Physico chemical forcing on phytoplankton size classes and associated reflectance in coastal waters of western Bay of Bengal using satellite remote sensing

Abstract

Phytoplankton are the major driver contributing to large fraction of global primary production and hence considered as one of the key players in the ocean regulating climate. These primary producers are at the base of marine food web and can fix inorganic carbon and convert solar to chemical energy thereby significantly contributing to global carbon cycle. The variability and distribution of phytoplankton is predominantly due to physico-chemcial forcing including light absorption, nutrient uptake, sinking rate and export, which is also sensitive to phytoplankton size classes (PSC). The PSC are defined as micro (MP) (gt20and#956;m), nano (NP) (lt20and#956;m and gt2and#956;m) and pico-phytoplankton (PP) (lt2and#956;m and gt0.2and#956;m). The advancement in satellite technology has provided variety of bio-optical models for retrieval of PSC making it potential to study long-term trend at synoptic sale. The study investigates spatio-temporal distribution of physico-chemical variables affecting chlorophyll-a (chl-a) at two locations in coastal waters off Gopalpur and Visakhapatnam along northwestern Bay of Bengal (BoB). Further, spectral characteristics of phytoplankton absorption coefficient (aph) in various size classes (MP, NP and PP) and its relationship with respective chl-a concentration were studied. In addition, two quotabundancequot based PSC models were evaluated and the best model was used to understand the spatial distribution at climate scale using MODISA satellite data.The long-term trend in physico-chemical-biological parameters and environmental determinants of chl-a was studied using SATellite Coastal and Oceanographic REsearch (SATCORE) in situ data. The in situ PSC and absorption data were acquired onboard ORV Sagar Manjusha. The long-term synoptic trend in distribution of PSC and their fractions was studied with MODISA satellite data. newlineThe study showed strong seasonality in distribution of physico-chemical-biological variables off Gopalpur and Visakhapatnam. newline