Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes

Murphy, Melissa J.; Porcelli, Don; Strandmann, Philip A.E. Pogge von; Hirst, Catherine; Kutscher, Liselott; Katchinoff, Joachim; Mörth, Carl‐Magnus; Maximov, Trofim C.; Andersson, Per

doi:10.1016/j.gca.2018.10.024

Cited by 70 publications

(34 citation statements)

References 80 publications

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“…Mg/Na ratios should therefore provide information on dissolution of primary minerals vs. formation and uptake by secondary minerals. However, unlike the isotope ratios of trace elements such as lithium Murphy et al, 2019), we do not observe a simple relationship between δ 26 Mg and Mg/Na or Ca/Mg for either coast, which is not necessarily to be expected, given the variable isotope ratios of both silicates and carbonates. Similarly, there is no relationship between δ 26 Mg and the ratio of divalent to monovalent cations, which has also been used as a proxy for silicate weathering (Tranter et al, 2002;Hatton et al, 2019).…”

Section: Riverine Magnesiumcontrasting

confidence: 92%

“…In other words, the enhanced dissolution of primary silicates in mountainous regions causes a correlation of Li and Si isotopes (also observed in the Himalayan foothills; Pogge von Strandmann et al, 2017). This co-relationship between the two systems can be modeled using a Rayleigh relationship (Vigier et al, 2009;Pogge von Strandmann et al, 2012, 2014b, 2017Murphy et al, 2019), and by assuming a continental crust starting composition (Savage et al, 2010;Sauzéat et al, 2015). Using a kaolinite fractionation factor of α = 0.979 for Li isotopes (Pistiner and Henderson, 2003;Hindshaw et al, 2019), and of 0.9989 for Si isotopes (close to values for allophane, which is compositionally similar to kaolinite; Ziegler et al, 2005;Delstanche et al, 2009), we can model the co-isotopic behavior for the western samples with between 20 and 60% of Li and Si removal (Figure 4E).…”

Section: Riverine Siliconmentioning

confidence: 99%

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The Response of Magnesium, Silicon, and Calcium Isotopes to Rapidly Uplifting and Weathering Terrains: South Island, New Zealand

et al. 2019

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Silicate weathering is a dominant control on the natural carbon cycle. The supply of rock (e.g., via mountain uplift) has been proposed as a key weathering control, and suggested as the primary cause of Cenozoic cooling. However, this is ambiguous because of a lack of definitive weathering tracers. We use the isotopes of the major cations directly involved in the silicate weathering cycle: magnesium, silicon and calcium. Here we examine these isotope systems in rivers draining catchments with variable uplift rates (used as a proxy for exposure rates) from South Island, New Zealand. Overall, there is no trend between these isotope systems and uplift rates, which is in contrast to those of trace elements like lithium or uranium. Li and Si isotopes co-vary, but only in rapidly uplifting mountainous terrains with little vegetation. In floodplains, in contrast, vegetation further fractionates Si isotopes, decoupling the two tracers. In contrast, Mg and Ca isotopes (which are significantly affected by the weathering of both carbonates and silicates) exhibit no co-variation with each other, or any other weathering proxy. This suggests that lithology, secondary mineral formation and vegetation growth are causing variable fractionation, and decoupling the tracers from each other. Hence, in this context, the isotope ratios of the major cations are significantly less useful as weathering tracers than those of trace elements, which tend to have fewer fractionating processes.

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Section: Riverine Magnesiumcontrasting

confidence: 92%

Section: Riverine Siliconmentioning

confidence: 99%

The Response of Magnesium, Silicon, and Calcium Isotopes to Rapidly Uplifting and Weathering Terrains: South Island, New Zealand

et al. 2019

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“…Thus, while there are apparently subtle differences in fractionation between different terrains (bearing in mind that riverine suspended loads do not necessarily only consist of secondary minerals), observed fractionations appears to be broadly similar, around ~20‰. The observed fractionation in these experiments is also similar to the overall variability observed in a global compilation of published riverine values (Murphy et al, 2019), and the mean discharge-weighted d 7 Li of ~23‰ observed in rivers (Huh et al, 1998).…”

