14 Germanium Isotope Geochemistry

Rouxel, Olivier; Luais, Béatrice

doi:10.1515/9783110545630-015

Cited by 2 publications

(1 citation statement)

References 89 publications

(188 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Two recent studies have shown that Ge isotopes behave similarly to Si during weathering, with fluids enriched (δ 74 Ge = 0.9 to 5.5‰; Baronas et al (2018)) and weathered solids depleted in heavy isotopes (δ 74 Ge = -0.1 to 0.6‰; Qi et al (2019)) relative to primary igneous silicates (δ 74 Ge = 0.4 to 0.8‰; Rouxel and Luais (2017)). Over geological timescales, the heavy isotopic signatures of the fluids can only be maintained if the secondary solids are continuously eroded from the continents (Bouchez et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Ge and Si isotope behavior during intense tropical weathering and ecosystem cycling

Baronas¹,

West²,

Burton³

et al. 2020

Preprint

View full text Add to dashboard Cite

Chemical weathering of volcanic rocks in warm and humid climates contributes disproportionately to global solute fluxes. Geochemical signatures of solutes and solids formed during this process can help quantify and reconstruct volcanic weathering in the past. Here, we measured silicon (Si) and germanium (Ge) isotope ratios of the soils, clays, and fluids of a tropical lowland rainforest in Costa Rica. The bulk topsoil is intensely weathered and isotopically light (mean±1σ: δ30Si = –2.1±0.3‰, δ74Ge = –0.13±0.12‰) compared to the parent bedrock (δ30Si = –0.11±0.05‰, δ74Ge = 0.59±0.07‰). Neoforming clays are even lighter (δ30Si = –2.5±0.2‰, δ74Ge = –0.16±0.09‰), demonstrating a whole-system isotopic shift in extremely weathered systems. The lowland streams represent mixing of dilute local fluids (δ30Si = 0.2 – 0.6‰, δ74Ge = 2.2 – 2.6‰) with solute-rich interbasin groundwater (δ30Si = 1.0±0.2‰, δ74Ge = 4.0‰). Using a Ge-Si isotope mass balance model, we calculate that 91±9% of Ge released via weathering of lowland soils is sequestered by neoforming clays, 9±9% by vegetation, and only 0.2±0.2% remains dissolved. In contrast, vegetation plays an important role in the Si cycle, sequestering 39±14% of released Si. Globally, volcanic soil δ74Ge closely tracks the depletion of Ge by chemical weathering (τGe), whereas δ30Si and Ge/Si both reflect the loss of Si (τSi). Because of the different chemical mobilities of Ge and Si, a δ74Ge-δ30Si multi-proxy system is sensitive to a wider range of weathering intensities than each isotopic system in isolation.

show abstract