The Arabian Gulf is exposed to intensive dust storms during summer until early winter. We investigated the nutritive effect of the dust on microbial biodiversity of the water column and the productivity of the Gulf. We collected samples from three sites in a transect perpendicular to the shore in March (before the strong dust storms) and in October (after the dust season) in 2013. At the three sites, we sampled the water column at three depths, and see-floor sediments using a HAPS corer. We also sampled the sand dunes that are the source of the dust. We analyzed the samples for pigments, microbial community composition using a 16S rRNA analysis, and nutrients. Our results showed that species richness and biodiversity were higher in October than in March. The relative abundances of key-player microorganisms were strongly pronounced in October. We assume that the dust rapidly sinks to the seafloor where the nutrients Fe and P are liberated through iron reduction. Assuming that all phosphate diffusing from the seafloor originates from the dust particles after deposition, we estimated a contribution of minimum 30,000 tons of fish produced every year in the Gulf. We found no close temporal coupling between dust storms and productivity. This is because nutrient liberation from the seafloor is slow and its transport from the seafloor to the photic zone by circulation processes is irregular. This study highlights the importance of dust as a source of nutrients in the Gulf ecosystem.

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