Tracing the Persistence and Role of Deep‐Sea Iron Sources in the Pacific Ocean Over the Last 23 Million Years

Abstract Iron (Fe) plays a critical role in marine productivity and the global carbon cycle. The relative contribution of different Fe sources such as atmospheric aerosols, sediment dissolution, and submarine hydrothermalism influences the distribution and biogeochemical cycling of Fe in the ocean. However, distinguishing these Fe sources over time has proven challenging. Here we report Fe concentrations and isotopic compositions from a Fe‐Mn crust sample CXD31 in the Northwest Pacific Ocean over the last 23 Myr. Iron concentrations exhibit an increasing trend with several pronounced peaks, while Fe isotopic compositions vary within the range of modern oceanic Fe sources. Calculations based on Fe isotope ratios reveal variations in the relative importance of each Fe source since the Miocene. Three prominent periods (∼16.9, ∼11.6, and ∼2.7 Ma) characterized by higher Fe concentrations and isotope values in the reconstructed Fe record are attributed to enhanced dust fluxes associated with aridification of inland Asia.