oceanography

The tenth edition of the Copernicus State of the Ocean Report warns that the oceans are warming at an alarming rate, with consequences for marine life, coastlines and communities around the world. Produced by Mercator Ocean International with contributions from 125 specialists from various countries, the report uses satellite, in situ and modelling data to show that global ocean warming has been accelerating since 1960 and reached its highest level in 2025. With regard to Spain, the report highlights the impact of Storm Louis in late February 2024, which brought waves exceeding eight metres in some places, widespread power cuts, serious disruption at two ports and one fatality. As for the Mediterranean, although sea levels are rising at a similar rate in both the western and eastern Mediterranean, the rate of acceleration in the eastern part is much more pronounced, according to the report.

Every summer, algal blooms are common, from the Cantabrian Sea to the Mediterranean. Most play essential roles in aquatic ecosystems and have a high capacity to absorb CO₂. However, some can also cause problems, as is the case with the invasive alga Rugulopteryx okamurae, which has been spreading along the Spanish coastline for a decade.

An international team has analyzed sea surface temperatures in the Atlantic Ocean and at various points in the Mediterranean Sea. The analysis, published by World Weather Attribution (WWA), shows that this year's temperatures have been extraordinary, both in their intensity and how early they have reached such magnitude. This behavior is not only having an ecological impact on marine life, the authors state, but could also exacerbate potentially destructive regional climate events like those that occurred in Valencia in 2024.

Two Copernicus services have independently confirmed that global sea surface temperatures have broken records for this time of year. Daily data from the Copernicus Climate Change Service exceeded the 2024 levels on 21 June, reaching 20.86 °C, higher than the 20.83 °C recorded in 2023 and 2024. Data from the Copernicus Marine Watch Service show temperatures of 21.0 °C on 21 June, beating the 2023 and 2024 records by 0.1 °C. This unprecedented warming is linked to the onset of El Niño (announced by the WMO and declared by NOAA on 11 June) and to record-breaking sea surface temperatures in the North Pacific; consequences are anticipated for weather patterns, the global climate and marine ecosystems.

Rising sea levels have quadrupled the frequency of extreme events related to this phenomenon along coastlines since 1900. This is one of the conclusions of a study, which included Spanish participation, suggesting that climate change has already altered the risk of coastal flooding and highlighting the need to integrate these changes into adaptation and risk management strategies. More than 680 million people worldwide live in low-lying coastal regions, where small changes in sea level can significantly affect flood risk. The study is published in Nature Climate Change and aligns with another paper, published the same day in Science Advances, which states that since the 1970s, the number of days on which sea levels have exceeded annual averages has tripled.

As discussions around a possible “Blue COP31” gain momentum, a recent analysis published in Nature Portfolio warns that record ocean heat, intensifying marine heatwaves and accelerating sea-level rise are beginning to challenge international systems designed for a far more stable climate reality. The analysis proposes several priority actions to integrate the ocean more directly into international climate governance.

More than 60,000 ships cross the Strait of Gibraltar each year, making it one of the busiest shipping lanes on the planet and generating noise pollution that can affect communication between animals. An international team, including Spanish researchers, has studied more than a thousand calls between 18 long-finned pilot whales, an endangered cetacean, and observed that these animals increase the volume of their calls as ambient noise increases, comparable to "that of a noisy restaurant or being next to a vacuum cleaner," as noted in a press release. However, this attempt at compensation is not always enough, which could hinder the reunion of members of the same group. The results are published in Journal of Experimental Biology. 

A new study, based on oceanographic data collected by ships and robotic floating buoys over several decades, provides the first evidence that a warm mass of deep circumpolar water is approaching Antarctica, threatening the fragile ice shelves that border it from below. This warming in the Southern Ocean has implications not only for Antarctic ice melt and sea-level rise, but also for global heat regulation, carbon storage and the global climate system. The study is published in Communications Earth & Environment.

Researchers have reviewed nearly 400 scientific articles related to sea level rise and associated risks and concluded that most studies may have underestimated global sea level rise by an average of 0.3 meters. In some areas of the Global South, these levels could be up to 1 meter higher than previously thought. According to the authors, a reassessment of the methodology used to characterize the impact of sea level rise is necessary, as this could have implications for policy, climate finance, and coastal adaptation plans. The study is published in Nature.

New research analysing more than 33,000 fish populations in the northern hemisphere between 1993 and 2021 reveals that chronic ocean warming is driving a long-term decline in biomass of up to 19.8% per year for species in the Mediterranean, North Atlantic and North-East Pacific. At the same time, in the short term, more fish are thriving in cold areas due to the heat, but these increases are temporary and the authors warn that relying on them would lead to unsustainable exploitation. The study, by the National Museum of Natural Sciences (MNCN-CSIC) and the National University of Colombia, is published in Nature Ecology & Evolution.