Displays

The arid central Asia composed of northwestern China and central Asia, is one of the most arid regions in the mid-latitudes and also the core area of the Silk Road civilization. Climate have dramatically changed during Holocene in the region. Prior to 6 ka, moisture conditions increased gradually, and then rapidly, with the most humid period occurring during the late Holocene. Over the last millennium, a dry climate during the Medieval Warm Period and a wet climate during the Little Ice Age is present on the centennial timescale. Instrumental observations showed that precipitation, moisture, and stream runoff all have gradually increased on the decadal scale under global warming. Comparing these results to those in the mid-latitude monsoonal Asia and Mediterranean, the moisture evolution since the Holocene over westerlies Asia featured unique characteristics on various timescales. We proposed the theoretical framework of a ‘westerlies-dominated climatic regime’ (WDCR) for hydroclimatic changes. Further studies of physical mechanisms showed that external factors e.g. orbital-induced insolation changes generated WDCR on the sub-orbital timescale, while a circum-global teleconnection/Silk Road pattern was the most important factor responsible for WDCR on the centennial and decadal timescales. Climate change has impacted on the civilization evolution along the Silk road in arid central Asia. The oasis route in this region played a significant role in the development of trans-Eurasia exchange since the late third Millennium BCE. Such route laid the foundation for the formation of ancient Silk Road during the second century BCE that accounted for the most important center for civilization evolution in the planet till the sixteenth century CE. Multi-discipline studies suggest that special warm-humid climate might have facilitated the rise and development of ancient empires, e.g. Tubo Empire (618-842 CE) in and around the high Tibetan Plateau. But climate deterioration, especially severe droughts lasting decades-centuries, triggered the expansion of deserts and shrinkage of oases along the Silk Road. Such land degradation led to the delayed onset of transcontinental exchange, the decline of ancient civilizations such as ancient Loulan Kingdom (176 BCE-630 CE), and the abandonment of Dunhuang area between 1539-1723 CE by Chinese central government that was ascribed as a landmark event for the end of the traditional Silk Road. Further analysis proposed that the evolution of ancient civilizations was likely influenced by precipitation variation in surrounding mountains instead of basins in arid areas of the Silk Road.

How to cite: Chen, F., Chen, J., Dong, G., Huang, W., Hou, J., and Wang, T.: Climate change and Silk Road civilization in the arid central Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7335, https://doi.org/10.5194/egusphere-egu2020-7335, 2020.

Holocene moisture evolution in the arid Central Asia region, dominated by the westerly circulation system, has been shown to be in drastic contrast with that in Asian monsoonal regions. Yet, water isotope records, including stalagmite oxygen isotopes and terrestrial long-chain n-alkane/acid hydrogen isotopes, show many common features in the two regions. Here we present several new isotopic records from the arid Central Asia region to examine the isotopic differences from various archives/media, together with existing water isotopic records from both regions. Isotopic records more reflecting terrestrial signal in arid regions appear to follow the pattern in monsoonal regions, while those likely affected by isotopic enrichment due to lake water evaporation display various patterns, and not necessarily resemble moisture changes inferred from the same lakes. It thus appears that the terrestrial water isotopes in both regions may record the isotopic signature in precipitation, but not necessarily linked to aridity changes. Meanwhile, those isotopic records affected by lake evaporation, after subtracting the original precipitation isotopic signal, show good correspondence to moisture changes.

How to cite: Liu, Z., Jiang, J., Wang, Z., Krivonogov, S., Jiang, Q., Hou, J., Zhao, C., Zhou, A., Liu, W., and Chen, F.: Holocene Water Isotope Records Not Reflecting Aridity Changes in Arid Central Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7827, https://doi.org/10.5194/egusphere-egu2020-7827, 2020.

 Razavi Khorasan Province in the northeast of Iran, located at the Crossroads of Eurasia, was an important point of the middle part of the Silk Road. Neyshabur Plain is situated an important transporting hub of the major thoroughfare of Eurasia. A large number of sites are distributed in the river valleys and the alluvial fans in front of the mountains. Archaeological survey was carried out in Neyshabur Plain, and more than 10 sites were discovered, which are in form of mounds of earth, named as Tape. Seen from the cultural relics on the surface, these sites were occupied by successive cultural sequences, mainly ranging from Neolithic, Chalcolithic, Bronze to Iron Age. This appearance indicates that the climate and environment in the past was better than now. Today, the region is characterized by dry climate, and poor land resources. The land is dominated by Gobi Desert, and the wide vegetation is dominated by Camel thorn (Alhagi sparsifolia). Only in which Karez irrigation system exists, can wheat (Triticum aestivum), barley (Hordeum vulgare) and saffron (Crocus sativus) be cultivated, while a few orchard is present in some river valley areas.

