Thermohaline front at the mouth of Tokyo Bay in winter

A detailed structure of the remarkable thermohaline front, which exists from late autumn to early spring at the mouth of Tokyo Bay, Japan, is investigated by the field observation and the simple numerical experiment. The fresh, cool and nutrient-rich coastal water and the salty, warm and nutrient-poor offshore water converge in the surface layer at the thermohaline front. These two water masses mix at the thermohaline front and move downward spreading like a skirt under the front near the bottom. Such a current system accompanied with the thermohaline front results in transport of bay water into the mid-depth of the open ocean. We conclude that the thermohaline front at the bay mouth, heretofore considered as a barrier for the water exchange, plays an important role in the water exchange between the coastal water and the offshore water in winter.