Showing papers on "Atmospheric methane published in 2001"
TL;DR: The similarity of changes in CO2 concentration and variations of atmospheric methane concentration suggests that processes in the tropics and in the Northern Hemisphere, where the main sources for methane are located, also had substantial effects on atmospheric CO2 concentrations.
Abstract: A record of atmospheric carbon dioxide (CO2) concentration during the transition from the Last Glacial Maximum to the Holocene, obtained from the Dome Concordia, Antarctica, ice core, reveals that an increase of 76 parts per million by volume occurred over a period of 6000 years in four clearly distinguishable intervals The close correlation between CO2 concentration and Antarctic temperature indicates that the Southern Ocean played an important role in causing the CO2 increase However, the similarity of changes in CO2 concentration and variations of atmospheric methane concentration suggests that processes in the tropics and in the Northern Hemisphere, where the main sources for methane are located, also had substantial effects on atmospheric CO2 concentrations
1,200 citations
TL;DR: In this article, the atmospheric global warming potential of methane (GWP M ) with annual methane emission/carbon dioxide exchange ratio of wetlands ranging from the boreal zone to the near-subtropics.
Abstract: Carbon fixation under wetland anaerobic soil conditions provides unique conditions for long-term storage of carbon into histosols. However, this carbon sequestration process is intimately linked to methane emission from wetlands. The potential contribution of this emitted methane to the greenhouse effect can be mitigated by the removal of atmospheric CO 2 and storage into peat. The balance of CH 4 and CO 2 exchange can provide an index of a wetland's greenhouse gas (carbon) contribution to the atmosphere. Here, we relate the atmospheric global warming potential of methane (GWP M ) with annual methane emission/carbon dioxide exchange ratio of wetlands ranging from the boreal zone to the near-subtropics. This relationship permits one to determine the greenhouse carbon balance of wetlands by their contribution to or attenuation of the greenhouse effect via CH 4 emission or CO 2 sink, respectively. We report annual measurements of the relationship between methane emission and net carbon fixation in three wetland ecosystems. The ratio of methane released to annual net carbon fixed varies from 0.05 to 0.20 on a molar basis. Although these wetlands function as a sink for CO 2 , the 21.8-fold greater infrared absorptivity of CH 4 relative to CO 2 (GWP M ) over a relatively short time horizon (20 years) would indicate that the release of methane still contributes to the overall greenhouse effect. As GWP M decreases over longer time horizons (100 years), our analyses suggest that the subtropical and temperate wetlands attenuate global warming, and northern wetlands may be perched on the “greenhouse compensation” point. Considering a 500-year time horizon, these wetlands can be regarded as sinks for greenhouse gas warming potential, and thus attenuate the greenhouse warming of the atmosphere. DOI: 10.1034/j.1600-0889.2001.530501.x
414 citations
TL;DR: In this article, the authors report neutron and synchrotron X-ray diffraction studies that determine the thermodynamic behavior of methane hydrate at pressures up to 10 GPa.
Abstract: Methane hydrate is thought to have been the dominant methane-containing phase in the nebula from which Saturn, Uranus, Neptune and their major moons formed. It accordingly plays an important role in formation models of Titan, Saturn's largest moon. Current understanding assumes that methane hydrate dissociates into ice and free methane in the pressure range 1-2 GPa (10-20 kbar), consistent with some theoretical and experimental studies. But such pressure-induced dissociation would have led to the early loss of methane from Titan's interior to its atmosphere, where it would rapidly have been destroyed by photochemical processes. This is difficult to reconcile with the observed presence of significant amounts of methane in Titan's present atmosphere. Here we report neutron and synchrotron X-ray diffraction studies that determine the thermodynamic behaviour of methane hydrate at pressures up to 10 GPa. We find structural transitions at about 1 and 2 GPa to new hydrate phases which remain stable to at least 10 GPa. This implies that the methane in the primordial core of Titan remained in stable hydrate phases throughout differentiation, eventually forming a layer of methane clathrate approximately 100 km thick within the ice mantle. This layer is a plausible source for the continuing replenishment of Titan's atmospheric methane.
309 citations
TL;DR: In this paper, the authors measured in situ CH4 emission and CH4 oxidation in an Italian rice field in 1998 and 1999, and studied CH4 production in soil and root samples.
