Geochemical identity of pre-Dogon and Dogon populations at Bandiagara (Mali, 11th–20th cent. AD)

Bone geochemistry of pre-Dogon (11th–16th cent. AD) and Dogon (17th–20th cent. AD) populations buried in two caves of the Bandiagara Cliff (Mali) was examined for the purpose of exploring their diet and mobility. While the Dogon were the subject of extensive ethnographic studies, the lifestyle of the pre-Dogon, so-called “Tellem” is not known. We therefore compared the geochemical composition of Dogon bones with the results obtained from modern dietary surveys in Mali, to establish the parameters of a dietary model that was further applied to the pre-Dogon in order to expand our knowledge concerning their way of life. The exceptional preservation of the bones of both populations was confirmed not only at the macroscopic scale, but also at the mineralogical, histological and geochemical levels, which resemble those of fresh bones, and therefore offered ideal conditions for testing this approach. 15The application of the Bayesian mixing model FRUITS, based on bone δ13C (apatite and collagen) and bone δ N values, suggested a dietary continuity through time, from the 11th century to today. Bone barium (Ba) content revealed very restricted mobility within the Cliff while bone δ18O values indicated that Pre-Dogon and Dogon most likely occupied the Bandiagara Plateau and the Cliff, respectively

Couplage de la technique d'injection en flux continu avec la spectrometrie d'emission atomique a plasma induit par haute frequence (FIA/ICP-AES)

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 82368 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Determination of uranium to calcium and strontium to calcium ratios in corals by inductively coupled plasma mass spectrometry

A method has been developed to determine Ca (about 40% m/m in corals), Sr (about 1-2%) and U (3-5 microg/g) in the same aliquots. All the samples were spiked with 45Sc, 89Y and 236U. None of these isotopes are present in significant amounts in corals. The Ca and Sr were determined using two different approaches. Firstly, 45Sc and 89Y were used as spikes to measure 43Ca and 86Sr, respectively, by the isotope dilution technique (external isotope dilution). It was established that the behaviour of the various elements in the plasma varied from day to day and cannot be modelled with good accuracy (i.e., better than 1%). Therefore, a second approach was developed using 45Sc and 89Y as internal standards. This method yielded extremely good reproducibility within a run and also on a day to day basis, providing the ICP-MS instrument is properly tuned. Values for %RSD of 0.2-0.3% for Ca and Sr measurements were routinely obtained, as were calibration curves with correlation coefficients better than 0.9998. The U was determined by classic isotope dilution. Analyses on a standard solution of coral powder over 5 d yielded %RSDs of 0.25% for Sr:Ca and 0.5% for U:Ca. Accuracy was assessed using the certified reference material CCH-1 and a coral standard (NC20), which were both analysed by ICP-MS and ICP-AES. (Résumé d'auteur

Determination of uranium to calcium and strontium to calcium ratios in corals by inductively coupled plasma mass spectrometry

A method has been developed to determine Ca (about 40% m/m in corals), Sr (about 1-2%) and U (3-5 microg/g) in the same aliquots. All the samples were spiked with 45Sc, 89Y and 236U. None of these isotopes are present in significant amounts in corals. The Ca and Sr were determined using two different approaches. Firstly, 45Sc and 89Y were used as spikes to measure 43Ca and 86Sr, respectively, by the isotope dilution technique (external isotope dilution). It was established that the behaviour of the various elements in the plasma varied from day to day and cannot be modelled with good accuracy (i.e., better than 1%). Therefore, a second approach was developed using 45Sc and 89Y as internal standards. This method yielded extremely good reproducibility within a run and also on a day to day basis, providing the ICP-MS instrument is properly tuned. Values for %RSD of 0.2-0.3% for Ca and Sr measurements were routinely obtained, as were calibration curves with correlation coefficients better than 0.9998. The U was determined by classic isotope dilution. Analyses on a standard solution of coral powder over 5 d yielded %RSDs of 0.25% for Sr:Ca and 0.5% for U:Ca. Accuracy was assessed using the certified reference material CCH-1 and a coral standard (NC20), which were both analysed by ICP-MS and ICP-AES. (Résumé d'auteur

Evidence for the non-influence of salinity variability on the <i>Porites</i> coral Sr/Ca palaeothermometer

International audiencePorites coral-based sea surface temperature (SST) reconstructions are obtained from the measurement of skeleton Sr/Ca ratio. However, the influence of salinity in the incorporation of these trace elements in the Porites aragonitic skeleton is still poorly documented. Laboratory experiments indicate that in three different coral species (not including the widely used Porites genus), salinity does not influence the Sr/Ca thermometer. In this study, we test the salinity effect on Porites Sr/Ca-based SST reconstructions at monthly and interannual timescales in open-ocean environmental conditions. We use a large spatial compilation of published Porites data from the Red Sea and Pacific and Indian oceans. Additionally to those published records, we add a new eastern Pacific coral Sr/Ca record from Clipperton Atoll.Using two different salinity products (Simple Ocean Data Assimilation (SODA) SSS reanalyses version 2.2.4, Carton and Giese, 2008; and instrumental SSS from the Institut de Recherche pour le Développement, France (IRD) Delcroix et al., 2011), we find no evidence of salinity bias on the Sr/Ca SST proxy at monthly and interannual timescales. We conclude that Porites Sr/Ca is a reliable palaeothermometer that is not influenced by salinity variability

Coral barium/calcium record of mid-Holocene upwelling activity in New Caledonia, South-West Pacific

A variety of inimical factors, i.e. sea surface temperature, nutrient input, nature of substrates, were invoked previously to explain the retardation in reef settlement in New Caledonia during the Holocene. In order to clarify the respective role played by temperature and nutrient level in the growth of fringing reefs along the southwest coast of the island, trace element ratios, i.e. Sr/Ca and Ba/Ca, were used, respectively, as a paleothermometer and as a tracer of nutrient load from modem and mid-Holocene (about 6000 calendar years old) massive Porites coral colonies. The results obtained from the modem coral record indicate that, near the outer barrier reef, upwelling activity is controlled by southeast winds blowing in summer. By contrast, along the southwest coastline, the fringing reefs are subjected to barium input mainly derived from weathering of barite-rich rocks cropping out in the adjacent mainland. Comparison between the fossil and modem coral Sr/Ca and Ba/Ca records shed light on three different aspects of the mid-Holocene climate and coral reef evolution in New Caledonia: (1) the variability of paleo-sea surface temperature (SST) seems to have been similar to the modem one, although the island probably experienced SST about 1 degrees C higher than at present; (2) upwelling activity appears to have been greater than at present. Barium being supplied from the open sea to coastal zones by strong-wind generated upwelling currents, in relation to cooling events; (3) the onset of reef development in the southwest areas of New Caledonia was delayed due to the stronger upwelling of nutrient-enriched waters during the early-middle Holocene. The flowing of upwelled waters over the southwest coastal areas began at 8200 calendar years BP, and ceased at the time when the outer barrier reef crest reached present-day sea level, about 5500 to 5000 calendar years ago. (c) 2006 Elsevier B.V. All rights reserved