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V. V. S. S. Sarma M. S. Krishna R. Viswanadham G. D. Rao V. D. Rao B. Sridevi B. S. K. Kumar V. R. Prasad Ch. V. Subbaiah T. Acharyya D. Bandopadhyay 《Journal of Oceanography》2013,69(1):45-55
A study on biogeochemical cycling in the west coastal Bay of Bengal was undertaken during the peak discharge period to understand the influence of enhanced stratification and primary production on the possible intensification of the oxygen minimum zone (OMZ). Our study reveals that oxygen concentrations were below the detection limits in the northwestern (NW) coastal Bay of Bengal between 100 and 500 m associated with strong stratification and high phytoplankton biomass. Such low oxygen concentrations have never been reported so far from the coastal Bay of Bengal. Despite the existence of an environment conducive to denitrification in the coastal Bay of Bengal, accumulation of neither secondary nitrite nor nitrous oxide (N2O) was observed. The absence of denitrification was reported to be caused by faster scavenging of organic matter and low bacterial respiration rates; in contrast, our results suggest that neither of these factors are potential reasons for the absence of denitrification in the coastal Bay of Bengal. 相似文献
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Thomas?Oommen Debasmita?MisraEmail author Anupma?Prakash Sukumar?Bandopadhyay Sathy?Naidu John?J.?Kelley 《Natural Resources Research》2011,20(1):11-24
Multiple Regressive Pattern Recognition Technique (MRPRT) is an adapted approach for improved geologic resource estimation.
We developed and tested this approach for the Platinum (Pt) bearing region near Goodnews Bay, Alaska, which presents an example
of a complex depositional environment. We applied geospatial and pattern recognition methods to assess the spatial distribution
of offshore Pt in the Goodnews Bay area from point data collected by various agencies. We used the coefficient of correlation
(r) and the Nash–Sutcliffe efficiency (E) to quantitatively assess the degree of accuracy of the estimated Pt distribution. We split the study area, based on trend
analysis, into two regions: inside the Bay and outside the Bay. We could not obtain appreciable estimates from the geospatial
and pattern recognition methods. Using MRPRT, we were able to improve r from 0.57 to 0.93 and the E from 28.31 to 92.91 inside the Bay. We achieved improvement in r from 0.55 to 0.61 and E from 28.46 to 34.52 outside the Bay. The reasons for a non-significant improvement outside the Bay have been discussed. The
results indicate that the proposed MRPRT has wide application potential in georesource estimation where input data is often
scarce. 相似文献
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Priya Narayanan Ashoke Basistha Sumana Sarkar Sachdeva Kamna 《Comptes Rendus Geoscience》2013,345(1):22-27
Spatial and temporal variability of rainfall over different seasons influence physical, social and economic parameters. Pre-monsoon (March, April and May – MAM) rainfall over the country is highly variable. Since heat lows and convective rainfall in MAM have an impact on the intensity of the ensuing monsoons, hence the pre-monsoon period was chosen for the study. The pre-whitened Mann Kendall test was used to explore presence of rainfall trend during MAM. The results indicate presence of significant (at 10% level) increasing trend in two stations (Ajmer, Bikaner). The practical significance of the change in rainfall was also explored as percentage changes over long term mean, using Theil and Sen's median slope estimator. Forecast using univariate ARIMA model for pre-monsoon months indicates that there is a significant rise in the pre-monsoon rainfall over the northwest part of the country. 相似文献
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Prediction of Arsenic in Bedrock Derived Stream Sediments at a Gold Mine Site Under Conditions of Sparse Data 总被引：2，自引：0，他引：2
Navin K. C. Twarakavi Debasmita Misra Sukumar Bandopadhyay 《Natural Resources Research》2006,15(1):15-26
Arsenic is often present in gold mining areas. The high sensitivity of arsenic to biogeochemical conditions may lead to catastrophic
consequences through contamination of resources such as ground water. Therefore, it is critical to understand the spatial
occurrence of arsenic across a given site. Previous studies using traditional pattern recognition techniques such as neural
networks and kriging have not been entirely successful in predicting arsenic concentrations across a gold mining area. The
methods used in this paper are the support vector machines (SVM) and robust least-square support vector machines (robust LS-SVM).
