Changes in continental weathering regimes inhibited global marine deoxygenation during the Paleocene-Eocene thermal maximum

The moderate impact of rapid global warming on oceanic redox and biodiversity during the Paleocene-Eocene thermal maximum (PETM; ~55.9 Ma) contrasts with other hyperthermal events in Earth’s history, and remains mostly unexplained. Here, we use lithium isotope (δ7Li) proxy and Earth system model simulations to reconstruct continental weathering regimes during the PETM. Negative δ7Li excursions of 3–4‰ in shallow-marine carbonates suggests globally increased erosion rates and decreased weathering intensities. Further, large negative δ7Li excursions of 4–5‰ in siliciclastic successions reflect enhanced accumulation of detrital clays exhumed from previous clay-rich sedimentary rocks, rather than those from weathering of igneous rocks. Changes in continental weathering regimes and associated flux of nutrients to oceans provide an explanation to the muted increase in oceanic anoxia and overall biodiversity loss during the PETM. The concomitant increases in physical erosion and clay delivery also enhanced organic carbon burial efficiency, permitting rapid return of global climate to pre-perturbation state. Lithium isotope records in marine carbonates and siliciclastic rocks reveal that shifts in continental weathering regime and source reduced ocean environmental stress and biodiversity loss during the global warming 56 million years ago.