共查询到20条相似文献，搜索用时 31 毫秒
1.
James C. G. Walker 《Pure and Applied Geophysics》1978,117(3):498-512
There may have been three stages in the growth of oxygen in the terrestrial atmosphere. Prior to the origin of photosynthesis the only source of oxygen was photolysis of water vapor followed by escape of hydrogen to space. The rate of this process was probably less than the rate of release of reduced gases (principally hydrogen) from volcanoes, so the oxygen partial pressure was held to negligibly low values by photochemical reactions with an excess of hydrogen. The photosynthetic source of oxygen was probably in operation as long ago as 3.8 billion years. It released oxygen to the ocean. Presumably most of this oxygen was destroyed in the ocean as long as its rate of supply was less than the rate of supply of readily oxidizable material (principally Fe2+) provided by the weathering of rocks. This phase appears to have lasted until about 2 billion years ago, during which period most banded iron formations were deposited. During this period the production of oxygen by algae was limited by competition with photosynthetic bacteria, which preempted the supply of nutrient phosphorus as long as reduced chemicals were available in the environment. Once the photosynthetic oxygen source exceeded the rate of supply of reduced minerals exposed by erosion and weathering, the accumulation of oxygen in the ocean and atmosphere could be controlled only by reaction of oxygen with reduced organic material. This is the stabilization mechanism that operates today. It seems unlikely that oxygen could be consumed at a significant rate by this process until oxygen levels sufficiently high to support respiration had been achieved. I therefore suggest that atmospheric oxygen rose rapidly from essentially zero to approximately its present value (within a factor of 10) when the photosynthetic source of oxygen rose above the weathering source of reduced minerals, probably about 2 billion years ago. The ozone layer and the ultraviolet screen were absent prior to this time and essentially fully developed after this time.Presented at IAGA/IAMAP Symposium on Minor Neutral Constituents in Middle Atmosphere-Chemistry and Transport, Seattle, August, 1977. 相似文献
2.
Keisuke Nagao Nobuo Takaoka Osamu Matsubayashi 《Earth and Planetary Science Letters》1981,53(2):175-188
Isotopic and elemental compositions of rare gases in various types of gas samples collected in the Japanese Islands were investigated. Excess3He was found in most samples. Many samples showed a regionally uniform high3He/4He ratio of about 7 times the atmospheric ratio. The He concentrations varied from 0.6 to 1800 ppm, and they were low in CO2-rich gases and high in N2-rich gases. Ne isotopic deviations from the atmospheric Ne were detected in most volcanic gases. The deviations and the elemental abundance patterns in volcanic gases can be explained by a mixing between two components, one is mass fractionated rare gases and the other is isotopically atmospheric and is enriched in heavy rare gas elements. Ar was a mixture of mass fractionated Ar, atmospheric Ar and radiogenic Ar, and the contribution of radiogenic40Ar was small in all samples. Except for He, elemental abundance patterns were progressively enriched in the heavier rare gases relative to the atmosphere. Several samples were highly enriched in Kr and Xe relative to the abundance pattern of dissolution equilibrium of atmospheric rare gases in water. The component which is highly enriched in heavy rare gases may be released from sedimentary materials in the crust. 相似文献
3.
The 1970 Mount Etna volcanic gas analyses (Huntingdon, 1973) are among the most reduced volcanic gas samples ever reported. They contain 20–40% H2, 2–3.5% CO, and 2–5% H2S. Calculated oxygen fugacities for most of the analyses are well below quartz-fayalite-magnetite, several are more reduced than magnetite-wustite and all are many orders of magnitude less than those measured by Sato and Moore (1973) in the gas-streams of the collection sites at the time the samples were taken. The analyses show no similarity to calculated equilibrium compositions at any temperature. Deviations between analytical and equilibrium compositions indicate the gases have undergone extensive reduction involving mainly loss of oxygen. There also is limited evidence of sulfur loss. The reduced analyses are not the products of unusually reduced lavas, but originated from reactions of the erupted gases with the metal sampling device used in the collection procedure. The oxygen deficiencies of the analyses have been restored using the atomic hydrogen, carbon and sulfur data of Huntingdon and the oxygen fugacity data of Sato and Moore. The restored analyses are much more representative of the erupted gases which were remarkably rich in CO2 (15–35%) and SO2 (15–35%), and they show relatively steady compositions at each collection site over periods of observation ranging from hours to days. 相似文献
4.
