Long Term Changes And Impact Factors Of The Upwelling In Midwest Of The South China Sea

Upwelling is an important component of ocean circulation, usually due to thedivergence of the surface water. Upwelling has a significant impact on the transportation ofthe material and the environment, since it will bring nutrient-rich waters from the sea bottomto the upper surface. The nutrient-rich waters from the bottom provides the material basis forthe growth of phytoplankton, and similarly, phytoplankton provides good living conditionsfor the zooplankton, fish, shrimp, cephalopods and other biological organisms. Studying theupwelling is important for the development and utilization of fishery resources.There are six upwelling in the South China Sea, including Taiwan Bank upwelling, theeastern coastal upwelling of Guangdong, western coastal upwelling of Guangdong,Qiongdong upwelling, and Luzon upwelling in Philippine waters northwest, and oneupwelling in the Midwest of the South China Sea upwelling. There are abundant tunaresources in the Midwest of the South China Sea upwelling. However, this area is basicallynot within the scope of our Chinese fishery and its information about the region, durationand migration of the fishing ground is very little.It is a main fishing season during southwest monsoon in the Midwest South China Seafishing ground. The fishing season closely associates with the upwelling. The occurrence,development and demise of the upwelling will inevitably lead to changes in the fishingground and fishing season. Several studies have focused on the environmental characteristicsand physical mechanisms of this upwelling. The long term changes in the environmentfactors and spatial location are rarely reported. Using sea surface temperature (SST) data andwind field data of2003~2012, the sea surface temperature data was extracted by matlabsoftware programming. A continuous temperature curve was drawn out with the daily meansea surface temperature. We analyzed the duration and periodic variation of the upwelling.Combining center extraction methods, we determined the changes in center of the upwelling.The results were found that the upwelling phenomenon occurs mainly in5~9month, and theduration days are from92to139days. The upwelling centers present irregular changes. Itvaries from109.13°E~112.61°E，9.16°N~15.36°N. The distribution of the centerspresented three types, offshore aggregated, offshore-dispersed, and near shore coastal alongdistribution pattern. El Nino phenomenon enhanced the intensity of the upwelling, while LaNi a suppressed the intensity of the upwelling. It has little effect on the development ofupwelling except minimums disturbance in the SST near the track of typhoon. This basicresearch can provide a reference for changes in fishing grounds, while offering basicinformation for the development of marine fisheries resources and marine resources．...