Climatic structures and intensities of the last two glacials documented by terrestrial molluscs from Chinese loess sequences

Abstract

Knowledge of the structures and intensities of past glaciations is crucial for understanding Quaternary palaeoclimatic evolution. Terrestrial molluscs are a reliable proxy of past environmental conditions and can provide specific climatic insights into glacials. Here we compare the climatic evolution of the last two glacials, based on mollusc fossils from the L2 and L1 loess units (equivalent to Marine Isotope Stages (MIS) 6 and 4–2, respectively) of the Xifeng and Luochuan sections of the Chinese Loess Plateau (CLP). The results show that both glacials had a tripartite structure but with different intensities, as indicated by variations in the abundance of the dominant cold‐aridiphilous (CA) mollusc species, Vallonia tenera and Pupilla aeoli. The first stage, from ~191 to 184 ka for MIS 6, and from ~71 to 57 ka for MIS 4, was characterized by a cold, arid climate, as indicated by the abundance of V. tenera and P. aeoli, and the limited occurrence of thermo‐humidiphilous (TH) species. The second stage, from ~184 to 155 ka for MIS 6, and from ~57 to 29 ka for MIS 3, was characterized by a relatively mild, humid climate, indicated by a decrease in V. tenera and P. aeoli, and an increase in TH species. The last stage, from ~155 to 130 ka for MIS 6, and from ~29 to 11.7 ka for MIS 2, experienced the coldest and driest conditions, as indicated by the dominance of V. tenera and P. aeoli in late MIS 6 and by the reduced occurrence of the grassland biomass, necessary for the growth of CA species, in MIS 2. The climate during MIS 2 was much colder and drier than that during late MIS 6. We suggest that the structures of the glacials were controlled mainly by insolation driven by changing astronomical configurations, amongst which obliquity likely played the major role. The different glacial intensities across the CLP may also have been related to variations in Northern Hemisphere ice sheets and the temperature of the tropical oceans.