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51.
K. Sreelash Rajat Kumar Sharma J. A. Gayathri B. Upendra K. Maya D. Padmalal 《Journal of the Geological Society of India》2018,92(5):548-554
The Western Ghats plays a pivotal role in determining the hydrological and hydroclimatic regime of Peninsular India. The mountainous catchments of the Ghats are the primary contributors of flow in the rivers that sustains the life and agricultural productivity in the area. Although many studies have been conducted in the past decades to understand long term trends in the meteorological and hydrological variables of major river basins, not much attention have been made to unfold the relationship existing among rainfall and river hydrology of natural drainages on either side of the Western Ghats which host one of the unique biodiversity hotspots across the world. Therefore, an attempt has been made in this paper to examine the short term (last three decades) changes in the rainfall pattern and its influence on the hydrological characteristics of some of the important rivers draining the southern Western Ghats as a case study. The short term, annual and seasonal trends in the rainfall, and its variability and discharge were analyzed using Mann-Kendall test and Sen’s estimator of slope. The study showed a decreasing trend in rainfall in the southwest monsoon while a reverse trend is noticed in northeast monsoon. Correspondingly, the discharge of the west and east flowing rivers also showed a declining trend in the southwest monsoon season. The runoff coefficient also followed the trends in the discharge. The runoff coefficient of the Periyar river showed a decreasing trend, whereas the Cauvery river exhibited an increasing trend. A high-resolution analysis of rainfall data revealed that the number of moderate rainfall events showed a decreasing trend throughout the southern Western Ghats, whereas the high intensity rainfall events showed an opposite trend. The decline in groundwater level in the areas which recorded an increase in high intensity rainfall events and decrease in moderate rainfall events showed that the groundwater recharge process is significantly affected by changes in the rainfall pattern of the area. 相似文献
52.
Molecular characterization of dissolved organic matter associated with the Greenland ice sheet 总被引：1，自引：0，他引：1
Maya P. Bhatia Krista Longnecker Elizabeth B. Kujawinski 《Geochimica et cosmochimica acta》2010,74(13):3768-9950
Subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial-interglacial timescales. The likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores. We examined the composition of carbon pools associated with different regions of the Greenland ice sheet (subglacial, supraglacial, proglacial) in order to elucidate the type of dissolved organic matter (DOM) present in the subglacial discharge over a melt season. Electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes. Specifically, a larger proportion of protein-like compounds were observed in the supraglacial samples and in the early melt season (spring) subglacial discharge. In contrast, the late melt season (summer) subglacial discharge contained a greater fraction of lignin-like and other material presumably derived from underlying vegetation and soil. These results suggest (1) that the majority of supraglacial DOM originates from autochthonous microbial processes on the ice sheet surface, (2) that the subglacial DOM contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism, and (3) that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season. These conclusions are consistent with the hypothesis that, given sufficient time (e.g., overwinter storage), resident subglacial microbial communities may oxidize terrestrial material beneath the Greenland ice sheet. 相似文献
53.
Maya García-Comas Manuel López-Puertas Bianca M. Dinelli Alberto Adriani Angioletta Coradini 《Icarus》2011,214(2):571-583
After molecular nitrogen, methane is the most abundant species in Titan’s atmosphere and plays a major role in its energy budget and its chemistry. Methane has strong bands at 3.3 μm emitting mainly at daytime after absorption of solar radiation. This emission is strongly affected by non-local thermodynamic equilibrium (non-LTE) in Titan’s upper atmosphere and, hence, an accurate modeling of the non-LTE populations of the emitting vibrational levels is necessary for its analysis. We present a sophisticated and extensive non-LTE model which considers 22 CH4 levels and takes into account all known excitation mechanisms in which they take part. Solar absorption is the major excitation process controlling the population of the v3-quanta levels above 1000 km whereas the distribution of the vibrational energy within levels of similar energy through collisions with N2 is also of importance below that altitude. CH4-CH4 vibrational exchange of v4-quanta affects their population below 500 km. We found that the ν3 → ground band dominates Titan’s 3.3 μm daytime limb radiance above 750 km whereas the ν3 + ν4 → ν4 band does below that altitude and down to 300 km. The ν3 + ν2 → ν2, the 2ν3 → ν3, and the 13CH4ν3 → ground bands each contribute from 5% to 8% at regions below 800 km. The ν3 + 2ν4 → 2ν4and ν2 + ν3 + ν4 → ν2 + ν4 bands each contribute from 2% to 5% below 650 km. Contributions from other CH4 bands are negligible. We have used the non-LTE model to retrieve the CH4 abundance from 500 to 1100 km in the southern hemisphere from Cassini-VIMS daytime measurements near 3.3 μm. Our retrievals show good agreement with previous measurements and model results, supporting a weak deviation from well mixed values from the lower atmosphere up to 1000 km. 相似文献
54.
