Methane Gas Likely Spewing Into The Oceans Through Vents In Sea Floor

Scientists worry that rising global temperatures accompanied by melting permafrost in arctic regions will initiate the release of underground methane into the atmosphere. Once released, that methane gas would speed up global warming by trapping the Earth’s heat radiation about 20 times more efficiently than does the better-known greenhouse gas, carbon dioxide.

An MIT paper appearing in the Journal of Geophysical Research online Aug. 29 elucidates how this underground methane in frozen regions would escape and also concludes that methane trapped under the ocean may already be escaping through vents in the sea floor at a much faster rate than previously believed. Some scientists have associated the release, both gradual and fast, of subsurface ocean methane with climate change of the past and future.
“The sediment conditions under which this mechanism for gas migration dominates, such as when you have a very fine-grained mud, are pervasive in much of the ocean as well as in some permafrost regions,” said lead author Ruben Juanes, the ARCO Assistant Professor in Energy Studies in the Department of Civil and Environmental Engineering.
“This indicates that we may be greatly underestimating the methane fluxes presently occurring in the ocean and from underground into Earth’s atmosphere,” said Juanes. “This could have implications for our understanding of the Earth’s carbon cycle and global warming.”
Juanes explains that some of the naturally occurring underground methane exists not as gas but as methane hydrate. In the hydrate phase, a methane gas molecule is locked inside a crystalline cage of frozen water molecules. These hydrates exist in a layer of underground rock or oceanic sediments called the hydrate stability zone or HSZ. Methane hydrates will remain stable as long as the external pressure remains high and the temperature low. Beneath the hydrate stability zone, where the temperatures are higher, methane is found primarily in the gas phase mixed with water and sediment.
But the stability of the hydrate stability zone is climate-dependent.
If atmospheric temperatures rise, the hydrate stability zone will shift upward, leaving in its stead a layer of methane gas that has been freed from the hydrate cages. Pressure in that new layer of free gas would build, forcing the gas to shoot up through the HSZ to the surface through existing veins and new fractures in the sediment. A grain-scale computational model developed by Juanes and recent MIT graduate Antone Jain indicates that the gas would tend to open up cornflake-shaped fractures in the sediment, and would flow quickly enough that it could not be trapped into icy hydrate cages en route.
“Previous studies did not take into account the strong interaction between the gas-water surface tension and the sediment mechanics. Our model explains recent experiments of sediment fracturing during gas flow, and predicts that large amounts of free methane gas can bypass the HSZ,” said Juanes.
Using their model, as well as seismic data and core samples from a hydrate-bearing area of ocean floor (Hydrate Ridge, off the coast of Oregon), Juanes and Jain found that methane gas is very likely spewing out of vents in the sea floor at flow rates up to 1 million times faster than if it were migrating as a dissolved substance in water making its way through the oceanic sediment — a process previously thought to dominate methane transport.
“Our model provides a physical explanation for the recent striking discovery by the National Oceanic and Atmospheric Administration of a plume 1,400 meters high at the seafloor off the Northern California Margin,” said Juanes. This plume, which was recorded for five minutes before disappearing, is believed not to be hydrothermal vent, but a plume of methane gas bubbles coated with methane hydrate.
The Jain and Juanes paper in the Journal of Geophysical Research also explains the short-term consequences of injecting carbon dioxide into the ocean’s subsurface, a method proposed by some researchers for reducing atmospheric greenhouse gas. Juanes found that while some of the CO2 would remain trapped as a hydrate, much would likely spew up through fractures just as methane does.
“It is important to keep both methane and carbon dioxide either in the pipeline or underground, because the consequences of escape can be quite dangerous over time,” said Juanes.
This research was funded by the U.S. Department of Energy.
Adapted from materials provided by Massachusetts Institute of Technology, Department of Civil and Environmental Engineering.

Warming Of Arctic Current Over 30 Years Triggers Release Of Methane Gas

The warming of an Arctic current over the last 30 years has triggered the release of methane, a potent greenhouse gas, from methane hydrate stored in the sediment beneath the seabed.

