Petrographic and trace-element distribution studies on the dolomite-calcite in the regional metamorphic marble of the Griesscharte,Tyrol, Austria/Italy

Petrographic investigations on the light yellow marble outcrops in the Griesscharte, Tyrol, Austria/Italy revealed them to be dolomite. The white to blue-grey veins in these marbles were those of calcite. Inside these calcites and along the calcite-dolomite phase boundaries minute and microscopically unidentifiable crystallites (? 10 μ) were observed. These crystallites were recognised by X-ray diffractometry as dolomite and their form and distribution were established by scanning electron microscopy. Trace-element distributions on the calcite-dolomite neighbours were studied by neutron-activation method to elucidate the formation mechanism of these calcites in the marble.Genetic relationships of the dolomite crystallites, the calcite host and the surrounding dolomite marble have been discussed in the light of the petrographic and chemical studies. These findings substantiate a deposition of a new formed vein of calcite from the solution circulating in the fissures of the dolomite marble during prograde metamorphism rather than a simple deposition of mobilized sedimentary calcite. The dolomite crystallites in the calcite seem to have been formed post-tectonically, partly by the nucleation in the calcite cleavage planes during Mg-metasomatism and partly from the exsolutions during retrograde metamorphism.     

Indian summer monsoon rainfall variability during 2014 and 2015 and associated Indo-Pacific upper ocean temperature patterns

Theoretical and Applied Climatology - In this study, factors responsible for the deficit Indian Summer Monsoon (ISM) rainfall in 2014 and 2015 and the ability of Indian Institute of Tropical...     

North Indian Ocean warming and sea level rise in an OGCM

The variability in the long-term temperature and sea level over the north Indian Ocean during the period 1958–2000 has been investigated using an Ocean General Circulation Model, Modular Ocean Model version 4. The model simulated fields are compared with the sea level observations from tide-gauges, Topex/Poseidon (T/P) satellite, in situ temperature profile observations from WHOI moored buoy and sea surface temperature (SST) observations from DS1, DS3 and DS4 moored buoys. It is seen that the long (6–8 years) warming episodes in the SST over the north Indian Ocean are followed by short episodes (2–3 years) of cooling. The model temperature and sea level anomaly over the north Indian Ocean show an increasing trend in the study period. The model thermocline heat content per unit area shows a linear increasing trend (from 1958–2000) at the rate of 0.0018 × 10¹¹ J/m² per year for north Indian Ocean. North Indian Ocean sea level anomaly (thermosteric component) also shows a linear increasing trend of 0.31 mm/year during 1958–2000.     

Influence of magnesium on the ion-activity product of calcium and carbonate dissolved in seawater: A new approach

The influence of Mg²⁺ ions on the ion-activity product of calcium and carbonate dissolved in seawater has been investigated. The present approach is based mainly on: (1) the preponderance of this element in the marine system; (2) the observations by Weyl (1965), Jansen and Kitano (1963), and more recently by Plummer and Mackenzie (1974) on the higher solubility of magnesian calcite relative to pure calcite; and (3) the inferences drawn from our laboratory studies on the Ca²⁺—Mg²⁺ ion-exchange behaviour on surfaces of pure calcite. From these considerations, the pK value corresponding to a calcite containing 12 mole% of MgCO, has been estimated to be 7.7± 0.1 at 20°C. This value has serious reflections on the extent of saturation of seawater with respect to calcium-carbonate polymorphs. The reassessed degree of carbonate saturation for an average warm-surface ocean turns out to be only between 1.0 and 2.2.     

A model study on oceanic processes during the Indian Ocean Dipole termination

In this study, the processes affecting the temperature variability over the Southeastern Tropical Indian Ocean (STIO) during 1958–2000, accomplishing the positive and negative Indian Ocean Dipole (IOD) events are analyzed. The upper ocean heat budget analysis of the STIO has been carried out to understand the oceanic process during the termination of the recent strongest IOD events. The three recent strongest positive IOD events (1961, 1994 and 1997) and a strong negative IOD event (1996) are considered for detailed analysis. The heat budget analysis revealed that the positive net-surface heat flux and vertical advection played dominant roles in the termination of 1997 IOD event, whereas horizontal and vertical advections are responsible for the termination of IOD events during 1961 and 1994. The anomalous negative surface heat flux and horizontal advection caused the dipole termination during the negative dipole year 1996. The findings are well supported by the analysis of anomaly correlation between model upper ocean heat content tendency and heat budget components. Significant intra-seasonal oscillations (ISOs) in sea surface temperature (SST) anomaly are seen during the initial phase of termination in the eastern equatorial Indian Ocean during 1961 and 1994 IOD events. The influence of ISOs in SST is not so evident during the IOD termination in 1997. It is found that the termination processes have started more than a month prior to the actual IOD termination.     

The application of Tb/Ca-Tb/La abundance ratios to problems of fluorspar genesis

A comprehensive review of the authors' and their co-workers' results on the fractionation of Rare Earth Elements (REE) during the crystallization and/or recrystallization of Fluorspar is given. The fractionation can be explained as the result of REE complexation in the ore forming solution and systematic changes in distribution coefficients of REE. It is shown that the Tb/Ca and Tb/La ratios are sufficient to characterize pegmatitic (pneumatolytic), hydrothermal and sedimentary fluorspar. This has been confirmed by numerous investigations on various types of deposits.     

An investigation on dewatering kinetics of ultrafine coal

Ultrafine coal dewatering is of great importance to the coal industry due to its impacts on the handling and utilization characteristics of coal products. Commercially available filtration techniques are either ineffective or costly for dewatering of ultrafine coal to the desired moisture level of about 20%. Considerable efforts have been devoted to understanding the dewatering process and developing new technologies for applications in the coal industry. Most of the previous work on ultrafine coal filtration was focused on the final filter cake moisture and few studies have been conducted to investigate the filtration kinetics. The present investigation was undertaken to better understand the kinetics of vacuum filtration of ultrafine coal under various conditions. The filtrate weight was continuously monitored using a precise load cell during the entire filtration process. Operating parameters such as vacuum pressure and reagent conditioning time were examined for their impacts on filtration kinetics. Use of cationic and anionic flocculants showed significant improvement in filtration kinetics. Kinetic data obtained from the study were used to determine the fundamental parameters of filtration such as cake permeability, specific cake resistance, and filter medium resistance using the integrated form of the Darcy's law.