陆生蜗牛壳体碳氧同位素组成与气候

CARBON AND OXYGEN ISOTOPIC COMPOSITION OF LAND SNAIL SHELLS AND CLIMATE

陆生蜗牛响应气候环境变化敏感,其壳体化石碳氧同位素组成(δ^(13)C和δ^(18)O)具有重建古生态和古大气水文条件的巨大潜力。然而目前针对中国黄土古土壤沉积序列中蜗牛化石碳氧同位素组成开展的古环境古气候重建研究却仍然不足,根源在于对蜗牛壳体δ^(13)C和δ^(18)O指标气候意义的认识仍不明确。文章从现代过程研究着手,综述了目前有关蜗牛壳体δ^(13)C和δ^(18)O气候环境意义的研究进展,并指出各自指标存在受控因子的复杂性和多解性等问题。通过总结这些研究认为:陆生蜗牛壳体δ^(13)C值主要通过反映植物(尤其C3)δ^(13)C值变化来进一步响应当地降水量变化,进而指示环境的干湿程度,但同时需要考虑环境碳酸盐、大气CO_(2)等额外因子对壳体δ^(13)C的影响;壳体δ^(18)O值可以在较大程度上反映大气降水δ^(18)O值变化,但同时需要考虑蒸发作用和温度等因素对壳体δ^(18)O的影响;壳体δ^(13)C和δ^(18)O在作为气候指标时常受区域和蜗牛种属等因素影响。此外,还介绍了目前中国北方黄土地层中蜗牛壳体化石稳定同位素组成重建季风变化的研究进展和近十年来有关蜗牛壳体团簇同位素新方法的研究进展。最后,论文针对壳体δ^(13)C和δ^(18)O指标存在的问题提出可能的解决办法,并对以后蜗牛碳氧同位素古环境研究方向进行展望。

The carbon and oxygen isotopic composition(δ^(13)C andδ^(18)O)of the fossil shells of land snails,which are sensitive to climatic and environmental changes,has great potential to reconstruct the palaeoecology and palaeohydrology conditions.However,the research onδ^(13)C andδ^(18)O of snail fossils from Chinese loess-palaeosol sequences is still badly lacking,because the climatic significance of shellδ^(13)C andδ^(18)O proxies is still unclear.In this paper,we review the research progress on the climatic and environmental significance ofδ^(13)C andδ^(18)O in land snail shells from the perspective of modern process,and point out the complexity and multiplicity of controlled factors for each proxy.In conclusion,land snail shellδ^(13)C values respond to the change of local precipitation by reflecting the change ofδ^(13)C value of ingested plants(especially for C3 plants),and then indicate the humidity or aridity of an environment.However,the influence of additional factors such as environmental carbonate and atmospheric CO_(2)on the shellδ^(13)C value should be considered.To a certain degree,the shellδ^(18)O can record the variation of theδ^(18)O of meteoric water,but the influence of evaporation effect and temperature on the shellδ^(18)O values could not be ignored.Moreover,shellδ^(13)C andδ^(18)O as climatic indicators are often region-dependent and species-dependent.In addition,this paper introduces the recent advances about the palaeomonsoon reconstructions using stable isotope compositions of snail fossils from the Quaternary loess sequences in Northern China,and the advances about the clumped isotope of snail shells during the past decade.Finally,possible solutions for solving the controversy in shellδ^(13)C orδ^(18)O climate proxy,and the main future application directions of paleoenvironment reconstruction based on stable isotope compositions of land snails,are proposed.