Variation of carbon and nitrogen uptake capacity in a regional upwelling area around Hachijo Island

Capacities for inorganic carbon, nitrate and ammonium uptake were measured around Hachijo Island, 300 km south of Tokyo, where local upwelling occurred. The phytoplankton population inside the upwelling area had a high capacity for nitrate uptake and a low capacity for uptake of ammonium. Nutrient concentration and phytoplankton biomass were higher in the upwelling plume than outside. On a chlorophylla basis, phytoplankton populations inside the upwelling area showed a lower capacity for carbon and nitrogen uptake than those outside the upwelling. Low temperature, relatively limited availability of light caused by extensive water mixing within the upwelling plume, and the difference in species composition of phytoplankton must be considered in explaining these lower uptake capacities.