Abstract: Summary
Irrigated rice fields are an important source of atmospheric methane. In order to improve our understanding of the controlling processes, we measured in situ CH4 emission and CH4 oxidation in an Italian rice field in 1998 and 1999, and studied CH4 production in soil and root samples. The CH4 emission rates were correlated with diurnal temperature variations and showed pronounced seasonal and interannual variations. The contribution of CH4 oxidation to total CH4 flux, determined by specific inhibition with difluoromethane, decreased from 40% at the beginning to zero at the end of the season. The stable carbon isotopic composition of the emitted CH4 also decreased. The CH4-oxidizing bacteria probably became limited by nitrogen as indicated by the seasonal decrease of NH4+. Thus, CH4 oxidation had little effect on CH4 emission. Methane production on rice roots was relatively constant over the season. Methane production in soil slowly increased after flooding and was highest in the middle of the season. Pore water concentrations of CH4 showed a similar seasonal pattern. In 1999, CH4 production increased later in the season and reached lower rates than in 1998. An additional drainage in 1999 resulted in higher ferric iron concentrations, higher soil redox potentials and lower acetate concentrations. As a result, acetate-utilizing methanogens were probably out-competed by iron-reducers so that a larger percentage of [2–14C]acetate was converted to 14CO2 instead of 14CH4. The residual CH4 production was relatively low and was mainly due to H2/CO2-dependent methanogenesis. Experiments with radioactive bicarbonate and with methyl fluoride as specific inhibitor showed that the theoretical ratio of 7:3 of methanogenesis from acetate vs. H2/CO2 was only reached later in the season when total CH4 production was at the maximum. In conclusion, our results give a mechanistic explanation for the intraseasonal and interannual differences in CH4 emission.
250 citations
TL;DR: Gas hydrates are crystalline solids that form from mixtures of water and light natural gases such as methane, carbon dioxide, ethane, propane and butane.
230 citations
TL;DR: In this article, a regression model based on temperature and precipitation anomalies was used to calculate emission anomalies of 11.6 Tg CH4 from wetlands north of 30 N and 13 TgCH4 for tropical wetlands during 1998 compared to average emissions calculated for 1982-1993.
Abstract: Measurements of atmospheric methane from a globally distributed network of air sampling sites indicate that the globally averaged CH4 growth rate increased from an average of 3.9 ppb/yr during 1995-1997 to 12.7 +/- 0.6 ppb in 1998. The global growth rate then decreased to 2.6 +/- 0.6 ppb during 1999, indicating that the large increase in 1998 was an anomaly and not a return to the larger growth rates observed during the late 1970s and early 1980s. The increased growth rate represents an anomalous increase in the imbalance between CH4 sources and sinks equal to approximately 24 Tg CH4 during 1998. Wetlands and boreal biomass burning are sources that may have contributed to the anomaly. During 1998, the globally averaged temperature anomaly was +0.67 C, the largest temperature anomaly in the modern record. A regression model based on temperature and precipitation anomalies was used to calculate emission anomalies of 11.6 Tg CH4 from wetlands north of 30 N and 13 Tg CH4 for tropical wetlands during 1998 compared to average emissions calculated for 1982-1993. In 1999, calculated wetland emission anomalies were negative for high northern latitudes and the tropics, contributing to the low growth rate observed in 1999. Also 1998 was a severe fire year in boreal regions where approximately 1.3x10(exp 5) sq km of forest and peat land burned releasing an estimated 5.7 Tg CH4
173 citations
TL;DR: It is demonstrated that coastal wetlands are potentially significant sources of atmospheric methane and could be a greater source if anthropogenic perturbations continue at the current rate.
Abstract: For the first time, the methane emissions from diverse coastal wetlands of South India have been measured. Annual emission rates varied widely, ranging from 3.10 mg/m2/hr (Bay of Bengal) to 21.56 mg/m2/hr (Adyar River), based on nature of the perturbance to each of the ecosystems studied. Distinct seasonality in methane emission was noticed in an unpolluted ecosystem (mangrove: 7.38 mg/m2/hr) and over a twofold increase was evident in the ecosystem that was disturbed by human activities (21.56 mg/m2/hr). The wide ranges in estimate suggest that methanogenesis occurs by both natural and anthropogenic activities in these coastal wetlands. Several physical and chemical factors such as salinity, sulfate, oxygen, and organic matter content influenced methanogenesis to a large degree in each of these ecosystems in addition to individual responses to human-induced stress. For example, there was a clear negative correlation between oxygen availability (0.99), sulfate (0.98), and salinity (0.98) with CH4 emission in the Adyar river ecosystem. Although similar results were obtained for the other wetland ecosystems, CH4 emission was largely influenced by tidal fluctuations, resulting in a concomitant increase in methanogenesis with high sulfate concentrations. This study demonstrates that coastal wetlands are potentially significant sources of atmospheric methane and could be a greater source if anthropogenic perturbations continue at the current rate.
