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181.
Hitoshi Tomaru Udo Fehn Zunli Lu Rika Takeuchi Fumio Inagaki Hiroyuki Imachi Ryosuke Kotani Ryo Matsumoto Kan Aoike 《Resource Geology》2009,59(4):359-373
Iodine concentration and radioisotopic composition (129I/I) were measured in the pore waters from the gas hydrate occurrence in the forearc basin offshore Shimokita Peninsula, north-eastern Japan, to determine the source formation of I and accompanying hydrocarbons. Iodine concentrations correlate well with the alkalinity and SO4 patterns, reflecting degradation stages of I-rich buried organic matter, rapidly increasing in the sulfate reduction interval, and becoming constant below 250 meters below the seafloor with an upwelling flux of 1.5 × 10−11 µmol cm−2 year−1. The 129I/I ratios of 300 × 10−15–400 × 10−15 in deep pore waters suggest ages for iodine and hydrocarbon sources as old as 40 Ma. These ages correlate well with the coaly source formations of the Eocene age thought to be responsible for the conventional natural gas deposits underlying the gas hydrate stability zone. Similar profiles are observed in 129I/I ratios of pore waters in the gas hydrate stability zone from the forearc basin in the eastern Nankai Trough, offshore central Japan, where pore waters are enriched in I and reach ages as old as ∼50 Ma through the sediment column. At the outer ridge site along the trough, on the other hand, relatively younger I are more frequently delivered probably through thrusts/faults associated with subduction. The nature of source formations of I and hydrocarbons in the offshore Shimokita Peninsula has a more terrestrial contribution compared with those in the Nankai Trough, but these formations are also considerably older than the host sediments, suggesting long-term transport of I and hydrocarbons for the accumulation of gas hydrates in both locations. 相似文献
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183.
The concentration levels of 12 priority volatile organic compounds (VOCs) were determined in two species of vertebrates and four species of invertebrates from sampling stations in the southern North Sea, using a modified Tekmar LSC 2000 purge and trap system coupled to gas chromatograph–mass spectrometer (GC–MS). In general, concentration levels of VOCs found in this study were of the same order of magnitude as those previously reported in the literature. The concentrations of the chlorinated hydrocarbons (CHCs), with the exception of chloroform, tended to be lower than those of the monocyclic aromatic hydrocarbons (MAHs). The experimental data were statistically evaluated using both cluster analysis and principal component analysis (PCA). From the results of cluster analysis and PCA, no specific groups could be distinguished on the basis of geographical, temporal or biological parameters. However, based on the cluster analysis and the PCA, the VOCs could be divided into three groups, C2-substituted benzenes, CHCs and benzene plus toluene. This division could be related to different types of sources. Finally, it was shown that organisms can be used to monitor the presence of VOCs in the marine environment and the observed concentrations levels were compared with proposed safety levels. 相似文献
184.
Latent and Sensible Energy Flux Over Deforested Land Surfaces in the Eastern Amazon and Northern Thailand 总被引:1,自引:0,他引:1
T.W. Giambelluca M.A. Nullet A.D. Ziegler & L. Tran 《Singapore journal of tropical geography》2000,21(2):107-130
Land cover change may impact watershed hydrology and regional climate by altering land-atmosphere exchanges of energy and water. Conversion of forest to pasture has previously been shown to decrease the rate of evaporation (including transpiration) because of reduced aerodynamic roughness, less canopy rainfall interception and greater canopy resistance during dry periods. However, less is known about the effects of forest replacement land covers other than pasture. In this study, field measurements of meteorological processes, stomatal resistance, and Leaf Area Index (LAI) were taken over various deforested land surfaces in the eastern Amazon Basin and in northern Thailand. Based on these measurements, evaporation and sensible heat flux were estimated over each site. Results show the degree to which different land covers replacing tropical forest affect energy partitioning. In comparison with forest, non-irrigated, actively and recently cultivated sites had sharply lower rates of evaporation. Secondary vegetation generally had higher rates of evaporation than actively or recently used sites. The proportion of energy used for evaporation increased rapidly with age in secondary vegetation. Evaporation rates at sites eight and 25 years after abandonment in the Thailand study area were enhanced by positive sensible energy advection from nearby cultivated areas, and were similar to those of primary forest. Differences in dry season evaporation rates of 3-, 8- and 25-year secondary vegetation are explained, in part, by the differences in canopy resistance. Minimum canopy resistance was 223, 61 and 58 s m −1 , respectively at the 3-, 8- and 25-year sites. 相似文献
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186.
