Showing papers in "Indian Journal of Marine Sciences in 2009"

Potential microbial diversity in mangrove ecosystems: a review.

Abstract: Mangroves provide a unique ecological niche to different microbes which play various roles in nutrient recycling as well as various environmental activities. Mangrove forests are large ecosystems distributed in 112 countries and territories comprising a total area of about 181,000 km is over a quarter of the total coastline of the world. The highly productive and diverse microbial community living in mangrove ecosystems continuously transforms nutrients from dead mangrove vegetation into sources of nitrogen, phosphorous and other nutrients that can be used by the plants and in turn the plant-root exudates serve as a food source for the microbes. Analysis of microbial biodiversity from these ecosystems will help in isolating and identifying new and potential microorganisms having high specificity for various applications. The present study consists literature on diversity of predominant microbes such as bacteria, fungi and actinomycetes from mangrove ecosystems.

Assessment of metal concentration in the sediment cores of Manakudy estuary, south west coast of India.

Abstract: Base line data on the metal concentration was obtained from three core sediments (S1, S2 and S3) of Manakudy estuary on the south west coast of India. The acid leachable trace metals (Cr, Cu, Ni, Co, Pb, Zn and Cd) showed peak values at sulphidic phase . There is moderate level of pollution related to anthropogenic activities. The trace metals were associated with Fe and Mn indicating their adsorption onto Fe-Mn oxyhydroxides. The correlation of trace metals with sulphur indicates that they were precipitated as metal sulphides. Correlation matrix showed elegant association between trace metals and Fe, Mn, S and mud. The Igeo values revealed that all the core samples fell within uncontaminated to moderately contaminated category. The concentration factor was low (Cf i <1) indicating low contamination in the core samples. The anthropogenic factor (AF) values indicate moderate anthropogenic inputs.

Textural characteristics of the surface sediments of a tropical mangrove Sundarban ecosystem India.

Abstract: Surficial sediments of Sundarban Mangroves in West Bengal India have been studied for grain size spectrum and textural parameters namely phi mean, standard deviation, skewness and kurtosis Grain size spectrum shows a marked variation in the upstream riverine stretch Observed variation of energy conditions is controlled by the fluvial profile in the channel Textural pattern is highly complex owing to the fluctuation in the physico-chemical conditions prevailing in the system Textural analysis of very fine sand shows existence of comparatively low energy condition in the fluvial and mangrove creek zones Linear Discriminant Function Analysis (LDF) of the samples indicates a shallow marine environment origin for all samples of the mangrove ecosystem The riverine sediments also show a wide range of textural facies They show a progressive enrichment of silty-sand in the downstream in the creeks The CM diagram (C=one percentile in microns, M=Median in microns) of Sundarban suggests that sediment deposition takes place by (1) rolling (2) rolling and suspension and (3) graded suspension The river and creeks sediments represent deposits are of uniform suspension

Metal phytoremediation potential of Rhizophora mucronata (Lam.)

Abstract: The present study consist the absorption, accumulation and partitioning of eight metals in order to find out the phytoremediation potential of the mangrove species Rhizophora mucronata (Lam.) in Alibag, Maharashtra, India. The concentrations of Cu, Cd, Ni, Mn, Cr, Zn, Fe and Pb in the sediments of the mangrove area were determined to be 92.59, 5.31, 63.29, 1020.00, 545.00, 78.18,68164.26 and 19.51 ppm, respectively on dry weight basis. Metal concentrations were different in specific parts of the plant, and the highest concentration (in ppm on dry weight basis) of each metal was found in the following pattern: leaves for Ni (1.74 ± 0.58) and Cr (16.78 ± 7.06; senescent leaves for Zn (6.29 ± 0.80); bark for Cd (1.34 ± 0.04) and Pb (7.35 ± 0.45), and roots for Fe (1236.69 ± 754.69) and Mn (618.31 ± 186.08). There were different translocation rates for each metal from root to shoots. The translocation ratios of Cd, Cr and Pb (1.53, 1.66 and 1.08, respectively) exceeded one in the case of senescent leaves, as these metals were being accumulated in leaves before falling off and thus eliminated. The trend of the phytostabilization capacity of R. mucronata in the Alibag mangrove ecosystem is confined to only the highly abundant metals in nature and the phytoremediation capacity of R. mucronata varies from metal to metal.

