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Summer precipitation in the north fringe of East Asian Summer Monsoon (NFEASM) accounts for the majority of annual regional precipitation and plays an important role in regional climatology and agriculture development. Here we analyze variations in summer precipitation in the NFEASM over the past millennium using several simulations with Earth System Models and compare with two dendroclimatological hydroclimate reconstructions that partly cover the past millennium. Both reconstructed records show good agreement on past hydroclimate variations but do not show overly anomalous hydroclimate periods, except for clear drying trends in the second half of the twentieth century. The reconstructed decadal hydroclimate variations are not correlated with any of the simulations, and the simulations are not correlated among themselves either, which strongly suggests that the decadal variability is not linked to the external climate forcing. In addition, the superposed epoch analysis also does not identify a response of simulated precipitation to volcanic eruptions. Therefore, precipitation variability in this region over the past millennium seems to have been driven by internal climate processes. In the simulations, regional summer precipitation is positively and significantly correlated with sea-level-pressure (SLP) over the North Pacific and is negatively and significantly correlated with SLP in southwestern China at both interannual and decadal time scales. This agrees with the teleconnection patterns identified from meteorological reanalysis datasets, indicating that this dipole correlation pattern is robust. Therefore, the SLP difference between these two areas is used as an index to identify the atmosphere circulation pattern favorable to summer precipitation in the NFEASM. This SLP index shows spatial variable correlations with sea-surface-temperature (SST) in the North Pacific: there is a significant positive correlation in the northern North Pacific, while a significant negative correlation in the southern North Pacific. Although the underlying mechanisms for these correlations likely differ between two subareas, it appears that the atmosphere drives SST anomalies in the both subareas. [ABSTRACT FROM AUTHOR]

Based on a database of 106 annually resolved tree-ring chronologies and 244 Palmer Drought Severity Index (PDSI) grid data, we attempted to reconstruct gridded spatial drought patterns in each year over the past four centuries in the arid, semiarid, and semihumid East Asia. The results showed that these regions mainly experienced drought events during the periods from AD 1601 to AD 1652, AD 1680 to AD 1718, AD 1779 to AD 1791, AD 1807 to AD 1824, AD 1846 to AD 1885, and AD 1961 to AD 1999. In the middle of the 16th century, severe droughts occurred mainly in North China; during the period from AD 1876 to AD 1878, droughts occurred in most parts of northern China; and from the 1920s to 1940s, catastrophic drought events spread across almost all of northern China and Mongolia. These historical drought events caused severe ecological and environmental problems and substantially affected the development of human society. In these regions, temperature and summer monsoon precipitation are the main factors influencing drought events. In western areas, PDSI and temperature exhibit a close relationship, whereas in eastern areas, summer monsoon rainfall is the dominant factor influencing variations in PDSI. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the geochemical and magnetic characteristics of fine-grained surface sediments (fractions <63μm) of 182 samples collected at 20 sites in potential dust source areas of arid China (along the southern border of Mongolia). We found coefficients of variation ranging from 2.8 to 35.2% for the four magnetic parameters (χlf, ARM, SIRM, and the S-ratio) in these samples, and this variation may have great significance for interpreting the magnetic characteristics of aeolian deposits far from their source regions. In addition, the results also show that chemical weathering in the potential dust source areas did not play a major role in pedogenesis and evolution of the characteristics of the fine-grained surface sediments because there were variations of only 5% in the values of the chemical index of alteration, which is usually considered to indicate the intensity of chemical weathering, versus variations of 14% in the Rb/Sr ratio. In addition, there was no significant positive correlation between the magnetic susceptibility and the Rb/Sr ratio, which shows that in the source areas, weathering caused little magnetic enhancement in the fine-grained surface sediments. Therefore, in addition to pedogenesis effects on the windblown sediments deposited far from their source regions, the geochemical and magnetic characteristics of fine-grained surface sediments in source areas exhibited complicated patterns. [Copyright &y& Elsevier]

Abstract: A source analysis to characterize the composition of dust fallout in arid and semiarid North China, an important source area of dust for East Asia, was performed. Monthly samples were obtained from April 2001 to March 2002 at 29 sites in sandy and gobi deserts, steppes, and loess areas, and the following elements were analyzed: Ce, Co, Cs, Eu, Fe, Hf, Lu, Nd, Rb, Sc, Ta, Tb, Th, As, La, Na, Sb, Sm, U, Yb, Al, Ca, Mg, Mn, Ti, and V. Although the dust compositions differed, it was difficult to determine the potential dust source areas based solely on the elemental fingerprints of the dust. Principal components analysis showed that at most sites Sm, Sc, La, Ce, Eu, and Th were most strongly correlated (r >0.7) with other elements, whereas crustal elements such as Al, Fe, and Ti were only strongly correlated with the other elements at a few sites. Of the 26 elements that we analyzed, maybe only Sb was representative of anthropogenic pollution, but pollutant sources were unclear because at most sites, in different months, the crustal-derived elements and those derived from anthropogenic pollutants always appeared synchronously, creating difficulties and high uncertainties in source identification. [Copyright &y& Elsevier]

Abstract: A database of 39 annually resolved, tree-ring width chronologies covering the Mongolian Plateau, northeastern China region, and the Yellow River drainage was established to identify variations in sandy desertification cycles over the past three centuries. Our results show that the arid, semiarid, and semi-humid East Asia experienced multiple sandy desertification cycles over the past 300 years. The Mongolian Plateau experienced sandy desertification from the 1730s to the 1750s and the 1810s to the 1910s. Northeastern China region was subject to sandy desertification from the 1700s to the 1720s, the 1770s to the 1820s, and the 1830s to the 1860s. In the Yellow River drainage, sandy desertification occurred from the 1700s to the 1730s, the 1750s to the 1780s, and the 1810s to the 1850s. The occurrence of sandy desertification was closely related to weakened summer monsoon and enhanced winter monsoon associated with decreases in precipitation and increases in aeolian activity during the Little Ice Age; reversals of sandy desertification resulted mainly from increases in precipitation and decreases in aeolian activity during the Current Warm Period. The sandy desertification cycles we reconstructed have been verified by monitoring results of modern sandy desertification trends and evidence from ancient archives and archaeological records. [Copyright &y& Elsevier]