Intensifying concurrent marine–atmospheric heatwaves in the marginal seas of the Arabian Peninsula: implications for coral bleaching and ocean productivity

Marine heatwaves (MHWs) and atmospheric heatwaves (AHWs) are intensifying under climate change, yet their concurrent occurrence can amplify thermal stress and pose greater risks to marine ecosystems than either event alone. This study investigates the spatiotemporal variability, physical drivers, and ecological impacts of concurrent marine–atmosphere heatwaves (CHWs) across the marginal seas of the Arabian Peninsula during 1982–2021. The strength of compounding was quantified using a likelihood multiplication factor, while ecological thermal stress was assessed using Degree Heating Weeks and cumulative intensity. CHWs occur most frequently in the northern Red Sea, Arabian Gulf, and western Arabian Sea, and least frequently in the southern Red Sea. Their frequency and duration have increased significantly, with duration rising by up to 7.5 days per decade in the northern Red Sea. Concurrent conditions also extend MHWs and AHWs by an average of 6 and 2.2 days, respectively, substantially increasing cumulative thermal exposure. Our findings show that CHWs are the dominant drivers of coral bleaching and productivity loss in the region, with nearly 70-80% of severe coral-bleaching events are associated with enhanced CHW thermal stress. They also triggered more than 20% decline in chlorophyll-a concentrations– nearly 1.4 times that of standalone MHWs. Case studies of the 1998 and 2010 events highlight the infulence of high-pressure anomalies and weakened winds in shaping the development and spatial expansion of widespread CHWs. These findings demonstrate that atmospheric heat can substantially intensify marine thermal stress and ecological impacts, highlighting the importance of incorporating concurrent ocean–atmosphere extremes into marine heat-risk assessment and ecosystem conservation strategies.