Section: Mineral Saturation Statessupporting

confidence: 70%

Experimental determination of Li isotope behaviour during basalt weathering

et al. 2019

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Silicate weathering is the primary control of atmospheric CO2 concentrations on multiple timescales. However, tracing this process has proven difficult. Lithium isotopes are a promising tracer of silicate weathering. This study has reacted basalt sand with natural river water for ~9 months in closed experiments, in order to examine the behaviour of Li isotopes during weathering. Aqueous Li concentrations decrease by a factor of ~10 with time, and d 7 Li increases by ~19‰, implying that Li is being taken up into secondary phases that prefer 6 Li. Mass balance using various selective leaches of the exchangeable and secondary mineral fractions suggest that ~12-16% of Li is adsorbed, and the remainder is removed into neoformed secondary minerals. The exchangeable fractionation factors have a D 7 Liexch-soln =-11.6 to-11.9‰, while the secondary minerals impose D 7 Lisecmin-soln =-22.5 to-23.9‰. Overall the experiment can be modelled with a Rayleigh fractionation factor of a = 0.991, similar to that found for natural basaltic rivers. The mobility of Li relative to the carbon-cycle-critical cations of Ca and Mg changes with time, but rapidly evolves within one month to remarkably similar mobilities amongst these three elements. Th evolution shows a linear relationship with d 7 Li (largely due to a co-variation between aqueous [Li] and d 7 Li), suggesting that Li isotopes have the potential to be used as a tracer of Ca and Mg mobility during basaltic weathering, and ultimately CO2 drawdown.

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“…Instead, the light Li isotope ( 6 Li) is preferentially taken up by secondary minerals (clays, oxides, zeolites) formed during weathering, enriching residual waters in isotopically heavy Li. Hence, surface water δ 7 Li is controlled by the ratio of primary rock dissolution to secondary mineral formation, known as the weathering congruency (Misra and Froelich, 2012;Pogge von Strandmann and Henderson, 2015), which in turn can act as a tracer of weathering intensity (that is, the ratio of the weathering rate to the denudation rate, Dellinger et al, 2015;Pogge von Strandmann et al, 2017;Murphy et al, 2019;Gou et al, 2019). This also relates to the efficiency of CO 2 drawdown, as cations retained on the continents in secondary minerals do not end up in the oceans to assist carbon sequestration (Pogge von Strandmann and Henderson, 2015;Pogge von Strandmann et al, 2017).…”

Section: Application Of Sr Os LI and Ca Isotopes As Proxies Of Weatmentioning

confidence: 99%

Inclusion of a suite of weathering tracers in the cGENIE Earth System Model – muffin release v.0.9.10

Adloff¹,

Ridgwell²,

Monteiro³

et al. 2020

Preprint

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Abstract. The metals strontium (Sr), lithium (Li), osmium (Os) and calcium (Ca) and their isotopes are important tracers in the study of changes in weathering rates and volcanism, two main processes which shape the long-term cycling of carbon and other biogeochemically important elements at the Earth's surface. Traditionally, isotopic shifts of these four elements in the geologic record are interpreted with isotope-mixing, tracer-specific box models because of their long residence times in the ocean. However, these models often lack mechanistic links between the cycling of the four metals and other geochemically relevant elements, particularly carbon. Here we develop and evaluate the implementation of Sr, Li, Os and Ca isotopes into the Earth system model cGENIE. The model has the potential to study these metal systems at equilibrium and under perturbations alongside other biogeochemical cycles. We provide examples of how to apply this new model to investigate Sr, Li, Os and Ca isotope dynamics and responses to environmental change.

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Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes

Abstract: Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes. Geochimica et Cosmochimica Acta 245 , pp. 154-171.

Cited by 70 publications

References 80 publications

The Response of Magnesium, Silicon, and Calcium Isotopes to Rapidly Uplifting and Weathering Terrains: South Island, New Zealand

The Response of Magnesium, Silicon, and Calcium Isotopes to Rapidly Uplifting and Weathering Terrains: South Island, New Zealand

Experimental determination of Li isotope behaviour during basalt weathering

Inclusion of a suite of weathering tracers in the cGENIE Earth System Model – muffin release v.0.9.10

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