Moisture changes in a mountain–basin system since the last deglaciation revealed by the pollen record of Genggahai Lake, northeastern Qinghai-Tibetan Plateau

Abstract

Asia’s mountainous arid and semiarid regions feature forests in wet high-mountain areas and grasslands/deserts in dry basins. Assessing changes in millennial-scale effective moisture in mountain–basin systems can provide a valuable reference for understanding how climate change and human activities affect terrestrial water resources and drylands. Here, a continuous pollen record from Genggahai Lake on the northeastern Qinghai-Tibetan Plateau exhibited detailed changes in regional vegetation and effective moisture since ∼ 15.3 ka. The pollen sequence suggests that steppe vegetation developed in the basin and that sparse forest vegetation developed in the surrounding mountain areas during 15.3–11.7 ka and 6.3–0 ka, and that desert steppe vegetation developed in the basin and denser forest vegetation developed in the surrounding mountain areas during 11.7–6.3 ka. Based on comparison of regional palaeoclimatic records, the pollen assemblage results suggest antiphase moisture changes between mountains and the basin and imply that the low Artemisia/Chenopodiaceae (A/C) ratio during 11.7–6.3 ka in the basin likely indicates that the low effective moisture conditions likely resulted from the high permeability of loose and porous sediments and the high evaporation in the basin induced by high summer solar insolation. In contrast, the high A/C ratio during 15.3–11.7 ka and 6.3–0 ka indicates a high level of effective moisture during these periods, possibly in response to less evapotranspiration loss in the basin caused by the strong water-binding capacity of palaeosols, ameliorated vegetation conditions, and low summer solar insolation. Our results also suggest that both climatic conditions and anthropogenic activities may have altered the natural vegetation in the late Holocene and that change in the percentage of tree pollen from Genggahai Lake were synchronous with changes in the intensity of the Indian summer monsoon.