The <Emphasis Type="Italic">n</Emphasis>-alkanol paleoclimate records in two peat deposits: a comparative study of the northeastern margin of the Tibetan Plateau and Northeast China

A number of studies have revealed that the climate in the eastern margin of the Tibetan Plateau and Northeast China is sensitive to postglacial changes. Unfortunately, the link of the past climate evolution between the two regions is not well understood. In this study, two cores are analyzed to determine this link directly. The high-resolution n-alkanol distribution patterns from two typical peat sequences covering the past 16,000 cal years in the northeastern margin of the Tibetan Plateau and Northeast China, respectively, are closely examined by gas chromatograph–mass spectrometry analysis. In combination with other palaeoclimatic proxies, it is proposed that the n-alkanol average chain length and (C₂₂ + C₂₄)/(C₂₆ + C₂₈) ratio could reflect past climate changes in the two peat sequences. The n-alkanol proxies reveal several climatic intervals in the period from the last deglaciation through the Holocene. A comparison of n-alkanol records between the northeastern margin of the Tibetan Plateau and Northeast China indicates that the start and end of the warm Holocene Optimum differed at the two locations. The spatially asynchronous pattern of climatic change is possibly a result of different responses to change in solar radiation. The evolution of the Holocene paleoclimate is more consistent with changes in Northern Hemisphere solar radiation in Northeast China than on the Tibetan Plateau. The Holocene Optimum began and terminated earlier in Northeast China than in the northeastern margin of the Tibetan Plateau. Thus, the two n-alkanol proxies provide valuable insights into the regional Holocene climate and local environmental conditions.     

Evolution of organic matter indicators in response to major environmental changes: The case of a formerly cut-over peat bog (Le Russey, Jura Mountains, France)

To assess whether the biochemical characteristics of peat can provide clues for past ecosystem changes or not, a study was carried out combining elemental analysis, micro-morphological counts and neutral monosaccharide determination of peat organic matter (OM) and the dominant living plants from a formerly cut-over peat bog in the Jura Mountains. Peat profiles (up to 50 cm depth) from two distinctive zones (bare peat, FRA and a regenerating stage, FRC) were compared with the reference profile (FRD) taken from an unexploited area of the bog. The results show contrasting OM composition along the profiles. In the upper sections of the FRD and FRC profiles, high C/N ratios and sugar contents (in the same range as in the source plants) and the large predominance of well preserved plant tissues indicate good preservation of primary biological inputs. In contrast, in peat from the FRA profile and deeper levels of the FRC profile, lower C/N ratios, lower amounts of sugars and a predominance of amorphous OM and mucilage suggest more extensive OM degradation. These features delineate a clear threshold between an uppermost “new” regenerating peat section and an “old” catotelm peat below. Nevertheless, even in the latter, the sugar contents remain relatively high (>80 mg/g) compared with other organic and mineral soils. Analysis of typical peat-forming plants and of bulk peat and fine grained fractions allowed identification of the following source indicators: xylose and arabinose for Cyperaceae; rhamnose, galactose and mannose for mosses; and ribose (and to a lesser extent, hemicellulosic glucose) possibly for microbial synthesis.     

Effect of climate change on delivery and degradation of lipid biomarkers in a Holocene peat sequence in the Eastern European Russian Arctic

Lipid biomarkers from a peat plateau profile from the Northeast European Russian Arctic were analyzed. The peat originated as a wet fen ca. 9 ka BP and developed into a peat bog after the onset of permafrost ca. 2.5 ka BP. The distributions and abundances of n-alkanols, n-alkanoic acids, n-alkanes, n-alkan-2-ones and sterols were determined to study the effect of degradation on their paleoclimate proxy information. Plant macrofossil analysis was also used in combination with the lipid distributions. The n-alkanol and n-alkanoic acid distributions in the upper part of the sequence generally correspond to compositions expected from plant macrofossil assemblages. Their carbon preference index (CPI) values increase with depth and age, whereas those of the n-alkanes decrease. The different CPI patterns suggest that n-alkanoic acids and n-alkanols deeper in the sequence may be produced during humification through alteration of other lipids. Excursions in the n-alkanoic acid content also suggest an important contribution of invasive roots to the lipid biomarker composition. The CPIs associated with these compounds show that under permafrost conditions organic material from Sphagnum is better preserved than material from vascular plants. Increasing stanol/stenol ratio values and decreasing n-alkane CPI values indicate progressive degradation of organic matter (OM) with depth. The n-alkan-2-one/n-alkane and n-alkan-2-one/n-alkanoic acid ratios were shown to be useful proxies that can reflect the degree of OM preservation and suggest that both microbial oxidation of n-alkanes and decarboxylation of n-alkanoic acids produce n-alkan-2-ones in this peat sequence.     

