Elsevier

Journal of Asian Earth Sciences

Volume 69, 5 June 2013, Pages 185-195
Journal of Asian Earth Sciences

A new approach for reconstruction of the Holocene climate in the Mongolian Altai: The high-resolution δ13C records of TOC and pollen complexes in Hoton-Nur Lake sediments

https://doi.org/10.1016/j.jseaes.2012.12.002Get rights and content

Abstract

δ13C of total organic carbon (TOC) and pollen grain, TOC, C/N ratio, and δ15N of total organic nitrogen (TON) in a 2.57-m long core from Hoton-Nur Lake in Mongolian Altai have been measured for reconstruction of the Holocene climates. The δ13C values of TOC and pollen carbon have similar average values but different ranges. Pollen δ13C has negative correlation with %AP (arboreal taxa pollen) and positive correlation with %NAP (herbaceous pollen and spores) that are connected with conditions of humidity in the area. Taiga-biome has lighter δ13C than steppe-biome. Hence, pollen δ13C composition is more sensitive to changes of humidity in the analogous spectra than palynotaxonomical structure and δ13C of TOC. Based on our results, the Holocene climates in Mongolian Altai are: (1) dry conditions prior to 11.5 kyr BP; (2) wet conditions between 11.5 and 6.0 kyr BP; (3) a relatively dry/cool episode during 6–4 kyr BP; (4) stable cool and semiarid conditions with moderately effective moisture during the past 4000 years. Two abrupt climatic changes occurred at ∼7.45 kyr BP and ∼11.5 kyr BP might be related to glacial activities. The Holocene climatic trend in Mongolian Altai which is controlled by the Westerlies is similar to the trend of monsoonal climate shown by the Chinese speleothem records as well as the lake/sand dune evidence in the deserts of NW China. The contact of the two climatic systems and shift of the monsoonal boundary during the past need to be further studied.

Highlights

Holocene climate of Mongolian Altai was reconstructed by a Hoton-Nur Lake core. ► δ13C of TOC and pollen grain, TOC, C/N, and δ15N were measured. ► δ13C of pollen is a reliable method for paleoenvironmental reconstructions. ► Comparison of westerly and monsoonal climates is conducted. ► The Hoton record has a similar Holocene trend to that of the monsoonal records.

Introduction

Located in the central Asia and bounded with Russia to the north and China to the south, Mongolia is an extremely continental territory. Its climatic setting is strongly influenced by the Siberian–Mongolian High (SMH) pressure cell, with cold and semi-arid climatic conditions in general. The variation of SMH affects strongly the strength of Asian Winter Monsoon (AWM) and average position of northern limit of the East Asian Summer Monsoon (EASM) on different time scales during Quaternary (Ding et al., 1995, An et al., 2000). In a review paper, An et al. (2008) interpreted that the climate changes of Mongolia are influenced by Westerlies and the EASM. Yang et al., 2002, Yang et al., 2003 described the influence of changes in Westerlies and monsoons on precipitation variability in the Tarim Basin of Xinjiang and in the Alashan Plateau of western Inner Mongolia during the late Quaternary. According to the modern meteorological observation, however, the EASM northern limit does not cross the boundary between Mongolia and China, and no maritime moisture source reaches Mongolia in general (Wang et al., 2010). Even during the early Holocene (10–9 kyr BP) when the solar insolation at mid-latitudes of N. Hemisphere reached the highest of the entire Holocene, the northern limit of the EASM boundary did not reach the southern boundary of Mongolia according to the reported geological evidence (Winkler and Wang, 1993). On the other hand, the influence of the Westerlies on paleoclimate and environmental changes of Central Asia is still unclear and controversial (Chen et al., 2008, Schwanghart et al., 2009). Therefore, how did the SMH, Westerlies and Asian monsoon affect the Holocene climate of Mongolian Altai, and what were the connections among these climatic systems during Holocene? We need more paleoclimate records to address the above questions.

Based on modern climatic settings and vegetation features, five bioclimatic zones in Mongolia can be identified (An et al., 2008, Wang et al., 2011). Thus, the temporal variations of the Holocene climate in Mongolia may have spatial difference. Furthermore, according to the summary of previous studies on paleoclimate changes during the late Quaternary in the drylands of China, interpretations of climatic conditions in the same area might not be consistent depending on time resolution and meanings of climatic proxies (Yang and Scuderi, 2010, Yang et al., 2011). For instance, Schwanghart et al. (2009) interpreted that a warm and wet mid Holocene (ca. 8–4 kyr BP) was prevailing in Ugii Nuur basin of central Mongolia. In contrast, Wang et al. (2011) reported a persistently warm and dry mid-Holocene (5830–3080 14C yr BP) climate recorded in the same lake basin. Obviously, more high-resolution, continuous and multi-proxy records of the Holocene climates in Mongolia are needed in order to understand the mechanisms that control climatic changes of this large and variable continental region.

