Climate In Central Asia Research Articles

Variability of the Cold Season Climate in Central Asia. Part I: Weather Types and Their Tropical and Extratropical Drivers

AbstractTo understand the atmospheric mechanisms resulting in a pronounced cold season climate variability in central Asia, an objective weather-type classification is conducted, utilizing a k-means-based clustering approach applied to 500-hPa geopotential height (GPH) fields. Eight weather types (WT) are identified and analyzed with regard to characteristic pressure patterns and moisture fluxes over Eurasia and specific near-surface climate conditions over central Asia. To identify remote drivers of the central Asian climate, WT frequencies are analyzed for their relationships with tropical and extratropical teleconnection modes. The results indicate an influence of Northern Hemispheric planetary wave tracks on westerly moisture fluxes with positive anomalies of precipitation associated with the formation of a Rossby trough over central Asia. Particularly the propagation of the east Atlantic–western Russia and the Scandinavian patterns is shown to modulate regional climate conditions. Variations of ENSO are shown to affect the frequency of particular WTs because of the formation of an anticyclonic anomaly over the Indian Ocean and an increase of tropical fluxes of moisture and heat into central Asia during El Niño events. Further a WT internal influence of ENSO is distinctly defined, with enhanced moisture supply during the ENSO warm phase. The analysis of climatic trends shows that 50% of observed temperature changes can be assigned to variations of the WT composition, indicating that most likely changing regional circulation characteristics account for the enhanced warming rates in central Asia. Trends of precipitation sums are likewise shown to be associated with changing WT frequencies, although the WT–precipitation relationships include large uncertainties.

Mid- to late Holocene climate-driven regime shifts inferred from diatom, ostracod and stable isotope records from Lake Son Kol (Central Tian Shan, Kyrgyzstan)

Arid Central Asia represents a key region for understanding climate variability and interactions in the Northern Hemisphere. Patterns and mechanisms of Holocene climate change in arid Central Asia are, however, only partially understood. Multi-proxy data combining diatom, ostracod, sedimentological, geochemical and stable isotope analyses from a ca. 6000-year-old lake sediment core from Son Kol (Central Kyrgyzstan) show distinct and repeated changes in species assemblages. Diatom- and ostracod-inferred conductivity shifts between meso-euhaline and freshwater conditions suggest water balance and regime shifts. Organism-derived data are corroborated by stable isotope, mineralogical and geochemical records, underlining that Son Kol was affected by strong lake level fluctuations of several meters. The δ13Ccarb/δ18Ocarb correlation shows repeated switchovers from a closed to an open lake system. From 6000 to 3800 and 3250 to 1950 cal. yr BP, Son Kol was a closed basin lake with higher conductivities, increased nutrient availability and a water level located below the modern outflow. Son Kol became again a hydrologically open lake at 3800 and 1950 cal. yr BP. Comparisons to other local and regional paleoclimate records indicate that these regime shifts were largely controlled by changing intensity and position of the Westerlies and the Siberian Anticyclone that triggered changes in the amount of winter precipitation. A strong influence of the Westerlies ca. 5000–4400, 3800–3250 and since 1950 cal. yr BP enhanced the amount of precipitation during spring, autumn and winter, whereas cold and dry winters prevailed during phases with a strong Siberian Anticyclone and southward shifted Westerlies at ca. 6000–5000, 4400–3800 and 3250–1950 cal. yr BP. Similarities between variations in winter precipitation at Son Kol and records of the predominant NAO-mode further suggest a teleconnection between wet (dry) winter climate in Central Asia and a positive (negative) NAO-mode. Thus, this study identifies climate fluctuations as the main driver for hydrological regime shifts in Son Kol controlling physicochemical conditions and consequently causing abrupt species assemblage changes. This emphasizes the importance of multi-proxy approaches to identify triggers, thresholds and cascades of aquatic ecosystem transformations.

