Early-Mid Holocene climatic changes inferred from colors of eolian deposits in the Mu Us Desert

Climatic changes of the early-mid Holocene in the monsoon margin of northwest China have long been debated. The extensive eolian deposits of the desert/loess transition in central China provide important terrestrial archives of paleoclimate change, especially the evolution of the East Asian Summer Monsoon (EASM). As yet, however, due to the specific geographical location of the region, relatively few eolian sedimentary records have been reported since the Holocene. Here we investigated paleoclimatic implications of color parameters and grain size end-member (EM) components in three eolian sand-paleosol sequences. The chronology framework of the stratigraphic sections was established using 11 radiocarbon dates from organic material and 9 optically stimulated luminescence (OSL) ages from quartz. We reconstructed the early-mid Holocene climate changes in the southeastern margin of the Mu Us Desert by combining magnetic susceptibility (MS) and total organic carbon (TOC) analyses. Similar to the loess-paleosol sequence in central China, the lightness was significantly negatively correlated with TOC, MS and fine EM and all were controlled primarily by effective moisture. However, the redness and blueness were more influenced by the sand's parent materials rather than from weak pedogenesis and therefore reflected eolian activity. This was supported by the significant positive correlation between redness and blueness and coarse EM that represented components transported by saltation and creep from near-source areas during dust outbreaks in cold and dry climate condition. Our multi-proxy analysis indicated that during the Younger Dryas and early Holocene, the Mu Us Desert was dominated by cold and dry climate conditions with frequent strong eolian activities. During 8.5-3.7 ka BP, the climate shifted to warm and humid that effectively fixed dunes and the paleosol was widely developed confirming the occurrence of the Holocene climate optimum. In addition, these alterations during the Holocene were primarily controlled by the EASM that was driven by summer insolation in the Northern Hemisphere, as well as changes in high latitude ice-sheets area and the ocean-atmosphere interaction patterns in the Atlantic and Pacific Oceans on different scales.