Interglacial Paleosol Research Articles

Paleo-pedological record in loess deposits in the south of the East European plain, based on Beglitsa-2017 section study

Loess-paleosol sequences (LPSs) are one of the main components of the natural environment, which traces how the climate has changed in the past. The article discusses changes in the landscape and climatic conditions from the Middle Pleistocene to the present, identified by the results of the LPS of the Beglitsa-2017 section study. We obtained new data on soil cover change in the Late and Middle Pleistocene in the North-Eastern Azov region based on multi-proxy analysis with high-resolution sampling along the section. The first data on the polygenetic origin of the Salyn interglacial paleosol (MIS 5e) profile which developed according to the Gypsic Calcic Chernozems type in the interglacial optimum, was obtained. Still, in the last stage of soil formation, its type changed to the more arid Gypsic Chernozems (Arenic). During MIS 5c and MIS 5a, the paleosols developed in a more arid climate; their modern analogues may be Gypsic Kastanozems and Calcic Gypsisols, respectively. The period of MIS 3 in the study area is marked by severe cryo-arid conditions, which influenced the formation of incipient Calcic Gypsisols. The profiles of the Middle Pleistocene paleosols in the lower part of the LPS of the Beglitsa-2017 section were subject to gleying processes, which formed specific Gleysols or Stagnosols paleosols. The preliminary age of these paleosols corresponds to MIS 13/15 and 8/9. The MIS 7 paleosols are structurally similar to modern Calcic Kastanozems, currently distributed in the dry steppe zone. Reconstruction of the formation of the LPS paleosol cover in the Beglitsa-2017 section made it possible to trace the trend of changes in climatic conditions in the past. Climate aridity decreases in the interval between MIS 5e and MIS 1, and the maximum drought peaks were recorded in MIS 3 paleosols. Earlier, climate aridization intensified from MIS 13/15 and continued until MIS 7/6. The results will complement our understanding of the soil cover changing over time and will expand the reconstruction of climate change throughout the East European Plain.

Driving factors of interglacial paleosol formation on the Chinese loess plateau and the effect of precession and ice sheets

The loess-paleosol sequences in the Chinese Loess Plateau (CLP) are an important terrestrial paleoclimate record. However, quantitative understanding of the response of paleosol development to various climate and environmental factors remains poor. Based on simulations with combined soil-climate models (SoilGen2-LOVECLIM1.3), this study investigates the sensitivity of paleosol development to different soil forming factors as well as the influence of ice sheets and astronomical forcing during the interglacials of the past 500 ka. Sensitivity analyses show that precipitation, dust addition and evapotranspiration are the dominant factors controlling the interglacial paleosol formation, but their relative importance varies between intergalcials and for different soil properties such as calcite and clay contents. Our results show that the simulated S1, S2, S3, S5-1 paleosols, which correspond to MIS 5, 7, 9 and 13 respectively, exhibit strong relationship with precession through its control on precipitation, whereas the precession signal is weak in the simulated S4 paleosol, in line with the weak precession variation during MIS 11. The results also show variable length of lags between different soil properties and precession and also in different interglacials. The lag between the simulated calcite and precession is shorter than that of clay. Moreover, clay content also shows strong relation with temperature during MIS 5 and MIS 13. Large ice sheets in the early and late phases of the interglacials have substantial impact on both temperature and precipitation in the CLP and thus on carbonate leaching and clay migration. Therefore, the simulated paleosols result mainly from the joint effect of precession and ice sheets via their control on local climate, and they show qualitative agreement with observations.

Revisiting Late Pleistocene Loess–Paleosol Sequences in the Azov Sea Region of Russia: Chronostratigraphy and Paleoenvironmental Record