Research on trend of warm-humid climate in Central Asia

Central Asia is a typical arid area, which is sensitive and vulnerable part of climate changes, at the same time, Central Asia is the Silk Road Economic Belt of the core district, the warm-humid climate change will affect the production and economic development of neighboring countries. The average annual precipitation, average anneal temperature and evapotranspiration are the important indexes to weigh the climate change. In this paper, the annual precipitation, annual average temperature and evapotranspiration data of every pixel point in Central Asia are analyzed by using long-time series remote sensing data to analyze the trend of warm and humid conditions. Finally, using the model to analyzed the distribution of warm-dry trend, the warm-wet trend, the cold-dry trend and the cold-wet trend in Central Asia and Xinjiang area. The results showed that most of the regions of Central Asia were warm-humid and warm-dry trends, but only a small number of regions showed warm-dry and cold-dry trends. It is of great significance to study the climatic change discipline and guarantee the ecological safety and improve the ability to cope with climate change in the region. It also provide scientific basis for the formulation of regional climate change program. The first section in your paper

WRF simulation and downscaling of local climate in Central Asia

ABSTRACTProgresses in understanding climate variation and its ecosystem responses and feedback in Central Asia have been limited by availability of high resolution and quality climate data. To ease this limitation, the Weather Research and Forecasting (WRF) model is implemented in Central Asia in this study after repeated yearly sensitivity evaluations. The optimized WRF is used to downscale the ERA‐Interim reanalysis data, producing a new regional dataset of 20 × 20 km spatial resolution covering 1980–2015. The downscaled precipitation and daily maximum and minimum temperatures of seven years from 1980–1986, when the observational data are the most abundant, are compared in statistical measures to station observations and also contrasted with the comparison results between the ERA‐Interim data and the observations. Results of those comparisons show that the downscaled data have overall comparable accuracy in precipitation and daily extreme temperatures to the ERA‐Interim data. An outstanding improvement of the downscaled data is in their describing the variance in precipitation and temperatures at daily to annual timescales, while the downscaled extreme precipitation and temperature events also show more accurate comparisons to the observed at some sub‐regions in Central Asia. The validated WRF model, which can be used to further downscale past as well as future climate data for specific research needs, and the downscaled high resolution and quality data present both a tool and a useful dataset for ecological and detailed climate research in Central Asia.

Long-term Pleistocene aridification and possible linkage to high-latitude forcing: New evidence from grain size and magnetic susceptibility proxies from loess-paleosol record in northeastern China

Loess deposits are regarded as good indicators of the inception and development of arid and semi-arid climate in central Asia and northern China during the late Cenozoic. In northeastern China extensive loess deposits are found surrounding the Horqin and Otindag sand fields, and they have great potential for reconstructing the long-term aridification history of the region. However, these loess deposits are currently poorly understood. Here, we present a high-resolution magnetic susceptibility (MS) and grain-size record spanning the last 1.0Ma from a 36.6-m-thick loess-paleosol sequence at Niuyangzigou site (NYZG) in NE China. The grain-size record reveals a long-term drying trend in NE China since ca. 1.0Ma, punctuated by two significant abrupt drying events at ~0.65Ma and ~0.3Ma. These results demonstrate a process of stepwise intensification of drying in NE China over the past 1Ma, and lend support to the hypothesis that global ice volume/temperature changes were the major driver of the long-term aridification of Asian dust source areas. However, unlike the widely studied loess deposits on the central Chinese Loess Plateau (CLP), the MS record in paleosol units S1, S2 and S4 from the NYZG site do not show evidence of enhanced monsoon precipitation resulting from decreased global ice volume and the prolonged episodes of interglaciation after the Mid-Pleistocene Transition evident in the ice volume record. We hypothesize that this may be due to differences in the climatic sensitivity of the MS of Chinese loess deposits on a regional scale, rather than to in regional differences in monsoon intensity.

