Fluxes of material in the Arabian Sea and Bay of Bengal — Sediment trap studies

In order to investigate how monsoons influence biogeochemical fluxes in the ocean, twelve time-series sediment traps were deployed at six locations in the northern Indian Ocean. In this paper we present particle flux data collected during May 1986 to November 1991 and November 1987 to November 1992 in the Arabian Sea and Bay of Bengal respectively. Particle fluxes were high during both the SW and NE monsoons in the Arabian Sea as well as in the Bay of Bengal. The mechanisms of particle production and transport, however, differ in both the regions. In the Arabian Sea, average annual fluxes are over 50gm^-2y^-1 in the western Arabian Sea and less than 27gm^-2 y^-1 in the central part. Biogenic matter is dominant at sites located near upwelling centers, and is less degraded during peak flux periods. High particle fluxes in the offshore areas of the Arabian Sea are caused by injection of nutrients into the euphotic zone due to wind-induced mixed layer deepening. In the Bay of Bengal, average annual fluxes are highest in the central Bay of Bengal (over 50gm^-2y^-1) and are least in the southern part of the Bay (37gm^-2y^-1). Particle flux patterns coincide with freshwater discharge patterns of the Ganges-Brahmaputra river system. Opal/carbonate and organic carbon/carbonate carbon ratios increase during the SW monsoon due to variations in salinity and productivity patterns in the surface waters as a result of increased freshwater and nutrient input from rivers. Comparison of S years data show that fluxes of biogenic and lithogenic particulate matter are higher in the Bay of Bengal even though the Arabian Sea is considered to be more productive. Our results indicate that in the northern Indian Ocean interannual variability in organic carbon flux is directly related to the strength and intensity of the SW monsoon while its transfer from the upper layers to the deep sea is partly controlled by input of lithogenic matter from adjacent continents.     

Evaluating pedogenesis and soil Atterberg limits for inducing landslides in the Western Ghats,Idukki District of Kerala,South India

Natural Hazards - In the Western Ghats of India, the soil properties, particularly Atterberg limits, are of relevance to the landslides. Pedogenic processes in the Western Ghats and plateaus on it...     

Changes in the angular separation of the lensed images PKS 1830-211 NE & SW

We present 8 epochs of 7 mm dual-polarization VLBA observations of the gravitational lens system PKS 1830-211 made over the course of 14 weeks. Clear changes in the relative positions of the cores of up to 80 μarcseconds (μas) were observed between epochs (each separated by ≈2 weeks). A comparison with previous 7 mm VLBA maps shows that the separation of the cores has changed by almost 280 μas over 12 months. This leads us to conclude that changes in the brightness distribution of the mm-VLBI core of the background source must be occurring rapidly. This is the first clear observation of significant radio source evolution in a gravitational lens system. It is also the first time that changes in source structure have been detected in a distant extra-galactic source on such short time-scales. This is partly accounted for by the magnification provided by the lens system.     

Isolating the impacts of anthropogenic water use within the hydrological regime of north India

The effects of anthropogenic water use play a significant role in determining the hydrological cycle of north India. This paper explores anthropogenic impacts within the region's hydrological regime by explicitly including observed human water use behaviour, irrigation infrastructure and the natural environment in the CHANSE (Coupled Human And Natural Systems Environment) socio-hydrological modelling framework. The model is constrained by observed qualitative and quantitative information collected in the study area, along with climate and socio-economic variables from additional sources. Four separate scenarios, including business as usual (BAU, representing observed irrigation practices), groundwater irrigation only (where the influence of the canal network is removed), canal irrigation only (where all irrigation water is supplied by diverted surface water) and rainfed only (where all human interventions are removed) are used. Under BAU conditions the modelling framework closely matched observed groundwater levels. Following the removal of the canal network, which forces farmers to rely completely on groundwater for irrigation, water levels decrease, while under a canal-only scenario flooding occurs. Under the rainfed-only scenario, groundwater levels similar to current business-as-usual conditions are observed, despite much larger volumes of recharge and discharge entering and leaving the system under BAU practices. While groundwater abstraction alone may lead to aquifer depletion, the conjunctive use of surface and groundwater resources, which includes unintended contributions of canal leakage, create conditions similar to those where no human interventions are present. Here, the importance of suitable water management practices, in maintaining sustainable water resources, is shown. This may include augmenting groundwater resources through managed aquifer recharge and reducing the impacts on aquifer resources through occasional canal water use where possible. The importance of optimal water management practices that highlight trade-offs between environmental impact and human wellbeing are shown, providing useful information for policy makers, water managers and users. © 2019 John Wiley & Sons, Ltd.     

