Description: Compound-specific radiocarbon dating often requires working with small samples of 〈 100 µg carbon (µgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by extraneous carbon of unknown composition, a procedural blank, which is introduced to the samples during the steps necessary to prepare a sample for radiocarbon analysis by accelerator mass spectrometry (i.e., isolating single compounds from a heterogeneous mixture, combustion, gas purification and graphitization). Reporting accurate radiocarbon dates thus requires a correction for the procedural blank. We present our approach to assess the fraction modern carbon (F14C) and the mass of the procedural blanks introduced during the preparation procedures of lipid biomarkers (i.e. n-alkanoic acids) and lignin phenols. We isolated differently sized aliquots (6-151 µgC) of n-alkanoic acids and lignin phenols obtained from standard materials with known F14C values. Each compound class was extracted from two standard materials (one fossil, one modern) and purified using the same procedures as for natural samples of unknown F14C. There was an inverse linear relationship between the measured F14C values of the processed aliquots and their mass, which suggests constant contamination during processing of individual samples. We used Bayesian methods to fit linear regression lines between F14C and 1/mass for the fossil and modern standards. The intersection points of these lines were used to infer F14Cblank and mblank and their associated uncertainties. We estimated 4.88±0.69 μgC of procedural blank with F14C of 0.714±0.077 for n-alkanoic acids, and 0.90±0.23 μgC of procedural blank with F14C of 0.813±0.155 for lignin phenols. These F14Cblank and mblank can be used to correct AMS results of lipid and lignin samples by isotopic mass balance. This method may serve as a standardized procedure for blank assessment in small-scale radiocarbon analysis.

Description: The Amazon River transports large amounts of terrestrial organic carbon (OCterr) from the Andean and Amazon neotropical forests to the Atlantic Ocean. In order to compare the biogeochemical characteristics of OCterr in the fluvial sediments from the Amazon drainage basin and in the adjacent marine sediments, we analysed riverbed sediments from the Amazon mainstream and its main tributaries as well as marine surface sediments from the Amazon shelf and fan for total organic carbon (TOC) content, organic carbon isotopic composition (d13CTOC) and lignin phenol compositions. TOC and lignin content exhibit positive correlations with Al/Si ratios (indicative of the sediment grain size) implying that the grain size of sediment discharged by the Amazon River plays an important role in the preservation of TOC and leads to preferential preservation of lignin phenols in fine particles. Depleted d13CTOC values (-26.1 per mil to -29.9 per mil) in the main tributaries consistently correspond with the dominance of C3 vegetation. Ratios of syringyl to vanillyl (S/V) and cinnamyl to vanillyl (C/V) lignin phenols suggest that non-woody angiosperm tissues are the dominant source of lignin in the Amazon basin. Although the Amazon basin hosts a rich diversity of vascular plant types, distinct regional lignin compositions are not observed. In marine sediments, the distribution of d13CTOC and Lambda8 (sum of eight lignin phenols in organic carbon (OC), expressed as mg/100mg OC) values implies that OCterr discharged by the Amazon River is transported north-westward by the North Brazil Current and mostly deposited on the inner shelf. The lignin compositions in offshore sediments under the influence of the Amazon plume are consistent with the riverbed samples suggesting that processing of OCterr during offshore transport does not change the encoded source information. Therefore, the lignin compositions preserved in these offshore sediments can reliably reflect the vegetation in the Amazon River catchment. In sediments from the Amazon Fan, low lignin content, relatively depleted d13CTOC values and high (Ad/Al)V ratios indicating highly degraded lignin imply that a significant fraction of the deposited OCterr is derived from petrogenic (sourced from ancient rocks) sources.

