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Circulation, biogeochemistry and carbon cycling in ocean margins
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Dynamics of the carbonate system on the shelf of northern South China Sea
P-M1-19-S
Wei Yang* , State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
Xianghui Guo, State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
Yi Xu, State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
Liguo Guo, State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
Minhan Dai, State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
Presenter Email: yangwei@stu.xmu.edu.cn |
| Based upon surveys conducted in four different seasons during 2009-2011, the distribution and dynamic of carbonate parameters on the shelf of Northern South China Sea (NSCS) were investigated. We observed obvious seasonal cycle of the carbonate system largely controlled by complex circulation modulated by the seasonally reversing monsoon as well as the variable geometry of the coastline and bottom topography. In winter, the inner shelf of the NSCS was influenced by the China Coastal Current (CCC), which is characterized by low salinity (~32.2-33.5), low temperature (~16.0-20.0 oC) and high abundant nutrients (~0.8 mmol kg-1 for PO4). The saturation state of aragonite (Warag) in this area ranged from ~2.5 to ~3.1. Using a three end-member mixing model between CCC, the NSCS surface water and subsurface water, we estimated that the CCC water induced a pCO2 drawdown of ~-20±13 matm. This CCC led to an increase in Warag by 0.9 through both water mixing and biological metabolism. In the offshore areas away from the CCC, the Warag in winter was 3.3±0.1. A quantitative analysis suggested that the intensive water mass mixing driven by strong winter monsoon, high biological uptake and strong CO2 sink contributed -26.4%, 24.5% and -38.3% to its seasonal variation, while the contribution of temperature was minor (-10.7%). In spring, the Warag was 3.5±0.1, high temperature increased Warag in 29.7%, and water mass mixing, biological process and air-sea CO2 exchange contributed -27.0%, 22.9% and 20.3%, respectively. In summer, the NSCS was featured by two coastal upwellings (YDU and QDU) and Pearl River Plume (PRP). The Warag in the upwelling centers was <3.5, reflective of the upwelling of carbon-enriched subsurface water. In the plume area, the Warag was >4.1, likely due to the high biological production sustained by abundant nutrients from rivers. The Warag in the offshore area in summer was 3.1±0.1, which was mainly controlled by temperature (47.9%), biological process (25.1%) and air-sea CO2 excahnge (14.9%), while the contribution of water mass mixing was reduced to -11.9%. In fall, the Warag was augmented to 3.4±0.1, which was attributed to the enhanced CO2 outgassing (41.9%) associated with high wind velocity. Mixing and biological processes were strengthened by the intensive mixing, contributed -25.9% and 23.1%, respectively, while the temperature effect was minor (5.5%). |
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