This study investigates the coupling between Chromophoric Dissolved Organic Matter (CDOM) and Dis... more This study investigates the coupling between Chromophoric Dissolved Organic Matter (CDOM) and Dissolved Inorganic Carbon (DIC) in eighteen Indian estuaries across salinity gradient of the east and west coasts during the monsoon season, characterized by significant river discharge. The hypothesis that humic acids (HA) and fulvic acids (FA), prominent in estuarine CDOM, closely correspond to the ‘organic alkalinity’ (Aorg) component of total alkalinity is examined. In most estuaries, specifically those along the northeast coast (NE) and southwest coast (SW), a significant linear relationship exists between DIC, CDOM abundance, and pH level. Notably, minor estuaries along the southeast coast (SE) and northwest coast (NW) exhibit elevated DIC levels beyond what this relationship predicts. These estuaries also reveal heightened ammonium levels, increased δ15N values, and decreased δ13C values, indicative of anthropogenic influence. CDOM properties, such as spectral slope (S300–500) and spectral slope ratio (SR, S275–295:S350–400), align with these findings, with SE and NW estuaries displaying higher values. On average, CDOM contributes 110.5 μM (6.8 %) to DIC in NE, 390.7 μM (11 %) in SE, 24.4 μM (4.8 %) in SW, and 122.2 μM (4 %) in NW estuaries. The relationship between total alkalinity minus DIC (TA-DIC) and pH25 suggests that CDOM, mediated by HA/FA, buffers the inorganic carbon system in estuaries. This buffering capacity weakens at elevated DIC levels, and this condition is marked by anomalous SR values compared to the baseline salinity-SR linear regression. This Study suggests that estuarine CDOM could largely represent “organic alkalinity” and could help monitor acidification in estuaries.
Dunaliella salina is cultivated extensively in natural ponds or intensively in race way ponds for... more Dunaliella salina is cultivated extensively in natural ponds or intensively in race way ponds for β-carotene production. The ponds are seeded with culture inoculum developed in laboratory conditions or in pilot plant. Because of its high light requirement for growth, D. salina cultures are very cell dilute. Therefore, a large volume of culture inoculum is required to seed mass culture units. The feasibility of culture of D. salina in mixotrophic mode to obtain cell dense inoculum was investigated with an Indian isolate-I3. The constituents of the mineral medium and their concentration were first standardized in growth assays. The optimized mineral medium was supplemented with organic carbon sources-glycerol, sodium acetate and malt extract and organic nitrogen sources-yeast extract and peptone to test for the best results of mixotrophic culture. A mineral medium with 100 mg L −1 potassium nitrate or urea, 0.35 mg L −1 potassium phosphate, 1 ml L −1 trace elements mix (Walne's medium) without borate and 12.5 % NaCl in sea water was found optimal. Malt and yeast extracts in the proportion of 1:3 g L −1 in optimized mineral medium was found to result in cell dense cultures. Mixotrophically cultured inoculum grown photoautotrophically in optimized mineral medium resulted in increased biomass production with higher carotene content than when photoautotrophically cultured. The production cycle decreased by 11 days compared to autotrophic cultures
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
Wind systems are known as nutrient sources playing significant roles in the oceanic realm and glo... more Wind systems are known as nutrient sources playing significant roles in the oceanic realm and global climate oscillations. This study explores, for the first time, the effect of winds on the winter blooms of the mixotrophic dinoflagellate, the green variant of Noctiluca scintillans (NS G) in the northern Arabian Sea. When the NS G abundance was lower (i.e., < ∼10000 cells l −1), it was coupled to silicic acid (H 4 SiO 4), on which diatoms (phytoplankton) in turn depended. At higher abundance (i.e., NS G > ∼10000 cells l −1), H 4 SiO 4 and H 4 SiO 4 :DIN (dissolved inorganic nitrogen) ratio fell. The NS G was then intensely green and chlorophyll-a richer, attributed to a change in the mode of NS G's nutrition from heterotrophy to autotrophydominance. The back-trajectory model revealed that the winds were mostly northeasterly (NE) initially (during February) and were north-westerly (NW) towards the end of winter (March). Separately for the NE and NW winds, the NS G abundance was 10655 ±18628 and 28896 ±46225 cells l −1 , respectively. The H 4 SiO 4 :DIN ratio correspondingly reached < 0.2 and ≥0.4. The NS G was modelled with high significance (p < 0.001, N = 33) versus the NE and NW wind speeds. Thus, while the NE winds deepened the mixed layer and caused nutrient enrichment and phytoplankton production, the NW winds facilitated the recovery of the H 4 SiO 4 :DIN ratio and economical
compared to the baseline salinity-SR linear regression. This Study suggests that estuarine CDOM c... more compared to the baseline salinity-SR linear regression. This Study suggests that estuarine CDOM could largely represent "organic alkalinity" and could help monitor acidification in estuaries.