Seasonal variations of phytoplankton in Mahanadi estuary, east coast of India

Abstract: Seasonal variations of phytoplankton and chlorophyll-a along with its environmental variations including nutrients were studied from June-2004 to March-2007. Samples were collected in three different seasons pre-monsoon (May-June), post-monsoon (October-November) and summer (February-March) from the Mahanadi estuary. Seventy seven species of phytoplankton were encountered during the study period of which, diatoms (Bacillariophyceae) was the dominant group followed by dinoflagellates (Dinophyceae) and cyanobacteria (Cyanophyceae). Higher phytoplankton counts and chlorophyll-a concentrations were recorded in post-monsoon season. Nutrient concentration was also very high in the above season as compared to other two seasons. Cyanobacteria population was more during post-monsoon season. Positive correlations of phytoplankton, with chlorophyll-a and dissolved oxygen were recorded in all three sampling seasons. Positive correlation of phytoplankton population with Chl-a, DO, NO 2-N, NH 4-N indicated that the phytoplankton population in the estuary is controlled by above nutrients. Diatoms are dependent on NO 2-N and NH 4-N, dinoflagellates depend on NO 2-N and SiO 4. Cyanobacteria in the estuary depend on NO 2-N, NH 4 and PO 4.

Study of variations in water quality of Mumbai coast through multivariate analysis techniques

Abstract: Multivariate statistical techniques, such as Cluster Analysis (CA), Discriminant Analysis (DA), and Principal component analysis (PCA) were applied to evaluate the temporal/spatial variations in marine water quality of Mumbai and to identify pollution sources. Hierarchical CA grouped 12 sampling sites into three clusters of similar water quality characteristics. DA gave the best results both spatially and temporally. It provided an important data reduction as it used only four parameters (DO, Total coliform, Ammonical nitrogen and pH) affording 100% correct assignment in temporal analysis. For spatial DA, DO and temperature; Feacal strptococii, DO and Total coliform; temperature and phosphate were used for summer, monsoon and winter seasons respectively. DA gave 100% correct assignment in spatial analysis except for summer season, step wise mode DA rendered 91.6% correct assignment. PCA resulted in four factors explaining 81.4% of the total variance. The first factor obtained represents organic pollution from domestic waste water. The second factor represents natural pollution which includes the surface run off. The third factor represents nutrient pollution whereas the fourth factor represents seasonal effects of temperature.

Occurrence and distribution of bacterial indicators and pathogens in coastal waters of Orissa

Abstract: Bacterial population in the coastal water of Orissa, up to 10 km from shoreline along 6 transects were observed during 2005-06 and 2006-07. Total viable counts (TVC), total coliforms (TC), faecal coliforms (FC), faecal streptococci (FS), presumptive E. coli , Shigella, Salmonella, Proteus/Klebsiella, total Vibrio, Vibrio cholera, V. parahaemolyticus and Pseudomonas aeruginosa as well as physico-chemical parameters are determined. Bacterial population was higher in Mahanadi, Paradip and Puri transects compared to other transects. Higher microbial population was recorded in stations close to the shore than the offshore (5 km and 10 km) stations. FC showed positive significant correlation with presumptive E. coli, Shigella, Salmonella and Proteus/Klebsiella, Total Vibrio, V. cholera, V. parahaemolyticus and P. aeruginosa . TC showed the positive significant correlation with presumptive E. coli , total Vibrio, V. cholera and P. aeruginosa . FS showed the positive significant correlation with Salmonella , total Vibrio, V. cholera and V. parahaemolyticus and Shigella . Correlation analysis revealed positive relationships between faecal indicators and pathogenic microorganisms. Bacterial population showed positive relationship with BOD and negative relationship with salinity indicating dominant influence human activities.

