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In early September 1989 persistent southward w ~ n d s generated an upwelling region along the Oregon, USA, coast with a front (upwelling front) at its seaward edge. We examine and compare autotrophic production, biomass and species composition in the euphotic zones of 2 stations on either side of this front using a combination of analytical techniques. The upwelling front could be seen in satellite thermal imagery all along the southern Washington and Oregon coasts except where it was obscured by the outflow of the Columbia River. Hydrographic profiles at the seaward station showed a relatively warm and deep surface-mixed layer that was freshened by river water. At the landward station the river's influence was much less, and cold, saline water extended to within 10 m of the surface. Chl a concentrations were higher in cold water nearshore, and a deep chl a maximum was present offshore. On both sides of the front, production rates were highest above 10 % I,, but the integrated rate nearshore was higher by a factor of 3, and the energy conversion efficiency (from incident solar energy to fixed chemical) of the euphotic zone at the landward station was more than twice that of the seaward station. Flow cytometer analyses revealed 2 distinct autotrophic groups nearshore based on size (volume) and brightness of red fluorescence. Count and size comparisons with epifluorescence microscope observations show that the larger and brighter peak was caused by cryptomonads; this peak was absent seaward of the front. Volume estimates based on epifluorescence microscope observations reveal that at the productive inshore station Synechococcus spp., cryptomonads and small autotrophs (< 10 pm) dominated the phytoplankton biomass, and diatoms were a relatively minor component.

Autotrophic production, biomass and species composition at two stations across an upwelling front