Impact on primary production by mesoscale eddies in the northwest South China Sea: A case study by satellite and field observation

Phytoplankton biomass and production coupled with environmental parameters were investigated in northwestern South China Sea during the South China Sea Open Cruise by R/V “Shiyan 3” in September 2009. Both satellite and in situ data indicated that cold eddy decreased sea surface temperature and enhanced Primary production (PP) around Xisha Island adjacent sea. Nutricline, thermocline and chlorophyll a contour line were coincident generally in the eastern part of the Y area, indicating the impact of hydrological processes on ecological and environmental profiles. PP decreased with the increasing water depth in the euphotic layer, and the maximum value appeared in the surface layer. The surface PP value was 0.59 mgC m−3  h−1 and the integrated primary production (IPP) was 250 mgC m−2  d−1 at Y2, slightly lower than that at X5, with the surface PP value of 0.66 mgC m−3  h−1 and the IPP value of 259.33 mgC m−2  d−1. The descend range of IPP in Y area was higher than the ascensional range in X area, indicating that the impact of cold eddy on phytoplankton biomass and production was more obvious than the impact of the warm eddy in this study.