Sources of Strong Copper-binding Ligands in Antarctic Peninsula Surface Waters

Copper-binding organic ligands were measured during austral winter in surface waters around the Antarctic Peninsula using competitive ligand exchange-adsorptive cathodic stripping voltammetry with multiple analytical windows. Samples were collected from four distinct water masses including the Antarctic Circumpolar Current, Southern Antarctic Circumpolar Current Front, Bransfield Strait, and the shelf region of the Antarctic Peninsula. Strong copper-binding organic ligands were detected in each water mass. The strongest copper-binding ligands were detected at the highest competition strength in the Antarctic Circumpolar Current, with an average conditional stability constant of logKCuL,Cu2+cond=16.00±0.82" role="presentation">. The weakest ligands were found at the lowest competition strength in the shelf region with logKCuL,Cu2+cond=12.68±0.48" role="presentation">. No ligands with stability constants less than logKCuL,Cu2+cond=13.5" role="presentation"> were detected in the Antarctic Circumpolar Current at any competition strength, suggesting a shelf source of weaker copper-binding ligands. Free, hydrated copper ion concentrations, the biologically available form of dissolved copper, were less than 10 ⁻¹⁴ M in all samples, approaching levels that may be limiting for some types of inducible iron acquisition.