Dr. Hon-Kit Lui

Department of Oceanography, National Sun Yat-Sen University

Ocean acidification and deoxygenation are two major issues of global change in marine chemistry that are induced by the anthropogenic forcings. Coastal eutrophication and hypoxia may worsen the situation. However, in the case of coastal eutrophication, incoming offshore seawater has rarely been addressed. This study demonstrates that in the wide East China Sea (ECS) the nitrate and phosphate concentrations in the Kuroshio Intermediate Water (KIW) have increased, but the dissolved oxygen (DO) concentration and pH have decreased since as early as 1982, most likely owning to reduced ventilation in the North Pacific Intermediate Water (NPIW). The results thus obtained reveal that the drop in pH of the KIW in the ECS is a result of not only the intrusion of atmospheric CO2, but also a decrease in DO concentration. As KIW contributes substantially to the upwelling, the nitrate and phosphate concentrations in the bottom water on the outer shelf of the ECS appear to have increased as well, but the DO and pH have decreased. Given that the nutrient inputs from both the land and the Kuroshio Current have increased, yet the input of DO and pH from the Kuroshio have decreased, more severe eutrophication, hypoxia and seawater acidification may occur in the entire ECS. Similar processes may also affect other shelves that come into contact with NPIW.