Environmental Divers of Decoupled Marine Sulfate Oxygen and Sulfur Isotope Trends during the Toarcian Oceanic Anoxic Event

The Toarcian Oceanic Anoxic Event was a major carbon cycle perturbation associated with two pulses of extinction and widespread environmental change. Studies of the biogeochemical sulfur cycle provide insight into the evolution of bottom-water redox conditions, which influence elemental cycling and habitability in the ocean. In particular, a ~6‰ positive excursion in the sulfur isotope composition of marine sulfate (d34SSO4) has been interpreted to reflect enhanced pyrite burialdue to the expansion of anoxic and euxinic sedimentary environmentsand/or changes in sulfur isotope fractionation associated with sulfate reduction. Similarly, the T-OAE preservesa6‰ positive oxygen isotope (d18OSO4) excursion that precedesthe d34SSO4 excursionatMonte Sorgenza.Using these observations, wemodel the behaviour of marine sulfate reservoir using both classic box models and a new flux balance approach to address the question of expanding euxinia and the role ofbiology.This study highlights how coupled 34SSO4 andd18OSOapproaches can provide insight into environmental changes associated with major perturbations to the carbon cycle.