The Balearic Sea is scorching: it's also registering record temperatures at a depth of 500 meters.

PalmAverage sea surface temperatures have reached unprecedented levels in 2025, but researchers from the Balearic Islands Coastal Forecasting and Observation System (SOCIB) have also detected record levels of heat content in deeper layers, with the warming trend extending to depths of 500 meters. This year, the Balearic Sea has experienced temperature anomalies in all seasons. "They were significant in winter and spring and very significant in summer, with record highs in June and July," explains SOCIB researcher Mélanie Juza in an interview with EFE. "This has been the hottest June ever recorded since 1982, which is when we began collecting satellite data," emphasizes the head of the satellite remote sensing facility at the scientific center. Average temperatures in Balearic waters have been between 2 and 4 degrees Celsius above normal, reaching up to 5 degrees Celsius above average in early July. "That's a huge amount, it's a record for the entire region," he emphasizes. In addition to the high regional averages, SOCIB has detected even warmer temperatures locally, reaching 28.5 °C on July 7th, an absolute record for that date. And on July 1st, the Dragonera buoy recorded 31 °C, a total record for the month of July. Besides satellite data and buoys, the agency has other observation platforms, such as underwater gliders and profiling buoys, which record temperature, salinity, and pressure along vertical lines and allow them to calculate "the heat content of the entire water column for the first 150 meters and down to 700 meters." "And in the summer of 2025, in the Balearic Islands, a record for heat content in the deepest layers has been achieved," Juza points out.

210 days of extreme temperatures

Regarding ocean temperatures, they have remained at extreme values for more than five days – exceeding 90% of historical data – resulting in what are known as "marine heatwaves." The year with the most episodes in the Balearic Islands was 2022, but the maximum anomaly has been reached this year. "In June and July of 2025, for the first time in both the Balearic and Alboran Seas, a Category 3 marine heatwave, the highest severity level, was recorded," she points out.

This year, 210 days of marine heatwaves have been recorded around the archipelago, compared to the reference period of 1982-2015. In 2022, there were 232 days, "an enormous number," but there is still a month left in 2025, the scientist warns. After three consecutive years of record ocean temperatures and marine heatwaves, "2025 is already shaping up to be another record-breaking year and the fourth highly anomalous one in a row," Juza summarizes. "While the anomaly is more significant at the surface, we are now seeing that in the intermediate layer, around 500 meters deep, the upward trend is more intense." "And once the warm water is at depth, where it no longer connects with the surface, it is very difficult to cool it down," he explains. The specialist in Physical Oceanography points out that the increase in ocean temperatures in recent decades is a consequence of global warming: "The ocean acts as a natural heat reservoir and has already absorbed more than 90% of the excess heat associated with human activities." The Mediterranean is one of the regions most vulnerable to climate change because it is a semi-enclosed basin, relatively small, and where marine heatwaves occur in conjunction with atmospheric heatwaves. Rising temperatures and extreme heat events in the ocean threaten ecosystems and have "devastating consequences for marine species and habitats, both at the surface and in deeper waters," says Juza. Among these consequences, she mentions the deterioration of seagrass meadows, coral and gorgonian mortality, harmful algal blooms, mass mortality of organisms, disruption of fish reproductive and growth cycles, changes in the abundance and distribution of species, and tropical decline. In the Mediterranean, Posidonia oceanica is very sensitive to temperatures. It begins to deteriorate at 28°C and dies above 30 or 31°C. "Losing it is a problem because it provides habitat, protects marine species, produces oxygen, absorbs much of the carbon produced by human activity, and protects the coast from erosion," Juza emphasizes. The researcher underlines that ocean warming contributes to the reduction of oxygen. "And half of the oxygen we breathe comes from the ocean," she warns. Another effect is that, by adding more heat and moisture to the atmosphere, high ocean temperatures contribute to intensifying extreme weather events, such as storms with torrential rain. She explains that knowing the amount of heat at intermediate depths can help with weather forecasting. Juza emphasizes the need for action. "The international community has been clear: it is necessary to reduce greenhouse gas emissions immediately, sustainably, and on a large scale; it is necessary to preserve natural spaces such as seagrass meadows and protect the oceans, because they suffer from global warming, but also from the degradation resulting from overfishing, maritime traffic, pollution, and urbanization." The expert underlines the essential role of science and points out that SOCIB researches and shares knowledge, "facilitating access to information through tools and open access, to support evidence-based decision-making for effective and adaptive management in the face of climate change." For the conservation of ecosystems and habitats, "ocean monitoring systems must be implemented for informed management, because what is not observed cannot be managed; the transfer of scientific and technical knowledge to the sectors involved must be promoted; and more agile, innovative, and results-oriented public management models must be adopted."