Toxic Microbes Helped Cause and Prolong End-Permian Marine Mass Extinction, Study Suggests

Extreme warming at the end of the Permian period induced profound changes in marine biogeochemical cycling and animal habitability, leading to the largest extinction in Earth’s history. However, a causal mechanism for the extinction that is consistent with various records of geochemical conditions has remained unknown until now.

Climate warming driven by Siberian volcanic greenhouse gas release is widely regarded to be the underlying driver for the largest extinction event in Earth’s history at the end of the Permian period, when 80% of marine species were eliminated.

Various evidence revealed a 7-10-degree Celsius increase in sea surface temperature occurring in as little as 39,000 years, the development of euxinia (waters containing sulfide), an expansion in the extent of seafloor anoxia, and a decrease in the carbon isotopic signature recorded in carbonates.

Although the extinction event itself has been intensely studied and is relatively well characterized, the mechanisms behind the development of widespread de-oxygenation and biodiversity loss had not been fully understood until now.

According to the new study, the increase in sea temperature accelerated microbes’ metabolisms, creating deadly conditions.

“After oxygen in the ocean was used up to decompose organic material, microbes started to ‘breathe’ sulfate and produced hydrogen sulfide, a gas that smells like rotten eggs and is poisonous to animals,” said Dr. Dominik Hülse, a researcher in the Department of Earth and Planetary Sciences at the University of California, Riverside.

“As ocean photosynthesizers — the microbes and plants that form the base of the food chain — rotted, other microbes quickly consumed the oxygen and left little of it for larger organisms.”

“In the absence of oxygen, microbes consumed sulfate then expelled toxic, reeking hydrogen sulfide, creating an even more extreme condition called euxinia.”

These conditions were sustained by the release of nutrients during decomposition, promoting the production of more organic material which helped to maintain this stinky, toxic cycle.

“Our research shows the entire ocean wasn’t euxinic. These conditions began in the deeper parts of the water column,” Dr. Hülse said.

“As temperatures increased, the euxinic zones got larger, more toxic, and moved up the water column into the shelf environment where most marine animals lived, poisoning them.”

“The expanding euxinic zones can be detected through chemical signatures in sediment samples.”

Lessons from the ancient world may be important for understanding the processes that are challenging our modern oceans and waterways.

“It would be speculative to superimpose the ancient mass extinction event on today’s planet,” Dr. Hülse said.

“However, the study does show us that the ocean’s response to higher carbon dioxide concentrations in the atmosphere may be underestimated.”

The findings were published in the November 2021 issue of the journal Nature Geoscience.

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D. Hülse et al. 2021. End-Permian marine extinction due to temperature-driven nutrient recycling and euxinia. Nat. Geosci 14, 862-867; doi: 10.1038/s41561-021-00829-7