Spatial and temporal variability of marine heatwaves in the Mediterranean Sea over 39 years, and their possible physical drivers

Marine heatwaves (MHWs) are prolonged discrete anomalously warm water events that last for more than five successive days and can be described by their duration, intensity, rate of evolution, and spatial coverage. These episodes of large-scale anomalously high ocean temperatures can have many impacts on the marine ecosystems and major implications for the fisheries as well. As a result of the anthropogenic climate change, MHWs have been observed in many parts of the world's oceans and their intensity and frequency are expected to increase in the future. This work investigates the spatial and temporal variability of the Marine Heatwaves in the Mediterranean Sea over 39 Years (1982 - 2020), the net air-sea heat exchange anomaly associated with these MHW events, and their possible physical drivers. The results have shown dissimilarities between the western (WMED) and eastern (EMED) Mediterranean basins in the detected MHW events during the study period. In other words, the WMED marine heatwaves were more frequent and more intense than the EMED marine heatwaves, while the marine heatwaves that occurred in the EMED were longer in terms of the duration than the ones that occurred in the WMED. Moreover, the fluctuation of the net heat flux anomalies during the study period were linked to the occurrence of the MHWs, the high SSTa of the MHW events were combined with positive (gain) heat flux anomaly but, during a few events, the high SSTa induced a negative (loss) heat flux anomaly especially in the EMED basin. In addition, a combination of some physical conditions such as shallower mixed layer depth, high air temperature (> 25 ^oC), high MSLP (> 1014 hPa), and low to no wind shear were observed to significantly contribute to the formation of the Mediterranean Sea marine heatwaves.