The influence of critical zone processes on the Mg isotope budget in a tropical, highly weathered andesitic catchment

Lara, María Chapela; Buss, Heather L.; Strandmann, Philip A.E. Pogge von; Schuessler, Jan A.; Moore, Oliver

doi:10.1016/j.gca.2016.12.032

Cited by 56 publications

(51 citation statements)

References 114 publications

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“…, Chapela Lara et al . ). The most fractionated materials on Earth are found in low‐temperature environments, with the lowest δ 26 Mg values found in carbonates (δ 26 Mg of −5.6‰, Wombacher et al .…”

Section: Reference Materials Studied and Their Chemical Compositionmentioning

confidence: 97%

Mg Isotope Interlaboratory Comparison of Reference Materials from Earth‐Surface Low‐Temperature Environments

Shalev

Farkaš

Fietzke

et al. 2018

Geostandard Geoanalytic Res

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To enable quality control of measurement procedures for determinations of Mg isotope amount ratios, expressed as δ26Mg and δ25Mg values, in Earth‐surface studies, the δ26Mg and δ25Mg values of eight reference materials (RMs) were determined by interlaboratory comparison between five laboratories and considering published data, if available. These matrix RMs, including river water SLRS‐5, spring water NIST SRM 1640a, Dead Sea brine DSW‐1, dolomites JDo‐1 and BCS‐CRM 512, limestone BCS‐CRM 513, soil NIST SRM 2709a and vegetation NIST SRM 1515, are representative of a wide range of Earth‐surface materials from low‐temperature environments. The interlaboratory variability, 2s (twice the standard deviation), of all eight RMs ranges from 0.05 to 0.17‰ in δ26Mg. Thus, it is suggested that all these materials are suitable for validation of δ26Mg and δ25Mg determinations in Earth‐surface geochemical studies.

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Section: Reference Materials Studied and Their Chemical Compositionmentioning

confidence: 97%

Mg Isotope Interlaboratory Comparison of Reference Materials from Earth‐Surface Low‐Temperature Environments

Shalev

Farkaš

Fietzke

et al. 2018

Geostandard Geoanalytic Res

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“…Carbonate precipitation can therefore drive waters isotopically heavy . There is also an added fractionation effect by the formation of silicate secondary minerals, which mainly tend to preferentially take up heavy Mg isotopes, driving rivers waters isotopically lighter (Tipper et al, 2006a(Tipper et al, , 2008(Tipper et al, , 2012aBrenot et al, 2008;Pogge von Strandmann et al, 2008Huang et al, 2012;Lee et al, 2014;Opfergelt et al, 2014;Chapela Lara et al, 2017). Plants also fractionate Mg isotopes with a variable fractionation direction, although with a general enrichment in heavy isotopes (Black et al, 2006;Bolou-Bi et al, 2010.…”

Section: Riverine Magnesiummentioning

confidence: 99%

“…Magnesium is an element directly involved in the carbon cycle, via weathering of Mg-silicates, precipitation of Mgrich carbonates (both dolomites and high-Mg calcites) and the exchange of Ca for Mg at mid-ocean ridges (Holland, 2005). Therefore Mg isotopes have the potential to provide information on weathering (Tipper et al, 2006b(Tipper et al, , 2012aPogge von Strandmann et al, 2008, 2014aFoster et al, 2010;Higgins and Schrag, 2010;Teng et al, 2010;Opfergelt et al, 2014;Chapela Lara et al, 2017). However, the study of global rivers has revealed a large range in dissolved Mg isotope ratios (Tipper et al, 2006a(Tipper et al, , 2008(Tipper et al, , 2010(Tipper et al, , 2012aBrenot et al, 2008;Pogge von Strandmann et al, 2008Wimpenny et al, 2011;Huang et al, 2012;Liu et al, 2014;Teng, 2017;Oelkers et al, 2019a), and it has become clear that, like all major elements, Mg and its isotopes are affected by a wide range of processes.…”

