Late Miocene–Pliocene Paleoclimatic Evolution Documented by Terrestrial Mollusk Populations in the Western Chinese Loess Plateau

Abstract

The Neogene eolian deposits in the Chinese Loess Plateau (CLP) are one of the most useful continental deposits for understanding climatic changes. To decipher Late Neogene paleoclimatic changes in the CLP, we present a terrestrial mollusk record spanning the time interval between 7.1 and 3.5 Ma from the western CLP. The results indicate four stages of paleoclimatic evolution: From 7.1 to 6.2 Ma, cold and dry climatic conditions prevailed as evidenced by high values of the total number of cold-aridiphilous (CA) mollusk species and by low values of all of the thermo-humidiphilous (TH) mollusk indices. From 6.2 to 5.4 Ma, the climate remained cold and dry but was not quite as dry as during the preceding phase, as indicated by the dominance of CA mollusks and more TH species and individuals. From 5.4 to 4.4 Ma, a warm and moist climate prevailed, as indicated by high values of the TH species and individuals and by the sparsity of CA species and individuals. From 4.4 to 3.5 Ma, all of the CA indices increased significantly and maintained high values; all of the TH indices exhibit high values from 4.4 to 4.0 Ma, an abrupt decrease from 4.0 Ma and a further increase from 3.7 Ma. The CA species of Cathaica pulveraticula, Cathaica schensiensis, and Pupopsis retrodens are only identified in this stage, indicating that the CA species were diversified and that the climate was becoming drier. Moreover, the CA mollusk group exhibits considerable diversity from 7.1 to 5.4 Ma when a cold, dry climate prevailed; whereas the diversity of the TH group was high during the relatively warm, wet interval from 5.4 to 4.4 Ma. This indicates that variations in the diversity of the CA and TH mollusk groups were closely related to climatic changes during the Late Miocene to Pliocene.

Strong winter monsoon wind causes surface cooling over India and China in the Late Miocene

“…B. claimed a relatively strong winter monsoon in the Late Miocene. A winter monsoon dominated climate over the western Loess Plateau before 6 Ma is also reported by Li et al (2008Li et al ( , 2014, who use cold-philous species of fossil snails as an indicator for the winter monsoon strength. A recent model study using the ensemble of Mid-Pliocene global simulations also revealed a stronger-than-present winter monsoon wind in southern China and India (Zhang et al, 2013).This further supports the existence of a strong winter monsoon in the pre-Quaternary periods when the global climate was generally warmer.…”

“…Recent model studies have revealed that different parts of the Asian orography have distinct influence on the Siberian High and the westerly jet stream and therefore the winter monsoon (Shi et al, 2014;Zhang et al, 2014). Zhang et al (2014) showed that the presence of the middle TP can enhance the Siberian High but reduce the winter monsoon wind in East China (Fig.…”

“…Most studies have suggested a weak winter monsoon in the Late Miocene (Guo et al, 2002;Jia et al, 2003;Wan et al, 2007;Jiang and Ding, 2010;Jacques et al, 2013;Lu and Guo, 2014). They attributed this to the lower elevation of the Tibetan Plateau (TP) and the absence of the northern hemispheric ice sheet in the Late Miocene, both of which has been shown by climate models to favour a weaker Siberian High and a dampened winter monsoon wind (Kutzbach et al, 1993;An et al, 2001;Liu and Yin, 2002;Zhang et al, 2014). Conversely, there are some studies indicating a strong winter monsoon (or winter monsoon dominated climate) in the Late Miocene or even earlier periods (Vandenberghe et al, 2004;Li et al, 2008Li et al, , 2014Quan et al, 2012;Zhang et al, 2012), requiring different mechanisms to explain these changes.…”

“…They attributed this to the lower elevation of the Tibetan Plateau (TP) and the absence of the northern hemispheric ice sheet in the Late Miocene, both of which has been shown by climate models to favour a weaker Siberian High and a dampened winter monsoon wind (Kutzbach et al, 1993;An et al, 2001;Liu and Yin, 2002;Zhang et al, 2014). Conversely, there are some studies indicating a strong winter monsoon (or winter monsoon dominated climate) in the Late Miocene or even earlier periods (Vandenberghe et al, 2004;Li et al, 2008Li et al, , 2014Quan et al, 2012;Zhang et al, 2012), requiring different mechanisms to explain these changes. Better knowledge on temperature changes over the Asian monsoon region and its association with the winter monsoon strength in the Late Miocene would provide useful insights into the evolution of the winter monsoon system and its driving mechanisms at this period.…”

Molecular genetic and biochemical evidence for adaptive evolution of leaf abaxial epicuticular wax crystals in the genus Lithocarpus (Fagaceae)

“…The Miocene climate was slightly warmer and wetter and spawned the monsoon system which has affected Asian vegetation [ 97 – 99 ]. After the late Miocene, the climate gradually cooled and became arid [ 100 , 101 ]. The late-Miocene-to-Pliocene climate change accelerated the diversification of insular species [ 102 – 105 ], which may be partly due to sea-level fluctuations accompanying disjunction and connection between continents and islands [ 106 ].…”