an important component of the terrestrial ecosystems. The ferrous form of iron, Fe2+, is dominant in the Earth's mantle, core, or deep crust. The ferric form, Fe3+, is more stable in the presence of oxygen gas. Dust is a key component in the Earth's iron cycle. Chemical and biological weathering break down iron-bearing minerals, releasing the nutrient into the atmosphere. Changes in hydrological cycle and vegetative cover impact these patterns and have a large impact on global dust production, with dust deposition estimates ranging between 1000 and 2000 Tg/year. Aeolian dust is a critical part of the iron cycle by transporting iron particulates from the Earth's land via the atmosphere to the ocean. Volcanic eruptions are also a key contributor to the terrestrial iron cycle, releasing iron-rich dust into the atmosphere in either a large burst or in smaller spurts over time. The atmospheric transport of iron-rich dust can impact the ocean concentrations. Oceanic ecosystem The ocean is a critical component of the Earth's climate system, and the iron cycle plays a key role in ocean primary productivity and marine ecosystem function. Iron limitation has been known to limit the efficiency of the biological carbon pump. The largest supply of iron to the oceans is from rivers, where it is suspended as sediment particles. Coastal waters receive inputs of iron from rivers and anoxic sediments. Other major sources of iron to the ocean include glacial particulates, atmospheric dust transport, and hydrothermal vents. Iron supply is an important factor affecting growth of phytoplankton, the base of marine food web. Offshore regions rely on atmospheric dust deposition and upwelling. Other major sources of iron to the ocean include glacial particulates, hydrothermal vents, and volcanic ash. In offshore regions, bacteria also compete with phytoplankton for uptake of iron. In HNLC regions, iron limits the productivity of phytoplankton. Most commonly, iron was available as an inorganic source to phytoplankton; however, organic forms of iron can also be used by specific diatoms which use a process of surface reductase mechanism. Uptake of iron by phytoplankton leads to lowest iron concentrations in surface seawater. Remineralization occurs when the sinking phytoplankton are degraded by zooplankton and bacteria. Upwelling recycles iron and causes higher deep water iron concentrations. On average there is 0.07±0.04 nmol Fe kg−1 at the surface (<200 m) and 0.76±0.25 nmol Fe kg−1 at depth (>500 m). Therefore, upwelling zones contain more iron than other