The release of carbon dioxide 300 million years ago left 20% of the seabed without oxygen

An international research group led by scientists studied the Carboniferous deposits on

territories of southern China. Scientists have been sampling and measuring isotopes of carbon and uranium to investigate the global carbon dioxide cycle and marine anoxia.

"The Naqing and Narao sections in the Luodian area,province of Guizhou, expose continuous Carboniferous carbonate sequences that record geochemical signals from seawater,” said Chen Jitao, co-author of the study from Nanjing University in China.

The researchers used the global modelLOSCAR carbon cycle to simulate conditions that would produce the same carbon distribution traces that they had obtained from studying and analyzing rocks. It turned out that about 304 million years ago there was a large release of about 9 thousand Gt of carbon dioxide.

The emission, according to scientists, should havecontinue for about 300 thousand years and lead to an increase in sea surface temperature by 4°C. At the same time, the area of ​​the seabed devoid of oxygen should have increased from 4% to 22%. These changes have led to a sharp decline in biodiversity.

The researchers note that current observations andclimate models show that the dissolved oxygen supply in the modern ocean is declining. The key factor that leads to such changes is usually called a decrease in the solubility of oxygen due to an increase in water temperature. The authors believe that analyzing the effects of past seafloor anoxia will help to better predict future changes.

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