Glacial flours as a potential source of Fe(II) and Fe(III) to polar waters

Supply of Fe to high nitrate low chlorophyll (HNLC) waters, such as the Southern Ocean, is the principle limiting factor for primary production and the associated carbon uptake. Glacial meltwaters have recently been shown to provide a globally substantial input of Fe to both Antarctic and Arctic polar waters. The particulate Fe flux in glacial runoff is several orders of magnitude greater than the dissolved Fe flux and yet little is known, to date, about the potential bioavailability of this particulate Fe. A fraction of particulate Fe may be bioavailable to organisms and thus have a significant impact on biota in HNLC zones. Here, we describe in detail the composition and speciation of Fe released from four different glacial flours. We show that the fraction of labile Fe varies markedly between different flours and is not proportional to total Fe. Furthermore a small fraction of the particulate Fe is available to the Fe(II) selective ligand ferrozine, which indicates active redox cycling on the surface of the flour.