    Tape Borj, which is the largest prehistoric settlement site in the east part of Neyshabur plain, Razavi Khorasan Province, NE Iran, covers an area of 13.5 ha. A total area of 110 m² was excavated in the north and northwest part of the site, and some geological survey were also conducted around the site in 2019. A total of 14 ash pits, 4 houses, 6 ovens, and one well were unearthed during the excavation. According to the AMS dates and material culture, the cultural deposits can be divided into two phases, including Chalcolithic Age during 6500 BP and 6000 BP and early Bronze Age during 5500 BP and 5000 BP. Some wheat, barley, oats (Avena sativa), and seeds of Celtis sinensis, as well as a large number of animal bones, which are dominated by sheep and goats were discovered. The results can basically reflect the economic structure and subsistence strategy of prehistoric ancestors. Geological survey indicates that two paleo river course ever went through the east and west sides of the site during the prehistoric period. In addition, some samples were systematically collected for pollen and phytolith analysis, in order to understand the paleoenvorinment and the utilization of plant resources by the ancient people at the site from the Chalcolithic to the Bronze Age. Our work can provide some precious material data for studying the evolution of the paleoenvrionment and development of agriculture and animal husbandry in this region.

How to cite: Zhang, J., Cui, Q., Luo, W., Yang, Y., and Garazhian, O.: Environmental survey and trial excavation at prehistoric settlement site in Neyshabur Plain, Northeastern Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7906, https://doi.org/10.5194/egusphere-egu2020-7906, 2020.

We collected the available relative pollen productivity estimates (PPEs) for 27 major pollen taxa from Eurasia and applied them to estimate plant abundances during the last 40 cal. ka BP (calibrated thousand years before present) using pollen counts from 203 fossil pollen records in northern Asia (north of 40°N). These pollen records were organised into 42 site-groups, and regional mean plant abundances calculated using the REVEALS (Regional Estimates of Vegetation Abundance from Large Sites) model. Time-series clustering, constrained hierarchical clustering, and detrended canonical correspondence analysis were performed to investigate the regional pattern, time, and strength of vegetation changes, respectively. Reconstructed regional plant-functional type (PFT) components for each site-group are generally consistent with modern vegetation, in that vegetation changes within the regions are characterized by minor changes in the abundance of PFTs rather than by increase in new PFTs, particularly during the Holocene. We argue that pollen-based REVEALS estimates of plant abundances should be a more reliable reflection of the vegetation as pollen may overestimate the turnover, particularly when a high pollen producer invades areas dominated by low pollen producers. Comparisons with vegetation-independent climate records show that climate change is the primary factor driving land-cover changes at broad spatial and temporal scales. Vegetation changes in certain regions or periods, however, could not be explained by direct climate change, for example inland Siberia, where a sharp increase in evergreen conifer tree abundance occurred at ca. 7–8 cal. ka BP despite an unchanging climate, potentially reflecting their response to complex climate–permafrost–fire–vegetation interactions and thus a possible long-term-scale lagged climate response.

How to cite: Cao, X., Tian, F., Li, F., Gaillard, M.-J., Rudaya, N., Xu, Q., and Herzschuh, U.: Pollen-based quantitative land-cover reconstruction for northern Asia covering the last 40 ka, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21976, https://doi.org/10.5194/egusphere-egu2020-21976, 2020.

In the North Atlantic and the surrounding region, more than 20 rapid millennial-scale climatic fluctuations occurred during the last glacial-interglacial cycle (Dansgaard et al. 1993). These oscillations, known as Dansgaard-Oeschger (D-O) and H-events. Simulate studies suggest that the millennial-scale climatic signals can spread to a wide area by atmospheric and oceanic circulations. However, it lacks such record in central Asia which is climatically characterized by arid and sensitive to climate change.

Here, we present the record of millennial-scale fluctuations from loess deposits in Tajikistan in Central Asia. The frequency-dependent magnetic susceptibility (X_fd, a moisture proxy) record in the Darai Kalon (DK) section (38º23′4″N, 69º50′1″N, 1561 m) can be readily matched with the NGRIP oxygen isotope curve, especially during the interval from 60-30 ka in which typical D-O cycles and H-events are well developed. Most of the long-lasting D-O cycles in Greenland, e.g., D-O 8, 12, and 14, are also evident in the Tajikistan loess. Similarly, the short-duration D-O cycles in Greenland, e.g., D-O 6, 7, 9, 10 cycles, have their damped counterparts in the Tajikistan loess. However, some significant differences in detail can be observed between the two records. The most distinct difference occurs in the case of last D-O cycle, which includes the well-documented Oldest Dryas (OD or H1), Bølling-Allerød (BA), and Younger Dryas (YD or H0) events, which are not clearly present in the X_fd curve.

