[A-OS15] Ocean circulation and material cycle in coastal seas

[AOS15-09] Long-term trends of oxygen concentration in the waters in bank and shelves of the southern Japan Sea

*Tsuneo Ono¹ (1.Fisheries Research and Education Agency)

Keywords:Ocean deoxygenation, Japan Sea, continental shef, coastal area

Many studies have investigated oxygen decrease in Japan Sea Proper Water (JSPW), but we must also investigate oxygen decrease in shallow waters above JSPW to assess socio-economic impact of deoxygenation in Japan Sea. In this study, histrical oxygen data in the waters of three continental shelves and a bank off the Japan coastof Japan Sea, off-Awashima area (AW), Wakasa Bay (WB), East of Tsushima Straight (ETS), and Yamato Bank (YB), were collected from public database and analyzed to assess the temporal variation of oxygen in each region from 1960s to 2000s. Significant decreasing trends of oxygen were detected in the waters below 150 m depth in WB and YB, and below 300 m in AW, in the summer season. Deoxygenation siginal was more extensive in summer ETS, where a deoxygenation trend was detected throughout the water column from the bottom to the sea surface. These are the first evidences that reveals occurrence of ocean deoxygenation in the continental shelves of Japanese waters.
Detailed analysis indicated that oxygen decreases in AW, WB, and YB were consequence of the upward propagation of the deoxygenation signal from JSPW, while that of ETS was caused by horizontal propagation of deoxygenation signal fromthe East China Sea.Assuming that the observed trend will continue in future, it is predicted that part of the subsurface water in the summerTsushima Strait area in the summer season will reach the general sublethal threshold of oxygen (134 umol·kg^-1, Vaquer-Sunyer and Duarte, 2008) by the end of this century.