Clumped and stable isotopes of land snail shells on the Chinese Loess Plateau and their climatic implications
Introduction
Widespread land snails are regarded as a valuable archive for studying environmental and climatic conditions because of their high sensitivity to temperature and humidity (Liu, 1985; Goodfriend, 1992; Wu et al., 2018). Moreover, their fossil remains are abundant in Quaternary deposits, such as the loess-paleosol sequences on the Chinese Loess Plateau (CLP), and they are considered typical ‘index animals’ in paleoenvironmental studies (Liu, 1985; Wu et al., 2018). Thus, snail faunal assemblages (Goodfriend, 1992; Rousseau and Wu, 1997; Wu et al., 2002, Wu et al., 2018) and isotopic compositions of snail shell carbonates (Goodfriend, 1992; Bonadonna and Leone, 1995; Abell and Plug, 2000; Goodfriend and Ellis, 2000; Balakrishnan et al., 2005a; Colonese et al., 2010, Colonese et al., 2013; Kehrwald et al., 2010; Yanes et al., 2011, Yanes et al., 2013a, Yanes et al., 2013b, Yanes et al., 2014, Yanes et al., 2017; Huang et al., 2012; Prendergast et al., 2016) have been widely used to decipher past climatic and environmental changes.
Many studies have suggested that the carbon isotope composition of land snail shell carbonate (δ13Cshell) is derived from three potential sources: diet, atmospheric CO2, and ingested carbonates (Goodfriend and Hood, 1983; Pigati et al., 2004; Quarta et al., 2007; Romaniello et al., 2008; Xu et al., 2011; Zhang et al., 2014). Laboratory studies indicated that the δ13Cshell reflects mostly the respired CO2 derived from ingested plants (Stott, 2002; Metref et al., 2003; Zhang et al., 2014). Thus, most published field investigations of modern/fossil land snails assume that they primarily consumed C3 and C4 plants in relation to their abundances in the surrounding environment, and δ13Cshell has therefore traditionally been used to deduce variations in C3/C4 plants in the landscape (Goodfriend and Ellis, 2000, Goodfriend and Ellis, 2002; Balakrishnan et al., 2005a, Balakrishnan et al., 2005b; Liu et al., 2007; Yanes et al., 2008, Yanes et al., 2009, Yanes et al., 2011, Yanes et al., 2013b, Yanes et al., 2014; Colonese et al., 2014; Prendergast et al., 2017). δ13Cshell can also be applied to infer changes in aridity in C3-dominated landscapes (Colonese et al., 2013; Prendergast et al., 2017). However, snails show a preferential use of C3 food when fed a mixed diet (Metref et al., 2003; Zhang et al., 2014). Moreover, radiocarbon dating work has indicated that carbon from ingested carbonates and atmospheric CO2 may also contribute to snail shells (Goodfriend and Stipp, 1983; Pigati et al., 2004; Quarta et al., 2007; Romaniello et al., 2008; Xu et al., 2011). These additions complicate the explanation of δ13Cshell from the perspective of climatic and environmental changes because the relative contributions from the three potential sources remain unclear.
Pioneering attempts showed that the oxygen isotope compositions of land snail shells (δ18Oshell) were inversely related to local relative humidity (Yapp, 1979). Goodfriend et al. (1989) and Baldini et al. (2007) found that the isotopic compositions of snail body water (δ18Obody water) and δ18Oshell were influenced by atmospheric water vapor. Other studies illustrated relationships between the oxygen isotope composition of meteoric water and those of land snail shells (Lécolle, 1985; Goodfriend et al., 1989; Zanchetta et al., 2005; Yanes et al., 2009, Yanes et al., 2017; Colonese et al., 2014; Prendergast et al., 2015). Zhang et al., 2018a, Zhang et al., 2018b suggested that food water should also be considered a water source, apart from rainwater. Thus, the flux balance model proposed that the δ18O value of snail shell carbonate represented the combined effects of the relative humidity, δ18O of ingested water (e.g., precipitation), and temperature at which the shell precipitated (Balakrishnan and Yapp, 2004). Overall, the explanation of the oxygen isotopes of land snail shells is more complex than that of the carbon isotopes due to the variable temperature, relative humidity and δ18O of water in the terrestrial environment.
