Spatial and temporal heterogeneity of the marine nitrogen cycle during the end-Triassic mass extinction

Li, Jing; Song, Huyue; Du, Yong; Wignall, Paul B.; Bond, David P.G.; Grasby, Stephen E.; Song, Haijun; Dal Corso, Jacopo; Tian, Li; Chu, Daoliang

Abstract

The end-Triassic mass extinction (ETME) marks a pivotal event in Earth's history, characterized by major environmental changes in both marine and terrestrial settings and significant perturbations in the carbon and nitrogen biogeochemical cycles alongside extinction events. Here we employ high-resolution organic carbon isotopes (δ13Corg), nitrogen isotopes from bulk samples (δ15Nbulk), total organic carbon (TOC) and nitrogen content (TN), complemented by carbon (δ13Ckerogen) and nitrogen isotopes (δ15Nkerogen) of kerogen extracts from the Kuhjoch section in Austria in order to investigate the interplay between marine redox state, nitrogen cycling, and the biotic crisis across the Triassic–Jurassic boundary. Our results reveal a significant positive shift (∼3 ‰) in δ15Nbulk values, indicating a perturbed marine nitrogen cycle and expansion of the oxygen minimum zone prior to the ETME. The δ15N profiles suggest a transition from a nitrate-limited ocean dominated by nitrogen fixation to a post-extinction ocean with increased proportion of assimilation of NO3− undergoing non-quantitative denitrification. We also examine the spatial and temporal heterogeneity of the marine nitrogen cycle from different paleoenvironmental settings across the Triassic–Jurassic transition. Bioavailable nitrogen (NO3− and NH4+) limitation prevailed at some localities before and during the ETME. However, the development of N limitation was not synchronous across different locations: it emerged before the ETME in some European basins and intensified after the ETME on Panthalassan shelves. The early Hettangian saw an expansion of euxinic waters into the photic zone and shoaling of the chemocline. Enhanced continental weathering and deep-water upwelling increased nutrient supply, thereby alleviating N limitation. Our new observations point to an unstable and stratified marine environment during the Triassic–Jurassic transition, and suggest that nitrogen bioavailability and redox conditions may be key factors for the devastation of marine ecosystems.

Citation

Li, J., Song, H., Du, Y., Wignall, P. B., Bond, D. P., Grasby, S. E., Song, H., Dal Corso, J., Tian, L., & Chu, D. (2025). Spatial and temporal heterogeneity of the marine nitrogen cycle during the end-Triassic mass extinction. Chemical Geology, 682, Article 122752. https://doi.org/10.1016/j.chemgeo.2025.122752

• Journal Article Type: Article
• Acceptance Date: Mar 20, 2025
• Online Publication Date: Mar 21, 2025
• Publication Date: Jun 5, 2025
• Deposit Date: Mar 21, 2025
• Publicly Available Date: Mar 22, 2026
• Journal: Chemical Geology
• Print ISSN: 0009-2541
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 682
• Article Number: 122752
• DOI: https://doi.org/10.1016/j.chemgeo.2025.122752
• Keywords: Kuhjoch GSSP, Austria; Nitrogen isotopes; Triassic–Jurassic; Marine redox state; Anoxia
• Public URL: https://hull-repository.worktribe.com/output/5087147