Cryolava flow destabilization of crustal methane clathrate hydrate on Titan

Cryolava flow destabilization of crustal methane clathrate hydrate on Titan

Authors:

Davies et al

Abstract:

To date, there has been no conclusive observation of ongoing endogenous volcanic activity on Saturn's moon Titan. However, with time, Titan's atmospheric methane is lost and must be replenished. We have modeled one possible mechanism for the replenishment of Titan's methane loss. Cryolavas can supply enough heat to release large amounts of methane from methane clathrate hydrates (MCH). The volume of methane released is controlled by the flow thickness and its areal extent. The depth of the destabilisation layer is typically ≈30% of the thickness of the lava flow (≈3 m for a 10-m thick flow). For this flow example, a maximum of 372 kg of methane is released per m2 of flow area. Such an event would release methane for nearly a year. One or two events per year covering ∼20 km2 would be sufficient to resupply atmospheric methane. A much larger effusive event covering an area of ≈9000 km2 with flows 200 m thick would release enough methane to sustain current methane concentrations for 10,000 years. The minimum size of “cryo-flows” sufficient to maintain the current atmospheric methane is small enough that their detection with current instruments (e.g., Cassini) could be challenging. We do not suggest that Titan's original atmosphere was generated by this mechanism. It is unlikely that small-scale surface MCH destabilisation is solely responsible for long-term (greater than a few Myr) sustenance of Titan's atmospheric methane, but rather we present it as a possible contributor to Titan's past and current atmospheric methane.

Carnian/Norian Boundary Environmental Changes Were NOT Caused by Methane Hydrates or Volcanic Eruptions

Paleoenvironmental changes across the Carnian/Norian boundary in the Black Bear Ridge section, British Columbia, Canada

Authors:

Onoue et al

Abstract:

The Black Bear Ridge section in northeastern British Columbia, Canada, consists of a continuously exposed sequence of Upper Carnian through Lower Norian (Upper Triassic) continental margin strata. The section has been proposed as a candidate Global Stratotype Section and Point (GSSP) for the Carnian/Norian boundary (CNB). In order to assess Late Carnian to Early Norian environmental changes recorded in the section, we examined stratigraphic variations in 87Sr/86Sr, δ13C, and δ18O values, and also values of redox sensitive elements (V, Ni and Cr), in the CNB interval. The study section is located along the north shore of Williston Lake, northeastern British Columbia. The Black Bear Ridge section was deposited in a distal ramp environment on the passive western margin of the North American craton.

The strata across the CNB display a positive shift in δ13C values and a corresponding increase in the redox indices V/(V + Ni) and V/Cr. The synchronous increase in δ13C values and redox indices suggests that burial rates of marine organic carbon increased in response to the development of anoxic conditions in the water column. An increase in δ13C values in carbonate rocks across the CNB has also been reported from Upper Triassic sections in the western Tethys (e.g., in the Pizzo Mondello section, Sicily), which suggests that the development of anoxic conditions within the CNB interval was widespread, affecting both the Panthalassan Ocean and Tethyan Sea. The geochemical data from this study, as well as from research into conodont biostratigraphy in the Black Bear Ridge section, show that the onset of oceanic anoxic conditions may have been responsible for the faunal turnover event at the CNB. The cause of this anoxic event is unknown, but the 87Sr/86Sr and δ13C isotope data largely exclude the possibility that the event was triggered by dissociation of methane hydrates and degassing related to large-scale volcanic activity.

Methanosarcina Developed Efficient Methanogenic Pathways at the Time of the Permian Extinction

Methanogenic burst in the end-Permian carbon cycle

Authors:

Rothman et al

Abstract:

The end-Permian extinction is associated with a mysterious disruption to Earth’s carbon cycle. Here we identify causal mechanisms via three observations. First, we show that geochemical signals indicate superexponential growth of the marine inorganic carbon reservoir, coincident with the extinction and consistent with the expansion of a new microbial metabolic pathway. Second, we show that the efficient acetoclastic pathway in Methanosarcina emerged at a time statistically indistinguishable from the extinction. Finally, we show that nickel concentrations in South China sediments increased sharply at the extinction, probably as a consequence of massive Siberian volcanism, enabling a methanogenic expansion by removal of nickel limitation. Collectively, these results are consistent with the instigation of Earth’s greatest mass extinction by a specific microbial innovation.

Real Climate on New Atmospheric Methane Papers

Lots of interesting methane papers this week. In Nature Geoscience, Shakhova et al (2013) have published a substantial new study of the methane cycle on the Siberian continental margin of the Arctic Ocean. This paper will get a lot of attention, because it follows by a few months a paper from last summer, Whiteman et al (2013), which claimed a strong (and expensive) potential impact from Arctic methane on near-term climate evolution. That economic modeling study was based on an Arctic methane release scenario proposed in an earlier paper by Shakhova (2010). In PNAS, Miller et al (2013) find that the United States may be emitting 50-70% more methane than we thought. So where does this leave us?

link.

Japan Begins Extracting Natural Gas From Methane Calthrates

Two years after the Fukushima meltdown, most of Japan’s nuclear reactors remain shuttered, and that anniversary this week has sparked discussion about Japan’s energy sources. The country has depended almost exclusively on imported fossil fuels since the disaster. But in news announced today, Japan has become the first country to successfully extract methane from frozen reserves under the ocean floor, opening a new potential energy source for the country.

Methane is the primary component of natural gas but methane hydrate offers an even more concentrated source. One cubic foot of hydrate traps about 164 cubic feet of methane gas, according to the U.S. Geological Survey. The methane in hydrate is frozen within an ice lattice, forming a sherbet-like substance.

