Variability of snail growing season at the Chinese Loess Plateau during the last 75 ka

Knowledge of seasonal climate change is one of the key issues facing Quaternary paleoclimatic studies and estimating seasonal climate change is difficult, especially changes such as seasonal length on glacial-interglacial timescales. The stable isotope composition from seasonal land snail shells provides the potential to reveal seasonal climatic features. Two modern land snail species, cold-aridiphilous Pupilla aeoli and thermo-humidiphilous Punctum orphana, were collected from different climatic zones in 18 localities across the Chinese Loess Plateau, spanning 11 degrees of longitude and covering a range of 1000 km(2). The duration of the snail growing season (temperature a (c) 3/410A degrees C) was shorter (202 +/- 6 d) in the eastern Loess Plateau compared with in the western Loess Plateau (162 +/- 7 d). The delta C-13 of P. aeoli shells was -9.1aEuro degrees to -4.7aEuro degrees and -5.0aEuro degrees to 0.3aEuro degrees for delta O-18. For P. orphana, the delta C-13 ranged from -9.1aEuro degrees to -1.9aEuro degrees and -8.9aEuro degrees to -2.9aEuro degrees for delta O-18. Both the delta C-13 and delta O-18 differences between the two snail species were reduced from the east to the western Loess Plateau (2.8aEuro degrees to 0.2 +/- 1.1aEuro degrees for delta C-13 and 4.7aEuro degrees to 2.9 +/- 1.3aEuro degrees for delta O-18). These isotopic differences roughly reflect the difference in the growing season lengths between the east and west Loess Plateau indicating that the duration of the snail growing season shortens by 15 d or 19 d if the difference decreases by 1aEuro degrees in delta C-13 or delta O-18, respectively. Thus, the difference in delta C-13 and delta O-18 between both snail species can be used to reveal the length of the snail growing season in the past. Based on our investigation, the length of the snail growing seasons from the Xifeng region during the last 75 ka was reconstructed. During the mid-Holocene (8-3 ka), the mean isotopic difference from both snail species reached maximum values of 2.6 +/- 0.7aEuro degrees and 2.1 +/- 1.4aEuro degrees for delta C-13 and delta O-18, respectively. This was followed by MIS 3 that ranged from 2.5 +/- 0.4aEuro degrees for delta C-13 and 1.6 +/- 0.8aEuro degrees for delta O-18. The Last Glacial Maximum changed by only 0.2aEuro degrees and 0.4aEuro degrees for delta C-13 and delta O-18, respectively. Therefore, we estimate that the duration of the snail growing seasons to be similar to 200 +/- 10 d during the mid-Holocene, 190 +/- 6 d in MIS 3 and 160 +/- 3 d during the last glacial period.