East-west asymmetry in the distribution of rainfall in the Chinese Loess Plateau during the Holocene

As the cradle of Chinese civilization the Chinese Loess Plateau (CLP) and its climatic and environmental history have attracted much research attention; however, the spatial characteristics of Holocene climatic conditions across the CLP remains unclear. We investigated five loess sections from the Ganjia Basin in the western CLP, and used paleoclimatic indexes from one well-dated loess-paleosol sequence to reconstruct precipitation variation during the past similar to 15,000 years. The chronology of the loess section is well established, based on 12 AMS C-14 dates from bulk organic matter. Loess deposited before 8 ka (1 ka = 1000 years before 1950 CE) indicates that precipitation was low from similar to 15 to 8 ka. Subsequently, a paleosol, characterized by higher magnetic susceptibility and more negative organic carbon isotopic values, developed under the moist conditions of the middle to late Holocene. Comparison with paleoclimatic records from the CLP revealed that precipitation across the CLP was low during the early Holocene and reached its highest level during 8-3 ka, against the background of an enhanced East Asian summer monsoon (EASM). In the eastern CLP (the region east of the Liupan Mountains), the climate became dry after 3 ka because of a weakening of the EASM; however, precipitation in the western CLP was relatively high at this time. This observation of an east-west asymmetry in precipitation in the CLP during the Holocene based on geological data is supported by numerical modeling results from PMIP3, which indicate that it could have been caused by the westward extension of the western Pacific subtropical high. Our findings provide an analog for the study of interglacials on a longer time-scale and they demonstrate that the pattern of moisture conditions between the eastern and western CLP may differ on sub-orbital timescales.