Loess-paleosol sequences are the most intensively studied terrestrial archives used for the reconstruction of Late Pleistocene environmental and climatic changes in the Azov Sea region, southwest Russia. Here we present a refined chronostratigraphy and a multiproxy record of Late Pleistocene environmental dynamics of the most complete and representative loess–paleosol sequences (Beglitsa and Chumbur-Kosa sections) from the Azov Sea region. We propose a new chronostratigraphy following the Chinese and Danubean loess stratigraphic models that refines the subdivision of the Last Interglacial paleosol (S1) complex in two Azov Sea sites, resolve the uncertainty of the stratigraphic position of the weakly developed paleosol (L1SSm) in Beglitsa section, and allow for direct correlation of the Azov Sea sections with those in the Danube Basin and the Chinese Loess Plateau. More importantly, it may serve as a basis for better constraining local and regional chronostratigraphic correlations, and facilitate the interpretation of climatic connections and possible forcing mechanisms responsible for the climatic trends in the region. In addition, a general succession of environmental dynamics is reconstructed from these two vital sections, which is broadly consistent with other loess records in the Dnieper Lowland and Lower Danube Basin, demonstrating similar climatic trends at Glacial–Interglacial time scales. Furthermore, our results have important implications for the chronostratigraphic representativeness of Beglitsa as a key regional loess section and for the reconstruction of the temporal and spatial evolution of Late Pleistocene climate in the Azov Sea region.

Calibrating SoilGen2 for interglacial soil evolution in the Chinese Loess Plateau considering soil parameters and the effect of dust addition rhythm

To better understand interglacial paleosol development by quantifying the paleosol development processes on the Chinese Loess Plateau (CLP), we need a soil genesis model calibrated for long timescales. Here, we calibrate a process-based soil genesis model, SoilGen2, by confronting simulated and measured soil properties for the Holocene and MIS-13 paleosols formed in the CLP for various parameter settings. The calibration was made sequentially on three major soil process formulations, including decalcification, clay migration and soil organic carbon, which are represented by various process parameters. The order of the tuned parameters was based on sensitivity analyses performed previously on the loess in West European and the CLP. After the calibration of the intrinsic soil process parameters, the effect of uncertainty of dust deposition rate on calibration results was assessed. Our results show that the simulated soil properties are very sensitive to ten reconstructed dust deposition scenarios, reflecting the propagation of uncertainty of dust deposition in model simulations. Our results also show the equal importance of calibrating soil process parameters and defining correct external forcings in the future use of soil models. Our calibrated model allows interglacial soil simulation in the CLP over long timescales.

Revisiting the Taman peninsula loess-paleosol sequence: Middle and Late Pleistocene record of Cape Pekla

Loess deposits are widely spread all over Eastern Europe, extending as far south as the Sea of Azov and the northern Black Sea. For many decades these regions have been noted for series of key sections. However, despite prolonged investigations, a lack of absolute dating and detailed lithological data has left many unresolved problems in the correlation of the regional stratigraphic schemes. In this study, integrated studies were undertaken on the loess-paleosol sequence exposed on the northern coast of the Taman Peninsula, separating the Sea of Azov from the Black Sea. The exposure in the coastal scarp near Cape Pekla was sampled in detail for standard lithological and stratigraphic analyses, and for the first time, detailed data on the sediments lithology and petromagnetic properties were obtained, as well as the first optically stimulated luminescence age estimates. The data lead us to conclude that the formation of continental series exposed in the Pekla section started at the beginning of the Middle Pleistocene. There are five well pronounced buried soil complexes (PS 1–5) exposed in the sequence, covering sedimentation from the Middle Pleistocene to the present day. We attribute two lower paleosols (PS 4 and PS 5) to two main warm intervals of the Middle Pleistocene – MIS 9 and MIS 13, and the Kamenka interglacial paleosol, correlated with MIS 7 from other parts of the Azov loess area, is represented in the Pekla section by a sand layer formed at the time of the marine transgression dated to interval 220–280 ka (MIS 7). The upper soil horizons (PS1, PS2 and PS3) developed between 20 and 220 ka. The Pekla section contains a considerable proportion of sand fraction – presumably, due to active eolian processes that developed in immediate vicinities of sources of the material. The paleosol characteristics and the structure of loess horizons in the Pekla subaerial series differ considerably from the well described loess-paleosol series of the Northern Azov Sea coasts. In all probability, this region of the Taman Peninsula belongs to a specific province located south of the North Azov loess-soil province.

