Phytoplankton primary productivity in the Santa BarbaraChannel: Effects of wind-driven upwelling and mesoscale eddies

[1] The patterns and drivers of phytoplankton primary productivity in the Santa Barbara Channel (SBC) were examined on 16 cruises conducted 3 times each year from 2001 to 2006. Empirical orthogonal function (EOF) analysis revealed 3 modes of variability that explained 89% of the variance in the productivity data set. The first mode, strongest during spring, describes seasonal productivity changes driven by coastal upwelling. The second mode, largest in spring and fall, describes productivity changes over the western SBC associated with cyclonic eddies. Eddy-enhanced productivity changes were superimposed on variable levels of channel-wide productivity caused by upwelling within the SBC. The cyclonic eddies influenced productivity through enhanced nutrient supply associated with the uplift of isopycnal surfaces and through the occasional entrainment of phytoplankton and nutrients from water upwelled north of Point Conception. The third EOF mode describes productivity gradients on the continental shelf along the mainland coast with enhanced productivity in the east during spring and fall. Overall, our analysis shows that coastal upwelling combined with the effects of cyclonic circulation on particle retention and vertical nutrient supply combine to enhance phytoplankton biomass and productivity in the western SBC.