Application of Fuzzy Classification to the Structure of the Water Mass Distribution in the Easter Waters of Taiwan

Abstract

Four seasonal sampling cruises, covering a grid of 22 sampling stations, were carried out to collect physical and chemical oceanographic data in the eastern waters east of Taiwan in 2008. The aim of this study was to document the spatial and seasonal variabilities of water masses, as defined by temperature-salinity (T-S), nutrients, and chlorophyll (Chl a) using fuzzy classification. In order to determine relationships among T-S water mass types, nitrate and phosphate (NP) water mass types, and Chl a water mass types, this study used fuzzy classification methods and applied a cross-classification analysis. Hydrographic data were classified into three different water mass types in various seasons in a T-S diagram. The same results from a cluster analysis of each water mass type defined Kuroshio Current, mixed, and upwelling water types, which had different characteristics in the various season. Results of the fuzzy classification of the vertical transect hydrographic data of T-S, nutrients, and Chl a indicated that there were high correlations among T-S, nutrients, and Chl a. When a typhoon struck, the correlation was significantly higher. The typhoon caused a cold vortex to well up bringing with it abundant nutrients in the waters east of Taiwan, which caused the phytoplankton to increase.