Accelerator Mass Spectrometry 14C Research Articles

High-resolution, multiproxy palaeoenvironmental changes recorded from Two Mile Lake, southern Western Australia: implications for Ramsar-listed playa sites

Numerous saline playa lakes exist across the arid, semiarid and temperate regions of Australia. These playa lakes exhibit a diverse range of hydrological conditions to which the Australian aquatic invertebrate biota have become adapted and which the biota can utilise as refugia in times of hydrological deterioration. Saline playas also yield palaeoenvironmental records that can be used to infer lacustrine and catchment responses to environmental variability. We present a palaeoenvironmental record recovered from Two Mile Lake, a saline playa from southern Western Australia. Dating, based on quartz optical luminescence and 14C accelerator mass spectrometry of biogenic carbonates and organic fibres, suggests that most of the sediment was rapidly deposited at 4.36 ± 0.25 thousand years ago. Ostracods and non-marine foraminifera preserved in the sediment show periods of faunal colonisation of the lake with oscillations between hypersaline and oligosaline conditions. The geochemistry of ostracod valves and foraminifera tests suggests higher-frequency variability within the lake, and palynological changes indicate landscape changes, possibly in response to fire. The Two Mile Lake record highlights the utility of saline playas as archives of environmental change that can be used to guide wetland health management, particularly under the impacts of a changing climate.

Stable nitrogen isotope record of lacustrine sediments in Lake Onuma (Northern Japan) indicates regional hydrological variability during the past four centuries

Discriminating natural and anthropogenic forcing on hydroclimatic changes is of fundamental importance for projecting future precipitation distribution under the warming climate. A sediment core (ON12C) obtained from Lake Onuma is used to study the evolution of precipitation in Northern Japan. The age-depth model for the core is based on three identified tephra layers, combined with accelerator mass spectrometry 14C measurements of plant remnants, 137Cs dating, and lithology. Multi-proxy records, including pollen concentration, Alnus pollen percentages and C/N atomic ratios, indicate that the δ15N record reflects nitrogen availability in the catchment where precipitation may exert a significant impact. The δ15N record shows that the precipitation was gradually increasing from 1640 AD, reaching peak strength in the middle of the 19th century, followed by a dry interval during the 20th century. The reconstructed variability in the precipitation from Lake Onuma is supported by other precipitation records from the Asian monsoon region. Solar irradiance is likely responsible for the changes in the summer monsoon precipitation on the centennial timescales during the late Little Ice Age, and the winter monsoon may also have played an important role in snow precipitation. However, the 20th century anomaly indicates that the Asian summer monsoon precipitation variability might be affected by anthropogenic forcing.

Palaeoenvironmental Interpretation of Yedoma Silt (Ice Complex) Deposition as Cold‐Climate Loess, Duvanny Yar, Northeast Siberia

Uncertainty about the geological processes that deposited syngenetically frozen ice-rich silt (yedoma) across hundreds of thousands of square kilometres in central and northern Siberia fundamentally limits our understanding of the Pleistocene geology and palaeoecology of western Beringia, the sedimentary processes that led to sequestration of hundreds of Pg of carbon within permafrost and whether yedoma provides a globally significant record of ice-age atmospheric conditions or just regional floodplain activity. Here, we test the hypotheses of aeolian versus waterlain deposition of yedoma silt, elucidate the palaeoenvironmental conditions during deposition and develop a conceptual model of silt deposition to clarify understanding of yedoma formation in northern circumpolar regions during the Late Pleistocene. This is based on a field study in 2009 of the Russian stratotype of the ‘Yedoma Suite’, at Duvanny Yar, in the lower Kolyma River, northern Yakutia, supplemented by observations that we have collected there and at other sites in the Kolyma Lowland since the 1970s. We reconstruct a cold-climate loess region in northern Siberia that forms part of a vast Late Pleistocene permafrost zone extending from northwest Europe across northern Asia to northwest North America, and that was characterised by intense aeolian activity.

