Effects of biogeochemical processes on magnesium isotope variations in a forested catchment in the Vosges Mountains (France)

Bolou‐Bi, Emile B.; Vigier, Nathalie; Poszwa, Anne; Boudot, Jean‐Pierre; Dambrine, Étienne

doi:10.1016/j.gca.2012.04.005

Cited by 109 publications

(126 citation statements)

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“…Thus, at the scale of a single plant, potentially different dietary sources with distinct δ 26 Mg values exist. In La Lopé, the analyzed plants fall in the δ 26 Mg range seen in other ecosystems (15,23,24) and cover the spectrum of values for mammal tooth enamel δ 26 Mg (below). Fruits, seeds, and roots are major constituents of the diet of many mammals (below).…”

Section: Discussionmentioning

confidence: 99%

“…Purified apatite and plant samples were diluted in 2% HNO 3 to a concentration of 100 ppb. Measurements were conducted at low resolution and each analysis consisted of 20 4-s integrations of the 24 Mg, 25 Mg, and 26 Mg signals in static mode. Each analysis was preceded by a measurement of blank 2% HNO 3 , and the signals for this background were subtracted from the analyte signal before calculation of isotope ratios.…”

Section: Fecesmentioning

confidence: 99%

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Magnesium stable isotope ecology using mammal tooth enamel

Martin

Vance

Balter

2014

Proc. Natl. Acad. Sci. U.S.A.

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Geochemical inferences on ancient diet using bone and enamel apatite rely mainly on carbon isotope ratios (δ 13 C) and to a lesser extent on strontium/calcium (Sr/Ca) and barium/calcium (Ba/Ca) elemental ratios. Recent developments in nontraditional stable isotopes provide an unprecedented opportunity to use additional paleodietary proxies to disentangle complex diets such as omnivory. Of particular relevance for paleodietary reconstruction are metals present in large quantity in bone and enamel apatite, providing that biologically mediated fractionation processes are constrained. Calcium isotope ratios (δ 44 Ca) meet these criteria but exhibit complex ecological patterning. Stable magnesium isotope ratios (δ 26 Mg) also meet these criteria but a comprehensive understanding of its variability awaits new isotopic data. Here, 11 extant mammal species of known ecology from a single locality in equatorial Africa were sampled for tooth enamel and, together with vegetation and feces, analyzed for δ 26 Mg, δ 13 C, Sr/Ca, and Ba/Ca ratios. The results demonstrate that δ 26 Mg incorporated in tooth enamel becomes heavier from strict herbivores to omnivores/faunivores. Using data from experimentally raised sheep, we suggest that this 26 Mg enrichment up the trophic chain is due to a 26 Mg enrichment in muscle relative to bone. Notably, it is possible to distinguish omnivores from herbivores, using δ 26 Mg coupled to Ba/Ca ratios. The potential effects of metabolic and dietary changes on the enamel δ 26 Mg composition remain to be explored but, in the future, multiproxy approaches would permit a substantial refinement of dietary behaviors or enable accurate trophic reconstruction despite specimen-limited sampling, as is often the case for fossil assemblages.stable isotopes | magnesium | carbon | equatorial mammals | paleoecology R econstructing the diet of extinct vertebrates is a challenging task, especially when direct evidence such as stomach contents or feeding traces is lacking. Geochemical studies using the 13 C/ 12 C ratio, the strontium/calcium (Sr/Ca) ratio, and the barium/calcium (Ba/Ca) ratio of the mineral fraction of the skeleton, bone, and enamel apatite have proved as useful as other methodologies, such as morphofunctional and microwear analyses (e.g., refs.

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Section: Discussionmentioning

confidence: 99%

Section: Fecesmentioning

confidence: 99%

Magnesium stable isotope ecology using mammal tooth enamel

Martin

Vance

Balter

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…The exchangeable Mg fraction of soil and saprolite samples was obtained by a 1 M NH 4 OAc extraction (Arunachalam et al, 1996). This procedure was specifically tested for Mg isotope measurements (Bolou-Bi et al, 2012). After extraction, the residual solids were analysed after HF/HNO 3 total digestion.…”

Section: Mg Isotope Analyses By Mc-icp-msmentioning

confidence: 99%

“…Unless the formation of secondary minerals is significant (Wimpenny et al, 2014), the main shift affecting the 26 Mg / 24 Mg ratio in weathering systems is the isotopic fractionation towards high ratios during nutrient uptake by plants (Black et al, 2008;Bolou-Bi et al, 2012;Mavromatis et al, 2014), such that the residual dissolved Mg is shifted towards the complementary low ratio. These two isotopically distinct compartments will remain separated if a fraction of the Mg accumulates in wood of a regrowing forest after clear cutting or if a fraction of the Mg is eroded after utilisation and is not released back into solution.…”

