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81.
A very long series of photographic observations of the comet Hale-Bopp has been made during January–April 1997 at the double
astrograph (400/2000) of the Main Astronomical Observatory (Kyiv, Ukraine). Some of the cometary photos were obtained with
two wide-band filter combinations. One of these combinations isolates C2 emission, another — the nearby dust continuum. The images were digitized by means of AMDPH-XY machine and then calibrated
following the standard procedure. After subtraction of the dust continuum the distribution of surface brightness in the C2 emission coma of comet Hale-Bopp was studied. We found an asymmetric brightness distribution both pre- and post-perihelion.
On 21.77 April 1997 a secondary brightness peak is found at the distance of 1.03 × 105 km from the nucleus. It is possible that this peak is related to the extended source of the C2 molecules.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
82.
83.
Evaporation over a Heterogeneous Land Surface: EVA_GRIPS and the LITFASS-2003 Experiment—An Overview
The Evaporation at Grid/Pixel Scale (EVA_GRIPS) project was realised in order to determine the area-averaged evaporation over a heterogeneous land surface at the scale of a grid box of a regional numerical weather prediction or climate model, and at the scale of a pixel of a satellite image. EVA_GRIPS combined surface-based and airborne measurements, satellite data analysis, and numerical modelling activities. A mesoscale field experiment, LITFASS-2003, was carried out in the heterogeneous landscape around the Meteorological Observatory Lindenberg (MOL) of the German Meteorological Service in May and June, 2003. The experiment was embedded in the comprehensive, operational measurement program of the MOL. Experimental determination of surface fluxes on a variety of spatial scales was achieved by employing micrometeorological flux stations, scintillometers, a combination of ground-based remote sensing instruments, and the Helipod, a turbulence probe carried by a helicopter. Surface energy fluxes were also derived from satellite data. Modelling work included the use of different Soil–Vegetation–Atmosphere Transfer schemes, a large-eddy simulation model and three mesoscale atmospheric models. The paper gives an overview on the background of EVA_GRIPS, and on the measurements and meteorological conditions during LITFASS-2003. A few general results are discussed. 相似文献
84.
Gil Penha-Lopes Erik Kristensen Perrine Mangion José Paula 《Marine pollution bulletin》2010,60(4):560-572
Benthic metabolism (measured as CO2 production) and carbon oxidation pathways were evaluated in 4 mangrove mesocosms subjected daily to seawater or 60% sewage in the absence or presence of mangrove trees and biogenic structures (pneumatophores and crab burrows). Total CO2 emission from darkened sediments devoid of biogenic structures at pristine conditions was comparable during inundation (immersion) and air exposure (emersion), although increased 2-7 times in sewage contaminated mesocosms. Biogenic structures increased low tide carbon gas emissions at contaminated (30%) and particularly pristine conditions (60%). When sewage was loaded into the mesocosms under unvegetated and planted conditions, iron reduction was substituted by sulfate reduction and contribution of aerobic respiration to total metabolism remained above 50%. Our results clearly show impacts of sewage on the partitioning of electron acceptors in mangrove sediment and confirm the importance of biogenic structures for biogeochemical functioning but also on greenhouse gases emission. 相似文献
85.
