Mg isotope fractionation during calcite precipitation: An experimental study

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

“…A similar range of fractionation (2.2%-2.7%) of LMC has been determined in the laboratory (Li et al 2012), but slightly different values have been obtained from a speleothem study (1.63%-2.24%) (Immenhauser et al 2010) and from another laboratory synthesis experiment (1.9%-3.2%) (Saulnier et al 2012). (2018) 37(1):1-18 11 The latter work also demonstrated that D inorg of LMC is sensitive to precipitation rate (Saulnier et al 2012). D inorg of aragonite precipitation is temperature-dependent, and is significantly smaller than that of calcite precipitation (0.95 at 25°C) .…”

“…Mg isotopic fractionation in inorganic carbonate precipitation (D inorg ) has been extensively studied (Galy et al 2002;Immenhauser et al 2010;Li et al 2012;Saulnier et al 2012;Wang et al 2013) and experimental studies indicate that D inorg of HMC is insensitive to temperature, pH, and Mg/ Ca of solutions, and ranges from 2.2% to 2.7% (Li et al 2012;Saulnier et al 2012). A similar range of fractionation (2.2%-2.7%) of LMC has been determined in the laboratory (Li et al 2012), but slightly different values have been obtained from a speleothem study (1.63%-2.24%) (Immenhauser et al 2010) and from another laboratory synthesis experiment (1.9%-3.2%) (Saulnier et al 2012). (2018) 37(1):1-18 11 The latter work also demonstrated that D inorg of LMC is sensitive to precipitation rate (Saulnier et al 2012).…”

“…Low-temperature hydrothermal reactions preferentially remove 26 Mg from seawater with limited fractionation (\0.7%) (Higgins and Schrag 2015). In contrast, carbonate precipitation significantly fractionates Mg (up to 5%) by preferential utilization of 24 Mg (Galy et al 2002;Higgins and Schrag 2010;Immenhauser et al 2010;Wombacher et al 2011;Li et al 2012;Saulnier et al 2012). For the above reasons, an increase in the size of the carbonate sink would result in higher seawater Mg isotopic composition (d 26 Mg sw ), while enhanced hydrothermal activities would shift d 26 Mg sw in the opposite direction (Tipper et al 2006b).…”

Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

“…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.…”

“…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).…”