Structure of the Korea strait bottom cold water and its seasonal variation in 1991

Precise CTD data taken bimonthly in 1991 show the structure and variation of the Korea Strait Bottom Cold Water (KSBCW) in detail. The KSBCW appears only near the Korean coast in the strait. It is found within about 50 km of the coast, and is about 20–50 m thick with seasonal variations. Its structure along the strait becomes sharply deeper toward the south throughout the year. The gradient along the strait is 0.7×10-3 in April and about 0.4×10-3 in the other months. It moves more than 100 km south in summer when the density of the upper layer is 1.022–1.025 g/cm3 and retreats in winter when it is 1.026 g/cm3. Except in August, the structure across the strait is characterized by a rise at its western end. In August it takes on an arch-shape which could not be described due to the deficiency of vertical resolution in the historical data. Using Bernoulli’s equation with the observed values for density stratification and velocity, it can be demonstrated that the East Sea Proper Water in the Ulleung Basin could not flow out to the Korea Strait, whereas the salinity minimum layer water could flow there.