The magnetic results support that the climate is humid in interstadials and dry in stadials in central Asia. And, the variation of humidity is much more remarkable in central Asia than in Chinese Loess Plateau which is climatically dominated by Asian Monsoon. It exhibits the humidity in central Asia is sensitive to millennial-scale climate oscillations during the last glacial. The comparison results further indicate propagations of millennial-scale climatic signals were different between these two regions. We assumed the former one is the Westerlier which can directly and effectively force the millennial-scale climatic variability in central Asia, and the latter one is thermohaline circulation and Asian Monsoon, the complex propagation weakened the millennial-scale climatic variability Northern China.

How to cite: Jia, J., Wang, Z., Wang, L., and Chen, J.: The millennial-scale climatic variability in central Asia during last glacial, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3875, https://doi.org/10.5194/egusphere-egu2020-3875, 2020.

The climate in the Altai Mountains is highly sensitive to large-scale forcing factors because of its special geographic location. Based on n-alkane data of 150 samples and with a chronologic support of 15 accelerator mass spectrometry (AMS) dates from a 600-cm core at GHZ Peat, the Holocene climatic changes in the Altai Mountains were reconstructed. The reconstruction revealed a warming and drying early Holocene (~10,750-~8500 cal. yr BP), a cooling and persistent dry middle Holocene (~8500-~4500 cal. yr BP), and a cooling and wetting late Holocene (~4500-~700 cal. yr BP). The Holocene temperature changes were primarily controlled by the summer solar radiation with a certain time lag in the early Holocene and also modulated by solar activity, and the time lag in the early Holocene was probably resulted from ice and permafrost melting. The Holocene moisture in the southern Altai Mountains was likely modulated by the North Atlantic Oscillations (NAO) or by the Atlantic Multi-centennial Oscillations (i.e., AMO-like) or by temperature, and or by any combination of the three (NAO, AMO-like, and temperature).

How to cite: Ran, M.: An n-alkane-based Holocene climate reconstruction in the Altai Mountains, northern Xinjiang, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3185, https://doi.org/10.5194/egusphere-egu2020-3185, 2020.

The origins and spread of agriculture was one of the milestones in human history. When and how prehistoric agriculture spread to mainland Southeast Asia is highly concerned, which contributed to the formation of modern Austroasiatic in this region. Previous studies mainly focused on the time and route of rice agriculture’s introduction into Southeast Asia while millet agriculture was not paid properly attention. Here we analyze 312 ¹⁴C dating data yielded from charred seeds of rice (Oryza sativa), foxtail millet (Setaria italica) and broomcorn millet (Panicum miliaceum) from 128 archaeological sites in China and mainland Southeast Asia. The result shows that millet farming was introduced to mainland Southeast Asia in the late third millennium BC and rice farming was in the late second millennium BC. The agriculture of mainland Southeast Asia might originate from three areas, Southwest China, Guangxi-West Guangdong and coastal Fujian. The spread route of ancient agriculture in Southwest China is close to the “Southwest Silk Road” recorded in literature, which infers there was possibly a channel of cultural exchanges on the eastern margin of Tibetan Plateau already in the late Neolithic period, laying the foundation of the Southwest Silk Road later.

How to cite: Gao, Y., Dong, G., Yang, X., and Chen, F.: A review on the spread of prehistoric agriculture from southern China to mainland Southeast Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12886, https://doi.org/10.5194/egusphere-egu2020-12886, 2020.

Ancient silk road had two main branches, one is north line across Xinjiang and the other is south line proposed as Highland Silk Road, jointing Tibetan Empire, Tang Dynasty and states in South Asia. Due to the harsh natural environment on the Tibetan Plateau (TP), a little archaeological work had carried out, and a few archaeological sites were excavated on the TP. How the highland silk road was developed is unclear.

In 2018, researchers from the Chinese Academy of Sciences (CAS) launched the second scientific expedition to the Qinghai-Tibet Plateau (STEP) that will last 5 to 10 years, following an expedition in the 1970s. Sponsored by the STEP, we had two systematic surveys along the Yarlung Tsangpo River regions, esp. the middle and lower regions to understand the prehistoric human activities on the central Tibetan Plateau where the mean altitude is above 4000 meters. We investigated the terraces along the River and its tributoraries, and terraces circled the lake banks. 99 archaeological sites were surveyed, including 58 new findings. The anthropic deposits were found at 31 sites and a profile was cleared at each site to collect dating materials. Charcoals and charred seeds were floated from the anthropic deposits and dated 60 samples by the AMS ¹⁴C.