High-resolution analysis of the Likhvin loess-paleosol sequence (the central part of the East European Plain, Russia)

Studies of the loess-paleosol sequence of the center of the East European Plain have a long history. Previously, samples from loess-soil sections were taken for paleoreconstruction of climate and environment with low resolution, usually 1–2 samples per stratigraphic unit. This led to an unclear interpretation of the processes of soil formation and deposition of loess material. Our article discusses the LPS of the Likhvin stratotype section. High-resolution analysis was applied, which will allow us to trace in detail the history of the formation of the paleosol cover from the Middle Pleistocene to the present. A total of 245 bulk samples were taken from sections Likhvin-1/18 and Likhvin-2/18 and analyzed using laboratory analytics (the particle-size distribution, magnetic susceptibility, the loss on ignition values, total organic carbon, pH). Nine samples were taken for OSL dating and two samples for AMS dating to determine the age of the deposits. The micromorphological characteristics were described in detail for paleosols. The Salyn interglacial paleosol (MIS 5e) appeared to be comparable to the modern Retisols in its macro- and micromorphology and physical and chemical characteristics. As to the Krutitsa interstadial paleosol (identified formerly with MIS 5c in the sequence), our results suggest its belonging to MIS 5a. The modern prairie soils – Folic Cambisols – may be considered as its modern analogue. During the MIS 3, the Bryansk paleosol developed. The paleosol is polygenetic; in cooling, its main type (Cambisol) changed to Gleysol and finally became Cryosol. The paleosol described as belonging to MIS 7 displays all the characteristics of the Early Kamenka interglacial paleosol and develops the characteristics of Luvisols (Cutanic) type, its analogues being found in Latvia, Poland, and Hungary. There is a level of soil-formation above the Early Kamenka interglacial paleosol corresponding to the Romny paleosol (MIS 6) in its stratigraphic position. The latter statement is difficult to assert with confidence; it is not improbable that the level presents the Late Kamenka interstadial paleosol, also attributable to MIS 6.

Provenance and paleoclimatic implications of loess deposits in Shandong Province, eastern China

AbstractThe loess deposits in Shandong Province in eastern China potentially provide valuable insights into past environmental changes. However, their precise provenance and paleoclimatic implications are unclear. We studied three loess sections located in the piedmont of the Central Shandong Mountains (PCSM) and in an offshore island in Bohai Gulf. Both the glacial loess and interglacial paleosol units are characterized by a coarse grain size, indicating a proximal sediment source. Using the “grain size–transport distance” model established for the Chinese Loess Plateau (CLP), the estimated source-sink distance is ~200–300 km for the PCSM loess and ~100–200 km for the coastal loess. This suggests that fluvial deposits of the Yellow River system in the North China Plain and sediments on the adjacent continental shelf are the major provenance for the Shandong loess. In contrast to the CLP, the Shandong loess does not show a consistent pattern of coarse grain size and low magnetic susceptibility values in glacial loess compared with interglacial paleosols, likely due to frequent changes in dust sources caused by diversions of the Yellow River and local hydroclimatic conditions. Nevertheless, the loess-paleosol alternations in the Shandong loess are a product of global glacial–interglacial cycles.

Quantifying soil-respired CO2 on the Chinese Loess Plateau

Soil respiration is one of the dominant fluxes of CO2 from terrestrial ecosystems to the atmosphere. Accurate quantification of soil respiration is essential for robust projection of future climate variation and for reliable estimation of paleoatmospheric CO2 levels using soil carbonates. Soil-respired CO2, which is the most uncertain factor in estimating atmospheric CO2 concentration, has been calculated from modern observations of surface soils and from proxy indicators of paleosols formed during time periods of known atmospheric CO2. However, these estimations provide a wide range of S(z) values from past to present. To directly compare modern observation with past estimation, here we first monitored soil CO2 profiles in a Holocene profile on the western Chinese Loess Plateau (CLP) for two years, providing direct measurements of soil-respired CO2 at the depth where carbonate nodules likely formed. We then collected carbonate nodules below last interglacial paleosol (S1) from two N-S-aligned transects across the CLP to back-calculate soil-respired CO2. The mean back-calculated S(z) from S1 carbonate nodules vary from 539 ± 87 ppm to 848 ± 170 ppm in the sections on the northwestern and southeastern CLP, respectively. The mean value of directly measured soil-respired CO2 on the western CLP is 572 ± 273 ppm before the onset of summer monsoon, consistent with the back-calculated S(z) in northwestern sections. Our results suggest that spatial S(z) variations are mainly controlled by monsoonal precipitation during the summer season on the CLP. To better constrain the high end of S(z), more monitoring work is needed in higher precipitation areas on the southeastern CLP.

