Quantitative Reconstruction of Paleoclimatic Changes in the Late Miocene Eastern Zhejiang Based on Plant Fossils

Abstract

With a series of Cenozoic climate fluctuations, the global paleoclimate shifted from a warm climate to a cold climate, causing Arctic ice caps to be formed. The Late Miocene is a critical time in this transition period, in which the climate was rapidly cooling. Plant fossils from this epoch could be used as ideal indicators for reconstructing climate change throughout this time interval. In this study, plant fossils were collected from the Shengxian Formation in Ninghai and Tiantai of eastern Zhejiang. We divided the fossiliferous strata of the Shengxian Formation into five layers according to different lithology and chronological order, which were named: JHU0, DLX, JHU1, JHUW, and JHU3 from old to new geological times, respectively. We used Leaf Margin Analysis and Climate Leaf Analysis Multivariate Program to reconstruct paleoclimatic changes in eastern Zhejiang during the Late Miocene. The paleoclimatic information of the five stages from old to new times was obtained based on the plant fossils of each layer. The mean annual temperature values in eastern Zhejiang were reconstructed using the Climate Leaf Analysis Multivariate Program and Leaf Margin Analysis at the same time. However, the former mean annual temperature values are lower than the latter values. After comparing the two sets of mean annual temperature data with previously reported values, it is found that the results obtained by Climate Leaf Analysis Multivariate Program are more reliable, whose values are 18.05 °C, 16.03 °C, 17.96 °C, 16.57 °C, and 15.52 °C from old to new times, respectively. Moreover, 11 climatic parameters were reconstructed using the Climate Leaf Analysis Multivariate Program PhysgAsia2 calibration, among which the growing season precipitation was found to be 195.54 cm, 181.25 cm, 207.99 cm, 180.7 cm, and 165.07 cm; while the difference between the coldest and warmest months was found to be 22.14 °C, 23.4 °C, 22.07 °C, 21.36 °C, and 23.37 °C. The relatively low difference between the coldest and warmest months values and the growing season precipitation values during the Late Miocene might be due to a weaker East Asian monsoon system in the Late Miocene than in modern times.