Dissolved iron in the Arctic Ocean: Important role of hydrothermal sources, shelf input and scavenging removal

Arctic Ocean waters exchange with the North Atlantic, and thus dissolved iron (DFe) in the Arctic has implications for the global Fe cycle. We present deep water (>250 m) DFe concentrations of the Central Arctic Ocean (Nansen, Amundsen and Makarov Basins). The DFe concentration in the deep waters varies considerably between these basins, with the lowest DFe concentrations (0.2-0.4 nM) in the Makarov Basin, higher concentrations (similar to 0.45 nM) in the Amundsen Basin and highest concentrations (similar to 0.6-0.7 nM) in the Nansen Basin. Atlantic input from the shelf seas and slopes enhances the DFe concentration in the Nansen Basin. Moreover, hydrothermal activity at the Gakkel Ridge causes a significant and widespread enrichment of DFe in the Eurasian Basins, at a depth of 2000-3000 m. Below this maximum, the important role of scavenging and absence of input sources are reflected in a strong relation with dissolved Mn (DMn) and in very low (<0.25 nM) DFe concentrations in the deepest (>3000 m) Amundsen and Makarov Basins. The depth profiles of DFe in the Arctic Ocean, notably in the Makarov Basin, deviate from the DFe distribution pattern observed in other parts of the world ocean.