Lithium Isotope Evidence for Enhanced Continental Weathering Triggering the Late Paleozoic Greenhouse-to-Icehouse Climate Transition

The causes of the transition from a greenhouse to an icehouse climate during the Early Mississippian (~359–347 Ma), marking the possible onset of the Late Paleozoic Ice Age (LPIA), remain an outstanding puzzle in Earth’s climate history. This transition coincides with the mid-Tournaisian carbon isotope excursion (TICE). It is hypothesized that intensified continental silicate weathering during this period sequestered CO₂, boosted nutrients, and increased marine productivity, causing the positive TICE. However, direct evidence for enhanced continental weathering has been lacking. We present lithium isotope (δ⁷Li) data from two carbonate sections showing a ~12‰ decline during TICE. Integrating δ⁷Li with carbon cycle models (GEOCLIM and COPSE) suggests silicate chemical weathering rates increased ~30% with declines in weathering intensity during the TICE event, likely due to uplift or vegetation, ultimately reducing atmospheric pCO₂ by ~1000 ppm. This provides evidence linking enhanced weathering, CO₂ drawdown, and the onset of the LPIA, shedding light on a key aspect of late Paleozoic climate change.