• DOI:10.1126/science.1214697
• Corpus ID: 42591236

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

@article{Misra2012LithiumIH,
  title={Lithium Isotope History of Cenozoic Seawater: Changes in Silicate Weathering and Reverse Weathering},
  author={Sambuddha Misra and Philip N. Froelich},
  journal={Science},
  year={2012},
  volume={335},
  pages={818 - 823}
}

• S. Misra, P. Froelich
• Published 17 February 2012
• Medicine
• Science

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. Historical changes in the lithium isotope ratio in seawater imply episodes of tectonic uplift and carbon dioxide drawdown. Weathering of uplifted continental rocks consumes carbon dioxide and transports cations to the oceans, thereby playing a critical role in controlling both seawater chemistry and climate. However, there are few archives of seawater chemical change that reveal shifts in global tectonic forces connecting Earth ocean-climate processes. We present a 68-million-year record of lithium isotopes in seawater (δ7LiSW) reconstructed from planktonic foraminifera. From the Paleocene (60 million years ago) to the present, δ7LiSW rose by 9 per mil (‰), requiring large changes in continental weathering and seafloor reverse weathering that are consistent with increased tectonic uplift, more rapid continental denudation, increasingly incongruent continental weathering (lower chemical weathering intensity), and more rapid CO2 drawdown. A 5‰ drop in δ7LiSW across the Cretaceous-Paleogene boundary cannot be produced by an impactor or by Deccan trap volcanism, suggesting large-scale continental denudation.