Global methane flux into the atmosphere and its seasonal variations

We have analyzed the regularities in the spatiotemporal behavior of the methane concentration and mass, recorded in different regions of the globe. In the southern hemisphere (SH), the methane concentration does not depend on latitude. In the northern hemisphere (NH), the methane concentration increases towards the Arctic zone. The maximum CH₄ concentration in the fall is due to the action of the additional methane sources in the NH Arctic region. The methane flux calculations showed that in the SH the methane flux into the Earth’s atmosphere is barely season dependent. In the NH during the fall season, the methane flux considerably increases, and the difference between the maximum flux in August-September and the flux in December-January reaches three. The additional, still disregarded sources, sustaining high methane emission in the spring season at high SH latitudes are estimated to be as strong as 100–120 Tg per year. To equilibrate the methane supply to the atmosphere and methane sink in SH, additional, yet unidentified sources of over 300 Tg/yr are required. The global methane flux into the Earth’s atmosphere should be no less than 1050–1100 Tg yearly.     

地层渗透率与水合物含量关系的模拟研究(英文)

本文通过人工变换T2分布和建立管-球模型模拟法研究含水合物地层渗透率与水合物含量之间的关系。首先,在渗透率的模拟试验中,我们改变了束缚水与可动水的比例、总孔隙度以及与之关联的T2分布。试验结果表明,相对渗透率与水合物含量之间的关系受到这些因素的制约。随后,我们用管-球模型表示水合物生长的孔隙空间,并把水合物的生长过程看成是向孔隙空间随机扔小球的过程。在此过程中,采用两种方法计算渗透率,一是Schlumberger’sT2公式(即SDR模型),二是Darcy定律与Poiseuille流动方程相结合的方法。前人的实验研究表明,在一定的水合物含量范围内,渗透率基本保持不变。以此为参考,我们将计算结果与之进行比较。我们发现,采用SDR模型时,渗透率的数值模拟曲线与Masuda模型N=15时的结果相近。而采用Darcy定律时,渗透率模拟值较高,但与实验结果的趋势相一致,都会出现渗透率的平直阶段。尤其,当水合物晶体在孔隙体内优先生成时,优先的概率越高,渗透率的平直范围越大。     

Observation of atmospheric methane in the Arctic Ocean up to 87° north

Although the Arctic methane reservoir is large,the emission of methane from the Arctic Ocean into the atmosphere remains poorly constrained.Continuous ship-borne measurements of atmospheric methane near the surface ocean were carried out during two cruises to investigate methane emission from the Arctic Ocean up to the latitude of 87°N.Three-day air mass back trajectories along the cruise tracks indicated that the surface Arctic Ocean could be a potentially important source of methane to the atmosphere.Rapid bursts in methane concentration occurred mainly along the ocean frontal area,suggesting that frontal upwelling in the upper layer of the Arctic Ocean might contribute to methane emissions into the atmosphere.     

Treatment of Groundwater Containing Methane – Combination of the Processing Stages Desorption and Filtration

Methane is produced under anaerobic conditions by metabolic processes in microbes and can occur in waters of the types anoxic‐anaerobic (RG 1/2) and anaerobic‐reduced (RG 2). If the concentration of methane lies below 0.2 mg/L, then no special treatment processes are required apart from dosing of oxygen and rapid sand filtration, which are performed to remove iron, manganese, and ammonium. The research results show that a higher concentration of methane must be specially treated. From the point of view of stable deferrisation, oxidation of up to 2 mg/L is tolerable in rapid sand filtration. However, an unusual increase in regrowth potential was observed. For this reason, the oxidation of methane should be reduced to 0.5 mg/L until further experiments yield results on the microbiological stability of treated water. Rapid sand filters for nitrification and demanganisation should have a maximum methane loading of 0.2 mg/L. The experiments show that nitrification first occurs at a methane concentration below 0.1 mg/L. During the working in of demanganisation, the inlet water should be free of methane. Therefore desorption is often required. If there is less than 1 mg/L to be degassed, then desorption can be achieved with overpressure in the oxidiser without any change in the carbonate‐bicarbonate equilibrium. With other systems, such as packed columns, wetted‐wall columns, or percolators, carbon dioxide is removed simultaneously. By means of the coefficients of similarity found, it was shown that methane and carbon dioxide desorb in different proportions depending on the system, and that the discharge of carbon dioxide can be reduced through a decrease in the air/water ratio.     

