Vegetation and climate change during the Miocene revealed by the pollen record of Otindag Dune field, northern China

Elucidating the processes and trends of aridification in inland Asia holds significant theoretical and practical importance for the evolution of the East Asian monsoon. The Otindag Dune field, situated in a semi-arid region of northern China, there is a scarcity of studies on the Neogene aridification history. Based on pollen analysis of the BYNE section, a red clay profile, combined with biomization method and coexistence approach, this study presents a reconstruction of vegetation and climate from∼17.35 to 16.12 Ma. The pollen records indicate that during∼17.35–16.12Ma, herbaceous plants dominated by Artemisia, Amaranthaceae, and Humulus were more prosperous. Tree plants were dominated by the warm and humidity-loving Quercus, Betula, and Juglandaceae. Overall, the climate was relatively warm-wet, corresponding to the Middle Miocene Climatic Optimum (MMCO). Accompanied by fluctuations in moisture levels, vegetation primarily comprised temperate forest steppe, temperate steppe, and temperate mixed forest. Through comprehensive analysis of pollen records from the late Miocene lacustrine deposit, the decreasing trends in the Artemisia/Chenopodiaceae (A/C) ratio and the arboreal to non-arboreal pollen (AP/NAP) ratio indicated a shift from humid to arid conditions, as well as the weakening of the East Asian summer monsoon (EASM) from the middle to late Miocene. The coexistence approach suggests that mean annual precipitation during the middle Miocene exceeded that of the late Miocene by approximately 100mm, further supporting the notion that the middle Miocene was wetter. A comparison of pollen records of the Otindag Dune field with those from the Tibetan Plateau and Loess Plateau, along with other Asian climate records, reveals significant consistency. The intensification of inland aridification in the Otindag Dune field throughout the Miocene is likely influenced by global cooling and uplift of the Tibetan Plateau, but the tectonic spreading of the Central Asian Orogenic Belt and North China Plate also contributed.