Late Cenozoic magnetostratigraphy and anisotropy of magnetic susceptibility of the Baiyanghe section from the Hoxtolgay Basin: Implications for the uplift of the West Junggar Mt Range, NW China

To better constrain the tectonic evolution of Central Asia under the influence of the India-Asia collision, we performed combined magnetostratigraphy and anisotropy of magnetic susceptibility (AMS) analysis of the Baiyanghe section on the northern margin of the Hoxtolgay Basin (West Junggar Mt Range, northwestern China). The observed magnetostratigraphy shows a total of 14 pairs of normal and reversed geomagnetic polarity zones in the well-exposed ∼360m thick section. In tandem with two ESR dating results, these zones can be reliably correlated with the geomagnetic polarity time scale (GPTS) from C3An.2r to C1n, and yield an age ranging from ∼7.0Ma to ∼0.2Ma. The long hiatus between the Mesozoic and the late Cenozoic, corresponding to the age of the basal conglomerates, suggests that uplift of the West Junggar Mt Range was initiated at least at ∼7.0Ma ago. Furthermore, the onset of massive conglomerate deposits, as well as marked increases in sedimentation rate, k, T and Pj of AMS, occurred at ∼3.6Ma. These notable changes are coeval with the peak deformation in Central Asia. Considering the depositional diachroneity of the Xiyu conglomerates and the predominantly dry climate in Central Asia since at least the late Cenozoic, we suggest that accelerated uplift of the West Junggar Mt Range at ∼3.6Ma should be the main factor controlling these multiple changes within the Baiyanghe section. Another marked increase in conglomerate content, sedimentation rate and κ occurred at ∼1.1Ma. The cause of this event deserves further investigation in the future.

Stepwise onset of the Icehouse world and its impact on Oligo-Miocene Central Asian mammals.

Central Asia is a key area to study the impact of Cenozoic climate cooling on continental ecosystems. One of the best places to search for rather continuous paleontological records is the Valley of Lakes in Mongolia with its outstandingly fossil-rich Oligocene and Miocene terrestrial sediments. Here, we investigate the response by mammal communities during the early stage of Earth’s icehouse climate in Central Asia. Based on statistical analyses of occurrence and abundance data of 18608 specimens representing 175 mammal species and geochemical (carbon isotopes) and geophysical (magnetic susceptibility) data we link shifts in diversities with major climatic variations. Our data document for the first time that the post-Eocene aridification of Central Asia happened in several steps, was interrupted by short episodes of increased precipitation, and was not a gradual process. We show that the timing of the major turnovers in Oligocene mammal communities is tightly linked with global climate events rather than slow tectonics processes. The most severe decline of up 48% of total diversity is related to aridification during the maximum of the Late Oligocene Warming at 25 Ma. Its magnitude was distinctly larger than the community turnover linked to the mid-Oligocene Glacial Maximum.

The Neogene de-greening of Central Asia

Abstract There remains substantial debate concerning the relative roles of tectonics and global climate in driving the evolution of climate in Central Asia. Today, interior Asia—including the Taklamakan, Gobi, and Ordos Deserts—is exceptionally arid and is surrounded by distinct rainfall boundaries, such as those generated by the Asian monsoon systems to the east and south and those generated by high topography to the north and west. Determining how and why these boundaries have varied over the Neogene is hindered by the lack of a single proxy that can be broadly applied through space and time. We construct isoscapes of pedogenic carbonate δ13C (δ13Cc) over the Neogene in Asia by combining a compilation of 2236 published measurements with new data from three localities in northern Central Asia. Pedogenic carbonate δ13C records local aridity—excepting localities impacted by C4 grasslands and during large changes in atmospheric pCO2—through variations in soil respiration, depth of carbonate formation, and the effect of water stress on plant δ13C. Together, these effects reflect changes in both primary productivity and mean annual precipitation. Throughout the Neogene, we find consistent and exceptionally high δ13Cc in interior Asia with a ring of lower δ13Cc that demarcates higher precipitation. This persistent ring of lower δ13Cc corresponds in the south and east with the influence of the Asian monsoon systems; in the west and north, it reflects both orographic rainfall due to uplift of the Tian Shan and to moisture delivery by the mid-latitude westerlies. Finally, δ13Cc and, hence, aridity increases regionally in the latest Neogene, reflecting the effects of Northern Hemisphere glaciation and cooling. This widespread “de-greening” would have increased regional albedo and modified basin-scale water balances, resulting in greater dust fluxes due to reduced vegetative cover and precipitation.

