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

Abstract

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 ≥10°C) was shorter (202 ± 6 d) in the eastern Loess Plateau compared with in the western Loess Plateau (162 ±7 d). The δ 13 C of P. aeoli shells was −9.1‰ to −4.7‰ and −5.0‰ to 0.3‰ for δ 18 O. For P. orphana, the δ 13 C ranged from −9.1‰ to −1.9‰ and −8.9‰ to −2.9‰ for δ 18 O. Both the δ 13 C and δ 18 O differences between the two snail species were reduced from the east to the western Loess Plateau (2.8‰ to 0.2 ± 1.1‰ for δ 13 C and 4.7‰ to 2.9 ± 1.3‰ for δ 18 O). 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 1‰ in δ 13 C or δ 18 O, respectively. Thus, the difference in δ 13 C and δ 18 O 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 ± 0.7‰ and 2.1 ± 1.4‰ for δ 13 C and δ 18 O, respectively. This was followed by MIS 3 that ranged from 2.5 ± 0.4‰ for δ 13 C and 1.6 ± 0.8‰ for δ 18 O. The Last Glacial Maximum changed by only 0.2‰ and 0.4‰ for δ 13 C and δ 18 O, respectively. Therefore, we estimate that the duration of the snail growing seasons to be ~200 ± 10 d during the mid-Holocene, 190 ± 6 d in MIS 3 and 160 ± 3 d during the last glacial period. . In other words, long-term climate change is governed by the variation of seasonality or seasonal length [2]. Knowing how seasonal lengths shifted during Quaternary G-IG cycles is an important key to further understanding the processes and mechanisms of long-term climate change. Climate in the Chinese Loess Plateau is significantly controlled by the East Asian winter and summer monsoon, with distinct seasonal changes that can be divided into four seasons. These are based on a pentad-temperature method that is a mean value of per five-day temperature [3]. Temperatures lower than 10°C are attributed to winter and those over 22°C to summer. Pentad temperatures between 10°C and 22°C are either spring or autumn [3]. It is generally accepted that in the monsoon regions, the seasonal length

The Holocene temperature conundrum answered by mollusk records from East Asia

“…In this way, mollusks that exhibit ~2–3 years’ growth or grow in a single year all incorporate biological imprints of the seasonal temperatures. This is confirmed by observations of different periods of activity in modern mollusks, ranging from late spring (e.g., Pupilla aeoli, Bradybaena ravida ) to mid-summer (e.g., P. orphana, Cathaica pulveratrix ), and even into early autumn 19 – 21 . Thus, snail assemblages and their abundance in topsoil can reveal seasonal and annual temperature changes in terms of both statistical and ecological criteria.…”

“…This is confirmed by observations of different periods of activity in modern mollusks, The grey lines are isotherms (MAT/°C). Insert shows the location of the study ranging from late spring (e.g., Pupilla aeoli, Bradybaena ravida) to midsummer (e.g., P. orphana, Cathaica pulveratrix), and even into early autumn [19][20][21] . Thus, snail assemblages and their abundance in topsoil can reveal seasonal and annual temperature changes in terms of both statistical and ecological criteria.…”

Stable Carbon and Oxygen Isotopes in Shell Carbonates of modern Land Snails in China and Their Relation to Environment Variables

“…Because of the large variability in climatic seasonality in China, the length of the growing season for land snails differs in different regions. For example, the length of snail activity differs by approximately 40 days (i.e., from 202 to 162 days) between the eastern and western parts of the Chinese Loess Plateau (Huang et al, ). Therefore, the exact growing season for land snail at each study site still needs further investigation.…”

Glacial-interglacial evolution of seasonal cooling events documented by land-snail eggs from Chinese loess

“…We propose that this may imply differences in seasonality during glacials and interglacials. Glacials and interglacials in the CLP have different dominant ecological groups of land snails (e.g., Li et al, 2006;Wu et al, 2018), and different ecological groups may have respective dominant seasons for their reproduction and growth (Wu et al, 2002;Huang et al, 2012;Dong et al, 2021). Therefore, it is possible that changes in the phase of anticorrelation during glacials and interglacials would be linked with the differences in the seasonalities favorable for the growth of different snail groups.…”