164 citations
TL;DR: Moisture content emerged as a critical variable that can limit a soil's CH4 oxidation potential, and the oxidation rate of the agricultural soil was seen to increase by an order of magnitude after increasing its moisture content from 6% to 10% of its dry weight.
Abstract: Current concern over the potentially negative impacts of climate change has brought attention to anthropogenic sources of methane, a primary greenhouse gas. Two such emission sources are methane leakage at heavy oil wells and sanitary landfills. At both of these sources, substantial quantities of methane could potentially be oxidised by methanotrophic microbes living in soils. Optimisation of this phenomenon may serve as an inexpensive technique for reducing methane emissions. Soil column and batch incubation experiments were performed on a landfill loam, an agricultural loam and a sedge peat to gain a better quantitative understanding of the biological and physical processes limiting CH4 oxidation in soils that undergo the freeze-thaw cycles associated with northern climates. Moisture content emerged as a critical variable that can limit a soil's CH4 oxidation potential. For example, the oxidation rate of the agricultural soil was seen to increase by an order of magnitude after increasing its moisture co...
120 citations
TL;DR: A simple coupled ecosystem-climate model is described that can predict levels of atmospheric CH4, CO2, and H2 during the Late Archean, and finds that methanogenic bacteria should have converted most of the available atmospheric H2 intoCH4, and that CH4 may have been equal in importance to CO2 as a greenhouse gas.
Abstract: A simple coupled ecosystem-climate model is described that canpredict levels of atmospheric CH4, CO2, and H2during the Late Archean, given observed constraints on Earth'ssurface temperature. We find that methanogenic bacteria shouldhave converted most of the available atmospheric H2 intoCH4, and that CH4 may have been equal in importance to CO2 as a greenhouse gas. Photolysis of this CH4 may have produced a hydrocarbon smog layer that would have shielded the surface from solar UV radiation. Methanotrophic bacteria would have consumed some of the atmospheric CH4,but they would have been incapable of reducing CH4 to modern levels. The rise of O2 around 2.3 Ga would have drastically reduced the atmospheric CH4 concentrationand may thereby have triggered the Huronian glaciation.
104 citations
TL;DR: In this paper, the authors present results from two experiments carried out with a coupled ocean-atmosphere-tropospheric chemistry model run continously over the period 1990 to 2100, where emissions of trace gases to the chemical model increase in line with an illustrative scenario for future trace gas emissions with medium high growth.
Abstract: We present results from two experiments carried out with a coupled ocean-atmosphere-tropospheric chemistry model run continously over the period 1990 to 2100. In the control experiment, climate is unforced, but emissions of trace gases to the chemical model increase in line with an illustrative scenario for future trace gas emissions with medium high growth. In the climate change experiment trace gas emissions are identical to the control, but climate is also forced using greenhouse gas concentrations and SO2 emissions from the same scenario. Global average methane in the climate change experiment increased from 1670 ppbv in 1990 to 3230 ppbv by 2100, compared to 3650 ppbv by 2100 in the control. The methane increase in the control experiment is therefore 27% more than in the control. This difference is due to both temperature and OH changes which increase the rate of methane oxidation and act in the opposite direction to the negative feedback of methane on itself through OH. Mid-latitude northern hemisphere ozone concentrations in July for the mid-troposphere rose from 39 ppbv in 1990s to 64 ppbv in the 2090s in the control experiment and to 49 ppbv in the climate change experiment. The direct role of climate change is therefore predicted to be a negative feedback on the radiative forcing from the change to tropospheric ozone and methane concentrations.
103 citations
TL;DR: In this paper, the authors used diurnal air sampling campaigns at the Royal Holloway site on the western fringe of London, United Kingdom, to verify the validity of using carbon isotopes to identify local methane sources, determine the isotopic signature of overnight build-up profiles, and verify statistical estimates of emissions.