Role of the westerlies in Central Asia climate over the Cenozoic

There remains substantial debate concerning the relative roles of tectonics and of global climate in pacing the evolution of aridity in Central Asia over the Cenozoic. Tibetan Plateau uplift, variable monsoonal strength, Paratethys retreat, and reduced moisture transport from the North Atlantic have all been hypothesized to drive aridity in Central Asia. Distinguishing between these mechanisms requires knowledge of moisture transport pathways to Central Asia through time. Presently, Central Asia receives recycled, high δ18O moisture that has been transported across Eurasia by the westerlies, while southern Tibet receives low δ18O moisture distilled by passage over the Himalaya. Here, we reconstruct the spatial distribution of oxygen isotopes in precipitation since the early Eocene, using a compilation of δ18O data from 2750 sedimentary carbonate samples. Across Asia, the spatial distribution of paleo-precipitation δ18O remains remarkably similar through time, with low δ18O values in the lee of the Himalaya in southern Tibet, constant, high δ18O values in Central Asia, and intermediate values on the central Plateau despite independent evidence for substantial changes in both topography and climate through time. These results suggest that a long-standing topographic feature has continuously blocked southerly moisture, and subsequent progressive uplift of the Tibetan Plateau has had little impact on Central Asian climate. In turn, southerly monsoonal moisture has never persistently extended northward of the central Plateau. As a result, the westerlies have remained the dominant moisture source in Central Asia since at least the early Eocene. Therefore, sedimentary aridity indicators in Central Asia, such as loess deposition, are controlled by the trans-Eurasian, westerly moisture flux rather than Tibetan Plateau uplift.

Westerly jet stream and past millennium climate change in Arid Central Asia simulated by COSMO-CLM model

This study tackles one of the most debated questions around the evolution of Central Asian climate: the “Puzzle” of moisture changes in Arid Central Asia (ACA) throughout the past millennium. A state-of-the-art Regional Climate Model (RCM) is subsequently employed to investigate four different 31-year time slices of extreme dry and wet spells, chosen according to changes in the driving data, in order to analyse the spatio-temporal evolution of the moisture variability in two different climatological epochs: Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). There is a clear regime behavior and bimodality in the westerly Jet phase space throughout the past millennium in ACA. The results indicate that the regime changes during LIA show a moist ACA and a dry East China. During the MCA, the Kazakhstan region shows a stronger response to the westerly jet equatorward shift than during the LIA. The out-of-phase pattern of moisture changes between India and ACA exists during both the LIA and the MCA. However, the pattern is more pronounced during the LIA.

Towards Secure and Sustainable Energy Supply in Central Asia: Electricity Market Reform and Investment Protection

This study focuses on the modernisation of the electricity infrastructure in Central Asia, in particular energy efficiency improvements and clean energy development. The starting point of the analysis is the recognition by the Central Asian states that the modernisation of electricity supply depends on the active participation of private – and in particular foreign – investors in these markets. Private capital and technology, know how and operational efficiency is needed to improve the efficiency of the system and finance the investments needed to ensure secure and sustainable energy supply. Taking an investor’s perspective, this study examines the regulatory framework governing the electricity market in Central Asia and questions the extent to which these rules and the ongoing reform initiatives provide a sufficiently strong basis for investments in the modernisation of energy supply. Taking into account the capital intensity and long term payback period of electricity investments, together with the perceived weaknesses of the general investment climate in Central Asia, this study focuses on investment risks and available protection against the occurrence of these risks.

Analysis of land degradation intensity and trend in Central Asia from 1999 to 2012

