Coupled continental and reverse weathering influence on Cenozoic cooling revealed by the marine lithium cycle

The Cenozoic transition from greenhouse to icehouse climate has been commonly attributed to enhanced silicate weathering driven by tectonic uplift and intensified erosion. However, the manner in which increased physical erosion translates into climate cooling via regulation of the long-term carbon-silicon cycle remains poorly constrained. We apply coupled seawater lithium concentration and lithium isotope composition to reconstruct the Cenozoic evolution of the marine Li cycle and associated surficial C-Si processes. Our results show a pronounced increase in riverine δ7Li (∼13‰) over the Cenozoic accompanied by a modest rise (0.5×) in weathering flux, but a modest decline (0.6×) in marine authigenic clay formation (reverse weathering). These trends indicate that with progressive denudation and climate cooling, weathering congruency significantly declined, reducing CO2 consumption and thereby allowing silicate weathering fluxes to rise only slightly. Concurrently, suppressed reverse weathering reflects a reorganization of marine Si cycling, which further reduced CO2 release to the atmosphere. Our refined marine Li cycle suggests that both continental silicate weathering and reverse weathering contributed to Cenozoic cooling, likely reflecting a reorganization of the global C-Si cycle.