Abstract: Diurnal air sampling campaigns at the Royal Holloway site on the western fringe of London, United Kingdom, have been used to: (1) test the validity of using carbon isotopes to identify local methane sources, (2) determine the isotopic signature of overnight build-up profiles, in order to estimate regional emissions, and (3) verify statistical estimates of emissions. For CH4 an overall London δ13C source mix of −48.7±0.3‰ has been calculated from gradual overnight methane buildup in air masses moving from the east. Isotopic characterization of specific methane peaks shows them to be derived either from natural gas leaks (δ13C −33‰ to −35‰) or waste treatment emissions (δ13C −51‰ to −53‰). While landfill/waste emissions dominate, gas distribution losses represent ∼20% of the bulk local source. Various estimates of total London methane emissions for 1996 were made, using diurnal excess, isotopic data and trajectory movement across London to the sampling station. The results are in the range 240–312 kt/yr, higher than the London estimate in current U.K. greenhouse gas inventory assessments of emissions but within error of earlier statistical estimates for 1996. The results show that it is possible to use atmospheric concentration, isotopic, and meteorological data together to verify statistical estimates testing them for internal consistency and using better constrained data to calibrate more poorly known source fluxes. Importantly, atmospheric data can place constraints on poorly constrained landfill emission estimates for the region. These quasi-independent methods for verification of greenhouse gas emissions will contribute in assessing compliance with the Kyoto agreement.
TL;DR: In this article, the authors present the current knowledge about the highly complex microbiology of flooded rice paddies and their function with particular regard to bacterial populations utilizing polysaccharides and simple sugars, and to the methanogenic archaea.
Abstract: Flooded rice paddies are one of the major biogenic sources of atmospheric methane. Apart from this contribution to the ‘greenhouse’ effect, rice paddy soil represents a suitable model system to study fundamental aspects of microbial ecology, such as diversity, structure, and dynamics of microbial communities as well as structure–function relationships between microbial groups. Flooded rice paddy soil can be considered as a system with three compartments (oxic surface soil, anoxic bulk soil, and rhizosphere) characterized by different physio-chemical conditions. After flooding, oxygen is rapidly depleted in the bulk soil. Anaerobic microorganisms, such as fermentative bacteria and methanogenic archaea, predominate within the microbial community, and thus methane is the final product of anaerobic degradation of organic matter. In the surface soil and the rhizosphere well-defined microscale chemical gradients can be measured. The oxygen profile seems to govern gradients of other electron acceptors (e.g., nitrate, iron(III), and sulfate) and reduced compounds (e.g., ammonium, iron(II), and sulfide). These gradients provide information about the activity and spatial distribution of functional groups of microorganisms. This review presents the current knowledge about the highly complex microbiology of flooded rice paddies. In Section 2 we describe the predominant microbial groups and their function with particular regard to bacterial populations utilizing polysaccharides and simple sugars, and to the methanogenic archaea. Section 3 describes the spatial and temporal development of microscale chemical gradients measured in experimentally defined model systems, including gradients of oxygen and dissolved and solid-phase iron(III) and iron(II). In Section 4, the results of measurements of microscale gradients of oxygen, pH, nitrate–nitrite, and methane in natural rice fields and natural rice soil cores taken to the laboratory will be presented. Finally, perspectives of future research are discussed (Section 5).
TL;DR: A review of the global cycle of methane is presented with emphasis on its isotopic composition, and the methane emissions by bacterial activity under anaerobic conditions in wet environments, in ruminant stomachs and termite guts, and that originating from fossil carbon sources are presented.
Abstract: A review of the global cycle of methane is presented with emphasis on its isotopic composition. The history of methane mixing ratios, reconstructed from measurements of air trapped in ice-cores is described. The methane record now extends back to 420 kyr ago in the case of the Vostok ice cores from Antarctica. The trends in mixing ratios and in δ13C values are reported for the two Hemispheres. The increase of the atmospheric methane concentration over the past 200 years, and by 1% per year since 1978, reaching 1.7 ppmv in 1990 is underlined. The various methane sources are presented. Indeed the authors describe the methane emissions by bacterial activity under anaerobic conditions in wet environments (wetlands, bogs, tundra, rice paddies), in ruminant stomachs and termite guts, and that originating from fossil carbon sources, such as biomass burning, coal mining, industrial losses, automobile exhaust, sea floor vent, and volcanic emissions. Furthermore, the main sinks of methane in the tropospher...
TL;DR: In this paper, the authors demonstrate that unlike mid-latitude wetlands, methane in northern peatlands is not derived from acetate or C1 compounds, and that warming-induced initiation of acetoclastic methanogenesis could substantially increase methane production.
