Advanced simulations indicate that oceanic nitrogen deposition may decline by 24% or increase by 6% by 2050, depending on emission pathways. Importantly, reducing one nitrogen pollutant alone may increase deposition of another, highlighting the need for coordinated multi-pollutant control strategies.
Atmospheric nitrogen deposition is a key component of the global nitrogen cycle. Reactive nitrogen from fossil fuel combustion, agriculture, livestock, and shipping is transported through the atmosphere and deposited onto land and oceans. In marine systems, this external nitrogen fertilizes phytoplankton, influencing ocean productivity and the carbon cycle. Previous studies show that anthropogenic nitrogen deposition already contributes to marine new production and carbon uptake. However, its future trajectory under climate and air-quality policies remains uncertain. Reduced nitrogen (NH₃/NHx) and oxidized nitrogen (NOx/NOy) interact chemically in the atmosphere, shaping deposition patterns, yet the global impacts of different emission control combinations have not been fully evaluated.
A study (DOI: 10.48130/nc-0025-0025) published in Nitrogen Cycling on 29 January 2026 by Lin Zhang’s team, Peking University, reveals that future air pollution controls will fundamentally reshape oceanic nitrogen deposition, with cascading consequences for marine productivity and climate feedbacks, highlighting the need for coordinated NH₃ and NOx management across the Earth system.
Using the global atmospheric chemistry transport model GEOS-Chem, the researchers first quantified global reactive nitrogen (NH₃ and NOx) emissions, simulated atmospheric transport and chemical transformations, evaluated wet and dry deposition fluxes against ground-based observations, and then projected future changes under three CMIP6 emission scenarios (SSP126, SSP434, SSP370), complemented by regional diagnostics, deposition-to-emission (DTE) ratios, sensitivity experiments with 25–100% emission reductions, and biogeochemical calculations of ocean productivity and N₂O responses. The model reproduced observed NH₄⁺ and NO₃⁻ wet deposition reasonably well (correlations 0.75 and 0.73). In 2015, global reactive nitrogen emissions reached 133.1 Tg N yr⁻¹, and oceanic deposition totaled 51.0 Tg N yr⁻¹ (39% of global deposition), nearly half as reduced nitrogen and about half via wet deposition, with hotspots along East and South Asia, Europe, and the eastern United States. By 2050, oceanic deposition ranges from 39 to 54 Tg N yr⁻¹ (−24% to +6%) depending on scenario: strong NOx cuts under SSP126 drive a 24% decline, whereas rising NH₃ and NOx under SSP370 produce a 6% increase, revealing nonlinear chemical interactions. Coastal regions show much higher deposition (2.4–19.5 kg N ha⁻¹ yr⁻¹) than open oceans and stronger sensitivity to emission changes. Sensitivity tests demonstrate chemical compensation: reducing NOx alone enhances NHx dry deposition, while reducing NH₃ alone increases NOy dry deposition; only joint controls substantially reduce total deposition. Biogeochemically, 2015 nitrogen deposition supports ~290 Tg C yr⁻¹ of ocean productivity (~1.3% of global new production). This contribution falls to 222 Tg C under SSP126 but rises to 306 Tg C under SSP370. Associated N₂O emissions change from ~1.5 Tg N yr⁻¹ in 2015 to ~1.2–1.6 Tg N yr⁻¹ by 2050, offsetting about 60% of the climate effect of productivity changes, though uncertainties remain due to nutrient limitation and steady-state assumptions.
Overall, the study demonstrates that single-pollutant air-quality controls may unintentionally sustain or even enhance nitrogen delivery to oceans through chemical compensation effects. Coordinated reductions of both NH₃ and NOx are therefore essential to effectively curb oceanic nitrogen deposition, especially in vulnerable coastal regions. These findings underscore the tight coupling between air pollution policy, marine ecosystem health, and climate feedbacks, calling for integrated, Earth-system-scale nitrogen management strategies.
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References
DOI
10.48130/nc-0025-0025
Original Souce URL
https://doi.org/10.48130/nc-0025-0025
Funding information
This work is supported by the National Key Research and Development Program of China (Grant No. 2023YFC3707404), and the National Natural Science Foundation of China (Grant Nos 42275106, 42371324).
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