In combination with previous published dates, we set up a brief history of human activities on the central TP that is, Neolithic people had occupied the Yarlung Tsangpo Valley in the third millennium BC, and moved along the River and its tributaries. The route of dispersal is similar with the historic highland silk road, indicating that this road had developed in prehistory.

How to cite: Yang, X.: Precursor of the Highland silk road on the Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7977, https://doi.org/10.5194/egusphere-egu2020-7977, 2020.

Many studies focusing on the physical and chemical indicators of the ice core reflected the climate changes. However, only few biological indicators indicated the past climate changes which are mainly focused in biomass rather than diversity. How the biodiversity response to the climate change during the past hundred years is still unknow. Glaciers in Mt. Muztagh Ata region are influenced by the year-round westerly circulation. We firstly disclosed annual variations of bacterial community compositions in ice core over the past 130 years from Muztagh Glacier, the western Tibetan Plateau. Temporal variation in bacterial abundance was strongly controlled by DOC, TN, δ¹⁸O, Ca²⁺, SO₄²⁻, NH₄⁺ and NO₃⁻. Proteobacteria, Actinobacteria and Firmicutes were the three most abundant bacterial phyla, accounting for 49.3%, 21.3% and 11.0% of the total community, respectively. The abundances of Firmicutes and Bacteroidetes pronouncedly increased over time throughout the entire ice core. UPGMA cluster analysis of the bacterial community composition separated the all ice core samples into two main clusters along the temporal variation. The first cluster consisted of samples from 1951 to 2000 and the second cluster contained main samples during the period of 1869-1950. The stage 1 and stage 2 bacterial community dissimilarities increased linearly with time on the basis of the Bray-Curtis distance, indicating a similar temporal–decay relationship between the stage 1 and stage 2 bacterial communities. Of all the environmental variables examined, only DOC and NH₄⁺ exhibited very strong negative correlations with bacterial Chao1-richness. ¹⁸O was another important variable in shaping the ice core bacterial community composition and contributed 1.6% of the total variation. Moreover, DistLM analysis indicated that the environmental variables explained more variation in the stage 1 community (20.1%) than that of the stage 2 community (19.9%).

How to cite: Liu, Y., Yao, T., and Xu, B.: Variation of bacterial communities in Muztagh ice core from 1869 to 2000, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6328, https://doi.org/10.5194/egusphere-egu2020-6328, 2020.

The study of the coupling relationship between climate change and civilization evolution along the Ancient Silk, can provide valuable insights for understanding the history, pattern and mechanism of man-land relation evolution from a long-run perspective. Here we provide two case studies from the Hexi Corridor and Qaidam basin in northwest China, where locates at eastern Ancient Silk Road, and became a center for trans-continental exchange since the second Millennium BC, hydrological change in these areas is very drastic. The results reveal three significant desertification events occurred in these two areas during late Holocene, which was likely related to precipitation variation in surrounding mountains instead of basins, and triggered the shrinkage of ancient oases and then the decline of ancient civilizations. We also try to explain the linkage between climate change and the evolution of ancient civilizations in the two areas.

How to cite: Dong, G., Li, R., Zhang, S., and Liu, F.: How climate change affected the evolution of ancient civilizations in eastern Ancient Silk Road?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1818, https://doi.org/10.5194/egusphere-egu2020-1818, 2020.

Knowledge of the alpine glacier mass fluctuations is a fundamental prerequisite for understanding glacier dynamics, projecting future glacier change, and assessing the availability of freshwater resources. The glaciers on the Tibetan Plateau (TP) are sources of water for most of the major Asian rivers and their fate remains unclear due to accurate estimates of glacier mass fluctuations are lacking over long time scales. Here, we used d¹⁸O record at a proglacial open lake as proxy to estimate the Holocene glacier mass fluctuations in the Western Kunlun Mountain (WKM) quantitatively and continuously. Relative to past decades, maximum WKM glacier mass loss (-28.62±25.76 Gt) occurred at 9.5-8.5 ka BP, and maximum glacier mass gain (24.53±25.02 Gt) occurred at 1.3~0.5 ka BP, the difference in WKM glacier mass between the two periods account for ~20% of the total glaciers. Long-term changes in glacier mass suggests the TP glaciers likely face severe threats at the current rates of global warming.

How to cite: Hou, J.: Quantitative Estimates of Holocene Glacier Mass Fluctuations on the Western Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6762, https://doi.org/10.5194/egusphere-egu2020-6762, 2020.

