TROPICAL GEOGRAPHY ›› 2016, Vol. 36 ›› Issue (3): 468-476.doi: 10.13284/j.cnki.rddl.002839

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Carbon Isotope Compositions and Climate Changes of the Past 20,000 Years Inferred from a Mountainous Peat Bog of Northern Guangxi

MAN Meiling1,ZHENG Zhuo1,LI Jie2,WANG Mengyuan1   

  1. (1.School of Earth Science and Geological Engineering,Sun Yat-sen University,Guangzhou 510275,China; 2.Qingdao Institute of Marine Geology,Qingdao 266071,China)
  • Online:2016-05-05 Published:2016-05-05

Abstract: This study concerns the organic carbon isotopes, TOC and C/N in a mountainous peat bog in northern Guangxi province. Result reveals the local vegetation variations and the climate changes since the LGM in subtropical China. Positive δ13Corg indicates vegetation types change due to the cold and dry climate during the LGM. However, cold and dry condition didn’t lead to vegetation degradation from forest to grassland even during the last glacial period, as δ13Corg shows the dominance of C3 plants around the mountains, which is also proved by pollen records. It can be inferred from the lithology and TOC that local peat-land began to accumulate during the period of 14-10 cal. ka B.P., which developed at fastest speed between 10 and 9 cal. ka B.P. Carbon isotope change towards negative values occurred slightly earlier than the formation of the swamp, indicating that strengthening of summer monsoon occurred at about 14 cal. ka B.P., which is basically concordant with the record from stalagmites. Obvious variation in carbon isotopes which occurred between 9-8 cal. ka B.P. may be relative to 8.2 ka cooling event or changes of organic matter sources. High input of organic matter and negative carbon isotopes in the period during 7.0-2.8 cal. ka B.P. corresponded to the wet and warm condition. Relatively positive change of δ13Corg at 1.7 cal. ka B.P. might be caused by prehistory human impact. The comparison between the δ13Corg data and those of the coastal lowland records from the Leizhou Peninsula shows that a big difference existed between plain and mountainous areas, probably because humidity didn’t reduce too much due to the effect of orographic precipitation in the mountains even during the LGM, while decrease in precipitation and high evaporation were apparently shown in the plains. It should be pointed out that the factors are quite complicated for the interpretation of δ13Corg values in the peat records. The changes in sediment environment, origin of the organic matter and geomorphologic conditions should be taken into consideration when using δ13Corg to reconstruct paleoclimate.

Key words: stable carbon isotope, climate change, subtropical, peat deposit, Gutian of Guangxi