A continuous 7.44 m lake core was successfully drilled at Gun Nuur Lake, northern Mongolia, and analyses on environment magnetic parameters, organic matter content and organic δ13C were conducted in an attempt to retrieve the Holocene chronosequence of climatic changes based on 6 AMS 14C dates. We found that the Holocene climate in northern Mongolia has been alternating between cold (or cool)/wet conditions and warm/arid conditions, and also punctuated with a series of abrupt climate shifts. The abrupt climate shifts occurred around 1750, 2800, 4000, 5200, 7200, and 9200 aBP (14C age), being chronologically correlative to those abrupt climatic events recorded in the highlatitude North Atlantic Ocean. The correlation indicates that the climatic changes in northern Mongolia were linked with those in the North Atlantic Ocean probably via the North Atlantic Oscillation-affected westerly winds. The strength and position of westerly winds might have modulated the Siberian-Mongolian high pressure system (winter monsoon), directly influencing the climate in China.

This study deals with desertification and its impacts on environment in the source region of the Yellow River. Our objectives were to reveal and quantify desertifcation changes from 1990-2000 by remote sensing and GIS, and discuss its impacts on carbon cycle. The results indicate that the study area is one of the most desertified regions in northeast Qinghai-Tibetan Plateau. The study area is now a carbon source. The desertification would have contributed to CO2 emission from grasslands of Qinghai-Tibetan Plateau. Otherwise, there are great potential to resequestration carbon through controlling grazing, restoring ecosystem, and reducing desertification.

This study focuses on the Khyaraany sand/loess/soil section (50.23N 106.73E) in the Northern Mongolian Plateau with the aim of deciphering the paleoenvironmental records and inferring the last glacial Gobi dynamics. The main "ndings are as follows: (1) silt percentage (with a negligible clay percentage) is positively correlated with the organic matter content. (2) The silt (%) and frequency-dependent magnetic susceptibility (%) are negatively correlated. (3) The magnetic susceptibility is positively related to sand percentage and negatively to silt percentage. Based on C dates and the extrapolated ages, the following observations can be made. (1) Unlike the Marine Isotope Stage (MIS) 3 paleosols (24,500, 28,900, 30,700, 34,400 yr BP) that formed under oxidizing-dominated conditions, two MIS 2 paleosols (15,090, 13,030 yr BP) and two Holocene paleosols (8300, 4070 yr BP) were formed under dominantly reducing conditions. (2) Less windy and/or better vegetation conditions generally dominated the later part of the last glacial (15,090-8300 yr BP), during which three paleosols (incipient histosols) were formed (15,090, 13,030, 8300 yr BP). (3) Windy and/or poor-vegetation conditions generally dominated the early part of the last glacial (&24,000-16,000 yr BP). (4) This section documents approximately thousand-year-long redox cycles. Two tentative conclusions can be drawn from this and previous (Feng et al., 1998) studies. (1) The northern boundary of the Gobi has shrunk as many as nine times during the past 40,000 yr: around 34,400, 30,700, 28,900, 24,500, 15,090, 13,030, 8300, 4070 yrBP and the recent 2000+yr. (2) Based on the negative correlation of the susceptibility with silt percentage and organic matter content, it is proposed that the reducing conditions of incipient histosol formations have contributed to the alteration of magnetic minerals from strong forms of oxidized iron to weak forms. Therefore, the magnetic susceptibility is basically an indicator of redox cycles.

Understanding potential evapotranspiration (PET) is essential in planning economic uses of water resource and in assessing the potential ecological conditions for ecological restoration. In the semi-arid western Chinese Loess Plateau. This work tested three models commonly used to estimate monthly PET rate (i.e. Behnk-Maxey, Prestley-Taylor and Hargreaves). The major purposes are: (1) to determine the model used to calculate PET with small data requirements and high accuracy in the Zuli River Basin; and (2) to calculate the areal distribution of potential evapo-transpiration in the study area. From the approach, conclusion can be drawn that Hargreaves model may be the best way to estimate PET in the semi-arid area of the Loess Plateau with sparsity of weather stations. The general methods described here are expected to be applicable to the entire Loess Plateau.

This study focuses on a Barton County loess-soil section in central Kansas in an attempt to retrieve the geochemical signature of the late Quaternary environmental change in the arid-semiarid region and provide a data base of loess geochemical characteristics in the Great Plains. The data indicate that the elements (expressed as oxides) of the windborne fraction (<63 mm) that are easily solubilized and lost from the soil by chemical weathering and leaching are relatively sensitive to soil-forming processes, whereas the insoluble elements of that fraction are controlled primarily by the chemical composition of the parent material. The geochemical imprint of pedogenesis superimposed on that of the loess parent material can be distinguished by comparing the magnetic susceptibility signature with the Fe2O3/Al2O3 ratio. Based on the geochemical imprint and radiometric dates (14C and thermoluminescence), the Bignell Loess (8000-5000 yr) is poorly weathered and the Brady Soil (10 000-8000 yr) is strongly weathered. The Peoria Loess (20 000-10 000 yr) has neither a traceable leaching nor weathering marker, and the Gilman Canyon pedocomplex (35 000- 20 000 yr) is strongly leached. The reddish pedocomplex (70 000- 35 000 yr) is the most strongly weathered, probably due to stable land surface conditions in a mild climate, and the Barton sand (92 000-70 000 yr) seems to have been subjected to a moderate weathering. Within the exposed portion of the Loveland Loess (260 000-92 000 yr), weathering indices are inversely correlated with the carbonate content and the carbonate-rich soils were developed under warm dry environments before 92 000, around 193 000, and before 260 000 yr. The data also show that the geochemical background of Fe2O3, and Al2O3 is high in two portions of the section: from the Brady Soil to the Gilman Canyon pedocomplex and from LL1 to LL2 within the Loveland Loess. The geochemical background of Fe2O3 and AI2O3 in the loess-soil sequence might have been dictated by that of eolian sources.