We have reconstructed the history of mid-late Holocene paleohydrological changes in the Chinese Loess Plateau using n-alkane data from a sediment core in Tianchi Lake. We used P_aq (the proportion of aquatic macrophytes to the total plant community) to reflect changes in lake water level, with a higher abundance of submerged macrophytes indicating a lower water level and vice versa. The P_aq -based hydrological reconstruction agrees with various other lines of evidence, including ACL (average chain length), CPI (carbon preference index), C/N ratio and the n-alkane molecular distribution of the sediments in Tianchi Lake. The results reveal that the lake water level was relatively high during 5.7 to 3.2 ka BP, and decreased gradually thereafter. Our paleohydrological reconstruction is consistent with existing paleoclimate reconstructions from the Loess Plateau, which suggest a humid mid-Holocene, but is asynchronous with paleoclimatic records from central China which indicate an arid mid-Holocene. Overall, our results confirm that the intensity of the rainfall delivered by the EASM (East Asian summer monsoon) is an important factor in affecting paleohydrological changes in the region and can be considered as further evidence for the development of a spatially asynchronous “northern China drought and southern China flood” precipitation pattern during the Holocene.

How to cite: Zhou, A.: Mid- to- late Holocene hydroclimatic changes on the Chinese Loess Plateau: evidence from n-alkanes from the sediments of Tianchi Lake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3862, https://doi.org/10.5194/egusphere-egu2020-3862, 2020.

Sheep and goats have been introduced into northwest China as important livestock for some four thousand years. The frequency of sheep/goats’ bones in prehistoric archeological sites in Xinjiang can be a proof of their importance in people’s life. This study focuses on food reconstruction of prehistoric sheep/goats across Xinjiang to illustrate whether there is a difference on sheep/goats husbandry. Bone samples from 11 sites were isotopically analyzed together with 4 sets of published data, 220 pairs of sheep/goats bone stable carbon and nitrogen isotopes in total from 15 sites across Xinjiang with time span of ca, 4000 cal BP to ca. 2000 cal BP were produced. 9 sites each with sample number no less than 10 were further studied. It revealed that generally sheep/goats from 4 oasis sedimentary farming societies have both higher ¹³C values and higher ¹⁵N values, although highly fluctuated. It is highly likely that C₄ plants such as foxtail millet or common millet must have not been a stranger around their environment. As for their remarkably high ¹⁵N values, drought stress in arid environment may have been one reason, fertilized soil after long time relatively intensive human activity may have also contributed to this. In the meanwhile, sheep/goats from 5 pastoralism or transhumance societies have homogenous and more negative ¹³C values, most of which are lower than -18‰, meaning that there was barely no C₄ plants in their diet. In contrast, ¹⁵N values of them are lower than that of farming societies as a whole but more scattered, seasonally different pastures with diversified ¹⁵N background could be the reason.

How to cite: Dong, W.: Prehistoric sheep/goats husbandry in Xinjiang, China—Evidence from bone stable carbon and nitrogen isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17666, https://doi.org/10.5194/egusphere-egu2020-17666, 2020.

Rapid monsoon changes since the last deglaciation remain poorly constrained due to the scarcity of geological archives. Here we present a high-resolution scanning X-ray fluorescence (XRF) analysis of a 13.5-m terrace succession on the western Chinese Loess Plateau (CLP) to infer rapid monsoon changes since the last deglaciation. Our results indicate that Rb/Sr and Zr/Rb are sensitive indicators of chemical weathering and wind sorting, respectively, which are further linked to the strength of the East Asia summer monsoon (EASM) and the East Asia winter monsoon (EAWM). During the last deglaciation, two cold intervals of the Heinrich event 1 and Younger Dryas were characterized by intensified winter monsoon and weakened summer monsoon. The EAWM gradually weakened since the beginning of the Holocene, while the EASM remained steady till 9.9 ka and then grew stronger. Both the EASM and EAWM intensity were relatively weak during the middle Holocene, indicate a mid-Holocene climatic optimum. Rb/Sr and Zr/Rb exhibit an anti-phase relationship between the summer and winter monsoon changes on centennial timescale during 16~1 ka BP. Comparison of these monsoon changes with solar activity and North Atlantic cooling events reveals that both factors can lead to abrupt changes on the centennial timescale in the early Holocene. During the late Holocene, North Atlantic cooling became the major forcing of centennial monsoon events.

How to cite: Liu, X., Sun, Y., Vandenberghe, J., Cheng, P., Zhang, X., Gowan, E., Lohmann, G., and An, Z.: Centennial to millennial-scale monsoon changes since the last deglaciation linked to solar activities and North Atlantic cooling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12828, https://doi.org/10.5194/egusphere-egu2020-12828, 2020.

