Transport of airborne Picea schrenkiana pollen on the northern slope of Tianshan Mountains (Xinjiang, China) and its implication for paleoenvironmental reconstruction

Abstract

The understanding of airborne pollen transportation is crucial for the reconstruction of the paleoenvironment. Under favorable conditions, a considerable amount of long-distance-transported pollen can be deposited far from its place of origin. In extreme arid regions, in most cases, such situations occur and increase the difficulty to interpret fossil pollen records. In this study, three sets of Cour airborne pollen trap were installed on the northern slope of Tianshan Mountains to collect airborne Picea schrenkiana (spruce) pollen grains from July 2001 to July 2006. The results indicate that Picea pollen disperses extensively and transports widely in the lower atmosphere far away from spruce forest. The airborne Picea pollen dispersal period is mainly concentrated between mid-May and July. In desert area, weekly Picea pollen began to increase and peaked suddenly in concentration. Also, annual pollen indices do not decline even when the distance increased was probably related to the strong wind may pick up the deposited pollen grains from the topsoil into the air stream, leading to an increase of pollen concentration in the air that is irrelevant to the normal and natural course of pollen transport and deposition. This, in turn, may lead to erroneous interpretations of the pollen data in the arid region. This study provided insight into the shift in the Picea pollen season regarding climate change in arid areas. It is recorded that the pollen pollination period starts earlier and the duration became longer. The results also showed that the temperature of May and June was positively correlated with the Picea pollen production. Furthermore, the transport of airborne Picea pollen data is useful for interpreting fossil pollen records from extreme arid regions.

Annual layer counting using pollen grains of the Grigoriev ice core from the Tien Shan Mountains, central Asia

“…Beer et al 2007;Huang et al 2015) and were likely derived from the lower arid steppe expanding in elevation between 1600-2000 m.a.s.l.Pinus-type pollen was found only in the ice below 75.8 m. As mentioned earlier, Picea is the dominant coniferous tree in the Tien Shan Mountains, but no Pinus tree is present in the modern forest in this region(Beer et al 2007;Pan et al 2013;Huang et al 2015).…”

“…Abundance became low and peaks were smaller below 60 m. In the layers below 80 m, the abundance slightly increased, and some higher peaks (10-40 grains mL −1 ) appeared between 81.0 and 83.2 m depth. Picea pollen is most likely from Picea schrenkiana, which is the most dominant coniferous tree in the Tien Shan Mountains and is distributed on the slope of the northern side of the Grigoriev Ice Cap (Beer et al 2007;Pan et al 2013;Huang et al 2015).…”

“…Concentrations of Picea and Artemisia pollen grains were also much greater than those of Chenopodiaceae and Ephedra, suggesting an abundant supply of the two pollen types on the ice cap. An observational study in the Tien Shan Mountains has shown that the dispersal of Picea pollen (Picea schrenkiana) is concentrated over one or two weeks during May or June (Pan et al 2013). The Artemisia flowering season near the glaciers is typically during August or September (Nakazawa et al 2005).…”

“…Furthermore, as pollen has been commonly used as a proxy of paleoclimate in lake sediments, pollen assemblages in ice cores may also be indicative of vegetation surrounding the glacier during the past (Liu, Yao, and Thompson 1998;Yang et al 2008;Brugger et al 2018). In the Tien Shan Mountains, a number of studies of pollen in lake sediments, surface soil layers, and its dispersal processes have been conducted (Beer et al 2007;Pan et al 2013;Huang et al 2015); however, there is a lack of information on pollen deposited on glaciers in the highest part of the mountains. Pollen in glacial ice could provide valuable information to understand the dispersal process of airborne pollen as well as the paleo-environment in this region.…”

Vegetation and climate changes in the western Chinese Loess Plateau since the Last Glacial Maximum

“…Therefore, it is generally considered that Picea pollen has low dispersal ability, with most pollen grains falling within hundreds of meters from their parent trees (Jackson, 1990;Bittencourt and Sebbenn, 2007). Modern surveys have also confirmed that Picea pollen percentages can reach more than 30% in surface samples collected 30 m away from the Picea forests, while they decreases to 9e30% and 3e5% with the distance increasing to 15 km and 50e110 km, respectively (Li, 1991;Zhu et al, 2004;Pan et al, 2013. ).…”