Magnesium stable isotope fractionation in marine biogenic calcite and aragonite

Wombacher, Frank; Eisenhauer, Anton; Böhm, Florian; Gussone, Nikolaus; Regenberg, Marcus; Dullo, Wolf-Christian; Rüggeberg, Andres

doi:10.1016/j.gca.2011.07.017

Cited by 166 publications

(176 citation statements)

References 147 publications

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“…This demonstrates that lighter Mg isotopes are preferentially incorporated into the solid phase. This observation is coherent with the results of previous studies on Mg isotope fractionation between aqueous fluids and biogenic skeletal carbonates (Chang et al, 2004;Buhl et al, 2007;Hippler et al, 2009;Wombacher et al, 2011), abiotically precipitated low Mg-calcite (Galy et al, 2002;Immenhauser et al, 2010), dolomite (Higgins and Schrag, 2010;Pokrovsky et al, 2011), and magnesite (Pearce et al, 2009;Mavromatis et al, 2011). The origin of the Mg isotope fractionation likely stems from the change in Mg coordination, symmetry, and bond distances in the reaction forming the mineral from the aqueous fluid.…”

Section: Magnesium Isotope Fractionation Between Minerals and Reactivsupporting

confidence: 91%

Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria

Mavromatis

Pearce

Shirokova

et al. 2012

Geochimica et Cosmochimica Acta

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How to cite:Mavromatis, Vasileios; Pearce, Christopher R.; Shirokova, Liudmila S.; Bundeleva, Irina A.; Pokrovsky, Oleg S.; Benezeth, Pascale and Oelkers, Eric H. (2012) AbstractThe hydrous magnesium carbonates, nesquehonite (MgCO 3 Á3H 2 O) and dypingite (Mg 5 (CO 3 ) 4 (OH) 2 Á5(H 2 O)), were precipitated at 25°C in batch reactors from aqueous solutions containing 0.05 M NaHCO 3 and 0.025 M MgCl 2 and in the presence and absence of live photosynthesizing Gloeocapsa sp. cyanobacteria. Experiments were performed under a variety of conditions; the reactive fluid/bacteria/mineral suspensions were continuously stirred, and/or air bubbled in most experiments, and exposed to various durations of light exposure. Bulk precipitation rates are not affected by the presence of bacteria although the solution pH and the degree of fluid supersaturation with respect to magnesium carbonates increase due to photosynthesis. Lighter Mg isotopes are preferentially incorporated into the precipitated solids in all experiments. Mg isotope fractionation between the mineral and fluid in the abiotic experiments is identical, within uncertainty, to that measured in cyanobacteriabearing experiments; measured d 26 Mg ranges from À1.54& to À1.16& in all experiments. Mg isotope fractionation is also found to be independent of reactive solution pH and Mg, CO 3 2À , and biomass concentrations. Taken together, these observations suggest that Gloeocapsa sp. cyanobacterium does not appreciably affect magnesium isotope fractionation between aqueous fluid and hydrous magnesium carbonates.

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Section: Magnesium Isotope Fractionation Between Minerals and Reactivsupporting

confidence: 91%

Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria

Mavromatis

Pearce

Shirokova

et al. 2012

Geochimica et Cosmochimica Acta

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“…Despite this strong biomineralisation control, due to temperature-dependent uptake during calcification, Mg in foraminifers is a proxy for palaeotemperatures (Anand et al, 2003;Elderfield and Ganssen, 2000;Nürnberg et al, 1996;Martinez-Boti et al, 2011;Lear et al, 2000). Foraminifera discriminate against heavy Mg isotopes, with foraminiferal carbonate being over 5 ‰ lighter than seawater, and ∼ 2.5 ‰ lighter than inorganic carbonate (Chang et al, 2004;Pogge von Strandmann, 2008;Wombacher et al, 2011;Li et al, 2012;Saulnier et al, 2012;Yoshimura et al, 2011;Saenger and Wang, 2014). There is significant species-specific fractionation (Pogge von Strandmann, 2008;Wombacher et al, 2011;Chang et al, 2004), although the causes of this fractionation are not yet understood.…”

Section: Introductionmentioning

confidence: 99%

“…Foraminifera discriminate against heavy Mg isotopes, with foraminiferal carbonate being over 5 ‰ lighter than seawater, and ∼ 2.5 ‰ lighter than inorganic carbonate (Chang et al, 2004;Pogge von Strandmann, 2008;Wombacher et al, 2011;Li et al, 2012;Saulnier et al, 2012;Yoshimura et al, 2011;Saenger and Wang, 2014). There is significant species-specific fractionation (Pogge von Strandmann, 2008;Wombacher et al, 2011;Chang et al, 2004), although the causes of this fractionation are not yet understood.…”

Section: Introductionmentioning

confidence: 99%

“…Fractionation is also not thought to be influenced by the size or existence of an internally controlled calcium pool, or by kinetic fractionation during aqueous transport (Pogge von Strandmann, 2008;Richter et al, 2006;Wombacher et al, 2011). The effect of temperature, though, is less well constrained, as there are contrasting reports as to whether Mg isotope fractionation during uptake into carbonates is temperature dependent.…”

Section: Introductionmentioning

confidence: 99%

“…The effect of temperature, though, is less well constrained, as there are contrasting reports as to whether Mg isotope fractionation during uptake into carbonates is temperature dependent. Some studies report a weak temperature dependence in high-Mg and inorganic calcite (Wombacher et al, 2011;Li et al, 2012;Yoshimura et al, 2011), while analysis of biogenic low-Mg calcite have no reported temperature-dependant fractionation over a temperature range of 5-35 • C (Saulnier et al, 2012;Pogge von Strandmann, 2008;Chang et al, 2004;Wombacher et al, 2011;Saenger and Wang, 2014).…”

Section: Introductionmentioning

confidence: 99%

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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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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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Magnesium stable isotope fractionation in marine biogenic calcite and aragonite

Cited by 166 publications

References 147 publications

Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria

Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria

Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

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

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