# Recurrent and Long-Term Oceanic Anoxia Contributed to Aborted Biotic Recovery Following the Permian–Triassic Crisis

## TL;DR

Long-term ocean anoxia in the Early Triassic repeatedly hindered the recovery of marine life after the Permian-Triassic mass extinction.

## Contribution

This study identifies recurrent ocean anoxia and its impact on biotic recovery in the Chaohu Area using geochemical data.

## Key findings

- Recurrent ocean anoxia in the Early Triassic prevented sustained biotic recovery.
- Two oxic intervals coincided with biotic recovery but were interrupted by environmental perturbations.
- A positive δ13Corg shift and low V/(V + Ni) ratios indicate oxic conditions promoting recovery.

## Abstract

The link between ocean chemistry and Early Triassic biotic recovery in the Chaohu Area remains unclear. Geochemical analyses (pyrite content, δ13Corg, pyrite S isotopes, and V/(V + Ni) ratios) of the northern Pingdingshan section reveal recurrent long-term ocean anoxia in this period, interrupted by two oxic intervals in the early Spathian. A positive δ13Corg shift (~4‰) at the Smithian/Spathian boundary was associated with significant biotic recovery due to oxic conditions, coincident with a positive δ34S excursion (~25‰) and low V/(V + Ni) ratios. Although the second episode of oxic conditions occurred in the late early Spathian, frequent environmental perturbations may have aborted the biotic recovery. Recurrent and long-term ocean anoxia made sustained recovery impossible in the Early Triassic.

The influence of ocean chemistry on Early Triassic biotic recovery is poorly understood in the Chaohu Area. Here, we evaluate the influence of ocean chemistry following the Permian–Triassic crisis using pyrite content, δ13Corg, and S isotopic composition of pyrite. The pyrite content, V/(V + Ni) ratio, and S isotopic composition of pyrite in the Early Triassic from the northern Pingdingshan section of the Chaohu area in eastern China reveal recurrent and long-term ocean anoxia and two episodes of oxic conditions that occurred in the earliest Spathian and the late early Spathian. A positive δ13Corg shift of ~4‰ around the Smithian/Spathian boundary (SSB) in the lowermost Spathian was associated with significant biotic recovery, coincident with a positive δ34S excursion of ~25‰ and a low V/(V + Ni) ratio. The results suggest that the oxic conditions contributed to this recovery. Enhanced global ocean circulation during the SSB climate cooling may also have promoted this recovery. Frequent environmental perturbations may have aborted the biotic recovery, although the second episode of oxic conditions occurred in the late early Spathian. Sustained recovery did not appear in the Early Triassic because of the recurrent and long-term ocean anoxia.