An Attempt to Recover a Paleomonsoon Signal in the Chinese Loess Plateau Using Anisotropy of Magnetic Susceptibility

The paleowind direction in the Chinese Loess Plateau (CLP) was studied using anisotropy of magnetic susceptibility (AMS) data. Magnetic fabrics were examined for the last glacial loess (L1) and last inter-glacial paleosol (S1) in the southern and central CLP along a present day precipitation zone of 600 mm per year. Statistical analyses of the orientations of AMS ellipsoids indicate that strong rainwater events may cause random distributions for the AMS azimuth of maximum axis and no deviation from the vertical plane for the average minimum axis. As high rainfall can distort paleowind analyses, it is challenging to conduct paleowind studies on the southern CLP - a topography of high precipitation density. Future studies could focus on the western and northern CLP, where there is less rainfall, making it more suitable for paleowind analysis by AMS.

Microbial Communities of Interglacial and Interstadial Paleosols of the Late Pleistocene

The taxonomic structure of microbial communities in the Late Pleistocene paleosols of different ages in the Central Russian Upland formed under contrasting climatic conditions were analyzed. The humic horizons of paleosols in the interstadial periods of the Early Valdai (105–95 kyr ago), Middle Valdai (33–24 kyr ago), Mikulino interglacial (130–117 kyr ago), and of the modern (Holocene) chernozem were considered. Microbial DNA was analyzed using quantitative PCR and 16S rRNA gene amplicon sequencing (DNA metabarcoding). The numbers of copies of archaeal, bacterial, and fungal genes gradually decreased with an increase in the soil age. All considered paleosols significantly differed from one another in the structure of their microbial communities. The Verrucomicrobia-to-Nitrospirae ratio was used as a diagnostic parameter reflecting the organic matter supply and the changes in carbon and nitrogen cycles. The Verrucomicrobia-to-Nitrospirae ratio in the interstadial soils was 140–200 times lower as compared with that in the modern soil (typical chernozem) and in the paleosols of the Mikulino interglacial. The share of gram-negative Proteobacteria and Acidobacteria increased with the soil age, whereas the share of gram-positive Actinobacteria and Firmicutes decreased. The modern chernozems and interglacial paleosols were characterized by similar values of microbial diversity, while the paleosols of the Valdai interstadial had significantly lower microbial diversity and species richness. Analysis of β-diversity showed that the paleosols of different types and ages maintained the difference in the structure and diversity of their microbial communities depending on the conditions of their formation. Thus, the microbial communities can be used as potential stratigraphic markers and indicators of different climatic conditions, under which the given paleosols were formed.

Micromorphology of the Late and Middle Pleistocene paleosols of the central East European Plain

In this paper we focused on the micromorphology of the Late and Middle Pleistocene paleosols exposed in twelve loess-paleosol sequences sections in the central part of the East European Plain. Each studied paleosol complex known as Mesin (MIS 5), Kamenka (MIS 6 (8) - 7 (9)), and Inzhavino (MIS 8 (10) - 9 (11)) pedocomplexes (PCs) consists typically of two members, the earlier - main - phase of the soil development taking place during an interglacial, and the later one - at the subsequent interstadial time. Interglacial paleosols formation is associated with the thermal optimum of climatic macrocycles and corresponds to conditions close to modern in the territory under consideration. Interstadial paleosols formation characterizes the intervals within the glacial period, accompanied by an increase in heat and moisture. However, the heat supply of such intervals did not reach modern level in this region (Velichko and Morozova 2015). As follows from the analysis of the soil micromorphology over the studied area, the soil microstructure experienced notable changes under changing latitudinal zonality. During the interglacial periods clay coatings and Fe-Mn pedofeatures dominated the soil microfabric; in the south loess-paleosol sequences coatings are in negligible quantities, Fe-Mn pedofeatures decrease in amount, and carbonate pedofeatures appear instead. In the microfabric of the interstadial paleosols, Fe-Mn pedofeatures are abundant, but unlike interglacial paleosols, the coatings are rare. Basically, the coatings are humus-clayey in composition, but in the more southern sections coatings are absent.