Computational Fluid Dynamical Modelling of Concentration Fluctuations in an Idealized Urban Area 总被引：2，自引：2，他引：0
Turbulent mixing induces variability in concentration that is important in many applications, such as reactive plumes, risk
assessments or odour impact analyses (when the effects can have time scales on the order of a second). In urban canopies,
the variability may be modified by the presence of buildings. Our purpose is to study concentration fluctuation variance in
built-up areas using an Eulerian approach. We performed numerical simulations with the computational fluid dynamics model
Mercure_Saturne, which is a three-dimensional model adapted to atmospheric flow and pollutant dispersion. We use a k − ϵ turbulence closure and predict the concentration variance with a transport equation model. The model performance is evaluated
with the near-full scale experiment MUST (Mock Urban Setting Test), a field experiment conducted in Utah’s West Desert Test
Center. The modelled root-mean-square of the concentration fluctuations is compared to measurements for 20 of the MUST trials.
The model shows good agreement with the measurements, with the fraction of predictions within a factor of two of observations
of 60.1%, with better results for horizontal lines of detectors than for the detectors on vertical masts (with fractions of
predictions within a factor of two of observations of respectively 66.4% and 52.6%). The influence of different parameters
on the fluctuation variance is also studied and we show the importance of taking into account the stability of the stratification
when modelling the turbulent kinetic energy. 相似文献
55.
Maya G. Kopylova John J. Gurney Leon R. M. Daniels 《Contributions to Mineralogy and Petrology》1997,129(4):366-384
More than 99% of mineral inclusions in diamonds from the River Ranch pipe in the Late Archean Limpopo Mobile Belt (Zimbabwe),
are phases of harzburgitic paragenesis, namely olivine (Fo92–93), orthopyroxene (Mg# = 93), G10 garnets and chromites. The diamond inclusion (DI) chemistry demonstrates a limited overlap
with River Ranch kimberlite macrocrysts: the DI garnets are more Ca-undersaturated, and DI spinel and garnet are more Mg-rich.
Most River Ranch diamond inclusions were equilibrated at T = 1080–1320 °C, P = 47–61 kbar, and f
O2 between IW and WM buffers. The P/T profile beneath the Limpopo Mobile Belt (LMB) is consistent with a paleo-heat flow of 41–42 mW/m2, similar to calculations for Roberts Victor, but hotter than for the Finsch, Kimberley, Koffiefontein and Premier Mines.
This is ascribed to the younger tectonothermal age of the LMB and its proximity to Late Archean oceans. Like diamond inclusions
from all other kimberlites studied, the River Ranch DI have a lithospheric affinity and therefore indicate that an ancient,
chemically depleted, thick (at least 200 km) mantle root existed beneath the Limpopo Mobile Belt 530–540 Ma ago. The mantle
root might have developed beneath the continental Central Zone of the LMB as early as the Archean, and could be alien to the
overthrust allochthonous sheet of the Limpopo Belt. Oxygen fugacity estimates for diamond inclusions at River Ranch are similar
to other diamondiferous harzburgites beneath the Kaapvaal craton, indicating that the Kaapvaal mantle as a whole was well
buffered and homogeneous with respect to f
O2 at the time of peridotitic diamond crystallization.
Received: 11 January 1995 / Accepted: 10 June 1997 相似文献
56.
In order to estimate the impacts of buildings on air pollution dispersion, numerical simulations are performed over an idealized
urban area, modelled as regular rows of large rectangular obstacles. The simulations are evaluated with the results of the
Mock Urban Setting Test (MUST), which is a near full-scale experiment conducted in Utah’s West Desert area: it consists of
releases of a neutral gas in a field of regularly spaced shipping containers. The numerical simulations are performed with
the model Mercure_Saturne, which is a three-dimensional computational fluid dynamics code adapted to atmospheric flow and dispersion simulations. It
resolves complex geometries and uses, in this study, a k–∈ closure for the turbulence model. Sensitivity studies focus on how to prescribe the inflow conditions for turbulent kinetic
energy. Furthermore, different sets of coefficients available in the literature for the k–∈ closure model are tested. Twenty MUST trials with different meteorological conditions are simulated and detailed analyses
are performed for both the dynamical variables and average concentration. Our results show overall good agreement according
to statistical comparison parameters, with a fraction of predictions for average concentration within a factor of two of observations
of 67.1%. The set of simulations offers several inflow wind directions and allows us to emphasize the impact of elongated
buildings, which create a deflection of the plume centerline relative to the upstream wind direction. 相似文献
57.
