Scientists find major changes in deep Adriatic waters

A 75-year analysis by scientists at the Ruđer Bošković Institute (RBI) has found that the Mediterranean Sea is not only becoming warmer and saltier, but that the pace of these changes is increasing, with signals now detectable deep beneath the surface.

The study, led by Dr Elena Terzić and Dr Ivica Vilibić, brings together measurements collected between 1950 and 2025, ranging from historical observations made from research vessels to data gathered by modern autonomous Argo floats.

The research shows that the changes are particularly pronounced in the Adriatic-Ionian region, providing a detailed picture of how the Mediterranean’s physical properties have evolved through the decades.

Changes extend far below the surface

According to the Ruđer Bošković Institute, temperatures in the upper 100 metres of the Mediterranean in the latest part of the analysed period were around 2°C higher than the average for the second half of the 20th century.

However, the researchers found that warming is not confined to surface waters. A clear signal is also present between 300 and 1,000 metres, while measurable changes can be detected at depths of between 1,000 and 2,000 metres.

“The average rate of warming tells us how the temperature of the sea has changed over a longer period. However, when we describe the entire period with one average rate, we cannot see whether the rate of warming itself is changing,” Dr Terzić explained, according to the Ruđer Bošković Institute.

“Our results show that it is increasing, meaning that an average can hide how much faster the changes have become in recent decades.”

The study also found increasing salinity, particularly in the central and eastern Mediterranean. Temperature and salinity together determine seawater density, which plays an important role in the circulation and mixing of the sea.

Adriatic-Ionian region stands out

The Adriatic has a particularly important role because it is one of the Mediterranean areas where dense water forms. During cold winters, surface water can cool sufficiently to become denser and sink, carrying its properties into deeper layers before continuing towards the Ionian and eastern Mediterranean.

The researchers identified particularly pronounced acceleration of changes in the Adriatic-Ionian system. In the southern Adriatic, a strong signal of accelerated warming was detected at depths of around 1,000 metres, alongside changes in salinity.

“When the signal of change is no longer visible only at the surface but also deep in the water column, we are talking about a much broader change in the properties of the sea. The deep layers are a kind of memory of what is happening in the system over a longer period,” Dr Vilibić said.

Connecting decades of measurements

One of the challenges was comparing measurements collected using very different technologies over 75 years.

The researchers combined historical ship-based observations with modern Argo float measurements, checked the quality of the datasets and tested whether the growing number of modern observations could artificially create the appearance of accelerating change.

The researchers repeated the analysis over different periods and using different statistical approaches, with the main pattern remaining visible.

The Institute said the findings do not identify a single cause for the acceleration. Atmospheric warming, evaporation and rainfall, exchanges with the Atlantic through the Strait of Gibraltar and changes in Mediterranean circulation may all contribute.

The results nevertheless show that the Mediterranean’s transformation is not simply a story of warmer surface water. Changes are increasingly detectable throughout the water column, including in the deep Adriatic and Ionian seas.