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

Jiale Wang,Luciane Fontana,Zongli Wang,Lixiong Xiang,Xiuxiu Ren,Xiaozhong Huang,Yulin Xiao,Jun Zhang

doi:10.3389/feart.2020.562426

Jiale Wang, Luciane Fontana + Show 6 more

Open Access

https://doi.org/10.3389/feart.2020.562426

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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 210Pb and 137Cs, 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 ratio (Artemisia/Chenopodiaceae) can be used to reconstruct changes in humidity conditions. Based on the pollen A/C ratio, two relatively wet periods are identified for ~1740-1750 and 1840-1980; and two dry intervals: ~1750-1840 and 1980-2018. This pattern of variation is similar to that reconstructed from nearby humidity records based on tree-ring width adjacent to Tian’E Lake area and with instrumental records from meteorological stations over the past several decades. However, there are significantly different records between pollen-based and tree-ring based humidity during ~1760-1830, 1880-1910 and 1920-2018 in the Qilian Mountains on a long timescales. We conclude that pollen-based humidity records from dryland areas may differ from those reconstructed from tree-ring widths in forested mountain areas, especially when the temperature was increasing. It was further suggested that there was anti-phased relationship in humidity conditions between westerlies-dominated central Asia and monsoon areas over the past century.

Highlights

Instrumental climate records show a clear record of increasing temperature in the Northern Hemisphere during the 20th century, humidity variations exhibit complex spatial patterns at the regional scale (IPCC, 2007)
A paleoenvironmental study of a 50-year pollen record with a near-annual resolution from Gahai Lake in the Qaidam basin showed that the A/C ratio was well correlated with moisture data from the Delingha Meteorological Station (Zhao et al, 2008)
During ∼1980–2018, the lower A/C ratio suggests that the climate became drier than the previous stage (Figure 5)

Summary

Introduction

Instrumental climate records show a clear record of increasing temperature in the Northern Hemisphere during the 20th century, humidity variations exhibit complex spatial patterns at the regional scale (IPCC, 2007). Increased global warming could lead to more frequent and sustained droughts (Cook et al, 2004; Dai et al, 2004), with increased aridity in arid and semiarid areas (Feng and Zhang, 2015; Huang et al, 2016). The Qilian Mountains, in the northern part of the Qinghai–Tibetan Plateau, is located in the marginal area of the arid region in central Asia and the semiarid or semi-humid region in the east. The climate of the region has warmed, and there is an increasing frequency and intensity of severe drought events (Zou et al, 2005)

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