In this paper,the methods of Theil-Sen and Mann-Kendall were used to calculate land degradation intensity and trend in Central Asia in the past 14 years based on SPOT-Vegetation remote sensing data. In combination with the elevation value,the impacts of human activities on land degradation were analyzed. The result shows that the city zone around two deserts( Kalakum desert and Kyzylkum desert) and the saline-alkali land in the west of Kazakhstan are regions suffering from most serious land degradation. The city zone around two deserts has excessively emphasized the development of economy and thus damaged the environment. And because of the natural conditions,saline-alkali land in the west of Kazakhstan has degraded significantly. Vegetation around the sea and lake,in the interior desert and in he region under the snow line has tended to increase,which coincides with previous studies of global warming and the tendency that the climate in Central Asia has gradually turned to warm wet. Climate change has caused ice melting. The regions which are not suitable for vegetation growth,such as the region in higher elevation and desert,are now growing vegetation. However,in these region,vegetation is largely desert vegetation,which can't be utilized and does not help promote economic development,thus of little significance to humans. On the whole,the human survival environment is still deteriorating. At the same time,vegetation around the deserts has increased a lot, which suggests that people have paid attention to the environmental problem and implemented some environmental engineering projects and windbreak and sand fixation projects.

A high resolution study of trace elements and stable isotopes in oyster shells to estimate Central Asian Middle Eocene seasonality

Modern Asian climate is characterized by strong seasonality caused by the duality between monsoon-dominated conditions in southeastern Asia and semi-arid to arid conditions in Central Asia. Eocene high-resolution proxy records which enable the reconstruction of the onset and magnitude of changes in seasonality are lacking to understand in details how and when this climatic turnover pattern occurred. Here, we propose an original method to estimate inter- and intra-annual variabilities in seawater temperature and salinity recorded by carbonate shell growth increments of the fossil oyster Sokolowia buhsii (Grewingk) collected from Late Lutetian marine strata of the Proto-Paratethys in the southwestern Tarim Basin (western China). Elemental ratio (Mg/Ca, Mn/Ca) and carbonate stable isotope composition (δ18O) were determined perpendicular to the growth lines of foliated calcite accumulated in the ligamental area during the oyster's lifetime. We use temperature dependant Mg incorporation to estimate seasonal temperature contrast in the past. Results suggest a warm annual average temperature (~27–28°C) with large offset between summer and winter temperatures (until ∆T≃19°C). Combining these temperature estimates with stable oxygen isotope analyses from the same growth increments we deconvolve seawater δ18Osw as a proxy for salinity. This suggests an average annual salinity about ~34–35 increasing strongly during summer months and decreasing in winter. Based on these data we conclude that during the Middle Eocene, Central Asian climate was characterized by a strong intra-seasonal variability in both temperature and salinity. Although the subtidal setting might have contributed to the strong seasonal offsets this still suggests that semi-arid to arid conditions prevailed during summer, whereas winter was characterized by enhanced rainfall. These results are consistent with previous regional palaeoenvironmental data and climate modelling experiments. They thus attest for the reliability of the method developed here as a seasonal palaeoclimatic indicator.

Quaternary paleolake nutrient evolution and climatic change in the western Qaidam Basin deduced from phosphorus geochemistry record of deep drilling core SG-1

Phosphorus (P) provides an important biologically limiting nutrient in lake ecosystems, and its concentrations furnish significant information on lake nutrient status, climatic change, and landscape development within a drainage area. This study explores the potential of calcium-bound P and iron-bound P in calcareous lacustrine sediments to reveal variations of the paleolake nutrient status and its related climatic changes. Data come from the nearly 1000-m long core (SG-1) from the western Qaidam Basin (NE Tibetan Plateau), which has been well-dated by paleomagnetism to between 2.77 and 0.1 Ma. Calcium-bound P and iron-bound P make up the two most frequent phases of inorganic phosphorus pools in the calcareous sediment. This study compares the variations of calcium-bound P and iron-bound P with the independent proxy for biologic production proxy Total Organic Carbon (TOC) as well as a climatic proxy for lake level fluctuation from the borehole. Those results indicate that calcium-bound P responds sensitively to paleolake nutrients and climatic changes, while the iron-bound P responds to more complex factors, more specific, to the content of iron oxides. Variations of the calcium-bound P in the core SG-1 show a long-term, stepwise decrease, with shifts at ∼2.5 Ma, 1.8 Ma, 1.2 Ma, and 0.6 Ma, indicating a long-term stepwise decrease of the paleolake nutrient supply in the drainage. This suggests that the ecologic systems experienced a long-term deterioration, and the climate in central Asia became increasingly arid since after the late Pliocene.

