Precipitation variations around ∼4.2 ka BP in the Luoyang Basin: A pollen-based quantitative reconstruction

Abstract

Luoyang Basin in the Central Plains of China is of great significant in human history because it witnessed a successful transition from Henan Longshan Culture to Erlitou Culture around ∼4.2 ka BP, enabling Chinese civilization to continue uninterruptedly. To explore the climatic and environmental conditions in the Luoyang Basin around 4.2 ka BP, we analyzed pollen assemblages from the HZ-1 section with a chronological framework established by 17 integrated AMS ¹⁴C dates, and reconstructed the histories of bioclimate evolution and precipitation change. Our reconstruction indicates that the precipitation was relatively low and the regional vegetation landscape was dominated by grassland from ∼4990 to ∼4330 cal. yr BP. In the subsequent period from ∼4330 to ∼4155 cal. yr BP, both precipitation and wetland water level reached their highest values accompanied with rather dense forests. In the following period from ∼4155 to ∼3995 cal. yr BP, precipitation became relatively low, and the regional vegetation landscape was dominated by grassland. Between approximately 3995 and 3890 cal. yr BP, the regional climate in the Luoyang Basin underwent a gradual transition—from a short-lived period of slightly enhanced precipitation, characterized by forest expansion and grassland contraction, to a subsequent dry phase marked by the maximum expansion of grassland vegetation. Further analysis reveals that the precipitation variations in the Luoyang Basin during ∼4990 and ∼ 3890 cal. yr BP exhibited an inverse relationship with the sea surface temperature (SST) variations of the Western Pacific warm pool and the associated ENSO-like phases. It should be particularly noted that the precipitation was relatively low around ∼4.2 ka BP in Luoyang Basin. But, if the aridification occurred around ∼4.2 ka BP is examined in the context of a large time window of the period from 5000 to 3600 cal. yr BP, the period around ∼4.2 ka BP was not the driest time within the examined window. This climate condition likely provided an advantageous background for the flourishing of the late Henan Longshan culture in the Luoyang Basin.