Strong impact of tropical cyclones on thegenesis of subsurface marine heatwaves

Subsurface marine heatwaves (sMHWs) are newly recognized extreme ocean events with profound impacts on global marine ecosystems. While some sMHWs are identified as extensions of their surface counterparts, a considerable proportion occur without a detectable signature on the sea surface. Previous studies have linked their formation to downwelling favorable surface winds, warm ocean eddies, and planetary waves, yet whether other potential drivers of these heatwaves exist remains unclear. The tropical cyclones (TCs) are well known to induce a pronounced warming in the subsurface. The strong wind stress associated with TCs induces intense mixing in the upper ocean, in which the warm surface water mixed down beneath the mixed layer can persist for more than 5 days, the criterion used to define the sMHW. Here, we show that the induced warming can efficiently trigger subsurface marine heatwaves. It is shown from an ocean reanalysis that such warming reaches the heatwave threshold at least once along the tropical cyclone life cycle for 79.4% of the tropical cyclones during 2001–2022, and the density of sMHW genesis induced by TCs is almost three times larger than the global average. In areas with intense TC activity, including the northern Philippine Sea, east of Madagascar, and along the coast of California, up to 40.0% of sMHWs at 50m can be attributed to subsurface warming induced by TCs. Over the past two decades, the increasing area and intensity of surface MHWs have been attributed to the warming trends of sea surface temperature with global warming. We find that the area and maximum intensity of TC-induced sMHWs have also increased significantly. The steady growth of the subsurface temperature is found as the main cause of the increased TC-induced sMHWs.