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A 236-cm-long core (designated core DP-2011-02), which was extracted in Sept. 2011 using a piston coring device produced by Christie Engineering (Australia) (CHPD 52), was used for this study. In the field, this core was cut lengthwise, photographed and described. Samples were then transported to the laboratory and stored at 4°C.
Eight organic-rich bulk sample cores (laboratory code LUG11-n) (Table 1) were collected from the study site for conventional radiocarbon dating using liquid scintillation technique at the Key Laboratory of Western China’s Environmental Systems (Ministry of Education of China) at the Lanzhou University, China. The specific method was detailed described in Zhong et al. (2015a). In this study, the radiocarbon ages were re-calibrated using the latest IntCal 20 calibration datasets (Reimer et al., 2020). A linear interpolation method (Yeloff et al., 2006; Machlus et al., 2015) was used to establish the core chronological sequence based on the mean sedimentation rates of the two adjacent calibration ages.
Table 1. Radiocarbon dating results using the Intcal 20 calibration dataset for the core DP-2011-02 in Daping swamp
Lab. code Depth /cm Material Age / 14C yr B.P. Calibrated age cal. yr B.P.
(2 sigma)Intercept
(cal. yr B.P.)LUG11-198 24−29 TOC 673 ± 87 542−1073 720 LUG11-199 54−59 TOC 2218 ± 113 2010−2786 2380 LUG11-200 67−72 TOC 3768 ± 94 3573−4303 3980 LUG11-201 81−86 TOC 4119 ± 95 4403−4969 4674 LUG11-202 108−113 TOC 5428 ± 158 5846−6773 6270 LUG11-204B1 151−156 TOC 8895 ± 128 9880−11132 10460 LUG11-205 183−188 TOC 11373 ± 127 12540−13444 13120 LUG11-206 223−228 TOC 12452 ± 167 14187−15409 14780 Notes:TOC, total organic carbon in lake sediments Samples were collected at 2-cm intervals for chemical element analysis. All samples were freeze-dried and ground using ZHM-1A vibration grinding prototype (Beijing Zhonghe Chuangye, China). After grinding, the particle size of the samples was < 74 μm. First, 6.0 g of powdered samples were taken and boric acid was used as the sides and bottom. The samples were then pressed into a round cake with a diameter of 3.2 cm and analyzed for the contents of major and trace elements using the polarization energy dispersive X-ray fluorescence spectrometer (Epsilon 5) procured from PANalytical B.V., The Netherlands. The analytical error in the contents of elements was less than 5%.
In order to assess the climatic significance of chemical elements, several published proxy climatic records of DP-2011-02 including dry bulk density (DD), coarse silt and sand fraction of particle size (CSSF) (Zhong et al., 2015a), organic carbon isotopes (δ13Corg) (Zhong et al., 2017) and pollen data (Zhong et al., 2015b) were also used in the present study.
Geochemistry of Sediments from a Subalpine Lake Sedimentary Succession in the Western Nanling Mountains, Southern China: Implications for Catchment Weathering During the Last 15 400 Years
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Abstract: In the present work, 15 400 yr old geochemical records of a core from the subalpine Daping swamp are presented with the aim to examine the relationship between the chemical weathering and the climatic changes in the region of the western Nanling Mountains, China. The climate of the study region was deeply controlled by the East Asian summer monsoon. The results indicate that, in the past 15 400 yrs, the values of chemical index of alteration (CIA) ranged from 73.9% to 88.2% (mean: 85.3%), suggested a medium and high intensity of chemical weathering. The local exogenous clastic materials, which were derived from the weathered residues, played a key role in contributing towards the sediments. Since the climate-induced chemical weathering exerted strong influences on the geochemical features of weathered residues, the geochemical characteristics of the sediments were deeply impacted by climatic conditions. Wetter and warmer conditions would favor increased chemical weathering, resulting in more leaching of soluble and mobile elements (e.g., Ba and Sr) and leaving the resistant and immobile elements (e.g., Al and Ti) enriched in the weathered residues. These materials were then eroded and transported into the lake, and led to the sediments characterized by the characteristic of having depleted soluble elements. In contrast, dry and cold conditions would result in an opposite trend. In this sense, the geochemical records can serve as proxies to indicate changes of chemical weathering intensity, which were closely related to the evolution of summer monsoon.
