Marine heatwave events near Weizhou Island, Beibu Gulf in 2020 and their possible relations to coral bleaching.

Marine heatwaves (MHWs) are events of anomalously high sea surface temperatures lasting for five days or more and have recently been linked to widespread environmental stress on marine organisms, though there are few studies in the Beibu Gulf. This study characterizes MHWs near Weizhou Island (21°00'-21°10' N, 109°00'-109°15' E) using a recently developed detection algorithm on a high-resolution satellite sea surface temperature (SST) product and considers their potential influence on coral bleaching events. Reanalysis data are used to investigate atmospheric factors in MHWs occurrences. Results showed that among a total of 112 MHWs having occurred from 1983 to 2020, eight discrete MHWs occurring throughout 2020 in Weizhou Island. Interestingly, although not the most intense in 2020, the June 3rd-August 2nd event lasted for an enormous 61 days with mean and maximum intensities of 2.68 °C and 1.73 °C above climatology, respectively. The reasons for the occurrence and severity of MHWs in 2020 the intensification of Northwest Pacific subtropical high and its extension leading to increased shortwave radiation reaching the sea surface during the summer, reduced typhoon activity in July, weakened wind fields north of 20.5°N, and an enhancement in sea level anomalies. These act in concert to prevent heat transport away from the Beibu Gulf and thus, more intense MHWs. A massive coral bleaching event occurred in 2020 and is highly likely to be linked to MHWs activity.