Scientists at the National Oceanography Centre Southampton working in collaboration with researchers from the University of Birmingham, Royal Holloway London and IFM-Geomar in Germany have found that more than 250 plumes of bubbles of methane gas are rising from the seabed of the West Spitsbergen continental margin in the Arctic, in a depth range of 150 to 400 metres.
Methane released from gas hydrate in submarine sediments has been identified in the past as an agent of climate change. The likelihood of methane being released in this way has been widely predicted.
The data were collected from the royal research ship RRS James Clark Ross, as part of the Natural Environment Research Council's International Polar Year Initiative. The bubble plumes were detected using sonar and then sampled with a water-bottle sampling system over a range of depths.
The results indicate that the warming of the northward-flowing West Spitsbergen current by 1° over the last thirty years has caused the release of methane by breaking down methane hydrate in the sediment beneath the seabed.
Professor Tim Minshull, Head of the University of Southampton's School of Ocean and Earth Science based at that the National Oceanography Centre, says: "Our survey was designed to work out how much methane might be released by future ocean warming; we did not expect to discover such strong evidence that this process has already started."
Methane hydrate is an ice-like substance composed of water and methane which is stable in conditions of high pressure and low temperature. At present, methane hydrate is stable at water depths greater than 400 metres in the ocean off Spitsbergen. However, thirty years ago it was stable at water depths as shallow as 360 metres.
This is the first time that such behaviour in response to climate change has been observed in the modern period.
While most of the methane currently released from the seabed is dissolved in the seawater before it reaches the atmosphere, methane seeps are episodic and unpredictable and periods of more vigorous outflow of methane into the atmosphere are possible. Furthermore, methane dissolved in the seawater contributes to ocean acididfication.
Graham Westbrook Professor of Geophysics at the University of Birmingham, warns: "If this process becomes widespread along Arctic continental margins, tens of megatonnes of methane per year – equivalent to 5-10% of the total amount released globally by natural sources, could be released into the ocean."
The team is carrying out further investigations of the plumes; in particular they are keen to observe the behaviour of these gas seeps over time.
Journal reference:
Westbrook, G.K. et al. Escape of methane gas from the seabed along the West Spitsbergen continental margin. Geophysical Research Letters, 2009; DOI: 10.1029/2009GL039191
Adapted from materials provided by National Oceanography Centre, Southampton (UK).

Methane-eating Microbes Can Use Iron And Manganese Oxides To 'Breathe'

Iron and manganese compounds, in addition to sulfate, may play an important role in converting methane to carbon dioxide and eventually carbonates in the Earth's oceans, according to a team of researchers looking at anaerobic sediments. These same compounds may have been key to methane reduction in the early, oxygenless days of the planet's atmosphere.

"We used to believe that microbes only consumed methane in marine anaerobic sediment if sulfate was present," said Emily Beal, graduate student in geoscience, Penn State. "But other electron acceptors, such as iron and manganese, are more energetically favorable than sulfate."
Microbes or groups of microbes -- consortia -- that use sulfates to convert methane for energy exist in marine sediments. Recently other researchers have identified microbes that use forms of nitrogen in fresh water environments to convert methane.
"People had speculated that iron and manganese could be used, but no one had shown that it occurred by incubating live organisms," said Beal.
Beal, working with Christopher H. House, associate professor of geoscience, Penn State, and Victoria J. Orphan, assistant professor of geobiology, California Institute of Technology, incubated a variety of marine sediments to determine if there were microbes that could convert methane to carbon dioxide without using any sulfur compounds. They report their results in the July 10 issue of Science.
Using samples of marine sediment taken 20 miles off the California coast and about 1,800 feet deep near methane seeps in the Pacific, Beal incubated a variety of sediment systems including as controls, an autoclaved sterile sample, a sample with sulfate as a control and a sample that was sulfate, iron oxide and manganese oxide free, but live. She also incubated samples that were sulfate free but contained iron oxide or manganese oxide. She placed methane gas that contained the non-radioactive carbon-13 isotope in the empty space in the flasks above the sediment and tested any resulting carbon dioxide produced by the samples. All the carbon dioxide had the carbon-13 isotope and so came from the methane samples.
The sterile control showed no activity, while the live control without sulfate showed minute activity. The sulfate control showed the most activity as expected, but both the iron and manganese oxide-laced samples showed activity, although less activity than the sulfate.
"We do not think that iron and manganese are more important than sulfate reduction today, but they are not trivial components," said House, who is director of Penn State's Astrobiology Research Center. "They are probably a big part of the carbon cycle today."
One reason they are important is that some of the carbon dioxide produced reacts with both the manganese and iron to form carbonates that precipitate and sequester carbon in the oceans. Even if the carbon dioxide escaped into the atmosphere, it is a less problematic greenhouse gas than methane.
On the early Earth, where oxygen was absent from the atmosphere, sulfates were scarce. Without sulfates, iron and manganese oxides may have been essential in converting methane to carbon dioxide.
"Sulfate comes mostly from oxidative weathering of rocks," said Beal. "Oxygen is needed for this to occur."
While manganese and iron oxides are made in today's oxygen atmosphere, they where also formed by photochemical reactions in a low oxygen atmosphere. These oxides were probably more abundant in the early Earth's oceans than sulfates.
While Beal has categorized the more than a dozen microorganisms living in the sediments she used, she does not know which of these microbes is responsible for consuming methane. It might be one bacteria or archaea species, or it may be a consortium of microbes. She is trying to identify the organisms responsible.
The National Science Foundation and the NASA Astrobiology Institute supported this work.
Adapted from materials provided by Penn State.

