Environments in arid and semiarid regions are extremely sensitive to climate changes. High wind activity in these regions has resulted in an extensively developed arid geomorphology, but past environmental changes are...Environments in arid and semiarid regions are extremely sensitive to climate changes. High wind activity in these regions has resulted in an extensively developed arid geomorphology, but past environmental changes are poorly understood because of the absence of relatively high-resolution proxies. The accumulation characteristics of nebkhas, which have developed extensively in these regions, can be used as a method of reconstructing environmental changes. Here we summarized recent advances in research on the formation, development, and sediment characteristics of nebkhas and their significance to environmental changes in arid and semiarid regions. Based on the studies of our colleagues, we suggested that research on nebkha formation can provide distinct clues about environmental changes in arid and semiarid regions; however, continued studies are needed.展开更多
Sandy desertification is land degradation characterized by wind erosionmainly resulted from the excessive human activities in arid, semiarid and part of sub-humid regionsin northern China, The research on sandy desert...Sandy desertification is land degradation characterized by wind erosionmainly resulted from the excessive human activities in arid, semiarid and part of sub-humid regionsin northern China, The research on sandy desertification has experienced more than 5 decades ofarduous course of the struggle along with the establishment and development of China's desertscience. Researches in this field have made a great contribution to the national economicconstruction, and environmental protection. This paper focuses on presenting the major progress andachievements in the sandy desertification research during the last 50 years, including the stages ofstudy on sandy desertification, background environment of sandy desertification and its changes,the conception, causes, process, monitoring and assessment of sandy desertification, the vegetationsuccession, landscape ecology, plant physiology, impacts on ecosystem, high-effective use of waterand land resources and sustainable development in sandy desertified regions, sandy desertificationcontrol models and techniques etc.展开更多
The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorpholog...The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorphologic and lithological evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates strong lake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summer monsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levels in the mid-Holocene around 5000—7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the present Asian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south Inner Mongolian Plateau. The period was also probably colder, at least in the high Asian plateaus and mountains.展开更多
Research on the geological data of Hunshan-dake Desert in China monsoon region revealed that Holocene summer monsoon had experienced six prevailing periods and seven weakening periods. The climatic humidity and the ve...Research on the geological data of Hunshan-dake Desert in China monsoon region revealed that Holocene summer monsoon had experienced six prevailing periods and seven weakening periods. The climatic humidity and the vegetation had also undergone the similar periodical varia-tion influenced by the monsoon periodicity. The period when summer monsoon prevailed or winter monsoon weakened and climatic humidity and vegetation coverage relatively increased, corresponded to the global warming events; whereas the period when summer monsoon weakened or winter monsoon prevailed and climatic humidity and vegeta-tion coverage relatively decreased, corresponded to the arid events in middle to low latitudes and the cold events in North Atlantic. As for the changing regularity of summer monsoon intensity there were two distinct periodicities of 1456 years and 494 years, also these two periodicities had global signifi-cance.展开更多
Regional decadal precipitation reconstructions for the arid and semi-arid zones of northern China were established by the use of different palaeoclimate archives such as ice-cores, tree-rings, lake sediments and writt...Regional decadal precipitation reconstructions for the arid and semi-arid zones of northern China were established by the use of different palaeoclimate archives such as ice-cores, tree-rings, lake sediments and written his-torical documents. Local rainfall reconstructions from single sites were averaged to obtain regional precipitation records for western and eastern regions of an arid and semiarid zone of northern China, respectively. All established regional pre-cipitation curves display 5 dry periods, each lasting about 50 years. Meanwhile, precipitation reconstructions show re-gional dissimilarities. During the last 500 years, the trends of precipitation change in the eastern arid region are basically consistent with those in the western and eastern regions of the semiarid zone. Precipitation variations in the western arid region are unique, showing significant local patterns of rainfall variability. Maximum entropy method (MEM) spec-tral estimates show that each regional precipitation series contains stationary century-scale periodicities of about 120 a. Singular spectrum analysis was applied to isolating the cen-tury-scale oscillation signals from the regional proxy pre-cipitation series. Significant periods with wavelengths of 121.4a, 154.6a, 124.3a, 118.6a, 108.5a and 121.4a were found 26.56%, 26.44%, 28.87%, 18.67%, 33.48% and 34.04% of the variances of the original series for the western arid zone, the eastern arid zone, the whole arid zone, the western semi-arid zone, the eastern semiarid zone and whole northern China, respectively.展开更多