A. Bechtel R. Gratzer W. Püttmann S. Oszczepalski 《International Journal of Earth Sciences》2000,89(1):72-89
max vs the present depth of the Kupferschiefer, soluble organic matter (SOM) yields, and relative proportions of saturated and
aromatic hydrocarbons of the SOM provide evidence for an oxidative alteration of organic matter in highly mineralized Kupferschiefer
samples near the Rote F?ule zones. This is confirmed by differences in the composition of the saturated and aromatic hydrocarbon
fractions of the soluble organic matter: Saturated hydrocarbons from Rote F?ule samples are dominated by short-chain n-alkanes
and higher abundances of pristane and phytane relative to heptadecane (n-C17) and octadecane (n-C18), respectively, compared
with samples more distant to the Rote F?ule zone. Compositional changes of the aromatic hydrocarbon fractions with decreasing
distance to that zone are characterized by the occurrence of polycyclic aromatic hydrocarbons and elevated ratios of phenanthrene
to methylphenanthrenes that are attributed to demethylation reactions and resulted in a decrease of the methylphenanthrene
index (MPI 1). Kupferschiefer samples from the barren zone of the Polish Basin do not show these alteration patterns. The
observed variations in organic matter composition with burial depth are consistent with changes due to increasing thermal
maturation. Maturity assessment is achieved from MPI 1 and the methyldibenzothiophene ratio (MDR). From the relationship between
the maturity of organic matter in terms of vitrinite reflectance values and depth of the Kupferschiefer strata, a continuous
increase in reflectance of vitrinite is obtained within the Polish Basin. The alteration pattern of organic matter related
to base metal mineralization of the Kupferschiefer corresponds to changes in the isotopic composition of organic carbon and
calcite. Kerogen within, or close to, Rote F?ule zone is enriched in 13C caused by the preferential release of isotopically light organic compounds through progressive degradation of organic matter.
The opposite tendency towards lower δ
13C and δ
18O values of calcite provides evidence for isotopic exchange between carbonate and the oxidizing, ore-bearing solutions and
for organic matter remineralization. In contrast, organic matter and calcite from the Kupferschiefer do not show regular trends
in δ
13C with increasing thermal maturation.
Received: 25 June 1999 / Accepted: 1 December 1999 相似文献
86.
James C. Hower Jennifer M.K. O'Keefe Kevin R. Henke Amirhossein Bagherieh 《International Journal of Coal Geology》2011,88(4):227
Coal fires in natural outcrops, in abandoned and active coal mines, and in coal and coal-refuse piles are responsible for the uncontrolled emissions of gases, including CO, CO2, H2S, hydrocarbons, and volatile aromatics. Typically, measurements of gases at a mine vent are made over a short time interval, perhaps no more than 10 min, including the time for replicate measurements. Such timing provides little information on longer-term variations in emissions, although comparisons of seasonal measurements suggest such changes do occur. To address this problem, we placed temperature and CO data loggers in coal fire vents to collect time series measurements for a period of up to three weeks. For one experiment, 11 days of data at one-minute intervals indicated that the CO emissions were generally in the 400–550 ppmv range. However near daily depressions in CO concentrations occurred and in some cases fell below 50 ppmv; followed by an increase to ~ 700–800 ppmv; in turn followed by a return to the ambient conditions. Data for a separate 21-day collection period in a different vent of the same fire exhibited similar trends, albeit at a higher CO concentration. The drop in CO concentration may be associated with a meteorologically-driven inhalation cycle of the fire, whereby air diluted the combustion generated CO. We propose this was followed by an increase in the intensity of the fire due to increased O2 from the inhaled air, producing increased CO concentrations, before settling back to the ambient conditions. 相似文献
87.
Although recent studies have recognized peatlands as a sink for atmospheric CO2, little is known about the role of Siberian peatlands in the global carbon cycle. We have estimated the Holocene peat and carbon accumulation rate in the peatlands of the southern taiga and subtaiga zones of western Siberia. We explain the accumulation rates by calculating the average peat accumulation rate and the long-term apparent rate of carbon accumulation (LORCA) and by using the model of Clymo (1984, Philosophical Transactions of the Royal Society of London Series B 303, 605-654). At three key areas in the southern taiga and subtaiga zones we studied eight sites, at which the dry bulk density, ash content, and carbon content were measured every 10 cm. Age was established by radiocarbon dating. The average peat accumulation rate at the eight sites varied from 0.35 ± 0.03 to 1.13 ± 0.02 mm yr−1 and the LORCA values of bogs and fens varied from 19.0 ± 1.1 to 69.0 ± 4.4 g C m−2 yr−1. The accumulation rates had different trends especially during the early Holocene, caused by variations in vegetation succession resulting in differences in peat and carbon accumulation rates. The indirect effects of climate change through local hydrology appeared to be more important than direct influences of changes in precipitation and temperature. River valley fens were more drained during wetter periods as a result of deeper river incision, while bogs became wetter. From our dry bulk density results and our age-depth profiles we conclude that compaction is negligible and decay was not a relevant factor for undrained peatlands. These results contribute to our understanding of the influence of peatlands on the global carbon cycle and their potential impact on global change. 相似文献
88.
