Scientists led by UC San Diego's Scripps Institution of Oceanography are warning that oxygen is disappearing rapidly from oceans and freshwater systems, potentially pushing the planet into an "unsafe space." Some of the resulting changes could persist for centuries and may not be reversible within human lifetimes.
The new review examines aquatic deoxygenation, which refers to declining levels of dissolved oxygen in the ocean (ocean deoxygenation), coastal waters, rivers, lakes and streams. The researchers assessed how this growing problem interacts with the nine major Earth system processes included in the Planetary Boundaries framework.
Introduced in 2009, the framework identifies environmental processes that are essential for maintaining a stable and resilient planet. It also tracks how human activity is pushing those systems beyond safe conditions.
The nine planetary boundaries are climate change, ocean acidification, biodiversity loss, atmospheric aerosol loading, stratospheric ozone depletion, freshwater change, land-use change, chemical pollution and biogeochemical flows (including the nitrogen cycle). The researchers argue that dissolved oxygen levels should also be formally included.
"The health and stability of our planet depends on the health and stability of aquatic ecosystems, which need oxygen to function normally," said lead author Erica Ferrer, a Scripps Oceanography alumna and current postdoctoral scholar at UC Santa Barbara's National Center for Ecological Analysis and Synthesis. "This study is designed to elevate the profile of aquatic deoxygenation as a global threat and show that it does not operate in isolation."
Warming and Pollution Are Draining Oxygen
Human-caused warming, excessive nutrient pollution and changes in the movement and ventilation of deeper waters are the main forces driving aquatic deoxygenation.
As oxygen levels fall, they can disrupt the biological and chemical processes that help regulate Earth's climate. The decline also threatens organisms across aquatic food webs, from microscopic life to fish and sharks.
Marine mammals can also suffer even though they breathe air at the surface. Oxygen loss can reduce or relocate their prey, damage habitats and alter the food webs they depend on.
Connecting Deoxygenation to Other Planetary Risks
Ferrer and Scripps biological oceanographer Lisa Levin, the study's senior author, developed the idea for the review after attending COP25, the 2019 United Nations Climate Change Conference held in Madrid.
They hope the findings will encourage researchers and policymakers to examine aquatic oxygen loss alongside climate change, pollution, biodiversity decline and other pressures on the planet rather than treating it as a separate problem.
"Adding aquatic deoxygenation to the Planetary Boundaries framework will help us understand its impacts on Earth system stability," said Ferrer. "Mitigating its impacts represents a critical component of maintaining biodiversity and climate."
Research Support and Publication
Ferrer completed the review during her doctoral research at Scripps. Her work was supported by the National Science Foundation's Graduate Research Fellowship Program, graduate funding from Scripps and UC San Diego, and later postdoctoral support from UC Santa Cruz and UC Santa Barbara.
The study was published June 30, 2026, in the journal Limnology and Oceanography.
Additional authors include four former Scripps PhD students: Shailja Gangrade, Lillian McCormick, Ariel Pezner and Yassir Eddebbar, who is now a Scripps climate scientist. Other contributors were De'Marcus Robinson of UCLA, Véronique Carcon of the Institut de Physique du Globe de Paris and Kevin Rose of the Rensselaer Polytechnic Institute.
