Origin, Variability, and Pathways of East Sea Intermediate Water in a High-Resolution Ocean Reanalysis

Abstract

The East Sea Intermediate Water (ESIW) is the subsurface salinity minimum layer in the depth range 200-400 m in the East/Japan Sea. The origin, variability, and pathways of the ESIW were investigated using a 4-year-long (2015-2018) high-resolution (1/24 degrees) ocean reanalysis and Lagrangian particle modeling. A backward particle tracking analysis revealed that the ESIW was formed south of Vladivostok and shows strong interannual variability. In 2018, owing to strong northwesterly winds, heat loss to the air intensified, and freshwater transport from the northern East/Japan Sea was simultaneously decreased by about 18% compared with the previous year. Furthermore, there was increased formation of water masses heavier than that of the typical ESIW, and the volume of the ESIW was reduced. A forward particle tracking analysis showed that the contribution of the particles originated from the northern end of the East/Japan Sea was about two times greater than those from the southern end. The major portion of the ESIW's freshwater came from the northern East/Japan Sea, where sea ice melted and the Amur River discharged. The remaining portion was from the Changjiang River, which came through the Korea Strait. The ESIW reached the Ulleung Basin over the course of a year mainly through the deep channel, the Ulleung Trough, located to the north of the basin. The diapycnal diffusivity of 1.0 x 10(-4) m(2) s(-1) could erode away the low salinity core in about 27 years.