Fractionation of oxygen isotopes in phosphate during its interactions with iron oxides     

Deb P. Jaisi  Ruth E. Blake 《Geochimica et cosmochimica acta》2010,74(4):1309-4227

Iron (III) oxides are ubiquitous in near-surface soils and sediments and interact strongly with dissolved phosphates via sorption, co-precipitation, mineral transformation and redox-cycling reactions. Iron oxide phases are thus, an important reservoir for dissolved phosphate, and phosphate bound to iron oxides may reflect dissolved phosphate sources as well as carry a history of the biogeochemical cycling of phosphorus (P). It has recently been demonstrated that dissolved inorganic phosphate (DIP) in rivers, lakes, estuaries and the open ocean can be used to distinguish different P sources and biological reaction pathways in the ratio of ¹⁸O/¹⁶O (δ¹⁸O_P) in PO₄³⁻. Here we present results of experimental studies aimed at determining whether non-biological interactions between dissolved inorganic phosphate and solid iron oxides involve fractionation of oxygen isotopes in PO₄. Determination of such fractionations is critical to any interpretation of δ¹⁸O_P values of modern (e.g., hydrothermal iron oxide deposits, marine sediments, soils, groundwater systems) to ancient and extraterrestrial samples (e.g., BIF’s, Martian soils). Batch sorption experiments were performed using varied concentrations of synthetic ferrihydrite and isotopically-labeled dissolved ortho-phosphate at temperatures ranging from 4 to 95 °C. Mineral transformations and morphological changes were determined by X-Ray, Mössbauer spectroscopy and SEM image analyses.Our results show that isotopic fractionation between sorbed and aqueous phosphate occurs during the early phase of sorption with isotopically-light phosphate (P¹⁶O₄) preferentially incorporated into sorbed/solid phases. This fractionation showed negligible temperature-dependence and gradually decreased as a result of O-isotope exchange between sorbed and aqueous-phase phosphate, to become insignificant at greater than ∼100 h of reaction. In high-temperature experiments, this exchange was very rapid resulting in negligible fractionation between sorbed and aqueous-phase phosphate at much shorter reaction times. Mineral transformation resulted in initial preferential desorption/loss of light phosphate (P¹⁶O₄) to solution. However, the continual exchange between sorbed and aqueous PO₄, concomitant with this mineralogical transformation resulted again in negligible fractionation between aqueous and sorbed PO₄ at long reaction times (>2000 h). This finding is consistent with results obtained from natural marine samples. Therefore, ¹⁸O values of dissolved phosphate (DIP) in sea water may be preserved during its sorption to iron-oxide minerals such as hydrothermal plume particles, making marine iron oxides a potential new proxy for dissolved phosphate in the oceans.  相似文献   

The simulation of heavy rainfall episode over Mumbai: impact of horizontal resolutions and cumulus parameterization schemes     

Sanjib K. Deb  C. M. Kishtawal  V. S. Bongirwar  P. K. Pal 《Natural Hazards》2010,52(1):117-142

In this study, the simulation of an extreme weather event like heavy rainfall over Mumbai (India) on July 26, 2005 has been attempted with different horizontal resolutions using the Advanced Research Weather Research Forecast model version 2.0.1 developed at the National Center for Atmospheric Research (NCAR), USA. The study uses the Betts–Miller–Janjic (BMJ) and the Grell–Devenyi ensemble (GDE) cumulus parameterization schemes in single and nested domain configurations. The model performance was evaluated by examining the different predicted parameters like upper and lower level circulations, moisture, temperature, and rainfall. The large-scale circulation features, moisture, and temperature were compared with the National Centers for Environmental Prediction analyses. The rainfall prediction was assessed quantitatively by comparing rainfall from the Tropical Rainfall Measuring Mission products and the observed station values reported in the Indian Daily Weather Reports from India Meteorological Department (IMD). The quantitative validation of the simulated rainfall was done by calculating the categorical skill scores like frequency bias, threat scores (TS), and equitable threat scores (ETS). It is found that in all simulations, both in single and nested domains, the GDE scheme has outperformed the BMJ scheme for the simulation of rainfall for this specific event.  相似文献   

Climate Change Studies Using Coupled Model: Land Surface Perspective     

Sukanta Kumar Das  Sanjib Kumar Deb  C. M. Kishtawal  P. C. Joshi  Pradip Kumar Pal 《Journal of the Indian Society of Remote Sensing》2011,39(3):323-336

