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Estimation of Chlorophyll-a, TSM and salinity in mangrove dominated tropical estuarine areas of Hooghly River, North East Coast of Bay of Bengal, India using sentinel-3 data

Mondal Ismail, De Aakash, Nandi Subhanil, Thakur Sandeep, Raman Mini, Jose Felix, De Tarun Kumar

Acta Geophysica

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2024

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Vol. 72, no. 1

303--322

EN

The study aims to assess variations in spatio-temporal characteristics of water quality parameters from three tropical estuaries, namely Muri-Ganga, Saptamukhi, and Hooghly, in the western portion of the Indian Sundarbans. Reliable retrieval of near-surface concentration of water quality parameters such as Chlorophyll-a, SST & TSM from diverse aquatic ecosystems with broad ranges of tropical requirements has always remained a complex issue. In this study, application of Case 2 Regional Colour Correction (C2RCC) processor has been tested for its accuracy across different bio-optical regimes in both inland and coastal waters. Satellite images for the same period were also collected and analysed using the C2RCC processing sequence to retrieve parameters like the depth of water, surface reflectance, water temperature, inherent optical properties (IOPs), chlorophyll-a, salinity, total suspended matter (TSM), etc., using the SNAP software. In situ sampling from specific locations within these estuaries and water quality analysis were conducted for the period 2017-2019. The OLCI retrieved datasets were compared and corroborated with field survey datasets. It was observed that the highest amount of TSM was recorded at Diamond Harbour during the 2018 pre-monsoon season (301.40 mg/L field-based value and 308.54 mg/L estimated value). Similarly, chlorophyll-a had higher concentrations throughout the monsoon season (3.03 mg m-3, (field survey), and 2.96 mg m-3, (estimated) at Fraserganj and Sagar south points. A very good correlation was observed for all seasons for Chl-a (r = 0.829) and TSM (r = 0.924) between the OLCI data and in situ measurements. Higher correlation and significant ‘r’ values highlight the importance of having both field-based as well as remotely-sensed information in understanding any dynamic system in a sustained manner. Results also confirm that the water quality model using OLCI Chl-a and TSM products outperforms conventional techniques. The study demonstrates the efficacy of using Sentinel 3 OCLI data for shallow marine and estuarine remote sensing applications, especially for monitoring TSM and Chl-a concentrations.

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Dinoflagellate cysts and benthic foraminifera from surface sediments of Svalbard fjords and shelves as paleoenvironmental indicators

Telesiński Maciej M., Pospelova Vera, Mertens Kenneth Neil, Kucharska Małgorzata, Zajączkowski Marek

Oceanologia

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2023

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Vol. 65 (4)

571--594

EN

Due to the Arctic amplification effect, the Svalbard archipelago is an important area for studying ongoing environmental changes. However, its marine ecosystem is extremely complex. In this study, we analyze modern assemblages of dinoflagellate cysts (dinocysts) and benthic foraminifera from surface sediment samples around Svalbard. We use multivariate statistical analyses to examine relationships between environmental conditions (summer and winter sea surface temperature and salinity, sea-ice cover, etc.) and both microfossil groups to evaluate their use as proxies for reconstructions of the marine environment in the region. Our results show that the most important factor controlling the environment around Svalbard is the Atlantic Water which mostly impacts the western coast, but its influence reaches as far as the eastern coast of Nordaustlandet. However, on a local scale, such factors as the sea-ice cover, the presence of tidewater glaciers, or even the morphology and hydrology of fjords become increasingly important. We found that two dinocyst species, cysts of Polarella glacialis and Echinidinium karaense, can be considered regional winter drift ice indicators. The relationships between environmental parameters and benthic foraminiferal assemblages are much more difficult to interpret. Although statistical analysis shows a correlation of benthic foraminiferal species with various environmental parameters, this correlation might be somewhat coincidental and caused by other factors not analyzed in this study. Nevertheless, the use of two complementary microfossil groups as (paleo)environmental indicators can provide a more comprehensive picture of the environmental conditions.

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Seasonal and annual variability in chlorophyll-a in the shelf region of the Northern Bay of Bengal using MODIS-Aqua data

Abdur Rouf Muhammad, Antu Al-Hasan, Noor Imran

Oceanological and Hydrobiological Studies

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2020

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Vol. 49, No. 4

398--407

EN

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 year−1. Chl-a concentration showed a weak inverse relationship with SST, both annually and seasonally, especially in the pre-monsoon season. River discharge masked the effect of SST on Chl-a variability during the southwest and northeast monsoon. A reasonable correlation (r = 0.78) was found between the MODIS-Aqua data and in-situ Chl-a observations.

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Characterization of the northern Red Sea's oceanic features with remote sensing data and outputs from a global circulation model

Eladawy A., Nadaoka K., Negm A., Abdel-Fattah S., Hanafy M., Shaltout M.

Oceanologia

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2017

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No. 59 (3)

213--237

EN

Sea surface temperature (SST) and surface wind (SW) are considered the most important components in air–sea interactions. This study examines the relationships between SST, SW and various oceanic variables in the northern Red Sea (NRS) during the period of 2000–2014. The current study is the first attempt to identify the SST fronts and their relationship with the dominant circulation patterns. SST fronts are mapped using the Cayula and Cornillon algorithms. The analysis is performed with available remote sensing and reanalyzed data together with 1/12° HYbrid Coordinate Ocean Model (HYCOM) outputs. Seasonal-trend decomposition procedure based on loess (STL) is applied for trend analysis, and Principal Component Analysis (PCA) is run for the atmospheric parameters. The SST, SW speed and Chlorophyll-a (Chl-a) changes show insignificant trends during the period of 2000–2014. Meridional SST fronts are more significant during the month of January, and fronts that are perpendicular to the sea's axis occur from February to May. Distinct monthly and spatial variations are present in all the examined parameters, although these variations are less pronounced for the wind direction. The SST is mainly controlled by the air temperature and sea level pressure. Significant correlations exist between the SST and the studied parameters (alongshore wind stress rather than the cross-shore wind stress, surface circulation, MLD, and Chl-a). Surface winds generally flow southeastward parallel to the Red Sea's axis explaining that alongshore wind stress is highly correlated with the studied parameters.