2023-08-17 16:03:57
Temperatures in the eastern Mediterranean and the Gulf of Eilat are reaching near-record levels this year and peaking much earlier than in previous years, experts say, with the eastern Mediterranean slowly turning into a tropical zone.
These two regions were already warmer than average at the end of winter, in March, and with the summer extending into September, they could still break local records.
According to the Copernicus service on climate change in the European Union, the mean sea surface temperature reached an all-time high of 20.96°C on 31 July. During June and July, marine heat waves hit regions from the northeast Atlantic and Baltic Sea to the waters around Florida.
According to Copernicus, in much of the Mediterraneansea surface temperature anomalies (deviations from average conditions) reached 3°C or even 5.5°C along the Italian, Greek and North African coasts.
In Israel, the national monitoring stations are located in Hadera, in the center of the country, in Ashkelon, on the southern coast of the Mediterranean, and in Eilat, on the Red Sea, at the southern end of the country.
According to Tal Ozer, who studies the southeastern Mediterranean and coordinates data from the national marine monitoring program at Israel’s Institute of Oceanographic and Limnological Research, the highest daily sea surface temperature this year was 30.4°C, recorded on July 24. This temperature was about one degree higher than the average for the past 12 years, during which time comparable data of current quality has been collected. It is half a degree lower than the maximum ever recorded, i.e. 30.9°C on August 16, 2021.
Ozer explained that the Mediterranean Sea, which is relatively small and whose connection with the Atlantic Ocean is limited to its western end, reflects and amplifies global trends. The southeastern part, which borders Israel, had the highest temperatures and salinity, as Atlantic Ocean water has plenty of time to warm up as it travels the distance.
What’s remarkable is not just that temperatures are rising, but that they are reaching such high levels much earlier in the year, Ozer continued.
Israelis and tourists enjoying the beach as a heat wave hits the country, in Tel Aviv, July 17, 2023. (Miriam Alster/FLASH90)
“We normally expect the temperature to peak between mid-August and early September,” Ozer said. “Some years, like 2012 and 2016, we reached 30.8°C in August. Today, it seems that we reach these temperatures as early as the end of July, when we are not even at the end of the warm period. »
Ozer pointed out that temperatures at the end of winter had also been abnormally high for the season. In March, the surface temperature in Hadera never fell below 18.6°C. This is 1.2°C higher than the average for the past 12 years.
In recent years, sea surface temperatures measured off Ashkelon have been 0.3-0.4°C warmer than Hadera, which lies further north. Real-time data has been lacking since March, when a crane collapsed at the Rutenberg power plant, damaging the monitoring station there.
Part of a coral reef in the Gulf of Eilat, southern Israel, February 19, 2021. (Noam Revkin Fenton/Flash90)
In Eilat, Yoni Shaked, who collects and analyzes marine data for the National Marine Monitoring Program, told a similar story to Ozer. Surface water temperatures in March were relatively warm – 18.6°C on March 20 – and during the summer the water got warmer.
“The highest sea surface temperature this year in the Gulf of Eilat was 30.5C on July 28,” Shaked said – just below the maximum measurements taken in August 2020 and 2021.
The topography of the Gulf of Eilat partly explains why its waters are warming at a relatively rapid rate, Shaked said. The Strait of Tiran – a narrow landmass that connects the Gulf to the Red Sea to the south – only allows surface water to flow north, and surface water is always warmer than deep water.
Gil Rilov, scientist at the National Institute of Oceanography, part of Israel’s Institute for Oceanographic and Limnological Research, and lecturer at the University of Haifa, said: “The eastern Mediterranean is moving from a temperate Atlantic ecosystem to a tropical Indo-Pacific ecosystem. »
The Strait of Tiran and the Island of Tiran. (Credit: Marc Ryckaert (MJJR), CC BY 3.0, Wikimedia Commons)
The southeastern Levant basin, where Israel is located, is “the hottest spot of change,” he added, a region that has become borderline comfortable for native marine species, many of which have disappeared, probably due to the rapid warming of the waters in the region. Many native species have been replaced by exotic species, mainly from the Red Sea, which is connected to the Indian Ocean by Bab-el-Mandeb and the Gulf of Aden.
