Towards a better understanding of magnesium-isotope ratios from marine skeletal carbonates

Hippler, Dorothee; Buhl, Dieter; Witbaard, Rob; Richter, Detlev K.; Immenhauser, Adrian

doi:10.1016/j.gca.2009.07.031

Cited by 109 publications

(78 citation statements)

References 58 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%

“…The importance of Mg in biogeochemical cycles, and the $8% mass difference between 24 Mg and 26 Mg suggest that Mg isotopes are potentially useful for resolving natural carbonate precipitation mechanisms. The potential for magnesium isotope fractionation in carbonate minerals has been recently documented for Mgbearing carbonates (Chang et al, 2004;Buhl et al, 2007;Hippler et al, 2009). The degree to which microbes may influence this fractionation has yet to be investigated quantitatively.…”

Section: Introductionmentioning

confidence: 99%

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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%

Section: Introductionmentioning

confidence: 99%

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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“…It seems likely, however, that the processes that dramatically reduce the Mg concentrations of foraminiferal tests relative to inorganic calcite are the same that drive the Mg isotope composition of the tests significantly lighter than inorganic calcite. Given that the Mg isotope ratio of seawater is well known (−0.82 ± 0.06 ‰, Foster et al, 2010), and that the thermodynamics and fractionation during the precipitation of inorganic carbonate is reasonably well constrained ( 26 Mg ∼ 2.6 ‰ at 20 • C, Busenberg and Plummer, 1989;Mucci, 1987;Galy et al, 2002;Pogge von Strandmann, 2008;Wombacher et al, 2011;Hippler et al, 2009;Immenhauser et al, 2010), other effects must account for a 26 Mg foram-inorg cc of −0.55 to −2.1 ‰ , which is the isotopic difference between inorganic calcite precipitated from seawater (at a given temperature) and the value measured in the foraminiferal tests.…”

Section: Mg Incorporation In Foraminifera -A Window Into Biomineralismentioning

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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“…fossil skeletons), precipitation from inorganic seawater, or induced precipitation by calcified bacteria (Riding 1991;Kaźmierczak et al 1996). Because Mg isotope fractionation for inorganic carbonate precipitation is mineralogy dependent (Li et al 2012;Saulnier et al 2012;Wang et al 2013) and biogenic carbonate formation has a significant vital effect (Pogge von Strandmann 2008;Hippler et al 2009;Immenhauser et al 2010) (Fig. 9), the isotopic composition of micrite might be highly variable and source-dependent.…”

Section: The Micrite Componentmentioning

confidence: 99%

“…In the Huangjin Formation, brachiopods and Rugosa corals are the two dominant carbonate-secreting fossil groups. In calculations, D brachiopod bc and D coral bc are set to 1.2% and 2.6%, respectively, (Pogge von Strandmann 2008;Hippler et al 2009;Wombacher et al 2011;Yoshimura et al 2011), which allows D bc to have a similar range of variation. Further assuming that biogenic carbonate formation accounts for 7% (f bc = 0.07) of the Mg sink in seawater, change from a brachiopoddominant fauna to a Rugosa-dominant fauna would result in *0.1% increase in d 26 Mg sw .…”

Section: The Micrite Componentmentioning

confidence: 99%

Heterogeneous Mg isotopic composition of the early Carboniferous limestone: implications for carbonate as a seawater archive

Huang

et al. 2017

Acta Geochim

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Carbonate precipitation and hydrothermal reaction are the two major processes that remove Mg from seawater. Mg isotopes are significantly (up (1) micrite samples ranged from -2.86% to -2.97%; (2) pure marine cements varied from -3.40% to -3.54%, while impure cement samples containing small amount of Rugosa coral skeletons showed a wider range (-3.27% to -3.75%); (3) values for the mixture component were -3.17% and -3.49%; and (4) 26 Mg sw was only slightly affected by the faunal composition of carbonate-secreting organisms, even though biogenic carbonate accounts for more than 90% of marine carbonate production in Phanerozoic oceans and there is a wide range (0.2%-4.8%) of fractionation during biogenic carbonate formation.

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Towards a better understanding of magnesium-isotope ratios from marine skeletal carbonates

Cited by 109 publications

References 58 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

Heterogeneous Mg isotopic composition of the early Carboniferous limestone: implications for carbonate as a seawater archive

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