Estimates of vertical eddy diffusion through the thermocline from phytoplankton nitrate uptake rates in the mixed layer of the eastern tropical Pacific1

Abstract

Vertical eddy diffusion coefficients ranging from 0.05–1.1 cm2·s−1 were calculated from phytoplankton nitrate uptake rates in the mixed layer and nitrate gradients at the top of the thermocline of the eastern tropical North Pacific. An empirical relationship was determined between these diffusion coefficients and density gradients in the thermocline. This relationship was used to calculate nitrate fluxes through the thermocline at several stations where nitrate uptake was not measured, and the fluxes indicated that an average of 29% of the primary productivity was supported by the uptake of nitrate‐nitrogen.