Anticyclonic Eddy Edge Effects on Phytoplankton Communities and Particle Export in the Northern South China Sea

We examined response of phytoplankton total chlorophyll a (TChl a) and community composition to three coherent anticyclonic eddies (ACEs) observed during a cruise to the northern South China Sea on 28 July to 7 August 2007. Photosynthetic pigments were measured to estimate the contribution of nine phytoplankton groups to TChl a. Although the water column-integrated TChl a inventory in the upper 100m was very similar among the three ACEs (17.6-18.9mg/m(2)) we observed during the cruise, there were remarkable enhancements in biomasses at the eddy edges. TChl a inventory was 20.83.0mg/m(2) at the edge, which was 33% or 60% higher than at the center and reference. The greatest enhancement of the TChl a at edge was attributed to haptophyte-8, which was 1.6 and 2.2 times the analogous concentrations at the center and reference sites. The Prochlorococcus Chl a was 50% greater at the edge relative to the reference and was intermediate at the center. Diatom Chl a at the edge was 2.5 times the concentrations at the center and reference sites. The positive correlation between particulate organic carbon flux and haptophyte-8 Chl a at the edge implied an important role of haptophyte-8 in particle export productivity. It is interesting to note that there occurred higher fluxes of biogenic Si at the center of the ACEs due likely to lateral transport of diatoms from the edge. The phenomenon of higher TChl a at the edge but higher export at the center may have been the combined result of vertical convection and lateral transport within the eddies. Plain Language Summary The response of different phytoplankton groups to three anticyclonic eddies (ACEs) and the relationship between the carbon export and phytoplankton community was studied in the northern South China Sea on July 28-August 7, 2007. The phytoplankton TChl a concentration inventory in the upper 100 m was very similar among the three ACEs. But the biomass and community composition varied in different parts of the ACEs, including the ACEs' centers, edges and outside the ACEs. The enhancement of TChl a at edge attributed to haptophyte-8 was siginificantly.The Prochlorococcus Chl a was 50% greater at the edge relative to the reference and was intermediate at the center. The haptophyte-8 played an important role of in particle export. The phenomenon of higher TChl a at the edge but higher export at the center may have been the combined result of vertical convection and lateral transport within the eddies