Magnesium isotopes reveal hydroclimatically amplified low-latitude weathering during the early Toarcian

The Toarcian Stage of the Early Jurassic experienced extreme global warming, marine anoxia, hydrological intensification, and enhanced continental weathering driven by carbon emissions. Low-latitude silicate weathering, a key climate regulator, is highly sensitive to climatic shifts, yet its response to Toarcian warming remains poorly understood. We present magnesium isotopes (δ26Mg) from carbonate-hosted silicates (acid-insoluble residues) in two geographically distinct, low-latitude carbonate platforms. Positive δ26Mg excursions, indicative of intensified continental weathering, are observed immediately following the Pliensbachian−Toarcian (Pl−To) boundary, temporally coincident with Karoo large igneous province (LIP) emplacement. δ26Mg values reached maxima during the onset interval of the Toarcian Oceanic Anoxic Event (T-OAE) negative carbon-isotope excursion (NCIE), temporally coincident with Ferrar LIP activity. The δ26Mg pattern suggests that carbon emissions around the Pl−To boundary time did not immediately induce maximum weathering. Rather, cumulative carbon emissions were required to surpass a critical tipping point just above the Pl−To NCIE, triggering a weathering intensification that culminated during the T-OAE NCIE onset interval. Our data, coupled with climate simulations using the Community Earth System Model, indicate that in tectonically inactive regions, elevated temperatures and extreme runoff caused severe soil stripping, exposing the underlying bedrock to intense chemical weathering.