Stable Carbon and Oxygen Isotopes in Shell Carbonates of modern Land Snails in China and Their Relation to Environment Variables

Abstract

Stable isotopes of land snail fossil shell carbonates (δ 13 C shell and δ 18 O shell ) provide the opportunity to decipher paleodietary and paleoenvironmental changes. However, the environmental meanings of δ 13 C shell and δ 18 O shell remain elusive especially in the monsoonal climate region. To elucidate this, δ 13 C shell and δ 18 O shell of the two most common land snails in China, Cathaica and Bradybaena, were analyzed in this study. Results show that Bradybaena has a wider distribution than Cathaica and provides considerable potential for use in paleoenvironmental reconstruction. In addition, δ 13 C shell of Bradybaena increases with altitude and temperature, decreases with mean annual precipitation, and reflects the isotopic signal of C 3 plants. In contrast, Cathaica δ 13 C shell documents a C 3 /C 4 mixing signal and exhibits only a strong altitude effect. δ 18 O shell of Bradybaena decreases with mean annual precipitation in the Indian monsoon and westerlies regions but increases with mean annual temperature in the East Asian monsoon region; as a strong correlation exists between the two variables, they could thus potentially be used to reconstruct paleotemperatures. However, uncertainties should be recognized due to the complexity of the land-snails' ecophysiological responses to environmental changes. Cathaica has slightly lower δ 18 O shell than Bradybaena, which suggests that the two land snails have different ecophysiological traits, and the δ 18 O shell of Cathaica follows mean annual temperature in northeast China. This study lays a ground for explaining land snail stable isotopes in paleorecord in China and reasserts the importance of different ecophysiological traits of land snails in paleoclimatic research.

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

“…From June to September, the δ 18 O of precipitation demonstrates a clear drop (i.e., down to −7.9‰ in July) due to the large rainfall amount (Figure 1 from Wang et al., 2016). This result is consistent with the amount effect on rainfall δ 18 O in monsoonal regions (e.g., Dansgaard, 1964; Wang et al., 2019).…”

“…Land snail fossils are abundant and widely distributed in the Asian monsoon region, especially in the Chinese Loess Plateau (Gu et al, 2009;Liu et al, 2006;Wu et al, 1996Wu et al, , 2002. However, research on the stable isotopes of snail shells has mainly focused on studying modern land snails in different climatic regions (Bao et al, 2018(Bao et al, , 2019Liu et al, 2006;Wang et al, 2016Wang et al, , 2019Zhai et al, 2019). In contrast, stable isotope analyses of fossil snails in sedimentary successions have been inadequately performed, and only a few species of land snails have been studied (Gu et al, 2009;Huang et al, 2012).…”

100 k.y. pacing of the East Asian summer monsoon over the past five glacial cycles inferred from land snails

“…This is supported by several other studies from the monsoon regions of China. For example, Wang et al (2019) found that δ 13 Cshell in Bradybaena snails throughout China reflects the δ 13 C of regional C3 plants controlled by rainfall amount, confirming the use of δ 13 Cshell as a precipitation proxy.…”

“…Thus, it is generally agreed that the δ 13 C of the plant material ingested by a snail is the dominant control on δ 13 Cshell, which in turn reflects the regional vegetation composition (i.e., C3, C4, and CAM) (e.g., Balakrishnan et al, 2005;Stott, 2002), and thus the humidity of the local environment (Prendergast et al, 2017;Yanes et al, 2009). However, δ 13 Cshell can also be influenced by a snail's environmental carbonate ingestion, atmospheric CO2, and several eco-physiologicallyrelated factors (i.e., food preference, metabolic rates, and the duration of activity), resulting in a regionally specific relationship between δ 13 Cshell and environmental variables (Balakrishnan, M., and Yapp, 2004;Bao et al, 2018;Goodfriend and Ellis, 2002;Wang et al, 2019). Therefore, it is necessary to evaluate the climatic significance of δ 13 Cshell in the EASM region before using it for paleoclimatic reconstruction.…”

High‐resolution stable isotope profiles from shells of the land snailPlacostylusreveal contrasting patterns between snails originating from New Zealand and New Caledonia

“…Due to differences in metabolic pathways, C4 plants (e.g. tropical grass) typically have a higher δ 13 C than C3 plants and therefore higher δ 13 C shell values are interpreted to reflect higher relative C4 plant intake when the snail's diet is mixed (Balakrishnan and Yapp, 2004; Wang et al, 2019). In non‐tropical settings and situations where the diet of the snail does not include C4 plants, differences in δ 13 C shell can reflect differences in water use efficiency of the plants ingested by the snail (Diefendorf et al, 2010; Tibby et al, 2016).…”