SEASONAL VARIABILITY OF CARBON FLUX IN THE NORTH-EASTERN BAY OF BENGAL: SEASONAL CARBON ABSORPTION

Abstract

Carbon dioxide emissions are the major contributor to global climate change. Increases of CO2 in atmosphere rise surrounding environment temperature and ocean acidification. By photosynthetic activity phytoplankton are responsible to remove CO2 from atmosphere. Globally 50% of carbon sinks into the ocean via process called biological pump. This research was conducted over four major seasons in the northeastern Bay of Bengal to measure the seasonal variation of carbon flux. An associated factor of carbon flux was the phytoplankton sinking rate determined by SETCOL method. The carbon flux showed that the monsoon season act as the major contributor to carbon flux (2.52 ± 2.33 mg C m-2 day- 1), followed by 2.03 ± 1.73 mg C m-2 day-1 in the winter season, whereas 1.65 ± 1.56 mg C m-2 day-1 and 1.56 ± 0.86 mg C m-2 day-1 found during pre-monsoon and post-monsoon season respectively. The data also demonstrated that the Kutubdia station exchanged more carbon than Cox’s Bazar station. Carbon flux correlated with the turbidity, SiO3-Si, PO4- P, total suspended solids, plankton density, phytoplankton sinking rate, and carbon content. Carbon flux negatively correlated nutrients (NO2-N, NO3-N) and positively related with SiO3-Si, PO4-P. ANOVA test showed carbon flux significantly differs among depths [F (1, 2) = 3.811, p<0.05]. Carbon flux-related factor phytoplankton sinking rate significantly varied with depth change and ranged from 0.04 to 1.86 m day-1. Major seasonal carbon sinking rate was observed in the winter season as 0.57 ± 0.52 m day-1. Phytoplankton sinking rate was correlated with nutrients, salinity, total suspended solids, total dissolved solids, and conductivity. This research finding gives us an understanding of seasonal carbon flux variation contributed by phytoplankton and demonstrated daily carbon sequestration in the northeastern Bay of Bengal and correlated with various biogeochemical factors.