Section: Introductionmentioning

confidence: 99%

Quantifying nutrient uptake as driver of rock weathering in forest ecosystems by magnesium stable isotopes

et al. 2017

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Abstract. Plants and soil microbiota play an active role in rock weathering and potentially couple weathering at depth with erosion at the soil surface. The nature of this coupling is still unresolved because we lacked means to quantify the passage of chemical elements from rock through higher plants. In a temperate forested landscape characterised by relatively fast ( ∼ 220 t km −2 yr −1 ) denudation and a kinetically limited weathering regime of the Southern Sierra Critical Zone Observatory (SSCZO), California, we measured magnesium (Mg) stable isotopes that are sensitive indicators of Mg utilisation by biota. We find that Mg is highly bio-utilised: 50-100 % of the Mg released by chemical weathering is taken up by forest trees. To estimate the tree uptake of other bioutilised elements (K, Ca, P and Si) we compared the dissolved fluxes of these elements and Mg in rivers with their solubilisation fluxes from rock (rock dissolution flux minus secondary mineral formation flux). We find a deficit in the dissolved fluxes throughout, which we attribute to the nutrient uptake by forest trees. Therefore both the Mg isotopes and the flux comparison suggest that a substantial part of the major element weathering flux is consumed by the tree biomass. The enrichment of 26 Mg over 24 Mg in tree trunks relative to leaves suggests that tree trunks account for a substantial fraction of the net uptake of Mg. This isotopic and elemental compartment separation is prevented from obliteration (which would occur by Mg redissolution) by two potential effects. Either the mineral nutrients accumulate today in regrowing forest biomass after clear cutting, or they are exported in litter and coarse woody debris (CWD) such that they remain in "solid" biomass. Over pre-forest-management weathering timescales, this removal flux might have been in operation in the form of natural erosion of CWD. Regardless of the removal mechanism, our approach provides entirely novel means towards the direct quantification of biogenic uptake following weathering. We find that Mg and other nutrients and the plant-beneficial element Si ("bio-elements") are taken up by trees at up to 6 m depth, and surface recycling of all bio-elements but P is minimal. Thus, in the watersheds of the SSCZO, the coupling between erosion and weathering might be established by bio-elements that are taken up by trees, are not recycled and are missing in the dissolved river flux due to erosion as CWD and as leaf-derived bio-opal for Si. We suggest that the partitioning of a biogenic weathering flux into eroded plant debris might represent a significant global contribution to element export after weathering in eroding mountain catchments that are characterised by a continuous supply of fresh mineral nutrients.

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“…The flux-weighted mean riverine input has a δ 26 Mg (‰ deviation of the sample 26 Mg / 24 Mg ratio from the standard DSM-3) of −1.09 ± 0.05 ‰ that is intermediate between that of silicate and carbonate sources. Additional fractionation is caused by Mg uptake into plants, or into secondary minerals formed during weathering (Tipper et al, 2010(Tipper et al, , 2006a(Tipper et al, , b, 2008Pogge von Strandmann et al, 2008Teng et al, 2010a, b;Huang et al, 2012;Black et al, 2006;Bolou-Bi et al, 2012. Modern oceans, which are isotopically uniform (Foster et al, 2010;Young and Galy, 2004), have an isotope ratio (−0.83 ± 0.01 ‰) close to the riverine input.…”

Section: Introductionmentioning

confidence: 99%

Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

2014

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Abstract. Magnesium is an element critically involved in the carbon cycle, because weathering of Ca-Mg silicates removes atmospheric CO 2 into rivers, and formation of Ca-Mg carbonates in the oceans removes carbon from the oceanatmosphere system. Hence the Mg cycle holds the potential to provide valuable insights into Cenozoic climate-system history, and the shift during this time from a greenhouse to icehouse state. We present Mg isotope ratios for the past 40 Myr using planktic foraminifers as an archive. Modern foraminifera, which discriminate against elemental and isotopically heavy Mg during calcification, show no correlation between the Mg isotope composition (δ 26 Mg, relative to DSM-3) and temperature, Mg / Ca or other parameters such as carbonate saturation ( CO 3 ). However, inter-species isotopic differences imply that only well-calibrated single species should be used for reconstruction of past seawater. Seawater δ 26 Mg inferred from the foraminiferal record decreased from ∼ 0 ‰ at 15 Ma, to −0.83 ‰ at the present day, which coincides with increases in seawater lithium and oxygen isotope ratios. It strongly suggests that neither Mg concentrations nor isotope ratios are at steady state in modern oceans, given its ∼ 10 Myr residence time. From these data, we have developed a dynamic box model to understand and constrain changes in Mg sources to the oceans (rivers) and Mg sinks (dolomitisation and hydrothermal alteration). Our estimates of seawater Mg concentrations through time are similar to those independently determined by pore waters and fluid inclusions. Modelling suggests that dolomite formation and the riverine Mg flux are the primary controls on the δ 26 Mg of seawater, while hydrothermal Mg removal and the δ 26 Mg of rivers are more minor controls. Using Mg riverine flux and isotope ratios inferred from the 87 Sr / 86 Sr record, the modelled Mg removal by dolomite formation shows minima in the Oligocene and at the present day (with decreasing trends from 15 Ma), both coinciding with rapid decreases in global temperatures.

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Effects of biogeochemical processes on magnesium isotope variations in a forested catchment in the Vosges Mountains (France)

Cited by 109 publications

References 44 publications

Magnesium stable isotope ecology using mammal tooth enamel

Magnesium stable isotope ecology using mammal tooth enamel

Quantifying nutrient uptake as driver of rock weathering in forest ecosystems by magnesium stable isotopes

Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

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