Impact of the Kuroshio Intrusion and Mesoscale Eddies on the Dynamics of Fluorescent Dissolved Organic Matter in the Northern South China Sea

Weidong Guo1, Chao Wang1, Yan Li1, Yizhen Li2, Guodong Song3 and Yuanyue Cheng4, (1)Xiamen University, State Key Laboratory of Marine Environmental Science, Xiamen, China, (2)North Carolina State Univ., Raleigh, NC, United States, (3)Ocean University of China, College of Chemistry and Chemical Engineering, Qingdao, China, (4)Chinese Academy of Sciences, South China Sea Institute of Oceanology, Guangzhou, China
Abstract:
Mesoscale eddies are ubiquitous in the northern South China Sea (SCS), and its nonlinearity is demonstrated to facilitate water mass and biogeochemical property exchanges with western Pacific Ocean through the Luzon Strait. However, very little is known about the impact of Kuroshio intrusion and mesoscale eddies on the dynamics of fluorescent dissolved organic matter (FDOM) in the SCS. In situ FDOM samples collected from the northern SCS and the Luzon Strait in spring 2014 were characterized by excitation-emission matrix spectroscopy. Five components were identified by parallel factor analysis, including two humic-like components (C1: 250, 365/456 nm; C2: 250, 330/388 nm) and one tryptophan-like component (C4: 275/344 nm. Isopycnal mixing model of the SCS and Kuroshio end members showed that two humic-like C1 and C2 in the euphotic zone of the SCS were mainly dominated by the Kuroshio intrusion, whereas protein-like C4 was more influenced by biological processes. The occurrence of a cyclonic eddy and an anticyclonic eddy to the west of the Luzon Strait increased the deviation of model results, highlighting the potential impact of mesoscale eddies on FDOM dynamics. The fluorescent intensities of humic-like C1 and C2 were significantly lower within the anticyclonic eddy regions than those in the cyclonic and other non-eddy regions, consistent with the lower primary production in the anticyclonic eddy regions. The ratio of C1 and C2 also showed distinct difference between eddies. The average integral C1/C2 ratio in the euphotic zone in the anticyclonic eddy regions was significantly higher than those in the cold-core eddy and no-eddy regions. Thus, this new fluorescence index may be used as an indicator of the active mesoscale eddies in the northern SCS, although future evidence remains needed to testify such hypothesis. The C1/C2-AOU relationship below the euphotic zone showed that the eddy influence on FDOM can be conveyed into the middle layer of the SCS.
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