Circulation and mixing processes in Chilika lagoon

Abstract: Chilika lagoon, along the east coast of India, is the largest brackish water lagoon in Asia. Hydrodynamics of an aquatic system like Chilika is extremely important. It has significant impact on sediment and pollutant transport, distribution of nutrients in water and sediments, and the productivity of the system. Data on salinity, temperature and wind procured during summer and winter season have been utilized to demonstrate circulation and mixing processes in Chilika lagoon. Density and wind driven circulation of this lagoon have been examined and depicted for the above period. Mixing of water masses in the lagoon are studied using straight line as well as triangle mixing methods. The present study infers the inherent seasonal variability in circulation (wind and density driven) and mixing pattern and also the variability due to opening of new mouth in Chilika lagoon .

Phytoplankton species assemblages and their relationship to hydrographic factors—a study at the old port in Mangalore, coastal Arabian Sea.

Abstract: Several environmental variables were monitored and water samples were examined from over a period of 17 days in December 2005 and January 2006 to understand the taxonomic structure of coastal phytoplankton communities at a coastal site near Mangalore. The phytoplankton community was characterized by identifying and quantifying microalgal taxa; in conjunction, also determined Chl a, inorganic nutrients, oxygen, salinity, temperature, total bacteria, and tidal range. Canonical correspondence analysis (CCA) was used to trace temporal phytoplankton community changes, and to examine the relationships between species composition and environmental factors. These variables were subjected to analysis, pairwise, to identify correlations. The species diversity of the phytoplankton community changed rapidly, and high species diversity coincided with significantly higher relative diatom abundance, and lower species diversity coincided with significantly higher proportions of phytoplankton taxa other than diatoms and dinoflagellates. In addition, the Chl a concentration was positively correlated to the relative proportion of dinoflagellates. The relative abundance of some species was dependent on specific environmental variables, such as Chaetoceros tenuissimus that was found inversely correlated to salinity. We also found that the stage of the tides may have implication on the sampling, because it has an influence on species diversity and the proportion of specific microalgal groups. At declined water level, the relative proportion of diatoms and dinoflagellates was low, and generally the Chl a concentrations were also lower during low tide.

Seasonal variation of Zn, Cu and Pb in the estuarine stretch of West Bengal

Abstract: Zn, Cu and Pb levels in the aquatic phase and underlying surface sediment from three stations (viz. Shankarpur, Canning and Bali Islands) of the coastal zone of West Bengal during different seasons in 2002 were recorded. The order of the heavy metal level in the ambient media of the selected stations is Zn> Cu> Pb. Highest concentrations of heavy metals were recorded in the surface water during monsoon, the period characterized by lowest salinity and pH of the ambient aquatic phase. During premonsoon season all the dissolved heavy metals exhibited minimum values. The biologically available heavy metals from surface sediment of the selected stations showed highest values during premonsoon and lowest during monsoon. Significant negative correlations between the concentrations of dissolved heavy metals and biologically available heavy metals from surface sediments elucidates a sharp exchange of selected metals between the aquatic phase and sediment in the study area.

Nutrient dynamics in the two lakes of Kerala, India

Abstract: Distribution and chemistry of major inorganic forms of nutrients along with physico-chemical parameters were investigated. Surface sediments and overlying waters of the Ashtamudi and Vembanad Lakes were taken for the study, which is situated in the southwest coast of India. High concentrations of dissolved nitrogen and phosphorus compounds carried by the river leads to oxygen depletion in the water column. A concurrent increase in the bottom waters along with decrease in dissolved oxygen was noticed. This support to nitrification process operating in the sediment-water interface of the Ashtamudi and Vembanad Lake. Estuarine sediments are clayey sand to silty sand both in Ashtamudi and Vembanad in January and May. Present study indicates that the sediment texture is the major controlling factor in the distribution of these nutrient forms. For water samples nitrite, inorganic phosphate was high in Vembanad in January and May compared to Ashtamudi. For sediments, enhanced level of inorganic phosphate and nitrite was found in Vembanad during January and May. It had been observed that the level of N and P is more in sediments. A comparative assessment of the Ashtamudi and Vembanad Lake reveals that the Vembanad wetland is more deteriorated compared to the Ashtamudi wetland system.

