The ancient oceans were surprisingly resilient to climate change, but today everything is different

Oxygen levels in the ancient oceans were surprisingly resilient to climate change, according to new research.

Scientists used geological samples to estimate ocean oxygen 56 million years ago during global warming and found “limited expansion” of sea floor anoxia (lack of oxygen).

Global warming, both past and present, consumes ocean oxygen, but a new study suggests that warming at 5 ° C in the Paleocene Eocene rm (PETM) led to anoxia, which covered no more than 2% of the global seabed.

However, today the conditions are different from PETM. Today’s rates of carbon emissions are much faster, we add nutrient pollution to the oceans, both of which can result in faster և extensive oxygen loss.

The study was conducted by an international team of researchers from the University of Exeter in London and Royal Holloway University in ETH Z Eurek.

“The good news of our study is that the Earth’s system was resistant to deoxygenation of the seabed 56 million years ago, despite obvious global warming,” said lead author Dr. Matthew Clarkson of the ETH in Eurerich.

“However, there are reasons why things are different today.

“In particular, we believe that the Paleocene had higher atmospheric oxygen than today, which would make anoxia less likely.

“In addition, human activity, through fertilizer pollution, introduces more nutrients into the ocean, which can lead to oxygen loss and accelerate the deterioration of the environment.”

To assess ocean oxygen levels during PETM, researchers analyzed the isotopic composition of uranium in ocean sediments, which tracks oxygen concentrations.

Sur erroneously, they hardly changed during PETM.

This sets the upper limit for how much the oxygen level in the ocean can change.

Based on the results, the computer simulation offers a maximum of tenfold increase in the de-oxygenated area of ​​the seabed, bringing the total to no more than 2% of the global seabed.

This is still significant: about 10 times the modern area of ​​anoxia, in some parts of the ocean there were obvious harmful effects of marine life.

Co-author Professor Tim Lenton, director of the Exeter Institute for Global Systems, says: “This study shows how the resilience of the Earth’s climate system has changed over time.

“The order of our mammals, the primates, originated in PETM. “Unfortunately, as we primates have evolved over the last 56 million years, it seems that the oceans are becoming less resilient.”

Professor Lenton added: “Although the oceans were more resilient than previously thought, nothing should distract us from the urgent need to reduce emissions and address the climate crisis.”

Reference. “Upper limits for the spread of seabed anoxia from uranium isotopes during PETM” January 15, 2021 Nature communications,
DOI: 10.1038 / s41467-020-20486-5:

The research team included the University of Cambridge և Cardiff University.

The newspaper that was published in the magazine Nature communicationshas the title: “Upper limits for the spread of seabed anoxia from uranium isotopes during PETM.”

This project was funded by the European Union’s Horizon 2020 Research and Innovation Program under Marie Sklodowska-Curie Grant Agreement No. 795722.

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