Iron is an essential micronutrient for organism growth, and iron concentrations are low enough to be biologically limiting in many parts of the surface ocean away from continents and sources of atmospheric dust. Iron limitation is linked to the presence of abundant macro-nutrients in the surface ocean, so-called high-nitrate, low chlorophyll (HNLC) areas in the Southern Ocean, Equatorial Pacific and sub-arctic North Pacific. In laboratory studies and deliberate open-ocean perturbation experiments, the addition of iron to these HNLC waters causes dramatic enhancement in aggregate phytoplankton growth and biomass and shifts in community structure toward larger diatoms that can contribute to increased downward export of organic matter via sinking particles. At subtropical latitudes, there is more limited evidence that iron availability may modulate nitrogen fixation, a key source of new nutrients in oligotrophic systems. These connections between the oceanic biological pump and iron availability suggests that large-scale variations of iron flux into the ocean from atmospheric dust deposition, remobilization from continental shelf sediments and glacial weathering could alter ocean carbon storage and thus atmospheric CO₂.
Results/Conclusions

In the talk, I will review the following aspects of iron-carbon coupling in the ocean: recent developments from field experiments on both deliberate and natural iron fertilization studies; scientific challenges behind proposed iron fertilization carbon mitigation strategies; paleoceanography studies on iron-carbon coupling, in particular evidence for the role of iron in controlling the variations in glacial-interglacial CO₂; recent progress on the incorporation of coupled iron-carbon dynamics with Earth System Models.