• Lohan, Mc
• Milne, A.
• Nasemann, P.
• Ellwood, Mj
• Boyd, P. W.
• Nodder, Sd
• Sander, Sg
• Strzepek, R.
• Hutchins, Da
• Wilhelm, Sw

Abstract

The supply and bioavailability of dissolved iron sets the magnitude of surface productivity for ∼40% of the global ocean.The redox state, organic complexation, and phase (dissolved versus particulate) of iron are key determinants of iron bioavailabilityin the marine realm, although the mechanisms facilitating exchange between iron species (inorganic and organic) and phasesare poorly constrained. Here we use the isotope fingerprint of dissolved and particulate iron to reveal distinct isotopicsignatures for biological uptake of iron during a GEOTRACES process study focused on a temperate spring phytoplankton bloomin subtropical waters. At the onset of the bloom, dissolved iron within the mixed layer was isotopically light relative toparticulate iron. The isotopically light dissolved iron pool likely results from the reduction of particulate iron via photochemicaland (to a lesser extent) biologically mediated reduction processes. As the bloom develops, dissolved iron within the surfacemixed layer becomes isotopically heavy, reflecting the dominance of biological processing of iron as it is removed from solution,while scavenging appears to play a minor role. As stable isotopes have shown for major elements like nitrogen, iron isotopesoffer a new window into our understanding of the biogeochemical cycling of iron, thereby allowing us to disentangle a suiteof concurrent biotic and abiotic transformations of this key biolimiting element.

Topics

• impedance spectroscopy
• surface
• phase
• Nitrogen
• iron