Decoupling of Neogene seawater lithium isotopes from uplift-driven weathering.

Abstract

The 9‰ increase in seawater lithium isotope (δ⁷Li) during the Cenozoic is widely regarded as evidence for uplift-driven enhancement of continental silicate weathering. Yet, the absence of long-term direct riverine δ⁷Li records has left this hypothesis largely untested. Given that the Tibetan Plateau contributes 16% of the modern global riverine Li flux, we present δ⁷Li records of paleowater spanning the past 15 million years covering the southern humid and northern arid Tibetan Plateau. Paleowater δ⁷Li reveals long-term decreases for the northern plateau, and low values for the southern plateau, reflecting a decrease in silicate weathering intensity in response to climatic cooling and high exhumations. Integrating our δ⁷Li record into a global Li cycle model, our study indicates that continental silicate weathering from tectonically active mountains is unlikely to have accounted for the observed rise in seawater δ⁷Li. These findings urge reconsideration of how tectonic uplift affects the chemistry of the ocean and carbon cycle.