This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Across its basins and thousands of meters down, the Mediterranean Sea is getting warmer and saltier. Now, a new study finds it is also doing so at an increasingly rapid pace.
The speedup is largest in the central and eastern Mediterranean and strongest of all in the Adriatic, where it reaches all the way to the sea floor. "What is really surprising is that we see significant changes in every region, reaching great depths," said Elena Terzić, a physical oceanographer at the Ruđer Bošković Institute and lead author of the study. The study will appear Wednesday, Sept. 16, in Geophysical Research Letters.
In recent years, the Mediterranean's upper 100 meters (330 feet) have been about 2 degrees Celsius warmer than their 1950–1999 average. Earlier studies had seen signs of the surface warming speeding up, but nobody had measured whether the change was accelerating below the surface across the whole basin. Terzić and co-author Ivica Vilibić, also at the Ruđer Bošković Institute, had recently documented unprecedented warming and salinification in the deep southern Adriatic, as well as signs of basinwide changes: pools of unusually salty surface water across the whole Mediterranean that were historically known to occur only at its far eastern end.
"We had seen notable changes in our recent studies, both in the deep Adriatic and at the sea surface, and we wanted to quantify the changes across the rest of the Mediterranean," Terzić said. To find out, the two compiled temperature and salinity measurements taken by research cruises and robotic floats across the Mediterranean from 1950 to 2025. Temperature and salinity are rising almost everywhere, and the rise is accelerating.
In some regions, warming is speeding up by as much as 0.3 degrees Celsius per decade each decade, with each kilogram of water getting about one-tenth of a gram saltier per decade. Since 2000, Mediterranean surface waters have warmed by about half a degree Celsius per decade, two to three times faster than the global ocean surface. That's up from less than one-tenth of a degree per decade in most of the basin in the second half of the 20th century.
"For us, what was alarming was the rate at which this is changing, and the depths that such significant changes reach," Terzić said. "The warming and salinification are statistically significant down to 3,000 or 4,000 meters (9,800 or 13,100 feet), and the speedup itself reaches down to about 2,500 meters (8,200 feet)." Differences in seawater density are what drive the sea's deep circulation. Warming makes seawater lighter and added salt makes it heavier, and because both are rising, the density of Mediterranean water has changed far less than its temperature or salinity.
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