Effect of Chattonella marina [(Subrahmanyan) Hara et Chihara 1982] bloom on the coastal fishery resources along Kerala coast, India.

Abstract: To assess the impact of the bloom on the coastal fishery resources of the region, the fish landing data of five gears such as outboard trawl net, outboard drift net, outboard gill net, outboard ring seine and country craft gill net were analysed in detail. The landings of fishes which belonged to lower trophic levels decreased. Fishes which were mainly zooplankton feeders like Stolephorus spp , Thryssa and Leiognathus were entirely absent . But there was an increase in catch of the predatory fishes mainly Euthynnus, Trichiurus, Carcharhinus, Saurida, Scoliodon, Scomberomorus, and Sepia spp which occupy higher trophic level. The variation in catch rate between the bloom and the non-bloom period was significant ( P<0.05) for Cynoglossus spp , Johnius spp , Thryssa spp and Parapenaeopsis stylifera caught in the outboard trawl net . The average taxonomic distinctness (Delta + ) was lower during the bloom period and a clear shift in the community structure was observed. The effect of the C. marina bloom on fish community was short-lived, and the taxonomic diversity was restored soon after the bloom subsided.

Coral disease prevalence in Mandapam group of islands, Gulf of Mannar, Southeastern India.

Abstract: Assessment of coral disease prevalence was carried out in six islands in the northern region of the Gulf of Mannar during February 2007. Assessment was made in two sites in each island and three transects were laid in each site. white band, white plaque, white spot, pink spot, black spot, black band, yellow spot, yellow band and tumors were the observed common diseases in this regime. Overall coral disease prevalence was 8.9%. Prevalence was highest at Poomarichan Island (10.90%), followed by Manoli (9.38%), Pullivasal (9.28%), Hare (8.64%), Krusadai (8.27%) and Shingle (6.82%). Most common disease was pink spot in Porites sp followed by black band in Porites sp., Pocillopora sp., Favia sp., and Favites sp. Tumors were also observed in low frequencies in Acropora cytheria. Other affected species were Acrpora cytherea, Favia pallida and Goniastrea sp. Present study also consists the frequency of temperature anomalies, which can increase the susceptibility of corals to disease, leading to outbreaks where corals are abundant both in cover and diversity.

Mercury enrichment in sediments of Amba estuary

Abstract: Concentrations of Hg, total organic carbon (TOC), Al, Fe and Mn were determined in sediment of the Amba Estuary between the mouth and the head over a distance of 24 km in December and May during 1997-2002. Temporal and spatial changes in metal concentrations appear to be due to sediment movement associated with tidal movements. The Hg concentration varies in 0.05 -2.66 μg g range and the profiles of its variation indicate Patalganga River that opens in the Amba Estuary is a major source of anthropogenic metal to the estuary. Geoaccumulation index and enrichment factor support Hg contamination of the estuarine sediment to a varying degree. Hg is not significantly correlated with TOC, Al, Fe and Mn in these sediments.

Water quality status and Primary productivity of Valanthakad Backwater in Kerala

Abstract: The water quality and primary productivity of Valanthakad backwater (9 ° 55 ′ 10. 24 ′′ N latitude and 76 ° 20 ′ 01. 23 ′′ E longitude) was monitored from June to November 2007. Significant spatial and temporal variations in temperature, transparency, salinity, pH, dissolved oxygen, sulphides, carbon dioxide, alkalinity, biochemical oxygen demand, phosphate-phosphorus, nitrate-nitrogen, nitrite-nitrogen as well as primary productivity could be observed from the study. Transparency was low (53.75 cm to 159 cm) during the active monsoon months when the intensity of solar radiation was minimum, which together with the run off from the land resulted in turbid waters in the study sites. The salinity in both the stations was low (0.10 ‰ to 4.69 ‰) except in August and November 2007. The presence of total sulphide (0.08 mg/ l to 1.84 mg/ l) and higher carbon dioxide (3 mg/ l to 17 mg/ l) could be due to hospital discharges and decaying slaughter house wastes in Station 1 and also from the mangrove vegetation in Station 2. Nitrate-nitrogen and phosphate-phosphorus depicted higher values and pronounced variations in the monsoon season. Maximum net primary production was seen in November (0.87 gC/ m

