A new estimate of global methane flux from onshore and shallow submarine mud volcanoes to the atmosphere

A new estimate of global methane emission into the atmosphere from mud volcanoes (MVs) on land and shallow seafloor is presented. The estimate, considered a lower limit, is based on 1) new direct measurements of flux, including both venting of methane and diffuse microseepage around craters and vents, and 2) a classification of MV sizes in terms of area (km²) based on a compilation of data from 120 MVs. The methane flux to the atmosphere is conservatively estimated between 6 and 9 Mt y^–1. This emission from MVs is 3–6% of the natural methane sources and is comparable with ocean and hydrate sources, officially considered in the atmospheric methane budget. The total geologic source, including MVs, seepage from seafloor, microseepage in hydrocarbon-prone areas and geothermal sources, would amount to 35–45 Mt y^–1. The authors believe it is time to add this parameter in the Intergovernmental Panel on Climate Change official tables of atmospheric methane sources.GEM     

The Geochemistry of Lake Joyce, McMurdo Dry Valleys, Antarctica

Lake Joyce is one of the least studied lakes of the McMurdo Dry Valleys. Similar to other lakes in this region, Lake Joyce is a closed-basin, permanently ice-covered, meromictic lake. We present here a detailed investigation of major ions, nutrients, and dissolved trace elements for Lake Joyce. Specifically, we investigate the role of iron and manganese oxides and hydrous oxides in trace metal cycling.Lake Joyce is characterized by fresh, oxic waters overlying an anoxic brine, primarily Na–Cl. Surface waters have a maximum nitrate concentration of 26M with a molar dissolved inorganic nitrogen to phosphorus ratio of 477. The supply of nitrogen is attributed to atmospheric deposition, possibly from polar stratospheric clouds. Dissolved phosphorus is scavenged by hydrous iron oxides. The pH is highest (10.15) just beneath the 7-m thick ice cover and decreases to a minimum of 7.29 in the redox transition zone. Dissolved Al exceeds 8M in surface waters, and appears to be controlled by equilibrium with gibbsite. In contrast, concentrations of other trace elements in surface waters are quite low (e.g., 5.4nM Cu, 0.19nM Co, <20pM La). Dissolved Fe, Mn, Ni and Cd were below our detection limits of 13 nM, 1. 8 nM, 4.7 nM and 15pM (respectively) in surface waters. There was a 6-m vertical separation in the onset of Mn and Fe reduction, with dissolved Mn appearing higher in the water column than Fe. Based on thermodynamic calculations, dissolved Mn appears to be controlled by equilibrium with hausmannite (Mn3O4). Co tracks the Mn profile closely, suggesting Co(III) is bound in the lattice of Mn oxides, whereas the Ce profile is similar, yet the Ce anomaly suggests oxidative scavenging of Ce. Release of Cu, Ni, Cd and trivalent REE appears to be controlled by pH-induced desorption from Fe and Mn oxides, although Cu (and perhaps Ni) may be scavenged by organic matter in surface waters.     

Three-dimensional numerical simulation of a nonstationary gravitating <Emphasis Type="Italic">N</Emphasis>-body system with gas

We developed a three-dimensional numerical model to investigate nonstationary processes in gravitating N-body systems with gas. We used efficient algorithms for solving the Vlasov and Poisson equations that included the evolutionary processes under consideration, which ensures rapid convergence at high accuracy. We give examples of the numerical solution of the problem on the growth of physical instability in the model of a flat rotating disk with a gaseous component and its three-dimensional dynamics under various initial conditions including a nonzero velocity dispersion along the rotation axis.     

Geochemical Constraints on the Origin of Volcanic Rocks from the Andean Northern Volcanic Zone, Ecuador