Spatial backshore processes were investigated through field observations of topography and median sand grain size at a sandy beach facing the Pacific Ocean in Japan. A comparison of the backshore profile and cross‐shore distribution of the median sand grain size in 1999 and 2004 revealed an unusual sedimentary process in which sand was coarsened in a depositional area in the 5‐year period, although sediment is generally coarsened in erosional areas. In support of these observations, monthly spatial field analyses carried out in 2004 demonstrated a remarkable backshore coarsening process triggered by sedimentation in the seaward part of the backshore during a storm event. In order to elucidate mechanisms involved in the backshore coarsening process, thresholds of movable sand grain size under wave and wind actions (a uniform parameter for both these cases) in the onshore and offshore directions were estimated using wave, tide, and wind data. The cross‐shore distributions of the estimated thresholds provided reasonable values and demonstrated a coarsening mechanism involving the intermediate zone around the shoreline under alternating wave and wind actions as a result of which coarse sand was transported toward the seaward part of the backshore by large waves during storms and then toward the landward part by strong onshore winds. The 5‐year backshore coarsening is most certainly explained by repetition of short‐term coarsening mechanisms caused by wave‐induced sand transport occurring from the nearshore to the intermediate zone. Copyright © 2010 John Wiley & Sons, Ltd 相似文献
187.
Geologic evidence of the prior existence of liquid water on Mars suggests surface temperatures Ts were once considerably warmer than at present; and that such a condition may have arisen from a larger atmospheric greenhouse. Here we develop a simple climate model for a CO2/H2O Mars atmosphere including water vapor-longwave opacity feedback in the atmosphere and temperature-albedo feedback at surface icecaps, under the assumption that once the Martian surface pressure was ps ≥ 1 atm CO2. Longwave flux to space is computed as a function of Ts and ps using band-absorption models for the effect of the 15-μm fundamental, and the 10- and 15-μm hot bands, of the CO2 molecule; as well as the pure rotation bands and e continuum of H2O. The derived global radiative balance predicts a global mean surface temperature of 283°K at 1 atm CO2. When the emission model is coupled to a latitudinally resolved energy balance climate model, including the effect of poleward heat transfer by atmospheric baroclinic eddies, the solutions vary, depending on ps. We considered two cases: (1) the present Mars (ps ? 0.007 atm) with pressure-buffering by solid CO2 icecaps, and limited poleward heat flux by the atmosphere; and (2) a hypothetical “hot Mars” (ps ? 1.0 atm), whose much higher CO2 amount augmented by H2O evaporative feedback yields a theoretical Ts distribution with latitude admitting liquid water over 95% of the surface, water icecaps at the poles, and a diminished equator-to-pole temperature gradient relative to the present. 相似文献
188.
Laboratory measurements of the cross-sections for double ionization of atomic oxygen by electrons are presented for energies from threshold to ~ 400 eV. A maximum cross-section of about 5.6 × 10?18 cm2 is observed at an electron energy of approx. 200 eV. Absolute cross-sections are obtained from measurements of the ratio of the cross-sections for double and single ionization, coupled with absolute cross-sections for single ionization previously measured by other investigators. The possible effects of excited oxygen reactants are examined, and the reported cross-sections are considered to be characteristic of ground state oxygen atoms. 相似文献
189.
Amanda Tosi Maria Elizabeth Zucolotto Diana Paula Andrade Othon Cabo Winter Daniela Cardozo Mourão Rafael Sfair Karen Ziegler Pablo Daniel Perez Sergio Suarez Iara Deniz Ornellas Marcelo Zurita Julio Cezar Mendes Alexander Wilhelm Kellner Wania Wolff 《Meteoritics & planetary science》2023,58(5):621-642
On August 19, 2020, at 13:18—UTC, a meteor event ended as a meteorite shower in Santa Filomena, a city in the Pernambuco State, northeast Brazil. The heliocentric orbital parameters resulting from images by cameras of the weather broadcasting system were semimajor axis a = 2.1 ± 0.1 au, eccentricity e = 0.55 ± 0.03, and inclination i = 0.15o ± 0.05. The data identified the body as an Apollo object, an Earth-crossing object with a pericenter interior to the Earth's orbit. The chemical, mineralogical, and petrological evaluations, as well as the physical analysis, followed several traditional techniques. The meteorite was identified as a H5-6 S4 W0 ordinary chondrite genomict breccia. The large amount of metal in the meteorite made a metallographic evaluation based on the opaque phases possible. The monocrystalline kamacite crystals suggest a higher petrological type and the distorted Neumann lines imply at least two different shock events. The absence of the plessite phase shows that the meteorite did not reach the highest shock levels S5 and S6. The well-defined polycrystalline taenite is indicative of petrologic types 4 and 5 due to the conserved internal tetrataenite rim at the boundaries. The presence of polycrystalline taenites and the characteristics of the Agrell Effect suggest that the Santa Filomena meteorite did not reheat above 700°C. The absence of martensite confirms reheating temperatures <800°C and a slow cooling rate. The Ni contents and sizes of the zoned taenite particles indicate a slow cooling rate ranging from 1 to 10 K Myr−1. 相似文献