Osmium Isotope Constraints on Magmatic Pulse Activity and Global Weathering Fluxes Across the Triassic-Jurassic Transition

The End-Triassic Mass Extinction (∼201.5 Ma) is inextricably linked to the episodic activity of the Central Atlantic Magmatic Province (CAMP), which induced severe global carbon cycle perturbations and abrupt atmospheric CO2 changes. While the crisis is primarily attributed to volcanogenic degassing, the governing Earth system feedbacks, specifically the efficiency of silicate weathering in sequestering excess CO2, remain a critical area of investigation. Characterizing the temporal relationship between pulsed magmatic outgassing and the subsequent weathering of basaltic provinces is vital for understanding climate stability under extreme greenhouse forcing and the mechanisms driving Early Jurassic environmental recovery. In this study, we employ the seawater osmium (Os) isotope proxy to resolve the complex interplay between magmatism, continental weathering, and the global carbon cycle. Seawater 187Os/188Os ratios reflect the competition between radiogenic continental runoff and unradiogenic mantle-derived inputs; owing to the short residence time of Os (~10–50 kyr), the system serves as a high-fidelity archive of rapid shifts in weathering fluxes. We present a high-resolution initial seawater Os-isotope (187Os/188Osi) record from the Prees Borehole (Cheshire Basin, UK), drilled by the International Continental Drilling Program (ICDP) Early Jurassic Earth System and Timescale (JET) project, which preserves an exceptionally continuous succession across the Triassic–Jurassic boundary. Integrated with established carbon-isotope and biostratigraphic frameworks, our data reveal two major shifts towards mantle-derived Os isotopic values across the Triassic–Jurassic transition, coinciding with the initial and the main carbon isotope excursions, likely linked to distinct pulses of CAMP activity. The magnitude of the Os isotope shifts also enable us to estimate the scale of CAMP basalt weathering immediately after the emplacement, and its potential role in modulating atmospheric CO2. By synthesizing these findings within a global context, we illustrate how the balance between volcanic emissions and rejuvenated weathering sinks modulated the ocean–atmosphere system, providing a mechanistic framework for the recovery of the Earth system following one of the Phanerozoic's most severe biotic crises.