Sea surface temperatures during the last heatwave exceeded 30°C for the third year in a row, marking a 5°C rise over the average 25.5°C of the past three decades.

But this year’s high temperatures had a longer duration and were more intense, said oceanography professor Aldo Drago. He uses satellite data and numerical models to measure the situation.

The water hit its warmest temperature on Sunday and Monday of last week, remaining at almost 31°C for the entire day without any oscillating, Drago noted.

The last time the sea surface reached such high temperatures was in 2018 but then it did not last as long, he said about the phenomenon that had occurred towards the end of July.

By Thursday, however, beachgoers seeking some respite from the heatwave by taking a dip will have found the sea to be slightly more refreshing, with the surface temperature dropping by 2°C as winds moved the water and mixed the top layer with the bottom.

It was the topmost metres that reached these higher temperatures, with warm water remaining on the surface because it was lighter, explained the lecturer at the Institute of Engineering and Transport of the Malta College of Arts, Science and Technology.

Measured at Marsaxlokk, the high temperatures were not consistent around the island due to a number of variables including currents. The warmest were mostly in the south, he said.

Concentrated in the central Mediterranean this time, the phenomenon was also recorded in the Tyrrhenian Sea between Sicily and mainland Italy, and off the Tunisian coast, where temperatures rose to 32°C, according to the satellite data.

Marine heatwaves are a common occurrence as they are defined as “an anomaly with the average” and not necessarily record-high temperatures, Drago explained.

This year’s was classified as “category 2, verging on 3”, which was “quite strong”, he noted.

Among its impacts on marine life was the higher exposure of fish that do not move – such as those in farms – to illness, if not death. Their metabolism is faster in warmer water, meaning they need more oxygen, but this declines in higher temperatures, Drago said.

Coastal species and immobile creatures on the seabed in shallower waters also suffered the same effects.

Reproduction could also be impacted, with autumn spawning being retarded if the sea was warmer in summer.

Globally, the sea is also a “carbon sink”, absorbing CO2 and reducing the greenhouse effect. But with high temperatures, the level of dissolved carbon dioxide decreases and is lost – “another setback of global climate change”, Drago pointed out.

We should have the capacity and know-how to investigate our own waters- Aldo Drago

Asked about the brownish colour of the water noted at Għadira Bay recently, Drago acknowledged it could be related to the warmer water, as the growth of microscopic organisms, known as phytoplankton, was speeded up in the hotter temperatures.

“This could be a factor that contributed to higher phytoplankton activity, but it needed to be studied properly,” Drago said.

“Malta is still trying to explain situations in our seas by looking at what happens elsewhere. But we should have the capacity and know-how to investigate our own waters,” the professor stressed.

A regular and routine observatory system was not only important to measure sea levels, last recorded in 1999, and temperature, but also biological indicators and to follow their evolution throughout the year, he said.

The equipment – and a team to maintain it – would be used for ongoing observation, for example, in the case of Għadira, as well as to investigate cases of foam in the northern coast near Magħtab, any dead fish and water quality.

“The country needs to start taking these things seriously, not just to tackle climate change and to mitigate its risks and effects, but also because data is important to improve services, create added value and for strategic planning,” Drago said.

“The more information, the more you can plan and offer services to, for example, tourists, fishermen…”

The sea surface temperature is being studied through an MCAST project called Stream, which uses satellite data for research, in collaboration with two SMEs.

Financed by the Malta Council for Science and Technology, the project aims to make the data more accessible for users, including students, researchers and entrepreneurs.

An app is being created to facilitate the use of satellite data and make it freely and readily accessible without requiring specific knowledge. The first prototype is planned to be launched early in 2024.

The app will provide on-demand information on sea surface temperature and water quality. The intention is to increase its parameters to include data on agriculture and coastal erosion, for example, Drago said.

Space technology is advancing and, in the near future, firms will be able to turn data into added value, he added.