Kategorie: News
Researchers warn of irreversible consequences
The oceans are suffocating – slowly but inexorably. Whilst we go about our lives on the surface, our seas, lakes and rivers are continuously losing the oxygen that all underwater life needs to breathe. A recent study by marine scientists warns that this process has already reached dangerous levels.
Over the last 50 years, the world’s oceans have lost around 2 per cent of their oxygen. That may not sound like much – but in some places, the situation is becoming increasingly dire. More than 200 coastal areas worldwide have already become so oxygen-depleted that marine life is restricted or can barely survive. In lakes, oxygen levels are even falling by 1.5 to 5 per cent per decade. The result: ‘dead zones’ where no fish can survive.
The main culprits are well known
Global warming: Warm water can hold less oxygen than cold water – that is a simple law of physics. Around half of the oxygen loss is directly attributable to global warming.
Eutrophication: Agricultural run-off leads to massive algal blooms in coastal areas. When these algae die off, bacteria consume enormous amounts of oxygen as they break them down – like a fire that consumes everything.
Reduced mixing: Warm surface water is mixing less and less with deeper, colder water. Oxygen from the atmosphere can no longer reach the depths – a second mechanism of suffocation.
The effects are dramatic and visible
Biodiversity is collapsing: where oxygen is lacking, fish disappear. Only a few specialised species can survive. Scientists have discovered that at least two of the major mass extinctions in Earth’s history were linked to oxygen depletion.
Large fish flee: Sharks, tuna and other large predatory fish require a lot of oxygen. They leave affected areas and concentrate in increasingly smaller regions – where they are more easily caught.
Corals and other inhabitants suffer: Even small losses of oxygen stress coral reefs and other marine organisms. They grow more poorly, suffer from more diseases and are less able to reproduce.
A vicious circle
The loss of oxygen is, in effect, self-perpetuating. In low-oxygen areas, bacteria produce greenhouse gases (N₂O (nitrous oxide) and CH₄ (methane) in extremely low-oxygen areas), which further fuel global warming. This, in turn, leads to further oxygen loss. A dangerous cycle.
Can we still stop it?
Yes – but time is running out: Climate action is the solution; as global warming is the main cause, we must reduce CO₂ emissions. Scientific models show that, with ambitious climate action, the decline in oxygen levels could be slowed and stabilised.
Less fertiliser in the water: Better farming practices and improved sewage treatment plants can reduce nutrient pollution. This works – in some regions, water quality is already recovering.
Protecting water bodies: More nature reserves, particularly in critical areas, help endangered species to survive.
Better monitoring: We need more monitoring stations in the oceans and lakes. This will enable us to identify problems earlier.
Summary
The loss of oxygen in our water bodies is real, is accelerating, and has far-reaching consequences. What is lost today can hardly be restored within a human timescale.
But there is hope: we know the main causes precisely – and we have effective solutions. Climate action and the reduction of nutrient inputs would already make an enormous difference.
Weitere Informationen:
Underwater oxygen loss threatens earth's stability, researchers warn
Original study: Abundant interactions and feedbacks between aquatic deoxygenation and the other planetary boundaries suggest “unsafe” levels of oxygen loss with far‐reaching impacts - Ferrer - 2026 - Limnology and Oceanography - Wiley Online Library