Changes in Paleovegetation and Climate Seasonality in Central China Over Last Two Glacial Cycles: A Stable Isotope Perspective From Land Snails

Modern investigations have shown that oxygen and carbon isotopes of land snail shells are useful indicators of climate and vegetation in monsoonal regions. However, stable isotope studies on snail fossil shells have seldom been done, and the reliability of those indicators needs further verification. Moreover, intrashell stable isotope analysis of individual snails is rather scarce, and seasonal variation in the glacial-interglacial monsoonal climate remains unclear. Therefore, we performed delta O-18 and delta C-13 analyses on fossil shells of cold-aridiphilous Cathaica pulveratrix and subhumidiphilous Metodontia yantaiensis from the loess section over the last two glacial cycles at the Beiyao site on the southern Chinese Loess Plateau. The delta O-18 values of fossil shells reflected monsoonal rainfall amounts and more rainfall during MIS3 and MIS7 than during MIS4 and MIS6. Meanwhile, the delta C-13 values of fossil shells indicated the relative abundance of C-3/C-4 plants and more C-4 biomass during MIS3 and MIS7 than during MIS4 and MIS6. The delta O-18 and delta C-13 values of the two species from the same horizon are significantly different, reflecting differences in their growing season and/or physiological habits. Intrashell variations in stable isotopes showed that climatic seasonality was much stronger during the glacial periods than during the interglacials. Our findings provide an environmental background for explaining past human activities at the Beiyao site. The investigation of stone artifacts showed that ancient human activities were relatively strong during MIS3 and MIS7. During these stages, the warm and humid climate with smaller seasonal contrast was favorable for the regional expansion of human activities.

Automated summary

Modern investigations have shown that oxygen and carbon isotopes of land snail shells are useful indicators of climate and vegetation in monsoonal regions. However, stable isotope studies on snail fossil shells have seldom been done, and the reliability of those indicators needs further verification. In addition, the study reveals that climatic seasonality was much stronger during glacial periods than during interglacials.