Asynchronous Holocene Climate Optimum across mid-latitude Asia

The Holocene Climate Optimum (HCO) was an important interval in the development of human civilization and has been the focus of many paleoclimatic studies. However, there are significant regional differences in the timing of the HCO due to the complex response of regional climates to insolation changes, associated with internal feedbacks within the climate system. Here, we present the results of a study of magnetic and geochemical properties of loess-paleosol sequences from across mid-latitude Asia, with the aim of assessing differences in the timing of the HCO. The HCO generally occurred after ~5 ka in Tajikistan and Xinjiang; during 5–2.5 ka in the western Chinese Loess Plateau (CLP); and during ~8–2.5 ka in the central CLP. This asynchroneity reflects differences in the response of regional climates to global climate change. Specifically, the difference in timing between the central and western CLP may have been related to shifts in the position of the East Asian summer monsoon rain belt, due to the changing longitudinal position of the Western Pacific Subtropical High, together with changes in the east-west thermal gradient in the equatorial Pacific (i.e. shifts between La Nina and El Nino conditions).