Biogeochemical processing of nitrogen transformation including nitrogen fixation and nitrification in the western part of the South China Sea

Based on in situ observations made in summer, 2009 along one transect near Xisha Islands, South China Sea (SCS), this study aims at understanding factors controlling nutrient biogeochemical cycling, especially on nitrogen cycling. The weak cold eddy may have important influence on supplies of nutrients in water column in Xisha islands. Nitrite reaches 0.49 μmol L^-1 at the depth of 50m. It is significant relationship between NO₂^- and Chl a (R²=0.58, p=0.00). Phytoplankton excretion had an important influence on primary nitrite maximum formation and maintenance in euphotic layer. In addition, the positive values of N* indicate that nitrogen fixation may occur in the surface water in the studying area. Our results indicate that cold eddy near Xisha Islands play a significant role in regulating biogeochemistry.