Research Article

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

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Science  26 Jan 2012:
1214697
DOI: 10.1126/science.1214697

Abstract

Weathering of uplifted continental rocks consumes CO2 and transports cations to the oceans, 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. Here, we present a 68-million-year record of lithium isotopes in seawater (δ7LiSW) reconstructed from planktonic foraminifera. From the Paleocene (60 Ma) to Present, δ7LiSW rose 9‰, requiring large changes in continental weathering and seafloor reverse weathering 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 nor by Deccan trap volcanism, suggesting large-scale continental denudation.