Temperature and methane records over the last 2 ka in Dasuopu ice core

High resolution δ¹⁸O and methane records over the last 2ka have been reconstructed from Dasuopu ice core recovered from the Himalayas. Analysis shows that the δ¹⁸O record correlates well with the Northern Hemispheric temperature, Dunde ice core record, and with temperature record in eastern China. The warming trend detected in δ¹⁸O record from the last century is similar to that during the Medieval warm period. There is a dramatic increasing in methane concentration in the Dasuopu ice core, which reached 1031 nmol ⋅ mol^-1 in 1997. Moreover, methane concentration in the Dasuopu ice core is about 15%-20% higher than that in Antarctica and Greenland. There is a positive correlation between methane concentration and δ¹⁸O in Dasuopu ice core.     

阜新盆地裂隙网络空间信息模型的建立及其应用

瓦斯(煤层气)突出是指煤矿生产过程中,从煤层、岩层及采空区放出的各种有害气体在工作面上富集并涌出,从而引起瓦斯爆炸的煤矿灾害.因此,查明煤层瓦斯富集区域,对可能瓦斯突出点进行预报和应用,是当前煤矿生产中亟待解决的重要课题.本文应用地理信息系统基本原理,结合煤层气地质学、构造地质学等学科的理论和方法,对游离态的煤层气进行深入研究.在此基础上借助ArcGIS平台,根据游离态的煤层气的生、储、盖条件建立了分析模型及空间分析数据库;应用于王营井田,在此基础上预测了王营矿区游离态的煤层气的可能聚集带,为今后的煤层气勘探指明了方向.     

Geochemical constraints on the methane seep activity in western slope of the middle Okinawa Trough,the East China Sea

Anaerobic oxidation of methane and sulfate reduction was studied in the pore waters of four cores at two stations of the middle Okinawa Trough. Pore water vertical distributions of sulfate, methane, sulfide, total alkalinity, ammonium, and phosphate were determined in this study. Our results show strong linear sulfate concentration gradients of 6.83 mmol/L m?1 in Core A and 5.96 mmol/L m?1 in Core C, which were collected from two stations. Concurrent variations of methane, total alkalinity and hydrogen sulfide all exhibit steep increases with depth at both cores, which indicate active methane seep activities around two stations. Pore water ammonium and phosphate concentrations reveal minor influences of organic matter degradation on sulfate reduction at two stations. Sulfate methane interface(SMI) was extrapolated from linear sulfate profiles in methane seep cores. Shallower SMI depths(A: 4.9 mbsf; C: 5.4 mbsf) indicate strong methane fluxes and active anaerobic oxidation of methane in the underlying sediments.     

基于密集台阵地震背景噪声成像预测煤矿瓦斯分布

瓦斯突出是一种常见的煤矿动力灾害现象,随着煤矿矿井开采深度的增加,煤层瓦斯含量、压力都呈上升趋势,发生煤与瓦斯突出的危险性加大.传统的瓦斯测量方法只能测量局部离散点瓦斯含量,难以从矿井及采区尺度对瓦斯含量进行预测.因此需要寻求一种能够在采区及工作面布设前预测煤层瓦斯富集程度的高效地球物理方法.背景噪声成像方法已经在城市地下空间、矿产资源等近地表成像中得到广泛的运用.本文将该方法首次应用到阳泉寺家庄煤矿井田区域,采用96个台站记录的连续背景噪声数据,通过互相关方法获得了台站对之间的瑞利面波经验格林函数,并进一步提取了5 Hz~1.4 s的基阶瑞利面波的群速度和相速度频散曲线.本研究首先通过区域的平均频散曲线获得该区域的平均一维横波速度结构作为三维反演的初始模型;其次,利用基于射线追踪的面波频散直接成像方法获得研究区1.0 km以浅的三维横波速度结构;最后,结合获得的三维速度结构,以及岩石物理实验获得的瓦斯含量与地震波速度的经验关系,预测了寺家庄井田15号煤的瓦斯含量,预测的瓦斯含量与实际巷道揭露的瓦斯含量具有较好的一致性.本研究成果表明,对于煤矿瓦斯分布预测来说,背景噪声成像方法是一种潜在有效的全新的技术形式.

