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81.
The widespread retreat of glaciers can be considered as a response to the climate change. Being the largest retreating glacier–ice
shelf system in East Antarctica, the Amery Ice Shelf–Lambert Glacier system plays an important role in contributing to sea
level rise as well as the surrounding environment and climate. The present study is focused on the investigation of surface
melting over the ice shelf using QuikSCAT Ku-band scatterometer data for more than 100 months covering the period from January
2000 to July 2009. The corresponding weather data of Davis Station was obtained from the website of Australian Antarctic Division.
Very prominent dips in the backscatter observed in the month of January form a distinct signature caused by physical process
of significant melting of the ice/snow surface. The steep increase again in February is attributed to the initiation of the
freezing phenomenon. The derived melting index compared well with the passive microwave-based melting index derived by other
researchers. A strong relationship was found between the scatterometer-derived melting index and the cumulative monthly mean
air temperature. The highest melting was observed in the summer (January) of 2004, and thereafter gradual cooling appeared
to take place in the subsequent years. The snow pack thickness, inferred from the backscatter variations, was found to be
higher during winters (June) of 2004 and 2005, compared with other years. 相似文献
82.
Abhijit Mukherjee Alan E. FryarBridget R. Scanlon Prosun BhattacharyaAnimesh Bhattacharya 《Applied Geochemistry》2011,26(4):600-613
The deeper groundwater (depending on definition) of the Bengal basin (Ganges-Brahmaputra delta) has long been considered as an alternate, safe drinking-water source in areas with As-enrichment in near-surface groundwater. The present study provides the first collective discussion on extent and controls of elevated As in deeper groundwater of a regional study area in the western part of the Bengal basin. Deeper groundwater is defined here as non-brackish, potable (Cl− ? 250 mg/L) groundwater available at the maximum accessed depth (∼80-300 m). The extent of elevated As in deeper groundwater in the study area seems to be largely controlled by the aquifer-aquitard framework. Arsenic-enriched deeper groundwater is mostly encountered north of 22.75°N latitude, where an unconfined to semi-confined aquifer consisting of Holocene- to early Neogene-age gray sand dominates the hydrostratigraphy to 300 m depth below land surface. Aquifer sediments are not abnormally enriched in As at any depth, but sediment and water chemistry are conducive to As mobilization in both shallow and deeper parts of the aquifer(s). The biogeochemical triggers are influenced by complex redox disequilibria. Results of numerical modeling and profiles of environmental tracers at a local-scale study site suggest that deeper groundwater abstraction can draw As-enriched water to 150 m depth within a few decades, synchronous with the advent of wide-scale irrigational pumping in West Bengal (India). 相似文献
83.
With the advent of mining activities at Raniganj coalfield in India, the natural topography has been defaced in some elongated tracts by either excavation or dumping. This paper deals with opencast mining induced defaced topography of Raniganj coalfield, which needs to be reclaimed properly right after mining. This paper investigated intensity of defacing topography, magnitude of topographic deformations through a number of ex-situ measurement. Consequences of these topographic deformations are also investigated in this study. Through a number of ex-situ measurement based on Geographical Information System (GIS) techniques, generating contour and profiling them over the spoil dumps and excavated lows using fine resolution digital elevation data (Remote Sensing image), a total 132 (85 are abandoned and 47 are working) patches of defaced topography have been identified, which covers 43.26 sq km. surface area. Some working opencast quarries are more than 95 m deep, with an area of more than 2.4 sq km and dumped ridges are more than 60 m high (peak), with area more than 1.5 sq km. In case of abandoned mine (more than 20 years) some quarries are more than 28 m deep with area 0.99 sq km. and some of dumped ridges are more than 28 m high (peak), with area 0.29 sq km. These kinds of defaced surface remain for a long time, such quarries contain acidic logged water and spoil dump leads to acid mine drainage and erosion of loose soil particle. It deteriorates the entire land, water system of the region. The study suggests restoring land right after mining and the area made to be ecologically conformable. 相似文献
84.
Kakoli Banerjee Rajrupa Ghosh Sumit Homechaudhuri Abhijit Mitra 《Journal of Earth System Science》2009,118(5):497-505
The biochemical composition of red seaweeds, Catenella repens was investigated in this present study along with subsequent analysis of relevant physico-chemical variables. In this study,
the relationship between the nutritive components of this species and the ambient environmental parameters was established.
Protein content varied from 2.78 ± 0.30% of dry weight (stn.3) to 16.03 ± 0.96% of dry weight (stn.1) with highest values
during monsoon. The protein levels were positively correlated with dissolved nitrate content and negatively correlated with
water temperature (except stn.3) and salinity. Carbohydrate content of this species varied significantly (p < 0.05) during pre-monsoon between stations and the values showed positive relationship with salinity and surface water temperature.
