Coastal Marine Heatwave Analysis: Distribution, Characteristics and Climate Change Impact

Marine heatwaves (MHWs) impose a growing threat on marine ecosystems, especially in the context of climate change. Most MHWs studies have focused on specific events and on a large spatial scale but with few systematic studies of MHWs. In this study, we used remote sensing sea surface temperature (SST) products from three different sources to assess the distribution and characteristics of MHWs on coastal systems during the past three decades. Results indicated that both MHW frequency and duration have increased in the coastal oceans globally during this period, leading to an increase of MHW annual stress. These positive trends were mostly attributed to changes in mean SST. The hot spots of MHW increases were mid-latitude enclosed seas and the western tropical Pacific and Atlantic. MHW frequency and duration and their long term changes were smaller along the coastline compared to offshore. This is likely to be the signature of nearshore cooling from increased upwelling and increased cloud formation due to the increasing temperature gradient between the oceans and the land. There were important differences in the mean MHW metrics derived from the different datasets which can be explained by the specificity of each product, stressing that future MHW studies should choose their dataset carefully, depending on their specific interest. Overall, this study provides insights into the global distribution and trends of MHWs in coastal areas and highlights the role of climate change in increasing the potential impact of MHWs on marine ecosystems.