Elemental and isotopic carbon and nitrogen records of organic matter accumulation in a Holocene permafrost peat sequence in the East European Russian Arctic

A peat deposit from the East European Russian Arctic, spanning nearly 10 000 years, was investigated to study soil organic matter degradation using analyses of bulk elemental and stable isotopic compositions and plant macrofossil remains. The peat accumulated initially in a wet fen that was transformed into a peat plateau bog following aggradation of permafrost in the late Holocene (～2500 cal a BP). Total organic carbon and total nitrogen (N) concentrations are higher in the fen peat than in the moss‐dominated bog peat layers. Layers in the sequence that have lower concentrations of total hydrogen (H) are associated with degraded vascular plant residues. C/N and H/C atomic ratios indicate better preservation of organic matter in peat material dominated by bryophytes as opposed to vascular plants. The presence of permafrost in the peat plateau stage and water‐saturated conditions at the bottom of the fen stage appear to lead to better preservation of organic plant material. δ¹⁵N values suggest N isotopic fractionation was driven primarily by microbial decomposition whereas differences in δ¹³C values appear to reflect mainly changes in plant assemblages. Positive shifts in both δ¹⁵N and δ¹³C values coincide with a local change to drier conditions as a result of the onset of permafrost and frost heave of the peat surface. This pattern suggests that permafrost aggradation not only resulted in changes in vegetation but also aerated the underlying fen peat, which enhanced microbial denitrification, causing the observed ¹⁵N‐enrichment. Copyright © 2012 John Wiley & Sons, Ltd.     

加拿大阿萨巴斯卡地区泥炭正构烷烃与正烷酮地球化学特征

通过对泥炭正构烷烃和正烷酮的地球化学特征的系统分析,以探讨阿萨巴斯卡地区Mildred泥炭沼泽的物源输入特征,以及正构烷烃和正烷酮的内在成因关系,从而揭示研究区泥炭记录的生物信息和植被演化特征。结果表明:Mildred泥炭正构烷烃和正烷酮均以高分子量C₂₃~C₃₃为主,呈后峰型分布,奇碳优势明显,物源以原地堆积的陆源高等植物为主,少量苔藓类、水生植物也有一定程度的贡献。根据主成分分析和正构烷烃指标,Mildred泥炭分子指示物源输入具有分段性,上段（地表至-17 cm）成炭植物以锈色泥炭藓为主,中段（-17 cm至-41 cm）沉积有机质主要来源于木质树根、杜鹃花科、黑云杉和莎草科等,下段（-41 cm至底部）莎草科类富集,少量松柏、杜鹃花科等木质植物发育。正构烷烃和正烷酮的分布极具相似性,同奇碳数正构烷烃与正烷酮极高的相关性论证了两者的内在成因联系。泥炭中正烷酮类化合物主要来源于相应正构烷烃的微生物氧化作用,剖面上部锈色泥炭藓的富集对正烷酮有一定程度的贡献;结合FT-MS资料,脂肪酸的微生物β-氧化和脱羧基作用是形成正烷酮的另一种有效路径,但不是主要的成因路径。     

Early Permian coal-forming floras preserved as compressions from the Wuda District (Inner Mongolia,China)

