Atmospheric iron inputs and primary productivity: Phytoplankton responses in the North Pacific

Abstract

As part of the Asian Dust Inputs to the Ocean System (ADIOS) project, atmospheric dust fluxes and primary productivity were monitored during the dusty season (spring) of 1986 at 26°N, 155°W, in the North Pacific Ocean. The arrival of major pulses of dust from Asia was followed by major increases in primary production. Extensive chemical analyses of the atmospheric particles showed that they were iron‐rich (10‐15%) and, further, that if only a small proportion (e.g. 10%) of this iron dissolved in the euphotic zone, it would be sufficient to support the increases in carbon production at this location. The systematic increases in production noted with increasing depth and time may result from a continual release of iron from the settling particles in the euphotic zone. At all depths, systematic decreases in production followed the initial surge in production, indicating that the phytoplankton may have evolved from being iron‐limited to being nitrogen‐limited. Comparison of particle concentrations calculated by a particle settling model with primary productivity profiles indicated that mineral particles with settling velocities equivalent to those of 14 to 18‐μm‐diameter spherical quartz particles were the most likely source for the iron stimulating the increases in primary production.