Magnesium-isotope fractionation during low-Mg calcite precipitation in a limestone cave – Field study and experiments

摘要: Abstract The chemical and isotopic composition of speleothem calcite particularly that stalagmites flowstones is increasingly exploited as an archive past environmental change in continental settings. Despite intensive research, including modelling novel approaches, data remain difficult to interpret. A possible way foreword apply a multi-proxy approach non-conventional isotope systems. For the first time, we here present complete analytical dataset magnesium isotopes (δ 26 Mg) from monitored cave NW Germany (Bunker Cave). set includes δ Mg values loess-derived soil above (−1.0 ± 0.5‰), water (−1.2 ± 0.5‰), carbonate hostrock (−3.8 ± 0.5‰), dripwater (−1.8 ± 0.2‰), low-Mg (stalactites, stalagmites; −4.3 ± 0.6‰), loam (−0.6 ± 0.1‰) runoff (−1.8 ± 0.1‰) cave, respectively. Magnesium-isotope fractionation processes during weathering interaction between cover, solute-bearing are non-trivial depend on number variables solution residence times, dissolution rates, adsorption effects potential neo-formation solids regolith aquifer. Apparent Mg-isotope about 1000ln α Mg-cc-Mg(aq)  = −2.4‰. similar (1000ln  ≈ −2.1‰) obtained by abiogenic precipitation experiments carried out at aqueous Mg/Ca ratios temperatures close conditions. Accordingly, discrimination formation caves highly related inorganic effects, which may comprise dehydration 2+ prior incorporation into calcite, surface entrapment light reaction kinetics. Relevance kinetics supported significant negative correlation with rate for experiments.