Zinc cycling in the Tasman Sea: Distribution, speciation and relation to phytoplankton community

Zinc (Zn) is essential for phytoplankton growth as it plays a central role within many enzymatic systems within phytoplankton. Here, we present dissolved Zn concentration and Zn chemical speciation results for samples collected at four stations in the Tasman Sea east of Australia. Dissolved Zn concentrations determined using isotope dilution inductively coupled plasma-mass spectrometry (ICP-MS) ranged between 0.02 to 0.19 nmol L− 1 (15 m depth) and 0.02 to 0.11 nmol L− 1 (150 m depth) along a north–south transect. Zn speciation determined using Anodic Stripping Voltammetry (ASV) on four selected profiles from the Tasman Sea indicated that dissolved Zn is strongly complexed to natural organic ligands, with the conditional stability constant for the Zn–ligand complex (log K′ZnL) ranging between 9.3 and 11.4. Dissolved ligand concentrations showed variations with concentrations ranging between 0.8 and 4 nmol L− 1. In surface waters, ligand concentrations always exceeded dissolved Zn concentrations, lowering free Zn2 + ion concentrations into the picomolar range. Based on comparisons between Zn speciation and the phytoplankton community of the Tasman Sea, we suggest that there is the potential for zinc limitation of certain phytoplankton groups in this region and feedback by phytoplankton on ligands, hence, on Zn biogeochemistry.