Zagreb, 26 August 2025 (Hina/MIA) -- An international study involving scientists from the Ruđer Bošković Institute has shown that the deepest parts of the Adriatic Sea are warming far faster than expected, with changes predicted only for the end of the century occurring today.

IRB researchers analysed data collected from the South Adriatic Basin, the deepest part of the Adriatic, and found accelerated warming and salinisation of deep waters, at rates far exceeding climate projections. "This means that changes expected only by the end of the century are happening now, with serious consequences for ecosystems, climate, and coastal communities," the IRB stated.

Sea temperatures at 1,000 metres depth have risen by 0.8 °C over the past decade, while salinity has increased by 0.2 PSU. These trends represent the fastest recorded changes in the deep waters of the Mediterranean and may signal a permanent shift in the region’s climate regime, the statement notes.

The work of Dr Elena Terzić and Dr Ivica Vilibić, published in Limnology and Oceanography Letters, is the result of international collaboration among Croatian, Italian and Slovenian scientists, combining data from various oceanographic platforms.

"Of particular concern is the fact that changes are accelerating. This is not gradual adaptation, but a rapid transition to a new state that we do not yet fully understand," Vilibić emphasised.

Accelerated warming and salinisation of deep waters have significant implications for biodiversity, climate, and coastal communities, highlighting the need for more precise modelling of changes in enclosed seas such as the Mediterranean.

The Mediterranean’s natural thermostat is failing

The Adriatic can be considered the Mediterranean’s natural "thermostat", as it influences temperature patterns across the entire basin through heat exchange, the IRB explains. In winter, cold dense water forms in the shallow northern Adriatic, sinks to the bottom, and flows through the Otranto Strait into the deep Mediterranean. For centuries, this has driven currents that stabilise the system and supply oxygen to the deep Mediterranean.

However, this natural system is now changing. Traditionally cold waters forming off the Croatian coast are becoming warmer and saltier, so instead of cooling deep Mediterranean waters, the Adriatic is sending warmer waters that further heat the system.

The main drivers of these changes are a combination of global warming and shifts in precipitation and river inflows. Higher air temperatures mean less cold water forms at the sea surface, while changes in rainfall and river discharge result in saltier waters in the northern Adriatic.

The IRB notes that this trend is accelerating: between 2012 and 2024, the warming rate of deep waters increased to 0.8 °C per decade, compared with around 0.2 °C per century previously.

Changes in the Adriatic present a European challenge

These changes are already affecting marine life. Species adapted to cold conditions that traditionally inhabited deep waters are now facing rapid habitat changes.

"Species adapted to cold deep waters have nowhere to go," Vilibić explained, adding that warmer waters are simultaneously encouraging the arrival of tropical species from the eastern Mediterranean, altering entire ecosystems.

Changes in the deep Adriatic could also affect the European climate system. Density changes in deep waters influence sea-level rise along Europe’s Mediterranean coast, and scientists estimate that current trends could lead to an additional 3.3 mm of sea-level rise per year.

Moreover, alterations in ocean currents could impact weather patterns, the Mediterranean climate system, and coastal communities across Europe.

"The interdisciplinary international team has provided a comprehensive perspective on a problem that transcends national borders. The research clearly shows that changes in the Adriatic are not merely a regional phenomenon but a European challenge requiring coordinated action," the statement emphasises.

IRB scientists continue to monitor the deep Adriatic through permanent measurement stations and international collaboration with partners in Italy, Slovenia and other Mediterranean countries. Measurements and research are supported by international and national projects, including the European research infrastructures Euro-ARGO ERIC and EMSO ERIC, regional cooperation projects under the Interreg Italy-Croatia programme (AdriaClimPlus), national research projects (GLOMETS, C3PO), and mobility programmes from the Croatian Science Foundation and Slovenian and Italian research agencies.

The next step will be developing improved climate models capable of more accurately predicting the pace of change in enclosed seas.