Rapid Reduction of pH and CaCO₃ Saturation State in the Tsugaru Strait by the Intensified Tsugaru Warm Current During 2012–2019

Abstract

Abstract To examine the ocean acidification of coastal water as the result of the oceanic uptake of anthropogenic atmospheric CO 2 , we initiated acidification monitoring in the eastern part of the Tsugaru Strait, through which the Tsugaru Warm Current flows eastward from the Sea of Japan to the North Pacific. Annual mean pH and CaCO 3 saturation state during 2012–2019 decreased considerably throughout all depths at rates of 0.0030–0.0051 and 0.017–0.036 years −1 , respectively. These rates of decrease are faster than those caused by increasing atmospheric CO 2 and faster than those observed during previous research. These fast rates are attributed to an enhanced increase in dissolved inorganic carbon concurrently with increases in salinity and density caused by elevated mixing of the upper and deeper waters from the Sea of Japan at the western part of the strait. The elevated mixing is attributable to the strengthening of the Tsugaru Warm Current.