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991.
992.
The influence of air mass source on the seasonal isotopic composition of precipitation, eastern USA 总被引:5,自引:0,他引:5
As part of the AIRMoN program, daily precipitation samples have been collected since the early 1990s throughout the eastern and central United States. Using precipitation stable isotope (δ18O and δD) and HYSPLIT back trajectory analysis of 591 samples collected by the AIRMoN program from Florida, Illinois, Pennsylvania, Tennessee, Vermont, and West Virginia, amount weighted seasonal average isotopic compositions were calculated for precipitation from Continental, Pacific, Gulf of Mexico, Arctic, North Atlantic, and Mid Atlantic sources. Our results suggest that these sources are isotopically distinct and variable at and among most sites during most seasons. However, in many instances, the isotopic differences of the sources require dramatic changes in precipitation amounts from these sources to modify the seasonal average isotopic composition at a particular site. The relative importance of each source type to the seasonal average isotopic composition is highly variable among and within sites. The largest differences in the isotopic compositions of different sources are in winter and spring precipitation from the high latitude sites. At the Vermont location, the seasonal average isotopic composition is potentially quite sensitive to the relative amounts of precipitation from Arctic and Gulf of Mexico sources. 相似文献
993.
Udo Harms 《Chemie der Erde / Geochemistry》2009,69(3):279-285
The mineral chemistry of two nickeloan pyrite samples from the Prangenhaus quarry, Wülfrath, is presented. Sample PRH 5: main zone=4.32-9.7 wt% Ni (0.089-0.202 atoms per formula unit (a.p.f.u.)), 0.21-1.31 wt% Co (0.004-0.027 a.p.f.u.); rim zone=11.76-22.38 wt% Ni (0.244-0.466 a.p.f.u. ), 1.35-8.16 wt% Co (0.028-0.168 a.p.f.u.). Sample PRH 6: 6.75-11.33 wt% Ni (0.139-0.234 a.p.f.u.), 0.86-2.46 wt% Co (0.018-0.051 a.p.f.u.). Estimated Fe/Ni and Fe/Co ratios of the hydrothermal fluids forming the nickeloan pyrite point to very local fluctuations in the chemistry of the ore forming fluids in the Prangenhaus quarry. The presence of nickeloan pyrite indicates formation temperatures below 137 °C, which is in accordance with earlier findings of formation temperatures for sphalerite (60-130 °C) in the Niederberg area. 相似文献
994.
995.
Zn在生物磷灰石中的晶体化学行为不同于在地质体中,传统的磷灰石类质同像替代理论对生物磷灰石中的Ca位替换并不完全适用。为了解释生物磷灰石中Zn的出现,本文对已知的生物磷灰石中Zn的存在情况、Zn对Ca的替代机制以及Zn替代对生物磷灰石的影响等内容进行了综述,并就Zn在生物磷灰石中的晶体化学研究对人体肿瘤诊疗的启示作用进行了简单的讨论。理论和实验均表明Zn可以进入生物磷灰石晶格,占据有Ca缺陷的磷灰石晶格中的Ca2位空缺,使局部结构整体收缩。Zn的掺入对生物磷灰石的晶粒尺寸、结晶度、晶胞参数等均会产生较大的影响。当Zn被固定在人体肿瘤伴有的病理性钙化晶格中时,其可能对周围组织及体液中的Zn含量产生影响,进而影响人体内Zn的新陈代谢。 相似文献
996.
997.
《Chemie der Erde / Geochemistry》2017,77(4):587-595
The Shergol ophiolitic peridotites along ISZ, Ladakh Himalaya are serpentinized to various degrees and are harzburgite in composition. Electron microprobe analyses of spinels from Shergol Serpentinized Peridotites (SSPs) were carried out in order to evaluate their compositional variation with alteration. Chemical discontinuity was observed from core to rim in analyzed spinel grains with Cr-rich cores rimmed by Cr-poor compositions. From unaltered cores to rims it was observed that Cr3+# and Fe3+# increases while Mg2+# decreases due to Mg2+ − Fe2+ and Al3+ (Cr3+) − Fe3+ exchange with surrounding silicates during alteration. These peridotites contain Al-rich spinels forming subhedral to anhedral grains with lobate and corroded grain boundaries; altered to ferritchromite or magnetite along cracks and boundaries by later metamorphism episode. The unaltered Cr-spinel cores are identified as Al-rich and are characterized by lower values of Cr3+# (0.34–0.40), high Al3+# (0.58–0.68) and Mg2+# (0.52–0.70). Mineral chemistry of these Al-rich Cr-spinels suggest that host peridotites have an affinity to abyssal and alpine-type peridotites. High TiO2 concentration of magmatic Cr-spinel cores are in agreement with MORB melt-residual peridotite interaction. Presence of unaltered magmatic Cr-spinel cores suggest that they do not have re-equilibrated completely with metamorphic spinel rims and surrounding silicates. Cr-spinel core compositions of SSPs suggest an ophiolitic origin derivation by low degrees of melting of a less-moderate depleted peridotite in a mid-ocean ridge tectonic setting. Based on textural and chemical observations the alteration conditions of studied spinel-group minerals match those of transitional greenschist-amphibolite facies metamorphism consistent with estimated metamorphic equilibration temperature of ∼ 500–600 °C. 相似文献
998.
