Degree of nutrient consumption as an aging index of upwelling or vertically mixed water in the northern Taiwan Strait

摘要

In order to determine the relative aging status ofupwelled or vertically mixed water in the northern Taiwan Strait, a recently developed method of calcularing the degree of nutrient consumption (DNC) was employed. Upwelling was detected at a water depth of about 75m in summer. Bottom waters in the aphoric zone and newly-upwelled waters in the euphoric zone were found to be low in terms of their DNC. In general, a low DNC was noted alongside the other traditional upwelling indicators, such as lower temperature and degree of oxygen saturation, but higher salinity, apparent oxygen utilization, nutrient contents and chlorophyll-a. Enhanced vertical mixing,but without an apparent upwelling signal, was detected near the same location in winter.