Chen Fahu

Loess stratigraphy of the Lanzhou profile and its comparison with deep-sea sediment and ice core record

After summarizing the results of Quaternary climatic fluctuations in China, authors describe the significance of the Lanzhou loess and paleosol sequence in Quaternary studies. In the Lanzhou area the loess sequence attains 400 m thickness, inwhich five stratigraphic units are identified with at least 21 intercalated paleosols, TL, paleomagnetic and fission track dating techniques have been applied to determine the age of the loess horizons. Correlations are made with the terrace of the Yellow River and oxygen isotope curves of the Pacific deep-sea cores V28-238 and V28-239 and the Vostok ice core isotope curves. The comparative study proves that the Lanzhou loess is a very sensitive recorder of climatic fluctuation.

Pedosedimentary development and palaeoenvironmental significance of the S1 palaeosol on the northeastern margin of the Qinghai-Xizang (Tibetan) Plateau

The S1 pedocomplex, correlated to Oxygen Isotope Stage 5 of the ocean cores, has been traced west of the Loess Plateau on to the extreme northeastern margin of the Qinghai-Xizang (Tibetan) Plateau in China. Detailed micromorphological analysis of closely spaced thinsections from the pedocomplex at this site provides the basis for reconstruction of the sequence of pedosedimentary processes and associated palaeoenvironmental changes occurring during this time interval. The six pedosedimentary stages identified are interpreted in terms of temporal variations in depositional rates, size of particles transported and availability of moisture for pedogenic alteration, as determined by changing balances in dominance of winter and summer monsoonal forces. Two main ‘soil-forming intervals’ are identified: the more extensive of the two in terms of resultant pedological features reflects pedogenic alteration at a relatively ‘stable’ land surface under a semi-arid climate during the later part of pedosedimentary stage 2. The other main period corresponds to pedosedimentary stages 4 and 5, when leaching and bioturbation processes were active at aggrading surfaces, leading to development of an accretionary unit without clear differentiation of horizons. Pedosedimentary stages 1, 3 and 6 were characterised mainly by rapid rates of coarse loess accumulation, with synsedimentary modification restricted to surface slaking and crust formation, and minor localised redistribution of calcite.

The discovery of annually laminated sediments (varves) from shallow Sugan Lake in inland arid China and their paleoclimatic significance

Detailed examination of sedimentary cores retrieved from Sugan Lake in the northern Qaidam Basin of northwest China’s Tibetan Plateau reveal that fine laminated beddings form in the sediments where water depth exceeds 3 m. Seasonal surface sediments trapped at the bottom of the lake suggest that sediments deposited during summer and autumn are mainly light colored monohydrocalcites, while those deposited in winter are dark organic matter, indicating that varve layers form under modern limnological conditions. Continuous varve sediments comprising four types have accumulated in the upper 5.5 m of Core SG03I from the center of the lake. All types exhibit clear seasonality indicative of annual deposition. Varve counts correspondence with 210Pb dates on recent sediments in the upper core suggest the continuous varves of the upper 5.5 m of the core formed in the late Holocene (2670 a BP). The Sugan Lake varve sequence is the first demonstration of annually laminated sediments reported in arid western China.

Study on modern plant C-13 in western China and its significance

Organic carbon isotopic composition (δ13C ) is one of the important proxies in paleoenvironment studies. In this paper modern plant δ13C in the arid areas of China and Tibetan Plateau is studied. It is found that most terrestrial plant species in western China are C3 plants with δ13C values ranging from -32.6‰ to -23.2‰ and only few species are C4 plants with δ13C values from -16. 8‰ to -13.3‰ The δ13C is closely related to precipitation (or humidity), i. e., light δ13C is related to high precipitation (or humid climate), while heavy δ13C to low precipitation (or dry climate), but there is almost no relation between plant δ13C and temperature. Submerged plants have δ13C values ranging from -22.0‰ to -12.7‰, like C4 plants, while merged plants have δ13C values ranging from -28. 1‰ to -24. 5‰, like C3 plants. It can then be concluded that organic δ13C variations in terrestrial sediments such as loess and soil in western China can indicate precipitation changes, but those in lake sediments can reflect organic sources and the productivity of different types of aquatic plants.

