Winter marine cold spells driven by intrusion of cold, low-salinity water in the western coast of the East/Japan Sea

Global ocean warming has led to a projected decrease in the frequency and intensity of marine cold spells (MCSs). However, the East/Japan Sea presents a climatic paradox, as winter MCSs continue to occur despite a clear, long-term warming trend. This study investigates the mechanisms underlying the sustained occurrence of these events. The analysis indicates that extreme coastal cold anomalies are closely linked to the intensified southward flow of cold and less saline North Korea Cold Water (NKCW) from East Korea Bay. Composite analyses and vertical profiles showed that cold, low-salinity water resulted from the intensified southward flow of the NKCW, which is associated with the weakened northward flow of the East Korea Warm Current. The time-lag correlation indicated that the low-salinity water causing MCSs in winter originated from freshwater inflows through the Korea Strait in summer and autumn. Low-salinity water could intensify upper ocean stratification and enhanced surface cooling, resulting in an increase in winter MCS events. Considering that the CMIP6 climate change scenario project indicate an increase in the Yangtze River discharge, which is the primary freshwater source through the Korea Strait, these findings suggest that the potential for coastal MCSs could be sustained in a warming ocean.