Atmospheric transport of iron and its deposition in the ocean

TLDR

Atmospheric transport of continental weathering products delivers the majority of iron to the open ocean, with up to eight times more deposition in the northern hemisphere, and the dissolved fraction (10–50%)—primarily Fe(II) formed by photochemical reduction—can limit primary productivity where other nutrients are abundant. Rapid dissolution of atmospheric iron allows Fe(II) to pass a 0.4‑µm filter and become immediately available to phytoplankton, and continental transport supplies roughly three times more dissolved iron to the oceans than rivers.

Abstract

The atmospheric transport of continental weathering products is responsible for much of the mineral material and Fe entering the open ocean and is probably the dominant source of nutrient Fe in the photic zone. In regions where other nutrients are present in high concentrations, the flux of Fe from the atmosphere may be a limiting factor in primary productivity. Due to the larger source regions for dust north of the equator, ∼8 times more atmospheric Fe is deposited in the northern hemisphere than in the southern hemisphere. The mineral aerosol and Fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes. Between 10 and 50% of the total atmospheric Fe entering the world ocean appears to dissolve (i.e. it will pass through a 0.4-µm pore-size filter) rapidly when the mineral matter enters the ocean. Much of the atmospheric Fe is present as Fe(II), apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport. This readily soluble Fe(II) should be available immediately for use as a nutrient by phytoplankton. Atmospheric transport from the continents is estimated to supply ∼3 times as much dissolved Fe to the oceans as that delivered via rivers.