Short-term variability of chlorophyll associated with upwelling events in the Taiwan Strait during the southwest monsoon of 1998

Abstract

SeaWiFS chlorophyll and AVHRR SST time series as well as in situ measurements in August 1998 were used to evaluate short-term variability of chlorophyll associated with upwelling events in the western Taiwan Strait. The extent of eutrophic waters (SeaWiFS Chlorophyll>1mg/m3), colder upwelling waters, and upwelling index were calculated for the western strait and for the northern and southern portions. Large extents of eutrophic waters were always accompanied by colder upwelling waters, indicative of the tight coupling of chlorophyll with upwelling activities. The phytoplankton growth lagged the upwelling activities by about 2 days. The temporal changes of upwelling events were found different in the northern and southern Taiwan Strait. A short relaxation of upwelling probably occurred between early and mid-August in the northern portion. One strong upwelling event likely lasted from early through mid-August, peaking before August 13 in the southern portion. It resulted in chlorophyll enhancement but with different timing of chlorophyll reaching maximum values in these two upwelling zones. The duration of one upwelling event in the western Taiwan Strait in August was estimated to be about 12 days. It seems that two distinctive northern and southern upwelling systems in the western Taiwan Strait were connected with, and affected by, the East China Sea and the South China Sea, respectively.