Abstract: High latitude wetlands are significant sources of atmospheric methane, with emission rates that are susceptible to effects of climate change Our data demonstrate that unlike mid-latitude wetlands, methane in northern peatlands is not derived from acetate or C1 compounds These latter compounds accumulate to high levels with acetate as the primary organic end product of anaerobic decomposition Acetate is ultimately degraded aerobically to carbon dioxide after diffusion into oxic regions of peat Therefore, organic precursors destined for methane in mid-latitude wetlands are degraded to carbon dioxide in northern wetlands A warming-induced initiation of acetoclastic methanogenesis could substantially increase methane production
TL;DR: The total annual source of methane to the atmosphere has been constrained to about 540 teragrams (Tg) per year by Cicerone and Oremland, 1988.
Abstract: Methane is the most abundant organic compound in the Earth's atmosphere. As a powerful greenhouse gas, it has implications for global climate change. Sources of methane to the atmosphere are varied. Depending on the source, methane can contain either modern or ancient carbon. Methane exiting from swamps and wetlands contains modern carbon, whereas methane leaking from petroleum reservoirs contains ancient carbon. The total annual source of methane to the atmosphere has been constrained to about 540 teragrams (Tg) per year “Cicerone and Oremland, 1988”. Notably absent from any identified sources is the contribution of geologically sourced methane from naturally occurring seepage.
01 Dec 2001
TL;DR: In this paper, the contribution of gas hydrates to the deglacial rise in atmospheric methane has been investigated, and it was shown that global carbon models will have to incorporate glacial-interglacial vegetation shifts of at least 1000 GtC, which many currently find difficult.
Abstract: The discovery that methane from dissociation of gas-hydrates could be an important factor in the global carbon cycle resolves the major discrepancy in estimates of the increase of terrestrial biomass from the Last Glacial period to the present. Carbon isotope budgeting using the marine carbon isotopic record results in an estimate centered around 500 GtC , whereas palaeovegetation reconstruction (with biosphere models) gives averages around 1000 GtC . The discrepancy may be resolved by considering release of isotopically light methane through destabilization of gas hydrates. This provides a unique means of estimating the contribution of gas hydrates to the deglacial rise in atmospheric methane. A release of ∼120 GtC methane, makes a biospheric carbon transfer of ∼1000 GtC compatible with the marine carbon isotope data. This, however, represents less than 30% of the enhanced atmospheric methane production between 18 and 8 ka observed in ice cores, supporting the theory that glacial–interglacial variations in atmospheric methane were driven primarily by changes in the extent of tropical and temperate wetlands and not by methane release from clathrates. By balancing the deglacial carbon budget we demonstrate that global carbon models will have to incorporate glacial–interglacial vegetation shifts of at least 1000 GtC , which many currently find difficult.
TL;DR: In this article, the effects of land-use on both the potential activity of CH 4 oxidizing bacteria and their diversity were assessed at a fully replicated experimental site within the Gisburn Forest Experiment.
Abstract: Methane is an important greenhouse gas and CH 4 oxidation in soil represents a significant sink for this gas. High capacity CH 4 oxidation potentials and molecular profiles of CH 4 oxidizing bacteria in soil were compared for five land-use treatments at a fully replicated experimental site within the Gisburn Forest Experiment, to assess the effects of land-use on both the potential activity of CH 4 oxidizing bacteria and their diversity. Forestry land-use was found to have a highly significant effect on CH 4 oxidation potentials. Highest CH 4 oxidation potentials were found in soils collected under stands of oak, in grassland plots, and in one soil under Norway spruce. A negative relationship between soil water nitrate concentration and CH 4 oxidation capacity was evident across the experimental site, with the high nitrate soils under stands of alder exhibiting little or no capacity for CH 4 oxidation even at optimal temperature and water content. Molecular profiles indicated that a diverse range of bacteria with the potential to oxidize CH 4 were present in all soils, however no clear correlation with CH 4 oxidation potential was identified.
TL;DR: In this article, the authors used the TM2 three-dimensional atmospheric tracer model with a methane source-sink budget based on existing literature to simulate small spatial and temporal variations in the 13C/12C ratio of atmospheric methane.
