Abstract
Abstract. To obtain a comprehensive picture of the spatial distribution of water-soluble organic nitrogen (WSON) in marine aerosols, samples were collected during research cruises in the tropical and southern Atlantic Ocean and also in the southern Indian Ocean (Amsterdam Island) for a 1-year period (2005). Samples were analyzed for both organic and inorganic forms of nitrogen, and the factors controlling their levels were examined. Fine-mode WSON was found to play a significant role in the remote marine atmosphere with enhanced biogenic activity, with concentrations of WSON (11.3 ± 3.3 nmol N m−3) accounting for about 84 % of the total dissolved nitrogen (TDN). Such concentrations are similar to those observed in the polluted marine atmosphere of the eastern Mediterranean (11.6 ± 14.0 nmol N m−3). Anthropogenic activities were found to be an important source of atmospheric WSON as evidenced by the levels in the Northern Hemisphere (NH) being 10 times higher than in the remote Southern Hemisphere (SH). Furthermore, the higher contribution of fine-mode WSON to TDN (51%) in the SH, compared to the NH (13%), underlines the important role of organic nitrogen in remote marine areas. Finally, there was a strong association of WSON with dust in coarse-mode aerosols in the NH.
Highlights
The ocean–atmosphere biogeochemical interactions are important in regulating atmospheric composition, marine ecosystem functioning, and the Earth’s climate
The present study provides new data for water-soluble organic nitrogen (WSON), acquired during oceanographic cruises in the Atlantic Ocean as well as long-term sampling in the Indian Ocean, contributing to the global picture of WSON distribution
The pristine oceanic conditions prevailing at Amsterdam Island and the very low level of local contamination from the scientific base have been documented for many atmospheric compounds such as CO, hydrocarbons, radon, black carbon, and total aerosol number concentration (Williams et al, 2001; Sciare et al, 2009)
Summary
The ocean–atmosphere biogeochemical interactions are important in regulating atmospheric composition, marine ecosystem functioning, and the Earth’s climate. An important fraction (1– 3 %) of dissolved organic matter (DOM) in the surface waters comprises N-containing organic compounds (Benner, 2002) These compounds could be a potential primary source of atmospheric organic nitrogen, since peptides and free amino acids have been detected in the marine atmosphere (Kuznetsova et al, 2005; Wedyan et al, 2007). The importance of WSON (water-soluble organic nitrogen) in marine biogeochemical cycles and its critical role in the atmosphere has been established. Both the origin and chemical composition of WSON in marine aerosols are largely uncertain (Kanakidou et al, 2012). Both organic and inorganic forms of nitrogen have been analyzed and the factors controlling their levels have been examined
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