THE MIXING OF WATER MASSES OFF SOUTHWEST COAST OF TAIWAN

Water mass mixing in the continental shelf is one of important phenomena regarding the interaction among seawater, river and groundwater discharges. Water samples were collected along three transects off the southwest coast of Taiwan from different seasons in 2001 and 2002 to explore the details of water mass movement. Temperature (T), salinity (S) and oxygen isotope compositions (d18O) in the seawater samples all exhibited apparent seasonal variations. In the wet season, there were distinct gradients of T, S, and d18O in illustrating the active mixing between seawater and river discharge in the surface layer. However, the surface gradients almost disappeared and seawater signal became dominant during the dry season due to very low output of river flow. The vertical profiles of T, S and d18O also displayed seasonal variations for each sampling site. Evidence of Kuroshio was barely detected for remote stations at a depth of 150m in summer, but was found everywhere for a layer from 50m to 300m in the winter. Traces of groundwater discharge were observed along the Kaoping Canyon at depths of 400-600m and 1200m, respectively, in the wet season. Our findings can serve as valuable basis for the understanding the coastal oceanography and a further modeling work of seawater encroachment in the southwestern Taiwan.