Effect of altitude on the stable carbon and oxygen isotopic compositions of land snails at the margin of the East Asian monsoon. (15th March 2020)

• Record Type: Journal Article
• Authors: Bao, Rui; Sheng, Xuefen; Li, Chenglong; Shen, Hua; Tan, Liping; Sun, Ling; Li, Chunqian; Peng, Hongke; Luo, Ling; Wu, Min; Lu, Huayu; Ji, Junfeng; Chen, Jun
• Is Part Of: Geochimica et cosmochimica acta. Volume 273(2020)
• Page Start: 99
• Page End: 115
• Publication Date: 2020-03-15
• Subjects: Carbon and oxygen isotopes -- Land snail shells -- Altitudinal effect -- Climatic factors -- East Asian monsoon marginal zone -- Helan Mountains; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2020.01.029
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: The carbon and oxygen isotopic composition of land snail shells (δ 13 Cshell and δ 18 Oshell ) has been used to reconstruct paleoenvironmental changes worldwide. Adding to the limited calibration information available for the monsoon marginal regions, we present δ 13 C and δ 18 O results for modern snails, plants and soils, collected from the Helan Mountains, in North China, spanning an altitudinal gradient of 1733–2851 m a.s.l. Linear regression analysis show that δ 13 Cshell is positively correlated with altitude on both slopes, with similar rates of altitudinal variation; in contrast, δ 18 Oshell is negatively correlated with altitude on the western slopes, but this effect is absent on the eastern slopes. The variations in the integrated δ 13 C signals of living vegetation and the flux of absorbed atmospheric CO2 attributed to changes in metabolic rates are likely responsible for the altitudinal effect on δ 13 Cshell above 2000 m a.s.l., while changes in vegetation type and/or carbonate ingestion by snails may be important in inducing the positive shift in δ 13 Cshell below 2000 m a.s.l. δ 18 Oshell is determined by the rainwater δ 18 O and by the fractionation processes between shell carbonate and snail body water, and both are controlled by the temperature of the alpine environment. In addition, evaporative enrichment of the body fluid or of the environmental water prior to ingestion by snails exerts an important influence on δ 18 Oshell . Notably, both δ 13 Cshell and δ 18 Oshell in the study region respond more sensitively to climate than in the monsoon core area. The rate of change of δ 13 Cshell in response to temperature and precipitation above the altitude of 2000 m a.s.l. are −0.87‰/°C and +2.76‰/100 mm, while the corresponding rates for δ 18 Oshell on the western slopes are +0.41‰/°C and −1.29‰/100 mm. Our results expand the range of application of δ 13 Cshell and δ 18 Oshell as climatic indicators, and emphasize the differences in the climatic sensitivity of these proxies between the monsoon margin and core areas. In addition, the differences in shell isotope composition in response to environment changes between adjacent locations (i.e. on different slopes) in mountainous terrain need to be considered in future studies.