Oxygen is declining across oceans, coastal waters, rivers, lakes and streams, threatening aquatic life and processes that help regulate Earth's climate, according to research highlighted by the University of California, San Diego, on July 20. The scientists argue that aquatic deoxygenation has reached unsafe levels and should be formally tracked as a planetary boundary.
The review, led by researchers connected to Scripps Institution of Oceanography, examined how falling dissolved oxygen interacts with nine major Earth-system processes in the Planetary Boundaries framework. Introduced in 2009, that framework assesses whether human activity is pushing environmental systems needed for a stable and resilient planet beyond safe conditions.
Human-caused warming, excessive nutrient pollution and changes in the movement and ventilation of deeper water are the main drivers identified by the researchers. Warmer water holds less oxygen, while nutrient inputs can fuel biological activity that consumes oxygen. The review links deoxygenation with climate change, ocean acidification, biodiversity loss and other environmental pressures rather than treating it as an isolated problem.
Lower oxygen can disrupt biological and chemical processes involved in climate regulation and affect organisms throughout aquatic food webs, from microscopic life to fish and sharks. Air-breathing marine mammals can also suffer indirectly when oxygen loss moves or reduces prey, damages habitat and changes the food networks on which they depend.
Lead author Erica Ferrer and senior author Lisa Levin developed the idea after attending the 2019 United Nations climate conference in Madrid. The review involved researchers from several institutions and received support including National Science Foundation funding. It appeared on June 30 in the peer-reviewed journal Limnology and Oceanography before the findings received wider attention Monday.
The authors want researchers and policymakers to evaluate oxygen decline alongside other connected threats and add it to the planetary-boundaries framework. They caution that some resulting changes could last for centuries and may not reverse within human lifetimes. Monitoring oxygen and reducing warming and nutrient pollution therefore form part of protecting biodiversity and the stability of Earth's climate system.
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