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11.
Pablo Sangrà Ananda Pascual Ángel Rodríguez-Santana Francisco Machín Evan Mason James C. McWilliams Josep L. Pelegrí Changming Dong Anna Rubio Javier Arístegui Ángeles Marrero-Díaz Alonso Hernández-Guerra Antonio Martínez-Marrero Maricel Auladell 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(12):2100-2114
We report, from remote sensing and in situ observations, a new type of permanent structure in the eastern subtropical Atlantic Ocean, that we call the “Canary Eddy Corridor”. The phenomenon, is a zonal long-lived (>3 months) mesoscale eddy corridor, whose source is the flow perturbation of the Canary Current and the Trade Winds at the Canary Islands. The latitudinal range of the corridor spans 22°N–29°N and extends from the Canaries to at least 32ºW, near the mid-Atlantic. This is the main region of long-lived westward-propagating eddies in the subtropical northeast Atlantic. From a age-distribution study we observe that at least 10% of mesoscale eddies in this region are long-lived, with a dominance of anticyclones over cyclones. Another four westward-propagating eddy corridors were also detected: two small corridors north and south of the Azores Front; a small zonal corridor located near 31ºN, south of the island of Madeira; and a small corridor located near the Cape Blanc giant filament. The existence of these corridors may change, at least for the northeastern subtropical Atlantic, the general idea that mesoscale eddies are disorganized, ubiquitous structures in the ocean. The Canary Eddy Corridor constitutes a direct zonal pathway that conveys water mass- and biogeochemical properties offshore from the Canary Island/Northwest Africa upwelling system, and may be seen as a recurrent offshore pump of organic matter and carbon to the oligotrophic ocean interior. Estimates of volume and mass transport indicate that Canary Eddy Corridor westward transport is more than one-fourth of the southward transport of the Canary Current. The westward transport of kinetic energy by the eddies of the Canary Corridor is as important as the southward transport by the Canary Current. The total primary production related to the Corridor may be as high as the total primary production of the northwest Africa upwelling system for the same latitude range. 相似文献
12.
Assessment and prediction of contaminant migration in ground water from chromite waste dump 总被引：3，自引：0，他引：3
Sukinda chromite valley is one of the largest chromite deposits of the country and produces nearly 8% of chromite ore. It
greatly contributes towards the economic development but at the same time deteriorates the natural environment. It is generally
excavated by opencast mining method. In the Sukinda mining area, around 7.6 million tons of solid waste have been generated
in the form of rejected minerals, overburden material/waste rock and sub-grade ore that may be resulting in environmental
degradation, mainly causing lowering in the water table vis-à-vis deterioration in surface and ground water quality. The study
conducted in and around one of the chromite mine of the valley reveals that the concentration of hexavalent chromium is found
in the water samples of ground and surface water, mine effluents and seepage water. Hexavalent Chromium (Cr+6) have been found varying between 0.02 mg/l and 0.12 mg/l in mine effluents and 0.03–0.8 mg/l in shallow hand pumps and 0.05
and 1.22 mg/l in quarry seepage. The concentration of Cr+6 in Damsal nalah, the main surface water source in the area, is found varying between 0.03 mg/l and 0.14 mg/l and a increasing
trend, which is in the downstream of mining activities, has been observed. Leachate study clearly shows that the soil lying
in the vicinity of mine waste dump shows highest concentration of Cr+6. Contaminant migration in ground water depends upon various geohydrological conditions of the area. The study shows that
aquifer resistivity varies between 15 Ωm to 150 Ωm and aquifer depth varies from 4 m to 26 m below ground level. The ground
water flow and mass transport models were constructed with the help of geo-hydrological and geophysical informations using
Visual Modflow software. Contaminant migration and path lines for 20 years have been predicted in two layers model of ground
water. The study provided an insight into the likely migration of contaminant in ground water due to leaching from overburden
dump of chromite ore and will be helpful in making strategic planning for limiting the contaminant migration in the ground
water regime in and around the mining areas. 相似文献
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R. Ananda Reddy 《Journal of the Geological Society of India》2014,83(3):235-251
