Probing for suitable climatology to estimate the predictability of monsoon onset over Kerala (MOK), India

Inter-annual variability in the onset of monsoon over Kerala (MOK), India, is investigated using daily temperature; mean sea level pressure; winds at 850, 500 and 200 hPa pressure levels; outgoing longwave radiation (OLR); sea surface temperature (SST) and vertically integrated moisture content anomaly with 32 years (1981–2013) observation. The MOK is classified as early, delayed, or normal by considering the mean monsoon onset date over Kerala to be the 1st of June with a standard deviation of 8 days. The objective of the study is to identify the synoptic setup during MOK and comparison with climatology to estimate the predictability of the onset type (early, normal, or delayed) with 5, 10, and 15 days lead time. The study reveals that an enhanced convection observed over the Bay of Bengal during early MOK is found to shift over the Arabian Sea during delayed MOK. An intense high-pressure zone observed over the western south Indian Ocean during early MOK shifts to the east during delayed MOK. Higher tropospheric temperature (TT) over the western Equatorial Ocean during early MOK and lower TT over the Indian subcontinent intensify the land–ocean thermal contrast that leads to early MOK. The sea surface temperature (SST) over the Arabian Sea is observed to be warmer during delayed than early MOK. During early MOK, the source of 850 hPa southwesterly wind shifts to the west equatorial zone while a COL region has been found during delayed MOK at that level. The study further reveals that the wind speed anomaly at the 200-hPa pressure level coincides inversely with the anomaly of tropospheric temperature.     

Influence of transient storage on stream nutrient uptake based on substrata manipulation

Quantification of the transient storage zone (A_s) has become critical in stream biogeochemical studies addressed to examine factors controlling nutrient uptake. It is expected that higher A_s may enhance the interaction between nutrients and biota and thus, increase nutrient uptake. However, results from the literature are controversial. We hypothesized that besides of the size of A_s, the intrinsic physical and biological characteristics of stream structures that generate A_s are also relevant for nutrient uptake. We performed 24 additions of phosphate, ammonium, and chloride in four reaches of a man-made channel where we introduced three types of naturally colonized substrata packs (mud, sand and cobbles) to modify A_s. We estimated ammonium and phosphate uptake coefficients in both the main channel and A_s using a solute transport model (OTIS-P) and compared the results among reaches with different substrata types. The introduction of substrata packs decreased water velocity and increased A_s similarly among treatments. Nutrient uptake coefficients in the main channel were similar among reaches with different type substrata packs; however, nutrient uptake coefficients measured in A_s differed among them as well as the ratio between ammonium and phosphorus uptake coefficients in A_s, which were 1.6 in reaches with mud packs and 0.02 in reaches with sand or cobble packs. Results obtained in this study suggest that the contribution of A_s in nutrient uptake not only depends on the size of A_s but on the type of materials used to increase A_s, and thus, have biogeochemical implications on restoration projects aimed to modify channel morphology.     

Fissures and fractures in the Koyna seismogenic zone,western India

Mn-rich ilmenites (up to 7 % MnO) have been identified in dykes cutting the Malanjkhand porphyry copper mining area in Madhya Pradesh. The dykes are hydrothermally altered and are of tholeiitic affinities. Lamprophyres have been reported from nearby areas. The presence of Mn-rich Ilmenites in the Malanjkhand copper mine dykes and the occurrence of lamprophyres and the pervasive potassium metasomatism in the area strongly suggests a possibility of finding diamondiferous rocks in the area. Such high-Mn bearing ilmenites are associated with diamondiferous deposits in other parts of the world, e.g. Juina kimberlites, Brazil. Mn-bearing ilmenite is considered as an indicator mineral for kimberlite/diamond occurrences. The presence of kimberlite pipes in Raipur district and the association of Mn-rich ilmenite with kimberlites is a fortuitous coincidence for venture-some mining companies. A probable explanation for the origin of manganese layers in the context of ‘rift’ tectonic environment is offered. Also a possible link between the dykes, quartz veins in the Malanjkhand granitic rocks and the copper mineralization is proposed.     

New REE and Trace Element Data on Two Kimberlitic Reference Materials by ICP-MS

Data on thirty-four minor and trace elements including all rare earth elements (REE) are reported for two kimberlitic international reference materials (SARM-39, MINTEK, RSA and MY-4, IGEM, Russia) by inductively coupled plasma-mass spectrometry (ICP-MS), some of them for the first time. Four digestion techniques (open acid, closed vessel acid, microwave and lithium metaborate fusion digestion) were used for the decomposition of samples for analysis by ICP-MS. Three other reference materials (USGS BHVO-1, CRPG BR-1 and ANRT UB-N) were analysed simultaneously using the same analytical methodology to assess the precision and accuracy of the determinations. The data obtained in this study compare well with working values wherever such values are available for comparison. Though open acid digestion was found to be very rapid, effective and convenient for the determination of several trace elements in kimberlitic samples, recoveries for heavy rare earth elements (HREE) were lower than the respective recoveries obtained by the other decomposition techniques used. The precision obtained was better than ± 6% RSD in the majority of cases with comparable accuracy. Chondrite-normalised plots of each RM for all the digestion techniques were smooth. The new data reported on the two kimberlitic reference materials make these samples useful for future geochemical studies of kimberlitic rocks.     

