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

Nozomu Takeuchi,Shuntaro Sera,Koji Fujita,Vladimir B Aizen,Jumpei Kubota

doi:10.1080/15230430.2019.1638202

Nozomu Takeuchi, Shuntaro Sera + Show 3 more

Open Access

https://doi.org/10.1080/15230430.2019.1638202

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Abstract

ABSTRACTPollen grains are commonly found in ice cores, particularly those from mountain glaciers at low to middle latitudes. Because the release of pollen from flowers has a seasonality and varies among the plant species, pollen concentrations in ice cores are useful for distinguishing annual or seasonal layers and inferring past vegetation near glaciers. We analyzed major pollen grains in an 87-m-deep ice core drilled at the top of the Grigoriev Ice Cap (4563 m.a.s.l.) in the Tien Shan Mountains, Kyrgyz Republic. Microscopy showed that mainly five pollen taxa were contained in the ice core. Their abundance fluctuated with the depth of the core, indicating their seasonal deposition on the ice cap, while the seasonality of the stable isotopes was not particularly clear because of melting and refreezing signatures. Based on the pollen profiles, annual layers were determined back in time to 1780 AD at a depth of 63.6 m; at greater depth, they could not be distinguished due to ice layer thinning in the glacier. The pollen assemblages have gradually changed during the last 220 years and were particularly distinctive in the deeper part, suggesting the drastic change of vegetation in this region during the Holocene.

Highlights

The Tien Shan Mountains are among the major mountain systems in central Asia and extend more than 2000 km across the vast arid region of the central part of the Eurasia continent
The pollen profile extracted from the ice core showed that layers with high and low pollen concentrations repeatedly appeared (Figure 3)
The most abundant pollen type observed in the ice core was Artemisia (Figure 2(c)), ranging from 0 to 32.8 grains mL−1 and accounting for 40 percent of the total pollen in the ice core

Summary

Introduction

The Tien Shan Mountains are among the major mountain systems in central Asia and extend more than 2000 km across the vast arid region of the central part of the Eurasia continent. A number of ice cores have been recovered from glaciers in central Asia during the last three decades, and their records have shown a long environmental history covering hundreds to a thousand years or the entire Holocene (Thompson et al 1989, 1997; Aizen et al 2016). Fluctuations in oxygen stable isotopes, annual ice thickness, mineral concentration, and soluble ions are used as proxies of air temperature, precipitation, dust storms, and anthropogenic pollution in this region, respectively (Grigholm et al 2015).

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