Variations in Summer Marine Heatwaves in the South China Sea

Marine heatwaves (MHWs) are prolonged anomalous warm seawater events that can severely impact marine ecosystems and have never been studied previously in the South China Sea. Here, we combine satellite sea surface temperature and reanalysis products to provide a systematic analysis of variations in summer MHWs in the South China Sea and potential influencing factors. The MHW days and duration, calculated as multiyear average, are mainly concentrated near the Nansha Islands and Beibu Gulf. Additionally, we find significant increasing trends in MHW days, duration, and frequency in the South China Sea during 1982-2020. The first empirical orthogonal function mode accounts for 60% of the total variance and exhibits a general mono-sign pattern over the entire South China Sea. Increased solar radiation and released latent heat during summer MHWs contribute to high pressure in the western North Pacific. The anticyclone induced by the anomalous intensification of the western North Pacific subtropical high and its westward extension bring easterly wind anomalies to low latitudes, weakening the summer southwest monsoon south of 12 degrees N in the South China Sea. The midwestern South China Sea upwelling weakens or even disappears due to a negative wind stress curl, causing basin-wide severe summer MHWs. The paper also points out that more attention should be given to inter-ocean interactions when monitoring the risks of unprecedented MHW-related coral bleaching and marine ranching in the South China Sea.