Dynamics of Tethyan marine de‑oxygenation and relationship to S-N-P cycles during the Permian-Triassic boundary crisis

Oceanic de‑oxygenation is considered to have been an important kill mechanism contributing to the latest Permian mass extinction and subsequent protracted recovery of marine biotas, but its extent, magnitude, and related controlling factors remain controversial. Here, we undertake a synthesis and reevaluation of previously published Fe-S-P-N data to better understand spatial and temporal variation of marine de‑oxygenation along a proximal-to-distal gradient in the eastern Paleotethys Ocean during the Permian-Triassic transition. Our results indicate: i) transient oxygenation of outer-shelf to basinal settings and de‑oxygenation of middle-shelf settings at the extinction horizon; ii) in outer-shelf to basinal settings, a shift from episodically euxinic conditions in the latest Permian (C. changxingensis Zone) to mainly ferruginous conditions in the earliest Triassic (H. parvus-I. isarcica zones); and iii) in middle-shelf settings, a shift from oxic-dysoxic (C. changxingensis Zone) to euxinic (C. yini-C. meishanensis zones) and then back to oxic conditions (H. parvus-I. isarcica zones). Proximal-to-distal redox variations are closely linked to spatial gradients in the marine sulfur, nitrogen and phosphorous cycles. A global comparison demonstrates that the Paleotethys, Neotethys, Boreal, and Panthalassic oceans all experienced shallow-marine de‑oxygenation during the latest Permian mass extinction, which may have been a major factor in the marine biocrisis. Globally, the extent and magnitude of oceanic de‑oxygenation presented a link to the distance to the Siberian Traps Large Igneous Province and, thus, to the volume of volcanic-related sulfur release during the Permian-Triassic boundary crisis.