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Iron is a vital micronutrient in the marine environment, and variations in the supply and transformation of this element can alter ocean productivity. In this web focus, we present a collection of articles that examine the modern marine iron cycle and assess how iron cycling has varied through time.
Iron is an essential fuel for life in the oceans. The influence of this element on biogeochemistry — and nitrogen cycling in particular — varies across environments and time.
The recent expansion of observational data has changed our understanding of the ocean iron cycle and its linkages with nutrients such as carbon and nitrogen.
External metal inputs to oceans affect ocean productivity and metal cycling. A synthesis of researchreveals that internal processes such as metal retention, recycling and remineralizationare also important.
Large iron deposits formed episodically in the Archaean oceans. Experimental data and geochemical modelling suggest that green rust was an important contributor to the formation of these deposits and the Archaean iron cycle in general.
Fixed nitrogen is lost from oxygen minimum zones. Experimental data from an anoxic lake show that the presence of Fe(II) limits this loss, suggesting that ancient anoxic and iron-rich oceans may not have been nitrogen limited.
The largest known hydrothermal plume moves dissolved iron halfway across the Pacific. In situ measurements show that dissolved and particulate iron transport is facilitated by reversible exchange of dissolved iron onto organic compounds.
Dust-borne nutrients can enhance productivity in the surface ocean. Two years of sediment trap data reveal that dust enhances carbon export to depth by increasing surface nitrogen fixation, productivity and carbon sinking rates in the North Atlantic.
Atmospheric oxygen was maintained at low levels throughout huge swathes of Earth's early history. Estimates of phosphorus availability through time suggest that scavenging from anoxic, iron-rich oceans stabilized this low-oxygen world.
Dissolved iron is mysteriously pervasive in deep ocean hydrothermal plumes. An analysis of gas, metals and particles from a 4,000 km plume transect suggests that dissolved iron is maintained by rapid and reversible exchanges with sinking particles.