Description: Compound-specific radiocarbon dating often requires working with small sample sizes (〈 100 µgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by extraneous carbon of unknown composition, which is introduced to the samples during processing (i.e., isolating single compounds from a heterogeneous mixture) prior to AMS measurements (procedure blank). Contamination sources include solvents, column bleed (from preparative HPLC and GC), carry-over and atmospheric carbon during combustion and vacuum line handling. Reporting accurate radiocarbon dates thus requires a correction for the procedure blank. We present our approach to assess the F14C and the mass of the blanks introduced during the preparation procedures of lipid biomarkers and lignin phenols. The treatments of these compound classes differ significantly which may lead to different F14Cblank and mblank. In order to assess the procedure blanks, we isolated fatty acids and lignin phenols from differently sized aliquots (20-80 µgC) obtained from standard materials with known F14C. Each compound class was extracted from two standard materials (one fossil, one modern). The measured F14C of the processed aliquots were graphically correlated to 1/mass of the respective sample. For aliquots of both, fossil and modern standard materials, this yielded an inverse linear relationship between the F14C and the sample size. The intercept of the regression lines obtained from the aliquots of fossil and modern standards is used to infer F14Cblank and mblank. The uncertainties of F14Cblank (σF14Cblank) and mblank (σmblank) were determined by the regression coefficients R2 of the linear regressions. Assuming constant contamination during processing of individual samples, the F14Cblank and mblank can be used to correct AMS results of lignin and lipid samples by isotopic mass balance.

Description: The preservation of terrestrial organic carbon (OC) in marine sediments is a crucial component of global carbon cycle on geological timescale. Characterizing the origins and compositions of the terrestrial OC is critical for understanding the fate of terrestrial OC in marine sediments and constraining the terrestrial OC cycling. The amount of terrestrial OC discharged by the Amazon River to the Atlantic Ocean every year is about 8-10 % of the global annual input of terrestrial OC to oceans. Therefore, the terrestrial OC in the Amazon system has been extensively investigated. However, until now, many aspects regarding the origin and fate of terrestrial OC in the Amazon system are still ambiguous and need to be elucidated. Firstly, little is known about the disperse pattern of lignin (a major component of higher plants biomass and can serve as a biomarker of terrestrial OC) and the factors controlling the characteristics of terrestrial OC in the Amazon continental margin. Secondly, it is questionable whether the Amazon continental margin can efficiently store terrestrial OC or serve as a sedimentary OC incinerator. Thirdly, the response of vegetation to climate change during late Pleistocene is debated. To fill these knowledge gaps, lignin and its isotope compositions (13C and 14C) are used as the major tools to provide a better understanding of the origins, pattern of distribution, processing, composition and fate of terrestrial OC in the Amazon system. In the first part, the biogeochemical characteristics of terrestrial OC in the fluvial sediments from the Amazon drainage basin and in the adjacent marine sediments are compared. Total organic carbon (TOC) and lignin content exhibit positive correlations with aluminium to silicon ratios (Al/Si, indicative of the sediment grain size) implying that the grain size of sediment discharged by the Amazon River plays an important role in the preservation of TOC and leads to preferential preservation of lignin phenols in fine particles. Low δ13C values of bulk OC in the main tributaries consistently correspond with the dominance of C3 vegetation. Compositions of lignin, syringyl to vanillyl (S/V) and cinnamyl to vanillyl (C/V), suggest that non-woody angiosperm tissues are the dominant source of lignin in the Amazon basin. Although the Amazon basin hosts a rich diversity of vascular plant types, distinct regional lignin compositions are not observed. In the marine sediments, the distribution of δ13C values of bulk OC and lignin contents implies that terrestrial OC discharged by the Amazon River is transported northwestward by the North Brazil Current and mostly deposited on the inner shelf. The lignin compositions in offshore sediments under the influence of the Amazon plume are consistent with the riverbed samples suggesting that processing of terrestrial OC during offshore transport does not change the encoded source information. Therefore, the lignin compositions preserved in these offshore sediments can reliably reflect the vegetation in the Amazon River catchment. In sediments from the Amazon Fan, low lignin content, relatively low δ13C values of bulk OC and high degradation degree of lignin demonstrate that a significant fraction of the deposited terrestrial OC is derived from petrogenic (sourced from ancient rocks) sources. In the second