Atmospheric deposition of nutrients to the North Atlantic Basin

Atmospheric chemical models are used to estimate the deposition rate of various inorganic oxides of nitrogen (NOy), reduced nitrogen species (NHx) and mineral dust to the North Atlantic Ocean (NAG). The estimated deposition of NOy to the NAO (excluding the coastal ocean) and the Caribbean is 360 x 10(9) Moles-N m(-2) yr(-1) (5.0 Tg N); this is equivalent to about 13% of the estimated global emission rate (natural and anthropogenic) and a quarter of the emission rate from sources in North America and Europe. In the case of NHx, 258 Moles-N m(-2) yr(-1) (3.6 Tg N) are deposited to the NAO and the Caribbean; this is about 6% of the global continental emissions. There is relatively little data on the deposition rate of organic nitrogen species; nonetheless, this evidence suggests that concentrations and deposition rates are comparable to those for inorganic nitrogen. Because of anthropogenic emissions, the present-day deposition rate of NOy to the NAO is about five times greater than pre-industrial times largely due to emissions from energy production and biomass burning. The present-day emissions of NHx from continental anthropogenic sources are about four-to-five times greater than natural sources, mostly due to the impact of emissions from animal wastes associated with food production. Indeed, present-day emissions of NHx from animal waste are estimated to be about 10 times greater than the pre-human era. The deposition rate of mineral dust to the NAO is about 170 Tg yr(-1); deposited with the dust (assuming average crustal abundances) is about 6 Tg yr(-1) of Fe and 0.2 Tg yr(-1) of P. Dust deposition in the NAO is almost completely attributable to transport from North African sources; a substantial fraction of the dust over the NAO is probably mobilized as a consequence of land use practices in arid regions and, consequently, it should be regarded as a pollutant.