Domestication is a complex evolutionary process in which wild organisms are moved to anthropogenic environments with a series of phenotypic changes in response to artificial selection and new habitats. In recent years, phenotypic variations have been detected between wild and domestic species, as well as different breeds of domestic species, through dental and skeletal elements. However, the mechanisms of phenotypic adaptations in the postcranial skeletons to new environments following domestication are still poorly understood. In this study, the morphological variations on the metacarpals of a primitive sheep (Ovis aries) breed – Soay sheep, are investigated. Controlled modern samples with known sex, age, and diets from those living feral on St Kilda (Scotland) as well as those re-located and raised on East Anglian farms were analysed using 3D geometric morphometrics. Specific morphotypes were found associated with the animals’ age, sex, and anthropogenic stressors in the new ecological niches under human control. Importantly, apart from the traditionally observed contributing factors to the morphological changes mentioned above, the animals’ locomotor adaptations to the different physical terrains – flat and enclosed East Anglian farms in contrast to the mountainous St Kilda – were observed, indicating that the animals’ movement into the new landscapes following humans’ management might be detected using the specific morphotypes. This study bears testament to the process of initial caprine domestication, and provides insights into the bovids biological mechanisms during the co-evolutionary process between the humans, animals, and physical environments. The specific interlinks between the phenotypic features and the animals’ adaptations following domestication and translocation could serve as a basis for the further studies on the process and effects of the beginnings and spread of farm animals across prehistoric Eurasia.

How to cite: Wang, Y., Bendrey, R., Schoenebeck, J., and Marchant, T.: Postcranial Phenotypic Adaptations to New Habitats Following Domestication --- An Investigation on Ovis Metacarpals by 3D Geometric Morphometrics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22270, https://doi.org/10.5194/egusphere-egu2020-22270, 2020.

The climate of eastern arid central Asia (ACA) is extremely dry and early human settlement and civilization in the region were dependent upon a potentially unstable water supply. Thus, knowledge of the history of hydrological fluctuations is essential for understanding the relationship between humans and the environment in the region. Here we present a record of variation in lake hydrodynamic intensity based on the grain size of suspended lacustrine silt isolated from the sediments of Bosten Lake, which feeds a river flowing to the northeastern Tarim Basin. The results show that lake hydrodynamic intensity was very weak, and/or that the lake dried-out completely, during the early Holocene (12.0–8.2 ka). Then it increased with two distinct centennial-millennial-scale intervals of weak intensity occurring during 4.7–3.5 ka and 1.2–0.5 ka. Notably, increases in lake hydrodynamic intensity occurred some 2.2 kyr prior to an increase in local precipitation and effective moisture. We speculate that this was a consequence of relatively high early summer temperatures during 8.2–6.0 ka that resulted in an increased water supply from melting snow and ice in mountainous areas of the catchment. Thus, we conclude that changes in the hydrodynamic intensity of Bosten Lake during the Holocene were affected by changes in both temperature and precipitation. The variations in the hydrodynamic intensity of Bosten Lake since the middle Holocene also influenced water availability for the human population that occupied the downstream area of the northeastern Tarim Basin. A persistent increase in hydrodynamic intensity during 2123–1450 B.C. may have been responsible for human occupation of the region that contains the noted archaeological sites of Xiaohe and Gumugou Cemetery. In addition, a drastic decrease in hydrodynamic intensity at around 400 A.D. likely caused the emigration of the inhabitants of Loulan.

How to cite: Xie, H.: Changes in the hydrodynamic intensity of Bosten Lake and its impact on early human settlement in the northeastern Tarim Basin, eastern Arid Central Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13015, https://doi.org/10.5194/egusphere-egu2020-13015, 2020.

Holocene variations in precipitation in central and eastern arid central Asia (ACA) have been widely investigated, but the pattern in western ACA remains unclear. We present records of the stable carbon isotope composition of bulk organic matter (δ¹³C_org), magnetic parameters, and sediment color, from five loess-paleosol sequences in NE Iran, in western ACA, with the aim of reconstructing Holocene precipitation. The Yellibadragh (YE) section (the thickest among the five sequences) was selected for OSL dating of the coarse-grained quartz (63-90 μm) fraction, and its δ¹³C_org record was used to quantitatively reconstruct mean annual precipitation (MAP). The record indicates a dry early Holocene (~11.8-7.4 ka), with nearly constant MAP (~93 mm), followed by a wetting trend from the mid-Holocene (~7.4 ka) onwards, with the wettest period in the late Holocene (~4.0-0.0 ka, ~390 mm). The stratigraphic observations and environmental proxies support the reconstruction. The other loess profiles show stratigraphic features and trends of environmental proxies which are similar to those of the YE profile. A dry early Holocene and wetting trend since the mid-Holocene, with the wettest climate in the late Holocene in NE Iran, are both consistent with records from sand dunes and lake sediments from adjacent areas, and with loess records from central and eastern ACA. Comparison with loess records from monsoonal Asia supports the interpretation of a “westerlies-dominated climatic regime” (WDCR) which was proposed mainly on the basis of lake sediment records from the region. Changes in solar insolation may have been responsible for the persistent wetting trend during the Holocene in western ACA.