Morphology and micromorphology of the loess-paleosol sequences in the south of the East European plain (MIS 1–MIS 17)

The micro- and macromorphological studies performed on the loess-soil sequences in the south of the East European Plain permitted to identify and describe the type of soil-formation processes that took part in the development of interstadial and interglacial paleosols. Four paleosol complexes are distinctly identified within the limits of the studied region: Vorona (MIS 13/15), Inzhavino (MIS 8/9 or MIS 10/11), Kamenka (MIS 6/7 or MIS 8/9), Mezin (MIS 5); besides, there are the Bryansk interstadial paleosol (MIS 3) and Rzhaksa interglacial paleosol (MIS 17), both well identifiable in the region. The results obtained are in general agreement with the earlier conclusions by Velichko et al. (2012) about a general reduction of heat and moisture supply and an increase in aridity from the earlier towards later stages of the Pleistocene. The new data revealed, however, a few differences from the earlier concept. To mention but one example, we have found that the Kamenka interglacial (MIS 7 or MIS 9) paleosols formed in environments more humid than those of the Likhvin interglacial (MIS 9 or MIS 11).

Microcodium in Chinese loess as a recorder for the oxygen isotopic composition of monsoonal rainwater

Records of Asia Summer Monsoon (ASM) from the Chinese loess and the speleothem display distinct features. The very different proxies that were applied to the two archives may be responsible for this discrepancy. A direct comparison between the speleothem and the loess records under the same proxy system of rainwater δ18O may help to resolve this puzzle. Here we show that the calcified microcodium in the loess deposits may record the oxygen isotopic composition of the summer rainwater. A microcodium based δ18O record covering the past 140 kyrs was generated, which shows similar magnitude of the overall variation to that of the speleothem records. However, much weaker precession variability was registered in the microcodium record during the last interglacial period. Instead, the microcodium δ18O record is more consistent with the widely used summer monsoon proxy of magnetic susceptibility in the loess deposits with clear glacial-interglacial pattern. This similarity may originate from the low sedimentation rate of the interglacial paleosol layer that preferentially record the peak ASM signals on the precession band. It is also possible that the orbital variability of ASM between the North China and South China is inherently different with more ice-volume related influence in the north. A longer microcodium δ18O record in sequences of higher sedimentation rate and a reliable record of summer rainfall may help to resolve these possibilities.

Optical dating of eolian deposits since the last interglacial along the northern margin of the Chinese Loess Plateau

Understanding the chronology of eolian sand-loess-paleosol sequences along the northern margin of the Chinese Loess Plateau (CLP) is crucial for comprehending climate change and the advance and retreat of the adjacent Mu Us desert. In this study, a sand-loess-soil sequence from the northern margin of the CLP was studied by applying the single aliquot regenerative (SAR) protocol to quartz grains, and the multi-elevated-temperature post-IR IRSL (MET-pIRIR) protocol to K-feldspar grains. For equivalent dose (De) determination, 63–90 μm quartz and K-feldspar grains were used. Our results indicate that the MET-pIRIR ages of K-feldspar grains in this sequence range from 94.4 ± 7.0 ka to 148.3 ± 13.3 ka for the last interglacial paleosol (S1); for the upper part of the section, quartz-based SAR-OSL dating was used, yielding ages spanning from 5.8 ± 0.4 ka to 35.9 ± 4.1 ka. After cross-checking these results with previously-reported isochron OSL and TL ages, the reliability of the MET-pIRIR protocol when applied to the last interglacial paleosol was confirmed. Based on a new OSL chronology of the Shimao profile, the studied eolian deposits can be broadly correlated with the last glacial-interglacial cycle, but their dating also points to sedimentary hiatuses occurring at 94.4 ka, 35.9 ka and 5.8 ka, due most probably to strong wind erosion caused by intensified cold-dry winter monsoonal circulations during the last glacial maxima.