Development of a neural network model for dissolved oxygen in seawater

Abstract: Present paper consists the results from a study conducted to test the adequacy of artificial neural networks in modelling of dissolved oxygen (DO) in seawater. The input variables for ANN DO models are selected by statistical analysis. The ranking of important inputs and their mode of action on the output DO are obtained based on the expert’s opinion. The calibrated neural network models predict the DO concentration with satisfactory accuracy, producing high correlations between measured and predicted values (R2>0.8, MAE<1.25 mg/L for training and overfitting test) at specified location and time in the selected domain where there are training stations. It is shown that one can forecast the next week’s DO level from antecedent measurements with an acceptable confidence. Introducion

Natural and anthropogenic threats to olive ridley sea turtles (Lepidochelys olivacea) at the rushikulya rookery of Orissa coast, India.

Abstract: An assessment of various threats to the olive ridley turtles at Rushikulya rookery of Orissa in India was investigated during 2003-04 and 2004-05 seasons Data on adult mortality, predation of eggs and juveniles, beach erosion and Casuarina plantation along the beach were collected Turtle mortality was low at Rushikulya compared to rest of the Orissa coast However, other anthropogenic pressures such as Casuarina plantation close to high tide level, beach erosion and artificial illumination that have emerged as visible threats at this rookery Protection of nests and minimization of artificial illumination are some of the immediate steps required for safeguarding sea turtles at the Rushikulya rookery

Fecal sterols and pahs in sewage polluted marine environment along the eastern Red Sea coast, South of Jeddah, Saudi Arabia.

Abstract: Water and sediment samples were takes near the sewage discharge point on the eastern Red Sea Coast of Jeddah and analyzed for PAH and fecal sterols like coprostanol, cholesterol and cholestanol. PAH were estimated spectrofluorometrically and then further analyzed by GC-MS. Sterols were derivatized by BSTFA into their corresponding trimethyl silyl derivatives and then analyzed by gas chromatography and quantified with standard sterols. PAH ranged from 1.5 to 6.5 μ g 1 -1 in eight stations. Concentration of coprostanol in water samples showed a maximum of 8.2 μ g 1 -1 at station XVIII and minimum 0.1 μ g 1 -1 at station 10C. The analysis of the sediment samples indicated much higher values for fecal sterols. It was found to be 785 μ g 1 -1 in sediment and 6.5 μ g 1 -1 in the water samples at station XVIII. PAH did not show any distinct increase in the sediment samples. According to Grimaldt equation the value of r* (5 β / 5 β + 5 α) was determined. Out of a total of sixteen samples, fourteen samples had a value of 0.7 or higher than 0.7. This indicate a definite and a positive sewage contamination infecting almost the whole area studied. The GC-MS of the PAH indicate the presence of phenanthrene, benzophenone and 2,4-diisoprophyl naphthalene, methylnaphthalene, and 9-H-methylene flourene. Present study infers that the sewage; either untreated or partially treated is dumped into the sea.

Estuarine characteristics of lower Krishna river.

Abstract: Present study consist the spatial and temporal variations of depth, temperature and salinity, currents, flushing times and classification of the Krishna estuary. Temperature exhibited a distinct seasonal variation with higher values in premonsoon (30.0±0.09°C) and monsoon (29.2±0.08°C) seasons compared to that of winter (26.6±0.06°C). Salinity and current pattrns shows distinct seasonal and spatial variations noticed. Changes in hydrodynamic conditions infers that the river mouth as a positive type of estuary. Flushing times varied with seasons and locations due to changes in river discharges and circulation pattern. Considering the two dimensional Hansen and Rattray's stratification and circulation diagram, the estuary has been classified as partially mixed with no stratification type during postmonsoon and stratified during monsoon and premonsoon seasons.

