A multinational team of researchers from the United States, Canada, and Germany has sounded the alarm about a rapid drop in dissolved oxygen across oceans, rivers, and lakes worldwide and the serious dangers this trend poses. The findings were reported in Nature Ecology and Evolution.
Just as land animals rely on atmospheric oxygen, underwater life depends on dissolved oxygen to breathe and thrive. The study emphasizes that declining oxygen levels threaten the balance of aquatic ecosystems, which support food security, drinking water, and livelihoods for millions.
The investigation, led by freshwater ecologist Kevin Rose of Rensselaer Polytechnic Institute in the United States, notes that deoxygenation was not fully considered in previous assessments of planetary stability. This oversight matters because oxygen content in water is a key indicator of ecosystem health and resilience in the face of climate change.
There are several reasons why dissolved oxygen can fall. Warmer water holds less oxygen, and as greenhouse gas emissions push temperatures higher, surface waters warm more quickly while deeper layers remain cooler. The resulting stratification reduces vertical mixing, limiting oxygen transport from the surface to deeper zones.
Human activity further accelerates oxygen loss. Runoff carrying nutrients, organic matter, and wastes from farms, cities, and industry fuels algal and bacterial blooms. These blooms consume available oxygen, especially in still or slow-moving waters, aggravating hypoxic conditions that stress or kill aquatic life.
In severe cases, oxygen becomes so depleted that microbes suffocate and die. Some microbial communities shift to anaerobic pathways, feeding on accumulated organic material and creating dense populations that block light and stunt photosynthesis. This virtuous cycle of eutrophication traps water bodies in a suffocating spiral and disrupts the entire ecosystem.
Another driver is the changing structure of the water column. Faster warming at the surface compared with deeper waters and shifts in salinity from melting ice intensify density differences between layers. The instability hinders the vertical exchange of oxygen, compounding stress on organisms at all depths.
The consequences extend beyond ecological harm. Many communities rely on clean water and fish as essential food sources and income. When deoxygenation undermines fish stocks and water quality, local economies and food security are placed at risk, underscoring the need for proactive management and monitoring.
The authors call for a coordinated, global effort to monitor dissolved oxygen levels and investigate deoxygenation processes in freshwater and marine systems. They advocate for strategies to slow or reverse oxygen loss and to mitigate its effects on ecosystems and human communities. Implementing robust surveillance, reducing nutrient pollution, and protecting critical habitats can help build resilience against ongoing deoxygenation.
Earlier warnings have also highlighted potential disruptions to climate-related ocean circulation patterns, such as the Gulf Stream, which could further affect regional oxygen distributions and food resources in the Atlantic. The research team emphasizes that addressing deoxygenation requires immediate, sustained action across nations and sectors to safeguard ecosystems and the people who depend on them. (Nature Ecology and Evolution, 2024)