Durbar Ray | National Institute of Oceanography (original) (raw)

Papers by Durbar Ray

Environmental Science and Pollution Research

Environmental Monitoring and Assessment

Chemical Geology, 2020

Ferromanganese crusts collected at selected locations along the ~7000 km long stretch of Carlsber... more Ferromanganese crusts collected at selected locations along the ~7000 km long stretch of Carlsberg, Central Indian and Southwest Indian ridges are studied for bulk geochemical composition and distribution of rare earths and yttrium in major geochemical phases; exchangeable/carbonate, Mn-oxide, Fe-oxyhydroxide and residual silicate. The crusts are dominated by vernadite with traces of quartz and calcite. A high concentrations of major (Fe, Mn), trace (Co, Ni, Cu & Zn) and rare earth elements indicates that these crusts are hydrogenous in nature. However, the negative or no cerium anomalies in the shale normalized REE pattern indicates that some of these crusts are of mixed type (hydrogenous and hydrothermal). Irrespective of their nature (mixed or hydrogenous), the phase distribution of REE-Y shows 70–83% of total REE-Y are associated with Fe-oxyhydroxide phase, whereas only about 17–30% are associated with Mn-oxide phase. Such phase-distribution is expected in mixed type crusts beca...

Environmental pollution, 2021

The versatile use of various synthetic polymers, including plastics, generates a large volume of ... more The versatile use of various synthetic polymers, including plastics, generates a large volume of non-degradable waste, which is eventually responsible for forming microplastics (MPs) in aquatic environments. The present study describes the significant spatial and seasonal variation on the abundance of MPs and their physiochemical nature along the Mandovi-Zuari estuarine system of Goa, west coast of India. During the wet season (September), the average abundance of MPs was found relatively higher in water (0.107 particles/m3) and sediment (7314 particles/kg) than those found in the dry season (April) (0.099 particles/m3 in water and 4873 particles/kg in sediment). During the wet season, heavy rain and excessive riverine freshwater influx carry more terrestrial plastic debris in the estuarine system which causes higher averages MPs density in surface water and sediment. <300 μm sized particles and black colored MPs were predominant equally in water and sediment during both seasons....

Current Science, 2008

Recently, an unusually large hydrothermal event (CR-2003) was reported over the slow-spreading Ca... more Recently, an unusually large hydrothermal event (CR-2003) was reported over the slow-spreading Carlsberg Ridge between 05°41'N, 61°30'E and 06°20'N, 60°33'E. To investigate the after effects (if any) of such a large-scale emission, almost a year later in July 2004, the water column along the 50 km ridge segment was surveyed. Results show that while the thermal and optical signatures have largely reduced with time, the chemical signatures do persist between 2500 and 2900 m. Geochemical features like Fe/Mn, Mn/heat ratios, characteristic of event plume, also show major changes. Distribution of dissolved manganese, methane, helium-3 and suspended particulates further down the water column was indicative of one more plume layer between 3150 and 3400 m. The high volatile and less particulate metal content of the deep layer points towards a relatively fresh event.

Mercury (Hg) is a toxic element which accumulates in fish and other aquatic organisms from variou... more Mercury (Hg) is a toxic element which accumulates in fish and other aquatic organisms from various sources and poses potential risk to the consumers. Methylmercury (MeHg), the common organic species of mercury, usually forms in aquatic environments and is known for neurotoxicity. In this study, the concentration of total Hg and MeHg in 12 commercial species of fish, shellfish, prawn, and crab from coastal areas of Goa were investigated. The total Hg contents varied between 18.5 -260 μg/kg; while the concentration of MeHg had a range of 7.2 -129 μg/kg. Both the ranges were well below the values recorded at other polluted coastal sites and also meet the permissible limits for human consumption. The interspecies comparison shows species from pelagic and benthic habitats with different food habits have significant difference in body loads of total Hg and MeHg, which increases across the trophic levels. The exposure to higher level of Hg in sediment is likely responsible for enhanced bio...

This study highlights the behaviour of Mercury in the abiotic and biotic segments of the Mandovi-... more This study highlights the behaviour of Mercury in the abiotic and biotic segments of the Mandovi-Zuari estuarine system. Spatial, seasonal (Premonsoon and Postmonsoon) and tidal, distribution of THg in dissolved / particulate fractions , sediment concentrations were mapped of the river mouths , Mormugao Port, inner and outer environs of this estuarine system. Observed seasonal partition studies provided an insight into the removal of the metal into the particulate fraction and subsequent deposition in sediments in the postmonsoon. Bioconcentration factor provided a link in the Hg cycle between the abiotic and biotic compartments of this ecosystem. Metal contaminations in different tissues of biota representing different trophic levels were evaluated by calculating the bioconcentration factor. Although biomagnification and bioaccumulation was observed in the representative biota of commercial importance, the observed total mercury levels are well within the safety limit 0.5ppm set by...

We analyzed iron and sulfur isotopic compositions of polymetallic sulfides from an extinct hydrot... more We analyzed iron and sulfur isotopic compositions of polymetallic sulfides from an extinct hydrothermal mound near the Kings Triple Junction of the northern Lau basin belonging to a back-arc basin for understanding the origin and mineral zoning processes in this study. Sulfides from the hydrothermal mound's pedestal slab consisting of chalcopyrite and pyrite show enrichment of heavy S-isotope (δ34SV-CDT = +8.3 to +9.6‰). Sphalerite-dominated chimney on the mound's slope also has variable δ34S values between +5.5 and + 8.3‰ from central orifice to outer wall. These isotopic ratios indicate the substantial contribution of heavy isotope rich sulfate-S in seawater circulating within the mound. Low Δ33S values in these sulfides also indicate that the sulfate reduction is of thermal origin, with minimal or no role for microbes. Circulating seawater induced changes in fluid composition and post-depositional zone refinement of certain minerals can explain the variation in δ34S in di...

Marine Environmental Research

Marine Pollution Bulletin

Marine and Freshwater Research

Seasonal nutrient dynamics were investigated in four rivers with a microtidal range (Terekhol, Ch... more Seasonal nutrient dynamics were investigated in four rivers with a microtidal range (Terekhol, Chapora, Sal and Talpona rivers) and were compared with those of two rivers with a mesotidal range (Zuari and Mandovi rivers) along the central west coast of India. Rainfall and freshwater discharge during the wet season led to salinity stratification of the water columns at the mouths of these rivers. Nutrient concentrations in all rivers were higher during the wet season than in the dry season due to considerable land run-off. Based on the estuarine mixing diagrams of the nutrients with regard to salinity, the mesotidal rivers showed greater flushing capacity and acted as corridors for the passage of nutrients between the estuary and open ocean. Conversely, of the microtidal rivers, the Terekhol and Chapora seemed to retain nutrients, whereas there was no indication of the presence of a nutrient sink or source in the Talpona River. The Sal River was eutrophic with high nutrient levels an...