A new global budget suggests no net source of ammonia from the open ocean
Ammonia is an important species in the neutralisation of atmospheric acidity and also in its role in climate forcing through enhancing new particle formation and growth, particularly in the marine atmosphere. Its ocean-atmosphere exchange has been shown in recent work to be strongly temperature-sensitive [Johnson, M.T., P.S. Liss, T.G. Bell et al., Global Biogeochemical Cycles, 22, GB1019]. Here, we present a global budget of the ocean-atmosphere exchange of ammonia, based on current best estimates of ammonia concentrations in the boundary layer marine atmosphere and ammonium concentrations in the surface ocean, along with temperature, pH and wind speed data from climatologies. We demonstrate that temperature dominates the magnitude and direction of the ammonia flux over the global open ocean. The budget predicts that to within the uncertainty in the budget (of approximately +/- 2 Tg-N yr-1) the net global flux of NH3 is not significantly different from zero, as opposed to previous estimates suggesting the ocean is a net source of approximately 8 Tg NH3-N yr-1. Although net flux is close to zero, the low latitudes tend to be regions of emission and the high latitudes of deposition. The reasons for the discrepancy between this and previous budgets are found to be due to the assumptions made about the concentrations of NHX in both atmosphere and ocean, which appear to be incorrect in previous studies.
in preparation
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