Fe‐Binding Organic Ligands in the Humic‐Rich TransPolar Drift in the Surface Arctic Ocean Using Multiple Voltammetric Methods

Abstract

[eng] Samples inside and outside the Arctic Ocean's TransPolar Drift (TPD) have been analyzed for Fe‐binding organic ligands (Lt) with Competitive Ligand Exchange Adsorptive Stripping Voltammetry (CLE‐AdCSV) using salicylaldoxime (SA). This analysis is compared to prior analyses with CLE‐AdCSV using 2‐(2‐thiazolylazo)‐p‐cresol (TAC). The TPD's strong terrestrial influence is used to compare the performance of both CLE‐AdCSV methods in representing the nature of natural organic ligands. These measurements are compared against direct voltammetric determination of humic substances (HS) and spectral properties of dissolved organic matter. The relationship between the two CLE‐AdCSV derived [Lt] versus HS in the TPD has a comparable slope, with a 40% offset toward higher values obtained with SA. Higher [Lt] values inside the TPD, most probably due to HS, explain high dissolved Fe concentrations transported over the Arctic Ocean by the TPD. Outside of the TPD in the surface Arctic Ocean HS occur as well but at lower concentrations. Here changes in HS relate to changes in dissolved Fe concentration and to [Lt] obtained with SA, whereas [Lt] obtained with TAC remain constant. Moreover, with decreasing HS the offset between the methods using TAC and SA decreases. We surmise that in the presence of HS, the TAC method detects HS only either at higher concentrations or of specific composition. On the other hand, the SA method might overestimate [Lt], as an offset with the TAC method that remains constant where HS are not detected. Regardless, HS are the dominant type of Fe‐binding organic ligand in the surface of the Arctic Ocean.