Distribution and Circulation of Autumn Low-salinity Water in the East Sea

Abstract

Seawater with salinity of 32.5 psu or less is observed in the southern Japan/East Sea (JES) every autumn. It is confined to a surface layer 30-45 m in depth that expands to cover the entire JES in October. Two sources of "autumn low-salinity water" have been identified from historical hydrographic data in the western JES: East China Sea (ECS) water mixed with fresh water discharge from the Yangtze River (Changjiang) and seawater diluted with melted sea ice in the northern JES. Low-salinity water inflow from the ECS begins in June and reaches its peak in September. Low-salinity water from the northern JES expands southward along the coast, and its horizontal distribution varies among years. A rare observational study of the entire JES in October 1969 indicated that water with salinity less than 33.0 psu covered the southwestern JES; the lowest salinity water was found near the Ulleung Basin. In October 1995, the vertical distribution of salinity observed in a meridional section revealed that water with salinity of 33.6 psu or less was present in the area north of the subpolar front.

Causes of Interannual Variation of Summer Mean Alongshore Current Near the East Coast of Korea Derived From 16‐Year‐Long Observational Data

“…It was found that the summer mean coastal current reverses against the annual mean of the poleward coastal current; the alongshore gradient of the wind stress curl is suggested as the main factor inducing the current reversal. In addition, coastally trapped low‐salinity buoyant water ( S < 34.0, T > 5 °C) of northern origin, distinguishable from both the NKCW and LSTWW, is found, which is consistent with an equatorward surface current near the coast during summer (Jeong et al, ; Lee & Lee, ; Park et al, ; see Figure c). Previous studies have addressed the dynamics underlying the seasonal mean of the equatorward coastal currents during summer; however, the characteristics of the interannual variability in summer current reversal and its main drivers and forcing mechanisms remain unknown, probably because of the lack of sufficiently long time series measurements.…”

“…The coastally trapped surface low‐salinity warm water ( S < 34.0, T > 5 °C), distinguishable from both the NKCW and LSTWW, originates from the northern coastal region as suggested by previous works (Jeong et al, ; Lee & Lee, ; Park et al, ; Seung, ) and was transported by local and remote wind‐force equatorward currents during summer. The surface low‐salinity (<32.9) water observed at the ESROB during 2006, 2011, and 2013 is consistent with the “northern coastal pattern” characterized by the same seawater property confined along the northern coast (Lee & Lee, ), supporting the idea of coastally trapped surface low‐salinity warm water of northern origin. During 2001, despite the northern coastal pattern, the summer mean salinity (33.24) observed at the ESROB was significantly higher than the summer climatology (33.06), probably because of the strong offshore EKWC influence (high EI) and the poleward anomaly in the alongshore current transporting a greater portion of the HSTWW.…”