Program
 
General Session 3: Biological oceanography & global change
 
 
 
Poster
N2 fixation in two coastal upwelling regions of the Taiwan Strait
GS3-57-S
Zuozhu Wen* , State Key Laboratory of Marine Environmental Science (Xiamen University), China
Wenfang Lin, State Key Laboratory of Marine Environmental Science (Xiamen University), China
Haizheng Hong, State Key Laboratory of Marine Environmental Science (Xiamen University), China
Dalin Shi, State Key Laboratory of Marine Environmental Science (Xiamen University), China
Presenter Email: wenzuozhu2014@stu.xmu.edu.cn
N2 fixation is an important process that provides fixed N to the surface ocean, which could sustain up to 50% of new primary production in oligotrophic environments. Recent studies indicate that N2 fixation may also be actively occurring in nutrient rich environments, such as coastal upwelling regions that are traditionally considered unfavorable for N2 fixation, but the underlying mechanisms remain poorly understood. Here we examined N2 fixation in surface waters of two upwelling regions in the Taiwan Strait, the Pingtan upwelling (PTU) and the Dongshan upwelling (DSU) systems. Surface N2 fixation rate ranged from 0.2 to 7.0 nmol N L-1 d-1 in the PTU, while the rate was below 0.2 nmol N L-1 d-1 in the DSU. Relativity high surface soluble reactive phosphorus (SRP) concentration (up to 0.37 ¦ÌM) was found in the PTU, whereas it was below detection limit at most stations in the DSU. Previous works reported significantly low N:P ratio (4¡«5 : 1) of the upwelled water in the middle of the strait, which likely led to the relatively sufficient P in the upper layer of the PTU, consequently stimulating the surface N2 fixation rate. The excessive P may result from denitrification in the water column or sediments, which remains to be further investigated. In contrast, sufficient N in surface waters, which was likely provided by upwelled water (with N:P ratio of up to 16 : 1) and/or the Pearl River plume, inhibited surface N2 fixation in the DSU. Our results demonstrated that N2 fixation could be significant in coastal upwelling areas where P was in excess, and also indicated a close spatial association between N2 fixation and denitrification.