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51.
S. Prasanna Kumar M. Madhupratap M. Dileep Kumar M. Gauns P. M. Muraleedharan V. V. S. S. Sarma S. N. De Souza 《Journal of Earth System Science》2000,109(4):433-441
Usingin situ data collected during 1992–1997, under the Indian programme of Joint Global Ocean Flux Study (JGOFS), we show that the biological
productivity of the Arabian Sea is tightly coupled to the physical forcing mediated through nutrient availability. The Arabian
Sea becomes productive in summer not only along the coastal regions of Somalia, Arabia and southern parts of the west coast
of India due to coastal upwelling but also in the open waters of the central region. The open waters in the north are fertilized
by a combination of divergence driven by cyclonic wind stress curl to the north of the Findlater Jet and lateral advection
of nutrient-rich upwelled waters from Arabia. Productivity in the southern part of the central Arabian Sea, on the other hand,
is driven by advection from the Somalia upwelling. Surface cooling and convection resulting from reduced solar radiation and
increased evaporation make the northern region productive in winter. During both spring and fall inter-monsoons, this sea
remains warm and stratified with low production as surface waters are oligotrophic. Inter-annual variability in physical forcing
during winter resulted in one-and-a-half times higher production in 1997 than in 1995. 相似文献
52.
M. V. Prasanna S. Chidambaram G. Senthil Kumar AL Ramanathan H. C. Nainwal 《Arabian Journal of Geosciences》2011,4(1-2):319-330
In the light of progressive depletion of groundwater reservoir and water quality deterioration of the Neyveli basin, an investigation on dissolved major constituents in 25 groundwater samples was performed. The main objective was detection of processes for the geochemical assessment throughout the area. Neyveli aquifer is intensively inhabited during the last decenniums, leading to expansion of the residential and agricultural area. Besides semi-aridity, rapid social and economic development stimulates greater demand for water, which is gradually fulfilled by groundwater extraction. Groundwaters of the study area are characterized by the dominance of Na?+?K over Ca?+?Mg. HCO3 was found to be the dominant anion followed by Cl and SO4. High positive correlation was obtained among the following ions: Ca–Mg, Cl–Ca,Mg, Na–K, HCO3–H4SiO4, and F–K. The hydrochemical types in the area can be divided into two major groups: the first group includes mixed Ca–Mg–Cl and Ca–Cl types. The second group comprises mixed Ca–Na–HCO3 and Ca–HCO3 types. Most of the groundwater samples are within the permissible limit of WHO standard. Interpretation of data suggests that weathering, ion exchange reactions, and evaporation to some extent are the dominant factors that determine the major ionic composition in the study area. 相似文献
53.
K. Srinivasamoorthy S. Chidambaram M. V. Prasanna M. Vasanthavihar John Peter P. Anandhan 《Journal of Earth System Science》2008,117(1):49-58
The study area Mettur forms an important industrial town situated NW of Salem district. The geology of the area is mainly
composed of Archean crystalline metamorphic complexes. To identify the major process activated for controlling the groundwater
chemistry an attempt has been made by collecting a total of 46 groundwater samples for two different seasons, viz., pre-monsoon
and post-monsoon. The groundwater chemistry is dominated by silicate weathering and (Na + Mg) and (Cl + SO4) accounts of about 90% of cations and anions. The contribution of (Ca + Mg) and (Na + K) to total cations and HCO3 indicates the domination of silicate weathering as major sources for cations. The plot for Na to Cl indicates higher Cl in
both seasons, derived from Anthropogenic (human) sources from fertilizer, road salt, human and animal waste, and industrial
applications, minor representations of Na also indicates source from weathering of silicate-bearing minerals. The plot for
Na/Cl to EC indicates Na released from silicate weathering process which is also supported by higher HCO3 values in both the seasons. Ion exchange process is also activated in the study area which is indicated by shifting to right
in plot for Ca + Mg to SO4 + HCO3. The plot of Na-Cl to Ca + Mg-HCO3-SO4 confirms that Ca, Mg and Na concentrations in groundwater are derived from aquifer materials. Thermodynamic plot indicates
that groundwater is in equilibrium with kaolinite, muscovite and chlorite minerals. Saturation index of silicate and carbonate
minerals indicate oversaturation during pre-monsoon and undersaturation during post-monsoon, conforming dissolution and dilution
process. In general, water chemistry is guided by complex weathering process, ion exchange along with influence of Cl ions
from anthropogenic impact. 相似文献
54.