Abstract: We use the TM2 three-dimensional atmospheric tracer model with a methane source-sink budget based on existing literature to simulate small spatial and temporal variations in the 13C/12C ratio of atmospheric methane. The results show that δ13C varies markedly with wind direction everywhere outside the extratropical Southern Hemisphere (ETSH). Within the ETSH, both methane mixing ratio and δ13C have regular seasonal cycles with differing and latitude-dependent phases. Phase diagrams constructed from these seasonal cycles, showing changes in δ13C versus changes in mixing ratio, have elliptical shapes. The slope of the major axis of these ellipses is determined by the kinetic isotope effect (KIE) of the single atmospheric methane removal process used in the model. The ellipse eccentricity is determined by seasonal variation in the source δ13CH4, which is dominated by the biomass burning source because of its isotopic enrichment relative to other sources. Comparison of the model results, for a KIE based on CH4 + OH oxidation, with observations in the South Pacific region shows significant discrepancies in both the ellipse major axis slopes and eccentricities. We suggest that this is an indicator of an additional sink process that discriminates strongly against 13CH4. Such a sink could be active chlorine in the marine boundary layer.
TL;DR: In this article, the atmospheric trend of methane isotopic ratios since the mid-20th century has been reconstructed from Antarctic firn air, where high volume air samples were extracted at several depth levels at two sites in East Antarctica.
Abstract: The atmospheric trend of methane isotopic ratios since the mid-20th century has been reconstructed from Antarctic firn air. High volume air samples were extracted at several depth levels at two sites in East Antarctica. Methane concentration and its 13C/12C and D/H ratios were determined by gas chromatography, mass spectrometry, and infrared spectroscopy. A firn air transport model was applied to reconstruct past atmospheric trends in methane and its isotopic composition. By subsequent application of an atmospheric model, changes in methane sources and OH sink compatible with the past atmospheric trends are explored. In step with increasing methane mixing ratios, δ13C increased by ∼1.7‰ over the last 50 years. These changes mainly reflect a shift in relative source strength toward the heavier anthropogenic methane source, such as biomass burning and methane of nonbiological origin. The δD (CH4) showed a period of decline between the 1950s and 1975, followed by a gradual increase of 0.55‰/yr, also toward the heavier anthropogenic source. Dependent on possible changes in the OH sink, to which δD of methane is very sensitive, the inferred isotopic trends of δ13C and δD over the last 50 years constrain the relationship between natural and anthropogenic sources over the last century. The observed δD minimum around 1975 suggests that the slowing down in the methane source growth took place during this period.
TL;DR: In this article, the authors found that adding mineral acids to intact soil cores in pulsed applications decreased atmospheric methane consumption in a mixed coniferous-hardwood forest with a broad optimum between 4.8 and 6.0.
TL;DR: The biogeochemical processes of methane production and oxidation were studied in the upper horizons of tundra and taiga soils and raised bogs and lake bottom sediments near the Tarko-Sale gas field in western Siberia.
Abstract: The biogeochemical processes of methane production and oxidation were studied in the upper horizons of tundra and taiga soils and of raised bogs and lake bottom sediments nearby the Tarkosalinsk gas field in western Siberia. Both in dry and water-logged soils, the total methane concentration (in soil particles and gaseous phase) was an order of magnitude higher than in the soil gaseous phase alone (22 and 1.1 nl/cm3, respectively). In bogs and lake bottom sediments, methane concentration was as high as 11 microliters/cm3. Acetate was the major precursor of the newly formed methane. The rate of aceticlastic methanogenesis reached 55 ng C/(cm3 day), whereas that of autotrophic methanogenesis was an order of magnitude lower. The most active methane production and oxidation were observed in bogs and lake sediments where the delta 13C values of CO2 were inversely related to the intensity of bacterial methane oxidation. Methane diffusing from bogs and lake bottom sediments showed delta 13C values ranging from -78 to -47@1000, whereas the delta 13C value of carbon dioxide ranged from -18 to -6@1000. In these ecosystems, methane emission comprised from 3 to 206 mg CH4/(m2 day). Conversely, the dry and water-logged soils of tundra and taiga took up atmospheric methane at a rate varying from 0.3 to 5.3 mg CH4/(m2 day). Methane consumption in soils was of biological rather than of adsorptive nature. This was confirmed by the radioisotopic method and chamber experiments, in which weighting of methane carbon was observed (the delta 13C value changed from -51 to -41@1000).
TL;DR: In this paper, the authors proposed a CO2-EGR-based method to sequester a total of 48 Gtonnes of CO2 in and around the Japanese Islands, with the prospect of also having enhanced production of nearly 10 trillion cubic meters of methane.