In order to assess the contribution of the pollen transported by wind and fluvial flows to the pollen spectra in Shiyang River drainage, a typical small endorheic drainage in arid lands of northwest China, preliminary...In order to assess the contribution of the pollen transported by wind and fluvial flows to the pollen spectra in Shiyang River drainage, a typical small endorheic drainage in arid lands of northwest China, preliminary studies on modern pollen rain along two transects with 91 surface soil samples, 8 atmospheric samples, 30 modern fluvial flow samples and 50 riverbed mud samples, were carried out. Results show that dispersal agents (air, flowing water) have dissimilar effects on transport of pollen and the structure of pollen spectra. Fluvial flow has a stronger capacity than wind to transport large quantities of pollen over long distances. Pollen transported by fluvial flow makes a large contribution to the pollen spectra of riverbed alluvial sediments. Paleoenvironmental reconstructions undertaken using pollen spectra from fluvial sediments in arid lands are strongly influenced by pollen transport. Therefore, the sources, the transportation agents and the depositional condition of pollen should be systematically investigated before pollen assemblages are used to derive the environmental significance in such settings.展开更多
A set of environmental magnetic parameters(i.e. magnetic susceptibility, xARM, IRMs, hysteresis loops and thermomagnetic curves) has been applied to two soil sections from SE Iceland. Results demonstrate that the main...A set of environmental magnetic parameters(i.e. magnetic susceptibility, xARM, IRMs, hysteresis loops and thermomagnetic curves) has been applied to two soil sections from SE Iceland. Results demonstrate that the main magnetic minerals in the tephras are ferrimagnetic minerals (e.g.magnetite) and canted antiferromagnetic minerals (e.g.haematite), with abundant paramagnetic material also present. Cross plots of Mrs/Ms vs. (B0)cr/(B0)c and xfd% vs.xARM/SIRM indicate that the main magnetic grain sizes in tephras are pseudo single domain (PSD) and multidomain(MD). Initial correlation of tephra layers was achieved, usingall the measured magnetic parameters, by use of the multi-variate statistical measures of Similarity Coefficient (SC) andEuclidean Distance (ED). This demonstrates that magnetictechniques can potentially assist in the identification andcorrelation of distal tephra.展开更多
基金National Natural Science Foundation of China, No.41071008
文摘Environments in arid and semiarid regions are extremely sensitive to climate changes. High wind activity in these regions has resulted in an extensively developed arid geomorphology, but past environmental changes are poorly understood because of the absence of relatively high-resolution proxies. The accumulation characteristics of nebkhas, which have developed extensively in these regions, can be used as a method of reconstructing environmental changes. Here we summarized recent advances in research on the formation, development, and sediment characteristics of nebkhas and their significance to environmental changes in arid and semiarid regions. Based on the studies of our colleagues, we suggested that research on nebkha formation can provide distinct clues about environmental changes in arid and semiarid regions; however, continued studies are needed.
文摘Sandy desertification is land degradation characterized by wind erosionmainly resulted from the excessive human activities in arid, semiarid and part of sub-humid regionsin northern China, The research on sandy desertification has experienced more than 5 decades ofarduous course of the struggle along with the establishment and development of China's desertscience. Researches in this field have made a great contribution to the national economicconstruction, and environmental protection. This paper focuses on presenting the major progress andachievements in the sandy desertification research during the last 50 years, including the stages ofstudy on sandy desertification, background environment of sandy desertification and its changes,the conception, causes, process, monitoring and assessment of sandy desertification, the vegetationsuccession, landscape ecology, plant physiology, impacts on ecosystem, high-effective use of waterand land resources and sustainable development in sandy desertified regions, sandy desertificationcontrol models and techniques etc.
基金supported by the National Natural Science Foundation of China(Grant No.40125001)the Hundred Talent Project of CAS and the International Collaboration Project(Grant No.2002CB714004).
文摘The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorphologic and lithological evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates strong lake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summer monsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levels in the mid-Holocene around 5000—7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the present Asian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south Inner Mongolian Plateau. The period was also probably colder, at least in the high Asian plateaus and mountains.