Widespread distribution of mafic dykes and scanty occurrence of ultrabasic intrusives of kimberlitic affinity around Proterozoic Cuddapah basin, parts of Eastern Dharwar craton of south India has been the focus of attention since their discovery, to understand the structural fabric in relation to their emplacement in geological time. Satellite Imagery, geomorphological, geophysical and radiometric age data of Narayanpet area, northwest of Cuddappah basin, have clearly displayed the alignments and structures of geological significance, such as deep seated fault / fracture / shear zones, stratigraphic / lithological contacts, basic / ultrabasic intrusives and younger granites etc,. Based on the field observations such as emplacement of mafic dykes, their cross cutting relationship, study of morphological and geophysical signatures, inferred linears drawn from satellite imagery, aeromagnetic and gravity maps are arranged in a chronological order. A system of long, narrow and widely spaced dykes trending NW-SE direction conformable to gneissic foliation, typically associated with migmatites in the southwestern part of the study area are the oldest. Followed by E-W dykes, cut across by the sparsely distributed dykes associated with NW-SE and N-S features and in turn off set by dykes of NE-SW trends are the youngest. Kimberlites of Narayanpet area, belongs to hypabysal facies, which are essentially controlled by E-W to ENE-WSW deep seated fault / fracture zone, their intersection with NW-SE, NE-SW to N-S trends, which may have been reactivated during Proterozoic period as indicated by the intrusion of mafic dykes (～2270 to 1701 Ma) and emplacement of kimberlitic magmatism (～1300 to 1100 Ma) suggesting different intrusive episodes. Kimberlite pipes of Narayanpet field, falls in an ellipsoid form trending WNW-ESE direction in the northern part of the area, associated with radial drainage / topographic high and a gravity low. In addition, physical properties such as density and magnetic susceptibilities of mafic dykes and kimberlites, their geophysical signatures, emplacement of kimberlites at the close vicinity of mafic dykes or at their intersections have also been discussed. 相似文献
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Stephen B. Weisberg J. Ananda Ranasinghe Daniel M. Dauer Linda C. Schaffner Robert J. Diaz Jeffrey B. Frithsen 《Estuaries and Coasts》1997,20(1):149-158
A multimetric benthic index of biotic integrity (B-IBI) was developed using data from five Chesapeake Bay sampling programs conducted between 1972 and 1991. Attributes of the index were selected by comparing the response of 17 candidate measures of benthic condition (metrics) between a set of minimally affected reference sites and at all other sites for which data were available. This procedure was conducted independently for each of seven habitats defined by salinity and substrate. Fifteen of the 17 candidate metrics differed significantly between reference sites and other sites for at least one habitat. No metric differed significantly in all seven habitats; however, four metrics, species diversity, abundance, biomass, and percent of abundance as pollution-indicative taxa, differed in six habitats. The index was calculated by scoring each selected metric as 5, 3, or 1 depending on whether its value at a site approximated, deviated slightly from, or deviated greatly from conditions at the best reference sites. Validation based on independent data collected between 1992 and 1994 indicated that the index correctly distinguished stressed sites from reference sites 93% of the time, with the highest validation rates occurring in high salinity habitats. 相似文献
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Ananda Gunatilaka 《Sedimentary Geology》1975,14(4):275-300
Laminated blue-green algal mats are forming in the intertidal zone of a clastic (non-carbonate), tropical, lagoonal tidal-flat in northwest Ceylon. On the basis of their surface morphology three distinct mat zones are recognised. From the high-water mark seawards these are: (1) a smooth rounded-mat zone with discrete structures; (2) a crinkled- and blistered-mat zone; and (3) a smooth flat-mat zone without any perceptible relief. These mats are formed by the trapping and binding of sediment particles on to a sticky and mucilaginous complex of algal filaments.The morphology and distribution of these mats appear to be controlled by the frequency and duration of their exposure, strength of tidal-current velocities and the rates of bottom sediment movement. The flat zone is characterised by tidal-current velocities of 10–15 cm/sec, greater rates of traction movement and twice daily tidal flooding. The crinkled zone is partly or completely exposed during neap tides, the rate of bottom sediment movement is less than in the flat zone and the tidal-current velocities vary from 6–12 cm/sec. The rounded-mat zone is flooded only during high-water spring tide, with no tidal exchange during the neap tidal phase, but there is a continuous water cover forming a tidal pool. Here the rate of bottom sediment movement is negligible and the tidal-current velocities vary from 1–10 cm/sec. The rounded—elliptical mat forms are elongated in the direction of tidal flow and with decreasing tidal velocities they tend to assume a more rounded shape. All three zones are characterized by laminations produced by the alternation of thick sediment-rich and thin algal-rich layers. They show an accretion rate of 5–15 mm/week. The above features indicate that they are potentially very useful environmental indicators. 相似文献
