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

Autor: Philip A.E. Pogge von Strandmann, Olivier Rouxel, Rachael H. James, J. Jotautas Baronas, A. Joshua West, Kevin W. Burton, Sophie Opfergelt, Douglas E. Hammond
Přispěvatelé: UCL - SST/ELI/ELIE - Environmental Sciences
Rok vydání: 2020
Předmět:
bepress|Physical Sciences and Mathematics
0106 biological sciences
Atmospheric Science
010504 meteorology & atmospheric sciences
sub-01
Si Cycling
bepress|Physical Sciences and Mathematics|Earth Sciences
Weathering
EarthArXiv|Physical Sciences and Mathematics|Earth Sciences
01 natural sciences
chemical weathering
Isotopes
Environmental Chemistry
Parent rock
0105 earth and related environmental sciences
General Environmental Science
Topsoil
geography
Global and Planetary Change
geography.geographical_feature_category
010604 marine biology & hydrobiology
Ge Si
EarthArXiv|Physical Sciences and Mathematics
Volcanic rock
es
EarthArXiv|Physical Sciences and Mathematics|Earth Sciences|Biogeochemistry
bulk soils
Phytolith
Isotopic shift
13. Climate action
Environmental chemistry
Soil water
volcanic soils
weathering
Environmental science
bepress|Physical Sciences and Mathematics|Earth Sciences|Biogeochemistry
Groundwater
Zdroj: Global biogeochemical cycles, 2020, Vol.34(8), pp.e2019GB006522 [Peer Reviewed Journal]
Global Biogeochemical Cycles, Vol. 34, no. 8 (2020), p. e2019GB006522 (1-25) (2020)
Global Biogeochemical Cycles (0886-6236) (American Geophysical Union (AGU)), 2020-08, Vol. 34, N. 8, P. e2019GB006522 (25p.)
ISSN: 0886-6236
Popis: 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 weathering intensity in the past. Here, we measured silicon (Si) and germanium (Ge) isotope ratios of the soils, clays, and fluids from a tropical lowland rainforest in Costa Rica. The bulk topsoil is intensely weathered and isotopically light (mean±1σ: δ 30Si = –2.1 ± 0.3‰, δ 74Ge = –0.13 ± 0.12‰) compared to the parent rock (δ 30Si = –0.11 ± 0.05‰, δ 74Ge = 0.59 ± 0.07‰). Neoforming clays have even lower values (δ 30Si = –2.5 ± 0.2‰, δ 74Ge = –0.16 ± 0.09‰), demonstrating a whole-system isotopic shift in extremely weathered systems. The lowland streams represent mixing of dilute local fluids (δ 30Si = 0.2 – 0.6‰, δ 74Ge = 2.2 – 2.6‰) with solute-rich interbasin groundwater (δ 30Si = 1.0±0.2‰, δ 74Ge = 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. Vegetation plays an important role in the Si cycle, directly sequestering 39 ± 14% of released Si and enhancing clay neoformation in surface soils via the addition of amorphous phytolith silica. Globally, volcanic soil δ 74Ge closely tracks the depletion of Ge by chemical weathering (τGe), whereas δ 30Si and Ge/Si both reflect the loss of Si (τSi). Because of the different chemical mobilities of Ge and Si, a δ 74Ge-δ 30Si multi-proxy system is sensitive to a wider range of weathering intensities than each isotopic system in isolation.
Databáze: OpenAIRE
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