Scientists warn oxygen is disappearing from Earth's oceans, rivers and lakes, and the damage could last for centuries

What the Planetary Boundaries framework is and why scientists want to expand it

Why oxygen is disappearing from oceans and freshwater systems

How the idea for this study began at a UN climate conference

What adding a tenth planetary boundary could mean going forward

Oxygen levels are quietly falling across oceans, coastal waters, rivers, lakes and streams around the world, and scientists are warning that this decline deserves far more attention than it currently gets. A new review led by researchers at the University of California San Diego's Scripps Institution of Oceanography argues that aquatic deoxygenation, the loss of dissolved oxygen from marine and freshwater environments, should be formally recognised as a critical planetary process under threat, joining a select group of nine processes already used to track how close Earth is moving toward dangerous, unstable conditions. The researchers say some of the resulting damage could last for centuries and may not be reversible within a human lifetime.According to a press release from Scripps Institution of Oceanography , the Planetary Boundaries framework was first introduced in 2009 to identify major Earth systems and track how human activity is pushing them beyond the limits needed to keep the planet stable. The framework currently includes nine processes, covering climate change, ocean acidification, biodiversity loss, atmospheric aerosol loading, stratospheric ozone depletion, freshwater change, land use change, chemical pollution and biogeochemical flows such as the nitrogen cycle.The new review, led by Scripps alumna Erica Ferrer alongside senior author Lisa Levin and many more, argues that dissolved oxygen deserves to be added as a tenth boundary. The researchers say oxygen loss is closely connected to nearly every one of the existing nine categories, meaning it cannot be properly understood or managed in isolation from the other pressures already being tracked.The review, published in the journal Limnology and Oceanography , identifies human-caused warming, excess nutrient pollution and changes in the natural circulation that carries oxygen into deeper water as the main drivers of aquatic deoxygenation. Warmer water simply holds less dissolved oxygen than cooler water, while nutrient pollution from agriculture and wastewater fuels algae blooms that consume oxygen as they decompose. Changes in ocean circulation can also disrupt the natural mixing process that normally carries oxygen-rich surface water down into deeper layers.These combined pressures are already affecting a wide range of species. According to the study, declining oxygen levels threaten organisms ranging from microbes to fish and sharks, and even disrupt some of the chemical processes that help regulate Earth's climate. Marine mammals are not spared either, since although they breathe air at the surface, oxygen loss can still reshape their habitats and disrupt the food webs and prey populations they rely on.Ferrer and Levin developed the idea for the review after attending COP25, the United Nations Climate Change Conference held in Madrid in 2019. The researchers said they wanted their work to push policymakers and scientists toward treating aquatic oxygen loss as part of a connected system of environmental pressures, rather than as a standalone regional problem confined to specific water bodies.Ferrer described the goal of the study as elevating the profile of aquatic deoxygenation as a global threat, stressing that ecosystems in oceans, rivers and lakes need oxygen to function normally, and that the stability of the wider planet depends on the stability of these aquatic systems. Levin, a biological oceanographer at Scripps, echoed this, saying that formally recognising oxygen loss within the Planetary Boundaries framework would help researchers better understand its wider impact on Earth system stability.If aquatic deoxygenation is formally added to the Planetary Boundaries framework, it would mark the first change to the list since it was introduced in 2009. Researchers hope this recognition would push funding agencies, policymakers and scientists to study oxygen loss alongside climate change, pollution and biodiversity loss rather than treating it as a separate, lower priority concern.Ferrer carried out much of this research as part of her doctoral work at Scripps, with support from the National Science Foundation's Graduate Research Fellowship Program along with funding from Scripps and the University of California San Diego. The study's authors say that mitigating the effects of aquatic oxygen loss is not just about protecting individual species or water bodies, but represents a critical piece of maintaining both biodiversity and climate stability at a planetary scale, making the case for why this quiet, often overlooked crisis deserves a permanent place in how scientists track the health of the entire planet.