In this study, we report the first carbon isotopic records of total organic carbon and pollen grains extracted from the lake sediments of Hoton-Nur Lake in Mongolian Altai which had previously been carried out pollen analysis and climate reconstruction (Rudaya et al., 2009). Up to date, rare available literatures examine the δ13C of pollen assemblages and compare the pollen δ13C with δ13C of TOC in the same core. If pollen δ13C provides a meaningful proxy of changes in vegetation and climate, this method will develop another fast and semi-quantitatively geochemical approach for lake study. Here, we establish the connection between the δ13C of pollen complexes and climate dynamics, and compare the pollen δ13C, δ13CTOC, TOC and C/N, and refine the history of climate and vegetation in Mongolian Altai during the Holocene.

Section snippets

Background of the studying area and sample description

Hoton-Nur Lake (48°35–42′N, 88°10–24′E, 2083 m a.s.l.) is located on the eastern slope in the northern high-elevated part of the Mongolian Altai (Fig. 1A), with a surface area of 50 km2 and maximum depth of 58 m. This region is bounded by Altai Mountains, Tannu-Ola Mountains (part of Sailughem Mountains), and Hangayn Mountains. The peak of Huytan Orgil with an elevation of 4082 m (a.s.l.) is on the west side of the lake valley (Fig. 1A). The lake region is characterized by continental climate with

Pollen data

A total of 100 samples (1–2 g of the dry sediment) taken with an average 2.5-cm interval from the core were treated for pollen analysis using standard procedure (Faegri and Iversen, 1989). One tablet containing 10679 of Lycopodium spores was added to each sample in order to calculate total pollen, spore and non-pollen palynomorphs concentrations. After chemical processing, the samples were stored in the polypropylene test tubes with 3–5 ml of glycerine. Acetolysis was applied during the chemical

Significance of the pollen δ13C

Carbon isotopic fractionation varies among C3, C4 and CAM plants. The mean value of δ13C for C4 plants is −12‰ with range of −10‰ to −14‰ and for C3 plants is −26‰ ranging −20‰ to −35‰. CAM plants owing to their biochemical and physiological features show large range of δ13C variations between −10‰ and −33‰ (Bender et al., 1973, Lerman, 1974, Ehleringer and Rundel, 1989, Ehleringer et al., 1991).

Smith and Epstein (1971) studied 104 plant and algae species on the basis of carbon isotope

The Holocene climatic history of the Hoton-Lake basin

Modern continental climate and high-mountain relief of Mongolian Altai result in two natural processes – aridization and cryogenesis that can strongly influence structure and distribution of vegetation (Gunin et al., 1999). Studies of central Asian vegetation found that vegetation changes in the region respond sensitively to changes in precipitation and soil moisture (Bezrukova et al., 2005, Humphries et al., 1996, Miyazaki et al., 2004, Ni, 2003).

In Hoton-Nur Lake cores, arboreal pollen are

Conclusions

Measurement of δ13C in pollen complexes is reliable method for paleoenvironmental reconstructions. In the regions where spread of vegetation types is mainly controlled by precipitation, dynamics of δ13C from pollen assemblages reflect changes in air humidity and soil moisture. In Mongolian Altai, heavy δ13C values indicate arid conditions with dry steppe development; whereas lighter values of δ13C coincide with increase of humidity and development of forest distribution. Using of δ13C analysis

Acknowledgments

We gratefully acknowledge the National Science Council of Taiwan (NSC 98-3114-E-006-014, NSC 98-2116-M-006-003 and NSC 100-3113-E-002-009). The research was supported by the Russian Foundation for Basic Research (Grants 08-05-00773, 09-05-09217, 09-06-1000009-05-13505, 10-06-00085) and by Russian Academy of Sciences, Siberian Branch (Project Nr. 92). We thank also Dr. I. Kalugin (UIGGM SB RAS, Novosibirsk, Russia) for the sediment samples and Mr. Tz-Shing Kuo (NCKU, Tainan, Taiwan) for

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