Four different compression/impression floras are preserved in only 4.32 m of the geologic section in the Early Permian Shanxi Formation of the Wuda District of Inner Mongolia, northwestern China. These floras represent four different plant communities and landscapes that followed each other in time. The oldest flora was rooted in sandy clay and initiated peat accumulation that lead to the formation of the lower coal seam. This seam is 230-cm thick and overlain by a 66-cm thick volcanic tuff that preserves a second different flora that grew on the peat at the time of the ash-fall. Standing stems and large plant parts are present. The upper part of the tuff is rooted by a single species of lycopsid (the third flora) again initiating peat accumulation. On top of this second seam of 120 cm thickness rests a roof-shale, deposited as mud in a shallow lake, the formation of which was responsible for the cessation of peat deposition. This fourth flora represents the plants growing around the lake on clastic substrate. Four different environments followed each other in this locality over a geologically short time span and each time conditions prevailed to preserve plant macrofossils. Three of these floras represent peat-forming plant communities of essentially the same time interval. This demonstrates the great variability of vegetation and landscapes in the tropical Cathaysian realm of the Late Paleozoic.     

Origin and fluxes of atmospheric REE entering an ombrotrophic peat bog in Black Forest (SW Germany): Evidence from snow, lichens and mosses

The fate of the Rare Earth Elements (REE) were investigated in different types of archives of atmospheric deposition in the Black Forest, Southern Germany: (1) a 70 cm snow pack collected on the domed part of a raised bog and representing 2 months of snow accumulation, (2) a snow sample collected close to the road about 500 m from the peat bog, (3) two species of lichens and (4) a peat profile representing 400 years of peat accumulation as well as a “preanthropogenic” sample and the living moss layer from the top of the core. REE concentrations in peat are significantly correlated to Ti which is a lithogenic conservative element suggesting that REE are immobile in peat bog environments. Snow, lichens and peat samples show similar PAAS (Post Archean Australian Shale) normalized REE distributions suggesting that the complete atmospheric REE signal is preserved in the peat profile. However, the annual flux of REE accumulated by the peat is ca. 10 times greater than that of the bulk winter flux of REE. This difference probably indicates that the REE concentrations in the snowpack are not representative of the average REE flux over the whole year. Despite the pronounced geological differences between this site (granite host-rock) and a previously studied peat bog in Switzerland (limestone host-rock) similar REE distribution patterns and accumulation rates were found at both sites. Given that both sites confirm an Upper Continental Crust signature, the data suggests both sites are influenced by regional and not local, soil-derived lithogenic aerosols.     

若尔盖高原湖沼沉积剖面饱和烃组分特征及地球化学意义

利用GC-MS技术对若尔盖高原一湖沼沉积剖面（深346 cm）沉积有机质的饱和烃馏分进行了分析,结合已有的AMS 14C年代、剖面岩性和TOC资料,探讨了该剖面分子化石分布特征及其相关参数对有机物来源、微生物活动和气候变化等环境信息的指示意义。分析表明,中高碳数占绝对优势的正构烷烃反映了有机物主要来源于高等植物,且草本高等植物输入丰富;岩相、TOC和Pr/Ph比值很好地指示了该剖面沉积物从早全新世（约11.4~7.3 cal ka BP,深度346~203 cm）强还原深湖条件到中全新世（约7.3~4.5 cal ka BP,>203 cm）弱还原沼泽条件的演化过程,正构烷烃参数奇偶优势（OEP1和OEP2）、C25/C31和轻烃/重烃比值（∑C21-/∑C22+）详细反映了这种水文演变过程中生物源的变化,尤其剖面120 cm以上很可能有泥炭藓(Sphagnum)的重要输入,而且敏感地指示了剖面120 cm以上有机物遭受了明显的微生物改造作用,从而引起正构烷烃组分的改变。另外,在约9.8~8.6 cal ka BP（深度286~240 cm）期间剖面岩性及其以上各项代用指标发生明显快速变化,说明早全新世若尔盖高原气候相对暖湿阶段具有不稳定性。     

Differential hydrogen isotopic ratios of Sphagnum and vascular plant biomarkers in ombrotrophic peatlands as a quantitative proxy for precipitation—evaporation balance

