Dust momentum as a metric linking atmospheric dynamics to ocean nutrient delivery

Dust deposition is a critical nutrient supply route for ocean ecosystems, yet the ecological implications of vertical transport polarity (updraft vs. downdraft) have not been systematically quantified. Here, we propose the dust momentum (DustM) diagnostic metric, defined as the product of near-surface dust concentration and atmospheric vertical velocity. Physically, DustM represents the advective mass flux of the dust component, and its sign diagnoses the polarity of resolved-scale vertical transport—negative for downdraft (enhancing deposition) and positive for updraft (promoting suspension). Combining multi-source observations with DustM-based nutrient estimates from 1998 to 2023, we identify a polarity-dependent nutrient regulation mechanism: negative DustM (downdraft-dominated regime) enhances dust-derived nutrient supply, whereas positive DustM (updraft-driven regime) induces atmospheric nutrient suspension. Notably, subtropical gyres serve as the primary nutrient receptors. Our calculations indicate the Northern Hemisphere subtropics receive 23 ± 33% of dissolved iron, 15 ± 24% of nitrate, and 0.5 ± 1% of phosphate from resolved-scale dust transport, significantly higher than the Southern Hemisphere. By linking atmospheric dynamics to marine biogeochemistry, DustM provides a regime-based diagnostic framework for characterizing the dust cycle and quantifying dust-derived nutrient fluxes, supporting projections of nutrient delivery in a changing ocean.