Final Activity Report Summary - FAIRY (Factors controlling the bioavailability of Atmospheric Iron in the maRine ecosYstems)
We have shown that kinetic aspects for both iron dissolution and scavenging processes are very important as we have identified very fast adsorption and desorption processes. In both cases, we have shown the significance of the dissolved organic matter related to biological activity:
(1) Fe dissolution is dependent on the water's ligand field rather than the type or quantity of dust deposited on the surface. Dissolved inorganic Fe is saturated at 0.1 nM in natural sea water. Because of these thermodynamics, an increase in dust deposition will not increase Fe in the ocean, unless initial Fe inputs fertilise the ocean in such a way that the biologically community within the region are accustomed to dust deposition events and can produce ligands which will hold Fe in the dissolved form. Ultimately, the Fe concentrations are determined by the concentrations of Fe binding ligands - and thus depends on biological activity.
(2) dissolved organic matter present in seawater can aggregate and form particulate material (particulate organic matter) that will compete with mineral particles such as dust for iron adsorption. Those new parameterisation are very important for our knowledge of biogeochemical cycles: they can be used in models of natural ecosystems to understand the role of particles, including atmospheric particles on the export of DFe to deep waters and the competition that may exist between different types of particles.
The complex view of atmospheric iron pathway in surface waters of the ocean can be better understood thanks to the results found in FAIRY.