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Pre-seismic, co-seismic and post-seismic displacements associated with the Bhuj 2001 earthquake derived from recent and historic geodetic data 总被引：1，自引：0，他引：1
Sridevi Jade M. Mukul I. A. Parvez M. B. Ananda P. D. Kumar V. K. Gaur R. Bendick R. Bilham F. Blume K. Wallace I. A. Abbasi M. Asif Khan S. Ulhadi 《Journal of Earth System Science》2003,112(3):331-345
The 26th January 2001 Bhuj earthquake occurred in the Kachchh Rift Basin which has a long history of major earthquakes. Great
Triangulation Survey points (GTS) were first installed in the area in 1856–60 and some of these were measured using Global
Positioning System (GPS) in the months of February and July 2001. Despite uncertainties associated with repairs and possible
reconstruction of points in the past century, the re-measurements reveal pre-seismic, co-seismic and post-seismic deformation
related to Bhuj earthquake. More than 25 Μ-strain contraction north of the epicenter appears to have occurred in the past
140 years corresponding to a linear convergence rate of approximately 10 mm/yr across the Rann of Kachchh. Motion of a single
point at Jamnagar 150 km south of the epicenter in the 4 years prior to the earthquake, and GTS-GPS displacements in Kathiawar
suggests that pre-seismic strain south of the epicenter was small and differs insignificantly from that measured elsewhere
in India. Of the 20 points measured within 150 km of the epicenter, 12 were made at existing GTS points which revealed epicentral
displacements of up to 1 m, and strain changes exceeding 30 Μ-strain. Observed displacements are consistent with reverse co-seismic
slip. Re-measurements in July 2001 of one GTS point (Hathria) and eight new points established in February reveal post-seismic
deformation consistent with continued slip on the Bhuj rupture zone. 相似文献
19.
Albert Palanques Emilio García-Ladona Dami Gomis Jacobo Martín Marta Marcos Ananda Pascual Pere Puig Josep-Maria Gili Mikhail Emelianov Sebasti Monserrat Jorge Guilln Joaquín Tintor Mariona Segura Antoni Jordi Simn Ruiz Gotzon Basterretxea Jordi Font Dolors Blasco Francesc Pags 《Progress in Oceanography》2005,66(2-4):89
Currents, particle fluxes and ecology were studied in the Palamós submarine canyon (also known as the Fonera canyon), located in the northwestern Mediterranean. Seven mooring arrays equipped with current meters and sediment traps were deployed along the main canyon axis, on the canyon walls and on the adjacent slope. Additionally, local and regional hydrographic cruises were carried out. Current data showed that mean near surface and mid-depth currents were oriented along the mean flow direction (NE–SW), although at 400 and 1200 m depth within the canyon current reversals were significant, indicating a more closed circulation inside the canyon. Mean near-bottom currents were constrained by the local bathymetry, especially at the canyon head. The most significant frequency at all levels was the inertial frequency. A second frequency of about three days, attributed to a topographic wave, was observed at all depths, suggesting that this wave was probably not trapped near the bottom. The current field observed during the most complete survey revealed a meandering pattern with cyclonic vorticity just upstream from and within the canyon. The associated vertical velocity ranged between 10 and 20 m/day and was constrained to the upper 300 m. This latter feature, together with other computations, suggests that during this survey the meander was not induced by the canyon but by some kind of instability of the mean flow.In the canyon, suspended sediment concentration, downward particle fluxes, chlorophyll and particulate C and N were significantly higher up-canyon from about 1200 m depth than offshore, defining, along with the different hydrodynamics, two canyon domains: one from the canyon head to about 1200 m depth more affected by the canyon confinement and the other deeper than 1200 m depth more controlled by the mean flow and the shelf-slope front. The higher near-bottom downward total mass fluxes were recorded in the canyon axis at 1200 m depth along with sharp turbidity increases and are related to sediment gravity flows. During the deployment period, the increase in downward particle fluxes occurred by mid-November, when a severe storm took place. On the canyon walls at 1200 m depth, suspended sediment concentrations, downward particle fluxes, chlorophyll and particulate C and N were higher on the southern wall than on the northern wall inversely to the current’s energy. This could be caused by an upward water supply on the southern canyon wall and/or the mean flow interacting with the canyon bathymetry. In the swimmers collected by the sediment traps, the dominant species was an elasipod holothurian, which has not been recorded in other canyons or elsewhere in the Mediterranean, indicating particular speciation. 相似文献
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