A study of euphotic depth at South China Sea using satellite imagery

Abstract

Euphotic depth is called critical depth in which the photosynthesis and respiration are balance with each other. Therefore, the retrieval of the euphotic depth is important on estimating ocean primary productivity and it plays an important role in global carbon cycle. The concentration of chlorophyll-a is one of the most important since it is used to estimate the primary productivity of water ecosystems. This study was conducted along Kuala Terengganu coastal waters in May 2009 and July 2009 which covers 32 stations. Secchi disc and light meter were used to measure water transparency while water samples were collected to analyze the concentration of chlorophyll-a. Euphotic depth was calculated from the secchi disc and light meter data. Maps of euphotic depth for South China Sea were produced from the satellite data. The regression analysis between sateJlite data and light meter confirmed that light meter give better accuracy to measure euphotic depth compared to secchi disc as the light meter can measure Kd with high accuracy. Euphotic depth is lower near coastal area and increase gradua1ly towards the open sea.