Marginal seas in the Western Pacific Ocean are located within the boundaries between the continents or islands and the open ocean. Given the advances of climate change, it is essential to understand what happens in the AMS, which is a very important region for human society due to its productivity, fishery resources, and human population on adjacent land. Significant changes in the hydrological and biogeochemical cycles due to the changing climate, together with increasing human economic activities, will affect the ocean structure and ecosystem in the AMS. These environmental changes in the marginal seas, including coastal and shelf regions, strongly influence the area’s biological structure, fisheries, and marine ecosystems. For example in the East China Sea, a significant reduction of catch in the fisheries during the past half-century have been caused by not only over-fishing but also environmental changes, which directly or indirectly influence the food web structure of those regions. To maintain healthy and productive marginal seas, international cooperative studies by countries around the marginal seas are absolutely essential.

There are various scientific questions that need to be addressed by cooperative studies, such as quantitative evaluation of water mixing, nutrient transport, and biological response, which are often controlled by a complex combination of physical and biogeochemical processes. Since the marginal seas are close to areas of human habitation, they can be expected to interact both positively and negatively with human life. It is an urgent issue to evaluate environmental risk, since the marginal seas are strongly linked to human society. In particular, the AMS is located from tropical to subpolar regions along the Asian continent. The AMS connects each region like a chain, and it is necessary to consider the interaction between the seas, instead of just a single marginal sea. These marginal seas play a decisive role in the sustainable development and environmental adaptation/protection in confronting global climate change. Therefore, it is an urgent matter to advance cooperative studies to improve our common understanding of the changes in heat and nutrient circulation in marginal seas, which would affect the primary production, marine ecosystems, fisheries, and society.