We have developed a new approach to quantitatively reconstruct past changes in evaporation based on compound-specific hydrogen isotope ratios of vascular plant and Sphagnum biomarkers in ombrotrophic peatland sediments. We show that the contrast in H isotopic ratios of water available to living Sphagnum (top 20 cm) and in the rooting zone of peatland vascular plants can be used to estimate “?”—the fraction of water remaining after evaporation. Vascular plant leaf waxes record H isotopic ratios of acrotelm water, which carries the D/H ratio signature of precipitation and is little affected by evaporation, whereas the Sphagnum biomarker, C₂₃n-alkane, records H isotopic ratios of the water inside its cells and between its leaves, which is strongly affected by evaporation at the bog surface. Evaporation changes can then be deduced by comparing H isotopic ratios of the two types of biomarkers. We calibrated D/H ratios of C₂₃n-alkane to source water with lab-grown Sphagnum. We also tested our isotopic model using modern surface samples from 18 ombrotrophic peatlands in the Midwestern United States. Finally, we generated a 3000-year downcore reconstruction from Minden Bog, Michigan, USA. Our new record is consistent with records of other parameters from the same peatland derived from different proxies and allows us to differentiate precipitation supply and evaporative loss.     

A proxy record of late Holocene climate change from May Moss,northeast England

Quantitative reconstruction of changes in mire surface wetness has been used to reconstruct proxy climate from an upland ombrotrophic blanket mire on the North York Moors in northeast England (May Moss). Testate amoebae, plant macrofossil and humification analyses were carried out for six peat profiles. Transfer functions are used to generate estimates of water table levels from the testate amoebae stratigraphy, which complement the semi‐quantitative indications of changing surface wetness provided by plant macrofossil and humification analysis. ¹⁴C dates provide the chronology for the stratigraphy. Differences were encountered between AMS ¹⁴C dates on pure Sphagnum remains and radiometric dates on bulk peat from the same horizon, which perhaps arise from the heterogeneity of peat. Replicate palaeoecological analysis of adjacent cores identifies consistency within testate amoebae and plant macrofossil stratigraphies, and reveals a strong agreement between the water table level proxies. The record of hydrological changes at sites across May Moss are in synchrony, and so climate change is the most likely cause of the moisture fluctuations. Changes to a wetter or cooler climate were identified cal. ad 260–540, ca. ad 550–650, cal. ad 670–980, ca. ad 1350–1450, cal. ad 1400–1620 and ca. ad 1700–1800. Periods with a drier or warmer climate precede all of these wet shifts, with particularly dry periods between cal. ad 650–860 and 690–980 and between cal. ad 1290–1410 and 1400–1620. Copyright © 2001 John Wiley & Sons, Ltd.     

A multiproxy climate record from a raised bog in County Fermanagh,Northern Ireland: a critical examination of the link between bog surface wetness and solar variability

A proxy climate record from a raised bog in County Fermanagh, Northern Ireland, is presented. The record spans the interval between 2850 cal. yr BC and cal. yr AD 1000 and chronological control is achieved through the use of tephrochronology and ¹⁴C dating, including a wiggle‐match on one section of the record. Palaeoclimatic inferences are based on a combination of a testate amoebae‐derived water table reconstruction, peat humification and plant macrofossil analyses. This multiproxy approach enables proxy‐specific effects to be identified. Major wet shifts are registered in the proxies at ca. 1510 cal. yr BC, 750 cal. yr BC and cal. yr AD 470. Smaller magnitude shifts to wetter conditions are also recorded at ca. 380 cal. yr BC, 150 cal. yr BC, cal. yr AD 180, and cal. yr AD 690. It is hypothesised that the wet shifts are not merely local events as they appear to be linked to wider climate deteriorations in northwest Europe. Harmonic analysis of the proxies illustrates statistically significant periodicities of 580, 423–373, 307 and 265 years that may be related to wider Holocene climate cycles. This paper illustrates how the timing of climate changes registered in peat profiles records can be precisely constrained using tephrochronology to examine possible climatic responses to solar forcing. Relying on interpolated chronologies with considerable dating uncertainty must be avoided if the climatic responses to forcing mechanisms are to be fully understood. Copyright © 2007 John Wiley & Sons, Ltd.     