In contrast to carbohydrate, lipid concentration was lowest in values and varied very slightly between seasons and stations.
Astaxanthin content of the seaweed species was greater in pre-monsoon than monsoon and post-monsoon in all the selected stations.
Compared with the three seasons, samples of red seaweed collected in pre-monsoon has high carbohydrate-astaxanthin in contrast
to protein-lipid which showed high values during monsoon. Statistical analysis computed among the environmental and biochemical
parameters suggests the potential role played by the abiotic parameters on biosynthetic pathways of seaweed. This paper also
highlights the influence of the nutritional quality of water that can be used for mass cultivation of Catenella repens. 相似文献
85.
Sk. Md. Equeenuddin Abhijit Panda Vishal Singh Prafulla Kumar Sahoo Subhashis Sahu Sumit Kumar Basantray 《Journal of the Geological Society of India》2017,89(2):209-215
Geophysical investigation using Vertical Electrical Sounding (VES), Electrical Resistivity Tomography (ERT) and Seismic Refraction at a proposed conference center site along Ajibode-Labani road, Ibadan, southwestern Nigeria has been carried out. The investigation aims at characterizing and delineating the subsurface strata to understand the weathered profile at the site. Understanding the weathered profile is essential in determining the suitability of the site for engineering construction of the future conference center. A total of 25 VES and 10 ERT profiles were acquired in a systematic grid pattern using both Schlumberger andWenner configurations with Allied omega terrameter. TheVES data were processed and analyzed using WinResist and the ERT data were inverted using RES2DINV. The data were combined to form a 3-D data set of the site and RES3DINV was used to produce the depth slices. Seismic refraction data were also acquired with an ABEM seismograph and processed using SeisImager and Fajseis software. Seismic data were used in understanding the velocity distribution and thickness. The results of VES, ERT and seismic refraction show good correlation. Four sub-surface layers were delineated: top layer of reworked sand, clayey sand/ lateritic hard pan, clay/ sandy clay and fracture/ fresh basement. The 3-D model permits a pictorial view of the sub-surface in relation to materials that overlie the basement. The thickness of unconsolidated materials to bedrock varies from 2.7 m to 12.2 m which revealed inhomogeneity in weathering under the shallow sub-surface. It is found that the integrated geophysical tool is well suited to characterize and delineate sub-surface structure (weathered profile) for engineering site characterization. 相似文献
86.
Osmium isotopic compositions, and Re and Os concentrations have been examined in one komatiite unit and two komatiitic basalt units at Dundonald Beach, part of the 2.7 Ga Kidd-Munro volcanic assemblage in the Abitibi greenstone belt, Ontario, Canada. The komatiitic rocks in this locality record at least three episodes of alteration of Re-Os elemental and isotope systematics. First, an average of 40% and as much as 75% Re may have been lost due to shallow degassing during eruption and/or hydrothermal leaching during or immediately after emplacement. Second, the Re-Os isotope systematics of whole rock samples with 187Re/188Os ratios >1 were reset at ∼2.5 Ga, possibly due to a regional metamorphic event. Third, there is evidence for relatively recent gain and loss of Re in some rocks.Despite the open-system behavior, some aspects of the Re-Os systematics of these rocks can be deciphered. The bulk distribution coefficient for Os (DOssolid/liquid) for the Dundonald rocks is ∼3 ± 1 and is well within the estimated D values obtained for komatiites from the nearby Alexo area and stratigraphically-equivalent komatiites from Munro Township. This suggests that Os was moderately compatible during crystal-liquid fractionation of the magmas parental to the Kidd-Munro komatiitic rocks. Whole-rock samples and chromite separates with low 187Re/188Os ratios (<1) yield a precise chondritic average initial 187Os/188Os ratio of 0.1083 ± 0.0006 (γOs = 0.0 ± 0.6) for their well-constrained ∼2715 Ma crystallization age. The chondritic initial Os isotopic composition of the mantle source for the Dundonald rocks is consistent with that determined for komatiites in the Alexo area and in Munro Township, suggesting that the mantle source region for the Kidd-Munro volcanic assemblage had evolved with a long-term chondritic Re/Os before eruption. The chondritic initial Os isotopic composition of the Kidd-Munro komatiites is indistinguishable from that of the projected contemporaneous convective upper mantle. The uniform chondritic Os isotopic composition of the Kidd-Munro komatiites contrasts with the typical large-scale Os isotopic heterogeneity in the mantle sources for ca. 89 Ma komatiites from the Gorgona Island, arc-related rocks and present-day ocean island basalts. This suggests that the Kidd-Munro komatiites sampled a late-Archean mantle source region that was significantly more homogeneous with respect to Re/Os relative to most modern mantle-derived rocks. 相似文献
87.
