This is the first comprehensive study of the relationship between the ionic forms of oxygen (phosphate oxygen and structural carbonate) in archaeological human dental enamel. The new equation will allow direct comparison of data produced by the different methods and allow drinking water values to be calculated from structural carbonate data with confidence.
In this paper we present data to demonstrate the applicability of laser-ablation MC-ICP-MS isotope analysis to archaeological artefacts, in this case Roman silver coins. The technique requires no chemical preparation, does minimal damage to the sample and yields external reproducibility that is better than conventional TIMS analysis; 207 Pb/ 206 Pb = ± 0.015% 2 σ in comparison with 207 Pb / 206 Pb = ± 0.04% 2 σ , respectively. We show that Pb isotope compositions give isotope fingerprints to mints despite the likely reworking of the metal during coin production.
Abstract. The first δ 30 Si diatom data from lacustrine sediment traps are presented from Lake Baikal, Siberia. Data are compared with March surface water (upper 180 m) δ 30 Si DSi compositions for which a mean value of +2.28 ‰ ± 0.09 (95 % confidence) is derived. This value acts as the prediatom bloom baseline silicic acid isotopic composition of waters (δ 30 Si DSi initial ). Open traps were deployed along the depth of the Lake Baikal south basin water column between 2012 and 2013. Diatom assemblages display a dominance (> 85 %) of the spring/summer bloom species Synedra acus var radians, so that δ 30 Si diatom compositions reflect predominantly spring/summer bloom utilisation. Diatoms were isolated from open traps and, in addition, from 3-monthly (sequencing) traps (May, July and August 2012) for δ 30 Si diatom analyses. Mean δ 30 Si diatom values for open traps are +1.23 ‰ ± 0.06 (at 95 % confidence and MSWD of 2.9, n = 10). Total dry mass sediment fluxes are highest in June 2012, which we attribute to the initial export of the dominant spring diatom bloom. We therefore argue that May δ 30 Si diatom signatures (+0.67 ‰ ± 0.06, 2σ ) when compared with mean upper water δ 30 Si DSi initial (e.g. prebloom) signatures can be used to provide a snapshot estimation of diatom uptake fractionation factors ( uptake ) in Lake Baikal. A uptake estimation of −1.61 ‰ is therefore derived, although we emphasise that synchronous monthly δ 30 Si DSi and δ 30 Si diatom data would be needed to provide more robust estimations and therefore more rigorously test this, particularly when taking into consideration any progressive enrichment of the DSi pool as blooms persist. The nearconstant δ 30 Si diatom composition in open traps demonstrates the full preservation of the signal through the water column and thereby justifies the use and application of the technique in biogeochemical and palaeoenvironmental research. Data are finally compared with lake sediment core samples, collected from the south basin. Values of +1.30 ‰ ± 0.08 (2σ ) and +1.43 ‰ ± 0.13 (2σ ) were derived for cores BAIK13-1C (0.6-0.8 cm core depth) and at BAIK13-4F (0.2-0.4 cm core depth) respectively. Trap data highlight the absence of a fractionation factor associated with diatom dissolution ( dissolution ) (particularly as Synedra acus var radians, the dominant taxa in the traps, is very susceptible to dissolution) down the water column and in the lake surface sediments, thus validating the application of δ 30 Si diatom analyses in Lake Baikal and other freshwater systems, in palaeoreconstructions.
Seasonal variations in hydrology and Si cycling in the Nile Basin were investigated using stable-isotope (H, O, and Si) compositions and dissolved Si (DSi) concentrations of surface waters, as a basis for interpreting lacustrine diatom sequences. δ
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