A weak cold eddy influencing nitrogen form in the western part of the South China Sea

Abstract

Nitrogen is an essential element for all life and it exhibits in three major dissolved inorganic chemical forms to participate in the marine nitrogen cycling. In this study, a transect through the weak cold eddy was undertaken near Xisha Islands of the South China Sea (SCS) in summer of 2009. There was a trend of decreased temperature inside the eddy, while PO4 and NO3 increased in comparison to outside the eddy The primary nitrite maximum (PNM) was found in the depth of about 50 m in the in-situ samples. Phytoplankton excretion has advantage of PNM formation and maintenance in the euphotic layer. Additionally, nitrate anomaly (N*) were positive, which implies that nitrogen fixation occurs in the surface water in the studying period. These results indicate that cold eddy has influence on regulating inorganic nitrogen biogeochemistry in the studying area during sampling period.