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This paper reviews recently published literature, most of which was published in Chinese, and searches for regional patterns of Holocene changes useful in depicting global patterns. The Holocene in the Xinjiang region can be divided into three stages: a warming and dry early stage (from 11 ∼ 10 to 8 ∼ 7 ka BP), a warm and wet middle stage (from 8 ∼ 7 to 4.5 ∼ 3 ka BP) and a fluctuating cool and dry late stage (since 4.5 ∼ 3 ka BP). The Holocene in the northern Tibetan Plateau can also be divided into three stages: a warming and wet stage (from 10.5 ∼ 10 to 5 ∼ 4 ka BP), followed by a variable drying and probably warm stage (5 ∼ 4 to 3 ka BP) and ending with a cool and dry stage (since 3 ka BP). In the Inner Mongolian Plateau, the early Holocene (from 10.5 ∼ 9.5 to 8 ∼ 7.5 ka BP) was warming and dry, and a warm and wet climate occurred from 7.5 to 3.5, during which the best time was 6.3–3.8 ka BP; the climate has been variably drying and probably cooling since 3.5 ka BP. In the northwestern part of the Loess Plateau, several Holocene palaeosols have been identified (10–9, 7.5–5, 4–3 and 2.7–2 ka BP) with the 7.5–5 ka BP palaeosol being most strongly expressed. The best-developed palaeosol-equivalent in major valleys is a swamp-wetland facies deposited between 8885 and 3805 14C yr BP under an extremely wet regime. The climate has fluctuated significantly at least three times around a dry and probably cool regime after the swamp-wetland facies-depositional period. Our summary shows that the Holocene Climatic Optimum occurred nearly contemporaneously (8–5 ka BP) at all sites in the Xinjiang region, in the Inner Mongolian Plateau and in the northwestern part of the Loess Plateau. A warming and wet early Holocene (10–8 ka BP) in the northern Tibetan Plateau is most likely related to high effective soil moisture resulting from snow and ice melting. We propose here that the middle Holocene Climatic Optimum (8–5 ka BP) in arid to semi-arid China was primarily a delayed response of the low latitude oceans to high latitude peak insolation (9–8 ka BP). [ABSTRACT FROM AUTHOR]

It is currently suggested that climate change on the northeastern Tibetan Plateau (TP) was influenced alternately by the monsoon and the Westerlies. However, the mechanisms driving Holocene climate change on the TP remain unclear, since the extent of the influence of individual atmospheric circulation systems has not yet been clearly defined because of the shortage of high-quality paleoclimatic records. This is especially true in the central TP, where only a few ice core and paleolimnological records are available. Here, we present a decadal-resolution temperature record from Dagze Co in the central TP for the past 2000 years, based on the unsaturation index of long-chain alkenones, using an updated temperature calibration, and a record of precipitation isotopes from compound-specific isotope ratios of leaf waxes. The centennial-scale variation of the temperature and precipitation isotope records captures well-known climatic events over the past 1000 years, for example, the ‘Little Ice Age’, which was cooler and drier than the ‘Medieval Warm Period’. However, the relationship between temperature and the precipitation isotope records differed during the interval at 2000–1000 cal. yr BP compared to the past 1000 years, probably because of changes in precipitation seasonality and the additional influence of the Westerlies on the central TP. In addition, the temperature records exhibit a prominent 210-year cyclicity, suggesting a possible influence of solar radiation on temperature variability. [ABSTRACT FROM AUTHOR]

The palaeoshorelines of a lake are the direct geomorphic evidences to reflect past water levels and record information on palaeoclimatic changes. Previous research indicates that the timing and forcing mechanisms of climatic change on the northeastern Qinghai-Tibetan Plateau (NE QTP) are still controversial. Here, we report quartz optically stimulated luminescence (OSL) ages for beach deposits and accelerator mass spectrometry (AMS) 14C age for plant remains, shoreline features and geomorphic exposures that contribute to a reconstruction of the lake-level history of Hurleg Lake on the NE QTP. The results imply that (1) three high lake levels are dated to 6.8–6.4, 5.0–4.7 and 2.2–1.4 kyr, corresponding to relatively wet and stable climate from pollen records of sediment core in this lake during mid–late Holocene; (2) the highest lake-level period occurred at 5.0–4.7 kyr, which is almost synchronous with the highest effective moisture phase from synthesized lake records influenced by the Westerlies and (3) no beach deposits around Hurleg Lake and lower lacustrine deposits in Toson Lake were found during early Holocene, suggesting lower lake level of Hurleg Lake in this period. These results might imply that the Westerlies and local topography rather than Asian summer monsoon dominate the moisture availability in this region during the Holocene. [ABSTRACT FROM AUTHOR]

Previous sedimentological studies on peat sequences from the eastern Tibetan Plateau showed that there have been eolian dust inputs to the wetlands on the eastern Tibetan Plateau, thereby providing an opportunity to reconstruct the history of the Asian winter monsoon at a higher temporal resolution. Here the dust flux and the content of trace metallic elements (Ti, Ni, and V) in a peat sequence from the Hongyuan Swamp (32°46.7′N, 102°31.0′E) are used to reconstruct variations in the intensity of the Asian winter monsoon during the Holocene. This record, when compared with the summer monsoon proxy, can help elucidate the phase relationship between these two systems. Our proxy-based reconstructions show different patterns of changes in the Asian winter and summer monsoons before and after 5.5 cal. ka BP. Generally, the two monsoons varied reciprocally before 5.5 cal. ka BP; however, after 5.5 cal. ka BP, these two systems exhibit synchronous changes. Moreover, both the frequency and amplitude of the variations in these two monsoons are different before and after 5.5 cal. ka BP. The rate of changes in the solar insolation during the Holocene matches well with these monsoon records, implying that the mid-Holocene climate transition may have resulted from orbital forcing. [ABSTRACT FROM PUBLISHER]

