Quaternary Geochronology (original) (raw)
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Scientific Reports, 2020
Based on infrared spectral characteristics, six archeological sample sets of charcoals from German (5) and Brazilian (1) sites, covering the time span from the nineteenth century CE to 3950 BCE, were compared to a chronological (present to the fifteenth century BCE) series of Austrian charcoals. A typical chronological trend of several bands (stretch vibrations: O-CO of carboxylates at 1,585-1,565 and 1,385-1,375 cm −1 , CO carboxylic acids at 1,260-1,250 cm −1) that indicate oxidation and subsequently increasing hydrophilicity (O-H stretch vibration at about 3,400 cm −1) was also contained in the archive samples. Three sample sets fit in the typical band development according to their age. For three sample sets this conformity was not observed. Despite the age of two sample sets (3950-2820 BCE), most charcoals were assigned to the Modern Period. Apart from the high degree of carbonization, anaerobic depositional conditions over a longer period of time seem to contribute to the surprising conservation. Non-removable mineral components in charcoals, as observed in a third sample set, strongly influence infrared band intensities and positions of organic compounds. The role of inorganic components in terms of charcoal aging, and the information we can obtain from spectral characteristics in an archeological context, are discussed. Black carbon (BC), a product of incomplete combustion, comprises a wide range of charred organic materials with different chemical and physical properties. Charcoal represents a main component. Apart from its function as remains in the historical and archeological context, its behavior, stability and turnover under different environmental conditions are the focus of numerous investigations in diverse research fields. Due to its recalcitrance, BC is considered to be a relevant sink in the carbon cycle 1. Stable and relatively persistent BC is found in deep marine sediments 2 , at archeological sites 3,4 and as component of Chernozems 5,6. Charcoals are archeological evidences for former land use and deforestation 7 and support the reconstruction of the long-term development of forest ecosystems 8,9 , forest fires 10-12 and anthropogenic activities associated with fire 13. Chemical changes in soils due to the aging of pyrogenic carbon from slash-and-burn practices and the evolution of stable carbon stocks were observed in the Fujian Province 14. The aim to quantify the stable carbon pool in soils and sediments and to understand the behavior of black carbon, its residence time, degradation, turnover rates and the associated influencing factors in the environment has prompted many studies, both lab and field experiments. These have led to apparently contradictory observations due to the individual chemistry of pyrogenic organic matter and different storage conditions in soils in terms of temperature, moisture and oxygen access 15. Some fundamental facts can be deduced from numerous open
Rapid communications in mass spectrometry : RCM, 2012
RATIONALEPyrogenic carbon (CP) is an important component of the global carbon budget. Accurate determination of the abundance and stable isotope composition of CP in soils and sediments is crucial for understanding the dynamics of the CP cycle and interpreting records of biomass burning, climate and vegetation change in the past. Here we test hydrogen pyrolysis (hypy) as a new technique potentially capable of eliminating labile organic carbon (CL) from total organic carbon (CT) in a range of matrices in order to enable reliable quantification of both the CP component of CT and the stable carbon isotope composition of CP (δ13CP).Pyrogenic carbon (CP) is an important component of the global carbon budget. Accurate determination of the abundance and stable isotope composition of CP in soils and sediments is crucial for understanding the dynamics of the CP cycle and interpreting records of biomass burning, climate and vegetation change in the past. Here we test hydrogen pyrolysis (hypy) as a new technique potentially capable of eliminating labile organic carbon (CL) from total organic carbon (CT) in a range of matrices in order to enable reliable quantification of both the CP component of CT and the stable carbon isotope composition of CP (δ13CP).METHODSWe mixed CP at a range of concentrations with common CP-free matrices (CL = cellulose, chitin, keratin, decomposed wood, leaf litter, grass and algae) and determined the amount of residual carbon not removed by hydrogen pyrolysis (CR) as a ratio of CT (CR/CT). Mixing CP with a unique δ13C value provided a natural abundance isotope label from which to precisely determine the ratio of CP to residual CL remaining after hypy.We mixed CP at a range of concentrations with common CP-free matrices (CL = cellulose, chitin, keratin, decomposed wood, leaf litter, grass and algae) and determined the amount of residual carbon not removed by hydrogen pyrolysis (CR) as a ratio of CT (CR/CT). Mixing CP with a unique δ13C value provided a natural abundance isotope label from which to precisely determine the ratio of CP to residual CL remaining after hypy.RESULTSAll CP-free matrices contained trace carbon after hypy, indicating that hypy does not remove all the CL. However, there was a strong correlation between CR/CT and CP/CT, viz. CR/CT = 1.02(CP/CT) + 4.0 × 10–3, r2 = 0.99, p <0.001, suggesting that only a small and reasonably constant fraction of CL remains after hypy. Uncertainties associated with the correction for contamination of CR by residual CL are minimal allowing for reliable determinations of both CP and δ13CP in many cases.All CP-free matrices contained trace carbon after hypy, indicating that hypy does not remove all the CL. However, there was a strong correlation between CR/CT and CP/CT, viz. CR/CT = 1.02(CP/CT) + 4.0 × 10–3, r2 = 0.99, p <0.001, suggesting that only a small and reasonably constant fraction of CL remains after hypy. Uncertainties associated with the correction for contamination of CR by residual CL are minimal allowing for reliable determinations of both CP and δ13CP in many cases.CONCLUSIONSHydrogen pyrolysis appears to be a robust technique for estimating CP abundance and δ13CP across a range of materials. Nevertheless, caution is required in interpreting δ13CP values when CP/CT is low, with CP/CT >4% being required for the determination of the δ13CP values within an interpretable error under our experimental conditions. Copyright © 2012 John Wiley & Sons, Ltd.Hydrogen pyrolysis appears to be a robust technique for estimating CP abundance and δ13CP across a range of materials. Nevertheless, caution is required in interpreting δ13CP values when CP/CT is low, with CP/CT >4% being required for the determination of the δ13CP values within an interpretable error under our experimental conditions. Copyright © 2012 John Wiley & Sons, Ltd.