Showing papers on "Atmospheric methane published in 2009"

Strong Release of Methane on Mars in Northern Summer 2003

Abstract: Living systems produce more than 90% of Earth9s atmospheric methane; the balance is of geochemical origin. On Mars, methane could be a signature of either origin. Using high-dispersion infrared spectrometers at three ground-based telescopes, we measured methane and water vapor simultaneously on Mars over several longitude intervals in northern early and late summer in 2003 and near the vernal equinox in 2006. When present, methane occurred in extended plumes, and the maxima of latitudinal profiles imply that the methane was released from discrete regions. In northern midsummer, the principal plume contained ∼19,000 metric tons of methane, and the estimated source strength (≥0.6 kilogram per second) was comparable to that of the massive hydrocarbon seep at Coal Oil Point in Santa Barbara, California.

Observational constraints on recent increases in the atmospheric CH4 burden

Abstract: [1] Measurements of atmospheric CH4 from air samples collected weekly at 46 remote surface sites show that, after a decade of near-zero growth, globally averaged atmospheric methane increased during 2007 and 2008. During 2007, CH4 increased by 8.3 ± 0.6 ppb. CH4 mole fractions averaged over polar northern latitudes and the Southern Hemisphere increased more than other zonally averaged regions. In 2008, globally averaged CH4 increased by 4.4 ± 0.6 ppb; the largest increase was in the tropics, while polar northern latitudes did not increase. Satellite and in situ CO observations suggest only a minor contribution to increased CH4 from biomass burning. The most likely drivers of the CH4 anomalies observed during 2007 and 2008 are anomalously high temperatures in the Arctic and greater than average precipitation in the tropics. Near-zero CH4 growth in the Arctic during 2008 suggests we have not yet activated strong climate feedbacks from permafrost and CH4 hydrates.

Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event

Abstract: It has been suggested that a decrease in atmospheric methane levels triggered the progressive rise of atmospheric oxygen, the so-called Great Oxidation Event, about 24 Gyr ago(1) Oxidative weathering of terrestrial sulphides, increased oceanic sulphate, and the ecological success of sulphate-reducing microorganisms over methanogens has been proposed as a possible cause for the methane collapse(1), but this explanation is difficult to reconcile with the rock record(2,3) Banded iron formations preserve a history of Precambrian oceanic elemental abundance and can provide insights into our understanding of early microbial life and its influence on the evolution of the Earth system(4,5) Here we report a decline in the molar nickel to iron ratio recorded in banded iron formations about 27 Gyr ago, which we attribute to a reduced flux of nickel to the oceans, a consequence of cooling upper-mantle temperatures and decreased eruption of nickel-rich ultramafic rocks at the time We measured nickel partition coefficients between simulated Precambrian sea water and diverse iron hydroxides, and subsequently determined that dissolved nickel concentrations may have reached similar to 400nM throughout much of the Archaean eon, but dropped below similar to 200nM by 25 Gyr ago and to modern day values(6) (similar to 9 nM) by similar to 550 Myr ago Nickel is a key metal cofactor in several enzymes of methanogens(7) and we propose that its decline would have stifled their activity in the ancient oceans and disrupted the supply of biogenic methane A decline in biogenic methane production therefore could have occurred before increasing environmental oxygenation and not necessarily be related to it The enzymatic reliance of methanogens on a diminishing supply of volcanic nickel links mantle evolution to the redox state of the atmosphere

Oceanic Nickel depletion and a methanogen famine before the Great Oxidation Event

