Distribution of plankton related to the mesoscale physical structure within the surface mixed layer in the southwestern East Sea, Korea

This study investigated the influence of mesoscale physical features on plankton distribution for the first time, in the southwestern East/Japan Sea using hydrographic data obtained in November 2000 and April and October 2001. Three different types of mesoscale physical features were observed in the upper layer during the three survey periods: (i) the southern front between the East Korean Warm Current (EKWC) and the Ulleung Warm Eddy (UWE) (November 2000), (ii) the central part of the UWE with no southern front (April 2001) and (iii) the strong EKWC and related subpolar front (October 2001). The chlorophyll a (Chl a) concentration and zooplankton abundance in the surface mixed layer were affected by the UWE-related nutrient upwelling in the southern front in November 2000 and in the central part of the UWE in April 2001. Further north, the zooplankton abundance was high around the subpolar front in October 2001, while the Chl a concentration was high in the southern part. The spatial heterogeneity of the Chl a was affected by variation of netplankton abundance, whereas seasonal differences of the Chl a concentration depended on the picoplankton. Results of cluster and principal component analysis show that the zooplankton-distribution patterns were associated with the Chl a concentration, water density (a,) and no special factors in November 2000 and April and October 2001 respectively. These results suggest that the firstly found UWE-related front and nutrient upwelling strongly influenced the mesoscale latitudinal heterogeneity of plankton through physical as well as biological process in the southwestern East/Japan Sea during the study period.