Spatial variability of nutrient sources determining phytoplankton Chlorophyll-a concentrations in the Bay of Bengal (original) (raw)
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Environmental Monitoring and Assessment, 2015
The present study focuses on understanding the long-term distribution of physico-chemical parameters and their influence on the distribution of chlorophyll-a (chl-a) at a coastal site in the northwestern Bay of Bengal. Chl-a showed large variability (0.12 to 10.05 mg m −3) on a spatio-temporal scale during the study period. However, the distribution showed a similar pattern with marginal variability from March 2010 to February 2011 and March 2011 to February 2012. The vertical distribution of salinity, pH, total suspended matter (TSM) and chl-a showed systematic temporal variability. However, dissolved oxygen (DO) and nutrients (nitrite + nitrate, phosphate, silicate) did not show any significant spatio-temporal trend. Chl-a showed bimodal distribution on an annual scale, with the first peak appearing during the pre-monsoon period in March due to a seasonal phytoplankton bloom, whereas the second peak occurring during September as a result of nutrient loading from river influx due to monsoonal precipitation. Factor analysis revealed the association of low salinity and high nutrients with chl-a. This infers that the nutrients brought by the influx of river into the study area were fuelling the growth and abundance of phytoplankton. Cluster analysis resulted in two distinct clusters among all physico-chemical datasets, indicating the presence of two distinct areas separated by the 30 m isobath that were strongly influenced by physicochemical characteristics associated with the seasonal monsoon.
Environmental Monitoring and Assessment, 2008
The interacting effects of abiotic processes in explaining variations of phytoplankton biomass in a coastal marine region off Cochin are evaluated. The control of environmental forcing on phytoplankton production and its relation on various interaction effects are reinforced to outline a predictive ecosystem model for the southwest coast of India. The first-order interaction effects between parameters are found to be highly critical since in biological activities, competition between abiotic species, which is difficult to measure directly, can be replaced by interaction between nutrient-factors. The present study by multivariate statistical analysis shows that the inter-relationships between phytoplankton variability and nutrient factors are highly sensitive to seasonal periodicity. The step-up multiple regression model explain chlorophyll a up to 77% variability for nonmonsoon periods and show that these coastal waters sustaining vertical gradients, are capable of inducing primary production through a variety of direct as well as interaction effects among the environmental variables. This study also indirectly suggests that grazing of zooplankton and supply of particulate organic matter either from the adjoining watershed or the periodically activated mudbanks of this region regulate the nutrient dynamics of these coastal waters, and their contribution should be duly considered for an effective ecological model to predict primary production. Despite the complexity of the interactions between nutrient availability, phytoplankton biomass and an equally important zooplankton grazing (not included in the present study), the results showed that it is possible to disentangle environmental processes causing observed trends in standing stock using multivariate statistical analysis during non monsoon period and improves our understanding of the governing role of environmental variables upon phytoplankton variability in Indian coastal waters.
The interacting effects of abiotic processes in explaining variations of phytoplankton biomass in a coastal marine region off Cochin are evaluated. The control of environmental forcing on phytoplankton production and its relation on various interaction effects are reinforced to outline a predictive ecosystem model for the southwest coast of India. The first-order interaction effects between parameters are found to be highly critical since in biological activities, competition between abiotic species, which is difficult to measure directly, can be replaced by interaction between nutrient-factors. The present study by multivariate statistical analysis shows that the inter-relationships between phytoplankton variability and nutrient factors are highly sensitive to seasonal periodicity. The step-up multiple regression model explain chlorophyll a up to 77% variability for non- monsoon periods and show that these coastal waters sustaining vertical gradients, are capable of inducing primar...