Abstract: An enormous amount of methane has accumulated in the shallow subsurface in many part of the world. However, most of this natural gas resource is not economically recoverable at the present time as the methane is adsorbed in coal seams, trapped in methane hydrate (clathrate), or dissolved in saline groundwater. Shallow accumulations of methane pose the threat of potentially increasing the rate of global warming. Enhanced gas recovery by subsurface CO2 injection (CO2-EGR) is potentially an option for greenhouse gas control, combined with use of potential energy resources. CO2 injection coupled with extraction of coal mine methane and coal-bed methane may make emission-free closed circuit power plants possible. Coal seams in Japan and under the seabed around Japan could potentially adsorb about 10 Gtonnes of CO2 and in so doing displace 2.5 trillion cubic meters of coal-bed methane. About 12 Gtonnes of CO2 could potentially be sequestered in hydrate layers, displacing 6 trillion cubic meters of methane hydrate under the deep seabed around Japan. Similarly, about 26 Gtonnes of CO2 could potentially be sequestered in saline groundwater, displacing 6 trillion cubic meters of methane in sedimentary basins in Japan. CO2-EGR could potentially sequester a total of 48 Gtonnes of CO2 in and around the Japanese Islands, with the prospect of also having enhanced production of nearly 10 trillion cubic meters of methane. The extremely light isotopic compositions of carbon in methane suggest that methanogens formed many of the subsurface accumulations of methane-rich natural gas in the world. Chemolithotrophic methanogens form methane from CO2, thereby obtaining energy without sunlight under anoxic circumstances. Methanogens are often blamed for greenhouse gas emissions as they produce methane in organisms and in rice paddies, for example. However, application of CO2-EGR for production of subsurface biogenic methane displaced by sequestration of CO2 might result in enhanced carbon recycling. Present-day subsurface ecosystems are probably somewhat similar to ancient ecosystems adapted to exist in an anoxic CO2-rich atmosphere under high pressure and temperature. Biogenic methanogenesis is thought to occur even in deep basaltic aquifers offering the opportunity for deep subsurface biogeochemical carbon recycling utilizing CO2-EGR to produce enhanced sequestration of greenhouse gases accompanied by the development of potential new energy resources.
TL;DR: In this article, the spatial and temporal behavior of atmospheric methane (CH 4 ) in the Nagoya metropolitan area was investigated in relation to the regional meteorological and topographical characteristics.
TL;DR: In this article, the air in bubbles embedded in the Dasuopu ice core, Qinghai-Tibetan Plateau, was extracted and analyzed for the past 2000 years.
Abstract: The concentrations of CH4 in the atmosphere over the past 2000 years have been deduced by extracting and analyzing the air in bubbles embedded in the Dasuopu ice core, Qinghai-Tibetan Plateau. Upon analyzing 57 ice core samples we found that the concentration of CH4 200 years ago and earlier was 0.85 mmol·mol-1 or about 40% of present atmospheric CH4 levels over Qinghai-Tibetan Plateau. A rapid and significant increase of atmospheric CH4 started about 200—250 a ago. For a given age before 19th century, the Dasuopu CH4 concentrations were about 15%—20% higher than those in Antarctic and Greenland references. It was also found that the Dasuopu CH4 concentrations changed more frequently, and its fluctuations could reflect the temperature change sensitively.
01 Jan 2001
TL;DR: This paper showed that all major aquatic habitats of northeast Siberia are potential sources of diffusive and ebullition flux of CH4 to the atmosphere, particularly in winter, and that much of this flux derives from terrestrial carbon that accumulated in loess sediments during the Pleistocene.
Abstract: The sizes of major sources and sinks of atmospheric methane, an important greenhouse gas, are poorly known. Our results indicate that all major aquatic habitats of northeast Siberia are potential sources of diffusive and ebullition flux of CH4 to the atmosphere, particularly in winter, and that much of this flux derives from terrestrial carbon that accumulated in loess sediments during the Pleistocene. These data provide evidence that northern aquatic sediments are a large enough winter CH4 source to explain the observed winter increase in atmospheric CH4 at high northern latitude.The clear positive relationship between active thermokarst and measured ebullition rates suggests that long-term changes in CH4 ebullition from Siberian aquatic systems will be most strongly influenced by thermokarst erosion rates.
TL;DR: In this article, five tested pesticides (the insecticide Dimethoat 40 EC, the herbicide Tolkan, and the fungicides Tilt 250 EC, Tilt Top, and Corbel) decreased the oxidation of atmospheric methane in slurries from a Danish forest soil.