The newly developed carbonate clumped isotope (expressed as Δ47) thermometry technique was proposed to quantitatively reconstruct the temperature of carbonate mineral growth under isotopic equilibrium conditions (Ghosh et al., 2006; Eiler, 2007). This technique is based on the abundance of 13C18O bonds in the carbonate lattice relative to those expected for a random distribution of isotopes among all isotopologues and is independent of the δ18O of the waters from which carbonates grew (Ghosh et al., 2006, Eiler, 2007). Recently, published data on different carbonate minerals of biogenic/inorganic origin demonstrated that Δ47 generally follows a universal Δ47-temperature calibration (Bonifacie et al., 2017; Kelson et al., 2017). Therefore, we apply this thermometry to simultaneously obtain the shell formation temperature and the δ18Obody water of land snails in combination with δ18Oshell, both of which are indispensable for understanding the stable isotope composition of snail shells.
However, current studies showed discrepant results when converting snail shell clumped isotopes to land snail shell calcification temperature (T47) or the environmental temperature. For example, Zaarur et al. (2011) indicated that T47 values of snail shells are typically higher than either the mean annual or the snail activity season ambient temperatures. In contrast, Eagle et al. (2013) and Wang et al. (2016) revealed that T47 values for land snails are strongly correlated with environmental temperatures, although they are still higher than the local warm month mean temperatures for Cathaica sp. and Bradybaena sp. (Wang et al., 2016). Recent work by Zhai et al. (2019) and Guo et al. (2019) also reported higher than expected T47 versus either environmental temperatures or estimated snail activity temperatures. Furthermore, snail culturing experiments suggested that Δ47 of Acusta despecta land snails can be used to reconstruct the mean seasonal temperature of snail activity (Zhang et al., 2018a, Zhang et al., 2018b). In this context, the Δ47 values of modern and fossil snails deserve further investigation.
Therefore, we comprehensively studied the clumped and stable isotopes (Δ47, δ13Cshell, δ18Oshell, and δ18Obody water) of modern and last glacial fossil land snail shells from the Luochuan and Weinan sections on the central and southern CLP. The aims of this study are 1) to quantitatively reconstruct the temperature changes from the last glacial to modern time using the clumped isotope technique and 2) to further understand the climatic implications of δ13Cshell and δ18Oshell as well as δ18Obody water on the CLP on glacial-interglacial timescales.
Section snippets
Materials and methods
The Luochuan (35.7° N, 109.4° E) and Weinan (34.5° N, 109.6° E) sections are located in the center and on the southern edge of the Chinese Loess Plateau (CLP), respectively, and the linear distance between the two sections is ~150 km (Fig. 1). Approximately 15 kg of sediment was excavated at 10 cm intervals from both profiles since the last interglacial (S1 paleosol). The sediments of each sample were washed and sieved in the field on a 0.5 mm mesh sieve, and the fossil snail shells were picked
Results
Table 1 presents the stable isotope values and clumped isotope without acid fractionation correction (Δ47CDES90) results for fossil and modern shells analyzed in 2012 and 2017 at Caltech, as well as the calculated snail body water isotope and clumped isotope temperature (T47). The δ18Owater was calculated using the aragonite–water fractionation proposed by Kim et al. (2007), and the Δ47–T calibration line and the acid fractionation factor of 0.088 in Petersen et al. (2019), who reprocessed data
Clumped isotopes of snails
Previous studies reported that the T47 of modern snails is higher than the mean annual temperature and even higher than the growing season temperature (GST), and this phenomenon was attributed to snail eco-physiological adaptations (Zaarur et al., 2011; Wang et al., 2016; Zhai et al., 2019; Guo et al., 2019). In contrast, our results show that both the range and mean values of T47 for our modern snails are very close to the temperature from April to October when the monthly average T is >10 °C
