Hydrogeochemistry and fractionation pathways of Mg isotopes in a continental weathering system: Lessons from field experiments

Riechelmann, Sylvia; Buhl, Dieter; Schröder‐Ritzrau, Andrea; Spötl, Christoph; Riechelmann, Dana F. C.; Richter, Detlev K.; Kluge, Tobias; Marx, Thomas; Immenhauser, Adrian

doi:10.1016/j.chemgeo.2012.01.025

Cited by 42 publications

(45 citation statements)

References 43 publications

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“…snow is 26 Mgdepleted compared to rain (Tipper et al, 2010;Riechelmann et al, 2012b), but the existing data set is perhaps too limited to draw solid conclusions. Tipper et al (2012) stated that the input of Mg from the rainwater (dust and aerosols) Fig.…”

Section: Environmental Equilibrium and Disequilibrium Factors Affectmentioning

confidence: 99%

“…Biological Mg isotope fractionation by plants and soil microorganisms affects the Mg-isotope composition of the soil water in variable degrees depending on the amount of Mg involved and plant and microbial metabolism (Tipper et al, 2010;Riechelmann et al, 2012b). Clearly, under warmer and wetter conditions, soil activity is increased (Harper et al, 2005) and enhanced plant growth induces a stronger biological fractionation.…”

Section: Environmental Equilibrium and Disequilibrium Factors Affectmentioning

confidence: 99%

“…Environmental, equilibrium and disequilibrium factors affecting Mg isotope fractionation in Earth surface systems have been described in Galy et al (2002), Young andGaly (2004), de Villiers et al (2005), Tipper et al (2006bTipper et al ( , 2008Tipper et al ( , 2010, Buhl et al (2007), Brenot et al (2008), Immenhauser et al (2010), Pokrovsky et al (2011) and Riechelmann et al (2012b). Considering the published work, the following parameters are of significance for the interpretation of speleothem δ 26 Mg time-series: (i) δ 26 Mg signature of all involved Mg sources -rainwater, soil cover (silicates) and host rock (limestone or dolostone); (ii) the biogenic activity of the soil zone controlled mainly by water availability and air temperature; (iii) the balance between the silicate (Mgbearing clay minerals) and carbonate weathering ratio in the soil zone.…”

Section: Environmental Equilibrium and Disequilibrium Factors Affectmentioning

confidence: 99%

“…The same trend was observed for 26 Mg-depleted cave drip water compared to soil water. In summary of these considerations, it was suggested that carbonate versus silicate weathering ratios are recorded in the speleothem Mg isotope record (Riechelmann et al, 2012b).…”

Section: Environmental Equilibrium and Disequilibrium Factors Affectmentioning

confidence: 99%

“…Previous work dealing with Mg isotope fractionation in Earth surface environments includes investigations from carbonate archives and field and laboratory precipitation experiments. Data available in the literature include δ 26 Mg values from rain, snow, riverine, soil and drip water as well as host rock and cave carbonates and soil and cave silicate data (Galy et al, 2002;Young and Galy, 2004;de Villiers et al, 2005;Tipper et al, 2006bTipper et al, , 2008Tipper et al, , 2010Buhl et al, 2007;Brenot et al, 2008;Immenhauser et al, 2010;Pokrovsky et al, 2011;Riechelmann et al, 2012b). Nevertheless, with the exception of the preliminary work shown in Buhl et al (2007), a critical application of the above-cited work to speleothem time series is lacking.…”

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confidence: 99%

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The magnesium isotope record of cave carbonate archives

et al. 2012

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Abstract.Here we explore the potential of magnesium (δ 26 Mg) isotope time-series data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semiarid to arid (Morocco), the warm-temperate (Germany), the equatorial-humid (Peru) and the cold-humid (Austria) climate zones. Changes in the calcite magnesium isotope signature with time are compared against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a number of environmental, equilibrium and disequilibrium processes governs the δ 26 Mg fractionation in continental settings. These include the different sources of magnesium isotopes such as rainwater or snow as well as soil and host rock, soil zone biogenic activity, shifts in silicate versus carbonate weathering ratios and residence time of water in the soil and karst zone. Pleistocene stalagmites from Morocco show the lowest mean δ 26 Mg values (GDA: −4.26 ± 0.07 ‰ and HK3: −4.17 ± 0.15 ‰), and the data are well explained in terms of changes in aridity over time. The Pleistocene to Holocene stalagmites from Peru show the highest mean value of all stalagmites (NC-A and NC-B δ 26 Mg: −3.96 ± 0.04 ‰) but only minor variations in Mg-isotope composition, which is consistent with the rather stable equatorial climate at this site. Holocene stalagmites from Germany (AH-1 mean δ 26 Mg: −4.01 ± 0.07 ‰; BU 4 mean δ 26 Mg: −4.20 ± 0.10 ‰) suggest changes in outside air temperature was the principal driver rather than rainfall amount. The alpine Pleistocene flowstones from Austria (SPA 52: −3.00 ± 0.73 ‰; SPA 59: −3.70 ± 0.43 ‰) are affected by glacial versus interglacial climate change with outside air temperature affecting soil zone activity and weathering balance. Several δ 26 Mg values of the Austrian and two δ 26 Mg values of the German speleothems are shifted to higher values due to sampling in detrital layers (Mg-bearing clay minerals) of the speleothems. The data and their interpretation shown here highlight the potential but also the limitations of the magnesium isotope proxy applied in continental climate research. An obvious potential lies in its sensitivity for even subtle changes in soil-zone parameters, a hitherto rather poorly understood but extremely important component in cave archive research. Limitations are most obvious in the low resolution and high sample amount needed for analysis. Future research should focus on experimental and conceptual aspects including quantitative and well-calibrated leaching and precipitation experiments.

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Section: Environmental Equilibrium and Disequilibrium Factors Affectmentioning

confidence: 99%

Section: Environmental Equilibrium and Disequilibrium Factors Affectmentioning

confidence: 99%

Section: Environmental Equilibrium and Disequilibrium Factors Affectmentioning

confidence: 99%

Section: Environmental Equilibrium and Disequilibrium Factors Affectmentioning

confidence: 99%

mentioning

confidence: 99%

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The magnesium isotope record of cave carbonate archives

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Limited magnesium isotope fractionation during metamorphic dehydration in metapelites from the Onawa contact aureole, Maine

Teng

Wing

et al. 2014

Geochem Geophys Geosyst

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Knowledge on the behavior of Mg isotopes during metamorphic dehydration is the prerequisite for applying Mg isotopes as tracers for crustal recycling. Here we report Mg isotopic compositions of metapelites from the Onawa contact aureole, Maine. Except one sample, all metapelites across the aureole, from the wall-rock regional metamorphic rocks to the partially melted rocks adjacent to the pluton, have similar Mg isotopic compositions (d 26 Mg 5 20.09 to 10.12&). This observation indicates limited Mg isotope fractionation during metamorphic dehydration and fluid-rock interaction, due to the low Mg concentration in fluids relative to rocks. Our results suggest that Mg isotopic compositions of metapelites can record those of their protoliths and, hence, recycled clastic sedimentary materials may preserve their low-temperature Mg isotopic signatures through subduction zones. Therefore, Mg isotopes may serve as new tracers for crustal recycling, for example, tracing components experienced weathering cycles within granite sources.

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