Organic matter as a driver of Fe(II) oxidation and persistence in the central Arctic Ocean and the Barents Sea: Implications for Marine Biogeochemistry

Abstract. This study examines how variations in organic matter sources and composition regulate Fe(II) oxidation dynamics in the central Arctic Ocean and the Barents Sea, two contrasting Arctic marine environments. Pseudo-first-order Fe(II) oxidation rate constants (log k′) deviated substantially from values predicted with the same pH, temperature, and oxygen conditions, indicating strong environmental control on Fe(II) reactivity. Under reference conditions (pH = 8, T = 15 °C, and oxygen saturation), the calculated Fe(II) half-life was 14.21 min, whereas experimentally determined half-life ranged from 0.76 to 14.7 min in the central Arctic Ocean and from 0.77 to 20.14 min in the Barents Sea. Experimental and tcalculated data yielded a standard error in log k′ of ±0.229 min⁻¹, corresponding to a half-life uncertainty of less than 1 min. The Fe(II) half-life directly reflects oxidation kinetics and constrains Fe(II) persistence, with implications for trace metal speciation and redox cycling.

Partial least squares regression (PLSR) analysis of samples from the Central Arctic station revealed significant associations (R² = 0.38, p < 0.05) between residual Fe(II) oxidation variability (Δk′) and humic-like organic matter, dissolved organic carbon (DOC), silicic acid, salinity, and nitrate, highlighting the combined influence of interrelated environmental factors on Fe(II) oxidation dynamics. Spatial variability in Fe(II) persistence across basins and depth profiles is attributed to differences in organic matter characteristics associated with distinct water masses.