Oceanological and Hydrobiological Studies, 2020
Chlorophyll-a (Chl-a) concentration is an important issue in ocean ecosystem management and research. This study investigates seasonal and annual variability in Chl-a and its relationship with sea surface temperature (SST) and river discharge in the shelf region of the Northern Bay of Bengal (BoB), as well as validates satellite data against in-situ data. Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite data on Chl-a concentration and SST from 2002–2018 were used in this study. River discharge data were obtained from the Bangladesh Water Development Board (BWDB). The annual Chl-a concentration ranged from 2.08 to 2.94 mg m−3, with an average of 2.43 ± 0.24 mg m−3. The Chl-a concentration was found higher (2.21 ± 0.56 mg m−3) during the northeast monsoon (October–February) and lower (1.81 ± 1.14 mg m−3) during the pre-monsoon season (March–May). The study revealed a declining trend in Chl-a concentration from 2002 to 2018, and the rate of change was −0.0183 mg m−3...
Remote Sensing in Earth Systems Sciences, 2020
The present study investigates seasonal variability of physicochemical parameters and phytoplankton community structure, abundance, and chlorophyll a (Chl a) during 2007-2009 in the Mahanadi estuary, Bay of Bengal (BoB). Seasonal variations of phytoplankton community depended upon the change in hydrographic conditions and nutrient concentrations of the estuarine ecosystem. The changing scenario of phytoplankton community structure in relation to the various physicochemical properties of the ambient water was influenced by the monsoon and post-monsoon cycle. Discernible variation was observed in phytoplankton species composition, population density, and Chl a concentration between the pre-monsoon (April), monsoon (July), and postmonsoon (October). The mean population density of phytoplankton varied from monsoon (29,276 cells l −1) to pre-monsoon (43,290 cells l −1) period. Multivariate analyses showed that diatom was the most dominant (57.63%) followed by dinoflagellates (33.05%) compared with other communities in the study area. The green and blue-green algae were dominant during monsoon, while coccolithophores and silicoflagellates were the major during pre-monsoon. The Chl a concentration leads to the population density and varied between 0.87 and 1.18 mg m −3 from pre-monsoon to post-monsoon. Salinity and suspended solids (SS) played a major role in the spatial and seasonal distribution of phytoplankton composition and showed a positive correlation (p < 0.01) between nitrogenous nutrients (NO 3 and NO 2) with phytoplankton density and Chl a, suggesting that nitrogenous nutrients have profound influence on the phytoplankton growth. The in situ Chl a data used for validation of composite satellite MODIS data and result found that both data showed a similar trend of distribution in the region. The Chl a concentration was significantly higher in the pre-monsoon period.
Mixed layer variability and chlorophyll a biomass in the Bay of Bengal
Biogeosciences, 2014
The mixed layer is the most variable and dynamically active part of the marine environment that couples the underlying ocean to the atmosphere and plays an important role in determining the oceanic primary productivity. We examined the basin-scale processes controlling the seasonal variability of mixed layer depth in the Bay of Bengal and its association with chlorophyll using a suite of in situ as well as remote sensing data. A coupling between mixed layer depth and chlorophyll was seen during spring intermonsoon and summer monsoon, but for different reasons. In spring intermonsoon the temperature-dominated stratification and associated shallow mixed layer makes the upper waters of the Bay of Bengal nutrient depleted and oligotrophic. In summer, although the salinity-dominated stratification in the northern Bay of Bengal shallows the mixed layer, the nutrient input from adjoining rivers enhance the surface chlorophyll. This enhancement is confined only to the surface layer and with...
Journal of Geomatics
Study has been carried out to monitor the phytoplankton biomass in Bay of Bengal (BoB) and Arabian Sea (AS) using Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite data. Cloud masking, geometric corrections and subsets generations were performed to retrieve chlorophyll images from MODIS-Aqua data during the periods January - December for the years 2007 and 2008. The two regions (BoB & AS) have been divided into four subsets; subset-1 (Northern Bay of Bengal), subset-2 (Southern Bay of Bengal), subset-3 (Northern Arabian Sea) and subset-4 (Southern Arabian Sea). The results were analyzed and confirmed that chlorophyll concentration mean range was high (0.97-1.89 mg m-3) in northern Arabian Sea during the months of July for both years 2007 and 2008 and low concentration range (0.12-0.35 mg m-3) was obtained during April month for both years in southern Bay of Bengal. This study found to be important as information about the chlorophyll concentration in the Northern ...
