The deep waters of the Mediterranean Sea face the frightening reality of climate change, but the Adriatic Sea, its northernmost basin, is becoming the epicenter of catastrophic changes that are happening at an alarming rate. Scientists they warn against unprecedented warming and salinization, which are occurring in the deep Adriatic with such intensity that it indicates a rapid transition to a new climate regime. If we do not intervene, the consequences could be irreversible.

Research revealed that over the past 15 years, there has been a a fivefold increase in the rate of warming and a doubling of salinization trends. Specifically, in the South Adriatic Basin (SAP), especially in its marginal parts, temperature has increased by 0.8°C and salinity by 0.2°C over the past decade, with these trends accelerating over time. These figures are particularly shocking, as they represent two to four times higher rate of change (0.4–0.8°C for temperature and 0.2 for salinity per decade between 2010 and 2024) than in the rest of the Mediterranean Sea. This acceleration is so dramatic that regional climate models that predict century-long changes could be reflected in the Adriatic in just 10–20 years, which is fivefold increase in regional climate change versus extreme scenarios of high greenhouse gas emissions. In 2024, the 14°C isotherm, which was located at a depth of 100 meters in early 2010, has moved almost to the bottom, while water with a salinity above 38.9 covers almost the entire SAP, except for the surface itself and depths below 1000 meters.

These changes are not just the result of distant processes. Although the warm and salty Levantine Intermediate Waters (LIW) flow into the Adriatic Sea, data show that local processes play a key role. Changes in winter heat loss, precipitation and river flows influence the formation of North Adriatic Dense Waters (NAddW). These dense waters, cascading down into the depths of the SAP, now bring significantly warmer and saltier waterAs a result, there is erosion of stratification below 100 meters in most of the SAP – vertical temperature gradients have decreased by more than 40% per decade in the upper 700 meters, with a maximum of 60% between 500 and 600 meters. This breakdown of stratification impairs vertical mixing and oxygen transport to deep waters.

The consequences are dire. The Adriatic Sea is heading towards decrease in dissolved oxygen and nutrient availability, which will have a catastrophic impact on primary production and the entire ecosystem. Species adapted to warmer seas may benefit and increase their abundance, while Cold-water species, which are key to biodiversity and demersal resources, are particularly threatened and are facing habitat loss or forced northward migration. Deep-sea benthic organisms, unadapted to such rapid and large-scale temperature changes, are particularly vulnerable. In addition, the trend in deep-sea density has reversed since 2006, which may amplify sea level rise in coastal areasWhile in the second half of the 20th century, sea level rise was mitigated by increasing deep water density, current changes are reversing this mitigation, meaning that the Adriatic Sea is facing steric sea level rise of 3.3 mm/year.

The Adriatic Sea is in a state of rapid transition that exceeds the assumptions of even the most extreme greenhouse gas scenarios. These Alarming observations indicate a new, uncertain future, where local warming and desiccation are becoming more important drivers of change in the deep sea than heat and salt transport from the Ionian Sea. The need for immediate and comprehensive research, as well as adaptation and mitigation strategies, is urgent to avoid irreversible transformation of this vital ecosystem. JRi