The Unaccounted Oceanic Sink of Anthropogenic Nitrous Oxide and Its Relationship With Anthropogenic Carbon Dioxide
De La Paz, Mercedes | Velo, Anton | Steinfeldt, Reiner | Perez, Fiz F.
Since 1800, the concentration of greenhouse gases like nitrous oxide (N2O) and carbon dioxide (CO2) has significantly increased due to anthropogenic activities. Oceanic anthropogenic CO2 (Cant) uptake from the atmosphere has been quantified and periodically re-evaluated given the implications for climate change. However, the potential oceanic uptake of N2O has been largely overlooked. This study quantifies the uptake of N2O of anthropogenic origin (N2Oant) taken up by the global ocean and how it relates with the anthropogenic CO2. The oceanic inventory of N2Oant has been quantified using two approaches which consider the anthropogenic perturbation of N2O and CO2 as conservative tracers: first, a direct approach using the Transient Time Distribution (TTD) method; and second, indirectly through a novel method, founded on the direct proportionality between the excess of both N2O and CO2 in the atmosphere since 1800. Our results show that the North Atlantic Ocean is a key region of maximum accumulation of N2Oant due to the confluence of cold and ventilated waters. The global oceanic uptake of N2Oant from the pre-industrial times to 2010 was estimated to be 11.5 +/- 2.3 Tg-N, with an annual uptake rate of 0.23 +/- 0.05 Tg-N yr-1. The study shows that oceanic sequestration contributes to a small portion of global N2O inventories, but it is comparable to other N2O oceanic budget numbers derived from atmospheric nitrogen deposition. Furthermore, connecting the N2Oant and Cant oceanic distributions is a valuable tool for linking the perturbation of the Anthropocene on the N and C cycles in the ocean.
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