Unlocking sub-annual hydroclimate and temperature variability through land snail shell records

Abstract

Currently available reconstructions of past East Asian monsoon (EAM) variability achieve annual resolution at best, which limits their ability to resolve seasonal variations in precipitation and temperature. To address this gap, we present sub-annual scale reconstructions of temperature and precipitation variability based on carbonate clumped isotope (Δ47) and stable oxygen isotope (δ18Oshell) measurements from modern and fossil land snail shells collected from the western (Yuanbao, YB) and southeastern (Lingbao, LB) edge of the Chinese Loess Plateau (CLP). Whole-shell Δ47-derived temperatures (T47) from different modern snail species are consistent with land surface temperatures measured during their growing season (mid-April to September at YB and mid-March to October at LB), and show minimal inter-species differences, highlighting the ecological robustness of snail-based T47 reconstructions. Our intra-shell Δ47–δ18O–δ13C data show no obvious evidence of disequilibrium fractionation, supporting that land snail shell aragonite forms near isotopic equilibrium in natural settings. Notably, the reconstructed intra-shell T47 profiles show a sub-annual temperature variability of 7–10 °C and potential signs of short-term thermal stress. Reconstructed body water δ18O (δ18Obw) values from whole-shells are significantly enriched (by ∼ 3–6.5 ‰, p < 0.05) compared to local precipitation δ18O (δ18Op), due to evaporative effects and micro-environmental conditions. Intra-shell δ18Obw profiles reveal sub-annual fluctuations that follow seasonal δ18Op patterns, capturing dry-season evaporative isotopic enrichment and wet-season depletion masked in whole-shell averages.The T47 from early Holocene and last glacial maximum (LGM)-aged shells provides geochemical evidence of a cooler growing season than today, perhaps caused by extended growing seasons during the early Holocene and climatically restricted ones during the LGM. Lower and more stable intra-shell T47 and more negative δ18Obw values during the wet seasons highlight seasonal hydroclimatic shifts under glacial boundary conditions. Together, our results demonstrate the sensitivity of snail shell geochemistry to hydroclimatic seasonality and support the use of combined intra-shell δ18O and Δ47 analyses to resolve climate seasonality beyond the resolution of traditional proxies.