Lipid profiles of Threadfin bream ( Nemipterus japonicus ) organs

Abstract: Present study of the lipid content in different organs of marine fish Threadfin bream ( Nemipterus japonicus ) indicates that a major amount of lipids are accumulated in liver (6.22%) when compared with remaining organs like muscle (2.7%) and skin (1.0%). Cholesterol studies reveal that muscle (36.2%) is having more quantities than liver (32.4%) and skin (24%). Fatty acid composition reveals that the lipids of each organ of threadfin bream are enriched in the unsaturated fatty acids and all the organs were found to be rich in linoleic (C 18: 2 ), oleic (C 18:1 ) and palmitic (C 16: 0 ). The present study further elucidates that a considerable amount of two physiologically important n-3 PUFAs, i.e. EPA and DHA were found more in skin (1.6% and 0.5%) and liver (1.6% and 0.6%) than in muscle (1.4% and 0.4%).

Effect of Miocene paleoceanographic changes on the benthic foraminiferal diversity at ODP site 754A (southeastern Indian Ocean)

Abstract: Miocene deep sea benthic foraminiferal diversity at ODP site 754A, in the southeastern Indian Ocean was examined in the present study. Paleoceanographic and paleoclimatic changes were inferred based on the above study. Species diversity was measured in terms of Shannon-Weaver Index [H(S)], Hurlbert’s Diversity Index (S100), Alpha Index (α) and Equitability (E’). Values of S100 show more positive correlation with H(S) and α value. All diversity parameters show almost similar pattern during the study interval. Present study infers that the changing trophic level has much influence on the faunal diversity. More diverse fauna of late early Miocene to early middle Miocene along with low δO and high δC values reflect warm and stable bottom waters with low food supply. This corresponds to the Miocene climatic optimum. This was also an interval of global warming and reduced Antarctic ice-sheet volume. Significant decline in diversity and δC values along with abrupt increase in δO values at ~ 14 Ma indicate cold, relatively less oxygenated and unstable bottom waters with increased food supply due to higher surface productivity. Development of thermal gradient between low and high latitudes in response to the expansion of Antarctic ice-sheet during 15-12.5 Ma was responsible for increased upwelling and high surface productivity. Decrease in faunal diversity at ~7 Ma onwards along with low δC and high δO values corresponds with the Chron-6 negative Carbon shift, expansion of west Antarctic ice-sheets and lowering of sea level.

Occurrence and distribution of some enteric bacteria along the southern coast of Kerala

Abstract: Six major groups of enteric bacteria, viz, Faecal coliforms , E. coli, Shigella spp., Salmonella spp., Vibrio parahaemolyticus and Vibrio cholerae were screened for the present study. The overall percentage occurrence of enteric bacteria in water and sediment was maximum accounted for Vibrio parahaemolyticus (81.7%) and minimum for Salmonella spp. (9.6%) and moderate reported against Vibrio cholerae (60.6%). The distribution of enteric bacteria was more in the water sample than sediment except Vibrio spp. and the highest occurrence was found to be at Cochin transect, which is the most polluted transect due to enteric microbes. Relationship between the stations on the occurrence of enteric bacteria was linear and significant variations was observed (R 2 =0.899) and the same pattern of linear regression model was also obtained in source wise occurrence (R 2 =0.777). The present study elucidates that the health status of the Kerala coast may deteriorates and will be detrimental to the coastal community.