Green Noctiluca scintillans (NSG) is a mixotrophic dinoflagellate that frequently forms intense b... more Green Noctiluca scintillans (NSG) is a mixotrophic dinoflagellate that frequently forms intense blooms in the north Indian Ocean, especially in the northeastern Arabian Sea during winter. This study investigates the conducive conditions and drivers associated with NSG blooms and proposes significant models for estimating NSG based on in situ (time-series) study during the bloom cycles. Two critical factors with regard to the blooms, i.e., phytoplankton abundance and sea surface temperature (SST), were examined. The first phase of heterotrophy dominance was when moderate blooms up to ~ 2.26 × 10 4 cells 1-1 occurred and, when NSG cells per unit chlorophyll-a (chl-a) increased, SST decreased up to ~ 24.5 ºC. The bloom intensity was proportional to the feed (diatoms/phytoplankton) availability and the degree of cooling (by the winter convection, i.e., nutrient enrichment). In the second phase of autotrophy dominance, intense blooms up to 1.9 × 10 5 cells l −1 occurred and NSG cells per unit chl-a fell, when the SST increased. During this period, bloom intensity was proportional to the degree of warming, i.e., nutrient and physiological stress. Phytoplankton are related to NSG by a single linear model through this SST cycle and is likely the NSG's essential biotic precursor. Attention is then focused on developing a remote sensing reflectance (R rs) model for efficient synoptic monitoring of NSG using ocean color satellites. The R rs band product ratio, a new metric, in combination with SST, notably modelled NSG abundance, which may be of potential routine application.
The alkali and alkaline earth metals both major (Na, K, Mg, Cal and minor (Li, Rb, Cs, Sr) were a... more The alkali and alkaline earth metals both major (Na, K, Mg, Cal and minor (Li, Rb, Cs, Sr) were analyzed in 75 surface sediment samples from an area covering the continental shelf, slope and the deep sea regions. Lithium, Rb, Cs and Sr averaged 7.2, 42.5, 12 and 27.2 ppm respectively. Rubidium and Sr showed north-south trends. Starting from the northern sector, the former increased and the latter decreased towards the mouth of R. Godavari. This behavior is explained by the dissolved transportation index (DTI) according to which the transport of Rb takes place mainly in the particulate and th at of Sr in the dissolved phases. Lithium and Rb are correlated well to K suggesting a detrital origin for the elements. The alkali and alkaline earth metal distribution of the study area revealed a strong signature of R. Godavari. Strontium showed a good anticorrelation with the biogenic fraction of Mg (Mg B). It attained peak concentrations in the carbonate sands of the northern outer shelf which according to previous reports are of the late Pleistocene age. Sediments although rich equall y in carbonate and from proximate stations, contain variable concentrations of Sr probably due to a differential time-dependent leaching of the metal as these carbonate deposits may have been formed at different stages of the regressive-progressive cycle of the late Quaternary sea level.
A rare gorgosterol type sterol, 22, 23-methylene (22S, 23S) cholesterol (3) and three other compo... more A rare gorgosterol type sterol, 22, 23-methylene (22S, 23S) cholesterol (3) and three other compounds 1, 2 and 4 were isolated from the marine sponge Sigmadocia fibulata, for the first time. Their structures were elucidated by spectroscopic (IR, 2D NMR and Mass spectral) data.
