Marie-Josée Nadeau

Correlation of marine 14C ages from the nordic seas with the GISP2 isotope record : Implications for 14C calibration beyond 25 ka BP

We present two new high-resolution sediment records from the southwestern Iceland and Norwegian Seas that were dated by numerous (super 14) C ages up to 54 (super 14) C ka BP. Based on various lines of evidence, the local (super 14) C reservoir effect was restricted to 400-1600 yr. The planktic stable isotope records reveal several meltwater spikes that were sampled with an average time resolution of 50 yr in PS2644 and 130 yr in core 23071 during isotope stage 3. Most of the delta (super 18) O spikes correlate peak-by-peak to the stadials and cold rebounds of the Dansgaard-Oeschger cycles in the annual-layer counted GISP2 ice core, with the major spikes reflecting the Heinrich events 1-6. This correlation indicates large fluctuations in the calibration of (super 14) C ages between 20 and 54 (super 14) C ka BP. Generally the results confirm the (super 14) C age shifts as predicted by the geomagnetic model of Laj, Mazaud and Duplessy (1996). However, the amplitude and speed of the abrupt decrease and subsequent major increase of our (super 14) C shifts after 45 (super 14) C ka BP clearly exceed the geomagnetic prediction near 40-43 and 32-34 calendar (cal) ka BP. At these times, the geomagnetic field intensity minima linked to the Laschamp and the Mono Lake excursions and confirmed by a local geomagnetic record, probably led to a sudden increase in cosmogenic (super 14) C and (super 10) Be production, giving rise to excess (super 14) C in the atmosphere of up to 1200 per mil.

RADIOCARBON LEVELS IN THE ICELAND SEA FROM 25-53 KYR AND THEIR LINK TO THE EARTH'S MAGNETIC FIELD INTENSITY

By correlating the climate records and radiocarbon ages of the planktonic foraminifera N. pachyderma(s) of deep-sea core PS2644 from the Iceland Sea with the annual-layer chronology of the GISP2 ice core, we obtained 80 marine (super 14) C calibration points for the interval 11.4-53.3 ka cal BP. Between 27 and 54 ka cal BP the continuous record of (super 14) C/cal age differences reveals three intervals of highly increased (super 14) C concentrations coincident with low values of paleomagnetic field intensity, two of which are attributed to the geomagnetic Mono Lake and Laschamp excursions (33.5-34.5 ka cal BP with maximum 550 per mil marine Delta (super 14) C, and 40.3-41.7 ka cal BP with maximum 1215 per mil marine Delta (super 14) C, respectively). A third maximum (marine Delta (super 14) C: 755 per mil) is observed around 38 ka cal BP and attributed to the geomagnetic intensity minimum following the Laschamp excursion. During all three events the Delta (super 14) C values increase rapidly with maximum values occurring at the end of the respective geomagnetic intensity minimum. During the Mono Lake Event, however, our Delta (super 14) C values seem to underestimate the atmospheric level, if compared to the (super 36) Cl flux measured in the GRIP ice core (Wagner et al. 2000) and other records. As this excursion coincides with a meltwater event in core PS2644, the underestimation is probably caused by an increased planktonic reservoir age. The same effect also occurs from 38.5 to 40 ka cal BP when the meltwater lid of Heinrich Event 4 affected the planktonic record.

Food Reconstruction Using Isotopic Transferred Signals ( FRUITS): A Bayesian Model for Diet Reconstruction

Human and animal diet reconstruction studies that rely on tissue chemical signatures aim at providing estimates on the relative intake of potential food groups. However, several sources of uncertainty need to be considered when handling data. Bayesian mixing models provide a natural platform to handle diverse sources of uncertainty while allowing the user to contribute with prior expert information. The Bayesian mixing model FRUITS (Food Reconstruction Using Isotopic Transferred Signals) was developed for use in diet reconstruction studies. FRUITS incorporates the capability to account for dietary routing, that is, the contribution of different food fractions (e.g. macronutrients) towards a dietary proxy signal measured in the consumer. FRUITS also provides relatively straightforward means for the introduction of prior information on the relative dietary contributions of food groups or food fractions. This type of prior may originate, for instance, from physiological or metabolic studies. FRUITS performance was tested using simulated data and data from a published controlled animal feeding experiment. The feeding experiment data was selected to exemplify the application of the novel capabilities incorporated into FRUITS but also to illustrate some of the aspects that need to be considered when handling data within diet reconstruction studies. FRUITS accurately predicted dietary intakes, and more precise estimates were obtained for dietary scenarios in which expert prior information was included. FRUITS represents a useful tool to achieve accurate and precise food intake estimates in diet reconstruction studies within different scientific fields (e.g. ecology, forensics, archaeology, and dietary physiology).

