The cation-exchange purification technique used here does not remove anions (in our case, mostly Cl-, SO 4 2-and to a lesser extent NO 3-) from solutions. In this case, the addition of a known artificial matrix in excess in both the sample and standard solution can be used to dilute the natural concentration of the contaminant and to homogenize sample and standard matrices (doping method, Georg et al., 2006; Hughes et al., 2011). Indeed, dissimilar matrices will affect differently the plasma and ionization efficiency and will induce artificial bias in the delta measurements, invalidating the use of the standard-sample bracketing technique. In our samples, Cl-originating from seawater can be neglected compared to Cladded as HCl (Merck Suprapur) to dissolve the brucite; and as solutions were analyzed in a HCl matrix largely in excess (up to 0.5 mol L-1) compared to natural Cl-concentration. Similarly, the occurrence of NO 3-in seawater was resolved by the use of HNO 3 (Merck Suprapur, 0.5 mol L-1) as a solvent in both the samples and standards. For Depth Depth (m) (m)

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.

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shown previously to be a strong proxy for regional water balance. After a dry period (i.e.

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