MEPS 189:65-75 (1999)  -  doi:10.3354/meps189065

ABSTRACT: The coupling between upwelling intensity off the NW Iberian coast and differential carbohydrate synthesis and utilisation in the water column has been investigated using the conservative chemical parameters 'NO', 'CO' and 'NCO'. Differences between the observed vertical distribution of 'NO' and 'CO' and that expected from Redfield stoichiometry indicate that an excess of carbohydrate synthesis occurs in the surface layer when nutrients become depleted during upwelling relaxation periods. Excess carbohydrate synthesised in upper layers is consumed at subsurface levels. This consumption can be attributed to the presence of autotrophic migratory organisms like the photosynthetic ciliate Mesodinium rubrum and several dinoflagellates which produce carbohydrates in the upper, well illuminated layers and take up nutrients in the subphotic zone. Conversely, situations of intense upwelling are associated with production of organic matter following the Redfield ratio and with a decrease in carbohydrate synthesis. Deviations from Redfield stoichiometry found in other marine areas could be explained by processes comparable to those occurring in the NW Iberian upwelling, suggesting that vertical migration by photosynthetic organisms may play a greater role in the vertical transport of nitrogen and carbon than generally recognized.

KEY WORDS: Upwelling · Carbohydrate · Redfield ratio