Corals are animals living in shallow seas (where they may form coral reefs) or in the deep sea. Because they fossilize well, these stones inform us in detail about the geological past; not only about the history of the Earth as a whole (rotation, tectonics, sea-level changes), but also about past local environmental conditions in the sea. Joint research of marine biology and marine geology can therefore solve many questions about our changing world, and can be used to discover what factors cause deterioration of living coral reefs. 相似文献
58.
Andrea De Stefano Nathalie Lefebvre Maya Kopylova 《Contributions to Mineralogy and Petrology》2006,151(2):158-173
A suite of 80 macrodiamonds recovered from volcaniclastic breccia of Wawa (southern Ontario) was characterized on the basis
of morphology, nitrogen content and aggregation, cathodoluminescence (CL), and mineral inclusions. The host calc-alkaline
lamprophyric breccias were emplaced at 2.68–2.74 Ga, contemporaneously with voluminous bimodal volcanism of the Michipicoten
greenstone belt. The studied suite of diamonds differs from the vast majority of diamond suites found worldwide. First, the
suite is hosted by calc-alkaline lamprophyric volcanics rather than by kimberlite or lamproite. Second, the host volcanic
rock is amongst the oldest known diamondiferous rocks on Earth, and has experienced regional metamorphism and deformation.
Finally, most diamonds show yellow-orange-red CL and contain mineral inclusions not in equilibrium with each other or their
host diamond. The majority of the diamonds in the Wawa suite are colorless, weakly resorbed, octahedral single crystals and
aggregates. The diamonds contain 0–740 ppm N and show two modes of N aggregation at 0–30 and 60–95% B-centers suggesting mantle
storage at 1,100–1,170°C. Cathodoluminescence and FTIR spectroscopy shows that emission peaks present in orange CL stones
do not likely result from irradiation or single substitutional N, in contrast to other diamonds with red CL. The diamonds
contain primary inclusions of olivine (Fo92 and Fo89), omphacite, orthopyroxene (En93), pentlandite, albite, and An-rich plagioclase. These peridotitic and eclogitic minerals are commonly found within single
diamonds in a mixed paragenesis which also combines shallow and deep phases. This apparent disequilibrium can be explained
by effective small-scale mixing of subducted oceanic crust and mantle rocks in fast “cold” plumes ascending from the top of
the slabs in convergent margins. Alternatively, the diamonds could have formed in the pre-2.7–2.9 Ga cratonic mantle and experienced
subsequent alteration of syngenetic inclusions related to host magmatism and ensuing metamorphism. Neither orogenic nor cratonic
model of the diamond origin fully explains all of the observed characteristics of the diamonds and their host rocks.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
59.
Spinifex-textured.magnesian(MgO 25 wt.%) komatiites from Mesoarchean Banasandra greenstone belt of the Sargur Group in the Dharwar craton,India were analysed for major and trace elements and~(147,146)Sm-~(143,142)Nd systematics to constrain age,petrogenesis and to understand the evolution of Archean mantle.Major and trace element ratios such as CaO/Al_2O_3.Al_2O_3/TiO_2,Gd/Yb,La/Nb and Nb/Y suggest aluminium undepleted to enriched compositional range for these komatiites.The depth of melting is estimated to be varying from 120 to 240 km and trace-element modelling indicates that the mantle source would have undergone multiple episodes of melting prior to the generation of magmas parental to these komatiites.Ten samples of these komatiites together with the published results of four samples from the same belt yield ~(147)Sm-~(143)Nd isochron age of ca.3.14 Ga with an initial ε_(Nd)(f) value of+3.5.High precision measurements of ~(142)Nd/~(144)Nd ratios were carried out for six komatiite samples along with standards AMES and La Jolla.All results are within uncertainties of the terrestrial samples.The absence of~(142)Nd/~(144)Nd anomaly indicates that the source of these komatiites formed after the extinction of ~(146)Sm,i.e.4.3 Ga ago.In order to evolve to the high ε_(Nd)(t) value of +3.5 by 3.14 Ga the time-integrated ratio of~(147)Sm/~(144)Nd should be 0.2178 at the minimum.This is higher than the ratios estimated,so far,for mantle during that time.These results indicate at least two events of mantle differentiation starting with the chondritic composition of the mantle.The first event occurred very early at ~4.53 Ga to create a global early depleted reservoir with superchondritic Sm/Nd ratio.The source of Isua greenstone rocks with positive ~(142)Nd anomaly was depleted during a second differentiation within the life time of ~(146)Sm,i.e.prior to 4.46 Ga.The source mantle of the Banasandra komatiite was a result of a differentiation event that occurred after the extinction of the ~(146)Sm,i.e.at 4.3 Ga and prior to 3.14 Ga.Banasandra komatiites therefore provide evidence for preservation of heterogeneities generated during mantle differentiation at4.3 Ga. 相似文献