Analysis On The Characteristics And Short-term Variation Of Summer Upwelling Of Eastern Guangdong And Southern Fujian Coast

Upwelling is a vertical current that delivers cold, nutrient-rich bottom waters to the upper layers or the surface and plays an important role in material and energy transport and ecological mixing. As a result, the sea area with upwelling often forms itself into a highly productive fishing ground. The study on upwelling has attracted great attention worldwide from physical oceanographers as well as ecologists for its scientific and economic significances. The present paper attempts to study the summer upwelling phenomenon off eastern Guangdong and southern Fujian coast and its short-term variation by analyzing hydrographic data, satellite remote sensing data and mooring data.Based on in situ measurements in summer 2006, the characteristics of upwelling phenomenon off eastern Guangdong and southern Fujian coast are analyzed. Results show that the area with strong upwelling is located offshore Shantou and Dongshan. The upwelling expands its range with water depth. It is concluded that topography has certain effects on the structure of upwelling. Analytical results also reveal that cold and nutrient-rich deep waters can upwell to the upper layers in coastal regions following the topographic changes.From sea surface temperature data by remote sensing, it is found that the centre of the upwelling is located at the area off the coast between Dongshan and Zhangpu. The upwelling appears in early July and shows greater intensity from early July to early August and less intensity after Mid-August. The distribution of chlorophyll concentration also reflects the variation of the upwelling intensity. As it coincides with the upwelling, the peak chlorophyll concentration occurs from early July to early August when the upwelling intensity is larger. The variation of the upwelling intensity is correlated to a certain extent with the variation of the wind fields. A more stable along-shore component of the wind vector plays an active role for the growth and maintenance of the upwelling. The analytical results reveal that local wind stress curl has only a little effect on the upwelling.Water movement in the upwelling area has its own characteristics and reflects the variation of the upwelling intensity. The alongshore flow at all levels are rather stable and guarantee to some extents the water source in the upwelling area. There is a continuous positive shoreward flow in the bottom layer while there is a continuous negative one in the upper layer during the observation period. In the middle layer, water moves towards shore in July when the upwelling is strong and leaves shore in August when the upwelling turns weak.The shoreward flow is well correlated to sea surface temperature which decreases when the shoreward flow is positive and increases when the shoreward flow is negative. The intensity of shoreward flow reflects the variation of the upwelling intensity.Results of time series analysis show a 7-day fluctuation period for both the shoreward flow and sea surface temperature, which reveals the same fluctuation period for the upwelling intensity...