Abstract: We found that five tested pesticides (the insecticide Dimethoat 40 EC, the herbicide Tolkan, and the fungicides Tilt 250 EC, Tilt Top, and Corbel) decreased the oxidation of atmospheric methane in slurries from a Danish forest soil. Dimethoat 40 EC was the most toxic with an EC50 value (i.e. the concentration which caused a 50% inhibition of the methane oxidation) of 10 mg active ingredient (AI) l 21 , followed by Tilt 250 EC (EC50a 56 mg AI l 21 ). EC50 of Tilt Top was 350 AI mg l 21 , the value of Tolkan was 410 mg AI l 21 , while Corbel had a value of 1600 mg AI l 21 . Dimethoat 40 EC and Tolkan inhibited the oxidation of atmospheric methane at concentrations expected in natural soil after application of the pesticides. Pesticides, therefore, may be partly responsible for the lowered methane oxidation rates in arable soils compared to forest soils. q 2001 Elsevier Science Ltd. All rights reserved.
TL;DR: In this paper, the seasonal variability of methane concentration in Beijing appeared in a double-peak pattern with one peak in winter and the other in summer, and the seasonal inter-annual variations of atmospheric methane in Beijing are different from year to year, which implies that in Beijing the biogenic sources have been decreasing but the non-biogenic ones such as fossil fuel combustion, have increased.
TL;DR: The Spectrometre a Diodes Laser Accordables (SDLA) as mentioned in this paper is a balloon-borne near-infrared diode laser spectrometer that provides simultaneous in situ measurements of methane and water vapor in the troposphere and the lower stratosphere.
Abstract: The Spectrometre a Diodes Laser Accordables (SDLA), a balloonborne near-infrared diode laser spectrometer, was developed to provide simultaneous in situ measurements of methane and water vapor in the troposphere and the lower stratosphere. The instrument was flown several times from stratospheric balloons operated by the Centre National d'Etudes Spatiales within the framework of the Third European Stratospheric Experiment on Ozone in 1998–2000. The SDLA is based on a multipass optical cell open to the atmosphere. Two near-infrared telecommunication-type laser diodes are connected with optical fibers to the cell to take in situ absorption spectra of methane (in the 6047 cm−1 spectral region) and water vapor (in the 7181 cm−1 spectral region) at 1-s intervals. Mixing ratios are obtained, with a precision error of within 5%–10%, from a nonlinear fit to the full molecular line shape in conjunction with in situ pressure and temperature measurements. The SDLA is described, and achieved atmospheric methane and water vapor vertical concentration profiles are reported.
01 Jan 2001
TL;DR: In this paper, a line-by-line (LBL) computation method was used to calculate theoretical atmospheric absorption in the wavelength range of 3. 410 -3. 438 μm, the absorption is mainly due to atmospheric methane and water vapor.
Abstract: Infrared solar spectra on clear days were measured automatically by an infrared solar spectrometer (ISS) with 0.4 cm 1 resolution developed by us. A line-by-line (LBL) computation method was used to calculate theoretical atmospheric absorption. In the wavelength range of 3. 410 -3. 438 μm, the absorption is mainly due to atmospheric methane and water vapor. Column atmospheric methane was retrieved from the recorded infrared solar spectra. The seasonal variation of column atmospheric methane in Hefei has been obtained from the measuremental data of nearly 18 months since the April of 1997, and found that it is similar to that of background data. The instruments; principles of measurement and some of results were introduced, and the results are also discussed briefly in the paper.
TL;DR: In this article, a 3D regional chemical transport model was applied to estimate the 3D distribution of methane in West Siberia, based on the current meteorological data fields(wind, temperature, geopotential) updated 4 times a day.
Abstract: The West Siberian region is one of the main contributors of theatmospheric greenhouse gas methane due to the large areas ofwetlands, rivers, lakes and numerous gas deposits situated there.But there are no reliable estimations of integral methane flux fromthis area into the atmosphere. For assessment of methane fluxes inWest Siberia the specially constructed 3-D regional chemicaltransport model was applied. The 3-D distribution of methane iscalculated on the basis of the current meteorological data fields(wind, temperature, geopotential) updated 4 times a day. The methaneconcentrations measured near the main gas fields of West Siberia inthe summer season of 1999, were used for correction of methane fluxintensity estimates obtained previously by comparison ofmeasurements carried out in summer 1993 and 1996 with modelledmethane mixing ratio distribution. This set of field and modelexperiments confirmed the preliminary conclusion about low leakageintensity: anthropogenic methane flux does not exceed 5–15% oftotal summer methane flux, estimated as 11–12 Mt CH4 in summer from this region, in spite of the large areas of gas deposits located there.