Buhl, D. and Immenhauser, A. and Smeulders, G. and Kabiri, L. and Richter, D.K. (2007) Time series δ26Mg analysis in speleothem calcite: Kinetic versus equilibrium fractionation, comparison with other proxies and implications for palaeoclimate research. Chemical Geology, 244 (3-4). pp. 715-729.

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Abstract

Magnesium-isotope time series MC-ICP-MS analyses from a Pleistocene speleothem - collected in a limestone cave in NW Africa (Morocco) - are reported and discussed in a process-oriented context. In addition, high-resolution C, O and Sr-isotope data, and Mg and Sr element abundances were compiled from the same stalagmite. Sub-samples were collected along the stalagmite growth axis and a second data set was drilled perpendicularly within one growth interval (Hendy test). The analytical results show clearly co-variant, systematic and cyclical fluctuations for all proxies collected along the growth axis and - with respect to the analytical error - invariant data within one growth increment. Magnesium-isotope ratios (δ26Mg) fluctuate between - 4.39‰ ± 0.02 2σ and - 4.17‰ ± 0.05 2σ and are within the range of published results of speleothem calcite from limestone caves. The difference of 0.22‰ is significantly beyond the error of the external reproducibility of ± 0.03‰ 2σ for δ26 Mg. Considering the analytical error, neither a purely kinetic nor an equilibrium fractionation process explains the observed isotope pattern. For the time being, it is suggested that two external factors drive the speleothem Mg-isotope cyclicity: (1) climate-driven (arid versus humid) variances in the precipitation rate of a carbonate phase from meteoric water within the karstic system prior to entering the cave system; and (2) changing rates of silicate (aeolian material) versus carbonate weathering. Both of these processes fractionate the Mg-isotopic composition of runoff/seepage water. There is evidence that the magnesium-isotope system, applied to speleothem archives, bears significant information concerning continental climatic variability in arid zones and deserves further research. © 2007 Elsevier B.V. All rights reserved.

Item Type: Article
Uncontrolled Keywords: calcite; inductively coupled plasma method; isotopic composition; isotopic fractionation; isotopic ratio; magnesium; mass spectrometry; paleoclimate; Pleistocene; speleothem; time series analysis, Africa; Morocco; North Africa
Subjects: Earth and Planetary Sciences
Divisions: SCIENTIFIC PRODUCTION > Earth and Planetary Sciences
Depositing User: Administrateur Eprints Administrateur Eprints
Last Modified: 31 Jan 2020 15:46
URI: http://eprints.umi.ac.ma/id/eprint/2946

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