Update and new insights on marine heat waves in the Mediterranean

Society is facing unprecedented challenges arising from climate change impacts. Among them, marine heat waves (MHWs) are prolonged periods of extreme ocean temperatures with major ecological and socio-economic impacts. The Mediterranean is the largest semi-enclosed sea, with 46.000 km of coastline and many islands, being also considered a hot-spot of biodiversity with many endemic species. It is also one of the most vulnerable regions to climate change and responds rapidly to global warming with strong spatial variations between sub-basins. In this study, we will update and provide new insights on MHWs in the Mediterranean, from sub-regional to local scales, from surface to subsurface, and from the open ocean to coastal waters using multi-platform remote sensing and in situ observations.

Continuous satellite-based sea surface temperature monitoring allows to detect MHWs at the surface and to estimate their spatio-temporal variations at sub-regional and local scales over the last four decades. At the same time, the Mediterranean network of moored buoys installed in shallow waters allows addressing the coastal ocean response to such extreme events over the last 10 years or more. Additionally, profiling floats in the whole basin and ocean gliders along endurance lines in key ‘choke points’ provide valuable information at the subsurface on sub-regional and local scales, respectively, about both the physical and biogeochemical properties from the coast to the open sea. Results on the thermal stress situation will be provided updating the results from Juza et al. (2022) from satellite and profiling floats observations. In particular, we will address the unprecedented MHW recent events (2022 and 2023) characteristics, providing also new insights with the use of coastal moorings and gliders and through the integration of available physical and biogeochemical data.

The multi-platform observations used in this study are open access and distributed by national and European marine data portals such as the Spanish Balearic Islands Coastal Observing and Forecasting System (SOCIB), the U.K. Meteorological Office and the E.U. Copernicus Marine Service. Particularly, historical and near real-time ocean data available in the latter are being also used in the web-based application (www.apps.socib.es/subregmed-marine-heatwaves) implemented by SOCIB. This user-friendly visualization tool helps to detect MHWs in real time and to monitor their long-term variations, aiming at supporting the marine conservation and policy decision-makings for climate change mitigation.