| Summary: | Atmospheric deposition of high N:P material to the subtropical North Atlantic has more than doubled in the past century due to anthropogenic activity, and is increasingly thought to be an important source of essential nutrients to the oligotrophic subtropical gyre. However, the long-term fate of North Atlantic atmospheric nitrogen deposition is not well understood. This modeling study evaluated an observed pool of N in excess of Redfield ratios located in the main thermocline as a potential sink for atmospheric N. Modeled atmospheric deposition was added to a coupled ocean ecosystem and circulation model. Results suggest that nearly half of the atmospheric nitrogen entering the North Atlantic is transported to the main thermocline, contributing ~15% of the annual growth of excess N there. Transport mechanisms include differential remineralization of N and P in sinking biogenic particles and physical transport. If atmospheric nutrient inputs from the year 2000 were maintained for 50 years, the model suggests that nutrient deposition would contribute to an increase in excess N of more than 0.4 μM, or an additional 45% of the present signal. Quantifying the fate and important transport mechanisms of deposited atmospheric nutrients will improve our understanding of N cycle dynamics in the North Atlantic, as well as improve N2 fixation estimates based on mass-balance techniques.
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