Stable isotopes of water show deep seasonal recharge in northern bogs and fens          下载免费PDF全文

Zeno F. Levy  Donald I. Siegel  Soumitri S. Dasgupta  Paul H. Glaser  Jeffrey M. Welker 《水文研究》2014,28(18):4938-4952

Ground water recharge is assumed to occur primarily at raised bog crests in northern peatlands, which are globally significant terrestrial carbon reservoirs. We synoptically surveyed vertical profiles of peat pore water δ¹⁸O and δ²H from a range of bog and fen landforms across the Glacial Lake Agassiz Peatlands, northern Minnesota. Contrary to our expectations, we find that local‐scale recharge penetrates to not only the basal peat at topographically high bog crests but also transitional Sphagnum lawns and low‐lying fen water tracks. Surface landscape characteristics appear to control the isotopic composition of the deeper pore waters (depths ≥0.5 m), which are partitioned into discrete ranges of δ¹⁸O on the basis of landform type (mean ± standard deviation for bog crests = ?11.9 ± 0.4‰, lawns = ?10.6 ± 0.1‰, fen water tracks = ?8.8 ± 1.0‰). Fen water tracks have a shallow free‐water surface that is seasonally enriched by isotope fractionating evaporation, fingerprinting recharge to underlying pore waters at depths ≥3 m. Isotope mass balance calculations indicate on average 12% of the waters we sampled from the basal peat of the fen water tracks was lost to surface evaporation, which occurred prior to advection and dispersion into the underlying formation. These new data provide direct support for the hypothesis that methane production in deeper peat strata is fuelled by the downward transport of labile carbon substrates from the surface of northern peat basins. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Partial melting of fertile peridotite fluxed by hydrous rhyolitic melt at 2–3 GPa: implications for mantle wedge hybridization by sediment melt and generation of ultrapotassic magmas in convergent margins     

Ananya Mallik  Jared Nelson  Rajdeep Dasgupta 《Contributions to Mineralogy and Petrology》2015,169(5):1-24

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Geometrical mechanism of inverse grading in grain-flow deposits: An experimental revelation     

Prabir Dasgupta  Priyanka Manna 《Earth》2011,104(1-3):186-198

The grain-flow has so far been defined with reference to the distinctive sediment-support mechanism, the dispersive pressure. The role of sediment-support mechanism, however, is required in a multiphase flow to prevent the gravitational settling of the particles through the driving medium during the flow. In a single-phase flow of non-cohesive grains no such secondary mechanism is required to counteract the gravitational pull, the driving force of the flow. So the definition of grain-flow needs a critical revision. This, in turn, involves proper understanding of the grain-flow mechanism, so that the relation between the process and the product can be properly established. The most distinctive feature often demonstrated by a grain-flow deposit is the particle size segregation, which leads to the development of inverse grading. The available explanations for this phenomenon find theoretical constraints. In the present study an attempt was made to understand the mechanism of single-phase non-cohesive granular flow of different flow regime and the particle segregation pattern in the resultant deposit through laboratory simulation. The experimental observations revealed that no sustained granular flow sets in on a slope deviating much from the limiting value of the angle of repose of the granular material. A persistent simple shear flow develops on slopes of this critical value. Each of the grains rolls in response to simple shearing. If the shear stress attains a critical value, theoretically the larger grains can even climb up the adjacent smaller ones towards the down-slope direction. In reality, however, high angle climb is not very common. The larger grains preferably roll over the smaller grains when the common tangent becomes almost horizontal or makes a very low angle with the direction of flow, and by this process gradually reaches the upper surface of the flow causing the development of inverse grading. The upper surface of the resultant deposit remains parallel to the sloping substratum. These properties readily distinguish this variety of granular flow from the other natural flows, and the flow may thus be assigned the distinct status of grain-flow.  相似文献   

Seismic clusters and their characteristics at the Arabian Sea Triple Junction: Supportive evidences for plate margin deformations     

Basab Mukhopadhyay  Manoj Mukhopadhyay  Sujit Dasgupta 《Journal of the Geological Society of India》2011,78(2):131-146

