The temporal and spatial variability of bioavailable iron delivered to the ocean may be controlled via in-cloud photochemical reduction of desert dust, assisted by the impact of oxalate released by fungi in the desert soil. The basic process in the photochemical production of bioavailable iron through decarboxylation reaction involves simultaneous action of oxalate released by the fungus encapsulated in a cloud droplet, above some threshold solar radiation. Therefore, diurnal and latitudinal variations in solar irradiation and the sporadic nature of rain along the path of the synoptic-scale atmospheric depressions are the governing factors that determine spatial and temporal distribution of phytoplankton growth and especially that of coccolithophorid blooms on the ocean surface.