THE delta18O OF PHOSPHATE OF ANCIENT HUMAN BIOGENIC APATITE CAN REALLY BE USED FOR QUANTITATIVE PALAEOCLIMATE RECONSTRUCTION?

It is well known that the oxygen isotope composition of phosphate apatite (δph) in mammal bones and teeth is strongly correlated to that of the drinking water (δw) ingested by the mammal itself. However, the relation between (δph) and (δw) has to be considered with caution when used for palaeoclimate reconstruction because of the uncertainty of the data. Usually, however, the authors underestimate this problem, that may led to misleading results. On the basis of the phosphate - water data existing in the literature for humans, we estimated that the prediction uncertainty for δw calculated from a new value of δph is on the order of 2.5‰. It means that only in the case the difference between two calculated δw values is higher than about 3- 4‰, the δw values may be considered significantly different. This represents a big limit which cannot be underestimated in the use of human δph for prediction of single δw values and subsequent estimation of palaeotemperature. A similar evaluation would be performed also for other mammals

Oxygen Isotope Phosphoric Acid Fractionation Factor and Uncertainty on the δ¹⁸O Measurements of Calcite

At present, the isotope ratio 18O/16O (in the text expressed as δ18O) of carbonate (CO32−) is usually determined by isotope ratio mass spectrometry measuring the CO2 gas produced dissolving the CO32−-bearing substance in concentrated H3PO4. As with any analytical data, the δ18O values of carbonate are also affected by uncertainty which must be considered mainly when data from different laboratories are compared. Usually, scientific papers report only repeatability and/or reproducibility of analytical results, which, have scarce significance for data comparison. With the aim of evaluating the overall uncertainty for new analytical data for low-Mg calcites, in this paper we reconsidered the δ18O data, which are reported in the literature. Two kinds of uncertainty must be taken into account: (1) that due to the calibration of the delta values using international standards (prediction uncertainty), (2) that due to small differences in the chemistry of low-Mg calcites. The two uncertainties must be added when comparing data produced in the same or different laboratories. We found that this overall uncertainty cannot be lower than about 0.2‰. Thus, uncertainty lower than 0.2‰, sometimes reported in the literature, is misleading

⁸⁷Sr/⁸⁶Sr Isotope Ratio as a Tool in Archaeological Investigation: Limits and Risks

During the last forty years, the use of strontium isotopes in archaeology and biogeochemical research has spread widely. These isotopes, alone or in combination with others, can contribute to trace past and present environmental conditions. However, the interpretation of the isotopic values of strontium is not always simple and requires good knowledge of geochemistry and geology. This short paper on the use of strontium isotopes is aimed at those who use this tool (archaeologists, but not only) but who do not have a thorough knowledge of mineralogy, geology, and geochemistry necessary for a good understanding of natural processes involving these isotopes. We report basic knowledge and suggestions for the correct use of these isotopes. The isotopic characteristics of bio-assimilable strontium depend not so much on the isotopic characteristics of the bulk rock as, rather, on those of its more soluble minerals. Before studying human, animal and plant remains, the state of conservation and any conditions of isotopic pollution should be carefully checked. Samples should be collected according to random sampling rules. The data should be treated by a statistical approach. To make comparisons between different areas, it should be borne in mind that the study of current soils can be misleading since the mineralogical modification of soil over time can be very rapid

Na-carbonate waters of extreme composition: possible origin and evolution

Na-carbonate (NaCW) waters are not concentrated in well defined areas, but usually widespread in areas where other water types (e.g., Ca-carbonate) are dominant. NaCW are the product of long-term water-rock interaction with dissolution of Na-silicates in presence of phyllosilicates, silica phases, and calcite. NaCW circulating in calcite-bearing sediments very probably have a Ca-carbonate parent with moderate to low PCO2, which changes its composition assuming increasing Na character as the water-rock interaction proceeds. However, the moderate to low PCO2 values of the potential parent Ca-carbonate waters do not account for the high Na content of many NaCW. The higher PCO2 required may be due to oxidation of organic matter of the sediments and, perhaps, to further addition of CO2 coming from deeper crustal levels, from the mantle, or from other sources. Na-Ca exchange involving a Na-exchanger could be an alternative genetic hypothesis. At present, however, at least for some areas (e.g., Northern Apennines, Italy), this hypothesis is not supported by mineralogical evidence. water types (e.g., Ca-carbonate) are dominant. Some analyses of different types of NaCW (mostly from Italy) are reported in Table 1 together with indications about the rocks involved in water-rock interaction. In the following pages we will focus on wa-ters of extreme composition, i.e., with na and calc higher than 0.85. In the Northern Apennines (Italy), waters with na and calc> 0.85 are wide-spread and thus, frequently, we shall implicitly refer to them. Data processing For water speciation and for other calculations we have used a recent version of PHREEQC (Parkhurst and Appelo, 1999), a flexible ad user-friendly software. The software is adequate for low ionic strength solutions (Debye-Hückel expres-sion), and suitable at higher ionic strength for so-dium chloride dominated systems. The limits o