Fluorescent Dissolved Organic Matter Dynamics in the Coastal Waters off the Central East Indian Coast (Bay of Bengal)

Abstract

Excitation Emission Matrix (EEM) fluorescence spectra and hydrochemical parameters were measured monthly for a year in the western coastal waters of the Bay of Bengal in a shore normal transect up to the mid-shelf region. The parallel factor analysis of the EEM spectral data showed five fluorescent components, two protein (Tyrosine and Tryptophan protein-like, represented as B and T respectively) and three humic (UV humic, Marine humic and Visible humic-like represented as A, M and C respectively). The B fluorophore was more enriched attributed to bacterial decay of photosynthetically produced organic matter and acted as proxy of primary production. The humic like fluorophores showed significant conservative behavior up to salinity ~31. During the pre-monsoon season, photobleaching caused significant loss of A and C fluorescence making them deviate from conservative behavior but not from the linear distribution against chlorophyll a. The vertical profiles revealed systematic maxima for the humic fluorophores at depths during pre-monsoon and it is inferred that they owe their origin to phytoplankton.