Role of atmospheric and oceanic factors on the August 2024 marine heatwave in northern Norway

Marine heatwaves (MHWs) are prolonged periods of extreme ocean warming that significantly impact marine ecosystems, fisheries, and aquaculture. In August 2024, northern Norway experienced one of the most intense MHWs recorded since 2012, which coincided with a sharp rise in salmon lice infestations at aquaculture sites in the area. This study investigates the atmospheric and oceanic drivers of this event, focusing on the interaction of local meteorological and oceanic conditions with large-scale climate variability. Using a combination of ocean model hindcast data (Norkyst), atmospheric reanalysis data (ERA5), and in situ observations, we characterized the MHW and identified key contributing factors. Our analysis revealed that the MHW was driven by a combination of weakened local wind patterns, high air temperatures, and strong stratification, alongside external heat supply from northward advection of warm and fresher water, facilitated by a positive phase of the summer North Atlantic Oscillation (NAO). The positive NAO phase enhanced southwesterly winds, which transported warm and humid air masses into the region, increasing the total heat flux from the atmosphere and further intensifying local warming. The ecological impacts of this MHW included increased salmon lice abundance, posing significant challenges to wild and farmed salmon populations in a region that hosts the world’s largest salmon aquaculture industry. Understanding the drivers of MHWs in northern Norway is essential for assessing their predictability and informing management strategies to mitigate their effects. This study highlights the importance of advancing regional MHW forecasting to enhance resilience in fisheries and aquaculture sectors under a warming climate.