EXPLORING SAMPLE SIZE LIMITS OF AMS GAS ION SOURCE C-14 ANALYSIS AT COLOGNEAMS

Increasing demands for small-scale radiocarbon (C-14) analyses required the installation of a SO-110 B type ion source (HVE Europa B.V.) at our 6 MV Tandetron AMS (HVE) dedicated for the direct injection of CO2 using either the gas injection system (GIS) from Ionplus AG or a EuroVector EA 3000 elemental analyzer (EA). We tested both systems with multiple series of C-14-free and modern standards (2.5-50 mu g C) combusted in quartz ampoules or EA containers and were able to quantify exogenous C introduced. In EA-GIS-AMS analysis exogenous C is mainly derived from the EA sample containers. Blank values for 50 mu g C combusted in solvent-cleaned tin (Sn) vessels were 0.0127 +/- 0.0012 (FC)-C-14 (boats) and 0.0090 +/- 0.0010 (FC)-C-14 (capsules), while they were much higher for thermally cleaned silver (Ag) capsules. The processing of gas samples for GIS-AMS yields similar blank values corresponding to 0.30 +/- 0.08 mu g exogenous C with 0.93 +/- 0.23 (FC)-C-14 consisting of 0.28 mu g C modern and 0.02 mu g C fossil C. The combustion of larger amounts of blank material (1 mg C) in a single quartz tube split into aliquots gives lower blanks (0.0064 +/- 0.0008 (FC)-C-14; 50 mu g C). Thus, C-14 analysis of small, gaseous samples is now possible at CologneAMS

Preparation and Handling of Methane for Radiocarbon Analysis at Cologneams

CH₄ is the second most important anthropogenic greenhouse gas and originates from different sources. The use of radiocarbon (¹⁴C) analysis of CH₄ opens up the possibility to differentiate geological and agricultural origin. At the CologneAMS facility, the demand for ¹⁴C analysis of CH₄ required the development of a sample handling routine and a vacuum system that converts CH₄ to CO₂ for direct injection of CO₂ into the AMS. We evaluated the processing of CH₄ using several series of gas mixtures of ¹⁴C-free and modern standards as well as biogas with sample sizes ranging from 10 to 50 µg C. The results revealed a CH₄ to CO₂ conversion efficiency of 94–97% and blank values comparable to blank values achieved with our routinely used vacuum system for processing CO₂ samples. The tests with a near modern CH₄:CO₂ biogas mixture gave reproducible results with a near modern ¹⁴C content of 0.967–1.000 F¹⁴C, after applying the background correction.ISSN:0033-822

Terrestrial carbon dynamics through time - insights from downcore radiocarbon dating

A relatively small change in the balance of in- and outgoing fluxes between terrestrial Carbon (Cterr) and the atmosphere, sustained over centuries to millennia can change Cterr from a carbon source to a sink. The net carbon balance of any ecosystem is mainly determined by climate (temperature, humidity, seasonality) via its influence on primary productivity, respiration and preservation, and by geomorphology (erosion). More recently, human perturbance has increasingly also become a major factor. In particular, the slow cycling component of Cterr, with turnover times of centuries to millennia, is relevant for the long-term carbon balance on land. Build-up of this carbon pool is inherently slow, but loss can be rapid and thereby form a significant carbon source to the atmosphere. One way to gain insight in the dynamics of this slow cycling carbon pool is to interrogate sedimentary records that, through time, have stored snapshots of terrestrial carbon, the latter being a mixture of pre-aged, long-stored Cterr and fresh material. By downcore measurements of the radiocarbon age of specific plant-derived organic compounds, interferences by aquatically produced organic carbon or petrogenic organic carbon can be circumvented, and insights can be gained into the carbon cycle processes in the corresponding catchment area. This study presents compound-specific 14C data compiled from studies over the last 20 years of sedimentary records derived from small lake catchments to deltaic and submarine fan deposits near large river mouths. The main conclusions that can be drawn are: 1) Modern but also (pre)historic human perturbance through land-use change has released long-stored ecosystem carbon that otherwise would have escaped mobilization. 2) Both positive and negative correlations between millennial-scale hydroclimate change and Cterr dynamics are evident, and are attributed to the opposing effects on primary productivity, respiration and erosion rates. 3). Catchment size and geomorphology also influence the extent of net ecosystem carbon storage. 4). The Younger Dryas cold period promoted release of Cterr built up during the preceding warm Bølling-Allerød period, illustrating the role rapid climate change can play in carbon dynamics

