Lateglacial and Holocene hydroclimatic variability documented by Cladocera of Tolbo Lake in the Altai Mountains, western Mongolia

Abstract

The Altai Mountains contain rivers, lakes, and glaciers critical for the survival of both social and ecological systems. Reconstructing past hydroclimatic changes is crucial for understanding human-environment interactions and predicting future hydroclimatic dynamics in this region. We reconstructed the water level fluctuations of Tolbo Lake in the Altai Mountains over the past 13.7 kyr using the sedimentary cladoceran fossils. The results show that a rising trend of the Holocene lake level resulted mainly from intensification of westerlies-driven precipitation. The results further reveal that the centennial timescale lake-level fluctuations during the mid–late Holocene was mainly modified by temperature-controlled meltwater input, resulting in low lake levels during the cold, glacier-advance periods and high lake levels during the warm, glacier-retreat periods. The intensification of westerlies-driven precipitation at ∼6 cal ka BP initiated a humid environment and facilitated the Neolithic trans-Eurasian spread of livestock and crops (i.e. barley, wheat, and sheep). Subsequently, occasional increases in glacial meltwater during the warm phase further boosted grassland growth and animal husbandry, likely contributing to the expansion of major nomadic empires such as the Huns (∼2.4–1.8 cal ka BP) and the Mongols (∼0.8 cal ka BP). Additionally, the depletion of alpine glaciers due to the current anthropogenic warming may eventually result in significant shrinkage of the lakes and severe crises for ecosystems and the human communities that rely on these lakes.