Petroleum hydrocarbons and trace metals in Visakhapatnam harbour and Kakinada Bay, east coast of India

148-150High concentrations of PHC were observed in the inner channels (viz., South lighter canal, Northern arm, North western arm and Western arm) of Visakhapatnam harbour. The estimation of trace metals (Cu, Zn, Pb, Cd, Co, Ni and Cr) in surficial sediments indicated higher contamination in Visakhapatnam harbour than in Kakinada Bay. Positive correlations between Cu, Zn, Pb and Cd suggests common sources of these metals. Lack of correlation between Co, Ni with the other metals indicates point sources. High concentrations of chromium reflects intense discharges due to electroplating and battery operations

Fresh water influence on nutrient stoichiometry in a tropical estuary, southwest coast of India

Cochin backwaters, a micro tidal estuary, undergo a characteristic transformation from a river-dominated system during summer monsoon to a tide-dominant system during pre-monsoon season. The present study observes that as the river flow weakens after monsoon, the flushing of the estuary diminishes and the nitrogen and phosphorous loadings through anthropogenic activities (industries) and sediment re-suspension alter the nutrient stoichiometry substantially. The increased tidal activity during pre-monsoon changes the estuary into a vertically mixed, eutrophic and flow-restricted system supporting an enhanced organic production. This implies that monsoon-induced hydrology plays an important role in regulating the nutrients, secondary production and even the migrant fauna of the estuary. The system is delicately poised, as continuous release of pollutants including nutrients into this estuary would suppress fish and shell fish production, where only pollution tolerant species can exist

On watermass mixing ratios and regenerated silicon in the Bay of Bengal

56-61Regeneration of silicon on mixing in the Bay of Bengal have been computed from six water masses [Bay of Bengal low saline water (BBLS), Bay of Bengal subsurface water (BBSS), northern southeast high salinity water (NSEHS), north Indian intermediate water (NIIW), Indonesian throughflow water (ITW) and Antarctic bottom water (AABW)]. The distribution of watermass fractions showed that BBLS with a maximum of 80-90% in the 40-60 m depth range and BBSS with 50% in the 150-300 m depth range are prominant. In the intermediate layers, NIIW shows a maximum percentage of 40% in 250-700 m depth region while ITW shows a maximum of 60% in 800-1000 m depth region. The deeper layers (below 3000 m) are predominantly occupied by AABW with a maximum of 70%. Silicon regeneration consequent upon watermass mixing has been worked out based on the characteristics of silicon for individual watermass

Chemical characteristics of Central Indian Basin waters during the southern summer

Chemical properties of the water column were examined at the Indian Deep-sea Environment Experiment (INDEX) site in the Central Indian Basin (CIB), as a part of baseline studies prior to the benthic disturbance experiment for the environmental impact assessment of mining of polymetallic nodules. The study shows three equatorward moving water masses. (a) The Subsurface Salinity Maximum in the depth range 125–200 m, characterized by high salinity (34.74–34.77 psu) and oxygen minimum associated with weak maxima in nutrients. (b) The Deep Oxygen Maximum (234–245 mM) in the depth range 250–750 m, associated with minima in nutrients and relatively high pH. (c) The Salinity Minimum Water (34.714–34.718 psu) corresponding to the Antarctic Intermediate Water (AAIW) at depths 800–1200m in the density (sy) range 27.2–27.5. Progressive changes in these characteristics are attributed to mixing with waters above and below, and to oxidation of organic detritus en route. Among the three water masses, the oxygen maximum water shows the lowest changes in its properties, which may suggest that this water mass is moving the fastest

Assessment of the impact of spatial resolution on ROMS simulated upper-ocean biogeochemistry of the Arabian Sea from an operational perspective

The resolution of the model emerges to be an important factor in simulating the real oceanic features. In this paper, the performance of two coupled bio-physical models, having spatial resolutions 1/12° (∼9 km) and 1/4° (∼25 km) configured using Regional Ocean Modeling System (ROMS), have been evaluated in simulating upper ocean dynamics of the Arabian Sea. A comparison of the model simulated physical and biogeochemical fields with the observations from remote sensing, in-situ ship-borne, and Biogeochemical-Argo (BGC-Argo) floats showed that the high-resolution model reproduced the ocean physical and biogeochemical dynamics, and their seasonality more efficiently. The upper ocean dynamics associated with the variability of mixed layer depth, persistent occurrence of deep chlorophyll maxima, and seasonal phytoplankton blooms. as well as deep ocean characteristics of oxygen minimum zone were much effectively captured by the high-resolution model than by its counterpart. Similarly, the former model performed very well in reproducing the upwelling dynamics over the eastern continental shelf indicating that the open ocean-coastal coupling has been better established. Our analysis indicates that the realistic representation of the eddy fields by the high-resolution model leads to the better representation of the ocean fields in comparison to the coarse-resolution model

Evaluation of changes in benthic standing stock and polychaete community structure along the south eastern Arabian Sea shelf during the monsoon trawl-ban

The south eastern Arabian Sea is characterized by moderate coastal upwelling, high biological production and subsurface oxygen depletion during the southwest monsoon(June–September). Concurrently,a seasonal closure to trawling activities(15th June–31st July)is implemented here,as a sustainable ecosystem management practise. The effects of monsoon driven environmental changes and consequences of trawling cessation on macrofauna were assessed, based on surveys at 12 sites(30–200m)preceding and during different phases of the southwest monsoon. Macrofaunal density and biomass increased considerably towards the mid and late monsoon along the inner shelf(30–50 m)where trawling is in- tense, while no temporal changes were observed along the outer shelf(100–200m).Density increased four-folds at the 30m contour and three-folds at 50m, while biomass nearly doubled at both depths,reflecting a marked increase in density of polychaetes(61–87% of macrofauna). The disproportionate increase in faunal density and biomass along the inner shelf(30–50 m) was due to abundance of juvenile polychaetes and dominance of small-sized opportunists towards late monsoon(August–September).A concurrent hike in nominal species count of polychaetes was also observed in the study area. The increase in polychaete standing stock and high density of planktonic larvaed uring onset and peak monsoon, coupled with occurrence of juveniles as well as gamete-bearing adults in sediments,indicates that the southwest monsoon is a peak breeding season for the dominant polychaetes in the region. The trawl-ban during this period facilitates the recoupment of benthos by maximising spawning success and larval settlement, thereby enhancing overall ecosystem integrity