A prolonged dry mid-Holocene climate revealed by pollen and diatom records from Lake Ugii Nuur in central Mongolia

A high-resolution pollen- and diatom-based bioclimatic reconstruction from Ugii Nuur lake core with a chronological support of 14 AMS dates revealed that a prolonged dry climate prevailed between 5830–3080 14C BP in central Mongolia, as indicated by a dramatic increase in Chenopodiaceae pollen percentages at the expense of Pinus, Poaceae, Cyperaceae and other mesophytic forbs pollen percentages. Higher values of pollen-based temperature index and lower values of pollen-based moisture index also support the notion that the mid-Holocene was persistently warm and dry relative to the preceding and following periods. This mid-Holocene drought is further confirmed by diatom and sedimentary variations, both the planktonic/benthic diatom ratio and the deposition rate being the lowest. Reviews of published regional palaeoclimate data suggest that a prolonged mid-Holocene drought might have prevailed extensively in the central-east Asian arid and hyper-arid areas. The prolonged and extensive drought might have been resulted from a well-documented large-scale temperature rise. The temperature rise-dictated enhancement of evaporation might have exceeded the precipitation increase (if any), resulting in the aridity increase.