Glacial and hydrothermal sources of dissolved iron(II) in Southern Ocean waters surrounding Heard and McDonald Islands
At Heard Island, the greatest DFe(II) concentrations (max 0.57 nmol L-1) were detected north of the island, and an inverse correlation of DFe(II) concentrations with salinity suggests the origin is from a sea-terminating glacier on the island. At McDonald Islands, the greatest DFe(II) concentrations (max 1.01 nmol L-1) were detected east of the island which, based on DFe(II) profiles from five targeted stations, appears likely to originate from shallow diffuse hydrothermalism. The elevated concentrations of DFe(II) around HIMI, a highly labile and bioavailable form of Fe, may increase Fe availability for biota in the region. High DFe(II) concentrations may also indicate slower oxidation kinetics in the region, which has implications for transport of Fe away from the islands to the broader northern Kerguelen Plateau where the annual plankton bloom is strongest.