Indicator value of oribatid mites in determining past permafrost dynamics in northern European sub‐Arctic peatlands

Permafrost dynamics play an important role in the surface hydrology and carbon balance of northern peatlands. Plant macrofossil analysis with radiocarbon dating has been widely used in detecting past permafrost dynamics in peatlands; however, there is a lack of permafrost‐specific plant indicator species, which makes it challenging to determine the exact timing of historical permafrost aggradation. We investigated the indicator value of oribatid mites in determining past permafrost dynamics in sub‐Arctic peatlands. Analyses of subfossil oribatid mite assemblages of Holocene peat profiles from two mires, one in northern Finland and one in northeastern European Russia, were carried out and interpreted using modern calibration data from the same study areas. The results were compared with previously published reconstructions of permafrost history based on plant macrofossil analyses from the same locations. The results suggest that the oribatid mites Carabodes labyrinthicus, Chamobates borealis and Neoribates aurantiacus are promising indicator species to detect past permafrost occurrence in peatlands. In addition, N. aurantiacus is clearly associated with the presence of lichens, which is particularly useful because lichen remains are rarely preserved in peat deposits. Results are in accordance with earlier studies showing that oribatid mites are useful indicators of past environmental change.     

Pyrolysis GC-MS as a rapid screening tool for determination of peat-forming plant composition in cores from ombrotrophic peat

Peat cores provide decadal to centennial records of climatic and environmental change, including evidence for human/environment interaction. Existing palaeoenvironmental proxies (macrofossils, pollen, humification, testate amoebae, lipid composition) require multiple laboratory preparation steps and may be subject to differential preservation that can limit production of a continuous time series. The potential for pyrolysis gas-chromatography-mass-spectrometry (Py-GC-MS) to be applied to bulk peat samples is investigated here. The only preparatory step required was freeze drying. Analysis of a range of important peat-forming plants demonstrates that Sphagnum moss species are unique in containing the pyrolysis product of sphagnum acid, 4-isopropenylphenol. In contrast, non-Sphagnum species are rich in lignin pyrolysis products, which are absent from Sphagnum. The presence of these pyrolysis markers is reflected in bulk peat composition and tested here using archives from Bolton Fell Moss and Butterburn Flow (UK), Kontolanrahka (Finland) and Bissendorfer Moor (Germany). A ratio between 4-isopropenylphenol and two lignin pyrolysis products is proposed as a proxy for total Sphagnum input to peat archives and shows potential for use as a rapid screening tool for characterising bulk peat composition before more intensive analysis.     

A multiproxy record of late Holocene natural and anthropogenic environmental change from the Sphagnum peat bog Dürres Maar,Germany: implications for quantitative climate reconstructions based on pollen

Pollen data are well established for quantitative climate reconstructions over long timescales, including the Holocene and older interglacials. However, anthropogenically induced environmental change in central Europe was strong during the last 4 ka, challenging quantitative reconstructions of this time period. Here we present quantitative climate reconstructions based on pollen analyses and evaluate them with the peat humification record and the stable carbon isotopes of Sphagnum plant material (δ¹³C_cellulose). All analyses were carried out on the same 7.5 m long, largely ombrotrophic peat bog section from Dürres Maar. Three different methods were used for the quantitative climate reconstructions on the basis of the pollen data: (1) a probabilistic indicator taxa approach (the ‘pdf method’); (2) a modern analogue technique based on pollen taxa from modern surface samples (cMAT); and (3) a modern analogue technique expanded by plant functional types (pMAT). At Dürres Maar the peat humification is only affected by peat cutting during the Roman period and the Middle Ages. The stable carbon isotopes are seemingly unaffected by human impact. Thus both proxies provide independent data to evaluate the reconstructions on the basis of pollen data. The quantitative climate reconstructions on the basis of the individual methods are in general relatively similar. Nevertheless, distinct differences between the individual approaches are also apparent, which could be attributed to taxa that reflect human impact on a local to regional scale. While the pdf method appears to be relatively robust to all observed anthropogenically induced vegetation changes, it potentially underestimates climate variability. This method is therefore expected to be independent of local site characteristics and to provide robust quantitative estimates of climatic trends rather than of climatic variability of small amplitude. This is of value for palaeoclimate reconstructions of older interglacials, for which neither multiple sites nor independent climate proxies are available for comparison. Copyright © 2009 John Wiley & Sons, Ltd.     