Abstract: It has been suggested that a decrease in atmospheric methane levels triggered the progressive rise of atmospheric oxygen, the so-called Great Oxidation Event, about 2.4 Gyr ago(1). Oxidative weathering of terrestrial sulphides, increased oceanic sulphate, and the ecological success of sulphate-reducing microorganisms over methanogens has been proposed as a possible cause for the methane collapse(1), but this explanation is difficult to reconcile with the rock record(2,3). Banded iron formations preserve a history of Precambrian oceanic elemental abundance and can provide insights into our understanding of early microbial life and its influence on the evolution of the Earth system(4,5). Here we report a decline in the molar nickel to iron ratio recorded in banded iron formations about 2.7 Gyr ago, which we attribute to a reduced flux of nickel to the oceans, a consequence of cooling upper-mantle temperatures and decreased eruption of nickel-rich ultramafic rocks at the time. We measured nickel partition coefficients between simulated Precambrian sea water and diverse iron hydroxides, and subsequently determined that dissolved nickel concentrations may have reached similar to 400nM throughout much of the Archaean eon, but dropped below similar to 200nM by 2.5 Gyr ago and to modern day values(6) (similar to 9 nM) by similar to 550 Myr ago. Nickel is a key metal cofactor in several enzymes of methanogens(7) and we propose that its decline would have stifled their activity in the ancient oceans and disrupted the supply of biogenic methane. A decline in biogenic methane production therefore could have occurred before increasing environmental oxygenation and not necessarily be related to it. The enzymatic reliance of methanogens on a diminishing supply of volcanic nickel links mantle evolution to the redox state of the atmosphere.

The indirect global warming potential and global temperature change potential due to methane oxidation

Abstract: Methane is the second most important anthropogenic greenhouse gas in the atmosphere next to carbon dioxide. Its global warming potential (GWP) for a time horizon of 100 years is 25, which makes it an attractive target for climate mitigation policies. Although the methane GWP traditionally includes the methane indirect effects on the concentrations of ozone and stratospheric water vapour, it does not take into account the production of carbon dioxide from methane oxidation. We argue here that this CO2-induced effect should be included for fossil sources of methane, which results in slightly larger GWP values for all time horizons. If the global temperature change potential is used as an alternative climate metric, then the impact of the CO2-induced effect is proportionally much larger. We also discuss what the correction term should be for methane from anthropogenic biogenic sources.

The quest for atmospheric methane oxidizers in forest soils

Abstract: Aerobic methanotrophs in forest soils are the largest biological sink for atmospheric methane (CH4 ). Community structures in 53 soils from Europe, Russia, North and South America, Asia and New Zealand located in boreal, temperate and tropical forests were analysed and maximal abundances of 2.1 × 10(7) methanotrophs g(-1) DW were measured. In acidic soils, the most frequently detected pmoA genotypes were Upland Soil Cluster α (USCα) and Methylocystis spp. Phospholipid fatty acids that were labelled by consumption of (14/13) CH4 suggested the activity of type II methanotrophs. Cluster 1 (Methylocystaceae), USCγ and Methylocystis spp. were frequently detected genotypes in pH-neutral soils. Genotypes with ambiguous functional affiliation were co-detected (Clusters MR1, RA21, 2) and may represent aerobic methanotrophs, ammonia oxidizers or enzymes with an unknown function. The physiological traits of atmospheric CH4 oxidizers are largely unknown because organisms possessing the key forest soil pmoA genotypes (USCα, USCγ, Cluster 1) have not been cultivated. Some methanotrophic strains belonging to the family Methylocystaceae have been shown to oxidize CH4 at atmospheric mixing ratios. Methylocystis strain SC2 was found to have an alternative particulate CH4 monooxygenase responsible for CH4 oxidation at atmospheric mixing ratios. pH, forest type and temperature might be environmental factors that shape methanotrophic communities in forest soils. However, specific effects on individual species are largely unknown, and only a limited number of studies have addressed environmental controls of methanotrophic diversity, pointing to the need for future research in this area.

Considerable methane fluxes to the atmosphere from hydrocarbon seeps in the Gulf of Mexico

Abstract: The flux of methane—a greenhouse gas—from submarine hydrocarbon seeps to the atmosphere is not well quantified. Direct measurements of methane concentrations and isotopic depth profiles in deepwater hydrocarbon plumes indicate that a significant amount of methane from deep-ocean sources could reach the surface ocean. The fluxes of the greenhouse gas methane from many individual sources to the atmosphere are not well constrained1. Marine geological sources may be significant2, but they are poorly quantified and are not included in the Intergovernmental Panel on Climate Change budget1. Previous results based on traditional indirect sampling techniques and modelling suggested bubble plumes emitted from marine seeps at depths greater than 200 m do not reach the surface mixed layer because of bubble dissolution and methane oxidation3,4,5. Here we report methane concentration and isotope-depth profiles from direct submersible sampling of deepwater (550–600 m) hydrocarbon plumes in the Gulf of Mexico. We show that bubble size, upwelling flows and the presence of surfactants inhibit bubble dissolution, and that methane oxidation is negligible. Consequently, methane concentrations in surface waters are up to 1,000 times saturation with respect to atmospheric equilibrium. We estimate that diffusive atmospheric methane fluxes from individual plumes are one to three orders of magnitude greater than estimates from shallow-water seeps6,7,8, greatly expanding the depth range from which methane seep emissions should be considered significant. Given the widespread occurrence of deepwater seeps, we suggest that current estimates of the global oceanic methane flux to the atmosphere1 may be too low.