Limno-tolerant bacteria govern nitrate concentration in Mandovi Estuary,India

The spatial and temporal abundances of limno-tolerant and halo-tolerant bacteria were investigated in the tide-dominated Mandovi estuary along the west coast of India. These investigations were carried out in relation to various environmental parameters on a monthly basis at three fixed stations for a year. On an annual basis, the estuary showed an average salinity of 28.2, 17.4, and 12.6 at the mouth, midstream and upstream region. Halo-tolerant retrievable count (HTRC) and limno-tolerant retrievable count (LTRC) of bacteria were in the order of 10⁶ L⁻¹. Among the environmental parameters, a strong negative relationship between salinity and nitrate (r = −0.806; p < 0.001) suggested that 64% of the variation could be due to fresh water influence in the estuary. The limno-tolerant retrievable count (LTRC) brought about 23% variations in nitrate concentration. This influence was maximum during the monsoon (r = 0.522; p < 0.05) especially in the surface waters (r = 0.624; p < 0.001) suggesting nitrate reduction by LTRC. Measurements of nitrate reducing activity (NRA) in whole-water samples along the salinity gradient in the estuary also revealed higher reduction rates at lower salinity upstream. This was further confirmed by culture experiments where the limno-tolerant bacteria showed higher NRA than halo-tolerant forms. It is therefore suggested that LTRC is more actively involved in the variation of nitrate that enters the Mandovi estuary particularly during the monsoon.     

Tidal switch on metabolic activity: Salinity induced responses on bacterioplankton metabolic capabilities in a tropical estuary

“Biolog” plates were used to study the changes in the metabolic capabilities of bacterioplankton over a complete tidal cycle in a tropical ecosystem (Cochin Estuary) along southwest coast of India. The pattern of utilization of carbon sources showed a definite shift in the community metabolism along a salinity gradient. Multivariate statistical analysis revealed two communities, namely allochthonous bacterioplankton sensitive to salinity and autochthonous bacterioplankton, which are tolerant to wide salinity fluctuations. Regression analysis showed salinity as the most important parameter influencing the physiological profile of bacterioplankton, irrespective of tide. Apart from salinity, limno-tolerant retrievable counts and halo-tolerant retrievable counts also accounted for the metabolic variation of bacterioplankton during low and high tides, respectively. The shift in the substrate utilization from carbohydrates to amino acids appears to be due to the physiological adaptation or nitrogen limitation of bacterial community with increasing salinity.     

Simulation of coastal winds along the central west coast of India using the MM5 mesoscale model

A high-resolution mesoscale numerical model (MM5) has been used to study the coastal atmospheric circulation of the central west coast of India, and Goa in particular. The model is employed with three nested domains. The innermost domain of 3 km mesh covers Goa and the surrounding region. Simulations have been carried out for three different seasons—northeast (NE) monsoon, transition period and southwest (SW) monsoon with appropriate physics options to understand the coastal wind system. The simulated wind speed and direction match well with the observations. The model winds show the presence of a sea breeze during the NE monsoon season and transition period, and its absence during the SW monsoon season. In the winter period, the synoptic flow is northeasterly (offshore) and it weakens the sea breeze (onshore flow) resulting in less diurnal variation, while during the transition period, the synoptic flow is onshore and it intensifies the sea breeze. During the northeast monsoon at an altitude of above 750 m, the wind direction reverses, and this is the upper return current, indicating the vertical extent of the sea breeze. A well-developed land sea breeze circulation occurs during the transition period, with vertical extension of 300 and 1,100 m, respectively.     

Sound speed variation in the coastal waters off Cochin and signature of subsurface maxima

Ocean Dynamics - We investigated the vertical and horizontal variation of the sound speed using the Thermodynamic Equation Of Seawater-2010 (TEOS-10) and monthly CTD observations at Cochin estuary...     

Adsorption of oleate on fluorite surface as revealed by atomic force microscopy

The adsorption of oleic acid / oleate on fluorite surface could be visualized using tapping mode of atomic force microscopy (AFM). The natural fluorite crystals were equilibrated with 10^− 3 to 10^− 7 M oleate solutions and their AFM images at each concentration along with height profiles were recorded. Even at low oleate concentration of 1 × 10^− 7 M, concomitant monolayer and bilayer structures were observed. It suggests that normal–normal bonding of hydrocarbon chains takes place before the surface is completely covered by the monolayer. Multi-layer adsorption of oleate was observed at oleate concentrations of above 10^− 4 M. The tapping mode AFM can be utilized to visualize the topography of surfaces adsorbed with surfactant molecules.