An orthogonal experimental study of phytolith size of Phragmites communis in northeast China

Based on the widespread distribution and abundant phytoliths produced by Phragmites communis, phytoliths of P. communis in northeast China were investigated to identify the primary influencing factors on phytolith size using an orthogonal experimental method. Temperature and precipitation were found to be the prominent factors influencing the sizes of short‐cell phytoliths including the saddle and the rondel morphotypes, whereas there were no obvious variations in the width‐to‐length ratios of short‐cell phytoliths in response to environmental factors. These results indicate that short‐cell phytoliths are genetically stable, confirming that they can be used for the classification of grasses. Moreover, precipitation was the main factor influencing the sizes of the lanceolate phytoliths and silicified stomata, and their width‐to‐length ratios changed significantly in response to precipitation and habitat differences. These findings reveal that lanceolate and silicified stomata phytoliths are sensitive to environmental changes, indicating their usefulness for palaeoenvironment reconstruction. Moreover, variations in their width‐to‐length ratios and their sizes may provide some information for plant classification, even at species level. Finally, the results of a principal component analysis of the sizes of P. communis phytoliths further verify the reliability of the orthogonal experiment results, in that temperature and precipitation were the prominent factors influencing the size of all P. communis phytoliths except for the length of saddle and width of the saddle morphotypes. This research into the primary environmental significance of the sizes of P. communis phytoliths may contribute to improving the precision of plant classification and the model for quantitative reconstruction of the palaeoenvironment to aid in reconstructions of palaeovegetation and palaeoclimate.     

Distribution of aliphatic des-A-triterpenoids in the Dajiuhu peat deposit, southern China

Aliphatic des-A-triterpenoids have been tentatively assigned in samples taken from a 260 cm thick peat sequence from the Dajiuhu Basin of southern China using gas chromatography–mass spectrometry (GC–MS). The compounds, possessing the carbon skeletons of oleanane, ursane or lupane, are generally considered as the microbial degradation products of plant triterpenoids under anoxic conditions. Abundant aliphatic des-A-triterpenoids were observed only in peat samples during the transitional period from the last glaciation to the early Holocene (9.5–11.6 cal ¹⁴C ka BP). Among these, des-A-lupane is the only saturated ring A-degraded compound, whilst mono- and di-unsaturated des-A-triterpenes are dominated by oleanane and ursane derivatives. The mono- and di-unsaturated des-A-triterpenes show a strong correlation (R² 0.94) in abundance, indicating that they may be derived from the same source or process. Des-A-lupane shows no correlation in abundance with the mono- or di-unsaturated des-A-triterpenes (R² < 0.25) and may be derived from a different source or process in the catchment. The period with abundant aliphatic des-A-triterpenoids corresponds to the interval with relatively high sedimentation rate (> 0.3 mm per year). These data indicate that the abundance of aliphatic des-A-triterpenoids in the Dajiuhu peat deposit in the early Holocene may result from the prevailing reducing conditions in the water table or surficial sediment and/or rapid preservation of the early diagenetic products. Our study highlights the potential application of des-A-triterpenes in the reconstruction of palaeoenvironments based on peat sequences.     

Holocene fire regime changes from multiple-site sedimentary charcoal analyses in the Lourdes basin (Pyrenees,France)

One lake and three peat bogs from the Lourdes glacial basin (France) were used for macrocharcoal analyses and fire frequency reconstruction over the entire Holocene (11700 years). The chronology was based upon thirty-three 14C AMS dates. Comparison of the distribution of both CHarcoal Accumulation Rate (CHAR) and fire return intervals showed that charcoal accumulation significantly differs between the lake and the peat bogs, but that frequency calculation overcomes the disparity between these site types. A composite frequency was built from the four individual records to assess regional versus local variability and fire regime controls by comparisons with regional fire activity, Holocene climatic oscillations and vegetation history. The millennial variability can be depicted as follows: relatively high frequency between 8000 and 5000 cal a BP (up to 5 fires/500 yrs), relatively low frequency between 5000 and 3000 cal a BP (down to 0 fires/500 yrs), and an increase between 3000 and 500 cal a BP (up to 4 fires/500 yrs). From 8000 to 5000 cal a BP, fire frequency displays strong synchrony between sites and appears to be mostly driven by increased summer temperature characterizing the Holocene Thermal Maximum (HTM). On the contrary, during the last 3000 years fire frequency was heterogeneous between sites and most probably human-driven. However, higher frequency at the millennial scale during the mid-Holocene strongly suggests that the perception of human-driven fire regime depends on the strength of natural controls.     

