Dunsheng Xia

Rapid oscillations of Chinese monsoon climate since the last deglaciation and its comparison with GISP2 record

The geographic extent of the climate oscillations during the last deglaciation is an open question in the world. Here a high resolution climate record from a 16 000 C-14 a loess sequence in the northwestern margin of the Chinese Loess Plateau is reported. Comparison with GISP2 record shows that all major climate oscillation (e. g. Oldest Dryas/ Boiling/ Older Dryas/ Allerod/ Younger Dryas) in the North Atlantic region also registered in the record. In addition, the sequence also contains some other distinctive strengthened winter monsoon periods. It is suggested that a coupling mechanism operate between the two areas, and climate oscillations in the North Atlantic region may not be a local phenomenon.

Detecting the sensitivity of magnetic response on different pollution sources--A case study from typical mining cities in northwestern China.

Rapid monitoring and discriminating different anthropogenic pollution is a key scientific issue. To detect the applicability and sensitivity of magnetic measurements for evaluating different industrial pollution in urban environment, characteristics of topsoil from three typical fast developing industrial cities (Jinchang, Baiyin and Jiayuguan in Gansu province, northwestern China) were studied by magnetic and geochemical analyses. The results showed that magnetic susceptibility was enhanced near industrial areas, and PSD-MD magnetite dominated the magnetic properties. Magnetic concentration parameters (χlf, SIRM, and χARM) showed different correlations with heavy metals and PLI in the three cities, indicating significantly different magnetic response to different pollution sources. Principal component analysis showed that ferrimagnetic minerals coexist with heavy metals of Fe, As, Cu, Pb, and Zn in Baiyin and Fe, V, Cu, Mn, Pb, and Cr in Jiayuguan. Fuzzy cluster analysis and regression analysis further indicated that the sensitivity of magnetic monitoring to fuel dust is higher than that to mineral dust near non-ferrous metal smelters, and fossil fuel consumption is an important factor for increasing magnetite content. In all the three cities, the sensitivity of magnetic monitoring to pollutants from steel plants is much higher than that from non-ferrous metal plants. Therefore, magnetic proxies provide a rapid means for detecting heavy metal contamination caused by multi-anthropogenic pollution sources in a large scale area, however, the sensitivity was controlled by pollution sources.

Source apportionment of soil-contamination in Baotou City (North China) based on a combined magnetic and geochemical approach

We studied the magnetic properties and trace element concentrations (Cr, Cu, Fe, Mn, Pb, Ti, V, Zn) of urban topsoils from 111 urban sites in a large REE-Nb-Fe mining and smelting city, Baotou, Inner Mongolia, China. The results show that pseudo-single domain and multi-domain magnetite dominates the magnetic properties of the soil samples, and the magnetic concentration parameters show a large positive anomaly near the Baotou iron and steel works. The average contents of all trace metals exceeded their background level in soils in Inner Mongolia, except for Pb. The spatial distribution and correlation analysis show that magnetic parameters related to the magnetite concentration and Cr, Fe, Mn, Ti, V and Zn show similar trends of variation. In addition, the results of PCA show that Fe, Ti, and V are highly correlated with the magnetic particles derived from the Baotou iron and steel works, tailing dam, chromium plant, and cement plant. In contrast, Cr, Mn, Pb and Zn are derived from both the steel plant and traffic pollution. Using a PMF model, three potential pollution sources are identified: industrial pollution, including the steel works, tailing dam, cement plant and chromium plant, are reflected by χlf, χARM, SIRM and SOFT, and they account for 71.2%; traffic pollution is reflected by Pb and Zn and accounts for 9.0%; and natural sources, reflected by χfd%, χARM/χ, χARM/SIRM, HARD%, S-300, S-100 and Ti, contribute 19.8%. The results are potentially useful for developing control measures for reducing trace metal contamination in soils in Baotou city, and in addition we conclude that a combined magnetic approach and geochemical approach is an effective means for qualitative and quantitative sources apportionment of urban surface soil pollution.

