News – Oxygen levels in the ancient oceans were surprisingly capable of climate change, a new study reveals.
Scientists used geological samples to estimate marine oxygen during global warming 56 million years ago – and found a “limited expansion” of seabed anoxia (without oxygen).
Global warming – both yesterday and today – is depleting the ocean’s oxygen, but the new study suggests a 5 ° C warming in the Paleocene Eocene Thermal Maximum (PETM) has caused anoxia more than 2% of the world’s soil.
However, conditions are different today with the PETM – today ‘s rate of carbon emissions is much faster, and we are adding nutrient pollution to the oceans – which could both result in faster and more oxygen loss. move wider.
The study was conducted by an international team comprising researchers from ETH Zurich, University of Exeter and Royal Holloway, University of London.
“The good news from our study is that the Earth’s system was able to disinfect the seabed 56 million years ago despite global warming,” said lead author Dr Matthew Clarkson, of ETH Zurich.
“However, there are reasons why things are different today.
“In particular, we believe that the Paleocene had higher atmospheric oxygen than it does today, which would have made anoxia less likely.
“In addition, human activity puts more nutrients into the ocean through fertilizers and pollutants, which can lead to oxygen loss and accelerate environmental degradation.”
To estimate marine oxygen levels during the PETM, the researchers analyzed the isotopic composition of uranium in marine sediments, which monitors oxygen concentration.
Surprisingly, these have hardly changed through PETM.
This sets an upper limit on the extent to which marine oxygen levels can change.
Computer simulations based on the results show a maximum tenfold increase in the area of the seabed without oxygen – bringing the majority to more than 2% of the global seabed.
This is still important, at about ten times the area of anoxia today, and it was clear that marine life in some parts of the ocean had been adversely affected and destroyed.
Co-author Dr Tim Lenton, Director of the Exeter Institute of Global Systems, notes: “This study shows how the sustainability of the Earth’s climate system has changed over time.
“The order of the mammals to which we belong – the prime ministers – came in the PETM. Unfortunately, given that our primacy has been growing for the last 56 million years, it seems unlikely. the oceans have become so strong. “
Dr Lenton said: “While the oceans have been more sustainable than we thought at this time in the past, nothing should distract us from the urgent need to reduce emissions and deal with them. to today’s climate crisis. “
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The research team included Cambridge University and Cardiff University.
The paper, published in the journal Nature Communication, entitled: “Upper seabed anoxia levels during PETM from uranium isotopes.”
This project has received funding from the European Union ‘s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie No. 795722.