Three years of greenhouse gas column-averaged dry air mole fractions retrieved from satellite - Part 2: Methane

Abstract: . Carbon dioxide (CO2) and methane (CH4) are the two most important anthropogenic greenhouse gases. SCIAMACHY on ENVISAT is the first satellite instrument whose measurements are sensitive to concentration changes of the two gases at all altitude levels down to the Earth's surface where the source/sink signals are largest. We have processed three years (2003–2005) of SCIAMACHY near-infrared nadir measurements to simultaneously retrieve vertical columns of CO2 (from the 1.58 μm absorption band), CH4 (1.66 μm) and oxygen (O2 A-band at 0.76 μm) using the scientific retrieval algorithm WFM-DOAS. We show that the latest version of WFM-DOAS, version 1.0, which is used for this study, has been significantly improved with respect to its accuracy compared to the previous versions while essentially maintaining its high processing speed (~1 min per orbit, corresponding to ~6000 single measurements, and per gas on a standard PC). The greenhouse gas columns are converted to dry air column-averaged mole fractions, denoted XCO2 (in ppm) and XCH4 (in ppb), by dividing the greenhouse gas columns by simultaneously retrieved dry air columns. For XCO2 dry air columns are obtained from the retrieved O2 columns. For XCH4 dry air columns are obtained from the retrieved CO2 columns because of better cancellation of light path related errors compared to using O2 columns retrieved from the spectrally distant O2 A-band. Here we focus on a discussion of the XCH4 data set. The XCO2 data set is discussed in a separate paper (Part 1). For 2003 we present detailed comparisons with the TM5 model which has been optimally matched to highly accurate but sparse methane surface observations. After accounting for a systematic low bias of ~2% agreement with TM5 is typically within 1–2%. We investigated to what extent the SCIAMACHY XCH4 is influenced by the variability of atmospheric CO2 using global CO2 fields from NOAA's CO2 assimilation system CarbonTracker. We show that the CO2 corrected and uncorrected XCH4 spatio-temporal pattern are very similar but that agreement with TM5 is better for the CarbonTracker CO2 corrected XCH4. In line with previous studies (e.g., Frankenberg et al., 2005b) we find higher methane over the tropics compared to the model. We show that tropical methane is also higher when normalizing the CH4 columns with retrieved O2 columns instead of CO2. In consistency with recent results of Frankenberg et al. (2008b) it is shown that the magnitude of the retrieved tropical methane is sensitive to the choice of the spectroscopic line parameters of water vapour. Concerning inter-annual variability we find similar methane spatio-temporal pattern for 2003 and 2004. For 2005 the retrieved methane shows significantly higher variability compared to the two previous years, most likely due to somewhat larger noise of the spectral measurements.

Early evaluation of potential environmental impacts of carbon nanotube synthesis by chemical vapor deposition.

Abstract: The carbon nanotube (CNT) industry is expanding rapidly, yet little is known about the potential environmental impacts of CNT manufacture. Here, we evaluate the effluent composition of a representative multiwalled CNT synthesis by catalytic chemical vapor deposition (CVD) in order to provide data needed to design strategies for mitigating any unacceptable emissions. During thermal pretreatment of the reactant gases (ethene and H2), we found over 45 side-products were formed, including methane, volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs). This finding suggests several environmental concerns with the existing process, including potential discharges of the potent greenhouse gas, methane (up to 1.7%), and toxic compounds such as benzene and 1,3-butadiene (up to 36000 ppmv). Extrapolating these laboratory-scale data to future industrial CNT production, we estimate that (1) contributions of atmospheric methane will be negligible compared to other existing sources and (2) VOC a...

