Alexander Dreves

A novel tertiary prep-HPLC method for the isolation of single amino acids for AMS-radiocarbon measurement

AMS-radiocarbon measurements of amino acids can potentially provide more reliable radiocarbon dates than bulk collagen analysis. Nonetheless, the applicability of such an approach is often limited by the low-throughput of existing isolation methods and difficulties in determining the contamination introduced during the separation process. A novel tertiary prep-HPLC amino acid isolation method was developed that relies on the combustion of eluted material without requiring any additional chemical steps. Amino acid separation was carried out using a gradient mix of pure water and phosphoric acid with an acetonitrile step in-between runs to remove hydrophobic molecules from the separation column. The amount of contaminant carbon and its 14C content were determined from two-point measurements of collagen samples of known 14C content. The amount of foreign carbon due to the isolation process was estimated at 4±1μg and its 14C content was 0.43±0.01 F14C. Radiocarbon values corrected for carbon contamination have only a minor increase in uncertainties. For Holocene samples, this corresponds to an added uncertainty typically smaller than 10 14Cyears. The developed method can be added to routine AMS measurements without implying significant operational changes and offers a level of measurement uncertainty that is suitable for many archaeological, ecological, environmental, and biological applications.

DATING BULK SEDIMENTS FROM LIMNIC DEPOSITS USING A GRAIN-SIZE APPROACH

Radiocarbon measurements on bulk subaqueous sediments typically provide ages significantly older than actual time of deposition. This is generally caused by the presence of reworked organic compounds, which are depleted in 14C. To explore this issue of age heterogeneity, we collected 4 organic-rich samples from varying depths in a lake sediment core at the Gemündener Maar (Eifel, Germany), a lake of volcanic origin. We divided each sample into 5 standard grain-size fractions: gravel, sand, silt, clay, and 1 fraction smaller than 0.45 μm. These were cleaned separately using a standard acid-alkaliacid treatment. The highly organic gravel-size fraction provided the youngest 14C ages of all grain-size fractions and seems to be associated most closely with the time of deposition. By contrast, the silt and clay fractions show significantly older ages. If the investigated limnic sediment layer does not contain any identifiable terrestrial macrofossils, extracting and measuring coarser grain-size fractions instead of measuring bulk sediment samples will provide a better approximation of the time of sedimentation.

Colloidal matter in water extracts from forest soils

Environmental context. Little is known about the proportion of tiny dispersed particles and true solutions in soil water although the distinction has a major influence on transport processes of organic matter, fertiliser and pollutants in soils and thus, e.g., on carbon storage, and its role in global warming. Our study has found a noticeable amount of tiny particles (range 17 nm to 1.0 μm) in filtered soil water, that have a different chemical composition and a lower bioavailability of their organic components in comparison to the soluble part. This significant occurrence and the ecological relevance of colloids for the transport and storage of soil constituents highlights the need to partition soil water content into ‘particulate’ and ‘dissolved’ since the access to soil pores determines particle transport. Abstract. Water-extracted organic matter (WEOM) is widely used as a surrogate for natural organic matter in soil water in the investigation of soil carbon dynamics. Information about the dissolved or colloidal nature of the organic matter is scarce since dissolved organic matter (DOM) is simply operationally defined by filtration: ‘DOM is what passes through the filter’. Water extracts of two topsoil horizons from both a deciduous (Steinkreuz) and a coniferous (Rotthalmunster) forest, located in Bavaria (Germany), were filtered through a 1-μm quartz filter and analysed regarding the amount of colloids in the range ~17 nm to 1.0 μm, the chemical composition and the radiocarbon concentration of both the colloidal and the dissolved fraction separated by high-speed centrifugation. Up to 13.9 wt-% of the total charge of the water extracts belongs to the colloidal fraction. The colloidal fraction has a higher relative proportion of metals and older organic C than the dissolved fraction. This demonstrates the dual nature of WEOM and the need for a more careful definition of DOM.

Preface—Radiocarbon and Diet: Aquatic Food Resources and Reservoir Effects

One of the most exciting fields in current radiocarbon research is the study of aquatic radiocarbon reservoir effects (RREs). Potential RREs pose a challenge when chronologies are based on 14 C dating of food or human remains, providing an impetus for new and improved efforts to detect and quantify RREs in archaeological materials. Examples of such developments include compound-specific isotopic and 14 C analysis, and novel statistical methods to reconstruct ancient diets. Awareness of RREs has also created new research opportunities; in particular, radiocarbon is increasingly being employed as an environmental and dietary tracer in ecological and archaeological studies, requiring a better understanding of the spatial and temporal variability of aquatic RREs.