Figure 4

(a) Time series of interannual variations of the northwestward salt transport with reference salinity of 34.0 (Q_S) averaged during April–May (black), observed standardized the second principal component (PC2) score of salinity along the ship-based CTD line in April (red circles in Fig. 1b; blue), and relative vorticity averaged over the region represented by the blue rectangle in Fig. 3a during April–May (green). (b) Time series of interannual variations of the same salt transport as (a) (Q_S; black), observed sea-surface chlorophyll-a averaged over the green rectangle of Fig. 3a during April–May (green) and observed longitude of the offshore branch of the Tsushima Warm Current (OBTWC) path averaged over the purple rectangle of Fig. 3a during March–May (blue). (c) Time series of interannual variations of model northeastward salt transport across the Tsushima Strait with reference salinity of 34.0 (Q_S) averaged during July–September (black), observed precipitation (including snowfall) over Akita and Yamagata Prefectures (blue circles in Fig. 1b), Japan averaged during December–February (green), and model sea-surface net surface heat flux (positive values represent upward flux) averaged over 36° N–41° N, 134° E–140° E during January–March (blue).