Long-term weakening of the East Asian summer and winter monsoons during the mid- to late Holocene recorded by aeolian deposits at the eastern edge of the Mu Us Desert

The East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM) are major drivers of environmental conditions in East Asia. However, due to the lack of high-resolution EAWM records, the phase relationship between the EASM and EAWM during the Holocene epoch is still debated. Here, we use magnetic and grain-size measurements from a sequence of aeolian sediments from the eastern edge of the Mu Us Desert to track the history of the EASM and EAWM from 7.5 to 2.5 ka. The results show that both the EASM and EAWM exhibit a similar long-term weakening trend during this interval. In view of the stable glacial boundary conditions and the significantly decreased rates of atmospheric CO2 rise since the mid-Holocene, we suggest that orbitally-induced insolation was the major cause of the weakening of both the EASM and EAWM. Decreasing summer insolation and increasing winter insolation reduced the thermal contrast between the ocean and the Asian continent in both summer and winter time, resulting in the weakening of both monsoon systems during the mid- to late Holocene. (C) 2016 Elsevier B.V. All rights reserved.