The evolution of coupling of Asian winter monsoon and high latitude climate of Northern Hemisphere -: Grain evidence from 8.1 Ma loess-red clay sequence on the Chinese central Loess Plateau

The evolution and driving mechanism of the Asian winter monsoon system are of great importance to understanding the present-day climate. Through high-resolution particle size analysis of the oldest loess-red clay sequence known so far (with a basal age of about 8 Ma) and comparison of the results with oxygen isotope curves from North Atlantic marine sediments, 4 stages of the evolution of the Asian winter monsoon were clearly demonstrated. During the first stage, between about 8.1 and 4.3 Ma, there was no relation between Asian winter monsoon and Northern Hemisphere ice volume and high latitude climate inferred from marine sediments. A weak relation developed during the second stage, about 4.3 to 3.5 Ma. During the third stage (3.5 to 2.6 Ma) an Asian winter monsoon system similar to the present formed, initiating a stronger relation between the winter monsoon and Northern Hemisphere ice volume and high latitude climate. In the final stage (2.6 to 0 Ma) the present Asian winter monsoon system was fortified and stabilized and changes in the winter monsoon system were almost in phase with Northern Hemisphere ice volume and climate. The staggered uplift of Tibetan Plateau at similar to8, 3.6, 2.6 Ma and later might be the driving force for the evolution of the Asian winter monsoon.