Investigating atmospheric Fe supply to the ocean using stable isotope ratios and chemical speciation

Abstract

Iron (Fe) is a key regulator of marine primary production and thus plays an important role in ocean ecosystems and climate. Atmospheric aerosols constitute a major source of Fe to the ocean; however, the contribution of anthropogenic emissions remains poorly constrained. Our studies demonstrate that anthropogenic Fe exhibits substantially lower stable Fe isotope ratios (δ⁵⁶Fe) than mineral dust, reflecting isotope fractionation during high-temperature vaporization processes. Exploiting this distinct isotopic signature as a tracer, we estimate that anthropogenic Fe can contribute up to 50% of total Fe in marine aerosols over the North Pacific during summer. In contrast, δ⁵⁶Fe values measured in aerosols are not directly reflected to surface seawater, indicating that additional isotope fractionation processes occur during oceanic transport and internal cycling. This paper summarizes research on atmospheric and oceanic Fe cycling using stable Fe isotope ratios, focusing primarily on our previous studies, and outlines recent developments and future prospects.