Regolith mass balance inferred from combined mineralogical, geochemical and geophysical studies: Mule Hole gneissic watershed, South India   总被引：3，自引：0，他引：3  

Jean-Jacques Braun  Marc Descloitres  Jean Riotte  Simon Fleury  Jean-Loup Boeglin  Eva Lacarce  M. Sekhar  M.S. Mohan Kumar  S. Subramanian  Bernard Dupré 《Geochimica et cosmochimica acta》2009,73(4):935-24

The aim of this study is to propose a method to assess the long-term chemical weathering mass balance for a regolith developed on a heterogeneous silicate substratum at the small experimental watershed scale by adopting a combined approach of geophysics, geochemistry and mineralogy. We initiated in 2003 a study of the steep climatic gradient and associated geomorphologic features of the edge of the rifted continental passive margin of the Karnataka Plateau, Peninsular India. In the transition sub-humid zone of this climatic gradient we have studied the pristine forested small watershed of Mule Hole (4.3 km²) mainly developed on gneissic substratum. Mineralogical, geochemical and geophysical investigations were carried out (i) in characteristic red soil profiles and (ii) in boreholes up to 60 m deep in order to take into account the effect of the weathering mantle roots. In addition, 12 Electrical Resistivity Tomography profiles (ERT), with an investigation depth of 30 m, were generated at the watershed scale to spatially characterize the information gathered in boreholes and soil profiles. The location of the ERT profiles is based on a previous electromagnetic survey, with an investigation depth of about 6 m. The soil cover thickness was inferred from the electromagnetic survey combined with a geological/pedological survey.Taking into account the parent rock heterogeneity, the degree of weathering of each of the regolith samples has been defined using both the mineralogical composition and the geochemical indices (Loss on Ignition, Weathering Index of Parker, Chemical Index of Alteration). Comparing these indices with electrical resistivity logs, it has been found that a value of 400 Ohm m delineates clearly the parent rocks and the weathered materials. Then the 12 inverted ERT profiles were constrained with this value after verifying the uncertainty due to the inversion procedure. Synthetic models based on the field data were used for this purpose. The estimated average regolith thickness at the watershed scale is 17.2 m, including 15.2 m of saprolite and 2 m of soil cover.Finally, using these estimations of the thicknesses, the long-term mass balance is calculated for the average gneiss-derived saprolite and red soil. In the saprolite, the open-system mass-transport function τ indicates that all the major elements except Ca are depleted. The chlorite and biotite crystals, the chief sources for Mg (95%), Fe (84%), Mn (86%) and K (57%, biotite only), are the first to undergo weathering and the oligoclase crystals are relatively intact within the saprolite with a loss of only 18%. The Ca accumulation can be attributed to the precipitation of CaCO₃ from the percolating solution due to the current and/or the paleoclimatic conditions. Overall, the most important losses occur for Si, Mg and Na with −286 × 10⁶ mol/ha (62% of the total mass loss), −67 × 10⁶ mol/ha (15% of the total mass loss) and −39 × 10⁶ mol/ha (9% of the total mass loss), respectively. Al, Fe and K account for 7%, 4% and 3% of the total mass loss, respectively. In the red soil profiles, the open-system mass-transport functions point out that all major elements except Mn are depleted. Most of the oligoclase crystals have broken down with a loss of 90%. The most important losses occur for Si, Na and Mg with −55 × 10⁶ mol/ha (47% of the total mass loss), −22 × 10⁶ mol/ha (19% of the total mass loss) and −16 × 10⁶ mol/ha (14% of the total mass loss), respectively. Ca, Al, K and Fe account for 8%, 6%, 4% and 2% of the total mass loss, respectively.Overall these findings confirm the immaturity of the saprolite at the watershed scale. The soil profiles are more evolved than saprolite but still contain primary minerals that can further undergo weathering and hence consume atmospheric CO₂.  相似文献   

Great Eastern Japan Earthquake--possible marine environmental contamination by toxic pollutants     

Tanabe S  Subramanian A 《Marine pollution bulletin》2011,62(5):883-884

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Dielectric constants of chrysoberyl,spinel, phenacite,and forsterite and the oxide additivity rule     

R. D. Shannon  M. A. Subramanian 《Physics and Chemistry of Minerals》1989,16(8):747-751

The dielectric constants and dielectric loss values of BeAl₂O₄ (chrysoberyl), MgAl₂O₄ (spinel), Be₂SiO₄ (phenacite), and Mg₂SiO₄ (forsterite) were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: chrysoberyl, κ′ _a =9.436, κ′ _b =9.071, κ′ _c =8.269; spinel, κ′ _a =8.18; phenacite, κ′ _a =6.28, κ′ _c =6.06; and forsterite, κ′ _a =6.867, κ′ _b =7.392, κ′ _c =6.739. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to α_D(M₂M′X₄) = 2α_D(MX)+α_D(M′X₂) is ~ 1.0%.  相似文献   

Wind-wave relationship for bay of Bengal from GEOSAT data     

Usha Natesan  S P Subramanian 《Journal of the Indian Society of Remote Sensing》1992,20(2-3):159-164

Stellite Remote Sensing is an emerging technique for observation of oceans. The important oceanic parameters, wave heights and wind speeds derived fron GEOSAT Altimeter data, are analysed in the present paper. Relation between wind speed and height of ‘sea waves’ are obtained for southwest monsoon, northeast monsoon and nonmonsoon seasons, and regression equations are arrived at for each case. Good correlation and high accuracy are observed for all the seasons. This assures the usage of remotely sensed data for oceanic studies.  相似文献   

The variational technique of data assimilation using adjoint equations in a shallow water model     

