Coupled survey of lithium isotopes and Li/Ca in biogenic and inorganic carbonates - Faculté des Sciences de Sorbonne Université Access content directly
Journal Articles Earth-Science Reviews Year : 2023

Coupled survey of lithium isotopes and Li/Ca in biogenic and inorganic carbonates

Abstract

Geochemists have long considered Li isotope composition of marine carbonates as one of the most straightforward oceanic archives, tracing climate regulation by continental silicate weathering. However, despite an isotopically homogenous ocean, a large range of δ7Li values were reported in the literature for modern biogenic carbonates. Additionally, laboratory studies highlighted variable Li isotope fractionations during foraminifera growth and during precipitation of inorganic carbonates. Despite an increasing interest in this topic, there is still limited understanding of Li isotopic fractionation and of Li incorporation mechanisms in carbonates. The present review aims to filling this gap by compiling and meta-analyzing the past findings from the literature. More specifically, Li/Ca and δ7Li data concerning the influence of mineralogy, temperature, pH, growth rate and biological processes have been exhaustively reviewed and statistically examined, including by PCA (Principal Component Analysis). For inorganic carbonate, we demonstrate that (1) the influence of mineral type is insufficiently explored (2) the effect of temperature on Li isotopes is negligible, although temperature changes can affect calcite Li/Ca ratio, and (3) calcite δ7Li and Li/Ca are primarily influenced by pH and growth rate. For marine modern biogenic carbonates, our cartography highlights an uneven geographical distribution, and further studies are required in the Pacific, Indian, and Southern Oceans. Also, for both Li/Ca and δ7Li, there are statistically significant and systematic differences between ‘bulk carbonates’ and all studied marine biogenic groups (i.e. foraminifera, mollusks, brachiopods). A detailed examination of foraminifera data reveals that planktic species display δ7Li values statistically higher than benthic ones, and both anti-correlate with Li/Mg ratios. Overall, this review underlines the necessity of filling the identified gaps of knowledge and of attentively considering the impact of environmental parameters and biological processes for interpreting past δ7Li variations displayed by fossil shells.

Domains

Geochemistry
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Dates and versions

hal-04311023 , version 1 (28-11-2023)

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Dongyu Chen, Fanny Thibon, Axel Felbacq, Lucas Weppe, Marc Metian, et al.. Coupled survey of lithium isotopes and Li/Ca in biogenic and inorganic carbonates. Earth-Science Reviews, 2023, 244, pp.104500. ⟨10.1016/j.earscirev.2023.104500⟩. ⟨hal-04311023⟩
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