MILLENNIAL-SCALE OSCILLATIONS OF THE EAST-ASIAN SUMMER MONSOON OVER THE LAST 0.220MA
二十二万年以来东亚夏季风的千年尺度变化及其在不同时期的差异

In this study, a high-resolution paleoweathering record of the loess-soil sequence from the central Loess Plateau covering the last 0.220Ma has been generated using the ratio between the CBD (citrate bicarbonate dithionite) extractable free Fe2O3 (Fed) andtotal Fe2O3(Fet). The new record shows a series of millennial oscillations, which are not documented by magnetic susceptibility changes at the same site. Since chemicalweathering in this region depends mainly upon the summer precipitation and temperatures, we interpret these changes as a result of millennial-scale variations in the strength of the East-Asian summer monsoon. Over the last glacial Period, general agreement can be observed between the loess weathering record and the GRIP-δ18O record.However, our loess weathering Timeseries seems to suggest a rather stable climatepattern for the typical last interglacial Period (marine δ18O stage 5e) although smallfluctuations can be observed. At least the three warm peaks and the two cold peaksshown in the GRIP data cannot be clearly defined in our weathering record. Thesummer monsoon may have not experienced such drastic changes or its amplitudeswere much smaller than in the Greenland region. This interpretation seems to besupported by the well-developed Luvisol within the S1 soil complex in the easternand southern loess Plateau, which would have been formed under relatively stablewarm-humid conditions.Our data also show that high amplitude fluctuations were more characterishcs forthe last glacial period while the older portion (including the L2 and S2 units) showsrather smoothed variations. This seems to suggest that the instability of climate in theEast-Asian monsoon zone be significantly amplified since the termination of the lastinterglacial period. Moreover, the fluctuation pattern of Fed / Fet for the portion olderthan 140 000aB. P. is significantly different from that of the GRIP-δ18O record,suggesting that the millennial oscillations in the North Atlantic and northern Chinamay be less coupled for earlier glacial-interglacial cycles in comparison with the lastglacial Period.