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General Session 2: Marine & estuarine biogeochemistry |
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Summer subsurface oxygen minimum in Min-Zhe coastal upwelling zone
GS2-02
Bin Wang* , Second Institute of Oceanography
Jianfang Chen, Second Institute of Oceanography
Haiyan Jin, Second Institute of Oceanography
Shengquan Gao, Second Institute of Oceanography
Shichao Tian, Second Institute of Oceanography
Lin Sun, Second Institute of Oceanography
Haizhou Zhang, Second Institute of Oceanography
Linwei Li, Second Institute of Oceanography
Presenter Email: wangbin@sio.org.cn
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| Based on the data obtained in August 2014 summer cruise in the Yangtze River Estuary and adjacent East China Sea, the oxygen minimum occurred in the mid-water depth layer (15~20m) in Min-Zhe coastal upwelling zone, rather than in the bottom water. This phenomenon has never been observed in East China Sea, and rarely occurred in other estuary system. These subsurface oxygen minimum sites appeared mainly in the region of Taiwan warm water along the 50m bathymetric contour flow in Min-Zhe coastal area southern off Yangtze River Estuary area. The area affected by the Yangtze River diluted water, Fujian and Zhejiang coastal water and Taiwan warm current. The strong summer Taiwan warm water intrusion, together with the southern expansion of Changjiang plume water, forming a strong upward flow and there depth layer. At this mid-depth, nitrate and phosphate showed a high value, with minimum of DO, which implied the importance of biological effects imposed on this physical thermocline. According to our multi parameter analysis, the surface formed particulate organic matter may be trapped in the upper thermocline, subsequently degraded and remineralized here, resulting in a minimum value of DO in this mid-water depth. Meanwhile, the hypoxia water layer depth in this year expanded from the 20m to 40m~50m,which indicate an depth expansion of bottom hypoxia. Hence, the high-resolution nitrate and DO profiles were used to to clarify the water column metabolic processes and status, to reveal the biochemical mechanism of the East China Sea subsurface hypoxic phenomenon. |
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