part, a new method of assessing procedural blank for compound-specific 14C analysis is developed with a Bayesian model. This method is successfully used in the third part of this thesis, which is about radiocarbon dating of source-specific biomarkers (n-alkanoic acids and lignin phenols) in riverbed sediments from the lowland Amazon basin and offshore sediments. The results show that Δ14C values of terrestrial OC on the Amazon continental margin are substantially influenced by matrix association effects, where terrestrial OC associated with the finer-grained particles is better preserved and more resistant to decomposition during residence in intermediate reservoirs. The compoundspecific Δ14C values imply that as expected short-chain n-alkanoic acids represent recently biosynthesized organic matter from riverine or marine primary production whereas both long-chain nalkanoic acids and lignin phenols used as markers for land vegetation have pre-aged in soils where they resided attached to mineral surfaces. By using a ternary mixing model, a well-constrained quantitative estimate of the composition of sedimentary OC in riverbed and marine sediments is obtained. Despite the variable composition of sedimentary OC in the Amazon system, the burial of fossil rock-derived OC is relatively constant. Based on the absolute content of bulk terrestrial OC, lignin, and long-chain n-alkanoic acids and their 14C ages, half-lives of bulk terrestrial OC, lignin and long-chain n-alkanoic acids during transport are estimated to be about 2310 years, 13860 and 470 years, respectively. This suggests that the preservation of terrestrial OC in the mud belt on the Amazon shelf is more efficient than previously assumed. In the fourth part, the δ13C analysis of lignin phenols are applied in marine surface sediments from the Amazon shelf and sediment core GeoB16224-1 recovered from the continental margin NW of the Amazon mouth. The weighted average δ13C values of lignin indicate that the modern terrestrial OC on the Amazon shelf is dominated by C3 plants and the vegetation source remained constant over the past 12.8-50 kyr, in agreement with previous studies. A general pattern of phenolic δ13C values is observed with the acid monomers of V and S phenols displaying lower δ13C values than their aldehyde counterparts, while C phenols are always more enriched in 13C than V and S phenols. The lignin content and composition paired with δ13C of lignin are used to reconstruct the characteristics of terrestrial OC deposited on the continental margin NW of the Amazon mouth over the period 12.8-50 kyr. Lignin composition, δ13C values of lignin, BIT index, δ13C and δD values plant-wax lipids show clear in-phase variation. Therefore, it can be proposed that next to vegetation change, the variation of δ13C values of lignin and plant-wax lipids during HS could reflect either enhanced discharge of more degraded terrestrial OC and/or more contributions of terrestrial from high altitude regions. These two possible scenarios suggest that the Amazon basin was still a stable ecological system dominated by C3 forest and the increases of δ13C values of lignin and plant-wax lipids were actually the consequence of changes of sources of terrestrial OC through the late Pleistocene.

Description: Compound-specific radiocarbon (14C) dating often requires working with small samples of 〈 100 μg carbon (μgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by extraneous carbon of unknown composition, a procedural blank, which is introduced to the samples during the steps necessary to prepare a sample for radiocarbon analysis by accelerator mass spectrometry (i.e., isolating single compounds from a heterogeneous mixture, combustion, gas purification and graphitization). Reporting accurate radiocarbon dates thus requires a correction for the procedural blank. We present our approach to assess the fraction modern carbon (F14C) and the mass of the procedural blanks introduced during the preparation procedures of lipid biomarkers (i.e. n-alkanoic acids) and lignin phenols. We isolated differently sized aliquots (6–151 μgC) of n-alkanoic acids and lignin phenols obtained from standard materials with known F14C values. Each compound class was extracted from two standard materials (one fossil, one modern) and purified using the same procedures as for natural samples of unknown F14C. There is an inverse linear relationship between the measured F14C values of the processed aliquots and their mass, which suggests constant contamination during processing of individual samples. We use Bayesian methods to fit linear regression lines between F14C and 1/mass for the fossil and modern standards. The intersection points of these lines are used to infer F14Cblank and mblank and their associated uncertainties. We estimate 4.88 ± 0.69 μgC of procedural blank with F14C of 0.714 ± 0.077 for n-alkanoic acids, and 0.90 ± 0.23 μgC of procedural blank with F14C of 0.813 ± 0.155 for lignin phenols. These F14Cblank and mblank can be used to correct AMS results of lipid and lignin samples by isotopic mass balance. This method may serve as a standardized procedure for blank assessment in small-scale radiocarbon analysis.

