Project A3

Chemical weathering as a sink for atmospheric CO2 – the lithium isotopic composition of seawater (δ7Li) as a weathering proxy

Sandra Huber (PhD)

Principal Investigators: Silke Voigt, Horst Marschall, Michael Seitz (Goethe University Frankfurt)

Reconstructed weathering intensity based on lithium isotopes (δ7Li) between 100-30 Ma in comparison to CO2, seawater temperature and strontium isotopic composition [1-6].

Subproject A3 aims at reconstructing the temperature-dependent intensity of silicate weathering as sink for atmospheric CO2 during late Cretaceous climate cooling (95-66 Ma). The lithium isotopic composition of marine carbonates records secular changes in sea-water δ7Li and thus reflects relative changes in the weathering of continental and oceanic silicates as well as the isotopic fractionation during the formation of clay minerals. We will perform isotopic and geochemical analyses (δ7Li, 87/86Sr, Δ47, Mg/Ca, Sr/Ca) in marine carbonates, and develop conceptual models in cooperation with project partners towards a quantitative assessment of the geodynamic and climatic coupling.

Chemical wheathering of ultramafic rocks. White carbonate veins in altered peridotite (from Keleman and Matter 2008).

Suspension load from physical erosion.

[1] Misra und Froelich, Science 335, 818–823 (2012). [2] Pogge von Strandmann und Henderson, Geology 43, 67–70 (2015). [3] Pogge von Strandman et al., Nat. Geosci. 6, 668–672 (2013). [4] McArthur et al., Cambridge Univ. Press, pp. 127–144 (2012). [5] Foster et al., Nat. Commun. 8, 14845 (2017). [6] Friedrich et al., Geology 40, 107–110 (2012).