Pollen Record of Humidity Changes in the Arid Western Qilian Mountains Over the Past 300 Years and Comparison With Tree-Ring Reconstructions

Abstract

In arid central Asia, the geo-ecological environment of the well-vegetated high mountains differs from that of the extensive arid Gobi desert areas, with the forested areas having experienced a different pattern of humidity variations compared to the dryland regions. Therefore, the moisture history of the forest areas reconstructed by tree rings may differ from that of the dryland areas. In the extremely arid area of the western Qilian Mountains and the surrounding dryland areas, where forest is absent, it is unclear how humidity conditions have changed over the past several centuries. Here, we use a pollen record from Tian'E Lake, with a chronology based on 210 Pb and 137 Cs, and with an average temporal resolution of ∼2 years, to reconstruct the humidity changes over the past 300 years. The results show that the pollen assemblage is dominated by Artemisia and Amaranthaceae (Chenopodiaceae), and therefore, the A/C (Artemisia/ Chenopodiaceae) ratio can be used to reconstruct changes in humidity conditions.

An inverse relationship between moisture and grazing intensity in an arid mountain-basin system

“…As Artemisia requires more water than Chenopodiaceae (the family name has been changed to Amaranthaceae (APG, 1998)) during the growing season, a high A/C ratio (ratio of Artemisia to Chenopodiaceae) indicates more humid conditions when the sum of the two pollen types exceed 50% in arid and semi-arid regions (Zhao et al, 2012). The A/C ratio has also been used as an effective proxy for regional moisture in arid and semi-arid areas (Huang et al, 2009; Wang et al, 2020; Zhang et al, 2018; ). In addition, the median value of the A/C ratio from surface samples around Tian’E Lake is similar to that of the desert vegetation zone in the lower elevation drylands (Supplementary Figure.…”