Purification of fire derived markers for μg scale isotope analysis (δ13C, Δ14C) using high performance liquid chromatography (HPLC)

Black carbon (BC) is the residue of incomplete biomass combustion. It is ubiquitous in nature and, due to its relative persistence, is an important factor in Earth’s slow-cycling carbon pool. This resistant nature makes pure BC one of the most used materials for ¹⁴C dating to elucidate its formation date or residence time in the environment. However, most BC samples cannot be physically separated from their matrices, precluding accurate ¹⁴C values. Here we present a method for radiocarbon dating of the oxidation products of BC, benzene polycarboxylic acids, thereby circumventing interference from extraneous carbon. Individual compounds were isolated using high performance liquid chromatography (HPLC) and converted to CO₂ via wet chemical oxidation for ¹³C and ¹⁴C isotope analysis. A detailed assessment was performed to identify and quantify sources of extraneous carbon contamination using two process standards with distinct isotopic signatures. The average blank was 1.6 ± 0.7 μg C and had an average radiocarbon content of 0.90 ± 0.50 F¹⁴C. We successfully analyzed the ¹⁴C content of individual benzene polycarboxylic acids with a sample size as small as 20–30 μg C after correcting for the presence of the average blank. The combination of δ¹³C and F¹⁴C analysis helps interpret the results and enables monitoring of extraneous carbon contribution in a fast and cost efficient way. Such a molecular approach to radiocarbon dating of BC residues enables the expansion of isotopic BC studies to samples that have either been too small or strongly affected by non-fire derived carbon

DO RADIOCARBON AGES OF PLANT WAX BIOMARKERS AGREE WITH C-14-TOC/OSL-BASED AGE MODELS IN AN ARID HIGH-ALTITUDE LAKE SYSTEM?

To elucidate the dynamics of terrestrial leaf waxes in a high-altitude lake system, we performed compound-specific radiocarbon analysis (CSRA) of long-chain n-alkanes in two sediment core sections from Lake Karakul (Pamirs, Tajikistan) and in surface soil samples from the catchment area. We aimed to answer the question whether the n-alkanes are delivered into the lake sediment with substantial delay due to storage in soils, which may cause a potential bias when used as paleoenvironmental proxies. In the surface soils, the CSRA results reveal an age range of n-alkanes from modern to 2278 +/- 155 cal BP. In the two sediment core samples, three of the four n-alkane ages fell on the lower ends of the 1 sigma-uncertainty ranges of modeled ages of the sediments (based on AMS C-14-TOC and OSL dating results). We conclude that sedimentary leaf waxes represent compounds with intermediate turnover time in soils, for example originating from alluvial plains close to the shores. Overall, the results provide evidence that sedimentary leaf wax compounds in this cold and arid setting are potentially older than the conventional age model indicates, but these findings need to be interpreted in context of the generally large uncertainty ranges of such age models

Diatom-inferred late Pleistocene and Holocene palaeolimnological changes in the Ioannina basin, northwest Greece

