Organic matter stable isotopic composition of loess deposits in semiarid to humid climate regions of China and the vegetation variations since the last interglaciation
(2015) Quaternary Sciences — Vol. 35, n° 4, p. 809-818 (2015)
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- Abstract
- Comparative studies of environmental factors and vegetation changes deduced from the organic matter stable carbon isotopic composition(δ 13 CTOC)of the loess deposit in semiarid to humid regions would provide clues to understand the vegetation dynamics, in particular under the future climatic changes. However, the relationships between soil organic carbon isotopic composition and vegetation or climate in the subtropical climate areas south of the Qinling Mountains remain unclear. In this study, we selected five loess deposit sections across semiarid to humid climates since the beginning of the last interglacial period at Zhenbeitai, Xifeng, Luochuan which have been reported by other researchers and Luoning(34°25' 56.6"N, 111°39' 23.0"E), Zhenjiang(32°12'N, 119°39'E) in this study to investigate the paleoclimatic and vegetation implication of the δ 13 CTOC. Luoning section located in the temperate sub-humid zones and is 3.8m in depth. The bottom of the Luoning section is about 60ka. Zhenjiang section located in the subtropical humid zones and is about 8m in depth. The bottom of Zhenjiang section is about 130ka. Loess samples were taken at 10cm interval in Luoning section and 20cm interval in Zhenjiang section. The results showed that δ 13 CTOC in Luoning section ranges from -21.8 ‰ to -19.0 ‰ and -20.2 ‰ on average. The δ 13 CTOC have a good correlation with the magnetic susceptibility, and the high values of δ 13 CTOC(-20.2 ‰ ~-19.0 ‰) corresponds to paleosols layers, low values(-21.8 ‰ ~-20.2 ‰)corresponds to loess layers. Values of δ 13 CTOC in Zhenjiang section ranges from -21.2 ‰ to -15.6 ‰ and -18.0 ‰ on average. The δ 13 CTOC also have a good correlation with the magnetic susceptibility and high values of δ 13 CTOC(-18.0 ‰ ~-15.6 ‰)corresponds to paleosols layers, low values (-21.2 ‰ ~-18.0 ‰) corresponds to loess layers. Since last interglaciation(Zhenbeitai and Luoning from the last glaciation)the proportions of C4 plant is 12 % in Zhenbeitai, 14 % in Xifeng, 16 % in Luochuan, 38 % in Luoning and 60 % in Zhenjiang on average. Percentage of C4 plant progressively increased from semiarid to humid regions. C4 plant once reached up to 82 % in last interglacial, 84 % in the Holocene and 61 % in the last glacial. Changes of δ 13 CTOC in the Luoning and Zhenjiang loess sections most likely reflect temperature and the East Asian monsoon intensity. Since the last interglaciation, areas mantled by loess in the sub-humid temperate zones and humid subtropical zones were covered by C4/C3 mixed grassland in which C4 plants were dominated. The monsoon precipitation plays a key role in controlling C3/C4 plant abundance in these areas. Our investigation presents direct evidence that the δ 13 CTOC of loess deposit in the humid climate in Southeast China can be used as a priority proxy indicator of the past monsoon precipitation and vegetation changes.
- Affiliations
Laboratory of Earth Surface Process and Environment, School of Geographic and Oceanographic Sciences Nanjing University
Citations
Zhang, H., Lu, H., Gu, Z., Li, X., Zhang, Z., Chen, Y., Zhao, W., Lyu, A., & Zhao, L. (2015). Organic matter stable isotopic composition of loess deposits in semiarid to humid climate regions of China and the vegetation variations since the last interglaciation. Quaternary Sciences, 35(4), 809-818. https://doi.org/10.11928/j.issn.1001-7410.2015.04.03 (Original work published 2015)