A new multi-telescope scanning Raman lidar designed to measure the water vapor mixing ratio in the atmospheric boundary layer for a complete diurnal cycle with high resolution spatial (1.25 m) and temporal (1 s) resolutions is presented. The high resolution allows detailed measurements of the lower atmosphere and offers new opportunities for evaporation and boundary layer research, atmospheric profiling and visualization. This lidar utilizes a multi-telescope design that provides for an operational range with a nearly constant signal-to-noise ratio, which allows for statistical investigations of atmospheric turbulence. This new generation ground-based water vapor Raman lidar is described, and first observations from the Turbulent Atmospheric Boundary Layer Experiment (TABLE) are presented. Direct comparison with in-situ point measurements obtained during the field campaign demonstrate the ability of the lidar to reliably measure the water vapor mixing ratio. Horizontal measurements taken with time are used to determine the geometric characteristics of coherent structures. Vertical scans are used to visualize nocturnal jet features, layered structures within a stably stratified atmosphere and the internal boundary layer structure over a lake. 相似文献
5.
Neodymium isotope and REE analyses of recent volcanic rocks and spinel lherzolite nodules from the Afar area are reported. The143Nd/144Nd ratios of the volcanic rocks range from 0.51286 to 0.51304, similar to the range recorded from Iceland. However, the87Sr/86Sr ratios display a distinctly greater range (0.70328–0.70410) than those reported from the primitive rocks of Iceland. Whole rock samples and mineral separates from the spinel lherzolite nodules exhibit uniform143Nd/144Nd ratios (ca. 0.5129) but varied87Sr/86Sr ratios in the range 0.70427–0.70528.The SrNd isotope variations suggest that the volcanic rocks may have been produced by mixing between two reservoirs with distinct isotopic compositions. Two possible magma reservoirs in this area are the source which produced the “MORB-type” volcanics in the Red Sea and Gulf of Aden and the anomalous source represented by the nodule suite. The isotopic composition of the volcanics is compatible with mixing between these two reservoirs.It is shown that the anomalous source with a high87Sr/86Sr ratio cannot have been produced by simple processes of partial melting and mixing within normal mantle. Instead the high87Sr/86Sr is equated with a fluid phase. A primitive cognate fluid, subducted seawater or altered oceanic lithosphere may have been responsible for the generation of the source with a high87Sr/86Sr ratio. 相似文献
6.
A field gas chromatograph, built in 1978, was used in the field to directly analyse volcanic gases before water vapor condensation. Tested in Vulcano (Italy), Kilauea (Hawaii) and Merapi (Indonesia), this field measurement technique provides the actual composition of the volcanic gas mixture. The technique avoids the depletion of sulfur gases and the dissolution of the acid gases in the condensed water during the cooling. Thus the mixture of H2S and SO2 in fumarolic and high temperature gases (up to 819°C) in equilibrium at the emission temperature was examined. 相似文献
7.
M. Martini 《Bulletin of Volcanology》1984,47(3):483-489
Volatile compunds play a very important role in both the evolution of magmas and the eruptive processes. Despite great interest in the knowledge of volatile distribution in magma chambers prior to eruptions, direct evidence of this kind is very difficult to obtain because a major quantity of gaseous species is released to the atmosphere during volcanic phenomena.Good estimates of volatile contents in magmas have been obtained by their distribution in coexisting mineral phases and microprobe analysis of glass inclusions; however, a sufficient set of data is not yet available to provide direct evidence of volatile concentrations in magma chambers before eruptive processes.Owing to their volatility, water, hydrogen, carbon dioxide, sulphur and chlorine compounds are largely concentrated in the explosive cloud. On the other hand, molecular species of fluorine, which are more soluble than water in magmatic melts, strongly partition into this latter phase rather than into the fluid. As a consequence, fluorine compounds are normally present in small concentrations in fumarolic gases and are not expected to degas appreciably from quenched volcanic products.With reference to the influence of weathering processes, recent research has shown that unaltered volcanic glasses have lost but a minor quantity of fluorine as a result of secondary reactions. Because of this, analytical data for fluorine in fresh igneous rocks would not differ significantly from the actual values pertaining to the magmatic stage.The distribution of fluorine in samples from Italy (Vesuvius, Vulcano, Lipari, Roccamonfina, Phlegraean Fields) and Greece (Santorini) appears to be correlated with the concentration of potassium, which is in accordance with theoretical assumptions and analytical results in other areas.According to experimental data, the presence of fluorine in magmas of silicate composition considerably enhances the solubility of water.Higher concentrations of water would mean a higher potential explosivity, and the possibility that the observed concentrations of fluorine can serve as a measure of different degrees of stored energy is considered.Contribution of C.N.R. Centro di Studio per la Mineralogia e la Geochimica dei Sedimenti. 相似文献
8.
