Hot and Cold Marine Extreme Events in the Mediterranean over the last four decades

Marine heat waves (MHWs) and cold spells (MCSs) are anomalous ocean temperature events that occur in all oceans and seas with great ecological and economic impacts. The quantification of the relative importance of marine temperature extreme events is often done through the calculation of local metrics, the majority of them not considering explicitly the spatial extent of the events. Here, we propose a ranking methodology to evaluate the relative importance of marine temperature extreme events between 1982 and 2021 within the Mediterranean basin. We introduce a metric, generically termed activity, combining the number of events, duration, intensity and spatial extent of: i) summer MHWs and ii) winter MCSs. Results at the entire Mediterranean scale show that the former dominate in the last two decades while the latter are prevalent in the 1980s and 1990s. Summers with the highest MHW activity were 2018, 2003 and 2015 and winters with the strongest MCS activity took place in 1992, 1984 and 1983. The highest MHW activity occurred in the Gulf of Lion while the highest MCS activity took place preferably in the Aegean basin. According to our proposed definition, the three strongest MHWs almost double the duration, mean intensity, and activity of the three strongest MCSs. The long-term tendency of activity shows a rapid increase for summer MHWs and a linear decrease for winter MCSs in the Mediterranean over the last four decades.

 

We acknowledge the financing support from FCT – JPIOCEANS/0001/2019