Holocene non-orbital climatic events in present-day arid areas of northern Africa and China

A preliminary comparison between the climatic evolution of the arid regions in northern Africa and northern China showed that the variations in continental aridity, on time scales of 104 years, were roughly synchronous over the last 140 ka. Whether this relationship can be established for the Holocene drought events on a century-scale, as reported for tropical and equatorial Africa, is still not known. The comparison of 560 radiocarbon dates on surface fresh water indicators from the Sahara with 158 dates on palaeosols and lake sediments from the arid regions in northern China demonstrates that the Holocene humid phase has been affected in both regions by several drier events, inlaid in the slow trend attributable to orbital forcing. The variations of the southern margins of the deserts, associated with the northern monsoon front, are documented by the latitudinal distribution of these indicators through time. The most startling aspects are a prolonged somewhat drier interval between 7000 and 5600 years BP and the onset of severe aridity at c. 4000 years BP similar to glacial conditions.