Subsurface temperature anomaly observed by Argo floats during the 2022 Mediterranean Marine heatwave

Marine Heatwaves are periods of persistent anomalously warm ocean temperatures, which can have significant impacts on ecosystems as well as coastal communities and economies. Their magnitude and frequency have increased over the last couple of decades as shown by surface satellite observations, but our understanding of the structure of their depth is still limited. 

The present work investigates the temperature anomaly of the 2022 Marine Heatwave in the Mediterranean Sea down to 2000 m depth using in-situ Argo floats observations. The Ocean Heat Content anomaly of 2022, estimated with respect to a float-derived climatology relative to the period 2001-2020, was used to define the regions most affected by warming in different layers. In these areas (North-Western Med, Central Ionian Sea, Southern Adriatic) float profiles were divided in three categories, based on the heat vertical penetration: category 1 (shallow, 0-150 m), category 2 (intermediate, 150-800 m), category 3 (deep, > 800 m). Profiles from category 1 showed near-zero or slightly negative temperature anomaly in a thin layer between 50 m and 150 m of depth, while displaying a warming below the intermediate layer. Profiles characterized by larger heat vertical penetration (categories 2 and 3) were mainly located within mesoscale or sub-basin scale structures and showed the largest positive temperature anomaly in the surface layer and in the thermocline. All profile categories exhibited a warming between 200 and 800 m depth. This study highlights the impact of Marine Heatwaves on the Mediterranean subsurface layers and the influence of ocean circulation on their characteristics, opening the way to describe their consequences on the deep ecosystems.