Early and late Holocene sediment yield of Austdalsbreen glacier, southwest Norway

Early and late Holocene sediment yield of Austdalsbreen glacier, an eastern outlet glacier of Jostedalsbreen ice cap in southwest Norway, was investigated by studies of sedimentation rates in the proglacial lakes Austdalsvatn and Styggevatn, along with subglacial topography radar survey and seismic surveys of the lake bed sediment. Sediment cores were taken from both lakes. Annual sedimentation throughout the cores was identified from high resolution photographs and X-ray scan analyses. Three accelerator mass spectrometry (AMS) 14C datings were carried out to assist dating of sedimentation during different periods. The seismic survey profiles revealed the distribution of these sediments. The impact of the subglacial topography on the sediment delivery from upstream, along with grain-size distribution and organic content analyses, were also taken into account in the interpretation of sediment cores. Possible impact of climate change on sediment delivery from the glacier was discussed by comparison of the average lake sedimentation rates during two periods of postglacial time. Around calibrated years 9000–8870BP, Austdalsbreen glacier was subject to rapid retreat and calving. It was found that the glacier retreated rapidly from its maximum extension, which had totally covered the two lakes, in the 130years in the early Holocene. About 1.4milliontonnes suspended load was delivered from the glacier during this short period, giving an average sediment yield of 400t/y/km2. Such a high sediment yield is hypothesised to be caused by rapid calving, fast ice motion, abundance of meltwater, and larger areal extension and volume of the glacier at that time. The glacier probably disappeared from the catchment around 6000BP. The glacier advanced after the 1100s, reaching its Little Ice Age maximum before retreating to its present position. About 3.5milliontonnes suspended load was delivered from the glacier during the 800years from A.D. 1186 to 1986, corresponding to an average sediment yield of 290t/y/km2, 30% lower than that of the early Holocene retreat. This difference is probably mostly caused by the smaller area of the modern glacier.

Where does the time go?: Mixing and the depth-dependent distribution of fossil ages

Knowing how time is distributed within a fossil record is fundamental to paleobiology. Many efforts to quantify temporal resolution have estimated rates of specimen decay from the frequency distribution of specimen ages in near-surface assemblages. The implicit assumption has been that the shape of these distributions is invariant with depth and thus decay-rate estimates reflect the temporal resolution of a fossil record’s deeper layers as well. Here we present a new model that predicts how age-frequency distribution shape will change with depth due to the interplay of burial, mixing, and decay. Unlike previous models, this model distinguishes the dimensions of time, specimen age, and depth, and predicts a right-to-left shift in age-frequency distribution skewness, and a decrease in kurtosis, with increasing stratigraphic depth. We find support for these predictions with the accelerator mass spectrometry 14C dating of 80 small mammal specimens spanning the Quaternary fossil record of Homestead Cave, Utah (United States). Our study indicates (1) that previous models overestimate rates of specimen decay, (2) that the acuity of ecological information captured in near-surface assemblages is higher than previously inferred, and (3) how time-averaging can alter the apparent dynamics of biodiversity over time. We thereby offer a new quantitative framework to account for time-averaging, to merge modern and paleontological archives, and to place ecological systems within the context of their past dynamics.

A new AMS facility at Inter University Accelerator Centre, New Delhi

Inter University Accelerator Centre (IUAC), a national facility of government of India, is having a 15UD Pelletron accelerator for multidisciplinary ion beam based research programs. Recently, a new accelerator mass spectrometry (AMS) facility has been developed after incorporating many changes in the existing 15UD Pelletron accelerator. A clean chemistry laboratory for 10Be and 26Al with all the modern facilities has also been developed for the chemical processing of samples. 10Be measurements on sediment samples, inter laboratory comparison results and 26Al measurements on standard samples are presented in this paper. In addition to the 10Be and 26Al AMS facilities, a new 14C AMS facility based on a dedicated 500kV tandem ion accelerator with two cesium sputter ion sources, is also being setup at IUAC.

Microscale characterization and trace element distribution in bacteriogenic ferromanganese coatings on sand grains from an intertidal zone of the East China Sea.