Registration of Precession Signal in the Last Interglacial Paleosol (S1) on the Chinese Loess Plateau

AbstractSolar insolation plays an essential role in driving orbital‐scale East Asian Monsoon (EAM) variability. Unlike Chinese speleothem δ18O records characterized by dominant precessional cycles, many loess proxies from the Chinese Loess Plateau (CLP) usually display damped precessional‐scale variability. To reconcile the precessional monsoon variability recorded in two classic archives, it's critical to investigate which factor can significantly affect the sensitivity of loess proxies to precessional forcing. In this study, we synthesize grain size (GS) and magnetic susceptibility (χ) results of 18 paleosol (S1) profiles over the CLP, with effort to evaluating the relative impacts of sedimentation rate (SR), and pedogenesis on the precessional signal intensity (PSI) during the last interglaciation. Based on unified grain‐size age models, amplitude contrast between normalized GS and χ variations of five substages of the last interglaciation is employed to infer the PSI. The results indicate that precessional signals are evident in the GS/χ records of the high‐SR loess profiles on the northern and western CLP. Comparison of the PSI variations with the SR and mean annual precipitation (MAP) changes suggests that the GS‐PSI is positively correlated to the SR changes, while the χ‐PSI is negatively/positively related to the SR/MAP changes. Our results confirm that distinct precessional cycles in high‐resolution loess proxies permit a plausible reconciliation of monsoon variability recorded in Chinese loess and speleothem.

The geochemistry of loess: Asian and North American deposits compared

Loess is widely distributed over Asia and North America and constitutes one of the most important surficial deposits that serve as terrestrial records of the Quaternary. The oldest Pleistocene loess in China is likely ∼2.6 Ma, thus spanning much or all of the Pleistocene. In North America, most loess is no older than the penultimate glacial period, with the exception of Alaska, where the record may go back to ∼3.0 Ma. On both continents, loess deposits date primarily to glacial periods, and interglacial or interstadial periods are represented by paleosols. Both glacial and non-glacial sources of silts that comprise the bulk of loess deposits are found on both continents. Although loess has been considered to be representative of the average upper continental crust, there are regionally distinctive compositions of loess in both Asia and North America. Loess deposits in Asia from Yakutia, Tajikistan, and China have compositionally distinct major element compositions, due to varying abundances of silicate minerals, carbonate minerals, and clay minerals. In North America, loess in the Mississippi River valley, the Great Plains, and Alaska are also distinguishable with regard to major element composition that reflects highly diverse source sediments. Trace element geochemistry (Sc-Th-Zr and the rare earth elements) also shows regional diversity of loess bodies, in both Asia and North America. On both continents, most loess bodies show significant contributions from later-cycle, altered sedimentary rocks, as opposed to direct derivation from igneous rocks. Further, some loess bodies have detectable contributions from mafic igneous rocks as well as major contributions from average, upper-crustal, felsic rocks. Intercalated paleosols in loess sections show geochemical compositions that differ significantly from the underlying loess parent materials. Ratios of soluble-to-insoluble elements show depletions in paleosols due to chemical weathering losses of calcite, dolomite, plagioclase, mica, apatite, and smectite. In Asia and North America, the last interglacial paleosol is more weathered than equivalent modern soils, which could be due either to a climate that was warmer and more humid, a longer period of pedogenesis, or both. In Asia, early Pleistocene loess and paleosols are both more weathered than those from the middle and late Pleistocene, forming prior to a mid-Pleistocene aridification of Asia from uplift of the Tibetan Plateau. Understanding the geochemistry of loess and paleosols can tell us much about past atmospheric circulation, past temperature and moisture regimes, and even tectonic processes.

Saharan dust deposition in the Carpathian Basin and its possible effects on interglacial soil formation

Several hundred tons of windblown dust material are lifted into the atmosphere and are transported every year from Saharan dust source areas towards Europe having an important climatic and other environmental effect also on distant areas. According to the systematic observations of modern Saharan dust events, it can be stated that dust deflated from North African source areas is a significant constituent of the atmosphere of the Carpathian Basin and Saharan dust deposition events are identifiable several times in a year. Dust episodes are connected to distinct meteorological situations, which are also the determining factors of the different kinds of depositional mechanisms. By using the adjusted values of dust deposition simulations of numerical models, the annual Saharan dust flux can be set into the range of 3.2–5.4 g/m2/y. Based on the results of past mass accumulation rates calculated from stratigraphic and sedimentary data of loess–paleosol sequences, the relative contribution of Saharan dust to interglacial paleosol material was quantified. According to these calculations, North African exotic dust material can represent 20–30% of clay and fine silt-sized soil components of interglacial paleosols in the Carpathian Basin. The syngenetic contribution of external aeolian dust material is capable to modify physicochemical properties of soils and hereby the paleoclimatic interpretation of these pedogene stratigraphic units.

