Controls of dimethyl sulphide in the Bay of Bengal during BOBMEX-Pilot cruise 1998   总被引：1，自引：0，他引：1  

D. M. Shenoy  M. Dileep Kumar  V. V. S. S. Sarma 《Journal of Earth System Science》2000,109(2):279-283

The air-sea exchange is one of the main mechanisms maintaining the abundances of trace gases in the atmosphere. Some of these, such as carbon dioxide and dimethyl sulphide (DMS), will have a bearing on the atmospheric heat budget. While the former facilitates the trapping of radiation (greenhouse effect) the latter works in the opposite direction through reflectance of radiation back into space by sulphate aerosols that form from oxidation of DMS in atmosphere. Here we report on the first measurements made on DMS in the Bay of Bengal and the factors regulating its abundance in seawater. Phytoplankton alone does not seem to control the extent of DMS concentrations. We find that changes in salinity could effectively regulate the extent of DMSP production by marine phytoplankton. In addition, we provide the first ever evidence to the occurrence of DMS precursor, DMSP, in marine aerosols collected in the boundary layer. This suggests that the marine aerosol transport of DMSP will supplement DMS gaseous evasion in maintaining the atmospheric non-sea salt sulphur budget.  相似文献   

A comparative study of Pleistocene phosphorites from the continental slope off western India   总被引：1，自引：0，他引：1  

V. Purnachandra Rao  S. W. A. Naqvi  M. Dileep Kumar  D. Cardinal  A. Michard  D. V. Borole  E. Jacobs  & R. Natarajan 《Sedimentology》2000,47(5):945-960

Two types of phosphorite recovered from the continental slope off western India are described. The first type, phosphorite 1, comprises a hard, grey nodule composed of carbonate fluorapatite (CFA) and calcite as major minerals. The phosphorite consists of light‐brown microcrystalline apatite containing a few skeletal fragments and planktonic foraminifera. Scanning electron microscope (SEM) studies show evidence of dissolution of skeletal calcite and filling of the resulting cavities by phosphate composed of ovoid to rod‐shaped apatite microparticles. Apatite also occurs as coatings on these particles. The P₂O₅ content of the phosphorite is 29%, and the CO₂ content of the CFA is about 4·5%. The rare‐earth element (REE) abundance (ΣREE=2·02 μg g^–1) is lower than in other modern phosphorites. The ⁸⁷Sr/⁸⁶Sr ratio and ?Nd value of this sample are 0·70921 and –9·9 respectively. The ¹⁴C age found through accelerator mass spectrometry (AMS) dating (18 720 ± 120 years BP) is much younger than that determined by the U‐series method (100 ka). The second type, phosphorite 2, comprises a friable, light‐brown nodule consisting of CFA as the only major mineral, with a CO₂ content of the CFA of 4·5%. In thin section, the phosphate is light brown and homogeneous, and a few bone fragments are present. The P₂O₅ content is 33%, and REE contents (ΣREE = 0·18 μg g^–1) are lower than in phosphorite 1. The age of phosphorite 2 is >300 ka. Phosphorite 1 appears to have formed during the late Pleistocene through replacement of carbonate by phosphate; phosphorite 2 is also of Pleistocene age but is much older than phosphorite 1. The initial substrate for phosphorite 2 was a fish coprolite, which was subsequently phosphatized during slow sedimentation under low‐energy conditions. Microbial mediation is evident in both phosphorites. The colour, density and P₂O₅ content of the phosphorites are found to be dependent on the nature of the initial substrates and physico‐chemical conditions during phosphatization. The CO₂ content of the CFA is not related to the precursor carbonate phase. The nature of sediments, rates of sedimentation and the time spent undergoing phosphogenesis at the sediment–water interface may control REE concentrations in phosphorites.  相似文献   

Organic Petrology     

Atul Kumar Varma 《Gondwana Research》2000,3(2)

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Influence of fluvial‐tidal interactions on the nature of cross‐stratified packages in a deltaic setting: examples from the Barakar Coal Measure (Permian), Satpura Gondwana Basin,central India     

Sanjoy Kumar Ghosh  Chandan Chakraborty  Tapan Chakraborty 《Geological Journal》2005,40(1):65-81

Nine different types of cross‐stratified packages from the coal‐bearing, deltaic succession of the Barakar Formation (Permian) of the Satpura Gondwana Basin, central India, are described. The deposits are characterized by periodic mudstone drapes, reactivation surfaces including all other features suggestive of deposition from periodically unsteady, tidally‐influenced flows. The inferred flow patterns varied from purely bidirectional to pulsating unidirectional. The different types of cross‐stratified packages are interpreted to have resulted from superimposition of ebb‐oriented, steady, unidirectional fluvial currents of variable strength on the tidal flow in a deltaic setting. The study helps to distinguish cross‐strata that may develop in settings where fluvial and tidal currents interact. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Climate drift of AMOC,North Atlantic salinity and arctic sea ice in CFSv2 decadal predictions     

Bohua Huang  Jieshun Zhu  Lawrence Marx  Xingren Wu  Arun Kumar  Zeng-Zhen Hu  Magdalena A. Balmaseda  Shaoqing Zhang  Jian Lu  Edwin K. Schneider  James L. Kinter III 《Climate Dynamics》2015,44(1-2):559-583

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Impacts of land–atmosphere coupling on regional rainfall and convection     

Yue Zheng  Anil Kumar  Dev Niyogi 《Climate Dynamics》2015,44(9-10):2383-2409

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Effects of complex interaction of Rayleigh waves with tunnel on the free surface ground motion and the strain across the tunnel-lining     

J. P. Narayan  D. Kumar  D. Sahar 《Natural Hazards》2015,77(1):479-495

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Time-dependent seismicity analysis in the Northwest Himalaya and its adjoining regions     

P. Chingtham  R. B. S. Yadav  S. Chopra  Arabind Kumar Yadav  A. K. Gupta  P. N. S. Roy 《Natural Hazards》2016,80(3):1783-1800

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Active and break events of Indian summer monsoon during 1901–2014     

D. S. Pai  Latha Sridhar  M. R. Ramesh Kumar 《Climate Dynamics》2016,46(11-12):3921-3939

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Detrital zircon U–Pb geochronology of a Cenozoic foreland basin in Northeast India: Implications for zircon provenance during the collision of the Indian and Asian plates     

Upendra Baral  Ding Lin  Tapos Kumar Goswami  Mondip Sarma  Muhammad Qasim  Devojit Bezbaruah 《地学学报》2019,31(1):18-27

Geochronology is useful for understanding provenance, and while it has been applied to the central and western Himalaya, very little data are available in the eastern Himalaya. This study presents detrital zircon U–Pb ages from the late Palaeocene–Eocene Yinkiong Group in NE India. The samples are from the late Palaeocene to early Eocene Lower Yinkiong Formation, and the Upper Yinkiong Formation deposited during the early to mid‐Eocene within the Himalayan foreland basin. The U–Pb ages of the detrital zircon within the Lower Yinkiong Formation are older than late Palaeozoic, with a cratonic and early Himalayan Thrust Belt affinity, whereas the Cenozoic grains in the Upper Yinkiong Formation indicate a Himalayan Thrust Belt source and possibly a granitic body within the Asian plate. The shift of the sources and the changes in the foreland basin system strongly suggest that the India–Asia collision in the Eastern Himalaya began before or immediately after the deposition of the Upper Yinkiong Formation, i.e., within the early Eocene (c. 56 to 50 Ma).  相似文献