W. C. Sidle 《Bulletin of Volcanology》1984,47(3):517-529
Soil gases have been measured, utilizing petroleum nearsurface exploration techniques, in the volcanic province of the Eastern Snake River Plain, In Idaho, U.S.A. The analyses of the soil atmosphere included light hydrocarbon gases, helium, hydrogen, and carbon dioxide. Samples were collected in and near recent basaltic rift zones. Characterization of rift zone soil gases has indicated variability of their compositional and magnitude makeup. Suggestion of some deeper sourced gases having migrated through fractures in the rift zones is advanced. Also differences among the samples rift zones are presented. 相似文献
9.
A one-dimensional atmospheric photochemical model with an altitude grid of about 1.5 km was used to examine the structure of the global mean vertical ozone profile and its night-time-to-daytime variation in the upper atmosphere. Two distinct ozone layers are predicted, separated by a sharp drop in the ozone concentration near the mesopause. This naturally occurring mesopause ozone deep minimum is primarily produced by the rapid increase in the destruction of water vapour, and hence increase in HOx, at altitudes between 80 and 85 km, a region where water-vapour photodissociation by ultraviolet radiation of the solar Lyman-alpha line is significant, and where the supply of water vapour is maintained by methane oxidation even for very dry conditions at the tropospheric-stratospheric exchange region. The model indicates that the depth of the mesopause ozone minimum is limited by the efficiency with which inactive molecular hydrogen is produced, either by the conversion of atomic hydrogen to molecular hydrogen via one of the reaction channels of H with HO2, or by Lyman-alpha photodissociation of water vapour via the channel that leads to the production of molecular hydrogen. The ozone concentration rapidly recovers above 85 km due to the rapid increase in O produced by the photodissociation of O2 by absorption of ultraviolet solar radiation in the Schumann-Runge bands and continuum. Above 90 km, there is a decrease in ozone due to photolysis as the production of ozone through the three-body recombination of O2 and O becomes slower with decreasing pressure. The model also predicts two peaks in the night-time/daytime ozone ratio, one near 75 km and the other near 110 km, plus a strong peak in the night-time/daytime ratio of OH near 110 km. Recent observational evidence supports the predictions of the model. 相似文献
10.
E. Kaminski A.-L. Chenet C. Jaupart V. Courtillot 《Earth and Planetary Science Letters》2011,301(1-2):171-178
Turbulent volcanic plumes disperse fine ash particles and toxic gases in the atmosphere and can lead to significant temperature drops in the atmosphere. In the geological past, the emplacement of large continental flood basalts (CFB) has been associated with large changes in the global environment and extinctions of biological species. The variable intensity of environmental changes induced by otherwise similar CFB events, however, begs for a reevaluation of physical controls on the environmental impact of volcanic eruptions. The climatic impact of an eruption depends on its ability to inject gases in the stratosphere and on the eruption rate. Using integral models of turbulent plumes above line and point sources, we find that mass rate estimates for CFBs are in general not large enough for volcanic plumes to reach the stratosphere on their own. Basaltic eruptions, however, are also associated with widespread lava flows which lose large amounts of heat and generate convection in the atmosphere. This form of convection, known as penetrative convection, acts to erode the stably stratified lower atmosphere and generates a thick well-mixed heated atmospheric layer in a few hours. The added buoyancy provided by such a layer almost always ensures that volcanic gases get transported to the stratosphere. The environmental consequences of CFBs are therefore controlled not by the inputs to the atmosphere from individual volcanic plumes, but by the dynamic response of the climate system to a succession of short eruptive pulses within a longer-lasting eruption sequence. 相似文献
11.
