Atmospheric soluble iron sustains nitrogen fixation in oligotrophic oceans

Productivity in oligotrophic oceans is strongly constrained by external nutrient inputs, yet the impact of decadal shifts in atmospheric deposition on nitrogen and iron supply remains uncertain. Here, we estimated potential nitrogen fixation by assuming full utilization of modeled deposited soluble iron, after accounting for non-diazotrophic consumption, in conjunction with the iron-to-nitrogen stoichiometry of diazotrophs. This upper-bound estimate of nitrogen fixation increased by 19–40% from the 1980s to the 2010s, partly offsetting an ~18% decline in direct modeled nitrogen deposition. Consequently, external nitrogen–fueled production rose from 4.0% to 4.7% of net primary production and from 26% to 32% of export production. These increasing trends remained robust under 30% uncertainty and alternative datasets. Although our approach simplifies internal biogeochemical processes, these results highlight the growing role of aerosols in sustaining productivity and shaping carbon cycling in oligotrophic oceans as internal nutrient supply declines under climate change. Iron input into the ocean from atmospheric aerosols can sustain productivity and influence carbon cycling in low-nutrient waters, as estimated through modelled atmospheric deposition and nutrient stoichiometry.