The initial desertification in the Asian interior is thought to be one of the most prominent climate changes in the Northern Hemisphere during the Cenozoic era. But the dating of this transition is uncertain, partly because desert sediments are usually scattered, discontinuous and difficult to date. Here we report nearly continuous aeolian deposits covering the interval from 22 to 6.2 million years ago, on the basis of palaeomagnetic measurements and fossil evidence. A total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils. This new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of Asia by the early Miocene epoch, at least 14 million years earlier than previously thought. Regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in Asia.

[1] This study aims to establish a stacked climate record of the Quaternary period from the Chinese loess sequence and to address the forcing mechanisms for the regional climate history of the Loess Plateau by correlating the stacked record with a composite d 18 O record in deep-sea sediments. A total of 18,352 samples were obtained from five loess sections, located at Baoji, Lingtai, Jingchuan, Puxian, and Pingliang in the southern and middle Loess Plateau. These yielded high-resolution grain size records. Between-section correlation of these shows that although small depositional hiatuses are present in places within a single section, most parts of the sections display near-continuous dust deposition throughout the Quaternary. The grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the Earth's orbit. The grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series, termed the ''Chiloparts'' record. This resolves most of the orbital timescale paleoclimate events buried in the loess-soil sequences of the southern and middle Loess Plateau and can be used as a regional archive of the Pleistocene climate history in the Loess Plateau. Comparison of the ''Chiloparts'' record with a composite marine d 18 O record shows that for the past 1.8 Ma, the loess-paleosol record can be correlated almost cycle by cycle with the marine record. Several discrepancies in the climatic events between the two records have also been identified, implying that regional forcing mechanisms may have played a part in the climatic evolution of the Chinese Loess Plateau.

Previous studies have shown that the oxygen isotope ratio (δ18O) of plant cellulose can serve as a sensitive proxy indicator of past climate, but its application has mainly been restricted to tree-rings. Here we present a 6000-year high-resolutionδ18O record of peat plant cellulose from northeastern China. Theδ18O variation is interpreted as reflecting changes in regional surface air temperature. The climate events inferred from the isotope data agree well with archaeological and historic evidence. The record shows a striking corre spondence of climate events to nearly all of the apparent solar activity changes characterized by the atmospheric radiocarbon in tree-rings over the past 6000 years. Spectral analysis of theδ18O record reveals the periodicities of around 86, 93, 101, 110, 127, 132, 140, 155, 207, 245, 311, 590, 820 and 1046 years, which are similar to those detected in the solar excursions. We consider these observations as further evidence for a close relationship between solar activity and climate variations on timescales of decades to centuries. Our results also have implications for distinguishing between natural and anthropogenic contributions to future climate change.