Understanding deep-time climatic feedbacks relies on quantifying the initial drivers of Earth system perturbations. Earth system perturbations are highly sensitive to, among other parameters, the timing and duration of volcanic degassing. Currently, these input parameters are coarsely constrained, with volatile estimates coming from melt inclusion data and radiometric dating1. However, recent work has highlighted the power of combining sedimentary mercury (Hg), a volcanic tracer, and simple Hg cycle box models to estimate the tempo and volume of volcanic degassing in deep time2.Here, we present a quantitative high-resolution degassing history through the Sinemurian - Pliensbachian Boundary Event (SPBE). This protracted negative “U-shaped” carbon isotope excursion lasted for over 3 million years in the Early Jurassic (ca. 190 Ma). We utilise over 1600 samples collected from the recently drilled core at Prees, Cheshire Basin, U.K., as part of the International Continental Scientific Drilling Program JET project, to create this history.The SPBE is broadly coeval with increased rifting and the associated opening of the Hispanic Seaway, and potentially a late pulse of volcanic activity from the Central Atlantic Magmatic Province3–5, all of which may have contributed to its shape and duration. We quantify the tempo and volume of volcanic degassing during the SPBE using a novel geochemical machine-learning framework to isolate volcanically sourced Hg, followed by identification of the best-fit degassing scenarios using a global Hg box model.The results of our method have implications regarding the sensitivity and feedbacks of the carbon cycle in deep time. Specifically, we quantify the evolution of emissions during this enigmatic excursion. This will directly aid in understanding climate sensitivity during this period, where the protracted “U-shaped” change in carbon isotopes must now be reconciled with our evidence for distinct pulses of volcanic emissions throughout.This work helps bridge the gap between the palaeoclimate modelling and proxy communities. By quantitatively linking Hg concentrations to volcanic degassing, we can provide volcanic inputs with a precision of a few thousand years to modellers aiming to simulate deep-time climate change.References:1. Hernandez Nava, A. et al. Reconciling early Deccan Traps CO2 outgassing and pre-KPB global climate. Proceedings of the National Academy of Sciences 118, e2007797118 (2021).2. Fendley, I. M. et al. Early Jurassic large igneous province carbon emissions constrained by sedimentary mercury. Nat. Geosci. 17, 241–248 (2024).3. Franceschi, M. et al. Early Pliensbachian (Early Jurassic) C-isotope perturbation and the diffusion of the Lithiotis Fauna: Insights from the western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology 410, 255–263 (2014).4. Ruhl, M. et al. Astronomical constraints on the duration of the Early Jurassic Pliensbachian Stage and global climatic fluctuations. Earth and Planetary Science Letters 455, 149–165 (2016).5. Jiang, H. et al. Large-scale volcanogenic Hg enrichment coincided with the Sinemurian-Pliensbachian boundary event (Early Jurassic). Geological Society of America Bulletin https://doi.org/10.1130/B37640.1 (2025)