A dinoflagellate under the ambit of Harmful Algal Blooms (HAB), the bioluminescent Noctiluca scin... more A dinoflagellate under the ambit of Harmful Algal Blooms (HAB), the bioluminescent Noctiluca scintillans (NS), has been infesting the northern Arabian Sea increasingly over the last few decades during late winter. Their occurrence is found to be due to seasonal oscillations in the coastal currents. The physical and biogeochemical parameters associated with the seasonal blooms are reasonably well known. But accurate quantitative estimation capability using remote sensing sensors over the extensive oceanic regime is still lacking. This is especially due to a lack of information on bio-optical properties associated with cell density measurements. We attempted to show that remote sensing reflectance and chl-a show significant relationship e.g., R rs (531)/R rs (510) = 0.8261 + 6.06 × 10 − 6 NS + 0.02323chl-a (N = 19, R 2 adj = 0.99, p = 2.5 × 10 − 17 , RMSE = 0.1083) which is applicable over diverse areas of the northeastern Arabian Sea e.g., coastal, shelf and offshore regions. The model is supported by a second dataset with an RMSE of 0.022893 (N = 8) for the R rs (531)/R rs (510) ratio. The NS cell densities were derived from the Rrs(510)/Rrs(531) band ratio within reasonable error and accuracy limits. Including sensor capability at 510 nm is suggested in future satellite launches.
International Journal of Environmental Science and Technology, Aug 21, 2021
The optical characteristics of dissolved organic matter (DOM) and physicochemical properties were... more The optical characteristics of dissolved organic matter (DOM) and physicochemical properties were studied in the coastal waters of the Bay of Bengal off Visakhapatnam for one year from April 2010 to March 2011. The objective was to test the ability of coloured dissolved organic matter (CDOM) as a signature constituent to record the environmental perturbations due to seasonal and spatial dynamics. The a CDOM (440) showed negative relationship with salinity during monsoon indicating conservative mixing of marine (autochthonous) and terrestrial (allochthonous) end members. During pre-monsoon, a CDOM (440) showed positive relationship with chlorophyll (chl-a) due to in situ primary production. The spectral slope (S 300-500) which is an indicator of CDOM composition showed significant nonlinear relationship with a CDOM (440) for all the seasons and indicated mixing of different source waters arising from change of direction of East Indian Coastal Current (EICC). The a CDOM (440) showed positive relationship with dissolved inorganic nitrogen (DIN) for all seasons, which indicated that the DOM is non-labile. The spatial variability of CDOM in this region was affected by cyclonic and anticyclonic eddies. The annual rainfall was highest in 2010 for the 2000-2010 decade, and it showed a positive relationship with a CDOM (440), which indicated that rain water may be a secondary source of CDOM. The principal component analysis of optical and physicochemical properties clearly distinguished the sources and the seasonal classification and that the optical properties are useful as their proxy. Our study would help monitor the water quality and in improving the CDOM ocean colour algorithms in this region.
ChemInform Abstract: Marine Terpenes and Terpenoids. Part 16. Revised Structure of the Marine Furanoterpene (+)-Furospongin-1
ChemInform, Aug 20, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Vitamin C is analysed on monthly samples of 24 species of macroalgae collected for one year from ... more Vitamin C is analysed on monthly samples of 24 species of macroalgae collected for one year from the intertidal habitats of Visakhapatnam coast. Chlorophyll-a and carbohydrate are also analysed. In general, the algae belonging 10 Chlorophyceae and Phaeophyceae have higher annual mean contents of the vitamin (360 and 352 ~glg respecti vely) than Rhodophyceae (271 ~glg). The species which are rich in vitamin C are Padilla tetrastomatica (513 ~g/g), Spollgolll()/lJha illdica (510) and Chaetomorpha alltellllilla (488). The vitamin C maxima was observed during summer for Chlorophyceae and Phaeophyceae and during winter for Rhodophyceae. The vitamin C showed significant positive rel ationship with chlorophyll-a in Rhodophyceae and Chlorophyceae. It also showed a significant positive relationship with carbohydrate content of the latter. The distribution of vitamin C is associated with the morphogenetically important vegetative and reproductive phases indicating its key role in metabolic function.
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