5 research outputs found
Contrasting phytoplankton community structure and associated light absorption characteristics of the western Bay of Bengal
Absorption spectra, particulate pigments, and hydrochemical constituents were measured in the western Bay of Bengal (BoB) during July-August 2010 when influence of river discharge is at peak. Chromophoric dissolved organic matter (CDOM) absorption coefficient (aCDOM(440)) displayed a significant inverse linear relationship with salinity in the surface waters implying conservative mixing of marine and terrestrial end members. The northern part of the study area is influenced by discharge from the river Ganga and a dominant terrestrial CDOM signal is seen. The southern part receives discharge from peninsular rivers with corresponding signals of higher CDOM than the linear model would indicate and higher UV-specific absorption coefficient (SUVA) indicating more aged and humified DOM. Lower contribution of CDOM to total non-water absorption and higher phytoplankton biomass (chlorophyll a absorption coefficient, aph(440)) but lower chlorophyll a specific phytoplankton absorption coefficient (aph*(440)) characterize the northern part, compared to the southern part. Chlorophyll b had a distinct linear relationship with chlorophyll a in the latter. The Size Index (SI) indicated dominance of microphytoplankton in the northern and nano and picophytoplankton in the southern parts. Chlorophyll a is significantly related to aph*(440) by an inverse power model in the northern part but by an inverse linear model in the southern part. Our study suggests that knowledge of the phytoplankton community structure is essential to improve chlorophyll a algorithm in the coastal Bay of Bengal
Contrasting bio-optical characteristics of coastal water prior to and in the aftermath of a tropical super cyclone
<p>Apparent and inherent optical properties were measured in the coastal region off Visakhapatnam (Bay of Bengal) during pre-monsoon season (January–May) of successive years, in-between of which the (October 2014) Hudhud super cyclone had landfall across. For 5 months after the cyclone in the region up to 50 m isobath, or 15 km from the coast and 6 months after the cyclone in the region up to 30 m isobath, or 5 km away, the particle back-scattering coefficient (<i>b</i><sub>bp</sub>) and remote-sensing reflectance (<i>R</i><sub>rs</sub>) were anomalously higher throughout the spectral region (400–700 nm) than during other times. The <i>b</i><sub>bp</sub> spectral slope coefficient <i>γ</i> is abnormally higher than predicted from the <i>b</i><sub>bp</sub>(680)–<i>γ</i> model relationship, and <i>R</i><sub>rs</sub>(685) is also abnormally higher than the significant <i>R</i><sub>rs</sub>(685)–chlorophyll-<i>a</i> (chl-<i>a</i>) relationship would predict. These exceptional properties are attributed to the presence of little absorbing and highly reflecting sub-micrometre-sized particles in fine suspension that leached from the coastal deposits emplaced in the study region from the nearby harbour during the cyclone. The optical properties recovered subsequently. In the period when the reflectance and scattering spectra are not recovered, the <i>R</i><sub>rs</sub>(685) is no longer a proxy of chl-<i>a</i>. Remote-sensing algorithms for phytoplankton abundance of the coastal region during this period need correction.</p