Lithium Isotope History of Cenozoic Seawater: Changes in Silicate Weathering and Reverse Weathering

Abstract

Life of Li Because lithium primarily exists in silicate minerals on continents, the variations of Li isotopes in marine sedimentary rocks reflect the degree of silicate weathering and formation of new sediments on the seafloor, which in turn are largely controlled by climate and tectonic forces over geologic time. By analyzing sedimentary cores from eight drill sites around the world's oceans, Misra and Froelich (p. 818 , published online 26 January; see the cover; see the Perspective by Paytan ) assembled a 68-million-year record of the Li isotope composition of seawater. The record reveals a stepwise change in the Li isotopic ratio, suggesting that several intense episodes of tectonic uplift increased continental weathering rates and delivery of sediments to the oceans. Abrupt swings in the record at specific points in Earth's history, for example, around the time when dinosaurs became extinct, imply major changes in ocean chemistry—but their mechanisms remain enigmatic.