23-05-2025
Marine heatwave occuring in Irish waters, scientists say
Scientists from the Marine Institute have confirmed the occurrence of what is known as a marine heatwave in Irish waters, as a result of higher temperatures in recent weeks.
The phenomenon is defined when temperature values exceed the 90th percentile of the mean, for five or more days in a row.
Data gathered by the Marine Institute in recent days confirms that criterion has been met. However, forecasted winds over the coming week are expected to dissipate the warmer water with cooler levels below.
Researchers on board the Celtic Explorer are returning to port today, following a three-week expedition off the west coast.
"We monitor data for years and years and then we categorise that to get the average or the mean, and if it goes above the 90th percentile, for more than five days, that's technically a heatwave," said Marine Institute Oceanographer, Glenn Nolan.
Mr Nolan, who oversees Oceanographic and Climate Services at the Institute, said such events were becoming more common due to the changing climate.
"We've been in moderate heatwave conditions for a lot of this year so far, where it's just sitting above that 90th percentile.
"Then when you get a really calm period, like we've just had, it starts to pick up a bit more, because there's already an underlying warm ocean and the sunny weather adds additional heat to the upper few metres," he said.
Researchers plan to monitor the situation in the coming weeks but say that at present, there's no major concern about mass mortality of marine species due to warmer waters.
"Over the next six or seven days, the wind is going to blow up a little bit and that will probably mix all of this heat down, so this will be a non-event in about a week's time. But right now the conditions are about three degrees above normal in certain areas," said Mr Nolan.
He said the latest marine heatwave was not as big as one recorded in mid-2023. Analysis of data gathered by the Marine Institute at that time led to a determination that the temperatures were as a result of man-made climate change.
The present heatwave is said to be "quite ubiquitous around the shelf region and offshore waters".
But Mr Nolan remarked that the higher than usual temperatures were very close to the surface and that below ten metres, normal conditions are still being detected by the monitoring equipment used on the Celtic Explorer.