Luiz Carlos Ruiz Pessenda Adauto de Souza Ribeiro Ramon Aravena José Albertino Bendassolli 《Quaternary Research》2004,62(2):183-193
The study place is in the Barreirinhas region, Maranhão State, northeastern Brazil. A vegetation transect of 78 km was studied among four vegetation types: Restinga (coastal vegetation), Cerrado (woody savanna), Cerradão (dense woody savanna), and Forest, as well as three forested sites around Lagoa do Caçó, located approximately 10 km of the transect. Soil profiles in this transect were sampled for δ13C analysis, as well as buried charcoal fragments were used for 14C dating. The data interpretation indicated that approximately between 15,000 and ∼9000 14C yr B.P., arboreal vegetation prevailed in the whole transect, probably due to the presence of a humid climate. Approximately between ∼9000 and 4000-3000 14C yr B.P., there was the expansion of the savanna, probably related to the presence of drier climate. From ∼4000-3000 14C yr B.P. to the present, the results indicated an increase in the arboreal density in the area, due to the return to a more humid and probably similar climate to the present. The presence of buried charcoal fragments in several soil depths suggested the occurrence of palaeofires during the Holocene. The vegetation dynamic inferred in this study for northeastern Brazil is in agreement with the results obtained in areas of Amazon region, based on pollen analysis of lake sediments and carbon isotope analysis of soil organic matter (SOM), implying than similar climatic conditions have affected these areas during the late Pleistocene until the present. 相似文献
89.
在系统分析柴达木盆地西部各油田40余个原油样品碳同位素和饱和烃、芳烃组成的基础上,全面剖析了该地区第三系湖相原油的地球化学特征.研究结果表明,这些原油具有特殊的碳同位素组成和异常的生物标志物分布.其全油碳同位素偏重(-26‰~-24‰);正构烷烃系列单体烃碳同位素分布曲线呈水平状,表现出类同于海相有机质的碳同位素组成特征.它们的生物标志物中正烷烃系列兼具奇碳和偶碳优势双重碳数分布模式;呈强植烷优势,Pr/Ph值大多<0.6;伽玛蜡烷普遍异常丰富,C35藿烷含量高,表征高盐、厌氧的咸水湖相沉积环境性质.芳烃组份以萘、菲系列为主,而二苯并噻吩等含硫有机化合物相对含量较低,反映该地区咸水湖相原油源岩沉积相的特殊性.柴西各油田原油地球化学参数在区域上呈规律性变化趋势,与其源岩沉积相的时空变迁相一致. 相似文献
90.
Jessica C. North Russell D. Frew Robert Van Hale 《Journal of Geochemical Exploration》2006,88(1-3):49
Bacterially mediated methanogenesis in municipal solid waste landfills has been shown to cause an enrichment of carbon stable isotope ratios of dissolved inorganic carbon and hydrogen stable isotope ratios of water in landfill leachate. In the present study, we investigate the universality of this enrichment in leachate obtained from four diverse landfill sites in New Zealand. At each site, surface water samples upstream and downstream of landfills were analysed to examine the applicability of stable isotope ratios as a tool for monitoring leachate contamination in landfill-associated streams. The design of leachate collection systems, operational history, and landfill location appeared to strongly influence leachate isotopic values and the effectiveness of isotope ratios as an environmental monitoring tool for surface water. 相似文献