To get the methane gas out, Japanese engineers used a depressurization method that turns methane hydrate into methane gas. Extraction began this morning, about 30 miles offshore of Japan’s main island and at a depth of around 1,000 feet below the seabed.

Methane Hydrates May Already Be Collapsing

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.

hmmm.

Are the Methane Hydrates Starting to Collapse?

At the bottom of the Arctic Sea lie vast deposits of methane gas trapped in frozen, icy forms called methane hydrates, and climate scientists would very much prefer that it remains trapped down there. Methane is a powerful greenhouse gas, and some researchers worry that a warming ocean may melt the icy structures, allowing the gas to travel up through the water to the atmosphere, where it could further contribute to global warming. Now, scientists who have been scanning the seas for signs of trouble say they may have found some.

The researchers spotted 250 plumes of methane gas bubbling up through the sea north of Norway. The region where the team found the plumes is being warmed by the West Spitsbergen current, which has warmed by 1 °C over the past 30 years. “Hydrates are stable only within a particular range of temperatures,” says [study coauthor Tim] Minshull. “So if the ocean warms, some of the hydrates will break down and release their methane” [New Scientist]. However, the scientists couldn’t prove that the methane is being released as a direct result of the warming, and say it’s possible there have always been methane seeps like these.

The plumes, reported in the journal Geophysical Research Letters, were detected using a kind of sonar that is typically used by biologists searching for shoals of fish. All of the gas plumes spotted by the researchers dissolved into the water before reaching the ocean’s surface, meaning that bubbles of methane weren’t escaping into the atmosphere to contribute to global warming. Just because it fails to reach the surface doesn’t mean the methane is harmless, though, as some of it gets converted to carbon dioxide. The CO2 then dissolves in seawater and makes the oceans more acidic [New Scientist]

That'd also reduce the amount of CO2 that the oceans can take up as well, btw.

More Evidence of PETM Methane Release

Kick-starting ancient warming

E. G. Nisbet¹, S. M. Jones², J. Maclennan³, G. Eagles¹, J. Moed⁴, N. Warwick⁴, S. Bekki⁵, P. Braesicke⁴, J. A. Pyle⁴ & C. M. R. Fowler¹

Rapid global warming marked the boundary between the Palaeocene and Eocene periods 55.6 million years ago, but how the temperature rise was initiated remains elusive. A catastrophic release of greenhouse gases from the Kilda basin could have served as a trigger.

Introduction

The warm period known as the Palaeocene–Eocene Thermal Maximum (PETM) was a period of climatic turmoil that lasted more than 100,000 years1. Ocean temperatures increased by 3–10 °C, and atmospheric concentrations of methane and carbon dioxide rose sharply1. Meanwhile, the oceans became more acidic and the carbon isotopic values of marine carbonates declined significantly, a sign of a disrupted carbon cycle. These latter observations suggest that several thousand gigatonnes of isotopically light carbon must have been injected into the atmosphere–ocean system over the course of the event1, 2. Sources including the release of methane during the intrusion of magma into organic-rich sedimentary rocks, carbon dioxide outgassing from lava flows, and dissociation of methane gas hydrates in marine sediments2, 3, 4 have all been previously invoked in the perturbation — but we still do not know how much light carbon came from each source.

We are also unsure just what triggered the initial warming1, 2, 3, 4. More data on the environmental conditions of the PETM are becoming available, and it is now clear that the warming began several thousand years before the main disruption to the carbon cycle that is documented in the worldwide decrease in carbon isotope values5 often used to define the event. Therefore, the initial warming was probably a necessary precursor of the upheaval of the carbon cycle. Because, over a 20-year period, methane is 72 times more potent than carbon dioxide as a global warmer, a rapid injection of a relatively small amount of methane into the atmosphere could have caused the initial warming without leaving an identifiable isotopic signature. Mechanisms that have been suggested to provide such a methane burst include seabed hydrothermal activity and large submarine landslides3, 6.

Here we propose an alternative: we suggest that the early warming of the PETM was initiated by catastrophic expulsions of methane and also carbon dioxide that had accumulated over time in the stratified waters of the Kilda basin between Greenland and Norway, in a mechanism similar to that seen today in African rift lakes.

Correspondence to: E. G. Nisbet¹ e-mail: e.nisbet@es.rhul.ac.uk

Correspondence to: S. M. Jones² e-mail: stephen.jones@tcd.ie

Link to paper at the top. I can get it for anyone that wants it. I'll read it and add comments later. Press release here.

Methane Calthrates Not Source at End of Ice Age

An expansion of wetlands and not a large-scale melting of frozen methane deposits is the likely cause of a spike in atmospheric methane gas that took place some 11,600 years ago, according to an international research team led by Scripps Institution of Oceanography at UC San Diego.

The finding is expected to come as a relief to scientists and climate watchers concerned that huge accelerations of global warming might have been touched off by methane melts in the past and could happen again now as the planet warms. By measuring the amount of carbon-14 isotopes in methane from air bubbles trapped in glacial ice, the researchers determined that the surge that took place nearly 12,000 years ago was more chemically consistent with an expansion of wetlands. Wetland regions, which produce large amounts of methane from bacterial breakdown of organic matter, are known to have spread during warming trends throughout history.

"This is good news for global warming because it suggests that methane clathrates do not respond to warming by releasing large amounts of methane into the atmosphere," said Vasilii Petrenko, a postdoctoral fellow at University of Colorado, Boulder, who led the analysis while a graduate student at Scripps.

The results appear in April 24 editions of the journal Science.

I'll need that paper, folks, please!

More press releases here and here.