Automated SEM–EDS heavy mineral analysis reveals no provenance shift between glacial loess and interglacial paleosol on the Chinese Loess Plateau

Understanding provenance of glacial loess and interbedded interglacial paleosol deposits on the Chinese Loess Plateau (CLP) is important to understanding paleo-atmospheric circulation patterns. However, great debate exists about whether Chinese loess and paleosol deposits have similar provenance both spatially and temporally. Here we report heavy mineral assemblage results of two sets of loess–paleosol couplets (L1 and S1; L4 and S4) from western CLP based on scanning electron microscopy with linked energy dispersive spectrometers (SEM–EDS) analysis (QEMSCAN@). The results demonstrate no apparent provenance shift on the CLP between glacial and interglacial periods. Heavy mineral assemblage comparison between the western and the central CLP reveals no provenance shift spatially, either. Finally, a comparison of heavy mineral assemblage between loess–paleosol and potential source regions reveals that the western Mu Us desert, the Badain Jaran desert, the Ulan Buh desert as well as the Yellow river are likely key dust contributors for the CLP. In contrast, the northeastern Mu Us desert are less likely key dust sources for the CLP. The ultimate provenance history of the CLP relies no doubt on integrated provenance studies. However, due to its rapidity and robustness, integrated provenance analysis should incorporate the QEMSCAN-based heavy mineral analysis.

A 220 ka terrestrial δ18O and deuterium excess biomarker record from an eolian permafrost paleosol sequence, NE-Siberia

The natural abundances of stable oxygen (18O/16O) and hydrogen isotopes (2H/1H) are valuable proxies of climate changes in the past. Yet, to date no continuous δ18O and only few δ2H records are available from loess–paleosol sequences. Taking advantage of a recently developed method based on compound-specific δ18O analyses of hemicellulose sugar biomarkers in soils (Zech and Glaser, 2009. RCM 23, 3522-3532), we here present a first terrestrial δ18O biomarker record from an eolian permafrost paleosol sequence in NE-Siberia that covers the last ~220ka.The δ18O values of the hemicellulose biomarkers arabinose and xylose range from 22.5 to 32.8‰ and from 21.3 to 31.9‰, respectively, and reveal systematic glacial–interglacial shifts. The modern topsoil and the interglacial paleosols exhibit more positive δ18O values, whereas the glacial paleosols are characterized by more negative δ18O values. This is in agreement with the δ2H record obtained for sedimentary n-alkane leaf wax biomarkers. We present a conceptual model for interpreting the combined δ18O and δ2H biomarker record. Based on this model, we suggest that both our δ18O and the δ2H records primarily reflect the temperature-controlled isotopic composition of paleoprecipitation modified by evaporative isotope enrichment of leaf water during transpiration.Considering fractionation factors during sugar and n-alkane biomarker biosynthesis allows reconstructing the leaf water isotopic composition and the deuterium excess of the leaf water. The deuterium excess may serve as proxy for evaporative enrichment and allows calculating relative humidity using a Craig–Gordon model. Accordingly, relative humidity in NE-Siberia was higher during marine isotope stage (MIS) 6 compared to MIS 2, 4 and 5d and thus could help explaining the much larger extent of the Late Saalian glaciation compared to the Weichselian glaciations.Using the Craig–Gordon model, we also calculated δ18O of the plant source water (δ18Osource water), which can be assumed to primarily reflect δ18O of paleoprecipitation. Our 220ka δ18Osource water record is well in agreement with the δ18Odiatom record from Crater Lake El'gygytgyn in NE-Siberia and enables a regional paleoclimate reconstruction and interpretation. Accordingly, summer temperature was periodically warmer than at present during the Weichselian glacial period and there is a strong July insolation forcing of the summer temperature in the extremely continental study area. Overall, our study highlights the great potential of the novel hemicellulose biomarker δ18O method for paleoclimate reconstructions, especially when combined with δ2H analyses of n-alkane lipid biomarkers.

Last Interglacial paleosols with Argic horizons in Upper Austria and Central Russia

Last Interglacial paleosols with Argic horizons in Upper Austria and Central Russia