     

Impact of coupled perturbations of atmospheric trace gases on Earth's climate and ozone

We have studied the effects on the ozone concentration and surface temperature, of perturbations in the atmospheric content of nitrous oxide, methane, carbon dioxide and chlorofluorocarbons (CFC). The sensitivity study has been carried out with a radiative-convective-photochemical model. The doubling of carbon dioxide concentration has the effect of warming the troposphere and cooling the stratosphere. As a result of this cooling, the change of ozone columnar density produced by 10 ppb of chlorine amount to 9.3% as compared to –10.9% obtained without temperature feedback. Perturbation in nitrous oxide correspond to an increase in NO _x of the stratosphere with consequent ozone reduction while doubling the methane concentration correspond to a slight increase in columnar density. The effect of the increased methane concentration in the stratosphere contributes to reduce the effect of CFC due to the enhanced formation of HCl. The perturbation of these two minor constituents appreciably increase the greenhouse effect to 2.30 from 1.67°, obtained when carbon dioxide alone is considered.     

Effects of salinity on methane gas hydrate system

Using an approximately analytical formation, we extend the steady state model of the pure methane hydrate system to include the salinity based on the dynamic model of the methane hydrate system. The top and bottom boundaries of the methane hydrate stability zone (MHSZ) and the actual methane hy-drate zone (MHZ), and the top of free gas occurrence are determined by using numerical methods and the new steady state model developed in this paper. Numerical results show that the MHZ thickness becomes thinner with increasing the salinity, and the stability is lowered and the base of the MHSZ is shifted toward the seafloor in the presence of salts. As a result, the thickness of actual hydrate occur-rence becomes thinner compared with that of the pure water case. On the other hand, since lower solubility reduces the amount of gas needed to form methane hydrate, the existence of salts in sea-water can actually promote methane gas hydrate formation in the hydrate stability zone. Numerical modeling also demonstrates that for the salt-water case the presence of methane within the field of methane hydrate stability is not sufficient to ensure the occurrence of gas hydrate, which can only form when the methane concentration dissolved in solution with salts exceeds the local methane solubility in salt water and if the methane flux exceeds a critical value corresponding to the rate of diffusive methane transport. In order to maintain gas hydrate or to form methane gas hydrate in marine sedi-ments, a persistent supplied methane probably from biogenic or thermogenic processes, is required to overcome losses due to diffusion and advection.     

Inhibition by nitrite ion in the process of methane anaerobic oxidation by microorganisms and fractionation dynamics of stable carbon and hydrogen isotopes

In the process of methane oxidation by nitrite ion, the latter, when in high concentration, inhibits the oxidation process. The effect of inhibition is incorporated in the proposed model, describing the dynamics of anaerobic oxidation of methane and its heavy fractions δ¹³CH₄ and δC²H¹H₃ by nitrite ion. Two substrates—methane and nitrite—are considered in a modified Monod function, describing the oxidation rate. The model is calibrated against experimental data given in [8]. The dynamic behavior of the system under a deficiency of methane or nitrite ion is described. The dynamics of δ¹³CH₄ and δC²H¹H₃ are shown to be governed by the oxidation dynamics of total methane CH₄. By contrast to the conventional opinion that Rayleigh equation corresponds to 1st-order kinetics in terms of substrate concentration, this study shows that Rayleigh equation can be derived from dynamic equations for methane with heavy isotopes (¹³C and ²H), whatever the kinetic type of total methane oxidation.     

煤层采空区内煤层气储气构造半航空瞬变电磁探测——以沁水煤田为例

煤层气又称瓦斯, 它是一种赋存于煤层孔隙中的可燃气体.当浓度达到工业标准时, 可成为一种可以被开采、利用的气体能源.煤层气不仅存在于完整煤层中, 在采空区中也蕴藏有大量的煤层气资源.通常采用反射地震法勘探完整煤层中的煤层气.采空区中煤层气与周围空气的物性差异的特殊性和多变性, 使用地震勘探对采空区煤层气进行直接勘探受到限制.为此, 本文采用了一种间接的地球物理勘查方法.对于瓦斯含量较高的山西省沁水煤田, 利用半航空瞬变电磁法, 对研究区内的未知采空区进行快速、精确探测.根据"虚拟地震数据"的偏移成像结果, 发现测区采空区不完整, 研究结果间接达到了采空区煤层气储气构造的勘查目的.     