Scientists Find Increased Methane Levels In Arctic Ocean

A team led by International Arctic Research Center scientist Igor Semiletov has found data to suggest that the carbon pool beneath the Arctic Ocean is leaking.

The results of more than 1,000 measurements of dissolved methane in the surface water from the East Siberian Arctic Shelf this summer as part of the International Siberian Shelf Study show an increased level of methane in the area. Geophysical measurements showed methane bubbles coming out of chimneys on the seafloor.
“The concentrations of the methane were the highest ever measured in the summertime in the Arctic Ocean,” Semiletov said. “We have found methane bubble clouds above the gas-charged sediment and above the chimneys going through the sediment.”
The new data indicates the underwater permafrost is thawing and therefore releasing methane. Permafrost can affect methane release in two ways. Both underwater and on land, it contains frozen organic material such as dead plants and animals. When permafrost thaws, that organic material decomposes, releasing gases like methane and carbon dioxide. In addition, methane, either in gas form or in ice-like methane hydrates, is trapped underneath the permafrost. When the permafrost thaws, the trapped methane can seep out through the thawed soil. Methane, a greenhouse gas 20 times more powerful than carbon dioxide, is thought to be an important factor in global climate change.
The East Siberian Arctic Shelf is a relatively shallow continental shelf that stretches more than 900 miles into the Arctic Ocean from Siberia. The area is a year-round source of methane to the globe’s atmosphere. However, until recently, scientists believed that much of the area’s carbon pool was safely insulated by underwater permafrost, which is, on average, 11 degrees Celcius warmer than surface permafrost.
Semiletov said this year’s expeditions used both chemical and geophysical measurement techniques, a first in the area. He also noted that while the high-arctic ocean readings were surprisingly high, on par with those from high-arctic lakes, they are still much lower than is being found in subarctic regions.
“That means we cannot extrapolate the subarctic data to the entire Arctic,” he said.
Semiletov, as associate research professor at IARC, leads the International Siberian Shelf Study, which has launched the multiple expeditions to the Arctic Ocean to collect data on methane release of the East Siberian Arctic Shelf. The ISSS includes 30 collaborating scientists from five countries. The project, which gained momentum during the International Polar Year, established more than 1,000 oceanographic stations in the Arctic and performed a few million measurements of methane mixing ratios of the Arctic atmosphere in the last five years. It is part of UAF’s work during IPY, an international event that is focusing research efforts and public attention on the Earth’s polar regions.
Semiletov is a chemical oceanographer who has studied carbon cycling in the arctic atmosphere-land-shelf system with emphasis on carbon dioxide and dissolved methane from both terrestrial and oceanic sources since the early 1990s. He joined the International Arctic Research Center in 2001. Since 2004, he has collaborated with IARC scientist Natalia Shakhova to develop the methane study at IARC.
International Siberian Shelf Study collaborators University of Alaska Fairbanks: Igor Semiletov, Natalia Shakhova, John Kelly, Vladimir Romanovsky, Gleb Panteleev, Sergei Marchenko, Dmitry Nicolsky, Alexander Kholodov; FEBRAS: Oleg Dudarev, Anatoly Salyuk, Irina Pipko, Viktor Karnaukh, Alexander Charkin, Denis Kosmach, Nina Bel’cheva, Svetlana Pugach, Nina Savelieva, Vladimir Iosoupov, Valentin Sergienko; Stockholm University: Orjan Gustafsson, Per Andersson, Jorien Vonk, Laura Sanchez-Garcia, Christoph Humborg, Vanja Alling; Gotheburg University: Leif Anderson, Goran Björk, Anders Olsson, Sara Jutterström, Sofia Hjalmarsson, Irene Wåhlström; Swedish Museum of Natural History: Per Andersson; Utrecht University: Celia Sapart, T. Roeckmanm; Institute of Atmospheric Physics RAS: Georgiu Golytsin, Irina Repina; Moscow State University: Nicolai Romanovskii, Vladimir Tumskoy; University of Manchester: Bart van Dongen; Luleå University of Technology: Johan Ingri, Fredrik Nordblad, Johan Gelting; Oxford University: Don Porcelli.
Adapted from materials provided by University of Alaska

