Are Our Oceans at Risk of Mass Extinction From Anoxic Events?

Scientists warn that an extinction event with the potential to wipe out marine biodiversity may be inevitable without prompt action on climate change.

Researchers from the University of Exeter investigated ”anoxic events,” or incidents when the oxygen concentration in a body of water drops too low to support the majority of marine life.

But these resulting ”dead zones” are far from a new phenomenon. Over the years more than a few localized dead zones have hit the headlines.

In this investigation, however, researchers focused on factors that might lead to a mass extinction global anoxic event.

And to do so, they turned to the last major anoxic event: the Toarcian Oceanic Anoxic Event.

The event took place some 183 million years ago and is theorized to have contributed to the wider — if relatively minor – extinction level that occurred at the end of the Jurassic period.

The Toarcian Oceanic Anoxic Event harbored a major disruption to the global carbon cycle, which in turn depleted oxygen in the Earth’s ocean habitats — and, as a result, set off a mass extinction of marine species.

The chain of events begins when a decline in oxygen leads to species die-off. Not all areas suffer at the same rate though, and warmer regions tend to still team with life — but only organisms that can endure low-oxygen environments.

Bacteria, worms, urchins and bivalves continue to thrive, but larger marine species eventually die. And without those organisms, the low-oxygen adapted species increase, maintaining a low-oxygen environment. As a result, so-called dead zones emerge.

Encouragingly, researchers found that our oceans do recover from global anoxic events — but it can take up to a million years to do so.

In investigating what ended the Toarcian Oceanic Anoxic Event, the researchers theorize that wildfires may have been the major driver behind a revival of our oceans.

Fire activity likely burned away some plant life, interrupting the flow of nutrients from land to sea. As a result, the oceans didn’t receive the nutrients and minerals necessary to sustain marine life.

A steady increase in oxygen can’t support recovering marine life because it would likely lead to a “boom and bust” phenomenon, in which species use up the available oxygen and die off in relatively quick succession.

However, without enough nutrients in the oceans to support marine life, the oxygen content could continue to rise until it was plentiful enough for marine species to safely return.

Once again, our ecosystem appears to have happened upon a way of rescuing itself — but it’s by no means a quick fix.

“Once you get into a major event like anoxia, it takes a long time for the Earth’s system to rebalance,” lead researcher Sarah Baker explained. “This shows the vital importance of limiting disruption to the carbon cycle to regulate the Earth system and keep it within habitable bounds.”

Why should we be concerned about ocean anoxia?

Past climatic events allow scientists to model and investigate the planet’s response to climate change and provide clues as to what might be in our future.

Researchers have previously examined marine sediment cores, which essentially provide a timeline of oceanic events and can offer insight into how our oceans respond to oxygen loss.

And unfortunately, we’re seeing some of the warning signs for anoxic events today.

Estimates suggest that, over the past five decades, the oxygen level in our oceans has decreased by two percent. However, even this modest-seeming drop can be enough to trigger dead zones.

And even if we avoid a mass extinction event, increased dead zones could lead to a severe reduction in our already beleaguered fish stocks.

Anoxic events present yet another reason why we must hold our governments accountable and ensure they stick to their commitments to fight climate change. After all, it’s not an exaggeration to say that life as we know it today might very well depend upon it.

Photo Credit: eutrophication&hypoxia/Flickr


Telica R
Telica R3 months ago

Thanks for sharing

Mark Donner
Mark Donner8 months ago

There's two problems to address: One is radically stopping the global use of fossil fuels and the second is getting rid of the government psychopaths that want to destroy all life on Earth: Trump, Pruitt and Zinke have to be thrown out as soon as possible.

Jennifer H
Jennifer H8 months ago

This story leaves an emptiness in me.

Margie FOURIE8 months ago

This is terrible

Patricia H
Patricia Harris9 months ago

This is exactly why I've been pushing everyone so hard... I urgently need your help to put a stop to this madness... I can't bare any more tragedies... Not like this... I now have you wonderful people to depend on... For a better future of humanity... The animal kingdom... Please... I beg of you... If you won't do it for me... Then at the very least do it for the children of both today and tomorrow...

Carl R
Carl R9 months ago


william Miller
william Miller9 months ago


maria r
maria reis9 months ago

Bad news. Thanks for the information.

Janis K
Janis K9 months ago

Thanks for sharing.

Leo C
Leo Custer9 months ago

Thank you for posting!