How to cite: Wang, Q., Wei, H., Khormali, F., Wang, L., Xie, H., Wang, X., Huang, W., Chen, J., and Chen, F.: Holocene moisture variations in western arid central Asia inferred from loess records from NE Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4601, https://doi.org/10.5194/egusphere-egu2020-4601, 2020.

Understanding the Holocene moisture variations in the Arid Central Asia (ACA) is of a large-scale climatic significance simply because the vast ACA is influenced by several different climate systems. However, the temporal and spatial patterns and the modulating mechanisms of the Holocene aridity (or moisture) variations in the ACA remain in the center of controversies for the past two decades. Firstly, we in this research depicted the spatial and temporal patterns of the Holocene aridity variations in the Tianshan Mountains based on thirteen already-published aridity sequences and two recently obtained aridity sequences. Our depiction shows that the regionally-averaged standardized aridity-index (RA-SAI) curve for the Eastern Tianshan Mountains exhibits a wetting trend. In contrast, the RA-SAI curve for the Western Tianshan Mountains exhibits a drying trend. Secondly, we further examined these two RA-SAI sequences (one for the Eastern Tianshan and another for the Western Tianshan) within a much larger geographic context for exploring the mechanisms modulating the Holocene patterns. Our examination shows that the summer precipitation-dominated northern middle-latitude Eurasia (i.e., MLEA-N) has experienced a wetting trend and the winter precipitation-dominated southern middle-latitude Eurasia (i.e., MLEA-S) has experienced a drying trend. The wetting trend in MLEA-N is proposed to have resulted from increasingly more positively-phased AMO activities that have increasingly enhanced cyclonic pressure anomalies over the Atlantic regions, directly or indirectly bringing more and more summer precipitation to MLEA-N stretching from West Europe to the Eastern Tianshan. And, the drying trend in MLEA-S is proposed to have resulted from increasingly more negatively-phased NAO activities. That is, the negatively-phased NAO activities weakened the strength of Western Disturbances, therefore resulting in decreased winter precipitations in MLEA-S stretching from the Eastern Mediterranean to the Western Tianshan.

How to cite: Yang, Y.: Holocene moisture variations in the Tianshan Mountains and their geographic coherency in the mid-latitude Eurasia: A synthesis of proxy records, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3196, https://doi.org/10.5194/egusphere-egu2020-3196, 2020.

Previous studies demonstrated that the farmers spread into the Tibetan Plateau (TP) and permenantly settled there around 3600 yr cal BP, taking the ways on the northeastern edges of the TP and bearing the western crops of barley, and sheep. But, other studies argued the earlier permenant settlements or different ways to spread into the central TP. Meanwhile, the Yarlung Tsangpo River regions in southern TP, are considered to be one of the important routes for culture dispersal and human migration, jointing Tibetan Empire, Tang Dynasty and states in South Asia in history period, were proposed as highland silk road. However, the role of this route in prehistorical culture exchange and human colonization on the TP remains unclear, due to the scarce of archaeological work in these regions.

Systematic surveys along the Yarlung Tsangpo River regions had carried out in last two years. Charcoals and charred seeds were floated from the cultural layers in 31 sites and 60 new carbon-14 dates had been got. Charred seeds include wheat, barley and pea from the west, and broomcorn millet and foxtail millet from the east. In combination with previous published dates, we set up routes of crop dispersal and brief history of human activities on the central TP. Neolithic people had occupied the Yarlung Tsangpo Valley from the different direction of the TP in the third millennium BC with different western crops or eastern crops, and moved along the River and its tributaries. The route for dispersal is similar with the historic highland silk road, indicating this road had played a important role since prehistory.

How to cite: Yang, J. and Yang, X.: Crop dispersal along the prehistoric highland silk road on the Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12724, https://doi.org/10.5194/egusphere-egu2020-12724, 2020.