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Key words:
- lacustrine sediments /
- chemical weathering /
- asian summer monsoon /
- last deglacial /
- western Nanling Mountains /
- China
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Figure 1. Climate background, geographic location and profile of Daping area. a. the climatic system of China including the East Asian summer monsoon (EASM) and Indian summer monsoon (ISM); the East Asian winter monsoon (EAWM) winds associated with the Siberian-Mongolian High and the Westerly winds generalized as the mean locations of jet stream are indicated; the comparison sites are Dahu swamp (DH) (Wang et al., 2021), Dongge cave (DGC) (Dykoski et al., 2005) and Huguangyan Maar lake (HGY) (Wang et al., 2016), and the latitude position is similar to the Daping swamp, which is considered to be affected by EASM and ISM. b. the location of study region; c. the location of the study core (Modified after Zhong et al., 2015a)
Figure 2. Lithological structure and the newly constructed age-depth relationship of core DP-2011-02 in Daping swamp. The left part of the map shows the depth and lithology of core DP-2011-02. The gray band in the middle of the graph shows the age-depth relationship on 2σ range. Dark spaced symbols on band represent the marginal posterior distribution considering the depth model and the median of the corrected results. Sedimentation rates between the two adjacent calibrated ages are presented in years per cm (yr/cm). The figure was revised based on Zhong et al. (2015a)
Figure 3. Variations of major and trace elements contents in core DP-2011-02 of Daping Swamp. The dry bulk density (DD) and coarse silt and sand fraction of particle size (CSSF) data were based on Zhong et al. (2015a; b). H1 and YD refer to the Heinrich event 1 and the Younger Dryas event, respectively. HOP and B-A denote the wet and warm Holocene Optimum period and the Bølling-Allerød events
Figure 4. Variations of multi-proxy records and their possible responses to climatic conditions of core DP-2011-02 in Daping swamp. Data for herb pollen and organic carbon stable isotope (δ13C) were previously published in Zhong et al. (2015b; 2017), The coarse silt and sand fraction of particle size (CSSF) data were based on Zhong et al. (2015a). H1 and YD refer to the Heinrich event 1 and the Younger Dryas event, respectively. The gray bars indicate warm periods: Bølling-Allerød events (B-A) and Holocene Optimum period (HOP). The black dotted line refers to the ‘4200 yr cooling’ event
Figure 5. Comparison of chemical weathering indexes from Daping sediments with various regional climatic records. a: the Rb/Sr ratios from Daping swamp; b: East Asian Summer Monsoon Index (EASMI) (Li et al., 2013); c: δ13Corg record of Dahu swamp (Xue et al., 2009); d: percsentage of tropical plants in Huguangyan Maar lake (Wang et al., 2016); e: stalagmite δ18O record of Dongge cave (Dykoski et al., 2005); f: stalagmite δ18O record of Qunf cave in Oman (Fleitmann et al., 2003); g: the summer insolation at 25°N latitude (Berger and Loutre, 1991)
Table 1. Radiocarbon dating results using the Intcal 20 calibration dataset for the core DP-2011-02 in Daping swamp
Lab. code Depth /cm Material Age / 14C yr B.P. Calibrated age cal. yr B.P.
(2 sigma)Intercept
(cal. yr B.P.)LUG11-198 24−29 TOC 673 ± 87 542−1073 720 LUG11-199 54−59 TOC 2218 ± 113 2010−2786 2380 LUG11-200 67−72 TOC 3768 ± 94 3573−4303 3980 LUG11-201 81−86 TOC 4119 ± 95 4403−4969 4674 LUG11-202 108−113 TOC 5428 ± 158 5846−6773 6270 LUG11-204B1 151−156 TOC 8895 ± 128 9880−11132 10460 LUG11-205 183−188 TOC 11373 ± 127 12540−13444 13120 LUG11-206 223−228 TOC 12452 ± 167 14187−15409 14780 Notes:TOC, total organic carbon in lake sediments -
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