Whole-rock geochemical data on basaltic to rhyolitic samplesfrom 12 volcanic centers are used to constrain the role of continentalcrust in the genesis of magmas formed beneath the anomalouslywide subduction-related volcanic arc in Ecuador. Relativelyhomogeneous, mantle-like, isotopic compositions across the arcimply that the parental magmas in Ecuador were produced largelywithin the mantle wedge above the subduction zone and not byextensive melting of crustal rocks similar to those upon whichthe volcanoes were built. Cross-arc changes in ¹⁴³Nd/¹⁴⁴Nd and7/4Pb are interpreted to result from assimilation of geochemicallymature continental crust, especially in the main arc area, 330–360km from the trench. Mixing calculations limit the quantity ofassimilated crust to less than 10%. Most andesites and dacitesin Ecuador have adakite-like trace element characteristics (e.g.Y <18 ppm, Yb <2 ppm, La/Yb >20, Sr/Y >40). Availablewhole-rock data do not provide a clear basis for distinguishingbetween slab-melting and deep crustal fractionation models forthe genesis of Ecuador adakites; published data highlightinggeochemical evolution within individual volcanoes, and in magmaticrocks produced throughout Ecuador since the Eocene, appear tosupport the deep fractionation model for the genesis of mostevolved Ecuadoran lavas. A subset of andesites, which displaya combination of high Sr (>900 ppm), Nd >4·1 and7/4Pb <6·0, appear to be the best candidates amongEcuador lavas for slab-melts associated with the subductionof the relatively young, over-thickened, oceanic crust of theCarnegie Ridge. KEY WORDS: andesite; Ecuador; trace elements; isotopes; adakite     

Combined Trace Element and Pb-Nd-Sr-O Isotope Evidence for Recycled Oceanic Crust (Upper and Lower) in the Iceland Mantle Plume

We present the results of a comprehensive major element, traceelement and Sr–Nd–Pb–O isotopic study of post-glacialvolcanic rocks from the Neovolcanic zones on Iceland. The rocksstudied range in composition from picrites and tholeiites, whichdominate in the main rift systems, to transitional and alkalicbasalts confined to the off-rift and propagating rift systems.There are good correlations of rock types with geochemical enrichmentparameters, such as La/Sm and La/Yb ratios, and with long-termradiogenic tracers, such as Sr–Nd–Pb isotope ratios,indicating a long-lived enrichment/depletion history of thesource region. ⁸⁷Sr/⁸⁶Sr vs ¹⁴³Nd/¹⁴⁴Nd defines a negative array.Pb isotopes define well-correlated positive arrays on both ²⁰⁶Pb/²⁰⁴Pbvs ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb diagrams, indicating mixing ofat least two major components: an enriched component representedby the alkali basalts and a depleted component represented bythe picrites. In combined Sr–Nd–Pb isotopic spacethe individual rift systems define coherent mixing arrays withslightly different compositions. The enriched component hasradiogenic Pb (²⁰⁶Pb/²⁰⁴Pb > 19·3) and very similargeochemistry to HIMU-type ocean island basalts (OIB). We ascribethis endmember to recycling of hydrothermally altered upperbasaltic oceanic crust. The depleted component that is sampledby the picrites has unradiogenic Pb (²⁰⁶Pb/²⁰⁴Pb < 17·8),but geochemical signatures distinct from that of normal mid-oceanridge basalt (N-MORB). Highly depleted tholeiites and picriteshave positive anomalies in mantle-normalized trace element diagramsfor Ba, Sr, and Eu (and in some cases also for K, Ti and P),negative anomalies for Hf and Zr, and low ¹⁸O_olivine values(4·6–5·0) below the normal mantle range.All of these features are internally correlated, and we, therefore,interpret them to reflect source characteristics and attributethem to recycled lower gabbroic oceanic crust. Regional compositionaldifferences exist for the depleted component. In SW Icelandit has distinctly higher Nb/U (68) and more radiogenic ²⁰⁶Pb/²⁰⁴Pbratios (18·28–18·88) compared with the NErift (Nb/U 47; ²⁰⁶Pb/²⁰⁴Pb = 18·07–18·47).These geochemical differences suggest that different packagesof recycled oceanic lithosphere exist beneath each rift. A thirdand minor component with relatively high ⁸⁷Sr/⁸⁶Sr and ²⁰⁷Pb/²⁰⁴Pbis found in a single volcano in SE Iceland (Öræfajökullvolcano), indicating the involvement of recycled sediments inthe source locally. The three plume components form an integralpart of ancient recycled oceanic lithosphere. The slope in theuranogenic Pb diagram indicates a recycling age of about 1·5Ga with time-integrated Th/U ratios of 3·01. Surprisingly,there is little evidence for the involvement of North AtlanticN-MORB source mantle, as would be expected from the interactionof the Iceland plume and the surrounding asthenosphere in formof plume–ridge interaction. The preferential samplingof the enriched and depleted components in the off-rift andmain rift systems, respectively, can be explained by differencesin the geometry of the melting regions. In the off-rift areas,melting columns are truncated deeper and thus are shorter, whichleads to preferential melting of the enriched component, asthis starts melting deeper than the depleted component. In contrast,melting proceeds to shallower depths beneath the main rifts.The longer melting columns also produce significant amountsof melt from the more refractory (lower crustal/lithospheric)component. KEY WORDS: basalts; trace element and Sr, Nd, Pb, O isotope geochemistry; Iceland plume; isotope ratios; oceanic crustal recycling; partial melting; plume–ridge interaction     

