Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 5 6 2008 10.5194/bg-5-1705-2008 http://www.biogeosciences.net/5/1705/2008/ http://www.biogeosciences.net/5/1705/2008/bg-5-1705-2008.html http://www.biogeosciences.net/5/1705/2008/bg-5-1705-2008.pdf 1705 1721 2008-12-11 Spatial and temporal variations in dissolved and particulate organic nitrogen in the equatorial Pacific: biological and physical influences X. J. Wang wwang@essic.umd.edu R. Le Borgne R. Murtugudde A. J. Busalacchi M. Behrenfeld University of Maryland, College Park, Maryland, USA Institut de Recherche pour le Développement, Nouméa Cédex, New Caledonia Oregon State University, Corvallis, Oregon, USA To quote Libby and Wheeler (1997), "we have only a cursory knowledge of the distributions of dissolved and particulate organic nitrogen" in the equatorial Pacific. A decade later, we are still in need of spatial and temporal analyses of these organic nitrogen pools. To address this issue, we employ a basin scale physical-biogeochemical model to study the spatial and temporal variations of dissolved organic nitrogen (DON) and particulate organic nitrogen (PON). The model is able to reproduce many observed features of nitrate, ammonium, DON and PON in the central and eastern equatorial Pacific, including the asymmetries of nitrate and ammonium, and the meridional distributions of DON and PON. Modeled DON (5–8 mmol m^−3) shows small zonal and meridional variations in the mixed layer whereas modeled PON (0.4–1.5 mmol m^−3) shows considerable spatial variability. While there is a moderate seasonality in both DON and PON in the mixed layer, there is a much weaker interannual variability in DON than in PON. The interannual variability in PON is largely associated with the El Niño/Southern Oscillation (ENSO) phenomenon, showing high values during cold ENSO phase but low values during warm ENSO phase. 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