Hot and cold marine extreme events in the Mediterranean over the period 1982-2021

Abstract

Marine temperature extremes are anomalous ocean temperature events, often persisting over several weeks or longer, with potential impacts on physical and ecological processes that often encompass socio-economic implications. In recent years, a considerable effort has been directed at the development of metrics allowing an objective characterization of both marine heatwaves (MHWs) and marine cold spells (MCSs). However, the majority of these metrics do not consider explicitly the spatial extent of the events. Here, we rank and evaluate the relative importance of marine temperature extreme events thanks to a metric, called activity, that combines the number of events, duration, intensity and spatial extent. According to this definition, in the Mediterranean basin between 1982 and 2021, summer 2018 experienced slightly more MHW activity than summer 2003, documented as an exceptional extreme event. Besides, MHW activities were higher in the last two decades while winter MCS activities were higher in the 1980s-1990s. The highest MHW activities occurred preferentially in the western Mediterranean while the strongest MCS activities took place preferentially in the eastern Mediterranean. Moreover, the duration, mean intensity, and activity of the three strongest MHWs are twice as high as those of the three strongest MCSs. The long-term tendency of extreme events activity shows an accelerated increase for summer MHWs (about +150°C.days.10⁶km²) and a linear decrease for winter MCSs in the Mediterranean (about -60°C.days.10⁶km²) over the last four decades.

Marine heat waves in the Mediterranean Sea: An assessment from the surface to the subsurface to meet national needs

“…MHWs in the Mediterranean Sea have been addressed by previous studies at the basin scale (Galli et al, 2017;Darmaraki et al, 2019a;Darmaraki et al, 2019b;Garrabou et al, 2022;Simon et al, 2022), in smaller areas studies (Bensoussan et al, 2019;Ibrahim et al, 2021;Androulidakis and Krestenitis, 2022) and finally at sub-regional scale, splitting the basin into dynamical (Juza et al, 2022;Pastor and Khodayar, 2022) or biological (Dayan et al, 2022) sub-regions. To focus on the link with the marine habitat, a more detailed regional division of the Mediterranean basin should be considered (Simon et al, 2022).…”

“…MHWs in the Mediterranean Sea have been addressed by previous studies at the basin scale (Galli et al, 2017;Darmaraki et al, 2019a;Darmaraki et al, 2019b;Garrabou et al, 2022;Simon et al, 2022), in smaller areas studies (Bensoussan et al, 2019;Ibrahim et al, 2021;Androulidakis and Krestenitis, 2022) and finally at sub-regional scale, splitting the basin into dynamical (Juza et al, 2022;Pastor and Khodayar, 2022) or biological (Dayan et al, 2022) sub-regions. To focus on the link with the marine habitat, a more detailed regional division of the Mediterranean basin should be considered (Simon et al, 2022). According to Bianchi et al (2012), the areas of interest in the Mediterranean Sea should be defined biologically rather than geographically to address the MHW-related specific impacts on each species and therefore providing location-specific and species-specific monitoring and indicators to end-users.…”

“…Our choice to split and classify the Mediterranean Sea using EEZs to assess MHWs is motivated by the need for smaller-scale subdivisions (Juza and Tintore, 2021;Juza et al, 2022), as well as estimates of the subsurface extension of these processes (Simon et al, 2022). In particular, the EEZ classification has been chosen to respond to societal needs, although it is not based on specific ocean processes or ecosystem requirements.…”

“…To better understand how much each Mediterranean country's territorial sea and adjacent waters may be affected by these changes, this study assesses the variability of surface and subsurface -as ecological species may be more impacted in the subsurface (Simon et al, 2022) -MHWs over the period 1987-2019 in the whole Mediterranean Sea EEZ areas. Combining satellite observations and a regional reanalysis in the Mediterranean, both at daily and high spatial resolutions, over their common period 1987-2019, SST and OHC in the upper 20, 40 and 100 m layers are used to identify surface and subsurface MHWs.…”

Coastal and regional marine heatwaves and cold-spells in the Northeast Atlantic

“…As a result of global and regional warming heavily influenced by anthropogenic factors, the intensity and annual number of MHW will continue to accelerate globally (Oliver et al, 2019;Plecha et al, 2021). Conversely, as oceans warm, MCSs are diminishing (Schlegel et al, 2021;Simon et al, 2022) and are expected to continue fading in future climate conditions (Yao et al, 2022). However, these evolutions are not uniform regionally and it remains unknown if coastal areas follow the open-ocean trends.…”