Constraining the hydrocarbon expulsion history of the coals in Qinshui Basin, North China, from the analysis of fluid inclusions

From the comprehensive study on the homogenization temperatures and the occurrence of fluid inclusions in the framework minerals of the strata between or above the Carboniferous–Permian coals in the Qinshui basin, Shanxi, three stages are predicted of hydrocarbon expulsion from the coals. Combined with the known history of basin evolution, it is deduced that the expulsion of hydrocarbons happened during the J₁ (210–180 Ma), the early K₁ (150–130 Ma) and K₂E₁ (110–60 Ma). In the early stage, the coals produced and discharged coal-generated oils. The average GOI value of four sandstone samples is relatively high, as they have been exposed to high paleo-oil saturation in the strata between or above the coals. The biomarker compositions of oil-bearing fluid inclusions are similar to those of extracts from the coals, and so it is concluded that those oils were derived from the same family of the coals.     

Prediction of Resource Volumes at Untested Locations Using Simple Local Prediction Models

This paper shows how local spatial nonparametric prediction models can be applied to estimate volumes of recoverable gas resources at individual undrilled sites, at multiple sites on a regional scale, and to compute confidence bounds for regional volumes based on the distribution of those estimates. An approach that combines cross-validation, the jackknife, and bootstrap procedures is used to accomplish this task. Simulation experiments show that cross-validation can be applied beneficially to select an appropriate prediction model. The cross-validation procedure worked well for a wide range of different states of nature and levels of information. Jackknife procedures are used to compute individual prediction estimation errors at undrilled locations. The jackknife replicates also are used with a bootstrap resampling procedure to compute confidence bounds for the total volume. The method was applied to data (partitioned into a training set and target set) from the Devonian Antrim Shale continuous-type gas play in the Michigan Basin in Otsego County, Michigan. The analysis showed that the model estimate of total recoverable volumes at prediction sites is within 4 percent of the total observed volume. The model predictions also provide frequency distributions of the cell volumes at the production unit scale. Such distributions are the basis for subsequent economic analyses.

地面地下空间信息采集车及试验结果

介绍地面地下空间信息采集车的原理和结构,给出了利用GPS-RTK辅以全站仪和地下管线探测仪实现地下管线勘、测、管一体化的原理,以及获取管线三维坐标的数学模型。通过试验验证了地面地下空间信息采集车的可行性,其精度满足《城市地下管线探测技术规程》的要求。     

无控制DEM表面差异探测研究

本文提出了一个新的无控制DEM差异探测算法。它可以将不同时期获取的DEM纳入到统一坐标系中,这样就可以根据匹配后的DEM来定量探测地表变化情况。该方法通过差分模型考虑了观测量的数值及其相互关系。与目前差异探测能力最强的LMS-LZD方法相比,新方法具有更好的差异能力和更高的匹配精度。普歪沟泥石流沟多时相DEM差异探测实例验证了新方法的优越性。     

基于MODIS 250m遥感影像的变化检测

本文采用分辨率为250m的MODIS遥感影像对土地利用类型进行动态监测,其目的是探讨在MODIS影像上,能够快速准确地获取在不同时期的变化信息,并且为进一步分析提供参考。本文主要讨论运用MODIS影像进行变化检测的几个方面:一是相对辐射校正;二是变化区域的确定,采用基于像素的阈值分割和基于区域的松弛法进来确认变化/非变化像元,并提出一种基于缓冲区方法来消除部分伪变化信息;三是精度评价,根据MO-DIS高时相的特点,本文提出了基于缺少实地观测数据情况下的精度评价。