Prehistoric population expansion in Central Asia promoted by the Altai Holocene Climatic Optimum

How climate change in the middle to late Holocene has influenced the early human migrations in Central Asian Steppe remains poorly understood. To address this issue, we reconstructed a multiproxy-based Holocene climate history from the sediments of Kanas Lake and neighboring Tiewaike Lake in the southern Altai Mountains. The results show an exceptionally warm climate during similar to 6.5-3.6 kyr is indicated by the silicon isotope composition of diatom silica (delta Si-30(diatom)) and the biogenic silica (BSi) content. During 4.7-4.3 kyr, a peak in delta Si-30(diatom) reflects enhanced lake thermal stratification and periodic nutrient limitation as indicated by concomitant decreasing BSi content. Our geochemical results indicate a significantly warm and wet climate in the Altai Mountain region during 6.5-3.6 kyr, corresponding to the Altai Holocene Climatic Optimum (AHCO), which is critical for promoting prehistoric human population expansion and intensified cultural exchanges across the Central Asian steppe during the Bronze Age. The impact of climate change on Holocene human activity in the Altai-Sayan region of Central Asia is unclear. Here, the authors use pollen, biogenic silica, and isotope records from lake cores to show that the climate prompted human population expansion and intensified cultural exchange during the Bronze Age.