MEG Investigation of Low Pressure Silica — Shell model for polarization

We present a two-shell polarization model for the α-quartz and α-cristobalite structures. By allowing for polarization, we correct problems encountered in purely ionic bonding treatments of tetrahedrally coordinated silica phases. The shell model predicts zero pressure structures in very good agreement with experiment using no empirical parameters. The behavior of the shell model α-quartz lattice upon compression shows dramatic improvement over the distorted, rigid lattice given by the ionic model.     

A laboratory batch study on arsenic sorption and desorption on guava orchard soils of Baruipur,West Bengal,India

Groundwater contaminated with arsenic (As), when extensively used for irrigation, causes potentially long term detrimental effects to surface soils. Such contamination can also directly affect human health when irrigated crops, such as rice, vegetable and fruits, are used for human consumption. Therefore, an understanding of the sorption and desorption behavior of As in surface soils is of high importance, because these processes regulate the bioavailability of As in the soil environment. In this study, we have collected soils from guava orchards of Baruipur, West Bengal, and characterized soil chemistry and batch sorption and desorption behavior in the laboratory. The sorption and desorption behavior of As in the soils were examined using the Langmuir and Freundlich sorption equation. Regression analysis of the soil chemical characteristics and sorption equation parameters were also performed. The results suggest that the sorption behavior of arsenate is highly dependent on soil characteristics, specifically organic carbon, clay and Al₂O₃ content of the soils. Whereas desorption behavior is critically influenced by the presence of high concentrations of amorphous and/or crystalline Fe₂O₃ in the soils. Retention of the significant portion of As in the soils (~ 84% of the total) suggests that As in the orchard soils may not be highly bioavailable to plants for uptake. However, more detailed studies will be required to ascertain the role of individual soil components on the As sorption and desorption processes.     

Overprinting porphyry‐type veinlets on the intrusive rocks and phreatomagmatic breccias in the Southwest prospect,southwestern Sto. Tomas II (Philex), Baguio District,Philippines

The Southwest prospect is located at the southwestern periphery of the Sto. Tomas II porphyry copper–gold deposit in the Baguio District, northwestern Luzon, Philippines. The Southwest prospect hosts a copper‐gold mineralization related to a complex of porphyry intrusions, breccia facies, and overlapping porphyry‐type veinlets emplaced within the basement Pugo metavolcanics rocks and conglomerates of the Zigzag Formation. The occurrences of porphyry‐type veinlets and potassic alteration hosted in the complex are thought to be indications of the presence of blind porphyry deposits within the Sto. Tomas II vicinity. The complex is composed of at least four broadly mineralogically similar dioritic intrusive rocks that vary in texture and alteration type and intensity. These intrusions were accompanied with at least five breccia facies that were formed by the explosive brecciation, induced by the magmatic–hydrothermal processes and phreatomagmatic activities during the emplacement of the various intrusions. Hydrothermal alteration assemblages consisting of potassic, chlorite–magnetite, propylitic and sericite–chlorite alteration, and contemporaneous veinlet types were developed on the host rocks. Elevated copper and gold grades correspond to (a) chalcopyrite–bornite assemblage in the potassic alteration in the syn‐mineralization early‐mineralization diorite (EMD) and contemporaneous veinlets and (b) chalcopyrite‐rich mineralization associated with the chalcopyrite–magnetite–chlorite–actinolite±sericite veinlets contemporaneous with the chlorite–magnetite alteration. Erratic remarkable concentrations of gold were also present in the late‐mineralization Late Diorite (LD). High X_Mg of calcic amphiboles (>0.60) in the intrusive rocks indicate that the magmas have been oxidizing since the early stages of crystallization, while a gap in the composition of Al between the rim and the cores of the calcic amphiboles in the EMD and LD indicate decompression at some point during the crystallization of these intrusive rocks. Fluid inclusion microthermometry suggests the trapping of immiscible fluids that formed the potassic alteration, associated ore mineralization, and sheeted quartz veinlets. The corresponding formation conditions of the shallower and deeper quartz veinlets were estimated at pressures of 50 and 30 MPa and temperatures of 554 and 436°C at depths of 1.9 and 1.1 km. Temperature data from the chlorite indicate that the chalcopyrite‐rich mineralization associated with the chlorite–magnetite alteration was formed at a much lower temperature (ca. 290°C) than the potassic alteration. Evidence from the vein offsetting matrix suggests multiple intrusions within the EMD, despite the K‐Ar ages of the potassic alteration in EMD and hornblende in the LD of about the same age at 3.5 ± 0.3 Ma. The K‐Ar age of the potassic alteration was likely to be thermally reset as a result of the overprinting hydrothermal alteration. The constrained K‐Ar ages also indicate earlier formed intrusive rocks in the Southwest prospect, possibly coeval to the earliest “dark diorite” intrusion in the Sto. Tomas II deposit. In addition, the range of δ³⁴S of sulfide minerals from +1.8‰ to +5.1‰ in the Southwest prospect closely overlaps with the rest of the porphyry copper and epithermal deposits in the Sto. Tomas II deposit and its vicinity. This indicates that the sulfides may have formed from a homogeneous source of the porphyry copper deposits and epithermal deposits in the Sto. Tomas II orebody and its vicinity. The evidence presented in this work proves that the porphyry copper‐type veinlets and the adjacent potassic alteration in the Southwest prospect are formed earlier and at a shallower level in contrast with the other porphyry deposits in the Baguio District.     