14CH4 Measurements in Greenland Ice: Investigating Last Glacial Termination CH4 Sources

Abstract: The cause of a large increase of atmospheric methane concentration during the Younger Dryas–Preboreal abrupt climatic transition (~11,600 years ago) has been the subject of much debate. The carbon-14 ( 14 C) content of methane ( 14 CH 4 ) should distinguish between wetland and clathrate contributions to this increase. We present measurements of 14 CH 4 in glacial ice, targeting this transition, performed by using ice samples obtained from an ablation site in west Greenland. Measured 14 CH 4 values were higher than predicted under any scenario. Sample 14 CH 4 appears to be elevated by direct cosmogenic 14 C production in ice. 14 C of CO was measured to better understand this process and correct the sample 14 CH 4 . Corrected results suggest that wetland sources were likely responsible for the majority of the Younger Dryas–Preboreal CH 4 rise.

Hydrologic gradient and vegetation controls on CH4 and CO2 fluxes in a spring-fed forested wetland

Abstract: Four different habitats in a spring-fed forested wetland (Clear Springs Wetland, Panola County, Mississippi, USA) varying in hydrologic regime were examined for methane and carbon dioxide fluxes from soils over 15 and 9 months, respectively. There was an increasing gradient of CH4 flux rates from an unflooded upper-elevation forest site to an occasionally flooded bottomland forest site to a shallow permanently flooded site, and then to a deeper-water permanently flooded site. Depending on the time of year, all sites were sources of methane but only at the upper-elevation forest site, when gravimetric soil moisture content fell below 54%, was atmospheric methane consumed. On average, summer CH4 emission rates were higher than those in other seasons. A multiple regression model with soil temperature and soil redox potential as independent variables could explain 65% of the variation in CH4 flux rates. In the flooded zone, variation in CH4 flux rates was correlated with aboveground plant biomass and stem density of emergent vascular plants, and plant-mediated CH4 transport depended on plant type. The efflux of CH4 to plant biomass (Eff:B) ratio was generally lower in Hydrocotyle umbellata compared to Festuca obtusa. Compared to several other freshwater forested wetlands in the southeastern USA, this spring-fed forested wetland ecosystem was a strong source of atmospheric CH4, likely due to a long hydroperiod and high soil organic matter content. Carbon dioxide fluxes show a reverse spatial pattern than CH4 fluxes with highest CO2 emissions in the non-flooded zone at all times of the year, indicating the dominance of aerobic soil respiration. A multiple regression model also revealed a strong dependency of CO2 fluxes (r 2 = 0.73) on soil temperature and soil redox potential.

In situ measurement of methane fluxes and analysis of transcribed particulate methane monooxygenase in desert soils

Abstract: Aerated soils are a biological sink for atmospheric methane. However, the activity of desert soils and the presence of methanotrophs in these soils have hardly been studied. We studied on-site atmospheric methane consumption rates as well as the diversity and expression of the pmoA gene, coding for a subunit of the particulate methane monooxygenase, in arid and hyperarid soils in the Negev Desert, Israel. Methane uptake was only detected in undisturbed soils in the arid region (approximately 90 mm year(-1)) and vertical methane profiles in soil showed the active layer to be at 0-20 cm depth. No methane uptake was detected in the hyperarid soils (approximately 20 mm year(-1)) as well as in disturbed soils in the arid region (i.e. agricultural field and a mini-catchment). Molecular analysis of the methanotrophic community using terminal restriction fragment length polymorphism (T-RFLP) and cloning/sequencing of the pmoA gene detected methanotrophs in the active soils, whereas the inactive ones were dominated by sequences of the homologous gene amoA, coding for a subunit of the ammonia monooxygenase. Even in the active soils, methanotrophs (as well as in situ activity) could not be detected in the soil crust, which is the biologically most important layer in desert soils. All pmoA sequences belonged to yet uncultured strains. Transcript analysis showed dominance of sequences clustering within the JR3, formerly identified in Californian grassland soils. Our results show that although active methanotrophs are prevalent in arid soils they seem to be absent or inactive in hyperarid and disturbed arid soils. Furthermore, we postulate that methanotrophs of the yet uncultured JR3 cluster are the dominant atmospheric methane oxidizers in this ecosystem.

