Magmatism and continental weathering linked to carbon cycle change and climatic disturbance across the Triassic–Jurassic transition

The episodic emplacement of the Central Atlantic Magmatic Province (CAMP) triggered profound perturbations to the global carbon cycle, marked by abrupt pCO₂ elevations and climatic/environmental disturbance that led to the end-Triassic mass extinction (∼201.5 Ma). While volcanogenic degassing is recognized as the primary trigger of this environmental crisis, the subsequent Earth system feedbacks, particularly the role of silicate weathering in sequestering excess carbon, remain poorly understood. Resolving the temporal interplay between pulsed magmatic degassing and the weathering of fresh basaltic rock and associated carbon drawdown, is essential for understanding the stability of the global climate systems during extreme greenhouse forcing as well as the drivers of Early Jurassic Earth system recovery. In this study, we utilize the osmium (Os) isotope proxy to disentangle the intricacies of couplings between the global carbon cycle, magmatism and continental weathering.

Seawater ¹⁸⁷Os/¹⁸⁸Os ratios are highly sensitive to the balance between radiogenic continental runoff and unradiogenic mantle-derived inputs. Given the short residence time of Os (~10–50 kyr), this system can provide a detailed archive of rapid shifts in global weathering fluxes. We present a high-resolution initial seawater Os isotope ratio (¹⁸⁷Os/¹⁸⁸Os_i) record from the Prees Borehole (Cheshire Basin, UK), drilled by the International Continental Drilling Program (ICDP) Early Jurassic Earth System and Timescale (JET) project that offers an exceptionally complete stratigraphic succession across the Triassic–Jurassic transition. Our data, integrated with well constrained carbon-isotopic and biostratigraphic frameworks, reveal stratigraphic fluctuations in sedimentary Os-isotopic compositions that suggest temporal changes in global seawater ¹⁸⁷Os/¹⁸⁸Os_i, and by inference allow tracking of CAMP magmatism and changes in global weathering. By placing these findings in a global context, we demonstrate how the competition between volcanic carbon degassing and new weathering sinks governed the evolution of the global carbon cycle and, consequently, the ocean–atmosphere climatic system, providing a mechanistic framework for the environmental recovery following one of Earth’s most severe biotic crises.