Mercator Ocean International (MOi) publishes a monthly bulletin presenting the marine heatwave conditions for the month just passed. It includes:
- for regions of the Ocean in marine heatwaves situation the time this event started,
- the timeseries showing the total surface occupied by marine heatwaves globally and for the European region,
- and the total number of days of exposure to marine heatwave during the month (including only strong and higher intensity categories).
The results are obtained using the Copernicus Marine Service global analysis system.
Ongoing marine heatwave
August 31, 2024
The duration of ongoing Marine Heatwaves is monitored because prolonged events may induce important stress on marine ecosystems. Here we look at the Marine Heatwaves present on the 31 August 2024, and show when each Marine Heatwave appeared. The color indicates the month of onset for each Marine Heatwave. For instance ocean pixels in red are Marine Heatwaves that developped during August and are therefore less than one month old, in orange Marine Heatwaves between 1 and 2 months old, and soon.
The majority of regions in Marine Heatwave conditions are exposed to recent Marine Heatwave events, with 16% of the global Ocean (between 60°S and 60°N) affected by MHWs less than 1 month old and 5% by event between 1 and 2 month old.
Total surface exposed to Marine Heatwave
We monitor daily the surface occupied by Marine Heatwaves and show for the past year (since september 2023) the proportion of the global Ocean (between 60°S and 60°N) exposed to Marine Heatwaves. We focus on the evolution over the past August 2024 (denoted in grey).
We see that the total surface for August 2024 (black line) continues a decreasing trend initiated in May 2024 to reach 27.4 % of the global ocean. This contrasts with the same period last year when Marine Heatwaves extent reached lowest levels early July (~27%) to progressively reach 33.5% by the end of August.
Note that the maximum surface of Marine Heatwaves occurs during the January and February period, because this corresponds to the summer in the southern hemisphere (period when more heatwaves occur), that contains a larger proportion of ocean than its northern counterpart.
This reduction in total surface can be explained predominantly by a drop of strong and severe Marine Heatwaves (in orange and red). In contrast moderate categories have remained stable over the month (in yellow).
European zone
For the ocean region of Europe (including the Mediterranean Sea and the North Atlantic eastern coast, see extent in map of ongoing marine heatwave above), we see that the 3rd period of strong marine heatwaves of the year 2024 that started in July peaked early August with a maximum extent (black line) of 30.6%. This peak in marine heatwave extent is characterized by the presence of strong (10.5%.) Severe (2%.) and Extreme (0.04%.) marine heatwave events. A decline in total surface occurred during the second half of August.
Total number of Marine Heatwave days for August
Key messages:
– Surface of the ocean in Marine Heatwave conditions for at least 1 day : 22,92 %,
– Surface of the ocean in Marine Heatwave conditions during the entire month : 0,56 %.
August 2024: a month of extremes
Key messages:
– Surface of the ocean in Marine Heatwave conditions for at least 1 day : 22,92 %,
– Surface of the ocean in Marine Heatwave conditions during the entire month : 0,56 %.
August 2024: a month of record temperatures
Key messages:
– The Marine Heatwaves of August 2024 can be compared to those of august from previous years (since 1993) using the Marine Heatwave duration, intensity, surface occupied and activity (an index representing the sustained intensity over space and time).
– Linked to the unprecedented temperature for august in the Mediterranean Sea, we see a record Marine Heatwave for August 2024 in terms of mean intensity, duration, activity and total extent, surpassing levels observed in August 2003 and 2015.
– In the North Atlantic only August 2023 was more extreme than August 2024. Globally August 2024 is ranked as the 3rd most extreme.
The month of August saw record high sea surface temperature for the Mediterranean Sea with a monthly mean of 28.17 ºC. At global level and for the North Atlantic region, August 2024 was the second warmest month on records (after August 2023) with monthly mean values respectively reaching 20.94°C and 24.51°C.