M. A. Rasheed M. Veena Prasanna M. Lakshmi T. Madhavi M. S. Kalpana D. J. Patil A. M. Dayal 《Journal of the Geological Society of India》2012,80(2):267-275
Surface adsorbed gas surveys and geo-microbiological surveys are well known techniques of petroleum exploration and aim towards risk reduction in exploration by way of identifying the areas warm with hydrocarbons and to establish inter-se exploration priorities amongst the identified warm areas. The thermogenic surface adsorbed gaseous hydrocarbons distribution patterns in petroliferous areas are considered to be a credible evidence for the upward migration of hydrocarbons. The present investigation aims to explore correlation between the adsorbed gas distribution pattern and microbial oxidizers in identifying the upward migration of hydrocarbons especially in the tropical black soil terrain of known petroliferous Mehsana Block of North Cambay Basin, India. A set of 135 sub-soil samples collected, were analyzed for indicator hydrocarbon oxidizing bacteria, adsorbed light gaseous hydrocarbons and carbon isotope ratios (13Cmethane and δ13Cethane). The microbial prospecting studies showed the presence of high bacterial population for methane (5.4 × 106 cfu/gm), ethane (5.5 × 106 cfu/gm), propane (4.6 × 106 cfu/gm) and butane oxidizing bacteria (4.6 × 106 cfu/gm) in soil samples. The light gaseous hydrocarbon analysis showed that the concentration ranges of C1, C2, C3, iC4 and nC4 are 402 ppb, 135 ppb, 70 ppb, 9 ppb and 18 ppb, respectively, and the value of carbon isotope ranges of methane ?29.5 to ?43.0‰ (V-PDB) and ethane ?19.1 to ?20.9‰ (V-PDB). The existence of un-altered petroliferous microseep (δ13C, ?43‰) of catagenetic origin is observed in the study area. Geo-microbial prospecting method and adsorbed soil gas and carbon isotope studies have shown good correlation with existing oil/gas fields of Mehsana. Microbial surveys can independently precede other geochemical and geophysical surveys to delineate area warm with hydrocarbons, and mapped microbiological anomalies may provide focus for locales of hydrocarbon accumulation in the Mehsana Block of Cambay Basin. 相似文献
55.
The subject of interaction between the Corona Mass Ejections (CMEs) is important in the concept of space-weather studies. In this paper, we analyzed a set of 15 interacting events taken from the list compiled by Manoharan et al. (in J. Geophys. Res. 109:A06109, 2004) and their associated DH type II radio bursts. The pre and primary CMEs, and their associated DH type II bursts are identified using the SOHO/LASCO catalog and Wind/WAVES catalog, respectively. All the primary CMEs are associated with shocks and interplanetary CMEs. These CMEs are found to be preceded by secondary slow CMEs. Most of primary CMEs are halo type CME and much faster (Mean speed = 1205 km?s?1) than the pre CME (Mean speed = 450 km?s?1). The average delay between the pre and primary CMEs, drift rate of DH type IIs and interaction height are found to be 211 min, 0.878 kHz/s and 17.87 Ro, respectively. The final observed distance (FOD) of all pre CMEs are found to be less than 15 Ro and it is seen that many of the pre CMEs got merged with the primary CMEs, and, they were not traced as separate CMEs in the LASCO field of view. Some radio signatures are identified for these events in the DH spectrum around the time of interaction. The interaction height obtained from the height-time plots of pre and primary CMEs is found to have correlations with (i) the time delay between the two CMEs and (ii) the central frequency of emission in the radio signatures in the DH spectrum around the time of interaction. The centre frequency of emission in the DH spectrum around the time of interaction seems to decrease when the interaction height increases. This result is compared with an interplanetary density model of Saito et al. (in Solar Phys. 55:121, 1977). 相似文献
56.
R. Nagarajan M.P. Jonathan Priyadarsi D. Roy L. Wai-Hwa M.V. Prasanna S.K. Sarkar M. Navarrete-López 《Marine pollution bulletin》2013
Forty-three sediment samples were collected from the beaches of Miri City, Sarawak, Malaysia to identify the enrichment of partially leached trace metals (PLTMs) from six different tourist beaches. The samples were analyzed for PLTMs Fe, Mn, Cr, Co, Cu, Ni, Pb, Sr and Zn. The concentration pattern suggest that the southern side of the study area is enriched with Fe (1821–6097 μg g−1), Mn (11.57–90.22 μg g−1), Cr (51.50–311 μg g−1), Ni (18–51 μg g−1), Pb (8.81–84.05 μg g−1), Sr (25.95–140.49 μg g−1) and Zn (12.46–35.04 μg g−1). Compared to the eco-toxicological values, Cr > Effects range low (ERL), Lowest effect level (LEL), Severe effect level (SEL); Cu > Unpolluted sediments, ERL, LEL; Pb > Unpolluted sediments and Ni > ERL and LEL. Comparative results with other regions indicate that Co, Cr, Cu, Ni and Zn are higher, indicating an external input rather than natural process. 相似文献
57.
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59.
This paper evaluates the performance of eight state-of-art IPCC-AR4 coupled atmosphere-ocean general circulation models in their representation of regional characteristics of atmospheric water balance over South Asia. The results presented here are the regional climate change scenarios of atmospheric water balance components, precipitation, moisture convergence and evaporation (P, C and E) up to the end of the twenty-second century based on IPCC AR4 modelling experiments conducted for (A1B) future greenhouse gas emission scenario. The AOGCMs, despite their relatively coarse resolution, have shown a reasonable skill in depicting the hydrological cycle over the South Asian region. However, considerable biases do exist with reference to the observed atmospheric water balance and also inter-model differences. The monsoon rainfall and atmospheric water balance changes under A1B scenario are discussed in detail. Spatial patterns of rainfall change projections indicate maximum increase over northwest India in most of the models, but changes in the atmospheric water balance are generally widespread over South Asia. While the scenarios presented in this study are indicative of the expected range of rainfall and water balance changes, it must be noted that the quantitative estimates still have large uncertainties associated with them. 相似文献
60.