The two techniques were used to predict arsenic concentrations in the sediments of Circle City, Alaska, using the gold concentration
distribution present within the sediments. The analysis of the results shows an improved performance and better predictive
capabilities of SVM and robust LS-SVM than that of the neural networks and kriging techniques. The robust LS-SVM performed
better than the SVM. The performance of the SVM was affected by outliers. The removal of the outliers from the data set and
application of SVM showed improved results. 相似文献
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Mid-fan areas in the Bay of Bengal to the west of the Andaman-Nicobar Islands and to the east of the 90 E ridge display remarkable channel-levee and interlevee characteristics over the seabed. These subsea channels at 3,000 m or more water depth have specific orientations along NNE or NNW. Most of these major and minor channels are at present inactive, except one running along the eastern part of the area following the reported subduction suture (Currey et al., 1979). The other channels in the western part retain the configuration of a floor-bank combination but are covered with a thin deposition of pelagic organisms without any significant terrigenous inputs to a depth of around 25 cm below the seabed. On the other hand, the active channel to the east is filled with continuous hemipelagic to terrigenous inputs up to at least 1.5 m bsf. The pelagic organisms of the upper 25 cm of seabed over the inactive channels as well as in their banks and interlevee areas are mainly represented by foraminiferal tests and thus constitute foraminiferal ooze. Most of the seafloor is covered by such ooze except in the easternmost part, where the active channel brings a terrigenous influx in the form of turbidites. The fan deposition has been restricted to the easternmost active channel since the early Holocene. The age of the pelagites that constitute the 25-cm top sediment slice is assumed to represent about 8,000 years, calculated at the rate of deposition of 3 cm 1,000 years (Kennet, 1982). Thus, most of the western seabed has not experienced any fan deposition during the last 8,000 years. However, below 25 cm, the entire area is seen to have experienced fan deposition as evidenced by occurrence of terrigenous silt and clay. Significantly, incidence of thermogenic hydrocarbons is proved in the levee-in terlevee complexes of the central part. Being closer to the subduction zone, gas seepages through pervasive fissures are perhaps more pronounced here. 相似文献
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Lynn Margulis Elso S. Barghoorn Debra Ashendorf Sumana Banerjee David Chase Susan Francis Stephen Giovannoni John Stolz 《Precambrian Research》1980,11(2):93-123
In the hypersaline lagoon at Laguna Figueroa vertically stratified diverse communities of microorganisms thrive. The modern sediments of Baja California at Laguna Figueroa contain cyanobacterial communities and sedimentary structures produced by these blue greens that have already been studied by Horodyski and his colleagues. This paper provides an introduction to the complex microbial communities, primarily those that underlie the laminated Microcoleus mats. They are composed of anaerobic photosynthetic and heterotrophic bacteria.The following genera of cyanobacteria at least are components of these mat communities: Lyngbya, Microcoleus, Entophysalis, Phormidium, Pseudoanabaena, Anabaena and Schizothrix. Among the photosynthetic bacteria several species of Thiocapsa-like microbes formed major surface components of certain mats and scums; rhodospirilli, rhodopseudomonads, chromatis and others were seen.The following nonphotosynthetic bacteria were identified: Nocardia sp., three types of spirilli, two types of Spirochaeta sp., two types of Desulfovibria sp., a new strain of red Beneckea and four distinctive unidentified coccoid and filamentous bacteria. Reasons are given for believing several of the species are new to science and that the microbial diversity is far greater than the approximately twenty species reported here. Eukaryotes are extremely rare. Only one species of animal, a herpachtechoid copepod, was ever seen in the 8-km long microbial communities of the hypersaline basin. Dunaliella salina, a chlorophyte and Aspergillus sydowi, an ascomycetous fungus were the only eukaryotes that were observed to be regular components of mat communities. Ciliates, amoebae (including a chrysarchnion-like microbe) and diatom tests, mostly empty, were the only other eukaryotes observed. Attempts to enrich for eukaryotic microorganisms were not successful whereas attempts to enrich for bacteria, especially anaerobes led to such a profusion of forms that to continue detailed study of them was beyond our means. Unidentified small rods and cocci constituted the largest fraction of individuals in the subsurface community. The microbes isolated from mats are adapted for alternating dry and wet conditions as well as high concentrations of salt and low concentrations of oxygen. 相似文献
