Vertical structures of marine heatwaves.

A marine heatwave (MHW) is typically defined as an anomalous warm event in the surface ocean, with wide-ranging impacts on marine and socio-economic systems. The surface warming associated with MHWs can penetrate into the deep ocean; however, the vertical structure of MHWs is poorly known in the global ocean. Here, we identify four main types of MHWs with different vertical structures using Argo profiles: shallow, subsurface-reversed, subsurface-intensified, and deep MHWs. These MHW types are characterized by different spatial distributions with hotspots of subsurface-reversed and subsurface-intensified MHWs at low latitudes and shallow and deep MHWs at middle-high latitudes. These vertical structures are influenced by ocean dynamical processes, including oceanic planetary waves, boundary currents, eddies, and mixing. The area and depth of all types of MHWs exhibit significant increasing trends over the past two decades. These results contribute to a better understanding of the physical drivers and ecological impacts of MHWs in a warming climate.