Eco-environmental changes in the Chinese Loess Plateau during low-eccentricity interglacial Marine Isotope Stage 19

Eco-environmental changes during interglacials with an astronomical background similar to that of the Holocene are potentially helpful for understanding the future climatic evolution. Marine oxygen isotope stage (MIS) 19 is similar to the Holocene in astronomical background, both being characterized by a low eccentricity of the Earth’s orbit. However, MIS 19 has attracted research attention only recently and therefore less is known about eco-environmental changes during this interval, especially based on terrestrial records. In the Chinese Loess Plateau (CLP), the S7 paleosol can provide valuable terrestrial paleoclimatic and paleoenvironmental record for MIS 19. Here, high-resolution terrestrial snail records from the L8-L7 strata of the Huining, Xifeng and Luochuan sequences in the CLP were analyzed in order to characterize spatio-temporal changes in climate and eco-environment during MIS 20–18. The results show that in all three sections the late part of MIS 20 was dominated by abundant cold-aridiphilous mollusc species, indicating that cold and dry climatic conditions prevailed across the entire CLP, under the strong influence of the winter monsoon. The mollusc fauna of MIS 19 were dominated by warmth-loving and thermohumidiphilous species that enable the definition of two climatic stages. The early part of MIS 19 (～790–778 ka) was marked by warm and humid conditions, as evidenced by high abundances of warmth-loving and thermo-humidiphilous species. This interval was slightly warmer than today and it lasted for ～12 kyr. The climate of the later part of MIS 19 (～778–761 ka) was more moderate, and increased proportions of cold-aridiphilous and warmth-loving species were recorded. The warmth of this period was similar to that of today, but the climatic fluctuations were stronger. During the early part of MIS 18 (～761–745 ka), the Xifeng and Luochuan sections in the eastern CLP still maintained high abundances of warmth-loving and thermo-humidiphilous species, indicating that the moderate climatic conditions during late MIS 19 continued during early MIS 18, lasting for another ～15 kyr, and that the influence of the summer monsoon remained strong in the eastern CLP during early MIS 18. However, in the western CLP, cold-aridiphilous species in the Huining section became dominant during early MIS 18, reflecting the prevalence of a cold and dry glacial climate, with the strong influence of the winter monsoon. These findings indicate that a steeper climatic gradient and a pronounced regional environmental difference existed between the eastern and western CLP during the early part of MIS 18. Comparison of our mollusc results with the variation of Earth orbital parameters suggested that climate changes in the CLP during MIS 20-18 were likely controlled mainly by insolation changes forced by the configuration of Earth orbital parameters. The unique orbital configuration during the low eccentricity interglacial-to-glacial transition could have strengthened the East Asian summer monsoon which favored the amelioration of the eco-environment in the CLP, especially in the eastern CLP where the summer monsoon exerted a strong influence. Thus we speculate that, under natural climatic conditions, the climate of the CLP may remain in a warm, humid state for another 30 kyr, although climatic instability and the seasonal differences between winter and summer could strengthen.