Continental silicate weathering serves as a critical negative feedback mechanism regulating the global carbon cycle and climate over geological timescales. The Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) in the Early Jurassic was a prominent global warming episode accompanied by widespread marine anoxia and an intensified hydrological cycle, representing a classic deep-time hyperthermal. As a hub for global climate regulation, low-latitude silicate weathering is highly sensitive to climatic shifts. However, limited by the spatial heterogeneity of geological records and the scarcity of quantitative proxies, the response processes and dynamic mechanisms of low-latitude chemical weathering to Toarcian warming have remained poorly understood.
To address this issue, Associate Professor HAN Zhong from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS), in collaboration with researchers from domestic and international research institutions,extracted and analyzed the silicate fractions (acid-insoluble residues) hosted in Early Jurassic low-latitude shallow-marine carbonate platforms. By integrating their magnesium isotope (δ26Mg) variations with an Earth System Model, the team revealed the amplifying effect of extreme hydroclimate on continental weathering during the hyperthermal event. These findings were published online on July 24 in the premier international geoscience journal, Geology.
The research team conducted Mg-isotope analyses on two low-latitude profiles from the Early Jurassic Toarcian, located in the then-Southern Hemisphere (Kioto Carbonate Platform, Tibet) and Northern Hemisphere (Apennine Carbonate Platform, Italy) (Fig. 1). The results show that following the Pliensbachian-Toarcian (Pl-To) boundary (~184 Ma, corresponding to the Karoo Large Igneous Province activity), both sections recorded a significant positive excursion in Mg isotopes. This trend coincides with the initial rise in paleoseawater temperatures, indicating a gradual intensification of continental chemical weathering. Interestingly, this enhanced weathering signal continued to rise, reaching its maximum during the onset interval of the T-OAE negative carbon-isotope excursion (NCIE) (corresponding to the Ferrar Large Igneous Province activity) (Fig. 2), demonstrating a distinct delayed temporal response. The study suggests that early carbon emissions at the Pl-To boundary did not immediately trigger significant changes in the global weathering system. Instead, cumulative atmospheric carbon needed to surpass a critical tipping point to trigger the severe climatic and environmental crises during the T-OAE NCIE, thereby pushing silicate weathering to its peak.
To explore the physical mechanisms behind this weathering enhancement, the team conducted paleoclimate simulations using the Community Earth System Model (CESM). The simulations indicate that in tectonically quiescent low-latitude regions, thick soil mantles acted as a shielding layer, preventing contact between the underlying bedrock and fluids. Simple temperature increases alone (i.e., the Arrhenius effect) were insufficient to drive the observed weathering surge (Fig. 3). However, the hyperthermal event triggered extreme hydroclimatic volatility (e.g., tropical cyclones, intense precipitation, and flash floods). Such extreme precipitation and surface runoff stripped the surface soil cover, directly exposing the underlying unweathered bedrock and thereby drastically amplifying the intensity of chemical weathering.
By utilizing the Mg isotopes of carbonate-hosted acid-insoluble residues, this study confirms the weathering response of low-latitude regions during an extreme greenhouse period. From the perspective of "soil stripping–weathering coupling," it elucidates the role of extreme hydroclimatic events in accelerating Earth's climate self-regulation (weathering carbon sink). This research provides crucial theoretical support for understanding the non-linear coupling between the climate system and biogeochemical cycles during deep-time hyperthermals.
This research was jointly funded by the National Key R&D Program of China, the National Natural Science Foundation of China (NSFC), the Research Fund for International Scientists (NSFC), the Italian Ministry of University and Research, and the International Geoscience Programme (IGCP 739).
Reference: Han, Z.*, Hu, Z., Guo, J., Parente, M., Kemp, D.B., Remírez, M.N., Yuan, S., Li, X., Hu, Y., Jenkyns, H.C., Chen, X., Franceschi, M., Hu, X.*, 2026. Magnesium isotopes reveal hydroclimatically amplified low-latitude weathering during the early Toarcian. Geology, https://doi.org/10.1130/G54555.1.
Fig. 1. Early Toarcian paleogeographic map. The map shows the locations of the two low-latitude study sections (Nianduo, Tibet, and Mercato San Severino, Italy), along with the distributions of the Karoo and Ferrar Large Igneous Provinces (LIPs) and storm deposit records (yellow dots).
Fig. 2. Integrated Early Jurassic stratigraphic and geochemical correlation chart. It displays the positive excursion trend of magnesium isotopes (δ26Mg) in the studied sections and its relationship with carbon isotopes (δ13C), storm deposit records, paleotemperature changes, and the activity of Large Igneous Provinces (Karoo and Ferrar).
Fig. 3. Climate simulation results and conceptual model of continental weathering evolution. The upper panels (A-D) show the spatial distribution changes in global annual mean surface temperature and precipitation simulated by the CESM under different atmospheric CO2 concentrations. The lower panels (E-F) illustrate the physical mechanism by which climate change drives enhanced continental weathering, wherein extreme hydroclimatic events (e.g., tropical cyclones and intense precipitation-induced runoff) strip the surface soil layer, exposing the underlying unweathered bedrock, thereby intensifying chemical weathering and leading to the observed Mg-isotope excursion coupling.
Download：