Marine heatwaves (MHWs)—persistent oceanic warming events increasingly observed worldwide—pose significant threats to marine environments and ecosystems. Understanding their drivers and evolution is critical for safeguarding marine environmental security.
Recently, researchers from the South China Sea Institute of Oceanology, Chinese Academy of Sciences, China, have published a study titled "Classification of Marine Heatwaves in the South China Sea and Their Thermodynamical Features" in Atmospheric and Oceanic Science Letters , introducing an innovative classification framework to investigate thermal versus dynamical drivers of MHWs.
Different from traditional classification schemes based on duration or intensity thresholds, this study categorizes MHWs into two major types—intensified MHWs and attenuated MHWs—based on the overall trend of sea surface temperature during an MHW event. In intensified MHWs, sea surface temperatures show a continuous rise with time, whereas attenuated MHWs display the opposite trend. The distinct driving mechanisms of these two MHW types can be explained by combining this classification framework with heat budget diagnostic equations.
This study points out that nearly half of the intensified MHWs are primarily driven by oceanic dynamic processes (e.g., eddies and ocean currents), which challenges the traditional view that MHWs are mainly dominated by atmospheric heating.
"We used to blame the atmosphere for 'baking' the ocean. Now we can see the ocean itself is a powerful heat generator, like a giant underwater mixer," says the first author, Dr. Rongwang Zhang.
This study quantitatively reveals the role of air–sea heat exchange in the evolution of MHWs. In thermally dominated MHWs, the contribution rate of latent heat flux to the change in net heat flux is the highest, exceeding 50% in all cases. Additionally, the study also utilized a newly released air–sea heat flux dataset called CASFlux (Chinese Air–Sea heat Flux; http://dx.doi.org/10.12157/CASFlux), and found that its performance is comparable to that of ERA5 and NECP2.
These findings provide new insights for accurately predicting MHW variations, and could also provide an effective response to threats such as coral bleaching and fisheries disasters.
