Variability in the oxygen isotope compositions of modern rodent tooth carbonate: Implications for palaeoclimate reconstructions
Abstract The stable oxygen isotope values (δ18O) of small mammal teeth can potentially provide important palaeoclimate records for Quaternary sequences, due to the abundance of these remains in various depositional environments. However, the application of this proxy to Quaternary climate reconstructions has hitherto been limited, due to 1) uncertainties in the relationship between the δ18O of small mammal teeth and the δ18O of meteoric water, and 2) a lack of understanding regarding the importance of isotopic variability in influencing this relationship. The oxygen isotope values of 145 modern short-tailed field vole teeth (Rodentia: Microtus agrestis [L.]), collected from four UK sites, were analysed to address these uncertainties. The results demonstrate that in general, there are no significant δ18O offsets between molars and incisors from the same rodent population. Conversely, isotope variability between different individuals within a population is significant. Thus, when investigating the δ18O compositions of rodent teeth in modern and past environments, analyses must ideally be undertaken on 7–10 molars or incisors from the same site or sedimentary unit. This is in order to obtain reliable mean δ18O values at ≥90% statistical confidence. It is also demonstrated that statistically significant differences in the mean δ18O values of rodent teeth occur between lowland sites in the UK. The spatial trend in the mean δ18O of rodent tooth carbonate is shown to follow a linear relationship with the mean δ18O of local meteoric water. This relationship approximately parallels published calibrations for the δ18O of rodent tooth phosphate in Europe. The results additionally indicate that complex hydrological conditions in northern and highland areas can lead to a mismatch between the measured δ18O values of meteoric water and rodent teeth. A detailed understanding of the environmental controls on the δ18O values of water sources and rodents in these regions is therefore needed.