Feasibility of atmospheric methane removal using methanotrophic biotrickling filters.

Abstract: Methane is a potent greenhouse gas with a global warming potential ~23 times that of carbon dioxide Here, we describe the modeling of a biotrickling filtration system composed of methane-consuming bacteria, ie, methanotrophs, to assess the utility of these systems in removing methane from the atmosphere Model results indicate that assuming the global average atmospheric concentration of methane, 17 ppmv, methane removal is ineffective using these methanotrophic biofilters as the methane concentration is too low to enable cell survival If the concentration is increased to 500–6,000 ppmv, however, similar to that found above landfills and in concentrated animal feeding operations (factory farms), 498–357 tons of methane can be removed per biofilter per year assuming biotrickling filters of typical size (366 m in diameter and 115 m in height) Using reported ranges of capital, operational, and maintenance costs, the cost of the equivalent ton of CO2 removal using these systems is $90–$910 ($2,070–$20,900 per ton of methane), depending on the influent concentration of methane and if heating is required The use of methanotrophic biofilters for controlling methane emissions is technically feasible and, provided that either the costs of biofilter construction and operation are reduced or the value of CO2 credits is increased, can also be economically attractive

Effect of regional precursor emission controls on long-range ozone transport – Part 2: Steady-state changes in ozone air quality and impacts on human mortality

Abstract: . Large-scale changes in ozone precursor emissions affect ozone directly in the short term, and also affect methane, which in turn causes long-term changes in ozone that affect surface ozone air quality. Here we assess the effects of changes in ozone precursor emissions on the long-term change in surface ozone via methane, as a function of the emission region, by modeling 10% reductions in anthropogenic nitrogen oxide (NOx) emissions from each of nine world regions. Reductions in NOx emissions from all world regions increase methane and long-term surface ozone. While this long-term increase is small compared to the intra-regional short-term ozone decrease, it is comparable to or larger than the short-term inter-continental ozone decrease for some source-receptor pairs. The increase in methane and long-term surface ozone per ton of NOx reduced is greatest in tropical and Southern Hemisphere regions, exceeding that from temperate Northern Hemisphere regions by roughly a factor of ten. We also assess changes in premature ozone-related human mortality associated with regional precursor reductions and long-range transport, showing that for 10% regional NOx reductions, the strongest inter-regional influence is for emissions from Europe affecting mortalities in Africa. Reductions of NOx in North America, Europe, the Former Soviet Union, and Australia are shown to reduce more mortalities outside of the source regions than within. Among world regions, NOx reductions in India cause the greatest number of avoided mortalities per ton, mainly in India itself. Finally, by increasing global methane, NOx reductions in one hemisphere tend to cause long-term increases in ozone concentration and mortalities in the opposite hemisphere. Reducing emissions of methane, and to a lesser extent carbon monoxide and non-methane volatile organic compounds, alongside NOx reductions would avoid this disbenefit.

The Contribution of the East Siberian Shelf to the Modern Methane Cycle

Abstract: Methane-containing sediments, accumulated everywhere along continental margins, are a powerful source of atmospheric methane, the third (after carbon dioxide and water vapors) most significant greenhouse gas. Meanwhile, until recently, scientific literature lacked data on the contribution of arctic continental margins to the formation of the global methane budget, as well as realistic forecast scenarios of future climate changes. The results of five-year-long (2003–2007) biogeochemical studies on the East Siberian shelf, which characterize the main arctic methane sources and reservoirs, including unique shelf gas hydrates, are presented in the article below. The studies were conducted by researchers of the Pacific Institute of Oceanology, RAS Far Eastern Division, with the participation of researchers of the International Arctic Research Center of the University of Alaska, Fairbanks.

Global Methane Emissions From Wetlands, Rice Paddies, and Lakes

Abstract: The current concentration of atmospheric methane is 1774±1.8 parts per billion, and it accounts for 18% of total greenhouse gas radiative forcing [Forster et al., 2007]. Atmospheric methane is 22 times more effective, on a per-unit-mass basis, than carbon dioxide in absorbing long-wave radiation on a 100-year time horizon, and it plays an important role in atmospheric ozone chemistry (e.g., in the presence of nitrous oxides, tropospheric methane oxidation will lead to the formation of ozone). Wetlands are a large source of atmospheric methane, Arctic lakes have recently been recognized as a major source [e.g., Walter et al., 2006], and anthropogenic activities—such as rice agriculture—also make a considerable contribution.