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Sumana Basu Mohammed Y. Ali Asam Farid Karl A. Berteussen Garry Mercado 《Arabian Journal of Geosciences》2014,7(9):3815-3827
A microseismic experiment utilizing a single downhole array of eight 3-component receivers was conducted in an offshore oilfield in the emirate of Abu Dhabi in the United Arab Emirates. The Lower Cretaceous Thamama Group is the major carbonate reservoir in the field producing from six zones. Microseismic data was acquired in conjunction with gas injections that took place in the Thamama IV A and IV B reservoirs during 9 days of acquisition. The aim of the experiment was to monitor the microseismic activity arising in the carbonate reservoirs as a result of gas injection. A total of 103 microseismic events were detected from two of the receivers. For the majority of these events, there were no well-defined P wave arrivals, probably due to the presence of strong background noise and the very weak microseismic signals. The results from this experiment indicate that the detected events are probably related to the microseismic activities caused by the gas injection within the Thamama IV B reservoir. Therefore, downhole microseismic monitoring methods can potentially provide valuable information about the fracture systems within the carbonate reservoirs of Abu Dhabi's oilfields. 相似文献
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P. C. Bandopadhyay Utpal Chakrabarti Abhinaba Roy 《Journal of the Geological Society of India》2009,73(2):261-267
The Namunagarh grit of Eocene age in South Andaman island is a submarine fan deposit where sedimentation occurred in deep
marine environment mainly by turbidity currents. The mudstone and fine-grained sandstone of the turbidite sequence yielded
three ichnogenera viz Thalassinoides, Teichichnus and Lorenzinia.
Typically shallow marine Thalassinoides burrows co-occur with deep water burrows represented by Teichichnus and Lorenzinia, indicating a dominant control of substrate, availability of food and rate of sedimentation against bathymetry on distribution
of trace fossils. Trace fossils are particularly abundant in the mudstones pointing to a strong lithofacies control. A well-oxygenated
muddy bottom with a low rate of sedimentation is envisaged.
An order in the succession of traces could be deciphered. Simply constructed burrows of Thalassinoides appeared initially followed by complex structures of Teichichnus and ornate Lorenzinia. 相似文献
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Subaqueous effusive to low-explosive eruptive product composed of blocky and fluidal fragments of glass and sparsely crystalline glass of obsidian lava are present in fine-grained volcaniclastic debris flow conglomerate and turbidite, occurring in a deep marine sequence of thin- and even-bedded grey siliceous micritic limestone of the Chanda Limestone. The siliceous limestone conformably encloses stratiform manganese deposit. Obsidian glass fragments consist of coherent and amorphous glassy groundmass containing patches of devitrified fibrous glass, oriented microlites and microphenocrysts of quartz and K-feldspars. Euhedral crystals, resorbed-rounded and embayed crystals, spherical vesicles, microlites, and flow texture are distinctive volcanic features observed in these fragments chemically similar to obsidian lava.The blocky fragments represent the products of hydroclastic fragmentation whereas the fludial one may indicate formation under steam explosion. Gravitational instability of the resulting slurry of glass fragments and the ambient sea water-sediments at the site of eruption causes gravity flows that carries the fragments along with epiclasts away from vent to a distal site for final deposition. This study records maiden evidence of volcanism in the Chanda Limestone of the Neoproterozoic Penganga Group and infers rifting and partial melting of the sialic crust and silicic lava flow during deposition of limestone unusually rich in silica. The inferred tectono-sedimentary setting, facies association and mode of occurrence of the manganese deposit suggest a hydrothermal source for the metal. 相似文献