A Humid East Asia During the Early Pliocene Indicated by Calcite Nodules From the Chinese Loess Plateau

Abstract

The East Asian monsoon system dominates the regional hydrology of East Asia, which hosts one-third of the world's population. It is thus critical to quantify the dynamics of the East Asian hydroclimate in the context of anthropogenic warming. The warm intervals of the Pliocene Epoch (5.33-2.58 Ma), including the most intensively studied mid-Pliocene Warm Period (mPWP, 3.264-3.025 Ma), are considered the closest climate analog of the mid-twenty-first century (Burke et al., 2018;Haywood et al., 2016), with atmospheric CO 2 levels ranging between 300 and 450 ppm (de la Vega et al., 2020;Martinez-Boti et al., 2015). A comprehensive understanding of regional climate during this time could better inform us about the potential hydrological variations over East Asia in response to future climate change. Sitting on its northern border, the Chinese Loess Plateau (CLP) captures the nuances of the East Asian summer monsoon (An et al., 2014), manifested by the sizable climatic gradient from southeast to northwest (Figure 1). The Neogene global cooling and the high relief of the Tibetan Plateau led to the desertification of inland Asia and increased meridional thermal gradient (An et al., 2001;Lu et al., 2010;Richter et al., 2022), facilitating the deflation and entrainment of eolian dust from high-latitude deserts to the CLP by the northwesterly surface winds generated by the Siberian high (i.e., winter monsoon) (Maher, 2016). Alternatively, modern observations indicate maximum dust transport in spring dust storms initiated by cold air outbreaks (Roe, 2009). On the other hand, the summer monsoon brings moisture and heat from the low-latitude Indian and Pacific Oceans (Chiang et al., 2020), promoting subsequent pedogenesis. Eolian deposits on the CLP consist of two parts: (a) the Pleistocene loess-paleosol sequence, characterized by fossil soils (paleosols) formed during