Conclusions
We studied the clumped and stable isotopes (δ13Cshell, δ18Oshell, and δ18Owater) of modern land snail shells and fossil snail shells from the last glacial period at the Luochuan and Weinan sections on the CLP. Contrary to previous studies, our study shows that the clumped isotope temperature of snail shells is consistent with the snail growing season temperature at the studied locations and that it is ~10 °C lower for last glacial fossil snails than for their modern counterparts. Moreover, we
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We sincerely thank professor Peter Hale Molnar for comments on and revision of the manuscript, and we thank Dr. Linpei Huang for help in the identification of fossil snail species and Dr. Ryb Uri and Dr. Max Lloyd for help with data processing and discussion. This work was jointly supported by grants from the Training Program of the State Key Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences (QYZDY-SSW-DQC001 and ZDBS-SSW-DQC001), the MOST program (2016YFE0109500), the
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2023, Palaeogeography, Palaeoclimatology, PalaeoecologyEarly diagenetic imprints and U–Th isotope systematics of fossil land snail shells from the Chinese Loess Plateau
2023, Quaternary GeochronologyCitation Excerpt :The basic assumption is that the shell δ13C values are controlled by δ13C of ingested plants while the shell δ18O values reflect rainfall δ18O during the growing season of snail. Although both proxies are complicated by other processes (Bao et al., 2018; Dong et al., 2020), δ13C and δ18O of fossil land snail shells have been used to reconstruct monsoonal climate in East Asia (Wang et al., 2020). More recent work on clumped isotopes has calibrated the transfer function between summertime temperature and land snail clumped isotopes (Wang et al., 2016; Zhai et al., 2019), which has been applied to reconstruct the temperature change on the CLP since the Last Glacial Maximum (Eagle et al., 2013).
Carbon isotope composition of land snail shells as a proxy for precipitation amount in the East Asian Monsoon region: A case study from Hainan Island
2023, Palaeogeography, Palaeoclimatology, PalaeoecologyCitation Excerpt :Moreover, snail shells are generally buried in situ and are well preserved in Quaternary sedimentary sequences worldwide (e.g., Leone et al., 2000; Prendergast et al., 2016; Li et al., 2020). Thus, δ13Cshell has been widely used to reflect changes in continental environments, with ages from Late Pleistocene through Holocene (e.g., Goodfriend, 1988; Bonadonna et al., 1999; Goodfriend and Ellis, 2000; Balakrishnan et al., 2005a; Chiba and Davison, 2009; Colonese et al., 2007, 2013; Yanes and Romanek, 2013; Yanes et al., 2012, 2014; Prendergast et al., 2016; Zanchetta et al., 2017; Dong et al., 2020; Qin et al., 2021). Although fossil snails are abundant and well-preserved in the Quaternary loess-paleosol sequences of the China Loess Plateau (Liu, 1985; Wu et al., 2018; Dong et al., 2022), only a limited amount of research has been conducted on using snail δ13Cshell for quantitative paleoclimatic reconstruction (Dong et al., 2020; Qin et al., 2021; Bao et al., 2022), partly due to limitations in our understanding of the origin of the δ13Cshell signal.
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2021, Palaeogeography, Palaeoclimatology, PalaeoecologyCitation Excerpt :Snail cultivation studies indicate that food water is an important source of land-snail body water (Zhang et al., 2018a). Other recent studies have assessed the applicability of carbonate clumped isotope measurements to temperature reconstructions using modern land-snail shells (Zaarur et al., 2011; Wang et al., 2016; Zhang et al., 2018b; Guo et al., 2019; Zhai et al., 2019) and fossil shells (Eagle et al., 2013a; Dong et al., 2020). The clumped isotopic composition of carbonates is a powerful tool in reconstructing the formation temperature of carbonate (Ghosh et al., 2006; Eiler, 2007, 2011).