Fossil pollen from Nam Co and modern pollen from altitudinal vegetation belts around the lake are investigated to reveal alpine vegetation succession in response to climate changes during the Holocene in the central Tibetan Plateau. The discriminant analysis on 37 topsoil samples shows that pollen samples from alpine steppe at lower elevations (<4800 m) and alpine meadow on upper slopes (4800–5200 m) can be distinguished by their pollen assemblages. Samples from alpine steppe contain more Artemisia (25.1%) and Poaceae pollen (11.5%), whereas those from alpine meadow are dominated by Cyperaceae pollen (>60%). Our result indicates that the pollen ratio of Artemisia to Cyperaceae (A/Cy) can be used as an indicator of the vertical shift of vegetation belts and temperature changes in the central Tibetan Plateau as suggested by previous studies. A history of the vertical shift of vegetation belts on the northern slope of Nyainqentanglha Mountains and climate changes since 8.4 kyr BP are thus recovered by 198 fossil pollen assemblages from a 332 cm core of Nam Co. Paleovegetation reconstructed from fossil pollen assemblages through discriminant analysis shows a general downward shift of altitudinal vegetation belts, suggesting a decline in the temperature trend since 8.4 kyr BP. This result is consistent with the reduction of A/Cy ratios. The fossil pollen record also reveals warm and wet climate during the early to mid Holocene, and cold and dry conditions during the late Holocene in the Nam Co area. A comparison of Holocene climatic reconstructions across the Plateau indicates that termination of maximum moisture at around 6–5.5 kyr BP in our record is associated with the southeastward retreat of the Southwest Monsoon. [ABSTRACT FROM AUTHOR]

We analyzed spatial and temporal growth variations of Qilian Junipers over the northeastern Tibetan Plateau (TP) during the period 1450—2001 by applying the empirical orthogonal function (EOF) technique to seven moisture-sensitive tree ring-width chronologies. The first three principal components together explain 78.21% of the total variance. The first principal component (PC1) accounts for 51.58% of the total variance, and represents consistent tree-growth variations in the northeastern TP. The second EOF mode reveals an opposite structure for the southern and northern parts of the northeastern Tibetan Plateau, reflecting the effect of huge topography and associated atmospheric circulation on tree-growth anomalies. The third EOF mode represents an opposite structure for the eastern and western parts of the northeastern Tibetan Plateau, possibly indicating the influence of different branches of atmospheric circulation system in this area. The EOF analysis results of instrumental precipitation data resemble those derived from the seven regional chronologies, providing further support that tree growth is a good indicator of regional precipitation variations. According to the PC1, dry conditions occurred in AD 1450—1510, 1631—1739, 1765—1833, 1866—1883 and 1921—1947, whereas periods of relatively wet years are identified for AD 1511—1630, 1740—1764, 1834—1865, 1884—1920 and 1948—2001. During the past 550 years, 28 years with extreme regional growth depressions was identified. These ring-width extremes generally occurred in century-scale dry periods. The years 1467, 1484, 1641, 1721, and 1928 with extreme tree-growth reductions in the northeastern TP are coeval with severe drought events in eastern China. In addition, the dry intervals or extreme growth depressions generally coincided with cold periods in the northeastern TP and vice versa, implying that the probability of occurrence of wet events in the northeastern TP will be higher in the future under the ongoing global warming. [ABSTRACT FROM AUTHOR]

Information on changes in land-surface features on the Tibetan Plateau (TP) during the Holocene may help our understanding of the forcing of monsoonal circulation. We analyse vegetation changes during the last 9000 years from pollen records of four lakes (Hurleg Lake in the Qaidam Basin; Qinghai Lake on the northeastern TP; Zigetang Lake on the central TP and Koucha Lake on the eastern TP) which represent different regions and vegetation types on the Plateau today. A set of modern pollen assemblages from 111 lake sediment samples originating from different vegetation types is used for the interpretation of the Holocene pollen records. Four types of numerical analyses are used to infer different aspects of pollen-stratigraphical and inferred vegetation changes: biome reconstruction; ordination (to infer palynological compositional turnover); rate-ofassemblage- change analysis, and a pollen-LAI (leaf area index) transfer function. Our results show strong regional differences in inferred vegetation change in terms of timing, strength and the nature of change. The greatest changes in compositional turnover and LAI are found in the Qinghai Lake record, indicating that forests were replaced by steppe vegetation in a step-wise fashion since the mid Holocene. Alpine steppe vegetation on the central and eastern TP was relatively stable throughout the Holocene, only showing a gradual replacement of temperate steppe by high-alpine meadows. The Qaidam Basin was dominated by temperate desert throughout the Holocene. The documented palynological and inferred vegetation changes can be most parsimoniously explained by climate change, although human impacts cannot be excluded as a contributing factor. Comparison of our findings with sensitivity analyses of numerical climate simulations suggests that longterm vegetation change may have had only a weak influence on regional climate change on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]