New Pathway For Methane Production In The Oceans Discovered

A new pathway for methane production has been uncovered in the oceans, and this has a significant potential impact for the study of greenhouse gas production on our planet. The article, published in the journal Nature Geoscience, reveals that aerobic decomposition of an organic, phosphorus-containing compound, methylphosphonate, may be responsible for the supersaturation of methane in ocean surface waters.

Methane is a more potent greenhouse gas than CO2 on a per weight basis. Although the volume of methane in the atmosphere is considerably less than CO2, methane is much more efficient at trapping the long wavelength radiation that keeps our planet habitable but is also responsible for enhanced greenhouse warming. Today, between 20-30% of the total radiative forcing of the atmosphere is due to methane. Terrestrial sources of methane production are well known and studied (including extraction from natural gas deposits and fermentation of organic matter), but those known sources did not account for the levels of methane observed in the atmosphere.
David Karl, an Oceanographer in the School of Ocean and Earth Science and Technology at the University of Hawai'i at Mânoa and lead author of this paper, was interested in this "methane enigma" and why the surface ocean was loaded with methane, over and above levels found in the atmosphere. When looking at the literature, Karl found a possible solution to the enigma, in the compound methylphosphonates, a very unusual organic compound only discovered in the 1960s. In the laboratory, the aerobic growth of certain bacteria on methylphosphonate can lead to the production of methane, but until now this process of methylphosphonate degradation in the ocean had not been suggested as a possible pathway for the aerobic production of methane in the sea.
"When people began measuring methane in the ocean, they found that methane concentrations varied with geographical location and with water depth", says Karl. "If methane was inert in the ocean, its concentration should be constant and nearly equal to the concentration in the atmosphere. What the scientists found was that methane was lower than expected in deep waters, implying net consumption by microbes. However the big surprise was that near surface concentrations were higher than in the overlying atmosphere which indicated a local production of methane in the sea. Because methane is produced only in regions devoid of oxygen and since the surface ocean contains high oxygen levels this was very perplexing."
Karl was able to combine a long term interest in methane, 20 years of ocean observing data at the Hawaii Ocean Timeseries site Station Aloha, and new technology that Massachusetts Institute of Technology co-author Edward DeLong and colleagues have developed to produce methane in aerobic marine environments. "I think this work nicely demonstrates the complementarity of different methods and approaches, which include oceanography, microbial ecology, and genomics techniques," says DeLong. "In the case of genomics, the growing databases of marine microbial genomic and metagenomic data have great potential to help us link which organisms, and which genes, are responsible for driving important nutrient and elemental cycles in the sea, like aerobic methane generation.
With our colleagues at the Center for Microbial Oceanography: Research and Education (C-MORE, of which Karl is the Director, and DeLong the Co-Director), we plan next to learn how and when microbial communities turn on and off their methane production genes, in response to the methane precursors, like methylphosphonate, in their natural environment. This should provide new insights about the 'who' and the 'how' of this newly discovered methane generating process in the sea."
Although the implications for global climate change are still being studied, the warming and further stratification of the ocean seem likely to affect marine methane production. "This is a newly recognized pathway of methane formation that needs to be incorporated into our thinking of global climate," says Karl. "Since our oceans cover ¾ of the planet, you just need to stimulate this pathway a little bit and you're going to create more methane. And one way you can tweak it is to stratify the oceans, which we know will happen. All of the climate models show that the ocean will become more nutrient limited over time."
Phil Taylor, Acting Head of the Ocean Section, Division of Ocean Sciences at the National Science Foundation (NSF) agrees. "This remarkable discovery about methane production where we thought there would be none is a harbinger of many new insights on the ocean's changing biogeochemical nature, and the intricate microbiological reasons for those changes."
Interest in this research crosses many specialties. Oceanographers will be excited because it offers a solution to the long standing methane paradox. Microbiologists will be excited because it shows an aerobic production pathway of methane, which goes against everything that is currently known about methane, and Climatologists will be interested because it's a potent greenhouse gas that we don't have constraints on, and this new pathway is very exciting.
"NSF funded C-MORE with the hope that its scientists would make new discoveries about the vast genomic diversity and complexity in the microbial world, and its impacts from cellular to global scales," says Matt Kane, Program Director for the NSF Division of Environmental Biology. "These findings are an example of the payoffs that come from an interdisciplinary and integrative approach to microbial oceanography."
This research was supported by the Gordon and Betty Moore Foundation and the National Science Foundation.
Journal reference:
David M. Karl, Lucas Beversdorf, Karin M. Björkman, Matthew J. Church, Asuncion Martinez & Edward F. Delong. Aerobic production of methane in the sea. Nature Geoscience, Published online: 29 June 2008 DOI: 10.1038/ngeo234
Adapted from materials provided by University of Hawaii at Manoa.

