Slope Convection in the Peter the Great Bay and Ventilation of the Japan Sea

Cascading of dense shelf water along the slope (slope convection) of Peter the Great Bay in the northwestern Japan Sea in winter is one of the key mechanisms of ventilation of the Japan Sea deep layers. Results of direct observations of cascading by autonomous mooring systems and repeated CTD surveys during winters of 2012-2014 have been presented here. The events of dense water, formed by cooling and brine rejection on the shelf during ice formation, approaches the shelf edge (100 m) have been registered every winter usually in February – March. However their duration has been varied interannually reflecting climatic changes. Only one episode of deep down slope cascading was registered by mooring at 1150 m. Its duration was only around 12 hours. These very transient events however resulted in a number of intrusions of colder, less saline, higher oxygen content and higher turbidity water detected by CTD casts observed down to 2000-2800 m indicating penetration of cascading down to the bottom of the slope and thus ventilation of the intermediate, deep and bottom waters of the Japan Sea. Depending on a severity of winter the intrusions formed by cascading water ventilate intermediate layers (winters of 2013-2014) or may penetrate down to the bottom layer (extremely cold winter 2001). In any case this ventilation mechanism is important to understand water mass transformation in the Japan Sea.