Interactions between cold cyclonic eddies and a western boundary current modulate marine heatwaves

Abstract Marine heatwaves are known to cause severe ecosystem damage and therefore have received attention in recent years. However, the focus has tended to be on global (surface) studies, but not coastal waters. Cyclonic eddies are important and underappreciated components in the eddy-dominated western boundary current system, but their impacts on the path of the western boundary currents have largely been unexplored. Here we show that cold cyclonic eddies can modulate the most intense coastal marine heatwaves on record inshore of the East Australian Current. We show that the marine heatwave was driven and modulated by the lateral movement of the western boundary current jet and cyclonic eddies. This study reveals that the interplay of cyclonic eddies and a western boundary current can drive coastal ocean warming, paving the way for future investigations into eddy interactions and the evolution of coastal marine heatwaves in other western boundary current regions.