Mediterranean Sea Warming and Salting Faster, Affecting Israel

The Mediterranean Sea is warming and becoming saltier at an accelerating rate, with changes reaching depths of up to 3-4 kilometers, according to a study published in Geophysical Research Letters. Researchers analyzed data from 1950 to 2025, finding that the upper 100 meters of the sea are now, on average, two degrees Celsius warmer than the 1950-1999 period. While surface warming was known, the new study reveals this acceleration extends to deep waters, particularly in the central and eastern Mediterranean. In the Adriatic Sea, changes are impacting the seabed.

Dr. Elena Terzić of the Ruđer Bošković Institute, the study's lead author, highlighted the significance of these widespread, deep-water changes. She and colleague Ivica Vilibić compiled temperature and salinity measurements from expeditions and robotic buoys. Since 2000, Mediterranean surface waters have warmed about half a degree Celsius per decade, two to three times faster than the global ocean surface. This warming and increased salinity have been observed down to 3,000-4,000 meters, with accelerated changes noted down to 2,500 meters.

The combined effects of warming (making water lighter) and increased salinity (making it heavier) have altered the sea's density less than its temperature or salinity. In most areas, lighter surface water mixes poorly with deeper layers. However, in regions like the Adriatic, where dense water formation occurs due to cold winter winds, increased salinity helps maintain water density, allowing it to sink. This dense water, crucial for oxygen transport to the deep sea, is now warmer and saltier, potentially impacting marine life.

For Israel, the findings are particularly relevant as they affect the eastern Mediterranean, an area already among the warmest and saltiest. The study suggests potential shifts in fish populations, with some species struggling to survive and heat-loving invasive species from the Red Sea potentially expanding their range. The changes also necessitate consideration for Israel's desalination plants, which rely on seawater intake, though the study does not predict operational halts or cost increases.

Researchers view the Mediterranean as a "micro-model" for global ocean changes, given its faster water circulation compared to the open ocean. The study aims to identify factors accelerating these changes, such as atmospheric processes, evaporation, precipitation, river runoff, or Atlantic inflow. While not directly measuring oxygen levels, the researchers note that warmer water holds less oxygen, a trend already observed in parts of the Mediterranean.