天然气水合物体系的相平衡及甲烷溶解度计算

海洋环境中天然气水合物的形成除了合适的温压条件外,还必须有充分的甲烷供给.本文介绍了甲烷-水体系的甲烷饱和溶解度、水合物体系中甲烷水合物溶解度计算方法.在气-液二相平衡甲烷饱和溶解度计算中,关键在于状态方程的选择和合适的混合规则的运用,Duan的计算模型在温度、压力和盐度变化上都具有很大的适用性,且易于应用.在含水合物的相平衡体系中,在已知组分和假定可能存在相的前提下,可利用模拟退火算法优化总吉布斯自由能,确定是二相还是三相体系,并求解甲烷水合物溶解度.在海水环境下盐的存在使平衡发生移动,利用德拜—休克尔理论或Pitzer电解质溶液理论校正盐度对于海水活度的影响,求解海水环境中甲烷水合物溶解度.基于气-液二相平衡理论的K-K方程,在临近水合物生成条件下实验或计算确定亨利常数等参数后,可计算三相平衡甲烷水合物溶解度,且简单易用.     

Relationships between groundwater in permafrost zone and climate changes

The paper presents the results of statistical analysis and estimation of long-term changes in surface air temperature, the gas composition of the atmosphere, the depth of seasonal thawing, and the temperature and area of permafrost occurrence in the circumpolar zone of the Northern Hemisphere. Preliminary estimates were obtained for the possible influence of the current changes in the thermophysical parameters of permafrost rocks on the albedo of the underlying surface, air moisture content, and the concentrations of carbon dioxide and methane in the atmosphere. The density of anthropogenic and natural methane fluxes from the underlying surface to the atmosphere is evaluated. The possible formation mechanisms of global maximums in carbon dioxide and methane concentration in the atmosphere of circumpolar areas in the context of interaction between methane cycle and the processes of permafrost thawing are described.     

Relationship between substrate concentration and oxidation of ammonium and methane in a stratified water column

Distributions and oxidation rates of methane and ammonium were investigated during two cruises in Saanich Inlet, British Columbia in late summer. Distributions of inorganic nutrients were related to oxygen distribution, exhibiting large gradients associated with the oxic-anoxic interface. The depth distributions of oxidation rates were also defined by the oxic-anoxic interface: ammonium oxidation occurred at variable rates (up to 120 nM day⁻¹) between the photic zone and the oxic-anoxic interface. Methane oxidation occurred throughout the oxic layer and increased near the interface. The possibility of interactions such as inhibition and competition between the two substrates, methane and ammonium, were investigated in kinetic experiments. Ammonium oxidation rate was independent of both ammonium and methane concentrations. Methane oxidation rates were linearly related to methane concentration, both in manipulation experiments, and in relation to ambient methane concentrations. There was no evidence of interaction between methane and ammonium as alternative substrates for methanotrophic and ammonium oxidizing populations, which were both present in the environment. In September, we observed a bolus-type mixing event, which introduced oxygenated deep water into the inlet beneath a wedge of anoxic, methane-rich water. This kind of event is probably important in determining the rate of methane loss, due to increased microbial oxidation at the boundaries of the anoxic wedge.     

Geochemical characterization of the organic matter, pore water constituents and shallow methane gas in the eastern part of the Ulleung Basin, East Sea (Japan Sea)