Volatile Origin and Cycles: Nitrogen and Methane

Abstract: The story of Titan's two most abundant volatile constituents, nitrogen and methane, is intertwined. The focus of this paper is the origin and evolution of Titan's nitrogen atmosphere and the cycle of methane from its production to destruction to replenishment. Relevant observational results from Cassini—Huygens, Voyager and the Earth as well as various hypotheses and models are reviewed. The origin of nitrogen by direct capture, and from dissociation of primordial nitrogen-bearing molecules, especially ammonia, by impact, photolysis, thermal and other processes is evaluated. Similarly, the origin of methane from Saturn's sub-nebula or by water-rock reactions in Titan's interior is reviewed. The role of methane in regulating Titan's climate is noted, and similarities and differences between the methane cycle in Titan's troposphere and the hydrological cycle on Earth are discussed. The fate of methane in the stratosphere and the upper atmosphere/ionosphere is examined in order to evaluate the possibility and extent of an ocean of ethane, requirement of methane replenishment, and the role of product aerosols in maintaining Titan's nitrogen atmosphere.

The consumption of atmospheric methane by soil in a simulated future climate

Abstract: . A recently developed model for the consumption of atmospheric methane by soil (Curry, 2007) is used to investigate the global magnitude and distribution of methane uptake in a simulated future climate. In addition to solving the one-dimensional diffusion-reaction equation, the model includes a parameterization of biological CH4 oxidation that is sensitive to soil temperature and moisture content, along with specified reduction factors for land cultivation and wetland fractional coverage. Under the SRES emission scenario A1B, the model projects an 8% increase in the global annual mean CH4 soil sink by 2100, over and above the 15% increase expected from increased CH4 concentration alone. While the largest absolute increases occur in cool temperate and subtropical forest ecosystems, the largest relative increases in consumption (>40%) are seen in the boreal forest, tundra and polar desert environments of the high northern latitudes. Methane uptake at mid- to high northern latitudes increases year-round in 2100, with a 68% increase over present-day values in June. This increase is primarily due to enhanced soil diffusivity resulting from lower soil moisture produced by increased evaporation and reduced snow cover. At lower latitudes, uptake is enhanced mainly by elevated soil temperatures and/or reduced soil moisture stress, with the dominant influence determined by the local climate.

Global Warming and Carbon Dynamics in Permafrost Soils: Methane Production and Oxidation

Abstract: The Arctic plays a key role in the Earths climate system, because global warming is predicted to be most pronounced at high latitudes, and one third of the global carbon pool is stored in ecosystems of the northern latitudes. The degradation of permafrost and the associated release of climate-relevant trace gases from intensified microbial turnover of organic carbon and from destabilized gas hydrates represent a potential environmental hazard.The microorganisms, which are the drivers of methane production and oxidation in Arctic wetlands, have remained obscure. Their function, population structure and reaction to environmental change is largely unknown, which means that also an important part of the process knowledge on methane fluxes in permafrost ecosystems is far from completely understood. This hampers prediction of the effects of climate warming on arctic methane fluxes. Understanding these microbial populations is therefore highly important for understanding the global climatic effects of a warming Arctic. This talk will examine the activity and diversity of methane-cycling microorganisms in Siberian permafrost ecosystems.

Decreasing anthropogenic methane emissions in Europe and Siberia inferred from continuous carbon dioxide and methane observations at Alert, Canada