The plate margin features defining the Arabian Sea Triple Junction (ASTJ) are: the Aden Ridge (AR), Sheba Ridge (SR) with their intervening Alula-Fartak Transform (AFT), Carlsberg Ridge (CR) and Owen Fracture Zone (OFZ). Exact nature of ASTJ is presently debated: whether it is RRF (ridge-ridge-fault) or RRR (ridge-ridge-ridge) type. A revised seismicity map for ASTJ is given here using data for a period little more than a century. “Point density spatial statistical criterion” is applied to short-listed 742 earthquakes (mb ≥ 4.3), 10 numbers of spatio-temporal seismic clusters are identified for ASTJ and its arms. Relocated hypocentres help better constraining the cluster identification wherever such data exist. Seismic clusters actually diagnose the most intense zones of strain accumulation due to far field as well as the local stress operating at ASTJ. An earthquake swarm emanating from a prominent seismic cluster below SR provides an opportunity to investigate the pore pressure diffusion process (due to the active source) by means of “r-t plot”. Stress and faulting pattern in the active zones are deduced from 43 CMT solutions. While normal or lateral faulting is characteristic for these arms, an anomalous thrust earthquake occurs in the triangular ‘Wheatley Deep’ deformation zone proximal to ASTJ. The latter appears to have formed due to a shift of the deformational front from OFZ towards a transform that offsets SR. Though ASTJ is still in the process of evolution, available data favour that this RRF triple junction may eventually be converted to a more stable RRR type.  相似文献   

On conformity of the EEJ based ionospheric model to the fountain effect and resulting improvements     

Rajat Acharya  Bijoy Roy  M.R. Sivaraman  Ashish Dasgupta 《Journal of Atmospheric and Solar》2011,73(7-8):779-784

The total electron content (TEC) of the equatorial ionosphere is controlled by photochemical processes as well as the transport of the ionospheric plasma near the magnetic equator. The transport phenomenon is initiated by the vertical drift driven by the eastward electric field, which also drives the Equatorial Electrojet. The empirical relation between the Equatorial Electrojet and the anomaly component of the equatorial TEC has already been established. Taking this relation as a reference, a simplified physical model of the anomaly component of equatorial TEC is obtained as a function of Equatorial Electrojet. Influence of other factors like the solar incidence angle and the solar flux are also considered here and the extent of their influence are also investigated. This has been done using TEC data obtained from dual frequency GPS receivers during the low solar activity period of 2005. The derived model is based on the physics of the underlying fountain effect and matches with the observed empirical relation to a fair extent. Obtained results are found to corroborate with previous findings and these physical model values are found to have improved correlation with the observed data than the reference empirical relation. This establishes the conformity between the EEJ based ionospheric model and the physical phenomenon of the fountain effect.  相似文献   

Evolution of high-Mg–Al granulites from Sunkarametta, Eastern Ghats, India: evidence for a lower crustal heating–cooling trajectory     

Bose    Fukuoka    Sengupta  & Dasgupta 《Journal of Metamorphic Geology》2000,18(3):223-240.

A suite of high-Mg–Al granulites from Sunkarametta, Eastern Ghats Belt, India, shows contrasting prograde assemblages of extremely aluminous orthopyroxene+cordierite+sapphirine and similarly aluminous orthopyroxene+Ti-rich spinel in closely associated domains. Textural and compositional characteristics indicate that both were derived from prograde dehydration–melting of biotite–plagioclase–quartz-bearing protoliths. The former assemblage was stabilized at relatively more magnesian bulk composition. Geothermobarometric data and petrogenetic grid considerations place 'peak' metamorphic conditions at c. 950 °C and 9 kbar. Subsequent to peak metamorphism, the rocks cooled to c . 700–750 °C, with slight lowering of pressure, and the retrograde reactions also involved melt–solid interaction. The inferred P – T  trajectory is one of heating–cooling at lower crustal (25–30 km) depths.  相似文献   

Advances in understanding of the mechanism for generation of earthquake thermal precursors detected by satellites     

Arun K. Saraf  Vineeta Rawat  Swapnamita Choudhury  Sudipta Dasgupta  Josodhir Das 《International Journal of Applied Earth Observation and Geoinformation》2009

