Contribution of low-salinity water to sea surface warming of the East China Sea in the summer of 2016

Abstract

Substantial low-salinity water (< 26 psu) was observed in the northern East China Sea (ECS) in the summer of 2016, resulting in significant warming (similar to 2 degrees C) of sea surface temperature (SST) over the freshening area compared to normal year. By analyzing the ship-based hydrographic datasets, horizontal temperature and salinity distributions tracked by a wave glider, and results from a regional ocean model, this study examined the spatiotemporal behavior of low-salinity water over the northern ECS and its contribution to SST warming during summer. The observations revealed that a large amount of the freshwater originating from the Changjiang significantly stratified the surface layer above the top of the thermocline, resulting in a shallow mixed layer (ML) in which significant warming was found. The shallow ML led to a barrier layer formation between the ML and the layer below the ML that can enhance SST warming by restricting heat exchanges between the surface and the thermocline. Our model successfully captured the strong surface warming over the northern ECS observed during the summer of 2016, which corresponded to significant areas of surface freshening. The model-data comparisons demonstrate that the salinity-stratified ML had a significant impact on the enhancement of barrier layer formation, leading to increased SST warming over the areas wherein surface freshening was robust.