Abstract: [1] The rate of increase in global atmospheric methane (CH4) abundance has steadily declined since the late 1980s with near zero increase from 1999 through 2006. At the Canadian Baseline Observatory at Alert, Canada (82°28′N, 62°30′W), continuous measurements of methane (CH4) and carbon dioxide (CO2) have been made since 1987. During winter, both gases are frequently highly correlated during well-defined episodes lasting from 2 to 5 days. We observe a gradual decrease in the ratios of CH4/CO2 during these episodes from ∼16 ppb CH4 (ppm CO2)−1 to ∼12 ppb CH4 (ppm of CO2)−1 over the entire record. An atmospheric transport model with prescribed CO2 and CH4 source distributions is used to partition simulated CH4 events into contributions by region. We show that anthropogenic emissions from Europe and Siberia account for more than 85% of the CO2 and CH4 enhancements simulated at Alert, but without a change in CH4 emissions, modeled CH4/CO2 ratios remain constant. To reproduce the observed trend in the ratio of CH4/CO2, the model requires a reduction in emissions of CH4 on the order of 30 Tg (13.6 to 33.4 Tg) in Europe and Siberia over the observational period. This is about twice the drop reported by the Emission Database for Global Atmospheric Research (EDGAR) emissions inventory and large enough to account for the leveling off of the global atmospheric CH4 burden observed over the past 20 years.

Soil, plant, and transport influences on methane in a subalpine forest under high ultraviolet irradiance

Abstract: . Recent studies have demonstrated direct methane emission from plant foliage under aerobic conditions, particularly under high ultraviolet (UV) irradiance. We examined the potential importance of this phenomenon in a high-elevation conifer forest using micrometeorological techniques. Vertical profiles of methane and carbon dioxide in forest air were monitored every 2 h for 6 weeks in summer 2007. Day to day variability in above-canopy CH4 was high, with observed values in the range 1790 to 1910 nmol mol−1. High CH4 was correlated with high carbon monoxide and related to wind direction, consistent with pollutant transport from an urban area by a well-studied mountain-plain wind system. Soils were moderately dry during the study. Vertical gradients of CH4 were small but detectable day and night, both near the ground and within the vegetation canopy. Gradients near the ground were consistent with the forest soil being a net CH4 sink. Using scalar similarity with CO2, the magnitude of the summer soil CH4 sink was estimated at ~1.7 mg CH4 m−2 h−1, which is similar to other temperate forest upland soils. The high-elevation forest was naturally exposed to high UV irradiance under clear sky conditions, with observed peak UVB irradiance >2 W m−2. Gradients and means of CO2 within the canopy under daytime conditions showed net uptake of CO2 due to photosynthetic drawdown as expected. No evidence was found for a significant foliar CH4 source in the vegetation canopy, even under high UV conditions. While the possibility of a weak foliar source cannot be excluded given the observed soil sink, overall this subalpine forest was a net sink for atmospheric methane during the growing season.

Biogeochemistry: Less nickel for more oxygen.

Abstract: The availability (or lack) of oceanic trace elements is providing fresh lines of explanation for turning points in Earth's history — the Great Oxidation Event being one such momentous occasion. The Great Oxidation Event (GOE), an era on Earth about 2.4 billion years ago when oxygen began to accumulate in the atmosphere, is widely thought to have been triggered by a decrease in atmospheric methane levels. What could have caused methane to start to disappear has remained uncertain. Now based on the discovery of a decline in the molar nickel to iron ratio in banded iron formations, sedimentary rocks laid down about 2.7 billion years ago, Konhauser et al. offer a new hypothesis to explain the loss of methane. They attribute the scarcity of nickel to a reduced flux of nickel to the oceans due to a fall in upper mantle temperatures and a decreased eruption of nickel-rich ultramafic rocks at that time. Nickel is a key cofactor in several enzymes found in methanogens, so its decline may have stifled the activity of methane producing organisms in the ancient oceans and disrupted the supply of biogenic methane.

Methane from Gas Hydrates in the Black Sea

Abstract: Gas hydrates are crystalline solids that form from mixtures of water and light natural gases such as methane, carbon dioxide, ethane, propane, and butane. The Black Sea is the world's most isolated sea. Methane exists as gas hydrates or methane clathrate form in the Black Sea. Gas hydrates potential in the Black Sea is investigated as a source of methane. Methane gas hydrate is a solid combination of methane and ice. It is found under continental shelves and on land under permafrost and can contain from 80–99.9% of methane. Gas hydrate is found in sub-oceanic sediments and in continental slope sediments, where pressure and temperature conditions combine to make it stable. Natural gas hydrate contains highly concentrated methane, which is important both as an energy resource and as a factor in global climate change. The difficulty with recovering this source of energy is that the fuel is in solid form and is not amenable to conventional gas and oil recovery techniques.