Evidence for enhanced chlorophyll-a levels in the Bay of Bengal during early north-east monsoon
Journal of Oceanography and Marine Science
To understand the chlorophyll-a distribution in the neritic waters of the northern Indian Ocean, which comprises the Arabian Sea on the west and the Bay of Bengal on the east, seawater samples were collected during early northeast monsoon season (November, 2008). The column integrated chlorophyll-a over the Arabian Sea and the North Bay of Bengal exhibit high concentrations. However, the southernmost station (0806) shows enhanced chlorophyll-a concentration compared to other stations in the south Bay (0807, 0808 and 0809). This is attributed to eddy pumping of nutrients from subsurface to surface waters of the Bay during the study period due to cyclonic conditions. This observation is further supported by the lack of nutrients in the surface waters at the other stations from the south Bay compared to the station 0806, which has high nutrient concentrations. The observed salinity in the Bay of Bengal shows a strong north-south gradient with higher salinity in the southern part of the Bay. The supply of nutrients through fluvial input (that is, dominantly from the northern region) is insignificant. The enhanced chlorophyll-a concentration over the farthest station (0806) can be either due to Eddy mediated biological production or lateral advective transport of nutrients.
Indian Journal of …, 2008
In the present paper, we have carried out analysis of surface chlorophyll-a concentration in the seas around India obtained using the Indian Remote Sensing satellite IRS-P4 Ocean Colour Monitor (OCM) data. The focus was given to southwest Bay of Bengal where such studies are scanty. The study portraits the chlorophyll-a pattern during July 1999-June 2000. The monthly sea surface temperature (SST) trend and wind patterns using NOAA-NCEP and Quickscat Scatterometer data, respectively, were studied, to elucidate their impact on chlorophyll distribution. This helped to decipher how the reversing monsoon wind induces algal blooming in the surface waters of the study area. Several features like eddies, algal blooms and coastal plumes were observed. Highest mean chlorophyll was observed in January (northeast monsoon) and lowest in May (summer inter monsoon). Adjacent Arabian Sea water found predominantly productive than the Bay of Bengal water. Higher wind speed around 10 m/s in southwest and northeast monsoon shows about two fold increase in chlorophyll concentration to 1.0-2.0 mg/m 3 and the SST has shown gradient and decrease of about 1-2ºC in the BoB and off southern India, respectively.
Numerical Analysis of the Biogeochemical Parameters in the Bay of Bengal
Journal of Shipping and Ocean Engineering, 2016
Oceanic nutrient cycling plays a key role in understanding how oceanic biogeochemical parameters respond in varying physical and anthropogenically controlled processes. OA (Objective Analysis) of monthly climatology of WOA13 (World Ocean Atlas 13) nutrient data of 5 km resolution called Nutrient-Climo has been done in this paper for analyzing the nutrient-rich region in the BOB (Bay of Bengal) and the mechanisms of physical forces were examined using six years (2002-2007) global ocean monthly analysis datasets based on the SODA v2.0.4 (Simple Ocean Data Assimilation package). The upwelled zones established from the circulation pattern were well synchronized with the nitrate rich zones. The POC (particulate organic carbon) of 5 km resolution has been analyzed from MODIS (Moderate-resolution Imaging Spectroradiometer) data and Chl a (Chlorophyll a) concentration SeaWiFS (Sea-viewing Wide Field-of-view Sensor) data of 9 km resolution are used to predict the productive zones in the BOB. In this paper, we examined that Chl a concentration (above 0.5 mg/m 3) is found during the post-monsoon followed by winter in the northwestern , northeastern coast and head BOB as the source of nutrients is also supplementary due to high input of litter and sediment associated nutrients that are released during estuarine transport.