Phytoplankton community at warm eddies in the northern South China Sea in winter 2003/2004

Two anti-cyclonic (warm) eddies were located in the northern South China Sea (SCS) during winter 2003/2004. They were monitored using sea-level anomaly data provided by satellite altimetry, surface drifters and in situ hydrographic data. Phytoplankton Chl a biomass as well as community structure were determined using high-performance liquid chromatography. Both warm eddies displayed positive sea-level anomaly, high sea-surface temperature and similar phytoplankton Chl a biomass compared with the reference area. However, phytoplankton communities we observed in these two eddies were significantly different. In one warm eddy which was formed by the Kuroshio intrusion, the phytoplankton community was dominated by prochlorophyceae within the euphotic zone. In the other warm eddy, which might be formed in coastal waters of northern SCS, haptophyceae dominated in the euphotic zone. This difference in the phytoplankton community was due to the different origins and ages of the two warm eddies.