Variations in the Iron Mineralogy of a Loess Section in Tajikistan During the Mid‐Pleistocene and Late Pleistocene: Implications for the Climatic Evolution in Central Asia

The loess sequences in Tajikistan are an important archive of information about the development of climate and atmospheric circulation in central Asia during the Pleistocene. Here we present the results of an iron mineralogical study of a loess sequence in Tajikistan to reconstruct paleoclimate evolution during the mid-Pleistocene and late Pleistocene. The record indicates that interglacial intervals were relatively humid and glacials were dry. We propose a shift in the character of the interglacial climate of the region to more humid after beginning of MIS 9; however, temperature was relatively stable. The location and intensity of Westerlies have a close link with Asian Summer Monsoon (ASM) circulations. From the beginning of MIS 9, there was a southward movement of the Westerlies circulation, which corresponded to a retreat of the Indian Summer Monsoon (ISM). A similar relationship also existed between the East Asian Summer Monsoon (EASM) circulation and the Westerlies, which is evidenced by the formation of the most weakly developed soil unit in the EASM-dominated regions during MIS 9, in contrast with the formation of the most strongly developed soil unit in the Westerlies-dominated regions. As conditions in the areas of loess deposition became more humid, the sedimentary basins which are the dust source areas became progressively more arid. The aridification of the source areas may be the result of increased Northern Hemisphere ice volume and accelerated high mountains and/or plateaus uplift in the surrounding regions.

MAGNETIC PROPERTY AND DOMINATING FACTORS OF THE LOESS AT NORTHERN PIEDMONT OF TIANSHAN,XINJIANG

We carried out systemic rock-magnetic investigations on the loess/paleosol sequence at the northern piedmont of the Tianshan Mountain,Xinjiang.Results show that the main magnetic minerals of this sequence are magnetite,maghaemite,haematite,and the main magnetic grain size of magnetic minerals are PSD and MD.The magnetic susceptibility of the loess layer in the Tianshan Mountains is higher than that of paleosoil,which is different from the loess in Loess Plateau.Magnetic susceptibility of the sediments is controlled by native ferrimagnetic minerals from source.Fine grain magnetic materials produced by pedogenic progress make limited contribution to magnetic susceptibility of the loess.

CHARACTERISTICS OF MAJOR GEOCHEMICAL ELEMENTS OF TACHENG LOESS DEPOSITS IN XINJIANG AND ITS PALEOENVIRONMENTAL IMPLICATIONS

In this paper,we studied the characteristics of major geochemical elements and weathering intensity of the loess deposits at the Tacheng section,Xinjiang,northwest China.Results show that among the oxides of the major geochemical elements,SiO2,Al2O3,CaO,CO3,Fe2O3,MgO,K2O and Na2O occur in a decreasing order in the loess section.There is obvious differentiation of oxides in the palaeosol and loess layers and the average contents of Al2O3,Fe2O3 and CaO were markedly higher in paleosol layers.CaO,Fe2O3,MgO,and K2O were accumulated and Na2O,SiO2,Al2O3 depleted in the section compared to the upper continental crust(UCC).The oxides have different distribution pattern in loess and paleosols and some of the major geochemical elements exhibit different concentrations in the topsoils and the paleosols.Further analysis shows that the Tacheng section had experienced weak chemical weathering after deposition,which was similar to the Yili loess section but far weaker than the loess deposits in the Chinese Loess Plateau and the lower reaches of the Yangtze River.The differentiation of weathering degree between the loess and paleosol was also distinct,indicating that the paloesols have experienced stronger weathering process.However,the eluviation of paleosol layers was weaker than that of loess layers probably resulting from the decline of humidity during the period of pedogenesis.The heat-moisture pattern might exert important effect on the chemical weathering of loess/paleosol sequences in the arid area.