Community Climate System Model (CCSM3), a coupled model developed by National Center for Atmospheric Research (NCAR) containing atmosphere, ocean, sea-ice and land processes, simulation have been analysed for suitability in the Indian Monsoon region. A long control run of CCSM3 with constant forcing at every year has been done and the model climatology has been generated using 20 years of simulation. Atmospheric component of the model has been able to capture the large scale phenomena, however, regional monsoon variability not fully captured by the model simulation. A suitable modification in the flux coupler and the convective parameterization process in regional scale certainly improve the atmospheric part of the climate system. Another major component of the climate model is the representation of Land Surface Processes (LSP). A successful inclusion of LSP in climate model must address the issues related to the regional scale variation of the properties of LSP. A proper understanding of land surface processes is very crucial for climate simulations using numerical models. To understand the LSP-monsoon coupling, the offline Community Land Model (CLM), taken from CCSM3 land component, simulation forced with three hourly atmospheric boundary conditions have also been analyzed and compared with the CLM version of coupled CCSM mode. The distribution of surface heat flux in CCSM coupled mode shows some discrepancies compared to the offline CLM. Both the simulation results are compared with existing climatological features and assessment to improve CCSM3 for the regional climate change studies is made.  相似文献   

Crustal evolution and metallogeny in India     

Mihir Deb 《Journal of the Geological Society of India》2014,83(3):344-344

  相似文献   

Interaction of a Shield Structure with Surrounding Rock Strata Under Geo-static and Fatigue Loadings     

Islavath  Sreenivasa Rao  Deb  Debasis 《Geotechnical and Geological Engineering》2022,40(6):2949-2965

Geotechnical and Geological Engineering - Shields are deployed in a longwall panel to support incumbent rock strata and to protect shearer and persons working at the face. Shields undergo repeated...  相似文献   

Interaction between felsic granitoids and mafic dykes in Bundelkhand Craton: A field,petrographic and crystal size distribution study     

Tanwita Deb  Tapas Bhattacharyya 《Journal of Earth System Science》2018,127(7):102

In Bundelkhand Craton of central India, mafic dykes intruded when granitoids was partly crystallized. Cuspate–lobate boundary along the contact of granitoids and mafic magma indicates magma mingling in outcrop scale while textural evidence of mingling is represented by acicular apatite morphologies, titanite–plagioclase ocelli and ophitic–subophitic texture, mafic clots, resorbed plagioclase, and hornblende–zircon associations. Mingling also caused thermal exchange and fluid activity along the boundary between two coeval magmas. Crystal size distribution analyses for hornblende in the mafic rocks yield concave up curves which is also consistent with interaction of felsic and mafic magmas.  相似文献   

Impact of Kalpana-1 retrieved atmospheric motion vectors on mesoscale model forecast during summer monsoon 2011     

Inderpreet Kaur  Prashant Kumar  S. K. Deb  C. M. Kishtawal  P. K. Pal  Raj Kumar 《Theoretical and Applied Climatology》2015,120(3-4):587-599

  相似文献   

Racing climate change: Collaboration and conflict in California's global climate change policy arena     

Jonathan London  Alex Karner  Julie Sze  Dana Rowan  Gerardo Gambirazzio  Deb Niemeier 《Global Environmental Change》2013,23(4):791-799

Media accounts routinely refer to California's Assembly Bill 32 (AB 32), the Global Warming Solutions Act of 2006, as “landmark” climate change legislation. On its surface, this label is an accurate reflection of the state's forward-thinking stance across many environmental issues including pesticides, toxic substances, solid waste, and air quality. For all its promise, however, AB 32 can also be considered a low point in the landscape of conflict between state environmental regulators and California's environmental justice movement. While the legislation included several provisions to address the procedural and distributive dimensions of environmental justice, the implementation of AB 32 has been marked by heated conflict. The most intense conflicts over AB 32 revolve around the primacy of market mechanisms such as “cap and trade.” This article examines the drivers and the manifestations of these dynamics of collaboration and conflict between environmental justice advocates and state regulators, and pays particular attention to the scalar and racialized quality of the neoliberal discourse. The contentiousness of climate change politics in California offers scholars and practitioners around the world a cautionary tale of how the best intentions for integrating environmental justice principles into climate change policy do not necessarily translate into implementation and how underlying racialized fractures can upend collaboration between state and social movement actors.  相似文献   

An exact linearization and decoupling of the integral equations satisfied by time-dependent X- and Y-functions     

S. Karanjai  T. K. Deb 《Astrophysics and Space Science》1993,203(1):135-138

We discuss a simple method of linearization and decoupling of the integral equations satisfied by time-dependentX - andY -functions which play an important rôle in the study of non-stationary radiative transfer problems.  相似文献   

Similarity solutions for propagation of strong plane shock waves in an optically thin atmosphere     

G. Deb Ray  S. N. Banerjee 《Astrophysics and Space Science》1980,68(1):73-86

Similarity solutions, using Planck's diffusion approximation, for propagation of strong plane shock waves in an optically thin grey atmosphere of uniform density are obtained. Solutions for the ratio of specific heats 4/3 and several values of the radiation parameter are compared with those in the absence of any radiation. Excerpts from the results of integrations for different values of the ratio of specific heats are also given in Tables I-III.  相似文献