文摘Research on the geological data of Hunshan-dake Desert in China monsoon region revealed that Holocene summer monsoon had experienced six prevailing periods and seven weakening periods. The climatic humidity and the vegetation had also undergone the similar periodical varia-tion influenced by the monsoon periodicity. The period when summer monsoon prevailed or winter monsoon weakened and climatic humidity and vegetation coverage relatively increased, corresponded to the global warming events; whereas the period when summer monsoon weakened or winter monsoon prevailed and climatic humidity and vegeta-tion coverage relatively decreased, corresponded to the arid events in middle to low latitudes and the cold events in North Atlantic. As for the changing regularity of summer monsoon intensity there were two distinct periodicities of 1456 years and 494 years, also these two periodicities had global signifi-cance.
文摘Regional decadal precipitation reconstructions for the arid and semi-arid zones of northern China were established by the use of different palaeoclimate archives such as ice-cores, tree-rings, lake sediments and written his-torical documents. Local rainfall reconstructions from single sites were averaged to obtain regional precipitation records for western and eastern regions of an arid and semiarid zone of northern China, respectively. All established regional pre-cipitation curves display 5 dry periods, each lasting about 50 years. Meanwhile, precipitation reconstructions show re-gional dissimilarities. During the last 500 years, the trends of precipitation change in the eastern arid region are basically consistent with those in the western and eastern regions of the semiarid zone. Precipitation variations in the western arid region are unique, showing significant local patterns of rainfall variability. Maximum entropy method (MEM) spec-tral estimates show that each regional precipitation series contains stationary century-scale periodicities of about 120 a. Singular spectrum analysis was applied to isolating the cen-tury-scale oscillation signals from the regional proxy pre-cipitation series. Significant periods with wavelengths of 121.4a, 154.6a, 124.3a, 118.6a, 108.5a and 121.4a were found 26.56%, 26.44%, 28.87%, 18.67%, 33.48% and 34.04% of the variances of the original series for the western arid zone, the eastern arid zone, the whole arid zone, the western semi-arid zone, the eastern semiarid zone and whole northern China, respectively.
基金supported by the National Natural Science Foundation of China(Grant No.40271116)the International Cooperation Project(Grant No.2002CB714004).
文摘In order to assess the contribution of the pollen transported by wind and fluvial flows to the pollen spectra in Shiyang River drainage, a typical small endorheic drainage in arid lands of northwest China, preliminary studies on modern pollen rain along two transects with 91 surface soil samples, 8 atmospheric samples, 30 modern fluvial flow samples and 50 riverbed mud samples, were carried out. Results show that dispersal agents (air, flowing water) have dissimilar effects on transport of pollen and the structure of pollen spectra. Fluvial flow has a stronger capacity than wind to transport large quantities of pollen over long distances. Pollen transported by fluvial flow makes a large contribution to the pollen spectra of riverbed alluvial sediments. Paleoenvironmental reconstructions undertaken using pollen spectra from fluvial sediments in arid lands are strongly influenced by pollen transport. Therefore, the sources, the transportation agents and the depositional condition of pollen should be systematically investigated before pollen assemblages are used to derive the environmental significance in such settings.
文摘A set of environmental magnetic parameters(i.e. magnetic susceptibility, xARM, IRMs, hysteresis loops and thermomagnetic curves) has been applied to two soil sections from SE Iceland. Results demonstrate that the main magnetic minerals in the tephras are ferrimagnetic minerals (e.g.magnetite) and canted antiferromagnetic minerals (e.g.haematite), with abundant paramagnetic material also present. Cross plots of Mrs/Ms vs. (B0)cr/(B0)c and xfd% vs.xARM/SIRM indicate that the main magnetic grain sizes in tephras are pseudo single domain (PSD) and multidomain(MD). Initial correlation of tephra layers was achieved, usingall the measured magnetic parameters, by use of the multi-variate statistical measures of Similarity Coefficient (SC) andEuclidean Distance (ED). This demonstrates that magnetictechniques can potentially assist in the identification andcorrelation of distal tephra.
基金the National Natural Science Foundation of China(NSFC)(China)NSF(USA)+3 种基金DFG(Germany)NERC/British Council(UK)the NSFC(Grant No.40125001)for providing most of the Chinese research fundingthe Sino-German Centre for Science Promotion for its support of the RACHAD 2001 symposium.