Sulphur isotopic compositions of pyrite, anhydrite and native sulphur in volcanic ashes discharged by the 1979 eruption of Ontake volcano, Nagano, Japan were determined. The isotopic data indicate that sulphate in anhydrite and a part of native sulphur were produced by the disproportionation reaction of sulphite formed by dissolution of SO2 in volcanic gases into water which filled a mud reservoir probably located just below the crater zone. Some part of H2S in volcanic gases was fixed as pyrite and some was oxidised to form native sulphur. Hydrothermal alteration of country rocks to form pyrite, anhydrite and clay minerals had proceeded in the mud reservoir before eruption at temperatures ranging from 110° to 185°C which were estimated by oxygen isotopic fractionation between anhydrite and water.
相似文献12.
Bradford M. Clement Charles B. Connor Grenville Graper 《Earth and Planetary Science Letters》1993,120(3-4):499-510
Stoopes and Sheridan have mapped a volcanic debris avalanche of Nevado de Colima which has an exceptionally long runout (120 km) and low fall-height to length ratio (H/L = 0.04). We present paleomagnetic results from this volcanic debris avalanche deposit which provide evidence that this avalanche was emplaced at elevated temperatures. The majority of samples, collected from lithic clasts in the volcanic debris avalanche deposit, exhibit two-component remanent magnetizations with a low-temperature component (25–350°C) which is well grouped about the geomagnetic field direction at Colima and a high-temperature component (350–580°C) which is randomly oriented. Although the temperature of the deposit most likely varied with distance from the volcanic source and the thickness of the deposit, our results suggest an emplacement temperature of approximately 350°C at intermediate distances (18–26 km) from the source. In order for the rock clasts (20–40 cm diameter) to be heated to these temperatures, the avalanche was most likely the results of a magmatic, Bezymianny-type eruption. The mixing of hot, juvenile gases with the clasts provides an explanation for the high degree of fluidization of this material, as evidenced by the long runout of this avalanche deposit. 相似文献
13.
利用地质学、天文学、地球物理学、古生物学资料进行约束,对地球的去气作用进行研究发现：太阳系的部分冷物质,通过吸积作用形成早期地球.在碰撞动能转变的热能作用下,造成了早期地球的表面熔融.在熔融状态的高温高压作用下,构成地球表面物质的结晶水排出地表进入原始大气;在高温高压下分解的碳酸盐、硫酸盐、卤化物等产生的二氧化碳、硫化氢、二氧化硫、氯化氢、氟化氢等气体进入原始大气,和水蒸汽一道共同组成原始大气.当地球内部在重力势能和放射能的作用下继续熔融时,地球表面固化为原始岩石圈.后来,地球除表面岩石圈外,整个地球完全熔融.地球内部物质熔融形成的水和二氧化碳等气体,被岩石圈圈闭.只有当冰川形成和消融,引起造海和造陆作用,导致火山喷发和地震时,这些气体才可能排出地表.这些气体的排出,受地球内部的熔融状态、冰川形成的位置（是在海洋或是在陆地）、生物的演化、太阳光的强度等因素的综合影响. 相似文献
14.
Phreatic eruptions occurred at the Meakandake volcano in 1988, 1996, 1998, 2006, and 2008. We conducted geochemical surveillance
that included measurements of temperature, SO2 emission rates, and volcanic gas composition from 2003 to 2008 at the Nakamachineshiri (NM), Northwest (NW), and Akanuma
(AK) fumarolic areas, and the 96–1 vent, where historical eruptions had occurred. The elemental compositions of the gases
discharged from the different areas are similar compared with the large variations observed in volcanic gases discharged from
subduction zones. All the gases showed high apparent equilibrium temperatures, suggesting that all these gases originated
from a common magmatic gas. The gases discharged from each area also exhibited different characteristics, which are probably
the results of differences in the conditions of meteoric water mixing, quenching of chemical reactions, and vapor-liquid separation.
