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Based on compilation of a large number of archaeological and palaeosol 14C-ages, the Summed Probability Method is used to reconstruct population history and climatic patterns on the Chinese Loess Plateau during the period 8.5–3.5 cal. ka BP. During this period, the population experienced two major expansion periods and several climatic fluctuations. The first population expansion began at around 7.8 cal. ka BP, and the second at around 5.8 cal. ka BP. During the first period, although already in combination with cultivation of broomcorn millet the population growth was supported mainly by hunting and gathering. With the switch from broomcorn millet to foxtail millet, plant cultivation became the major factor promoting a second population increase. In this paper, we demonstrate that, initially, suitable climate and agriculture both can facilitate population growth and climate events had a significant influence on demographic fluctuations. However, when reaching the threshold of land capacity, population became increasingly more sensitive towards climate fluctuations. [ABSTRACT FROM AUTHOR]

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]

High-resolution macroscopic charcoal and sediment analysis was used to reconstruct fire history and environmental changes from three loess-paleosol profiles on the semi-arid loess tableland landscape during the Lateglacial period and the Holocene. Analysis of charcoal concentrations, influx, and the ratios of particle-size classes (from which changes in charcoal taphonomy over time are inferred) in the profiles show spatially coherent patterns of change that relate to regional variations in climate. Effective moisture variability on century to millennial timescales and regional differences in fuel availability appear to be the most important controls on fire from the Lateglacial period to the mid Holocene (12,000–3100 yr BP). Conversely, asynchronous fire patterns during the late Holocene appear to indicate regional and temporal variations as well as changing intensities of human activity. Land use intensified in the region during the late Holocene, when the climate became more arid, and a distinct increase in charcoal concentration then indicated an unprecedented increase in biomass burning. The increase in fire activity occurs in the recent loess layer (L0) and the surface soil (TS) consistent with the establishment of irrigated farming for cereal cultivation in the southern part of the study region about 3100 yr BP. Broad-scale land reclamation was extended to the loess tableland region about 2170–1730 yr BP (during the Qin-Han Dynasty period), and the rapidly decreasing charcoal concentration in the accumulated topsoil (at depths of less than 20 cm) at the CCY site since 1500 yr BP is consistent with the development of terrace farming in the northern part of the study region at that time. In summary, the evolution of fire history in the study profiles across the region is closely related to (1) gradients in humidity; (2) spatial and temporal variability in the distribution and intensity of human land use; and (3) the buildup of burnable biomass, among which there was a nonlinear complex relationship during the Holocene. Increased efforts to synthesize and analyze multiple paleo-environmental records and to combine these with multiproxy evidence are needed to understand wildfire history as well as human land use and social cultural development across the region in depth. [ABSTRACT FROM PUBLISHER]

Sedimentary records of the Holocene extraordinary floods were investigated in the upper reaches of the Weihe River, a major tributary in the middle Yellow River basin. Palaeoflood slackwater deposits (SWD) were identified at several sites on the riverbanks. These clayey silt beds are inserted into the Holocene aeolian loess-soil profiles and slope clastic deposits. They have recorded the extraordinary palaeoflood events which occurred between 3200 and 3000 yr BP as dated by OSL method and checked by the archaeological remains of the Neolithic and Bronze Age retrieved from the profile. The minimum flood peak discharges were estimated at between 22 560 and 25 960 m3/s by using palaeohydrological methods. It is 4.5–5.0 times the largest gauged flood (5030 m3/s) that has ever occurred since 1934. The palaeoflood slackwater deposits were found inserted into the pedostratigraphic boundary between the late-Holocene loess (L0) and the mid-Holocene Luvisol (S0) in the riverbank profile. This indicates that the extraordinary flood events were synchronous with the pedogenic regression at the end of the mid-Holocene climatic optimum. The climatic proxies from the studied profile and the correlative profiles in the river valley and the Loess Plateau show that the pedogenic regression was forced by climatic aridity and intensified dust storms and dust falls in connection with monsoonal shift over the Yellow River basin at about 3100 yr BP. The extraordinary flood events were documented not only on the Weihe River, but also on the mainstream and other tributaries of the Yellow River. These suggest that both extraordinary floods and droughts were parts of the climatic variability during the monsoonal shift. These findings are of great importance in understanding the interactions between hydrological system and climatic change in the semi-arid and subhumid regions of the world. [ABSTRACT FROM AUTHOR]

Based on published pollen data from 44 sites in the Loess Plateau and surrounding areas, we recalculate values of Picea abundance digitized from the original diagrams and construct six isopoll maps to reconstruct the distribution of spruce forest at 2000 yr intervals during the Holocene. Spruce forest gradually expanded from about 10 ka BP ago and reached its peak distribution around 8 ka BP. It retained its maximum extent between 8 ka BP and 6 ka BP, broadly covering the subalpine area and stretching to the valleys of the western Loess Plateau with high densities and even reaching the edges of the adjacent desert regions. After 6 ka BP, spruce forest began to retreat to higher elevations. This trend was accelerated after 4 ka BP. After 2 ka BP, it disappeared completely from the Loess Plateau and most of its surrounding areas. Precipitation strongly dominated by the Asian summer monsoon was the primary controlling factor in the distribution of spruce before 2 ka BP. After about 2 ka BP, the increasing intensity of human activity became the primary factor in the disappearance of spruce in the Loess Plateau, resulting in an enormous impact on the present landscape. [ABSTRACT FROM AUTHOR]

Optical dating was used to obtain a chronology for a loess-palaeosol sequence in the Guanzhong Basin on the Loess Plateau in China. The sedimentary sequence recorded two dry episodes (3.7~2.4 ka and 1.2~0.8 ka ago) in the Holocene as shown by the presence of two layers of loess within the Holocene deposits. These two arid events are consistent with records of global climate change in the Holocene and also coincident with major historic events in China. This finding suggests that loess-paleosol sequences in China can record global climate changes and implies that rapid climate change affected the progress of human civilization. In addition, changes in the sedimentation rate through the section suggest that agricultural expansion may have accelerated the rate of dust accumulation. [ABSTRACT FROM AUTHOR]