Agricultural intensification and its impacton environment during Neolithic Age in northern China

The nature of an Anthropocene has been increasingly discussed and debated in the last two decades, with a focus on the arguments for or against the “Anthropocene” as a geological epoch. Some argue for an onset of Anthropocene between 1945‒1964 AD, when intensive atmospheric nuclear testing resulted in peak values of 14C that is widely recorded in tree rings and sediments, while other scholars argued its beginning may be traced back to the early Holocene. This latter argument is related to the beginnings of significant landscape modification through the development and spread of agricultural practices in old world since 10000 a BP. The Yellow River valley of northern China is the center for the domestication of millet crops (broomcorn millet and foxtail millet), however, the intensification and expansion of millet-based agriculture during the Neolithic period and its impact on the environment has not been well understood. Recent development of archaeometry methods and their application to archaeological research, such as archaeobotanical studies, and carbon and nitrogen isotope analysis of human and animal bones unearthed from Neolithic and Bronze sites in north China, has greatly deepened our understanding of the timing of millet-based agriculture and its development. In parallel, the analysis of paleoenvironment proxies including black carbon and pollen assemblages from natural sediments, has shed light on the impact of human slash-and-burn cultivation on their surrounding environments during both prehistoric and historical times. This paper reviews carbon isotope analysis of human, pig and dog bones, and radiocarbon dates from Neolithic sites, and compares them with black carbon content from palaeoenvironment records in northern China, in order to explore the temporal-spatial intensification and expansion of millet-based agriculture in the area and its possible impact on environment. It can be concluded that millet cultivation was an auxiliary subsistence strategy in northern China from 10000 to 7000 a BP with hunting-gathering the primary subsistence strategy, the earliest millet-cultivation might have emerged in eastern Inner Mongolia post 7700 a BP. Millet cultivation transited from a secondary strategy to become dominant in the Guanzhong area of north-central China during 7000‒6000 a BP, and probably facilitated the development of early Yangshao culture in the middle reaches of the Yellow River valley. Intensive millet-based agriculture emerged and widely expanded across the Yellow River valley in northern China during 6000‒4000 a BP. This promoted rapid population growth and cultural evolution in the late Neolithic period, and was key in the subsequent emergence of the ancient Chinese civilization. The temporal-spatial variation of black carbon (EC-soot) corresponds well with the intensification and expansion of millet-based agriculture during Neolithic period. The content of EC-soot increased in sediments of Daihai lake and the Horqin sandy lands in Inner Mongolia from about 7500 a BP soon after farming of millet appeared in Xinglongwa and Xinglonggou sites nearby, which evidently increased in Shaanxi Province of north central China post 6000 a BP, when intensive millet-based agriculture firstly emerged in the area. This suggests millet agriculture production activities exerted significant impact on fire frequency in northern China during the Neolithic, and thus the scale and intensity of the impact of farming increased from that period. This work provides a valuable case study for understanding the temporal and spatial development of millet agriculture, and human-environment interactions in northern China during Neolithic period from an Anthropocene perspective.

Magnetic characteristics of dustfall in urban area of north China and its environmental significance

Urban particulate pollutants not only affect urban air quality but also directly threaten public health. Lanzhou has been one of the most seriously polluted cities in the world due to its special geophysical location and weather conditions, which makes it an ideal place for urban particulate pollution study. In this study a set of environmental magnetic parameters (χlf, χfd%, χARM, SIRM, HIRM, SOFT and back field IRM) were measured and analyzed for the dustfall samples collected monthly during 1997.4–2000.5 and 2004.11–2005.10 at Lanzhou University campus (KLD and CCS) and at a clear site of Gaolanxian (GLX). Results demonstrate that the main magnetic minerals in the dustfall are magnetite, with some maghaemite and haematite. Cross plots of Mrs/Ms vs. Bcr/Bc and χfd% vs. χARM/SIRM indicate that the main magnetic grain sizes are pseudo-single-domain (PSD). The high concentration of magnetic minerals in the dustfall indicates that Lanzhou is seriously polluted. The main pollution sources are anthropogenic activities and nature dust, with the former posing a great threat during the whole year, which is different from the general view that the natural dust is the main contributor in summer. With great efforts of the government and local authority in the past decades, the air quality in Lanzhou has been improved in winter, but it is not so obvious in summer. This study also reveals that as a simple, rapid and accurate technology, environmental magnetism could be a valuable tool for urban pollution study.

