Reconstructed moisture evolution of the deserts in northern China since the Last Glacial Maximum and its implications for the East Asian Summer Monsoon

摘要

The East Asian summer monsoon (EASM) affects rainfall variability and consequently terrestrial ecosystems in the densely populated Asian region. Understanding the nature of EASM evolution is vital for interpreting the pa-leoclimatic conditions of the region and for predicting future climate changes. However, the relative importance of factors such as high northern latitude ice volume, low northern latitude summer insolation and atmospheric carbon dioxide (C0_2) levels in controlling the EASM on orbital timescales remains controversial. The aeolian deposits and vegetation in the dry lands of northern China are highly sensitive to climatic changes. Here, we present a reconstruction of effective moisture levels in the region since the Last Glacial Maximum based on an analysis of changes in the sedimentary fades of aeolian deposits and vegetation type combined with reliable age control. The results demonstrate that extremely arid conditions prevailed from approximately 21-16 ka BP; that conditions gradually became wetter from 16-8 ka BP, reaching a peak in effective moisture from 8-4 ka BP; and that relatively arid conditions prevailed thereafter. This pattern of moisture evolution probably reflects changes in summer monsoon precipitation. Although the strengthening of the EASM lagged variations in northern hemisphere insolation and atmospheric CO_2 content, the strengthening was in phase with the rise in sea level from 21-6 ka BP which was controlled by changes in global ice volume. Therefore our results suggest that sea level rise may have been a major driver of EASM precipitation in the desert area of northern China during this period, as a result of shortening the transport distance of oceanic moisture sources to the continental interior and thus enabling the monsoon rainfall belt to reach the study region.