The Mediterranean offers early warning for larger oceans

Deep Adriatic waters are warming six times faster than elsewhere in the Mediterranean.(CN) — The Mediterranean is getting warmer and saltier, and the pace is picking up even thousands of meters below the surface.Researchers say the Mediterranean gives an early indication of how quickly larger ocean basins can change in response to a warming climate.Using measurements from 1950 to 2025, they found the acceleration was greatest in the central and eastern Mediterranean. In the Adriatic Sea, warming and increasing salinity reached all the way to the seafloor.“What is really surprising is that we see significant changes in every region, reaching great depths,” Elena Terzić, a physical oceanographer at the Ruđer Bošković Institute and the study’s lead author, said in a news release.The findings were published Wednesday in Geophysical Research Letters.In recent years, the upper 100 meters of the Mediterranean have been about 2 degrees Celsius warmer than the 1950-1999 average. Signs showed surface warming was accelerating, but it wasn’t clear how far below the surface those changes extended.Terzić and co-author Ivica Vilibić, also at the Ruđer Bošković Institute, compiled temperature and salinity measurements collected by research cruises and robotic floats over 75 years.Since 2000, surface waters have warmed by about half a degree Celsius per decade, roughly two to three times faster than the global ocean surface. During the second half of the 20th century, most of the Mediterranean was warming by less than a tenth of a degree per decade.In some areas, the rate of warming is increasing by as much as 0.3 degrees Celsius per decade, every decade. Salinity is also increasing at a faster pace.“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 three or four thousand meters, and the speed-up itself reaches down to about 2,500 meters.”Temperature and salt levels help determine seawater density, which drives deep-sea circulation. Warm water is lighter, while saltier water is heavier. Across much of the Mediterranean, warming is having the stronger effect, making surface water lighter and harder to mix with the water below.The Adriatic works differently. Cold winter winds help make its surface water dense enough to sink, while increasing salinity has so far kept that process going despite rising temperatures. The sinking water spreads into the central and eastern Mediterranean, carrying oxygen into the deep sea.Since 2000, deep water in the southern Adriatic has warmed about six times faster than in a typical Mediterranean basin.“Dense water is still forming, but we have indications that the way it forms is changing, and the water that sinks is now warmer and saltier than it used to be,” Terzić said.Researchers did not measure oxygen, though warmer water holds less of it, and oxygen declines have already been documented in parts of the Mediterranean. Marine species looking for cooler water may also have fewer places to go as warming reaches greater depths.Mediterranean waters move between the surface and depths about 10 times faster than in the open ocean, which researchers say could offer an early look at changes in larger oceans.Terzić and Vilibić now want to determine what’s driving the acceleration and whether climate models are capturing the speed of the changes.“The Mediterranean is small enough that we can watch how a sea responds, on timescales we can witness ourselves, and what we see is unprecedented change,” Terzić said. “It is a warning of how fast the ocean can change, and it will continue for as long as our economies keep relying on fossil fuels.”Subscribe to our free newslettersOur weekly newsletter Closing Arguments offers the latest about ongoing trials, major litigation and rulings in courthouses around the U.S. and the world, while the monthly Under the Lights dishes the legal dirt from Hollywood, sports, Big Tech and the arts.Additional Reads