Macronutrient-based model for dietary carbon routing in bone collagen and bioapatite

Carbon stable isotope ratios (δ13C), measured in human bone collagen (δ13Ccollagen) and bioapatite (δ13Cbioapatite), are commonly used indicators in ancient human diet reconstruction. The underlying assumption is that human tissues broadly reflect the δ13C signal of dietary food sources (δ13Cdiet) plus an isotopic offset. However, interpretation of results may be confounded by the differentiated routing of macronutrients (energy, that is carbohydrates and lipids, and protein) having associated different isotopic signals (δ13Cenergy, δ13Cprotein). Multiple regression analyses were conducted on data from controlled animal feeding experiments compiled by Froehle et al. (J Archaeol Sci 37:2662–2670, 2010). We derived a simple algebraic macronutrient-based model with δ13Cbioapatite = 10.1 + δ13Cdiet (‰) and δ13Ccollagen = 4.8 + 0.74 δ13Cprotein + 0.26 δ13Cenergy (‰). While the established relationship for δ13Cbioapatite is similar to previously known results, the model also suggests that δ13Ccollagen signal contributions originate from surprisingly consistent proportions of protein and energy macronutrients. Given that feeding experiments explore extreme variations in the proportion of diet macronutrients, the applicability of the proposed model and its predictions were tested in a variety of well-known, wild animal and human, natural contexts. Possible biochemical mechanisms explaining these empirical results are discussed.

Dietary history contributes to enterotype-like clustering and functional metagenomic content in the intestinal microbiome of wild mice

Significance Recent investigation of several mammalian hosts suggests that their intestinal bacterial communities display evidence of clusters characterized by differences in specific bacterial taxa, a concept referred to as enterotypes. By performing stable isotope analysis of environmental samples, monitoring communities during dietary shifts, and collecting functional metagenomic sequence data, we provide novel insight into the origins and dynamics of enterotype-like community clustering in wild house mice. Two clusters are present in wild mice, one associated with higher plant-derived and another with animal-derived food intake, which can shift within a period of 1 wk. Remarkably, these clusters display shared characteristics with those present in humans, chimpanzees, and laboratory mice, suggesting ancient shared traits among mammalian bacterial communities. Understanding the origins of gut microbial community structure is critical for the identification and interpretation of potential fitness-related traits for the host. The presence of community clusters characterized by differences in the abundance of signature taxa, referred to as enterotypes, is a debated concept first reported in humans and later extended to other mammalian hosts. In this study, we provide a thorough assessment of their existence in wild house mice using a panel of evaluation criteria. We identify support for two clusters that are compositionally similar to clusters identified in humans, chimpanzees, and laboratory mice, characterized by differences in Bacteroides, Robinsoniella, and unclassified genera belonging to the family Lachnospiraceae. To further evaluate these clusters, we (i) monitored community changes associated with moving mice from the natural to a laboratory environment, (ii) performed functional metagenomic sequencing, and (iii) subjected wild-caught samples to stable isotope analysis to reconstruct dietary patterns. This process reveals differences in the proportions of genes involved in carbohydrate versus protein metabolism in the functional metagenome, as well as differences in plant- versus meat-derived food sources between clusters. In conjunction with wild-caught mice quickly changing their enterotype classification upon transfer to a standard laboratory chow diet, these results provide strong evidence that dietary history contributes to the presence of enterotype-like clustering in wild mice.

Chemical removal of conservation substances by Soxhlet'-type extraction

At the Leibniz radiocarbon lab, art and archaeological objects, often chemically conserved and thus potentially contaminated with respect to their 14 C content, are treated using a computer-controlled Soxhlet-type series extractor. This device uses a continuous procedure of boiling and condensation of different solvents for extraction and vacuum filtration under constant process conditions. An elutrope sequence of five solvents that dissolve most customary conservation chemicals was selected. A study of these different contaminants applied to reference wood samples with subsequent accelerator mass spectrometry (AMS) measurements demonstrates that their effective removal is dependent on the use of adequate solvents. For many contaminants (e.g. wood glue, methyl cellulose, Klucel®, sugar, and polyethylene glycol), routine acid-alkali-acid (AAA) treatment already yields satisfactory results, whereas for Caparol® and beeswax a relatively mild treatment with acetone, methanol, water, and subsequent standard AAA extraction is sufficient. Complete removal of rubber glue, epoxy resin, and paraffin can only be accomplished with our full set of solvents. The latter procedure is also appropriate when no or only incomplete information about the type of conservation material is available. For epoxy resin the contamination appears to be enriched in the alkali residue, and the easily soluble humic acid fraction, even after standard AAA treatment, gives satisfactory results. Two case studies on the application of the extraction procedures are presented.