The highest apparent equilibrium temperatures (about 500°C) were observed in the case of NW fumarolic gases, despite the low
outlet temperature of about 100°C at these fumaroles. Since the NW fumaroles were formed as a result of the 2006 phreatic
eruption, the high-temperature gas supply to the NW fumarole suggests that the phreatic eruption was caused by the ascent
of high-temperature magmatic gases. The temperatures, compositions, and emission rates of the NM and 96–1 gases did not show
any appreciable change after the 2006 eruption, indicating that each fumarolic system had a separate magmatic-hydrothermal
system. The temperatures, compositions, and emission rates of the NM fumarolic gases were apparently constant, and these fumaroles
are inferred to be formed by the evaporation of a hydrothermal system with a constant temperature of about 300°C. The 96–1
gas compositions showed large changes during continuous temperature decrease from 390° to 190°C occurred from 2003 to 2008,
but the sulfur gas emission rates were almost constant at about four tons/day. At the 96–1 vent, the SO2/H2S ratio decreased, while the H2/H2O ratio remained almost constant; this was probably caused by the rock-buffer controlled chemical reaction during the temperature
decrease. 相似文献
15.
本文根据气体分子运动论导出了垂直动力传输函数,此函数可以代替Nicolet和Mangc的混合比,较好地描述高层大气中从完全混合状态向扩散分离状态的过渡过程。分析了高层大气中湍流运动的观测结果,给出了湍流系数随高度分布的几个模式,利用这些模式计算了惰性气体氩、氦与氮的数密度比的高度剖面,并与箭载质谱仪探空资料作了比较。根据光化-动力传输理论,计算了上中层及低热层大气主要化学成份的高度分布。结果表明:垂直动力传输明显地影响着大气成份的分布。文中还指出,氧分子的光离解系数与其数密度的高度剖面耦合在一起,因而应当由上向下数值求解有源有汇的连续方程组,这样可避免由于光离解系数的假设所造成的误差。 相似文献
16.
Ichiro Kaneoka 《Earth and Planetary Science Letters》1980,48(2):284-292
A simple model of mass fractionation may explain the isotopic ratios of rare gases in volcanic materials. Single-stage mass fractionation of atmospheric rare gases predicts an upper limit for20Ne/22Ne of 10.3 and a lower limit for40Ar/36Ar of 280. The rare gas data in volcanic materials seem to support this interpretation.Relatively low40Ar/36Ar ratios, as low as 282, have been observed in recent Japanese volcanic rocks. Such a low40Ar/36Ar ratio may be explained by mass fractionation of the atmospheric value if the rare gases represent those which were transported into the magma chamber with other volatile elements.Both the amounts and the fractionated rare gas abundance pattern of lighter elements which are observed in pumices from the recent eruption of Mt. Usu, Southern Hokkaido, Japan, suggest the possibility of air injection into its magma chamber. Thus, the fractionation of rare gases in volcanic materials may be a common occurrence, and it must be considered in models for the origin of isotopic differences between rare gases in volcanic materials and the atmosphere. 相似文献
17.
We report chemical compositions (major and trace components including light hydrocarbons), hydrogen, oxygen, helium and nitrogen
isotope ratios of volcanic and geothermal fluids of Mutnovsky volcano, Kamchatka. Several aspects of the geochemistry of fluids
are discussed: chemical equilibria, mixing of fluids from different sources, evaluation of the parent magmatic gas composition
and contributions to magmatic vapors of fluids from different reservoirs of the Kamchatkan subduction zone. Among reactive
species, hydrogen and carbon monoxide in volcanic vapors are chemically equilibrated at temperatures >300°C with the SO2-H2S redox-pair. A metastable equilibrium between saturated and unsaturated light hydrocarbons is attained at close to discharge
temperatures. Methane is disequilibrated. Three different sources of fluids from three fumarolic fields in the Mutnovsky craters
can be distinguished: (1) magmatic gas from a large convecting magma body discharging through Active Funnel, a young crater
with the hottest fumaroles (up to 620°C) contributing ~80% to the total volcanic gas output; (2) volcanic fluid from a separate
shallow magma body beneath the Bottom Field of the main crater (96–280°C fumaroles); and (3) hydrothermal fluid with a high
relative and absolute concentrations of CH4 from the Upper Field in the main crater (96–285°C fumaroles). The composition of the parent magmatic gas is estimated using
water isotopes and correlations between He and other components in the Active Funnel gases. The He-Ar-N2 systematics of volcanic and hydrothermal fluids of Mutnovsky are consistent with a large slab-derived sedimentary nitrogen
input for the nitrogen inventory, and we calculate that only ~1% of the magmatic N2 has a mantle origin and <<1% is derived from the arc crust. 相似文献
18.