The headwater region of the Yangtze River serves as major constituent of Chinese Water Tower and is critical in providing fresh water for hundreds of millions of people living downstream. Hydrological variation is mainly influenced by environmental changes. Therefore, a good understanding of climate changes in the source region of the Yangtze River (SRYR) is of great significance. Here, we provide a lacustrine sediment core from Saiyong Co in SRYR, northeastern Tibetan Plateau, China, to reconstruct hydrological variation and the main influencing factors based on the analysis of grain size, scanning XRF, loss on ignition (LOI), which cover the past 6 ka. It is remarkable that total organic matter (LOI-550℃) exhibits opposite patterns regarding to the PC1 of XRF, which represents the allochthonous input, indicating the majority of organic matter was mainly yielded within the lake. Clustering of palaeohydrological proxies, such as the reduced PC1 and increase in median grain size, seems coincide with the weakened strength of the Indian summer monsoon, which suggest a generally dry trend in the SRYR during the mid-late Holocene. However, short pulses of outrageous period occurred at 3.8-3.2 ka BP and 1.5-1.0 ka BP. The abrupt increase in PC1 and very coarse silt indicate the lake catchment became more humid with higher surface runoff, which is consistent with weaker lake productivity. The inferred hydrological change in SRYR since 6 ka BP not only have significant environmental influence, but also agree with other sequences from Tibetan Plateau and the adjacent regions This study provides long-term records of paleoenvironmental evolution which is particularly significant to understand recent and to predict future hydrological change in SRYR.

How to cite: Xiaohuan, H., Lina, L., Zhe, S., Xianyong, C., and Juzhi, H.: Mid-late Holocene hydroclimate variation in the source region of the Yangtze River revealed by lake sediment records, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5067, https://doi.org/10.5194/egusphere-egu2020-5067, 2020.

Precise age controls are fundamental prerequisites for reconstructing past climate and environment changes. Lakes on the Tibetan Plateau are one of the important archives for studying past climate and environment changes. However, radiocarbon ages for lake sediment core are subject to old radiocarbon reservoir effects, which caused severe problems in constructing age controls for lake sediment cores, especially on the Tibetan Plateau (TP). Here we present a varve chronology over the past 2000 years at Jiang Co on the central TP. The clastic-biogenic varves comprise of a coarse-grained layer and a fine-grained layer observed by petrographic microscope and Electron Probe Micro Analyzer. Varve chronology is supported by measurements of ²¹⁰Pb and ¹³⁷Cs, which is further used to determine the radiocarbon reservoir ages in the past ~2000 years. The percentage of coarse-grain layer thickness within single varves was considered as proxy for precipitation as the coarse grains were mainly transported by runoff, which is highly correlated with local meteorological observation. During the past 2000 years, the precipitation records show centennial-scale fluctuations that are consistent with regional records. The varve chronology at Jiang Co provides a valuable opportunity to examine variation in reservoir ages on the TP and a robust chronology for reconstructing paleoclimate.

How to cite: Ji, K., Zhu, E., Chu, G., and Hou, J.: Late Holocene Varve Chronology and High-Resolution Records of Precipitation in the Central Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4965, https://doi.org/10.5194/egusphere-egu2020-4965, 2020.

Asian summer monsoon (ASM) is one of the critical elements of the global climate system, and strongly affects food production and security of most people over Asia. However, the characteristics and the forcing drivers of the ASM system at decadal to centennial time scales remain unclear. To address these issues, we report four 1500-yr long climate model simulations based on the Community Earth System Model (CESM), including full-forced run (ALLR), control run (CTRL), natural run (NAT), and anthropogenic run (ANTH). After evaluating the performances of the CESM in simulating ASM precipitation, a 10-100 bandpass filter is applied to obtain the decadal-centennial signals in ASM precipitation. The main conclusions are (1) the variation of ASM intensity shows significant decadal to centennial periodicities in the ALLR, such as ~15, ~25, ~40, and ~70 years. (2) the major spatial-temporal ASM precipitation distributions in the ALLR show an external forced mode and climate internal variability mode, respectively. (3) The leading forced mode of ASM precipitation is mainly affected by natural forcing over the past 1500 years and characterizes a meridional spatial 'tripole' mode. In the NAT (solar irradiation and volcanic eruptions), the substantial warming (cooling) over the western tropical Pacific enhances (or reduces) the SST gradient change in the tropical Pacific, and modifying the ASM rainfall distribution. Our findings contribute to better understanding of the ASM in the past, and provide implications for future projections of the ASM under global warming.

How to cite: Wang, Z., Wang, J., Jia, J., and Liu, J.: The forced response of Asian Summer Monsoon precipitation during the past 1500 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3874, https://doi.org/10.5194/egusphere-egu2020-3874, 2020.