Polar processes set Arctic marine heatwaves apart

The Arctic is warming faster than any other ocean, yet its marine heatwaves remain poorly understood. No comprehensive assessment exists, particularly below the surface. Here we synthesise published Arctic marine heatwave studies alongside broader oceanographic literature, and offer our perspective on their drivers, impacts, and methodological challenges. Arctic marginal seas emerge consistently as surface marine heatwave hotspots, while subsurface events remain almost entirely uncharacterised despite likely being as intense and longer-lasting. Our synthesis reveals that Arctic marine heatwaves are shaped by processes absent from lower-latitude oceans: sea ice modulates heat fluxes, stratification, and temperature variability, while upward fluxes of warm subsurface water represent an overlooked driver class. We further identify key unknowns, including impacts on primary production and carbon exchange. Finally, we provide concrete methodological recommendations and priority directions for Arctic marine heatwave research: advancing this field is essential for anticipating ecological and climatic responses, in the Arctic and beyond. Arctic marine heatwaves are influenced by unique, overlooked drivers including sea ice (which modulates air-sea heat fluxes, mixed layer depth, and temperature variability) and upward fluxes of Arctic subsurface heat.