A Possible Impact of Cooling over the Tibetan Plateau on the Mid-Holocene East Asian Monsoon Climate

By using a 9-level global atmospheric general circulation model developed at the Institute of Atmospheric Physics (IAP9L-AGCM) under the Chinese Academy of Sciences, the authors investigated the response of the East Asian monsoon climate to changes both in orbital forcing and the snow and glaciers over the Tibetan Plateau at the mid-Holocene, about 600 calendar years before the present (6 kyr BP). With the Earth’s orbital parameters appropriate for the mid-Holocene, the IAP9L-AGCM computed warmer and wetter conditions in boreal summer than for the present day. Under the precondition of continental snow and glacier cover existing over part of the Tibetan Plateau at the mid-Holocene, the authors examined the regional climate response to the Tibetan Plateau cooling. The simulations indicated that climate changes in South Asia and parts of central Asia as well as in East Asia are sensitive to the Tibetan Plateau cooling at the mid-Holocene, showing a significant decrease in precipitation in northern India, northern China and southern Mongolia and an increase in Southeast Asia during boreal summer. The latter seems to correspond to the weakening, southeastward shift of the Asian summer monsoon system resulting from reduced heat contrast between the Eurasian continent and the Pacific and Indian Oceans when a cooling over the Tibetan Plateau was imposed. The simulation results suggest that the snow and glacier environment over the Tibetan Plateau is an important factor for mid-Holocene climate change in the areas highly influenced by the Asian monsoon.

Environmental and technological effects on ancient social evolution at different spatial scales

The rise and fall of ancient cultures and civilizations is a hotly debated topic that has generated disagreements and disputes. In this paper we summarize some case studies on the abandonment of ancient sites, the prosperity and collapse of ancient cultures, and demographic changes, as well as the influence of environment and technology during the prehistoric and historic periods. We then suggest that the dominant influencing factors for the evolution of ancient societies vary by spatial scale. At the local scale, sudden disasters are critical factors leading to the destruction and abandonment of large settlements. On a regional scale, climatic variations (e.g., droughts or cold events lasting for decades or centuries) are important factors that induce the collapse of ancient civilizations and mass migrations, while an enduring and stable optimal climate facilitated the prosperity of ancient civilizations. On a global scale, major technological innovations and their dispersion lasting for centuries and even millennia are major catalysts for population growth and social development. Lastly, we illustrate a possible mechanism under which environmental and technological factors played a critical role in ancient human survival and social evolution on different spatial scales.

Climate changes in China since the Last Glacial Maximum and Holocene human adaptation

Based on various geological records of high-resolutions, this project aims at addressing the climate and environmental histories in China since the Last Glacial Maximum (LGM) and human impacts on the Holocene environmental changes. Significant progresses have been obtained with regards to the impacts of past temperature changes to Asian monsoon and to the arid/semi-arid ecosystems in China. The results also suggest that changes in the concentrations of greenhouse gases in the pre-industrial era were mainly attributable to natural driven forces although early agriculture had significantly affected the landscapes.

The pattern of Holocene climate change in the arid central Asia: a case study based on lakes

The palaeoclimate records from lakes at the arid central Asian region (ACA) climatically dominated by the Westerly circulation shows synchronous and coherent moisture changes during the Holocene. Therefore, the sediment records from lakes in ACA with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five-class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200-year time slices. There are 8 lakes suitable for the synthesis. The results show that ACA as a whole experienced a dry early Holocene, a wetter (less dry) early to mid-Holocene, and a moderately wet late Holocene, which is different from Holocene monsoon history recently recovered by documents such as speleothem. We propose that the pattern of Holocene effective-moisture evolution in the westerly dominated ACA was mainly determined by North Atlantic sea-surface temperatures (SSTs) and high-latitude air temperatures that affect the availability, amount and transport of water vapor.