Oceanic Circulation Drives the Deepest and Longest Marine Heatwaves in the East Australian Current System

Although the impacts of marine heatwaves (MHWs) can extend well below the ocean surface, little is known about how oceanic and atmospheric forcings control their vertical structure. Here, we relate the MHW drivers to their sub-surface characteristics in different dynamical regimes including the East Australia Current. We detect MHWs in the depth-dependent surface mixed layer over 30-years and use a heat budget to identify the dominant mechanisms driving them. We show that MHWs in the Western Boundary Current (WBC) jet are predominantly driven by air-sea heatflux whilst in the WBC extension, MHWs are advection-driven. The deepest and longest MHWs are advection-driven and are more prevalent in autumn and winter. Surface (latent) flux-driven MHWs are shallower and occur predominantly in summer. Demonstrating how MHW characteristics are linked to their drivers facilitates their prediction through driver diagnosis, especially below the surface where observations are sparse and ecological impact is high.