An ancient wood layer dated at about 5600 yr BP by accelerator mass spectrometry (AMS) 14C was discovered in an intertidal zone of the East China Sea. Extensive and horizontally stratified sediments with black color on the top and yellowish-red at the bottom, and some nodule-cemented concretions with brown surface and black inclusions occurred in this intertidal zone. Microscale analysis methods were employed to study the microscale characterization and trace element distribution in the stratified sediments and concretions. Light microscopy, scanning electron microscopy (SEM) and backscattered electron imaging (BSE) revealed the presence of different coatings on the sand grains. The main mineral compositions of the coatings were ferrihydrite and goethite in the yellowish-red parts, and birnessite in the black parts using X-ray powder diffraction (XRD). SEM observations showed that bacteriogenic products and bacterial remnants extensively occurred in the coatings, indicating that bacteria likely played an important role in the formation of ferromanganese coatings. Post-Archean Australian Shale (PAAS)-normalized middle rare earth element (MREE) enrichment patterns of the coatings indicated that they were caused by two sub-sequential processes: (1) preferentially release of Fe-Mn from the beach rocks by fermentation of ancient woods and colloidal flocculation in the mixing water zone and (2) preferential adsorption of MREE by Fe-Mn oxyhydroxides from the seawater. The chemical results indicated that the coatings were enriched with Sc, V, Cr, Co, Ni, Cu, Zn, Ba, especially with respect to Co, Ni. The findings of the present study provide an insight in the microscale features of ferromanganese coatings and the Fe-Mn biogeochemical cycling during the degradation of buried organic matter in intertidal zones or shallow coasts.

Charge state distributions and charge exchange cross sections of carbon in helium at 30–258 keV

With the introduction of helium stripping in radiocarbon (14C) accelerator mass spectrometry (AMS), higher +1 charge state yields in the 200keV region and fewer beam losses are observed compared to nitrogen or argon stripping. To investigate the feasibility of even lower beam energies for 14C analyses the stripping characteristics of carbon in helium need to be further studied. Using two different AMS systems at ETH Zurich (myCADAS and MICADAS), ion beam transmissions of carbon ions for the charge states −1, +1, +2 and +3 were measured in the range of 258keV down to 30keV. The correction for beam losses and the extraction of charge state yields and charge exchange cross sections will be presented. An increase in population of the +1 charge state towards the lowest measured energies up to 75% was found as well as agreement with previous data from literature. The findings suggest that more compact radiocarbon AMS systems are possible and could provide even higher efficiency than current systems operating in the 200keV range.

Comparison between luminescence and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia

Dust depositions are critical archives for understanding interior aridification and westerly climatic changes in Central Asia. Accurate and reliable dating of loess is very important for interpreting and correlating environmental records. There remains a disparity between luminescence ages and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia. In this study, we establish a closely spaced quartz optically stimulated luminescence (OSL) chronology for the 20.5-m-thick Nilka loess section in the Ili Basin. Based on OSL ages, two intervals of higher mass accumulation rate occurred at 49–43 ka and 24–14 ka. We further compare these OSL ages with 23 accelerator mass spectrometry (AMS) 14C ages of bulk organic matter. The results indicate that the OSL and radiocarbon ages agree well for ages younger than ca. 25 14C cal ka BP. However, beyond 30 cal ka BP, there is no consistent increase in AMS 14C age with depth, while the OSL ages continue to increase. These differences confirm the observation that the AMS 14C ages obtained using conventional acid–base–acid (ABA) pretreatment are severely underestimated in other terrestrial deposits in Central Asia, which could be due to 2–4% modern carbon contamination. However, OSL dating is applicable for constructing an accurate chronology beyond 30 cal ka BP. We suggest caution when interpreting paleoenvironmental changes based on radiocarbon ages older than 25 cal ka BP.