Thermodynamics of U(VI) sorption onto Shewanella putrefaciens

We have conducted acid–base potentiometric titrations and U(VI) sorption experiments using the Gram negative, facultatively anaerobic bacterium Shewanella putrefaciens. Results of reversed titration studies on live, inactive bacteria indicate that their pH-buffering properties result from the equilibrium ionization of three discrete populations of functional groups. Carboxyl (pK_a=5.16±0.04), phosphoryl (pK_a=7.22±0.15) and amine (pK_a=10.04±0.67) groups most likely represent these three resolvable functionalities, based on their pK_a values. Site densities for carboxyl, phosphoryl and amine groups on the bacterial surface were approximately 31.7 μmol sites/g bacteria (0.35±0.02 sites/nm²), 8.95 μmol/g (0.11±0.007 sites/nm²) and 38.0 μmol/g (0.42±0.008 sites/nm²), respectively, based on an estimated bacterial specific surface area of 55 m²/g. Sorption experiments showed that U(VI) can reversibly complex with the bacterial surface in the pH 2–8 interval, with maximum adsorption occurring at a pH of 5. Sorption is not strongly sensitive to ionic strength (NaCl) in the range 0.02–0.10 M. The pH and ionic strength dependence of U(VI) sorption onto S. putrefaciens is similar to that measured for metal-oxide surfaces and Gram positive bacteria, and appears to be similarly governed by competitive speciation constraints. Measured U(VI) sorption is accounted for by using two separate adsorption reactions forming the surface complexes >COO–UO₂⁺ and >PO₄H–UO₂(OH)₂. Using S. putrefaciens as a model organism for dissimilatory metal-reducing Gram negative anaerobes, our results extend the applicability of geochemical speciation models to include bacteria that are capable of reductively solubilizing or precipitating a wide variety of environmentally and geologically important metals and metallic species.     

Geochemical characteristics of Holocene sediments from Chuadanga district,Bangladesh: Implications for weathering,climate, redox conditions,provenance and tectonic setting

The present research deals with the geochemical characteristics of the Holocene sediments from Alamdanga area, Chuadanga district, Bangladesh. Main goals of the study are to delineate source rock characteristics, degree of chemical weathering and sorting processes and behavior of redox conditions during deposition of the sediments. Geochemical characteristics of the sediments show comparatively a wide variation in accordance with stratigraphy in their major element contents （e.g. SiO2 69.46-82.13, A1203 2.28-8.88 in wt%）, reflecting the distinctive provenance and in part an unstable period in terms of tectonic activity. Geochemical classification of the sediments shows mostly sub-arkose with few sub-litharenites. Some major and trace elements display comprehensible correlation with A1203 confirming their possible hydraulic fraetionation. The chemical index of alteration （CIA＊）, W＊ index, index of compositional variability （ICV）, plagioclase index of alteration （PIA＊） values and the ratio of SIO2/Al2O3, suggest low degrees of chemical weathering in the source areas as well as immature to moderately mature the sediments. The sediments suggest semi-arid climatic trends within oxic deltaic depositional conditions during the Holocene, at 3-12 ka. Whole rock geochemistry and discrimination diagrams demonstrate the continental signature derivatives, which might have been derived from the felsic to intermediate igneous rocks （granitic plutonic rocks） as well as from quartzose sedimentary/metamorphic provenance. These typical sources are present in a vast region of the Himalayan belt and catchment areas of Ganges. The tectonic setting of the sediments demarcates typically passive margin with slightly continental arc system.