Biogeochemistry of iron in Patagonian fjords and waters of the Antarctic Peninsula
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- Institutt for kjemi 
Iron constitute an essential nutrient for marine life. Several metabolic processes in marine phytoplankton, are dependent on the presence of this trace element. Due to the chemistry of seawater, in certain marine environments iron reach such low concentrations, or is present in certain chemical forms, that acquiring it become a life challenge. Furthermore, the anthropogenic influence in marine ecosystems, play an important role in affecting the natural cycling of this element. Fjords and the Antarctic ecosystem are two examples, which are different in respect of the iron dynamics, but both are affected by different human triggered factors. From laboratory experiments in culture bottles to oceanic surveys, we addressed the question of the bioavailability of iron: which forms of iron can be utilized by certain species of marine phytoplankton, how aquaculture could alter the iron cycling and which constitute the main natural iron sources than contribute to make certain marine areas relative more productive. Manipulation experiments of the natural plankton community on a microscale level, showed how the presence of different organic matter (ligands) such as bacterial derived siderophores, can change the iron speciation, favoring growth in certain groups while constraining it in others. Monoculture experiments with selected species (dinoflagellate and diatom), showed different uptakes strategies for iron in the presence of siderophores. Moreover, interactions with the associated bacteria to these speciesa, showed different effect over the iron bioavailability resulting in 1) probable favorable growth of certain species that promote toxic blooms and 2) that initially iron constrained diatoms, may be relieved of the stress by the bacterial degradation of the ligand to obtain carbon, thus favoring the equilibrium for iron uptake. Larger scale experiments, revealed how increase ammonium inputs from aquaculture can change the species composition and hence the dynamics of export of iron out of the photic zone by changing the available surface for adsorption. Finally, large-scale surveys in the Antarctic Peninsula, provided supporting evidence of the role of the Weddell Gyre circulation in promoting lateral transport of iron to more oceanic iron-poor waters in the Scotia Sea, hence promoting enhanced biological productivity.