Section: Introductionmentioning

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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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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“…Research on the δ 26 Mg values of mineral separates has demonstrated variation in δ 26 Mg values which in some cases overlaps with the δ 26 Mg range in carbonate rocks (−5.57 to −0.38 , Teng, 2017), e.g., biotite (−0.40 to +0.44 , Shen et al, 2009;Ryu et al, 2011), chlorite (−1.82 to +0. 40 , Ryu et al, 2011;Pogge von Strandmann et al, 2015;Chapela Lara et al, 2017), clinopyroxene (−0.62 to +0.43 , Pogge von Strandmann et al, 2011;Wang et al, 2012Wang et al, , 2014Hu et al, 2016;Li et al, 2016;Chen et al, 2018;Stracke et al, 2018), and garnet (−1.96 to −0.37 , Wang et al, 2012Wang et al, , 2014Pogge von Strandmann et al, 2015;Hu et al, 2016;Li et al, 2016;Stracke et al, 2018). Within single rock samples, resolvable variation has also been observed e.g., 1.5 between chlorite and hornblende in granite (Ryu et al, 2011).…”

Section: Introductionmentioning

confidence: 98%

“…Within single rock samples, resolvable variation has also been observed e.g., 1.5 between chlorite and hornblende in granite (Ryu et al, 2011). This silicate mineral source variation in δ 26 Mg has only recently begun to be acknowledged as a source of variation in river δ 26 Mg values (Chapela Lara et al, 2017;Kimmig et al, 2018). Given that recent studies of chemical weathering in the Kangerlussuaq area of West Greenland have stressed the role of silicate weathering (Wimpenny et al, 2011;Andrews and Jacobson, 2018), we wanted to test whether silicate mineral variation in δ 26 Mg values could also account for low δ 26 Mg values in river samples from this area.…”

Section: Introductionmentioning

confidence: 99%

Mg and Li Stable Isotope Ratios of Rocks, Minerals, and Water in an Outlet Glacier of the Greenland Ice Sheet

2019

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Magnesium and lithium stable isotope ratios (δ 26 Mg and δ 7 Li) have shown promise as tools to elucidate biogeochemical processes both at catchment scales and in deciphering global climate processes. Nevertheless, the controls on riverine Mg and Li isotope ratios are often difficult to determine as a myriad of factors can cause fractionation from bulk rock values such as secondary mineral formation and preferential weathering of isotopically distinct mineral phases. Quantifying the relative contribution from carbonate and silicate minerals to the dissolved load of glacierized catchments is particularly crucial for determining the role of chemical weathering in modulating the carbon cycle over glacial-interglacial periods. In this study we report Mg and Li isotope data for water, river sediment, rock, and mineral separates from the Leverett Glacier catchment, West Greenland. We assess whether the silicate mineral contributions to the dissolved load, previously determined using radiogenic Sr, Ca, Nd, and Hf isotopes, are consistent with dissolved Mg and Li isotope data, or whether a carbonate contribution is required as inferred previously for this region. For δ 7 Li, the average dissolved river water value (+19.2 ± 2.5 , 2SD) was higher than bedrock, river sediment, and mineral δ 7 Li values, implying a fractionation process. For δ 26 Mg, the average dissolved river water value (−0.30 ± 0.14 , 2SD) was within error of bedrock and river sediment and within the range of mineral δ 26 Mg values (−1.63 to +0.06). The river δ 26 Mg values are consistent with the mixing of Mg derived from the same mineral phases previously identified from radiogenic isotope measurements as controlling the dissolved load chemistry. Glacier fed rivers previously measured in this region had δ 26 Mg values ∼0.80 lower than those measured in the Leverett River which could be caused by a larger contribution from garnet (−1.63) dissolution compared to Leverett. This study highlights that dissolved Mg and Li isotope ratios in the Leverett River are affected by different processes (mixing and fractionation), and that since variations in silicate mineral δ 26 Mg values exist, preferential weathering of individual silicate minerals should be considered in addition to carbonate when interpreting dissolved δ 26 Mg values.

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The influence of critical zone processes on the Mg isotope budget in a tropical, highly weathered andesitic catchment

Cited by 56 publications

References 114 publications

Mg Isotope Interlaboratory Comparison of Reference Materials from Earth‐Surface Low‐Temperature Environments

Mg Isotope Interlaboratory Comparison of Reference Materials from Earth‐Surface Low‐Temperature Environments

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

Mg and Li Stable Isotope Ratios of Rocks, Minerals, and Water in an Outlet Glacier of the Greenland Ice Sheet

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