An integrated study involving sedimentology, mineral chemistry and spectroscopy highlights a distinctive compositional evolution of Cretaceous glauconite within the Ukra Hill Member. Glauconite occurs at the top part of transgressive systems tract deposits built on a marine shelf. The concentration of glauconite steadily increases towards the maximum flooding surface, maximizing around 50%, and sharply falls at the onset of progradation. Unlike most Phanerozoic examples, Ukra glauconite forms by the variable degree of replacement of quartz, feldspar and mica grains. XRD, FEG-SEM and spectroscopy of glauconite pellets indicate an ‘evolved’ stage of maturation. Mossbauer spectroscopy reflects a minor substitution of Al3+-Fe3+ (total) in tetrahedral sites and significant substitution of the same in octahedral sites. A consistently high value of K2O as well as Fe2O3 contradicts the two popular theories, ‘layer lattice’ and ‘verdissement’, and support replacement origin of glauconite in a high aSi+ and high aK+ pore water environment. Incipiently formed glauconite records a marginal increase in K2O content accompanied by release of Al2O3 and SiO2 to form evolved glauconite pellets; those forming within quartz grains involve an addition of Fe2O3 (total) content during maturation. The minimal increase in K2O content of incipiently formed glauconite, best exhibited by those formed within quartz grains is possibly related to stratigraphic condensation. Compositional evolution like this is exhibited by Precambrian glauconites involving abiotic substrates, but is unusual for the Phanerozoic. Original K2O and Fe2O3 (total) content of glauconites is reduced around peripheries and fractures during diagenesis, adding to compositional variability. 相似文献
999.
Lightning can threaten human and equipment safety. An indicator of sever convective weather, it plays an important role in atmospheric chemistry. The intensive studies have advanced the lightning forecast in the mesoscale weather models and its application in global climate models. There are three methods to forecast lightning by using numerical weather models: Numerical diagnosis prediction based on synoptic background filed statistical relations; Flash rate parameterization developed with the relationship between dynamical, microphysical and electrification processes, and The numerical weather model coupled with the explicit electrification and lightning parameterization schemes. In this paper, the research progress in lightning forecast with three above-mentioned methods were reviewed, and the future research issues on lightning forecast were also discussed. 相似文献
1000.
A data analysis method is proposed to cluster and explore spatio-temporal characteristics of the 22 years of precipitation data (1982–2003) for Taiwan. The wavelet transform self-organizing map (WTSOM) framework combines the wavelet transform (WT) and a self-organizing map (SOM) neural network. WT is used to extract dynamic and multiscale features of the non-stationary precipitation time-series, and SOM is applied to objectively identify spatially homogeneous clusters on the high-dimensional wavelet-transformed feature space. Haar and Morlet wavelets are applied in the data preprocessing stage to preserve the desired characteristics of the precipitation data. A two-level SOM neural network is applied to identify clusters in the wavelet space in the clustering stage. The performance of clustering is evaluated using silhouette coefficients. The results indicate that singularities or sharp transitions are more significant than changes in the periodicity or data structure in the spatial–temporal precipitation data. The WTSOM results show that six clusters are optimal for both Haar and Morlet wavelet functions, but their corresponding geographic locations are different. The geographic locations of clusters based on the Haar wavelet, which captures the occurrence of extreme hydrological events, appear in blocks while those classified by the Morlet wavelet, which indicates periodicity changes and describes fine structures, appear in strips that cross the island of Taiwan. Principal component analysis is applied to the precipitation data of each cluster. The first principal components explain 62–90% of the total variation of data. Characteristics of precipitation data for each cluster are explored using scalogram analysis. The results show that both extreme hydrological events and periodicity changes appear in the spatial and temporal precipitation data but with different characteristics for each cluster. Recognizing homogeneous hydrologic regions and identifying the associated precipitation characteristics improves the efficiency of water resources management in adapting to climate change, preventing the degradation of the water environment, and reducing the impact of climate-induced disasters. Measures for countering the stress of precipitation variation for water resources management are provided. 相似文献