Measuring Quaternary time: A 50‐year perspective

ABSTRACTOver the last 50 years, there have been significant developments in the range and sophistication of the chronological tools now available to Quaternary scientists. Notable milestones include the introduction of new methods (e.g. optically stimulated luminescence, cosmogenic radionuclide dating, ice‐layer counting, molecular ‘clocks’) and the refinement of established techniques (e.g. accelerator mass spectrometry 14C dating, 14C calibration, high‐precision uranium‐series dating, argon–argon dating, cryptotephra analysis). Developing new techniques and methodologies for measuring Quaternary time is not an end in itself, however: it is stimulated by a parallel need, which is a deeper understanding of the mode, pattern and rates of environmental processes, and how different processes inter‐connect. Here we review some of the important limitations that continue to constrain our ability to provide coherent chronologies for Quaternary environmental reconstructions at both millennial and sub‐millennial timescales. We focus our discussion on two unique stratigraphic templates: first, the marine oxygen isotope sequence that spans the full Quaternary period; and, second, the Greenland ice‐core record, which provides a basis for dating environmental changes through the last glacial cycle.

AMS Radiocarbon Dating from the Neolithic of Eastern Ukraine Casts Doubts on Existing Chronologies

The Seversky Donets River (Northern Donets) basin in eastern Ukraine and the Lower Don River valley in Russia were inhabited by populations that have been considered to be one of the earliest pottery-using cultures in Europe. The early pottery sites are all located on riverbanks and contain middens with many mollusk shells and fish bones. This suggests the intense exploitation of freshwater resources. The accuracy of radiocarbon dates obtained from these locations is of crucial importance for understanding the development of new technologies, diversification of the food consumed and its preparation strategies, as well as the degree of sedentism in this region, associated with the beginnings of pottery-making technology. The chronology of Neolithic sites in this region, however, was developed on the basis of 14C dates commonly obtained through the dating of freshwater mollusk shells, pottery with mollusk shell temper, or organic residue on pottery shards. Such samples are potentially affected by the freshwater reservoir effect, raising concerns about the accuracy of those dates. This paper presents accelerator mass spectrometry (AMS) 14C dates from a small pilot study from sites in eastern Ukraine in order to test for the presence of the reservoir effect in this region. The AMS 14C dates presented in this paper challenge the 14C chronology based on mollusk shell or organic residue, which appears to generate much older dates than those on wood charcoal or terrestrial animal bone.

Matching Dendrochronological Dates with the Southern Hemisphere 14C Bomb Curve to Confirm Annual Tree Rings in Pseudolmedia rigida from Bolivia

This study used high-precision radiocarbon bomb-pulse dating of selected wood rings to provide an independent validation of the tree growth periodicity of Pseudolmedia rigida (Klotzsch & H. Karst) Cuatrec. from the Moraceae family, collected in the Madidi National Park in Bolivia. 14C content was measured by accelerator mass spectrometry (AMS) in 10 samples from a single tree covering over 70 yr from 1939 to 2011. These preliminary calendar dates were determined by dendrochronological techniques and were also used to select the samples for 14C AMS. In order to validate these preliminary dates using the established Southern Hemisphere (SH) 14C atmospheric concentration data set, the targeted rings were selected to be formed during periods before and after the 14C bomb spike nuclear tests (i.e. 1950s–1960s). The excellent agreement of the dendrochronological dates and the 14C signatures in tree rings associated with the same dates provided by the bomb-pulse 14C atmospheric values for the SH (SHCal zone 1–2) confirms the annual periodicity of the observed growth layers, and thus the high potential of this species for tree-ring analysis. The lack of discrepancies between both data sets also suggests that there are no significant latitudinal differences between the 14C SHCal zone 1–2 curve and the 14C values obtained from the selected tree rings at this geographic location (14°33′S, 68°49′W) in South America. The annual resolution of P. rigida tree rings opens the possibility of broader applications of dendrochronological analysis for ecological and paleoclimatic studies in the Bolivian tropics, as well as the possibility of using wood samples from some tree species from this region to improve the quality of the bomb-pulse 14C SHCal curve at this latitude.