Effect of salinity and dissolved nutrients on the occurrence of some seaweeds in Manakkudy estuary

Abstract: Manakkudy estuary, located on the South-West coast of India has production of seaweeds to an amount of 15.59 kg/m 2/ yr. Four different types of seaweeds viz., Chaetomorpha aerea, Enteromorpha compressa, Gracilaria verrucosa and Hypnea musciformis were observed in this estuary. Highest production of biomass ( C. aerea = 842.33± 32.21 g/m 2 ; E. compressa = 619±16.09 g/m 2 ; G. verrucosa = 563.33±13.32 g/m 2 and H. musciformis = 225.67±10.79 g/m 2 ) of seaweeds could be recorded in May. During November i.e., a period of peak monsoon rain it is not present. Sea weeds were observed to occur in the euryhaline salinity range of 11.15 ± 0.48 to 27.18±0.88 ppt and the temperature ranging between 23.57 °±1.00 and 31.70 ± 0.82 °C. The quantity of seaweed is more when levels of nutrients were moderately high.

Detection of genetic variation in four Ulva species based on RAPD technique.

Abstract: DNA yield was obtained by using 2 protocols, CTAB (Cetyltrimethylammonium bromide) and modified Wattier et al ; out of which the latter yielded more quantity of DNA (0.85 μg/g). Out of total amplified product 53% bands were shown monomorphic and remaining of the bands were polymorphic. The high frequency of polymorphic bands suggests that the isolates of Ulva represented in our collection have sufficient genetic diversity for conducting a valid heterosis experiment. The intra species genetic similarity (GS) value was found highest for U. lobata and lowest for U. fasciata . The interspecies GS value was found highest between U. fasciata/U. lactuca and lowest between U. lobata/U. reticulata . The large number of differences among isolates revealed by the RAPD technique indicate that it would be possible to establish a unique “fingerprint” for individual plants based on the combined results generated from a small collection of primers.

Changes in major carbon components during a fertilization experiment with surface water from the Central Indian Ocean.

Abstract: Shipboard iron- and macronutrient-addition experiment was conducted in the Central Indian Ocean, to investigate the variations of carbon in different forms and its records for plankton activities. Experiments were conducted in four 500-L acrylic barrels with the surface seawater near 24oS, 70oE. The concentration of chlorophyll a, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and particulate organic carbon (POC) were measured. DOC concentration had a dramatic increase when phytoplankton bloom, which is caused by the excretion of blooming phytoplankton. Another maximum of DOC concentration occurred after phytoplankton bloom corresponds to the bacterial degradation of organic matters or the excretion of phytoplankton. The decrease of DOC concentration following the two maxima might result from the absorption of DOC by bacteria. The increasing trends of POC before phytoplankton bloom were consistent with that of DOC and chlorophyll a, indicating that phytoplankton growth dominated the plankton activities. The variation of POC concentration just after bloom was controlled by the decomposition of phytoplankton and the growth of bacteria. However, POC concentration increased at the end of the experiment, which might be caused by the growth of bacteria with the utilization of DOC. The present study infers that the carbon records, particularly POC and DOC, in the seawater are indicative to plankton activities.

Utilization of high resolution satellite geoid data for estimation of lithospheric thickness in the Bay of Bengal

Abstract: Very high-resolution database generated from Seasat, Geosat GM, ERS-1 and TOPEX/ POSEIDON altimeters data of the northern Indian Ocean has been used for the first time for preparation of geoid and free-air gravity maps. In the present work, geoid height anomalies have been analyzed across the Ninetyeast and 85 °E Ridges within the Bay of Bengal. Present data sets are more accurate and detailed (off-track resolution: about 3.33 km and grid size: about 3.5 km). Observed geoid height – age and geoid height derivative (with respect to age) – age relationships have been established and compared with the plate model of lithospheric cooling to determine. The present endeavor is to determine the lithospheric plate thickness beneath both ridge structures. Attempts have been made to match the observed value with the computed value over the Bay of Bengal. The lithospheric plate cooling model correlates convincingly with the observed value. It has shown the efficacy of a plate model according to which geoid observations of the Bay of Bengal are better explained by a larger plate thickness of 90 – 125 km for the oceanic crust of age older than 30 Ma.