[A-OS22] Ocean circulation and material cycle in coastal seas

[AOS22-09] Seasonal and interannual variations in oceanographic conditions of Onagawa Bay, associated with intrusions of oceanic water

*Daisuke Takahashi¹, Kenji Kaneko² (1.Tokai University, 2.Fukuyama University)

Keywords:seasonal variation, interannual variation, oceanographic condition, intrusion of oceanic water, Onagawa Bay

Seasonal and interannual variations in oceanographic conditions, such as water temperature and salinity, were investigated in Onagawa Bay on the Sanriku ria coast, which faces the Pacific Ocean, using hydrographic observations over the period of May 2012 to March 2019. Water temperature and salinity structure below the sea surface layer in the bay was seasonally affected by intrusions of oceanic water associated with the Oyashio water and the Tsugaru Warm Current water. Water mass distributions in the bay over the period of 2012 to 2015 had clear seasonality, characterized by the Oyashio water in the lower layer in spring, Tsugaru Warm Current water in the lower layer in fall and the entire water column in winter. This seasonality of water mass distributions was not distinct over the period of 2016 to 2019, that is, the Oyashio water did not appear in spring, but the Tsugaru Warn Current water frequently and intermittently intruded to the bay from spring to summer. Additionally, both water temperature and salinity in the bay tended to gradually increase over the entire period. During this time, warm water from the Kuroshio Extension stayed off the Sanriku ria coast and weaken intrusions of the Oyashio water to the bay. The results lead us to the conclusion that the interannual as well as seasonal variations of water temperature and salinity in Onagawa Bay are accompanied by the intrusions of oceanic water associated with the Oyashio water and Tsugaru Warm Current water.