Holocene abrupt climate fluctuations: Sedimentary record from the inner-shelf mud area of the East China Sea

Sediment core MZ02 from the inner-shelf mud area of the East China Sea was studied to address paleoclimate and marine environment change during the Holocene epoch. This core was analyzed for accelerator mass spectrometry (AMS) 14C dating, grain size, magnetic susceptibility, geochemical index (Al/Ti, Ba/Ti), oxygen isotope, and Mg/Ca ratio of benthic for a minifera. Three significant climate change events were identified, which occurred at 8.4, 7.2 and 6.2 ka BP, respectively. The sediments are characteristic of the period, with coarse grain size and smaller Mg/Ca and δ 18O values. The study revealed that the characteristics of abrupt climate fluctuation were consistent with monsoon and paleoceanographic records of the adjacent land and tropical Pacific. There are century solar cycles in the sedimentary record. The 200-year cycle is the most significant, suggesting that solar activity was the major cause of rapid climate change in the research area during the Holocene.

Marine Radiocarbon Reservoir Values in Southern California Estuaries: Interspecies, Latitudinal, and Interannual Variability

Many studies use radiocarbon dates on estuarine shell material to build age-depth models of sediment accumulation in estuaries in California, USA. Marine 14C ages are typically older than dates from contemporaneous terrestrial carbon and local offsets (ΔR) from the global average marine offset need to be calculated to ensure the accuracy of calibrated dates. We used accelerator mass spectrometry (AMS) 14C dating on 40 pre-1950 salt marsh snail and clam shells previously collected from four California estuaries. The average ΔR and standard deviation of 217 ± 129 14C yr is consistent with previous calculations using mixed estuarine and marine samples, although the standard deviation and resulting age uncertainty was higher for our estuarine calculations than previous studies. There was a slight but significant difference (p = 0.024) in ΔR between epifaunal snails (ΔR = 171 ± 154 14C yr) and infaunal clams (ΔR = 263 ± 77 14C yr), as well as between samples from individual estuaries. However, a closer examination of the data shows that even for the same species, at the same estuary, ΔR can vary as much as ∼500 14C yr. In some cases, the bulk of this variation occurs between samples collected by different collectors at different times, potentially indicating time dependence in carbon sources and ΔR variation. These variations could also be attributed to differences in collection location within a single estuary and resulting spatial differences in carbon sources. Intertidal specimens located in the high marsh may have lower ΔR than fully marine counterparts because of increased terrestrial 14C input. The large variations in ΔR here highlight the need for conservative chronological interpretations, as well as the assumption of wide uncertainties, when dating samples from estuarine sources.

Paleodiet, Radiocarbon Chronology, and the Possibility of Freshwater Reservoir Effect for Preobrazhenka 6 Burial Ground, Western Siberia: Preliminary Results

This article presents the results of radiocarbon dating and a chronology of the Preobrazhenka 6 site of the Odino culture (Baraba forest steppe, western Siberia). Currently available 14C data for the necropolis do not allow accurate determination of the presence or absence of reservoir effects, and as such, further research is needed. Accelerator mass spectrometry (AMS) 14C dating of paired samples of terrestrial faunal and fish remains from a Neolithic pit suggest the absence of a reservoir effect in fish bone collagen. Middle Bronze Age burials have therefore been estimated to date to the 23rd–20th centuries cal BC. Pits with fish remains are dated earlier than burials, to the 63rd–61st centuries cal BC. Stable isotope measurements of human bone collagen (high δ15N and low δ13C values) indicate diets based on C3 plants and fish. Apparently, the role of animal protein in the diet was not significant. Dental paleopathology analysis has confirmed the important role of wild plants in human diet. Neolithic fish bones are elevated in δ13C [–13.5‰, average mean (n = 4)]. They are significantly different from the associated values of fish from the Late Bronze Age settlement of Chicha 1 [–22.5‰, average mean (n = 10)], which is also located in the Baraba forest steppe. The difference in δ13C values in fish bones may be determined by the origin of the samples, being derived either from lakes or rivers.