Paired Microbes Eliminate Methane Using Sulfur Pathway

Anaerobic microbes in the Earth's oceans consume 90 percent of the methane produced by methane hydrates -- methane trapped in ice -- preventing large amounts of methane from reaching the atmosphere। Researchers now have evidence that the two microbes that accomplish this feat do not simply reverse the way methane-producing microbes work, but use a sulfur compound instead.

"The dominant role anaerobic oxidation of methane plays in regulating marine methane makes it a significant component of the global methane and carbon cycles," the researchers report in the current issue of Environmental Microbiology. "Its importance in these cycles highlights the need to close gaps in the current understanding of the specific interaction between the microbial groups that work in concert to mediate anaerobic oxidation of methane."
In this case, the microbial consortia consist of an Archaea -- a single cell organism -- that consumes methane for energy and bacteria that reduce sulfates to obtain energy. The assumption has been that these microbes simply use reverse methanogenesis, the process in which methanogenic bacteria produce methane in the first place.
"Our research suggests that methyl sulfide is the intermediary used by these microbes," says Christopher H. House, associate professor of geosciences. "The Archaea take in the methane and produce a methyl sulfide, and then the sulfur-reducing bacteria eat the methyl sulfide and reduced it to sulfide."
The two single-celled organisms that live in the consortia arrange themselves in a cluster of about 100 cells 10 to 15 microns across. The microbes that consume methane are on the inside while those microbes-reducing sulfur are on the outside. These consortia live in the sediments on the ocean bottom around methane seeps.
Understanding how these symbiotic organisms remove methane from the oceans is important because, House notes that without these microbes, the atmospheric temperature would likely be warmer by about 14 degrees Fahrenheit.
House, working with James J. Moran, graduate student in geosciences now at McMaster University; Emily J. Beal, graduate student in geosciences; Jennifer M. Vrentas, a Penn State undergraduate at the time; Katherine Freeman, professor of geosciences, all at Penn State, and Victoria J. Orphan, assistant professor of geobiology, California Institute of Technology, first investigated the assumption that reverse methanogenesis was the method used by the microbes. They provided hydrogen to the consortium and checked to see if methane oxidation decreased. If hydrogen were the interspecies transfer molecule, than an abundance of hydrogen would turn off the methane oxidation.
"We observed a minimal reduction in the rate of methane oxidation, and conclude that hydrogen does not play an interspecies role in anaerobic oxidation of methane," the researchers say.
They then tried the methyl sulfides, methanethiol (methyl mercaptan) and dimethyl sulfide, to see if they reduced methane oxidation. The researchers found that methanethiol reduced oxidation. The researchers also substituted carbon monoxide for methane and found that the Archaea could oxidize that as well and produce these sulfur compounds.
"In climate models, researchers generally only consider the methane produced in bogs and lakes as dominant greenhouse gases," says House. "They do not need to consider ocean methane because these microbes destroy most of it before it is released from the sediments."
The National Science Foundation, NASA and the National Oceanic and Atmospheric Administration supported this work.
Adapted from materials provided by Penn State.