MARINE HEATWAVES

Manoterra decrypts the latest reports and news topics to help you grasp the essentials in less than 3 minutes of reading.

WHAT IS A MARINE HEATWAVE?

A marine heatwave occurs when the sea surface temperature is above seasonal averages (90th percentile) for more than five consecutive days.

THE MEDITERRANEAN, AN OVERHEATED SEA

Since the early 2000s, the deviation from the 1991–2020 average has shifted permanently into positive territory and is increasing, with increasingly marked summer peaks. In recent years, the average anomaly has been around +1°C, confirming structural warming in the Mediterranean basin.

Average temperature of the Mediterranean Sea
vs. 1990-2020 period

THE CONSEQUENCES OF MARINE HEATWAVES

Underwater heat waves cause: Mass mortality of immobile ecosystems (corals, seagrass beds, sponges) Significant displacement or loss of mobile biodiversity due to oxygen depletion caused by excessive water temperatures A decrease in carbon sequestration. Organisms such as phytoplankton are no longer able to act as carbon sinks. Risks of methane degassing

Correlation between marine heatwaves and mortality
(Northwestern coastal Mediterranean between 2015 and 2019)

OUR ANALYSIS & RECOMMENDATIONS

The signal is clear: seas and oceans are warming, marine heatwaves are intesifying and accelerating the decline of coastal ecosystems—with tangible economic impacts. Leaders are no longer content to simply “observe”: they are measuring, adapting their operations, reducing their emissions, and integrating nature into their investment decisions.

Sources : Marine Heatwave Tracker (NOAA & partenaires), Copernicus Marine – OMI Méditerranée