Description: The Amazon River transports large amounts of terrestrial organic carbon (OCterr/ from the Andean and Amazon neotropical forests to the Atlantic Ocean. In order to compare the biogeochemical characteristics of OCterr in the fluvial sediments from the Amazon drainage basin and in the adjacent marine sediments, we analysed riverbed sediments from the Amazon mainstream and its main tributaries as well as marine surface sediments from the Amazon shelf and fan for total organic carbon (TOC) content, organic carbon isotopic composition (δ13CTOC/, and lignin phenol compositions. TOC and lignin content exhibit positive correlations with Al = Si ratios (indicative of the sediment grain size) implying that the grain size of sediment discharged by the Amazon River plays an important role in the preservation of TOC and leads to preferential preservation of lignin phenols in fine particles. Depleted δ13CTOC values (-26.1 to -29.9 ‰) in the main tributaries consistently correspond with the dominance of C3 vegetation. Ratios of syringyl to vanillyl (S = V) and cinnamyl to vanillyl (C = V) lignin phenols suggest that non-woody angiosperm tissues are the dominant source of lignin in the Amazon basin. Although the Amazon basin hosts a rich diversity of vascular plant types, distinct regional lignin compositions are not observed. In the marine sediments, the distribution of δ13CTOC and 38 (sum of eight lignin phenols in organic carbon (OC), expressed as mg/100 mg OC) values implies that OCterr discharged by the Amazon River is transported north-westward by the North Brazil Current and mostly deposited on the inner shelf. The lignin compositions in offshore sediments under the influence of the Amazon plume are consistent with the riverbed samples suggesting that processing of OCterr during offshore transport does not change the encoded source information. Therefore, the lignin compositions preserved in these offshore sediments can reliably reflect the vegetation in the Amazon River catchment. In sediments from the Amazon fan, low lignin content, relatively depleted δ13CTOC values and high (Ad = Al)V ratios indicating highly degraded lignin imply that a significant fraction of the deposited OCterr is derived from petrogenic (sourced from ancient rocks) sources.

Description: The Lena River in central Siberia represents one of the major pathways for relocating pre-aged terrestrial organic matter (OMterr) stored in permafrost soils from its catchment to the coastal zone of the Laptev Sea. Future Arctic warming and permafrost thawing will likely enhance the re-mobilization and export of this pre-aged OMterr. Despite our improving knowledge about the fate of OMterr released from permafrost, the quality and age of particulate OMterr as well as the sources within the large watershed contributing to the exported OMterr are still not completely understood. To characterize the composition and sources of OMterr discharged by the Lena River, we analyzed the lignin phenol and carbon isotopic composition (δ13C and ∆14C) in Lena Delta soils, total suspended matter (TSM) from surface waters along with surface sediments offshore the delta. A simple linear mixing model based on the bulk lignin phenol distributions indicates that OMterr in TSM samples and coastal surface sediments contains comparable contributions from gymnosperms originating from the taiga forests south of the delta and angiosperms typical for tundra vegetation. Further, we present results of the lignin phenol compositions and inferred sources of OMterr transported with specific grain-size classes (〉2mm, 63µm – 2mm, 〈63µm) of soil and sediment samples associated with different hydrological conditions (spring flood vs. summer low flow). Overall stronger diagenetic alteration in TSM and coastal sediments relative to soils appears to reflect degradation of more labile components during permafrost thawing and transport. Moreover, Lignin phenols and ∆14C of surface sediments suggest that OMTERR deposited offshore is more degraded and older than materials present in river suspended particles and catchment soils.