Auto-correlation analysis of ocean surface wind vectors 总被引:1,自引:0,他引:1
Abhijit Sarkar Sujit Basu A. K. Varma Jignesh Kshatriya 《Journal of Earth System Science》2002,111(3):297-303
The nature of the inherent temporal variability of surface winds is analyzed by comparison of winds obtained through different
measurement methods. In this work, an auto-correlation analysis of a time series data of surface winds measuredin situ by a deep water buoy in the Indian Ocean has been carried out. Hourly time series data available for 240 hours in the month
of May, 1999 were subjected to an auto-correlation analysis. The analysis indicates an exponential fall of the autocorrelation
in the first few hours with a decorrelation time scale of about 6 hours. For a meaningful comparison between satellite derived
products andin situ data, satellite data acquired at different time intervals should be used with appropriate ‘weights’, rather than treating
the data as concurrent in time. This paper presents a scheme for temporal weighting using the auto-correlation analysis. These
temporal ‘weights’ can potentially improve the root mean square (rms) deviation between satellite andin situ measurements. A case study using the TRMM Microwave Imager (TMI) and Indian Ocean buoy wind speed data resulted in an improvement
of about 10%. 相似文献
88.
The problem of determining optimal power spectral density models for earthquake excitation which satisfy constraints on total average power, zero crossing rate and which produce the highest response variance in a given linear system is considered. The solution to this problem is obtained using linear programming methods. The resulting solutions are shown to display a highly deterministic structure and, therefore, fail to capture the stochastic nature of the input. A modification to the definition of critical excitation is proposed which takes into account the entropy rate as a measure of uncertainty in the earthquake loads. The resulting problem is solved using calculus of variations and also within linear programming framework. Illustrative examples on specifying seismic inputs for a nuclear power plant and a tall earth dam are considered and the resulting solutions are shown to be realistic. 相似文献
89.
The study aimed to assess the heavy metals(K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Pb, Sr, Zr) contamination in the soil of mine affected Singaran river basin and to analyse spatial variation in the contamination level considering 32 soil samples. Elemental analysis of soil samples has been performed through Energy Dispersive X-ray Analysis(EDX) to quantify the elemental concentration(mg kgà1). Heavy metal concentrations have been assessed through geo-accumulation index(Igeo) and enrichment factor(EF).Indices showed soils have moderate accumulation of most of the metals with moderate enrichment of Sr,Zr, Zn, Cu and Ni. Soil contamination level assessment has been carried out using indices like Contamination Factor(CF), degree of contamination(C_(deg)), modified degree of contamination(m C_(deg)) and Pollution Load Index(PLI). CF shows moderate to considerable contamination by Sr, Zr, Ca, Cu, Mn, Zn and Ni. Mean indices values(m C_(deg)and PLI for the entire basin are 3.38 and 2.23 respectively) show low to moderate level of soil contamination. These indices result have been mapped and analysed in GIS platform to get spatial variation of pollution level. Opencast mines dominate middle catchment area and so is comparatively contaminated. Sample sites 11, 18 and 25 evidenced high values of all indices of pollution load. From the ecological standpoint Ecological Risk Factor(Er) and Potential Ecological Risk Index(RI) have been estimated to assess regional threat to native soil environment and it shows low ecological risk potential. Analysis shows that mine dominated soil of the entire Singaran basin is less contaminated in all respect but tends to the moderate contamination level at the mid-catchment area,especially by Sr, Zr, Zn, Cu and Ni. 相似文献
90.
Shishir Gupta Smita Snehamoy Pramanik Abhijit Pramanik 《Arabian Journal of Geosciences》2018,11(9):220
The present paper is incorporated into a mathematical model of transmission and reflection of shear waves through the initially stressed dry sandy medium sandwiched between two initially stressed distinct orthotropic half-spaces. The formulae of transmission and reflection coefficients have been deduced for the propagation of SH waves in the described model subjected to certain boundary conditions applying Snell’s law and Cramer’s method. These coefficients are observed as a function of wave number, phase velocity, initial stress, rigidity, and dry sandiness coefficients. The concepts of energy partition, phase shift, conservation of energy, critical angle, and slowness section are introduced. Graphical approach has been carried out to accomplish a relation between reflection/refraction coefficient, phase shift, and energy ratio with an angle of incidence and wave number on the propagation of shear wave. The study reveals that sandiness parameter, initial stress, and wave number have a cogent respond to the scattering of shear wave that has been illustrated graphically. 相似文献