Extreme 2020 Summer SSTs in the Northern South China Sea: Implications for the Beibu Gulf Coral Bleaching

Abstract

Abstract A severe coral bleaching event occurred in the Beibu Gulf during boreal summer 2020. This event was caused by record-breaking warm sea surface temperature (SST) anomalies in the northern South China Sea (NSCS). Anomalous anticyclones (AACs) over the NSCS linked to the Indian Ocean warming and La Niña induced the extreme NSCS warming. In May–July 2020, anomalous anticyclonic-shear easterlies appeared over the tropical western Pacific as a Kelvin wave response to the Indian Ocean warming. These easterlies resulted in an AAC over the NSCS and tropical northwestern Pacific via the Ekman dynamics. Besides, the anomalous easterlies increased moisture fluxes from the Pacific to the Maritime Continent (MC), enhancing the MC convection and thus supporting the NSCS AAC via an anomalous Hadley circulation. In this stage, the increased incident shortwave radiation induced by the NSCS AAC was the major contributor to the NSCS warming. In September 2020, anomalous equatorial Pacific easterlies associated with the La Niña could trigger an NSCS AAC by enhancing the MC convection. The resultant AAC warmed the NSCS SST anomalies mainly by increasing downward latent heat flux and shortwave radiation. Downward heat advection associated with the NSCS AAC also contributed to the extreme NSCS warming.