Scientists Warn Ocean Oxygen Crisis Could Breach Critical Earth Stability Boundary
An international team of researchers is urging that the decline in oxygen levels in the Earth’s waters, termed aquatic deoxygenation, be included in the ‘Planetary Boundaries’ list. This globally recognised scientific framework defines safe limits for human activity to maintain the stability of the Earth’s ecological systems.
The study, led by scientists from the University of California San Diego (UC San Diego), reveals that oxygen depletion is drastically affecting both freshwater and marine environments due to climate change and nutrient pollution. This phenomenon threatens marine biodiversity, food security, and the balance of the global ecosystem.
The researchers note that marine waters have lost more than two per cent of their oxygen volume since the mid-20th century. Meanwhile, freshwater lakes and reservoirs have experienced a much faster decline in oxygen levels, ranging from 5.5 to 18.6 per cent in recent decades.
The primary cause is global warming, which increases water temperatures. Warmer water has a lower capacity to hold dissolved oxygen gas. Furthermore, rising water temperatures trigger stratification, or the separation of water layers, which blocks the circulation of oxygen from the surface to the deep ocean.
This threat is exacerbated by agricultural fertiliser runoff and waste entering water bodies, triggering algal blooms. When the algae die and decompose, microorganisms consume large amounts of dissolved oxygen, creating increasingly widespread ‘dead zones’ in oceans and lakes.
These conditions force various marine species to migrate to water areas with higher oxygen levels, often bringing them closer to the surface. As a result, these species become more vulnerable to fishing catches and other ecosystem disturbances.
The researchers assert that the critical safety boundary for oxygen in freshwater and marine environments is very close, or has already been exceeded in some water regions.
‘Deoxygenation is massively impacting oceans and freshwater systems,’ said Dr Lisa Levin, professor emeritus at the Scripps Institution of Oceanography, UC San Diego, and one of the study’s lead authors. ‘This oxygen decline threatens the web of life that sustains human societies, from fisheries to climate stability.’
The scientists stress that recognising aquatic deoxygenation as a new planetary boundary is crucial. This step is important to encourage more integrated global monitoring, trigger policies to reduce greenhouse gas emissions, and tighten controls on fertiliser waste before the damage to aquatic ecosystems becomes irreversible.