An enormous sulfur isotope excursion indicates marine anoxia during the end-Triassic mass extinction

Abstract

The role of ocean anoxia as a cause of the end-Triassic marine mass extinction is widely debated. Here, we present carbonate-associated sulfate δ34S data from sections spanning the Late Triassic–Early Jurassic transition, which document synchronous large positive excursions on a global scale occurring in ~50 thousand years. Biogeochemical modeling demonstrates that this S isotope perturbation is best explained by a fivefold increase in global pyrite burial, consistent with large-scale development of marine anoxia on the Panthalassa margin and northwest European shelf. This pyrite burial event coincides with the loss of Triassic taxa seen in the studied sections. Modeling results also indicate that the pre-event ocean sulfate concentration was low (<1 millimolar), a common feature of many Phanerozoic deoxygenation events. We propose that sulfate scarcity preconditions oceans for the development of anoxia during rapid warming events by increasing the benthic methane flux and the resulting bottom-water oxygen demand.

An oxygenated global ocean during the end-Triassic mass extinction event

“…Correlative horizons within the Schandelah-1 core contain δ 98 Mo and Mo EF shifts indicative of shoaling of the sulfate reduction zone and low-sulfur, oxygen poor (ferruginous) conditions. The very low enrichment of elements sensitive to reduction (U) and variable enrichment of elements sensitive to HS − availability (Mo, Cu, Zn) from this horizon within the Schandelah-1 core further supports ferruginous conditions (see supplementary information), as does overall low sulfate on the Triassic-Jurassic Tethyan shelf interpreted from δ 34 S data 7 . Pulsed oxygen-poor conditions within the basal Jurassic of the Carnduff-2 and Schandelah-1 cores coincided with photic zone euxinia within the Bristol Channel Basin 4, 8 (Fig.…”

“…Isotopically light values are inconsistent with oxide adsorption given the elevated TS (%) at this horizon 6 . Weakly sul dic conditions around the base of the initial CIE at Cloghan Point (Northern Ireland) and St. Audrie's Bay (Somerset, UK) are also suggested through positive δ 34 S excursions 4,7 , and low sulfate within Late Triassic seawater of the Tethyan shelf has been interpreted through δ 34 S data 7 .…”

“…CAMP activity is also thought to have caused Triassic-Jurassic marine acidi cation and marine de-oxygenation 2,3 . Studies of latest Triassic marine de-oxygenation indicate that locally sul dic conditions were prominent within marginal marine surface waters of the Tethys and Panthalassic oceans around the TJB [3][4][5][6][7][8] . Oxygen-poor conditions have been further identi ed from blooms of prasinophycean algae 3,9 , a negative excursion in carbonate U isotopes 10 , widespread Early Jurassic black shale deposition 9,11 , elemental redox proxies 3,12 , and Fe speciation data 13 .…”

“…Oxygen-poor conditions were present across Tethyan and Panthalassa marginal marine environments during the main extinction interval 5,7,12,13 . Such conditions have been further identi ed here on the basis of δ 98 Mo and Mo EF data with redox conditions varying according to both site and stratigraphy.…”

Anthropogenic-scale CO2 degassing from the Central Atlantic Magmatic Province as a driver of the end-Triassic mass extinction

“…The results of our biogeochemical box model indicate climate instability and environmental variability on a 100-1000 years timeframe, induced by the rapid and pulsed degassing activity of CAMP. This period of extreme climatic and environmental instability coincided in time with the end-Triassic biosphere crisis and likely drove it via stressors, such as extreme warming, ocean acidification and hypoxia (Kiessling and Aberhan, 2007;Deenen et al, 2010;Pálfy and Zajzon, 2012;Kocsis et al, 2014;van de Schootbrugge and Wignall, 2016;He et al, 2020;Wignall and Atkinson, 2020;Hautmann, 2021). This process is reflected by strong extinction selectivity in the marine and terrestrial realms (McRoberts and Newton, 1995;Dunhill and Wills, 2015;Dunhill et al, 2018b;Allen et al, 2019), casting doubt on the hypothesis of a crisis resulted from a gradual increase in extinction rates throughout the Late Triassic (Hallam, 2002;Tanner et al, 2004;Lucas and Tanner, 2018).…”