One-Year-Long Continuous and Synchronous Data Set of Fossil Carbon in Atmospheric PM2.5 and Carbon Dioxide in Debrecen, Hungary

Radiocarbon investigation of atmospheric PM2.5 aerosol synchronized with 14CO2 observations began in Debrecen in the winter of 2010. The aim of the study was to determine the contemporary and fossil carbon fractions in the aerosol and to set them against the fossil CO2 excess data referring to the same period. The mass of the collected PM2.5 mode on prebaked quartz filters was determined gravimetrically, while its total carbon mass was calculated from the pressure of CO2 gas produced after the combustion of the filters. As a result of the applied sampling and preparation method, the stable, nonvolatile carbon forms were principally studied. 14C measurements of the tiny aerosol bulk samples were performed using the EnvironMICADAS accelerator mass spectrometer at ATOMKI. The sample preparation method was tested using several blanks, standards, and real samples. Test results showed good reproducibility for the applied aerosol sample preparation and accelerator mass spectrometry (AMS) 14C analyses. Atmospheric fossil CO2 excess data were calculated according Levin et al. (2003), using the 14C results of collected CO2 samples measured by the gas proportional counting system at ATOMKI. Mass concentration of PM10 involving the PM2.5 mode in the city air exceeded the daily average of 50 μg/m3 (24-hr limit value in the EU) several times in 2011, mainly during the winter. The results showed that recently derived carbon most likely from domestic wood burning was causing the elevated carbon mass concentration of PM2.5 in Debrecen at the time. In the course of the 1-yr-long continuous and systematic comparison of fossil carbon mass concentration of PM2.5 mode and mole fraction of fossil excess of atmospheric CO2, similar and synchronous trends were observed during the studied period in Debrecen.

Erratum to: Evaluating environmental drivers of Holocene changes in water chemistry and aquatic biota composition at Lake Loitsana, NE Finland

This study presents a detailed analysis of geochemical and biotic proxies in a lake sediment profile to assess the effects of local and regional environmental drivers on the Holocene development of Lake Loitsana, situated in the northern boreal forest of NE Finland. Multi-proxy studies, in particular those that include a detailed plant macrofossil record, from the part of the northern boreal zone of Fennoscandia which has not been affected by treeline fluctuations, are scarce and few of these records date back to the earliest part of the Holocene. A 9-m sediment sequence of gyttja overlying silts representing the last c. 10,700 cal year, allowed for a high-resolution study with emphasis on the early to mid-Holocene lake history. The lacustrine sediments were studied using lithology, loss-on-ignition and C/N ratios, micro- and macro-fossils of aquatic and wetland taxa, diatoms, chironomids and accelerator mass spectrometry 14C dating on terrestrial plant macrofossils. Our study shows that the local development at Loitsana was complex and included a distinct glacial lake phase and subsequent drainage, a history of fluvial input affected by nearby wetland expansion, and lake infilling in an eventual esker-fed shallow lake. Enhanced trophic conditions, due to morphometric eutrophication, are recorded as Glacial Lake Sokli drained and open water conditions became restricted to a relatively small Lake Loitsana depression. pH appears to have been stable throughout the Holocene with a well-buffered lake due to the local carbonatite bedrock (Sokli Carbonatite Massif). The fossil assemblage changes are best explained by a complex mixture of drivers, including water-body conditions (i.e. depth, turbidity and turbulence), rate of sediment input, and the general infilling of the lake, highlighting the need to carefully evaluate the possible influence of such local factors as palaeoenvironmental conditions are reconstructed based on aquatic proxies.

