Marine heatwaves: a comparative analysis between low and high latitude regional seas in the Northern Hemisphere

While the frequency, duration and spatial extent of marine heatwaves (MHWs) have increased worldwide, this increase is neither temporally nor spatially uniform, but varies depending on the time and geographical region under consideration. Therefore, this study examined the characteristics of MHWs and their spatio temporal variability over the past four decades (1982-2022) in five warming hotspots of the Northern Hemisphere - the Red Sea, the eastern Mediterranean, the Black Sea, the North Sea and the Barents Sea. We found accelerated warming and high spatio temporal trend variability in MHW frequency in these regional seas, with an average trend (event/decade) ranging from 0.84 in the Red Sea to 1.12 in the eastern Mediterranean Sea. These results are consistent with observed SST warming rates. The occurrence of these events was influenced by large-scale climate patterns such as the El Niño-Southern Oscillation (ENSO) and the East Atlantic Pattern (EAP), with ENSO having the greatest influence on the Red Sea and Black Sea and EAP on the North Sea and Barents Sea. We also found that atmospheric forcing plays a larger role in the formation of MHWs, especially in shallow seas (e.g. North Sea and Barents Sea). These results suggest that as climate change progresses, more intense MHW episodes can be expected in these regional seas, with far reaching implications for marine ecosystems.