Program     Carbon Cycle in the South China Sea: Budget, Controls and Global Implications       Poster Impact of Kuroshio Current intrusion on N dynamics and the subsequent C cycling in the northern South China Sea P-SPS3-09 Shuh-Ji Kao* , State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University NCG (Nitrogen Cycle Group), State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University Presenter Email: sjkao@xmu.edu.cn Intrusion of Kuroshio Current largely regulates the nutrient and organic matter distribution of the northern South China Sea. Yet little is known about its subsequent biological consequences of such physical process. We examined the ammonia oxidation rates, nitrogen fixation rates, nitrogen and carbon uptake rates along an intrusion gradient in the northern South China Sea. The ammonia oxidation rates ranged from 0.001 to larger than 100 nmol N L-1 d-1 with highest integrated rates located at site with moderate intrusion intensity, suggesting stimulated DON remineralization and NH4+ regeneration during the lateral mixing process. Nitrogen fixation, in another aspect, was positively correlated with the fraction of Kuroshio water, indicating that enhancement of nitrogen fixation was likely due to the introduce of abundant Trichodesmium from Kuroshio water. Interestingly, nitrogen fixation rates shown significant correlation with primary production, demonstrating an important role of nitrogen fixation as a new nitrogen source in supporting the productivity in this region. Moreover, by comparing the DIN (NH4+, NO3-) uptake rates with carbon uptake rates, we found the DIN in this region only account for around 50% of nitrogen source for primary producers, other nitrogen source such as DON must substantially contributed to primary production in this region. Together, these results demonstrate a significant but complex effect of lateral intrusion on the biogeochemistry of western boundary system, more studies are urgent to further disentangle the underlying mechanism.