Record-breaking 2020 summer marine heatwaves in the western North Pacific

Record-breaking marine heatwaves (MHWs) occurred in the western North Pacific during the summer of 2020. These unprecedented MHWs were consistent with favorable large-scale conditions that are linked to an anom-alous western North Pacific subtropical high (WNPSH), resulting mainly from sea surface temperature (SST) anomalies across the tropical oceans. In addition, a moderate La Nin & SIM;a-like pattern was also conducive to transporting warm seawater to the western North Pacific. Mixed-layer heat budgets suggest that surface heat flux contributed to the SST anomaly in the western subtropical Pacific. In contrast, oceanic heat advection domi-nanted in the South China Sea and the western equatorial Pacific. Numerical model experiments indicated that the tropical Indian Ocean SST anomalies were responsible for the enhanced WNPSH. The increased zonal SST gradient across the tropical Pacific also played an important role. Inter-ocean interactions can modulate climate variability through ocean-atmospheric coupling and deserve more attention when predicting MHWs within the context of global warming. In addition, it is critical to consider MHWs as a powerful tool in detecting acute, intense thermal stress events in the coral bleaching pre-warning system.

Automated summary

Record-breaking marine heatwaves occurred in the western North Pacific in the summer of 2020. These unprecedented events were caused by favorable large-scale conditions associated with anomalous western North Pacific subtropical high and sea surface temperature anomalies across the tropical oceans. The heat budgets and numerical model experiments revealed that surface heat flux and oceanic heat advection were the dominant factors in different regions, while inter-ocean interactions and the zonal sea surface temperature gradient played important roles.