Internal hydraulic jump in the Tsugaru Strait

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

“…The strait is 100 km in length, 20-40 km in width, and has shallow sills (∼130 m depth) near its western part (Figure 1b). Being principally driven by sea level difference between the Sea of Japan and the North Pacific, the Tsugaru Warm Current (TWC) flows eastward from the Sea of Japan into the North Pacific and transports water at a rate of ∼1.5 Sv (1 Sv = 10 6 m 3 s −1 ) on average (e.g., Ito et al, 2003;Toba et al, 1982 (Conlon, 1981;Ito et al, 2003) Primary productivity and nutrients increase downstream along the TWC (Matsuura et al, 2007;Saitoh et al, 2008;Tanaka et al, 2021;Yamada et al, 2005) and fishery resources (e.g., scallop, abalone, sea urchin, squid, and Pacific bluefin tuna) are abundant (e.g., Kosaka, 2016;Sakurai et al, 2000;Shimose & Ishihara, 2015). Recently, Ohta et al (2015) revealed vigorous vertical turbulent mixing over the abrupt bottom of the sills in the western part of the Tsugaru Strait.…”

“…WAKITA ET AL. (Conlon, 1981;Ito et al, 2003) Primary productivity and nutrients increase downstream along the TWC (Matsuura et al, 2007;Saitoh et al, 2008;Tanaka et al, 2021;Yamada et al, 2005) and fishery resources (e.g., scallop, abalone, sea urchin, squid, and Pacific bluefin tuna) are abundant (e.g., Kosaka, 2016;Sakurai et al, 2000;Shimose & Ishihara, 2015). Recently, Ohta et al (2015) revealed vigorous vertical turbulent mixing over the abrupt bottom of the sills in the western part of the Tsugaru Strait.…”

Frontal Waves in the East of the Tsugaru Strait Revealed by the High-Frequency Radar Observation

“…In the Tsugaru Strait, recent studies reported significant disturbance due to the intense flow and tides (e.g., Yamaguchi et al, 2020;Tanaka et al, 2021), and subsequent characteristic change in ocean environment there (Wakita et al, 2021). Yamaguchi et al (2020) suggested generation of internal waves that have large-amplitude in the vertical direction behind a characteristic topography (sill) in the western part of the strait based on observations and numerical experiment.…”

“…Yamaguchi et al (2020) suggested generation of internal waves that have large-amplitude in the vertical direction behind a characteristic topography (sill) in the western part of the strait based on observations and numerical experiment. Around the sill where Yamaguchi et al (2020) made the investigation, Tanaka et al (2021) observed far stronger turbulence than that in the open ocean (the turbulent energy dissipation rate: O (10 −6 ) W kg −1 , the vertical diffusive coefficient: O (10 −2 ) m 2 s −1 ), and estimated subsequent vertical transport of nitrate behind the sill (1 mmol m −2 day −1 ). The value is far larger than that observed by Kaneko et al (2021) in the subarctic region of the Western North Pacific during summer as ~1 × 10 −2 mmol m −2 day −1 .…”

“…Kouketsu et al (2005) reported intrusion of low-salinity water into the subtropical gyre at the density of the North Pacific Intermediate Water (26.6-26.9 σθ; 300-600 dbar) associated with wave-like structure with the horizontal length-scale of about 100 km along the Kuroshio Extension. Therefore, if similar wave exhibits in the strait, such disturbance would be thought to play an important role for water exchange across the front, and may contribute to faster acidification as mentioned above (Wakita et al, 2021) through stirring and mixing of low pH water, in addition to significant vertical mixing that pumps up materials such as nitrate (Tanaka et al, 2021) including iron (Saitoh et al, 2008). However, observations that have resolution for such frontal waves in the strait are rare although many repeated observations of ships and moorings were conducted there, because of the intense velocity of the TWC and frequent ship traffic through the strait.…”