Abstract Geochemical analyses of sediments, pore water and headspace gas of the piston cores taken from the eastern part of Ulleung Basin of the East Sea (Japan Sea) were carried out to assess the origin of the sedimentary organic matter and interstitial fluid. Several tephra layers within the core are identified as the Ulleung‐Oki (10.1 ka), the Aira‐Tanzawa (23 ka) and the Ulleung‐Yamato (30.9 ka) tephras. With the exception of these volcanic layers, the cores consist predominantly of muddy sediments that contain >0.5% total organic carbon. Atomic C/N ratios and δ¹³C_org values suggest that the organic matter originated from marine algae rather than from land vascular plants, whereas Rock‐Eval pyrolysis suggests that the organic matter is thermally immature and comes from a land vascular plant (Type III). These conflicting results seem to be caused by the heavy oxidization of the marine organic matter. Sulphate concentration profiles of pore waters show strongly linear depletion (r² > 0.97) with sediment depth. The estimated sulphate–methane interface (SMI) depth using the sulphate concentration gradient was nearly 3.5 m below seafloor (mbsf) in the southern part of the study area, and deeper than 6 mbsf in the northern part of the area. The difference in SMI depths is likely associated with the amount of the methane flux. The methane concentration below the SMI in the two southern cores increases rapidly, implying the occurrence of methanogenesis and anaerobic methane oxidation (AMO). In contrast, the two northern cores have a low methane concentration below the SMI. values measured from all cores were in the range of −83.5 to −69.5‰, which suggests that the methane derives from a methanogenic microbe. values become decreased toward SMI, but increased below SMI; therefore, has eventually the minimum value near the SMI. The values are also decreased when the methane concentration is increased. These phenomena support the typical occurrence of AMO in the study area.     

Excess of bottom-released methane in an Arctic shelf sea polynya in winter

Latent heat polynyas are regions generating strong ice formation, convection and extensive water mass formation. Here we report on the effects of these processes on resuspension of sediments and subsequent methane release from the seafloor and on the resulting excess methane concentration in surface water on a polar shelf during winter. The study is based on measurements of concentration and δ¹³C values of methane, water temperature, salinity, light transmission and sea ice data collected in March 2003 in Storfjorden, southern Svalbard. In winter, strong and persistent northeasterly winds create polynyas in eastern Storfjorden and cause ice formation. The resulting brine-enriched water cascades from the Storfjordbanken into the central depression thereby enhancing the turbulence near the seafloor. A distinct benthic nepheloid layer was observed reflecting the resuspension of sediments by the cascading dense bottom water. High concentrations of ¹³C-depleted methane suggest submarine discharge of methane with the resuspended sediments. As the source of the submarine methane, we propose recent bacterial methanogenesis near the sediment surface because of extremely high accumulation rates of organic carbon in Storfjorden. Convective mixing transports newly released methane from the bottom to the sea surface. This eventually results in an excess concentration in surface water with respect to the atmospheric equilibrium, and a sea-air flux of methane during periods of open water. When a new ice cover is formed, methane becomes trapped in the water column and subsequently oxidized. Thus, the residual methane is strongly enriched in ¹³C in relation to the δ¹³_CCH4${\delta }^{13}{\mathrm{C}}_{{\mathrm{CH}}_4}$ signature of atmospheric methane. Our results show that latent heat polynyas may induce a direct pathway for biogases like methane from sediments to the atmosphere through coupling of biogeochemical and oceanographic processes. Extrapolating these processes to all Arctic ocean polynyas, we estimate a transfer of CH₄ between 0.005 and 0.02 Tg yr⁻¹. This is not a large contribution but the fluxes from the polynyas are 20–200 times larger than the ocean average and the methane evasion process in polynyas is certainly one that can be altered under climate change.     

Assessing Methane in Shallow Groundwater in Unconventional Oil and Gas Play Areas,Eastern Kentucky

The expanding use of horizontal drilling and hydraulic fracturing technology to produce oil and gas from tight rock formations has increased public concern about potential impacts on the environment, especially on shallow drinking water aquifers. In eastern Kentucky, horizontal drilling and hydraulic fracturing have been used to develop the Berea Sandstone and the Rogersville Shale. To assess baseline groundwater chemistry and evaluate methane detected in groundwater overlying the Berea and Rogersville plays, we sampled 51 water wells and analyzed the samples for concentrations of major cations and anions, metals, dissolved methane, and other light hydrocarbon gases. In addition, the stable carbon and hydrogen isotopic composition of methane (δ¹³C‐CH₄ and δ²H‐CH₄) was analyzed for samples with methane concentration exceeding 1 mg/L. Our study indicates that methane is a relatively common constituent in shallow groundwater in eastern Kentucky, where methane was detected in 78% of the sampled wells (40 of 51 wells) with 51% of wells (26 of 51 wells) exhibiting methane concentrations above 1 mg/L. The δ¹³C‐CH₄ and δ²H‐CH₄ ranged from ?84.0‰ to ?58.3‰ and from ?246.5‰ to ?146.0‰, respectively. Isotopic analysis indicated that dissolved methane was primarily microbial in origin formed through CO₂ reduction pathway. Results from this study provide a first assessment of methane in the shallow aquifers in the Berea and Rogersville play areas and can be used as a reference to evaluate potential impacts of future horizontal drilling and hydraulic fracturing activities on groundwater quality in the region.     