How Clean is Ultrafiltration Cleaning of Bone Collagen

As part of our bone dating development, we have tested the ultrafiltration of bone gelatin using 2 different filtersVivaspin 20 (VS20), a polyethersulfone, and Vivaspin 15R (VS15R), a cellulose, both with a 30,000 molecular weight cutoffand bone collagen from dated samples ranging in age from 1.5 to >50 kyr BP. A direct accelerator mass spectrometry (AMS) measurement yielded radiocarbon concentrations of ~0.5 pMC (~42 kyr) for the polyethersulfone, ~14.417.5 pMC (~15.614 kyr) for the cellulose, and ~107.4 pMC for the glycerin. The filters were cleaned before use similar to the Oxford protocol (Bronk Ramsey et al. 2004), and a series of freeze-dried archaeological bone gelatin samples and a modern pig-skin gelatin were passed through VS20 and VS15R filters (Vivascience). We recovered both the eluent ( 30 kD) in order to obtain a carbon mass and isotope balance. While the >30-kD collagen fraction that is usually selected for AMS analysis does not appear to be significantly contaminated, measurements show significant age differences between the eluent 30-kD fraction. Until a contamination with filter carbon of the >30-kD collagen fraction can be excluded, we would recommend caution in the use of ultrafiltration for cleaning bone collagen with VS20 or VS15R ultrafilters.

Quantitative diet reconstruction of a Neolithic population using a Bayesian mixing model (FRUITS): The case study of Ostorf (Germany)

OBJECTIVES The island cemetery site of Ostorf (Germany) consists of individual human graves containing Funnel Beaker ceramics dating to the Early or Middle Neolithic. However, previous isotope and radiocarbon analysis demonstrated that the Ostorf individuals had a diet rich in freshwater fish. The present study was undertaken to quantitatively reconstruct the diet of the Ostorf population and establish if dietary habits are consistent with the traditional characterization of a Neolithic diet. METHODS Quantitative diet reconstruction was achieved through a novel approach consisting of the use of the Bayesian mixing model Food Reconstruction Using Isotopic Transferred Signals (FRUITS) to model isotope measurements from multiple dietary proxies (δ13 Ccollagen , δ15 Ncollagen , δ13 Cbioapatite , δ34 Smethione , 14 Ccollagen ). The accuracy of model estimates was verified by comparing the agreement between observed and estimated human dietary radiocarbon reservoir effects. RESULTS Quantitative diet reconstruction estimates confirm that the Ostorf individuals had a high protein intake due to the consumption of fish and terrestrial animal products. However, FRUITS estimates also show that plant foods represented a significant source of calories. Observed and estimated human dietary radiocarbon reservoir effects are in good agreement provided that the aquatic reservoir effect at Lake Ostorf is taken as reference. CONCLUSIONS The Ostorf population apparently adopted elements associated with a Neolithic culture but adapted to available local food resources and implemented a subsistence strategy that involved a large proportion of fish and terrestrial meat consumption. This case study exemplifies the diversity of subsistence strategies followed during the Neolithic. Am J Phys Anthropol 158:325-340, 2015.

Radiocarbon intercomparison program for Chauvet Cave

We present the first results of an accelerator mass spectrometry (AMS) radiocarbon intercomparison program on 3 different charcoal samples collected in one of the hearths of the Megaceros gallery of Chauvet Cave (Ardche, France). This cave, rich in parietal decoration, is important for the study of the appearance and evolution of prehistoric art because certain drawings have been 14C dated to the Aurignacian period at the beginning of the Upper Paleolithic. The new dates indicate an age of about 32,000 BP, which is consistent with this attribution and in agreement with the results from the same sector of the cave measured previously at the Laboratoire des Sciences du Climat et de lEnvironnement (LSCE). Six laboratories were involved in the intercomparison. Samples were measured in 4 AMS facilities: Center for Isotope Research, Groningen University, the Netherlands; the Oxford Radiocarbon Accelerator Unit, UK; the Centre de datation par le carbone 14, Univ. Claude Bernard Lyon 1, France (measured by AMS facilities of Poznan University, Poland); and the LSCE, UMR CEACNRS-UVSQ, France (measured by the Leibniz-Labor of Christian-Albrechts-Universitt Kiel, Germany).

Carbonate 14C background: Does it have multiple personalities?

Measurements of the radiocarbon concentration of several carbonate background materials, either mineral (IAEA Cl Carrara marble and Icelandic double spar) or biogenic (foraminifera and molluscs), show that the apparent ages of diverse materials can be quite different. Using 0.07 pMC obtained from mineral samples as a processing blank, the results from foraminifera and mollusc background samples, varying from 0.12 to 0.58 pMC (54.0-41.4 ka), show a species-specific contamination that reproduces over several individual shells and foraminifera from several sediment cores. Different cleaning attempts have proven ineffective, and even stronger measures such as progressive hydrolization or leaching of the samples prior to routine preparation, did not give any indication of the source of the contamination. In light of these results, the use of mineral background material in the evaluation of the age of older unknown samples of biogenic carbonate (>30 ka) proves inadequate. The use of background samples of the same species and provenance as the unknown samples is essential, and if such material is unavailable, generic biogenic samples such as mixed foraminifera samples should be used. The description of our new modular carbonate sample preparation system is also introduced.