Sujit Basu  V Subramanian  P C Pandey 《Journal of Earth System Science》1993,102(4):521-536

The variational technique of data assimilation using adjoint equations has been illustrated using a nonlinear oceanographic shallow water model. The technique consists of minimizing a cost function representing the misfit between the model and the data subject to the model equations acting as constraints. The problem has been transformed into an unconstrained one by the use of Lagrange multipliers. Particular emphasis has been laid on finite difference formulation of the algorithm. Several numerical experiments have been conducted using simulated data obtained from a control run of the model. Implications of this technique for assimilating asynoptic satellite altimeter data into ocean models have been discussed.  相似文献   

Angular momentum transport in quasi-Keplerian accretion disks     

Prasad Subramanian  B. S. Pujari  Peter A. Becker 《Journal of Astrophysics and Astronomy》2004,25(1-2):81-91

We reexamine arguments advanced by Hayashi & Matsuda (2001), who claim that several simple, physically motivated derivations based on mean free path theory for calculating the viscous torque in a quasi-Keplerian accretion disk yield results that are inconsistent with the generally accepted model. If correct, the ideas proposed by Hayashi & Matsuda would radically alter our understanding of the nature of the angular momentum transport in the disk, which is a central feature of accretion disk theory. However, in this paper we point out several fallacies in their arguments and show that there indeed exists a simple derivation based on mean free path theory that yields an expression for the viscous torque that is proportional to the radial derivative of the angular velocity in the accretion disk, as expected. The derivation is based on the analysis of the epicyclic motion of gas parcels in adjacent eddies in the disk.  相似文献   

Primordial magnetic fields in the post-recombination era and early reionization     

Shiv K. Sethi  Kandaswamy Subramanian 《Monthly notices of the Royal Astronomical Society》2005,356(2):778-788

We explore the ways in which primordial magnetic fields influence the thermal and ionization history of the post-recombination Universe. After recombination, the Universe becomes mostly neutral, resulting also in a sharp drop in the radiative viscosity. Primordial magnetic fields can then dissipate their energy into the intergalactic medium via ambipolar diffusion and, for small enough scales, by generating decaying magnetohydrodynamics turbulence. These processes can significantly modify the thermal and ionization history of the post-recombination Universe. We show that the dissipation effects of magnetic fields, which redshifts to a present value   B ₀= 3 × 10⁻⁹ G  smoothed on the magnetic Jeans scale and below, can give rise to Thomson scattering optical depths  τ≳ 0.1  , although not in the range of redshifts needed to explain the recent Wilkinson Microwave Anisotropy Probe ( WMAP ) polarization observations. We also study the possibility that primordial fields could induce the formation of subgalactic structures for   z ≳ 15  . We show that early structure formation induced by nanoGauss magnetic fields is potentially capable of producing the early reionization implied by the WMAP data. Future cosmic microwave background observations will be very useful to probe the modified ionization histories produced by primordial magnetic field evolution and constrain their strength.  相似文献   

Geomorphic analysis of Chilka lake and adjoining area using remotely sensed data     

D. P. Rao  S. K. Subramanian  R. Sudarshana 《Journal of the Indian Society of Remote Sensing》1986,14(2):53-61

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Sediment and heavy metal accumulation in the Cauvery basin   总被引：2，自引：0，他引：2  

A. L. Ramanathan  V. Subramanian  B. K. Das 《Environmental Geology》1996,27(3):155-163

Eleven cores were collected from the Cauvery basin. Radiometric dates were used to determine modern sediment accumulation rates. Sediment accumulation rates ranged from 0.4 to 4 mm yr^–. Heavy metal concentration decreases with the increase of depth. The heavy metal concentrations at certain depths are attributed to the irregular input of metals and their remobilization. Heavy metal accumulations have been computed using sediment accumulation rates, and accumulation rates show an additional anthropogenic input of metals and sediments in the recent past. Factor analysis and correlation analysis show the diverse source and accumulation mechanism influencing the metal distribution in the basin.  相似文献   

Input by Indian rivers into the world oceans     

V Subramanian 《Journal of Earth System Science》1978,87(7):77-88

The chemical, sediment and total load carried by the major river basins in India—Ganges, Brahmaputra, Indus (Jhelum), Godavari, Krishna, Narmada, Tapti, Mahnadi and Cauvery have been calculated, based partly on new set of data and partly on existing data. There is a significant amount of chemical load transported by all the Indian rivers, and for global mass transfer calculation, these cannot and should not be ignored. The chemical mass transfer during the monsoon is not surprisingly small, as would be expected for excess discharge and dilution controlled run-off. The sediment mass transfer from non-Himalyan rivers, all within the same range of magnitude, accounts for less than a tenth of that of the Ganges but during the monsoon, except for Cauvery, all the Indian rivers carry a sediment load of greater than 1000 ppm. The total mass transfer from the Indian subcontinent accounts for 6·5 per cent of the global transfer. Except for the Ganges and the Brahmaputra, the erosion rates are similar for all Indian basins, independent of their size and these rates are agreeable with the continental earth average. The Ganges-Brahmaputra basin erosion rates are highest on the continental earth. Based on the average rate of denudation of the Indian subcontinent, the mean elevation of this landmass will be that of the present day mean sea level in 5 million years from now. The average denudation rate of 2·1 cm/100 years is different from the calculated average sedimentation rate of 2·1 cm/100 years is different from the calculated average sedimentation rate of 6·7 cm/100 years in the Bay of Bengal suggesting that an accurate erosion rate in the continent is needed to determine sedimentation rate in the oceans. The chemical and sediment mass transfer rates appear to have a logarithmic linear relationship on a global scale, as against the reported negative logarithmic trend for North America alone.  相似文献