The marine heatwave Malta has been experiencing since mid-May is the longest in recorded history, according to an oceanography professor.
The water temperature around the Maltese islands has remained, on average, about 1.1°C above climatological levels since mid-May and this makes the current marine heatwave (MHW) the longest in history, according to Aldo Drago.
“It is not the most intense, at least so far,” he said.
“The maximum temperatures (except in shallow areas closer to shore) have remained below the 30°C threshold which was exceeded in previous years,” Drago added, pointing to the summer of 2003 as an “exceptional” year for marine heatwaves.
According to Drago, a professor of oceanography at the MCAST Institute of Engineering and Transport, marine heatwaves do not necessarily imply “extreme high sea temperatures” but occur when the temperature rises above the norm for more than five days.
The current heatwave, he said, is “exceptional” also because of the increase above the average temperatures.
On June 6, he said, the sea surface temperature for the marine domain around Malta was around 4.29°C higher than the average calculated over the past 21 years.
“This is by far the largest sea surface temperature anomaly on record, and this is what makes the marine heatwave this year exceptional, the anomaly and not the highest recorded temperature,” Drago said.
Impact of long heatwave
On the impact of such a long heatwave, the professor said marine biota and habitats are facing “additional stress” as a result of the prolonged heatwave.
The crucial factor, Drago said, is that in the atmosphere, heat waves do not last very long but they do in the sea.
“This year the marine heatwave has been persisting with discontinuous vigour since mid-May. Marine heatwaves are not as researched as heatwaves on land, but it is recognised how damaging they can be on marine species and the eco-system structure,” he noted.
“High water temperatures disturb the ability of the sea to absorb carbon dioxide from the atmosphere and they can lead to changing circulation patterns in the sea. This, in turn, affects the ability of the sea to absorb excess heat from the atmosphere as it normally should.”
This would also impact the circulation of marine nutrients throughout the water column with “serious impacts” on marine ecosystem processes.
High water temperatures also lead to coral bleaching, declines in seagrass meadows, mass mortality of marine organisms, incidence of harmful algal blooms, changes in species behaviour with physiological damages, migration of fish species and irreversible redistributions of benthic communities.
“Understanding marine heatwaves is crucial to the prediction of climate change effects that will inevitably pound on the marine environment during this decade.”