Environmental Factors Associated With Natural Methane Occurrence in the Appalachian Basin

The recent boom in shale gas development in the Marcellus Shale has increased interest in the methods to distinguish between naturally occurring methane in groundwater and stray methane associated with drilling and production operations. This study evaluates the relationship between natural methane occurrence and three principal environmental factors (groundwater redox state, water type, and topography) using two pre‐drill datasets of 132 samples from western Pennsylvania, Ohio, and West Virginia and 1417 samples from northeastern Pennsylvania. Higher natural methane concentrations in residential wells are strongly associated with reducing conditions characterized by low nitrate and low sulfate ([NO₃^?] < 0.5 mg/L; [SO₄^2?] < 2.5 mg/L). However, no significant relationship exists between methane and iron [Fe(II)], which is traditionally considered an indicator of conditions that have progressed through iron reduction. As shown in previous studies, water type is significantly correlated with natural methane concentrations, where sodium (Na) ‐rich waters exhibit significantly higher (p<0.001) natural methane concentrations than calcium (Ca)‐rich waters. For water wells exhibiting Na‐rich waters and/or low nitrate and low sulfate conditions, valley locations are associated with higher methane concentrations than upland topography. Consequently, we identify three factors (“Low NO₃^? & SO₄^2?” redox condition, Na‐rich water type, and valley location), which, in combination, offer strong predictive power regarding the natural occurrence of high methane concentrations. Samples exhibiting these three factors have a median methane concentration of 10,000 µg/L. These heuristic relationships may facilitate the design of pre‐drill monitoring programs and the subsequent evaluation of post‐drill monitoring results to help distinguish between naturally occurring methane and methane originating from anthropogenic sources or migration pathways.     

Biogeochemical processes controlling methane in gassy coastal sediments—Part 2: groundwater flow control of acoustic turbidity in Eckernförde Bay Sediments

To understand the origin of the methane distributions in sediments of Eckernförde Bay, three sites were sampled in May 1994 for determination of methane, sulfate and chloride concentrations in the sediment porewaters. In much of the Bay, bubbles of biogenic methane gas within the sediments lead to widespread ‘acoustic turbidity’ seen in acoustic surveys, masking the sedimentary structure below the gassy horizon. Acoustic windows, where the gas does not appear to be present, occur in several locations in the Bay, often surrounded by acoustically turbid sediments. Pockmarks, shallow depressions in the sediment, are also found in Bay sediments and may show acoustic turbidity at even shallower depths below the interface than surrounding sediments. One site of each type was sampled in this study. The site probably representative of much of the bay below 20 m water depth, revealed methane saturated conditions by about 75 cm depth below the interface, confirming inferences from acoustic scattering data that free gas was present in the sediment. Above this, the methane concentration profile was concave-upward, indicative of methane oxidation in the overlying, sulfate-reducing sediments. These porewaters showed a slightly decreasing chlorinity with depth. At an acoustic window site, methane concentrations rose to a maximum at about 125 cm depth, but did not reach saturation. Below this depth they decreased in a concave-down pattern. Chloride concentrations decreased markedly with depth, indicative of vertical freshwater flow from below. The third site was a pockmark exhibiting very shallow acoustic turbidity at about 25 cm depth. Here methane concentrations rose to exceed saturation within 25 cm depth below the interface and the porewaters became almost fresh by 1.5 m depth, indicative of a stronger flow of freshwater from below. These groundwater flows have competing effects on the methane inventory. They help exclude sulfate from the sediment, allowing the earlier/shallower onset of methanogenesis, but they also aid loss of methane through advection. A diagenetic model that couples the biogeochemistry of sulfate and methane is used to explain the presence or absence of methane gas in these sediments in relation to the flow rate of fresh groundwater from below. Model results indicate that acoustic windows within otherwise acoustically turbid sediments of the bay are likely due to relatively higher rates of vertical advection of fresh groundwater. The gassy pockmark, however, with an even higher vertical advection rate, seems to require the input of additional reactive organic carbon to explain its vertical methane distribution.