松原5.7级地震震中区土壤氢气变化特征 总被引：2，自引：0，他引：2
2018年5月28日吉林松原发生5.7级地震,为了探究地震对断层气的影响以及震后断层气变化特征,震后在震中区进行了多期土壤氢气浓度观测工作,得到了震中区氢气浓度的最大值、背景值等多项指标。结合地震前后氢气浓度数据,分析震中区震前、震后氢气浓度趋势性变化情况,结果显示:在此次地震活动中,氢气浓度变化有"震前缓慢升高—临震下降—震后迅速升高—强余震前再次骤升"的现象;氢气浓度变化与地震活动间有很好的映震关系,主震对氢气浓度的上升起主要作用,而余震则起诱发作用,余震的活动会使赋存在地下岩石裂隙的氢气释放量增大,表明氢气对余震活动的响应较灵敏;另外,震后某一时刻空气中的氢气浓度也会升高,这可能与区域断层中的氢气逸散到大气中有一定关系。 相似文献
19.
Ian Hers Parisa Jourabchi Matthew A. Lahvis Paul Dahlen E. Hong Luo Paul Johnson George E. DeVaull K. Ulrich Mayer 《Ground Water Monitoring & Remediation》2014,34(4):60-78
A detailed seasonal study of soil vapor intrusion at a cold climate site with average yearly temperature of 1.9 °C was conducted at a house with a crawlspace that overlay a shallow dissolved‐phase petroleum hydrocarbon (gasoline) plume in North Battleford, Saskatchewan, Canada. This research was conducted primarily to assess if winter conditions, including snow/frost cover, and cold soil temperatures, influence aerobic biodegradation of petroleum vapors in soil and the potential for vapor intrusion. Continuous time‐series data for oxygen, pressure differentials, soil temperature, soil moisture, and weather conditions were collected from a high‐resolution monitoring network. Seasonal monitoring of groundwater, soil vapor, crawlspace air, and indoor air was also undertaken. Petroleum hydrocarbon vapor attenuation and biodegradation rates were not significantly reduced during low temperature winter months and there was no evidence for a significant capping effect of snow or frost cover that would limit oxygen ingress from the atmosphere. In the residual light nonaqueous phase liquid (LNAPL) source area adjacent to the house, evidence for biodegradation included rapid attenuation of hydrocarbon vapor concentrations over a vertical interval of approximately 0.9 m, and a corresponding decrease in oxygen to less than 1.5% v/v. In comparison, hydrocarbon vapor concentrations above the dissolved plume and below the house were much lower and decreased sharply within a few tens of centimeters above the groundwater source. Corresponding oxygen concentrations in soil gas were at least 10% v/v. A reactive transport model (MIN3P‐DUSTY) was initially calibrated to data from vertical profiles at the site to obtain biodegradation rates, and then used to simulate the observed soil vapor distribution. The calibrated model indicated that soil vapor transport was dominated by diffusion and aerobic biodegradation, and that crawlspace pressures and soil gas advection had little influence on soil vapor concentrations. 相似文献
20.
William I. Rose Jr. Richard D. Cadle Leroy E. Heidt Irving Friedman Allen L. Lazrus Barry J. Huebert 《Journal of Volcanology and Geothermal Research》1980,7(1-2)
Gas samples were collected by aircraft entering volcanic eruption clouds of three Guatemalan volcanoes. Gas chromatographic analyses show higher H2 and S gas contents in ash eruption clouds and lower H2 and S gases in vaporous gas plumes. H isotopic data demonstrate lighter isotopic distribution of water vapor in ash eruption clouds than in vaporous gas plumes. Most of the H2O in the vaporous plumes is probably meteoric. The data are the first direct gas analyses of explosive eruptive clouds, and demonstrate that, in spite of atmospheric admixture, useful compositional information on eruptive gases can be obtained using aircraft. 相似文献