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
July 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 July 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 July and are therefore less than one month old, in orange Marine Heatwaves between 1 and 2 months old, and soon.
Almost 18% of the global Ocean (between 60°S and 60°N) is affected by MHWs less than 1 month old.
Total surface exposed to Marine Heatwave
We monitor daily the surface occupied by Marine Heatwaves and show for the past year (since august 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 July 2024 (denoted in grey).
We see that the total surface for July 2024 (black line) decreases from 33.4 % to 28.6%, a level lower than the same period last year.
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 porportion of ocean than its northern counterpart.
This reduction in total surface can be explained predominantly by a drop of moderate Marine Heatwaves (yellow). In contast higher categories have gained in surface over the month (strong in orange, severe in red, and extreme in dark red).
European zone
For the ocean region of Europe (including the Mediterranean sea and the North Atlantic eastern coast, see extent in figure above) we see that the total surface (black line) increases from 9.8% to 25%, signalling the intense event of July 2024. This increase in surface occurs for every Marine Heatwave category: moderate in yellow, strong in orange, severe in red, and extreme in dark red.
Total number of Marine Heatwave days for July
Key messages:
– Surface of the ocean in Marine Heatwave conditions for at least 1 day : 27,24 %,
– Surface of the ocean in Marine Heatwave conditions during the entire month : 1,15 %.
