Distinct characteristics of the intermediate water observed off the east coast of Korea during two contrasting years

The intermediate water known as “East Sea Intermediate Water” found south of the Subpolar Front (SF) is known to be formed in the northern East/Japan Sea (EJS), and its physical properties are determined by wintertime air-sea interaction north of the SF. Hydrographic data collected off the Korean coast show significant decadal oscillations in spiciness (π) following isopycnals of intermediate layer, which are explained by the Arctic Oscillation (AO) and consequent cold-air outbreaks. During positive AO phases, the cold-air outbreak and water formation are more active and the intermediate water having the same π reaches higher density (higher π following the same isopycnals). At interannual time scale, however, the π variability is well beyond the relationship with the AO. Especially, significantly lower π (both fresher and colder) intermediate water was observed in spring of 2010 than 2001 under the same surface net-heat flux peaks in the northern EJS in the two winters. Such contrasting characteristics of intermediate water between 2001 and 2010 are consistent with the HYCOM reanalysis results which indicate widespread extension of low- (high-) π intermediate water in the southwestern EJS in 2010 (2001). A clear contrast in circulation pattern is suggested to derive the distinctly different characteristics of the intermediate water. Northward penetration of the East Korea Warm Current (EKWC) inhibited the southward extension of the intermediate water in 2001 off the east coast of Korea. On the other hand, the EKWC that poorly developed in 2010 allowed low-π intermediate water to prevail in the southwestern EJS.