The Permian-Triassic transition witnessed the largest mass extinction event in Earth’s history, with about 81% of marine life disappeared completely. 

Magnesium (Mg) has a relatively higher content in the ocean. Mg cycling is often accompanied by the carbon-oxygen cycle process, which is closely related to major land and sea changes as well as life processes.

Recently, an international research team from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS), Nanjing University, and University of Innsbruck investigated Mg isotopes of dolomite from three widely spaced carbonate sections in the Paleotethys to trace oceanic Mg cycling during Permian-Triassic transition period.  

The study was published in Earth and Planetary Science Letters on Jan. 5.

The researchers conducted systematic geochemical analysis of carbon-oxygen-magnesium isotopes.

They found remarkable variation of δ²⁶Mg_dolomite values around the end-Permian extinction interval and anti-correlated with global perturbations in δ¹³C_carbonate recorded from different localities in the Paleotethys. 

Based on the high-precision temporal model, the results suggested that the δ²⁶Mg of seawater fluctuated by 0.4‰ within ~750 kyr across the Permian-Triassic transition. 

Modeling revealed that the high rate of change in δ²⁶Mg_seawater was attributed to dramatically intensified dolomitization in a restricted oceanic environment.

The restriction could have occurred to local basins that were separated from each other, however, their data are also consistent with a hypothesis of the Paleotethys Ocean being episodically separated from the Panthalassa Ocean around the Permian-Triassic transition.  

The restriction events within the Paleotethys Ocean could have significantly weakened the ocean's buffering capacity against external disturbances, and exacerbated marine environmental crisis to the marine ecosystem. 

This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences, the National Natural Science Foundation of China and the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences.