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’ and its coastal mode ‘North Korea Cold Water’ found south of the Subpolar Front (SF) is formed in the northern East (Japan) Sea, and its physical properties are known to be determined by wintertime air-sea interaction north of the SF. Hydrographic data collected off the coast bi-monthly from 1994 to 2011 show significant decadal oscillations in spiciness following isopycnals of intermediate water (27.1-27.2 sigma-theta typically corresponding to 150 m depth), which are explained by the Arctic Oscillation (AO) and consequent cold-air outbreaks. During positive AO phases over the decades, the cold-air outbreak and water formation are more active and the intermediate water having the same spiciness reaches higher density (higher spiciness following the same isopycnals). At interannual timescale, however, the spiciness variability is well beyond the relationship with the AO. Especially, significantly lower spiciness (or both less saline and lower temperature) intermediate water was observed in spring of 2010 than 2001 under the similar AO condition (negative peaks). Strong cooling with common negative peaks in surface net-heat flux (with different patterns) and common negative peaks in the AO index are prominent in winter of the two years over past two decades. Such contrasting characteristics of intermediate water between 2001 and 2010 are consistent with the HYCOM reanalysis results which, along with the satellite altimetry-derived sea surface height maps, indicates widespread extension of low (high) spiciness intermediate water in the southwestern East Sea in 2010 (2001). A clear contrast in circulation pattern, along with net-heat flux pattern, is suggested to derive the observational results in the distinctly different characteristics of the intermediate water.