According to Rilov, more than 500 species have invaded the eastern Mediterranean from the Red Sea, either directly through the Suez Canal or through the ballast water of ships passing through it.
“A decade of research has shown the collapse of native biodiversity in the eastern Mediterranean,” he said. “Most of the species affected were invertebrates and some played important roles in their ecosystems,” he added.
A key predatory snail, the whelk, has nearly disappeared from the eastern Mediterranean, he said, along with some once-highly abundant sea urchins.
“At the same time, 60-100 alien species have invaded the region every five years since the late 1980s. snails (molluscs). »
A lionfish observed on the reef of Shaab Angosh, in the Red Sea. (Credit: Alexander Vasenin/Wikipedia/CC BY-SA 3.0)
Among the invasive species that have made their home in the eastern Mediterranean and are considered dangers around the world are the lionfish, a voracious predator native to the Red Sea, and the rabbitfish, which decimates algae.
According to Rilov’s research, most of the native species tested are only resistant up to 25-29°C, while exotic tropical species can survive up to 32-35°C or even more. Also, while some important native algae that create underwater forests are abundant in the spring, exotic algae have high cover year-round because they can withstand or even thrive in the hot summer temperatures of ‘Today.
An invasive rabbitfish. (Credit: Gil Rilov)
Global warming and melting icebergs at the poles are causing sea levels to rise.
Gil Rilov cited a rise of 15 centimeters in the Eastern Mediterranean since the 1990s, but said these figures were hotly contested.
Even the most conservative models predict a further rise of 50 to 60 cm, or even more, by the end of the century, he continued. “Even with a rise of 50cm, coastal ecosystems – including the unique and highly vulnerable Vermetidae reefs found along the Israeli coast – will disappear,” he said. These reefs are formed by small to medium sized sea snails.
Professor Maoz Fine, from the Hebrew University of Jerusalem and the Inter-University Institute of Marine Sciences in Eilat, said Israel’s corals were safe for now and had proved resistant up to 32°C. But he added that “the combination of these two factors could have a negative effect on Vermetidae reefs”.
“In combination with other local stressors, our corals won’t be safe for very long,” he added, however.
Unless pollution from multiple sources such as crude oil, agricultural chemicals, sewage and mariculture is brought under control, “we will see coral bleaching and, as the Gulf is a relatively closed basin, the damage will last for many years,” he said.
With regard to the resilience of fish, an article published in 2020 by Prof. Amatzia Genin – professor emeritus of marine ecology at the Hebrew University of Jerusalem and founder and former scientific director of the national Gulf of Eilat monitoring program – proposed that the speed of appearance of a marine heat wave, rather than its peak, is likely what triggered mass coral fish kills in the Gulf of Eilat in July 2017.
There have been two cases of sudden seawater warming this month – in one, temperatures soared 4.2°C in just two and a half days. Two weeks later, they rose by 3.4°C, also in two and a half days. In both cases, temperatures remained above 28°C for two or three days.
Hundreds of heat-stressed fish, from dozens of species, were fatally infected with a pathogen that had evidently become more virulent with the sudden increase in water temperature.
Some of the fish species that perished during a massive die-back in the Gulf of Eilat in the summer of 2017. (Amatzia Genin)
“Dead fish were floating everywhere,” Fine recalled. “And many of them were eaten by sea scavengers, which also got infected. »
Two weeks ago, Fine inaugurated a new monitoring station 42 meters below the surface of the water.
“Even at this depth, the temperature exceeds 27°C, which is unbelievable,” Fine said.
Noting that this is an El Nino year, likely to reinforce warming trends, he said he has yet to notice any changes in marine species off the coast of Eilat.
“But I’m sure there are changes in microorganisms and species that we can’t see,” he added. “We know and see so little of what’s down there. »
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