the feedstock, processing it faster and packing it in over what could have been millions of years," Dickens said.

While the event that began the carbon-discharge cycle remains a mystery, the implications are clear, Dickens said. "I've always thought of (the hydrate layer) as being like a capacitor in a circuit. It charges slowly and can release fast -- and warming is the trigger. It's possible that's happening right now."

That makes it important to understand what occurred in the PETM, he said. "The amount of carbon released then is on the magnitude of what humans will add to the cycle by the end of, say, 2500. Compared to the geological timescale, that's almost instant."

"We run the risk of reproducing that big carbon-discharge event, but faster, by burning fossil fuel, and it may be severe if hydrate dissociation is triggered again," Gu said, adding that methane hydrate also offers the potential to become a valuable source of clean energy, as burning methane emits much less carbon dioxide than other fossil fuels.

The calculations should encourage geologists who discounted hydrates' impact during the PETM to keep an open mind, Dickens said. "Instead of saying, 'No, this cannot be,' we're saying, 'Yes, it's certainly possible.'"

The United States Department of Energy supported the research.

Author: Mike Williams | Source: Rice University [November 09, 2011]