Inter-annual variability in the inherent optical properties along the southeastern Arabian Sea from 2009 to 2015

Abstract

A study was performed on the coastal waters of the southeastern Arabian Sea to understand the changes in the inherent properties of optically active substances (OAS). The objective of this study was to obtain insight into the temporal dynamics of OASs for various remote sensing applications. Both the absorption of light by phytoplankton (aph(440)) and detritus (ad(440)) varied the 2nd orders of magnitude, whereas the absorption of light by chromophoric dissolved organic matter (CDOM; aCDOM(440)) exhibited an increasing trend over the years. aCDOM(440) increased from 2009 to 2015 at a rate 0.012 m−1 year−1. The validation of the satellite data with in situ data indicated that ad(443) underestimated the in situ ad(443) when the in situ ad(443) was less than 0.3 m−1. The ternary analysis of ocean-colour-climate-change initiative (OC-CCI)–derived inherent optical properties (IOP) during the postmonsoon season indicated increased contribution by ad(443). Detritus was the primary light absorber in the coastal waters of Kochi followed by phytoplankton and CDOM. These long-term data sets and their seasonal variation will enable development of seasonal specific regional algorithms for chlorophyll-a, which are employed in potential fishing zone advisories and other applications.