Sub-thermocline chlorophyll maximum in the South China Sea, Area IV: Vietnamese waters

Abstract

Shipboard measurement of chlorophyll a and b by HPLC system were carried out on the M.V. SEAFDEC Cruise No. 57/3-1999 from 21 April to 5 June 1999, in the South China Sea, Vietnamese waters. Chlorophyll a and b in surface water (2 m), seasonal thermocline below the mixed layer, chlorophyll maximum depth and sub-chlorophyll maximum depth from 58 stations in the studied area were investigated. Chlorophyll maximum depth ranged 7-90m and the concentration of chlorophyll a and b in this layer were 0.07-1.75 mg/m³ and 0.003-0.31 mg/m³ respectively. High concentration of chlorophyll a and b were observed in nearshore water which may reflected the effect of run off from the coastal cities and lower Maekong delta. Observed chlorophyll concentrations in this area agreed well with other values reported for tropical seas.