Factors controlling shell carbon isotopic composition of land snail Acusta despecta sieboldiana estimated from laboratory culturing experiment

[摘要] The carbon isotopic composition (δ¹³C) of land snail shellcarbonate derives from three potential sources: diet, atmospheric CO₂,and ingested carbonate (limestone). However, their relative contributionsremain unclear. Under various environmental conditions, we cultured one landsnail subspecies, Acusta despecta sieboldiana, collected from Yokohama, Japan, and confirmed that all ofthese sources affect shell carbonate δ¹³C values. Herein, weconsider the influences of metabolic rates and temperature on the carbonisotopic composition of the shell carbonate. Based on results obtained fromprevious works and this study, a simple but credible framework is presentedto illustrate how each source and environmental parameter affects shellcarbonate δ¹³C values. According to this framework and somereasonable assumptions, we estimated the contributions of different carbonsources for each snail individual: for cabbage-fed (C₃ plant) groups,the contributions of diet, atmospheric CO₂, and ingested limestone vary in the ranges of 66–80, 16–24, and 0–13%, respectively. For corn-fed (C₄ plant) groups, because of the possible food stress (less ability to consumeC₄ plants), the values vary in the ranges of 56–64,18–20, and 16–26%, respectively. Moreover, according to the literature and ourobservations, the subspecies we cultured in this study show preferences towards different plant species for food. Therefore, we suggest that thepotential food preference should be considered adequately for some speciesin paleoenvironment studies. Finally, we inferred that only the isotopicexchange of the calcite-HCO₃⁻-aragonite equilibrium duringegg laying and hatching of our cultured snails controls carbon isotopefractionation.

[学科分类] 地球化学与岩石