A Holocene record of millennial-scale climate changes in the mud area on the inner shelf of the East China Sea

Core MZ01 from the mud area on the inner shelf of the East China Sea (ECS) was studied to detect millennial climate changes during the Holocene based on a modified version of accelerator mass spectrometry (AMS) 14C dating age model, sediment grain size, oxygen isotopes and the Mg/Ca ratio of benthic foraminifera shells. On the basis of multiproxies of this core, eight abrupt cooling events were identified that occurred at 8.2, 7.2, 6.2, 5.1, 4.2, 3.2, 2.3 and 1.2 ka BP, within the uncertainties of the revised age model. The timing of the abrupt Holocene surface hydrographic events reconstructed from the core, particularly 8.2 ka, expressed pronouncedly in the mud area on the inner shelf of the ECS appear to be coincident with the records from the North Atlantic, the South China Sea and an adjacent land cave and Greenland ice cores, suggesting global climatic teleconnections. The abrupt climate changes during the Holocene displays periodicities of 820–830 years and 350–420 years, which may be related to solar activity but suggests a robust regional feature of hydrographic changes in the western tropical Pacific. We conclude that the singularity of the particular hydrographic patterns and mechanisms responsible for the patterns and periodicities of these abrupt events merits further studies by more intensive dating controls and novel proxy reconstructions.

Mid- to late-Holocene East Asian summer monsoon variability recorded in lacustrine sediments from Jingpo Lake, Northeastern China

The Northeastern China involves complex interactions between the East Asian summer monsoon (EASM) circulation and the polar climate system, and plays a significant role as the bridge communicating low- and high-latitude climatic processes. High-resolution multi-proxy analysis of a robust accelerator mass spectrometry (AMS) 14C dated lacustrine sediment core recovered from Jingpo Lake in Northeastern China provides a detailed history of EASM variability and vegetation changes since ~5100 cal. yr BP. The period from ~5100 to 3600 cal. yr BP was characterized by the highest pollen percentages of Quercus, Ulmus, Juglans and Corylopsis; low Md (median grain size diameter); and high δ13Corg values, reflecting a relatively warm and humid period. The period between ~3600 and 2100 cal. yr BP is characterized by high Md and low δ13Corg values, and a rapid increase in pollen percentages of herbs, indicating cool and dry climatic conditions. From ~2100 to 150 cal. yr BP, a gradual increase in δ13Corg values and low Md values, and a rapid increase in Carpinus, Juglans and Corylopsis pollen percentages was observed, indicating climate change towards warmer and wetter conditions. After ~150 cal. yr BP, the highest values of total organic carbon mass accumulation rate (TOC-MAR), total nitrogen mass accumulation rate (TN-MAR) and magnetic susceptibility suggesting that the Jingpo Lake region has been severely affected by human activities. The EASM variability in Northeastern China during the mid- to late Holocene shows trends similar to EASM records in China. Furthermore, our findings indicate that the variability of the EASM during the mid- to late Holocene on the multi-decadal to centennial scale was forced by changes in both solar output and oceanic–atmospheric circulation interaction.

A rapid method for preparing low volume CH4 and CO2 gas samples for 14C AMS analysis

14C measurements of CH4 in environmental samples (e.g. soil gas, lake water, gas hydrates) can advance understanding of C cycling in terrestrial and marine systems. The measurements are particularly useful for detecting the release of old C from climate sensitive environments such as peatlands and hydrate fields. However, because 14C CH4 measurements tend to be complex and time consuming, they are uncommon. Here, we describe a novel vacuum line system for the preparation of CH4 and CO2 from environmental samples for 14C analysis using accelerator mass spectrometry (AMS). The vacuum line is a flow-through system that allows rapid preparation of samples (1h for CH4 and CO2, 30min for CH4 alone), complete separation of CH4 and CO2 and is an easy addition to multipurpose CO2 vacuum lines already in use. We evaluated the line using CH4 and CO2 standards with different 14C content. For CH4 and CO2, respectively, the total line blank was 0.4±0.2 and 1.4±0.6μg C, the 14C background 51.1±1.2 and 48.4±1.5kyr and the precision (based on pooled standard deviation) 0.9‰ and 1.3‰. The line was designed for sample volumes of ca. 180ml containing 0.5–1% CH4 and CO2, but can be adjusted to handle lower concentration and larger volume samples. This rapid and convenient method for the preparation of CH4 and CO2 in environmental samples for 14C AMS analysis should provide more opportunities for the use of 14C CH4 measurements in C cycle studies.