Atmospheric fluxes of organic N and P to the global ocean

[1] The global tropospheric budget of gaseous and particulate non-methane organic matter (OM) is re-examined to provide a holistic view of the role that OM plays in transporting the essential nutrients nitrogen and phosphorus to the ocean. A global 3-dimensional chemistry-transport model was used to construct the first global picture of atmospheric transport and deposition of the organic nitrogen (ON) and organic phosphorus (OP) that are associated with OM, focusing on the soluble fractions of these nutrients. Model simulations agree with observations within an order of magnitude. Depending on location, the observed water soluble ON fraction ranges from 3% to 90% (median of 35%) of total soluble N in rainwater; soluble OP ranges from 20–83% (median of 35%) of total soluble phosphorus. The simulations suggest that the global ON cycle has a strong anthropogenic component with 45% of the overall atmospheric source (primary and secondary) associated with anthropogenic activities. In contrast, only 10% of atmospheric OP is emitted from human activities. The model-derived present-day soluble ON and OP deposition to the global ocean is estimated to be 16 Tg-N/yr and 0.35 Tg-P/yr respectively with an order of magnitude uncertainty. Of these amounts 40% and 6%, respectively, are associated with anthropogenic activities, and 33% and 90% are recycled oceanic materials. Therefore, anthropogenic emissions are having a greater impact on the ON cycle than the OP cycle; consequently increasing emissions may increase P-limitation in the oligotrophic regions of the world’s ocean that rely on atmospheric deposition as an important nutrient source.