Scientists at the University of Cincinnati (USA) found that global anoxia in the seas of the Permian period regarding 260 million years ago led to a double mass extinction at the level of entire genera. This is reported in an article published in the journal Earth and Planetary Science Letters.
The researchers analyzed the distribution of uranium-238 isotopes in marine carbonate samples collected in the South China Sea. Two events were identified when global anoxia was observed – a phenomenon in which more than a twofold decrease in dissolved oxygen, necessary for the life of marine organisms, occurred in the World Ocean.
Anoxia events preceded two mass extinctions around 259 and 262 million years ago, in the mid-Permian period. The extinction of marine animals, called the Captainian extinction, was not as severe as during the Great Permian-Triassic Extinction 252 million years ago, when regarding 90 percent of marine and 70 percent of terrestrial species disappeared. However, in both cases, the episodic volcanic activity of the Big magmatic province of Emeishan in China became the cause of the ecological catastrophe.
Volcanic eruptions released ash into the atmosphere, which greatly reduced the amount of sunlight and contributed to short periods of cooling. However, this was followed by a longer period of global warming due to greenhouse gas emissions.
As a result of the warming of sea water, the amount of dissolved oxygen in the surface layer of the oceans decreased, and circulation worsened, which disrupted food chains. Shallow marine taxa such as fusulin foraminifera, corals, bivalves and ammonoids, as well as terrestrial organisms, have been affected.
