The riverine silicon isotope composition of the Amazon Basin

Hughes, Harold J.; Sondag, Francis; Santos, Roberto Ventura; André, Luc; Cardinal, Damien

doi:10.1016/j.gca.2013.07.040

Cited by 61 publications

(55 citation statements)

References 72 publications

(128 reference statements)

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“…Based on mass-balance De La Rocha et al (2000) concluded that 64 % of weathered silicon is retained in secondary clay minerals, which is in rough agreement with the stoichiometry of weathering reactions. Hughes et al (2013) find that between 25 and 100 % of Si is retained by clay formation in subbasins of the Amazon based on the ratios of Si and cations in bedrock and surface waters. A similar conclusion was reached in the basaltic terrain of Iceland (Georg et al 2007).…”

Section: Evidence For Continental Dsi Retention From River Geochemistrymentioning

confidence: 95%

Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

et al. 2014

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Weathering of silicate minerals releases dissolved silicate (DSi) to the soil-vegetation system. Accumulation and recycling of this DSi by terrestrial ecosystems creates a pool of reactive Si on the continents that buffers DSi export to the ocean. Human perturbations to the functioning of the buffer have been a recent research focus, yet a common assumption is that the continental Si cycle is at steadystate. However, we have no good idea of the timescales of ecosystem Si pool equilibration with their environments. A review of modelling and geochemical considerations suggests the modern continental Si cycle is in fact characterised in the longterm by an active accumulation of reactive Si, at least partially attributable to lakes and reservoirs. These lentic systems accumulate Si via biological conversion of DSi to biogenic silica (BSi). An analysis of new and published data for nearly 700 systems is presented to assess their contribution to the accumulating continental pool. Surface sediment BSi concentrations (n = 692) vary between zero and [60 % SiO 2 by weight, apparently independently of lake size, location or water chemistry. Using sediment core BSi accumulation rates (n = 109), still no relationships are found with lake or catchment parameters. However, issues associated with single-core accumulation rates should in any case preclude their use in elemental accumulation calculations. Based on lake/reservoir mass-balances (n = 34), our best global-scale estimate of combined lake and reservoir Si retention is 1.53 TMol year -1 , or 21-27 % of river DSi export. Again, no scalable relationships are apparent, suggesting Si retention is a complex process that varies from catchment to catchment. The lake Si sink has implications for estimation of weathering flux generation from river chemistry. The size of the total continental Si pool is poorly constrained, as is its accumulation rate, but lakes clearly contribute substantially. A corollary to this emerging understanding is that the flux and isotopic composition of DSi delivered to the ocean has likely varied over time, partly mediated by a fluctuating continental pool, including in lakes.

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Section: Evidence For Continental Dsi Retention From River Geochemistrymentioning

confidence: 95%

Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

et al. 2014

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“…For example, along the Yangtze River uptake of DSi by grasses in wetlands and rice in paddy fields drives a progressive increase in δ 30 Si DSi due to better phytolith preservation in areas of high phytolith production and/or low phytolith dissolution (Ding et al, 2004). In contrast the net impact of vegetation on δ 30 Si DSi seems to be minimal in the Okavango Delta, Congo and Amazon Basin due to the rapid dissolution/recycling of phytoliths Hughes et al, 2013;Frings et al, 2014b).…”

Section: Riversmentioning

confidence: 99%

A Review of the Stable Isotope Bio-geochemistry of the Global Silicon Cycle and Its Associated Trace Elements

et al. 2018

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“…Si clay-solution = -1.5 % (Georg et al 2007) and -2.05 % (Hughes et al 2013) obviously deviate from the theoretical predictions, which reveals that stiffer chemical bonds will enrich heavier isotopes, i.e., the precipitated minerals will preferentially incorporate heavy isotopes relative to the aqueous H 4 SiO 4 due to their shorter Si-O bonds.…”

mentioning

confidence: 91%

“…With the rapid progress of high-resolution analytical instruments including ICP-MS and SIMS, slight variations of Si isotopic compositions can be detected. Therefore, the Si isotope compositions in many of Earth's surface systems, including soils, rivers, oceans, silicon-accumulating algae and high plants, have all been investigated (Basile-Doelsch et al 2005;Ding et al 2008Ding et al , 2009Georg et al 2007Georg et al , 2009Hughes et al 2013;Ziegler et al 2005). One can refer to the comprehensive reviews of Si isotope geochemistry in Opfergelt and Delmelle (2012).…”

Section: Introductionmentioning

confidence: 99%

Equilibrium and kinetic Si isotope fractionation factors and their implications for Si isotope distributions in the Earth’s surface environments

Zhang

Zhu

et al. 2015

Acta Geochim

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Several important equilibrium Si isotope fractionation factors among minerals, organic molecules and the H 4 SiO 4 solution are complemented to facilitate the explanation of the distributions of Si isotopes in Earth's surface environments. The results reveal that, in comparison to aqueous H 4 SiO 4 , heavy Si isotopes will be significantly enriched in secondary silicate minerals. On the contrary, quadra-coordinated organosilicon complexes are enriched in light silicon isotope relative to the solution. The extent of 28 Si-enrichment in hyper-coordinated organosilicon complexes was found to be the largest. In addition, the large kinetic isotope effect associated with the polymerization of monosilicic acid and dimer was calculated, and the results support the previous statement that highly 28 Sienrichment in the formation of amorphous quartz precursor contributes to the discrepancy between theoretical calculations and field observations. With the equilibrium Si isotope fractionation factors provided here, Si isotope distributions in many of Earth's surface systems can be explained. For example, the change of bulk soil d 30 Si can be predicted as a concave pattern with respect to the weathering degree, with the minimum value where allophane completely dissolves and the total amount of sesquioxides and poorly crystalline minerals reaches their maximum. When, under equilibrium conditions, the well-crystallized clays start to precipitate from the pore solutions, the bulk soil d 30 Si will increase again and reach a constant value. Similarly, the precipitation of crystalline smectite and the dissolution of poorly crystalline kaolinite may explain the d 30Si variations in the ground water profile. The equilibrium Si isotope fractionations among the quadracoordinated organosilicon complexes and the H 4 SiO 4 solution may also shed light on the Si isotope distributions in the Si-accumulating plants.

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The riverine silicon isotope composition of the Amazon Basin

Cited by 61 publications

References 72 publications

Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

A Review of the Stable Isotope Bio-geochemistry of the Global Silicon Cycle and Its Associated Trace Elements

Equilibrium and kinetic Si isotope fractionation factors and their implications for Si isotope distributions in the Earth’s surface environments

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