Hydrogen isotopic ratios of plant wax n-alkanes in a peat bog deposited in northeast China during the last 16 kyr

Based on paleoclimatic reconstructions using various proxies, the Holocene Climate Optimum (10.5–6 ka) has been characterized as a warmer and wetter period in most of East Asia. The summer monsoons associated with the East Asian Monsoon evidently intensified and extended further inland from the Pacific Ocean, a source region of moisture. A notable exception to this general pattern exists in northeast China, where less wet conditions are recorded. We determined molecular compositions of individual plant wax hydrocarbons and their hydrogen isotope compositions (δD values) in a radiocarbon-dated peat core recovered from the Hani marsh in Jilin Province (China) and confirmed that the temperature-dependent effective precipitation in northeast China decreased during the Holocene Climate Optimum. A combination of P_aq, an indicator of the relative contribution of aquatic to terrestrial plants, and the difference in δD between low (C₂₃, C₂₅ and C₂₇) and high molecular weight (C₃₁) n-alkanes in the Hani peat bog indicates a dramatic change in vegetation from the deglaciation to the Holocene. No significant differences were observed between the δD values of low and high molecular weight n-alkanes with relatively high δD values and low P_aq during the early Holocene, indicating that all n-alkanes were produced by evapotranspiration-sensitive terrestrial plants during that time. However, lower δD values of mid-chain n-alkanes (C₂₃, C₂₅ and C₂₇) relative to the long chain n-alkane (C₃₁), together with higher P_aq values during the deglaciation (14–11 ka), suggest an increase in the contribution of aquatic plants and a higher water level during the period. The study demonstrates that northeast China was under a markedly wetter climate condition during the late deglaciation. For the 16 kyr record in the Hani peat sequence, we infer that moisture delivery by the East Asian Monsoon was relatively invariable in northeast China, but increased evaporation during the warmer Holocene Climate Optimum reduced the effective precipitation, defined by the balance between precipitation and evaporation.     

Geochemical appraisal of palaeovegetation and climate oscillation in the Late Miocene of Western Bulgaria

Palaeobotanical methods and geochemical techniques were used to assess plant contribution and palaeoenvironment for the Staniantsi Basin, Bulgaria. The aim was to connect palaeovegetation change and climate oscillation based on pollen and statistical analysis with organic geochemical proxies for a Late Miocene lacustrine to paludial sedimentary succession.Three samples from lignite/marl cycles were studied. The biomarker assemblage and bulk chemical data indicated that gymnosperms were not important in the palaeomire. The presence of des-A-triterpenoids, 17,21-seco-triterpenoids, hopanes, a high content of a D-ring monoaromatic hopane, and aromatized triterpenoids suggested that photochemical and microbial processes significantly contributed to the alteration of the organic matter (OM). A prolonged period of high water table and severe mechanical destruction promoted microbial activity prior to burial and enhanced decay. A geochemical appraisal of short term climate oscillation (ca. 21.7 kyr) was attempted within the limitations of the small number of samples studied. The cycles are expressed as lignite/marl-clay layers combined with cyclic changes in swamp vegetation related to cyclic changes in groundwater level and inundation of the basin. In periods of low water level (swamp phase) lignite accumulation took place. Preliminary results for selected samples suggest that the oscillation may be reflected in the content of friedelin vs. possible degradation products. The ratio of a chromatographic peak tentatively assigned as A-norfriedel-8-en-10-one to friedelin is proposed as a means of detecting short term environmental cycles, where values <1 represent the swamp phase and those >1 reflect periods of inundation. However, time-series analysis using densely sampled lignite-clay layer oscillations are needed to confirm the value of this biomarker ratio for environmental reconstruction.