Summary of Abstract Submission

Abstract Submission No. IO50-09-0041PresentationPoster

INFLUENCE OF FRESH WATER ADVECTION ON THE PICOPHYTOPLANKTON COMMUNITY STRUCTURE IN THE NORTHERN BAY OF BENGAL DURING THE SUMMER MONSOON

Smita Mitbavkar*1, Arga Chandrashekar Anil2, D. Narale2, R. Chitari2, S.A. Rao3, K. Mapari2

1 CSIR-National Institute of Oceanography, Dona Paula, Goa, , India
2 CSIR-National Institute of Oceanography, Dona Paula, Goa,, India
3 Indian Institute of Tropical Meteorology, Pune, India

ABSTRACT :

Picophytoplankton (< 3Ám cells) dynamics was investigated in the northern Bay of Bengal (BoB) during the summer monsoon focusing on a physical event of freshwater advection by conducting high resolution observations at an interval of 2-6h between 24th July and 1st August 2009. This is a part of the study conducted under the Continental Tropical Convergence Zone research/observational programme. From 24th-28th July, mixed layer (ML) water temperature was 28.4oC and salinity was 32.4. From 29th July, the water temperature increased to 28.8oC, salinity declined to 26.8 and the ML depth decreased from 40m to 14m. A simultaneous study carried out showed that the observed freshening of surface layer was due to the advection of river discharge influenced by rainfall over the Ganga-Brahmaputra catchment area. Temporal changes in the physical structure of the water column were reflected in the picophytoplankton community structure. Three picophytoplankton groups were discriminated flowcytometrically; Prochlorococcus, Synechococcus and picoeukaryotes. Prior to the lowering of surface salinity, Synechococcus was dominant within the ML and Prochlorococcus dominated below the ML. With the lowering of salinity, Synechococcus abundance declined significantly suggesting influence of advected waters. However, Synechococcus distribution below the ML and also that of Prochlorococcus was not affected. These observations suggest that physical processes such as freshwater advection can stratify the water column and significantly influence the composition and abundance of primary producers in the surface waters with not much impact on the sub-surface community thereby influencing the primary production and the biogeochemistry of the northern BoB.