Long-Term Variability of the East Sea Intermediate Water Thickness: Regime Shift of Intermediate Layer in the Mid-1990s

The shipboard measurements over approximately 55 years in the southwestern part of East Sea (Sea Japan) demonstrate a remarkable basin-wide, interannual-interdecadal variability temperature-based thickness Intermediate Water (ESIW) whose temporal shows strong correlation with density-based (r = 0.97). Relevant to long-term ESIW thickness, clear changes horizonal and vertical features have been observed at intermediate layer mid-1990s, such as 1) increases temperature gradient thermocline by shoaling 2°C–5°C isotherms, 2) relatively high correlations among isotherms interdecadal timescale, 3) appearance zonal phase difference after 4) change between Arctic Oscillation Index thickness. could be smaller when its formation is weaker deep-water mass below it becomes stronger. Based on observed, we hypothesized regime shift concerning meridional overturning circulation; before active mainly controlled variability, but rate predominantly affected own variability.