New record of climate history in central Asia

The climate in Central Asia, currently a semiarid region, has varied over the past 500,000 years. An accurate record of the past climate can help scientists understand current climate and better predict how the climate may change in the future. Previous studies with paleoclimate records, such as lake sediments and ice cores, show changes in moisture in the region, but climate history in Central Asia is debated, as some of those records are not high resolution or not well dated. Cheng et al. describe a new high‐resolution, well‐dated record of oxygen isotopes in stalagmites from the Kesang cave in western China. The researchers dated the stalagmites using radioactive thorium dating and then looked at the oxygen isotope record, which provides information on past atmospheric circulation and precipitation.

New discoveries of glirids and eomyids (Mammalia, Rodentia) in the Early Miocene of the Junggar basin (Northern Xinjiang province, China)

We report herein new discoveries of Gliridae and Eomyidae (Mammalia, Rodentia) from the new Early Miocene locality XJ 200604, located northwest to the Burqin city, northern Xinjiang province, China. These specimens represent three taxa of Gliridae, including a new species (Miodyromys asiamediae nov. sp., Microdyromys aff. orientalis and Eliomys? sp.), and four taxa of Eomyidae (Asianeomys aff. engesseri, Asianeomys sp., Keramidomys sp. and Eomyidae indet). The identification of two forms that are closely related to Microdyromys orientalis and Asianeomys engesseri suggests an Early Miocene age of the locality but does not allow a more precise age determination. The new discoveries of Gliridae and Eomyidae again reveal the relative scarcity of the two families in the Early Miocene of Central Asia, in contrast to the coeval rich European record. Such a discrepancy in taxonomic diversity and abundance is hypothesized as resulting from different environmental evolutions during the Early Miocene, most notably the onset of a mid-latitude dry climate in Central Asia linked to combine effects of the Tibetan Plateau uplift and the retreat of the Paratethys Sea.

Hydrological changes and settlement migrations in the Keriya River delta in central Tarim Basin ca. 2.7–1.6 ka BP: Inferred from 14C and OSL chronology

Over one hundred artifacts, including shards, chopped wood, bronze and iron ware debris as well as footprints, have been discovered during archaeological investigations at and around the central Taklamakan Desert Yuansha Site (38°52′N, 81°35′E). Dating (14C and OSL) and landform study show that the present-day dry Keriya River once sustained an oasis human settlement in 2.6 ka BP, historically falling into the Spring and Autumn Period (716–475 BCE) of Chinese history. The chronology and archaeological interpretations also show that some 400 years later, the local Keriya River channel had shifted 40 km southeast to sustain a Western Han (206 BCE-25 CE) Wumi settlement at the Karadun site. In the meantime, river-channel migration had allowed reoccupation of a site west of Yuansha City around 1.9 ka BP (abandoned again by 1.6 ka BP). The remains’ chronology shows that this site was affiliated to Wumi culture and Eastern Han (24–220 CE) dynasty rule. Palaeoclimatic records indicate that the migrations of the river and oasis settlers between 2.7 and 1.6 ka BP were coeval with Central Asian climate changes. Yuansha City was built just after the end of 2.8 ka BP glacier advances in western China, suggesting that release of more water during the subsequent glacier recession may have facilitated oasis development such that Iron Age European peoples could settle in the Tarim Basin. As shown from analysis of archeological remains, not only at Yuansha but also in other ancient cities in the Tarim such as Loulan and Jingjue (Niya), conditions around 1.6 ka BP were dry enough to cause oasis decline. Thus, the results reported here enhance our knowledge about environmental changes and their effects on human activities and cultural evolution in western China and will stimulate further interdisciplinary studies of landscape and oasis history in the Tarim Basin.