The character and impact of climate change since the last glacial maximum (LGM) in the eastern Mediterranean region remain poorly understood. Here, two new diatom records from the Ioannina basin in northwest Greece are presented alongside a pre-existing record and used to infer past changes in lake level, a proxy for the balance between precipitation and evaporation. Comparison of the three records indicates that lake-level fluctuations were the dominant driver of diatom assemblage composition change, whereas productivity variations had a secondary role. The reconstruction indicates low lake levels during the LGM. Late glacial lake deepening was underway by 15.0 cal kyr BP, implying that the climate was becoming wetter. During the Younger Dryas stadial, a lake-level decline is recorded, indicating arid climatic conditions. Lake Ioannina deepened rapidly in the early Holocene, but long-term lake-level decline commenced around 7.0 cal kyr BP. The pattern of lake-level change is broadly consistent with an existing lake-level reconstruction at Lake Xinias, central Greece. The timing of the apparent change, however, is different, with delayed early Holocene deepening at Xinias. This offset is attributed to uncertainties in the age models, and the position of Xinias in the rain shadow of the Pindus Mountains.</p

Les archives pédologiques : des concepts de base à la gestion des écosystèmes. Nouvelles approches en spectroscopie proche infrarouge (SPIR) et sur les biomarqueurs moléculaires lipidiques. Apports du programme GESSOL-APOGEE

Soil archives, like historical and sedimentary archives, allow past dynamics of ecosystems to be reconstructed and their current functioning to be understood. In this article, we first remind the principal specifics of soil archives, and then present two methodological approaches which were developed in the framework of the GESSOL-APOGEE program : qualitative near infrared spectroscopy and molecular plant biomarkers. These approaches are illustrated using three case studies.Au même titre que les archives historiques ou les archives sédimentaires, les archives pédologiques permettent de reconstituer la dynamique passée des écosystèmes et de mieux comprendre leur fonctionnement actuel. Après avoir rappelé les principales spécificités des archives pédologiques, nous présenterons deux approches méthodologiques développées dans le cadre du programme GESSOL-APOGEE : la spectroscopie proche infrarouge qualitative et l’analyse des biomarqueurs moléculaires végétaux. Nous illustrerons ces approches par trois exemples.Schwartz Dominique, Ertlen Damien, Froehlicher Lucie, Vyslouzilova Barbora, Bastien Claire, Courel Blandine, Schaeffer Philippe, Trendel Jean-Michel, Liaud Céline, Motsch Estelle, Adam Pierre, Šefrna Luděk, Hajdas Irka, Gierga Merle, Bernasconi Stefano. Les archives pédologiques : des concepts de base à la gestion des écosystèmes. Nouvelles approches en spectroscopie proche infrarouge (SPIR) et sur les biomarqueurs moléculaires lipidiques. Apports du programme GESSOL-APOGEE. In: Collection EDYTEM. Cahiers de géographie, numéro 18, 2015. Sols et matières organiques. Mémoires et héritages. pp. 19-32

Characterization, Quantification and Compound-specific Isotopic Analysis of Pyrogenic Carbon Using Benzene Polycarboxylic Acids (BPCA)

Fire-derived, pyrogenic carbon (PyC), sometimes called black carbon (BC), is the carbonaceous solid residue of biomass and fossil fuel combustion, such as char and soot. PyC is ubiquitous in the environment due to its long persistence, and its abundance might even increase with the projected increase in global wildfire activity and the continued burning of fossil fuel. PyC is also increasingly produced from the industrial pyrolysis of organic wastes, which yields charred soil amendments (biochar). Moreover, the emergence of nanotechnology may also result in the release of PyC-like compounds to the environment. It is thus a high priority to reliably detect, characterize and quantify these charred materials in order to investigate their environmental properties and to understand their role in the carbon cycle. Here, we present the benzene polycarboxylic acid (BPCA) method, which allows the simultaneous assessment of PyC\u27s characteristics, quantity and isotopic composition (13C and 14C) on a molecular level. The method is applicable to a very wide range of environmental sample materials and detects PyC over a broad range of the combustion continuum, i.e., it is sensitive to slightly charred biomass as well as high temperature chars and soot. The BPCA protocol presented here is simple to employ, highly reproducible, as well as easily extendable and modifiable to specific requirements. It thus provides a versatile tool for the investigation of PyC in various disciplines, ranging from archeology and environmental forensics to biochar and carbon cycling research