Iron and humic-type fluorescent dissolved organic matter in the Chukchi Sea and Canada Basin of the western Arctic Ocean

The concentrations of dissolved Fe ([D‐Fe]), total dissolvable Fe ([T‐Fe]), humic‐type fluorescence intensity (humic F intensity) as humic‐type fluorescent dissolved organic matter, and nutrients were vertically determined in the shelf, slope, and basin regions (Chukchi Sea and Canada Basin) of the western Arctic Ocean during 1–27 September 2008. In all stations, the remarkably high [D‐Fe] and humic F intensity were found at depths between 25 and 200 m with the subsurface maxima of [D‐Fe] (1.0–3.2 nM) and humic F intensity (4–5 quinine sulfate units) in the upper halocline layer (upper HL), being associated with a prominent nutrient maximum. The high [D‐Fe] and humic F intensity within the upper HL are probably attributed to the Fe(III) complexation with natural organic ligands, such as marine dissolved humic substances, resulting from main processes of the brine rejection during sea ice formation and interactions with sediments on the shelves. However, subsurface maxima (10–50 nM) of [T‐Fe] were found in the lower halocline layer, beneath the upper HL, of all slope and basin regions and are mainly attributed to the resuspension of sedimentary particles in the shelf region. The finding of subsurface iron maxima in the halocline water of all regions may be the first confirmation for the lateral iron transport into the halocline layer from the shelves to the Arctic Basin. Key Points Maxima of dissolved iron in the cold halocline layer of the western Arctic Ocean Lateral iron transport into the halocline layer from the shelves to the basin