Wood anatomy reflects the distribution of Krascheninnikovia ceratoides (Chenopodiaceae)

Wood anatomy characters of the Eurasian/North American half-shrub Krascheninnikovia ceratoides were investigated on plants from different parts of the wide distribution area. The secondary xylem is developed as result of anomalous secondary thickening. The vessels are small (commonly <50 μm) and the secondary xylem is rayless. Differences in vessel diameter exist between the main axis, basal branches and flowering shoots. The maximum as well as the minimum vessel diameter in the flowering shoots is significantly smaller compared to the basal branches, as well as in the main axis in all provenances. The length of thick-walled libriform fibre cells varies between the main axis and the basal branches of the same plant individual, but in the short main axis the length of libriform fibre cells is relatively constant (193–217 μm), independent of provenance and climate. Obviously, the length of libriform fibre cells is a conservative character and dependent on plant size. The vessel diameter is a more sensitive parameter for ecological studies. It varies more clearly, considering the vessel position in the plant axis system, in relation with climate differences of the provenances of the examined plants. Plants from a temperate, semi-humid climate have the largest vessel diameter in basal branches and flowering shoots, while the vessel diameter of plants from an arid temperate climate in Central Asia is smallest. The vessel diameters depend not only on climate, but also on the position in the axial system of the plants. There is a trade-off between average vessel number and their maximum diameter in flowering shoots of populations from Russia and Mongolia. Thus, vessel diameters depend on both, position in the axial system of the plant and climatic conditions.

Depositional environment in the southern Ulleung Basin, East Sea (Sea of Japan), during the last 48 000 years

The present study is based on the sedimentological data from a piston core KCES1 off the southern Ulleung Basin margin, the East Sea (Sea of Japan). The data include sediment color (L*), X-ray radiographs, grain size distribution and AMS14C date. Four kinds of sediments (homogeneous, laminated, crudely laminated and hybrid sediments) are identified according to the characters of the sedimentary structures that were considered to reflect changes in bottom-water oxygenation. Alternations of dark laminated/crudely laminated sediments and light homogeneous sediments represent millennial-scale variations that are possibly associated with the high-resolution changes in the East Asian monsoon (EAM). The relative contributions of the East China Sea Coastal Water (ECSCW) and the Tsushima Warm Current (TWC) were likely the main reasons for the repetition of the anoxic and oxic depositional conditions in the East Sea since the last 48 ka BP. During the interstadial, the strengthen summer EAM was attributed to the expansion of the ECSCW because of more humid climate in central Asia, and then more strongly low-salinity, nutrient-enriched water was introduced into the East Sea. The ventilation of deep water was restricted and therefore the dark laminated layer deposited under the anoxic bottom water condition. During the lowest stand of sea level in the last glacial maximum (LGM), the isolated East Sea dominated by stratified water masses and the euxinic depositional environment formed. The homogenous sediments have been predominating since 17.5 ka BP indicating that the TWC has intruded into the East Sea gradually with the stepwise rise of sea level and the bottom water oxygen level was high. During the late Younger Dryas (YD) period, the last dark laminated layer deposited because the ventilation of bottom water was restricted by stronger summer EAM. The TWC strengthened and the bottom water became oxic again from 10.5 ka BP.

A multiproxy lake record from Inner Mongolia displays a late Holocene teleconnection between Central Asian and North Atlantic climates

In order to study how the Holocene Central Asian climate is coupled to the global climate system, a 4.24 m long lake core from western Inner Mongolia in China was studied using a multiproxy approach. Sedimentology and geochemical parameters such as gypsum and dolomite content, presence of lakeshore sand changing to aeolian sand, and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late Holocene. Aridification is linked to the southward retreat of the northern boundary of the Asian summer monsoon, leaving central Asia under the influence of the westerly belt. The weakening of the Asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation. The weakening summer insolation also likely increased the intensity of the Siberian High pressure system, further promoting aridification of central Asia. On a shorter time scale, the multiproxy record shows the climate to have been relatively dry during the Medieval Warm Period (AD 800–1100) with the ensuing humid environment at the end of this period gradually turning to become extremely dry (AD 1100–1550) at the Little Ice Age Maximum. Switches in the North Atlantic Oscillation caused these changes through a teleconnection in the form of westerlies. These westerlies provided most of central Asia’s moisture after the retreat of the Asian summer monsoon. The central Asian climate therefore corresponds closely with late Holocene European climate changes.