ATMOSPHERIC DEPOSITION OF NUTRIENTS TO THE NORTH-ATLANTIC BASIN

Atmospheric chemical models are used to estimate the deposition rate o f various inorganic oxides of nitrogen (NOy), reduced nitrogen species (NHx) and mineral dust to the North Atlantic Ocean (NAG). The estimat ed 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 equi valent to about 13% of the estimated global emission rate (natural and anthropogenic) and a quarter of the emission rate from sources in Nor th 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 o n the deposition rate of organic nitrogen species; nonetheless, this e vidence suggests that concentrations and deposition rates are comparab le to those for inorganic nitrogen. Because of anthropogenic emissions , the present-day deposition rate of NOy to the NAO is about five time s greater than pre-industrial times largely due to emissions from ener gy production and biomass burning. The present-day emissions of NHx fr om continental anthropogenic sources are about four-to-five times grea ter than natural sources, mostly due to the impact of emissions from a nimal wastes associated with food production. Indeed, present-day emis sions of NHx from animal waste are estimated to be about 10 times grea ter 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 tran sport from North African sources; a substantial fraction of the dust o ver the NAO is probably mobilized as a consequence of land use practic es in arid regions and, consequently, it should be regarded as a pollu tant.