Stresses building up during an earthquake preparation phase also manifest themselves in the form of a so called increased land surface temperature (LST) leading to a thermal precursor prior to the earthquake event. This phenomenon has now been validated by our observations of short-term thermal anomalies detected by infrared satellite sensors for several recent past earthquakes around the world. The rise in infrared radiance temperature was seen to vary between 5 and 12 °C for different earthquakes. We discuss in this paper different explanations for the generation of such anomalies that have been offered. Emission of gases due to the opening and closure of micropores upon induced stresses and also the participation of ground water have been propounded as a possible cause for generation of thermal anomalies. Seismo-ionosphere coupling, by which gases like radon move to the earth–atmosphere interface and cause air ionization thus bringing about a change in air temperature, relative humidity, etc., has been put forth by some workers. A mechanism of low frequency electromagnetic emission was tested and experimented by scientists with rock masses in stressed conditions as those that exist at tectonic locations. The workers proposed the positive hole pair theory, which received support from several scientific groups. Positive holes (sites of electron deficiency) are activated in stressed rocks from pre-existing yet dormant positive hole pairs (PHPs) and their recombination at rock–air interface leads to a LST rise. A combination of remote sensing detection of rock mechanics behavior with a perception of chemistry and geophysics has been applied to propose the remote sensing rock mechanics theory. Remote sensing detections of such anomalies confirm so far proposed lab theories for such a hotly debated field as earthquake precursor study by providing unbiased observations with consistency in time and space distribution.  相似文献   

Solar Arcades as Possible Minimum Dissipative Relaxed States     

R. Bhattacharyya  M. S. Janaki  B. Dasgupta  G. P. Zank 《Solar physics》2007,240(1):63-76

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Analysing the spatio-temporal evolution of an active debris slide in Eastern Himalaya,India   总被引：1，自引：0，他引：1  

Saibal Ghosh  Anjan Bora  Sudipta Nath  Ashok Kumar 《Journal of the Geological Society of India》2014,84(3):292-302

Landslide is one of the prominent geohazards in the Himalayas where loss of lives and property are common. Owing to the complicated geomorphic and tectono-stratigraphic setting of this active Fold-thrust belt (FTB), landsliding of all possible types and spatial scales observed exhibit conspicuous spatio-temporal signatures and evolution. This evolution of landslides is commonly studied by regional assessment and by examining the multi-temporal landslide inventories of a particular area. The success of creating such multi-temporal landslide inventory depends on (i) the availability of relevant past source data (e.g., images, post event maps, air photos etc.) of suitable resolution, scale and quality, (ii) time of generation of source data with respect to the time of landsliding event, (iii) skill of the investigators in interpreting the old images, air photos etc. However, this method is of restricted use in studying the spatio-temporal evolution of a single landslide which is perennially active in the Himalayan terrain, where rapid changes in land use and land cover patterns readily obliterate the signatures of past landsliding. Moreover because of scale constraints, subtle and frequent changes in the spatial dimensions of these individual landslides, and their temporal activity become difficult to identify in such regional assessment carried out over a larger area. In this study therefore, a different approach is adopted whereby the spatio-temporal activity and style of Lanta Khola landslide, a perennially active and large (0.25 km²) debris flow in the Eastern Himalayas, has been studied in detail through detailed scale (1:1000) site-specific geological mapping in phases during the last 28 years (1983–2011). Such site-specific geological observations coupled with numerical slope stability analysis utilising the limit equilibrium method facilitate in detailed understanding of the temporal and spatial evolution and inherent mechanism of this perennial landslide.  相似文献   

Nonlinear kinetic analysis of phenol adsorption onto peat soil   总被引：1，自引：0，他引：1  

Supriya Pal  Somnath Mukherjee  Sudipta Ghosh 《Environmental Earth Sciences》2014,71(4):1593-1603

Phenolic compounds are considered as a serious organic pollutant containing in many industrial effluents particularly vulnerable when the plant discharge is disposed on land. In the present study, the phenol removal potential of peat soil as adsorption media was investigated as the adsorption process are gaining popular for polishing treatment of toxic materials in industrial wastewater. Batch experiments were performed in the laboratory to determine the adsorption isotherms of initial concentrations for 5, 8, 10, 15, and 20 mg/L and predetermined quantity of peat soil with size ranges between 425 and 200 μm poured into different containers. The effects of various parameters like initial phenol concentration, adsorbent quantity, pH, and contact time were also investigated. From experimental results, it was found that 42 % of phenol removal took place with optimized initial phenol concentration of 10 mg/L, adsorbent dose of 200 g/L, solution pH 6.0 for the equilibrium contact time of 6 h. The result exhibits that pseudo-first-order (R ² = 0.99) and Langmuir isotherm models are fitted reasonably (R ² = 0.91). Adams–Bohart, Thomas, Yoon–Nelson, and Wolborska models were also investigated to the column experimental data of different bed heights to predict the breakthrough curves and to determine the kinetic coefficient of the models using nonlinear regression analysis. It was found that the Thomas model is the best fitted model to predict the experimental breakthrough curves with the highest coefficient of determination, R ² = 0.99 and lowest root mean square error and mean absolute performance error values.  相似文献