Vegetation Response to the Subtropical Climate Changes before and during the Last Glacial Period in South China
Abstract:
This paper provided an insight into regional palaeovegetation and palaeoclimatic changes over the last 50000 years in subtropical China based on high-resolution pollen records with well constrained chronology of the SZY mountain peatbog from eastern subtropical China. Pollen records confirmed that the subtropical vegetation altered between evergreen and deciduous forest during the Last Glacial-Interglacial cycles in South China.Middle and late Marine Oxygen Isotope (MIS) 3 stages (ca. 50-30 cal ka BP), mainly the subtropical evergreen broadleaf trees with some temperate deciduous broadleaf trees, which coupled the strengthening of summer insolation, suggests a warm and humid subtropical climate. A cool and dry climate condition during during ca. 30-24 cal ka BP, which was coeval with the substantial alternation of vegetation recorded in SZY. During this period, a warm temperate deciduous forest was inferred by the predominant percentage of deciduous trees, mainly Fagus and Alnus, indicating a spatial transfer of the zonal vegetation of subtropical mixed deciduous from north to south during the global coldest period. During the Last Glacial Maximum (LGM, ca. 24-16 cal ka BP), no significant increase in the herbs (less than 10%), but the abundant emergence of alpine shrub Ericaceae (Rhododendron), indicated a deciduous forest rather than diffusion of grassland. Meanwhile, in comparison with modern beech forest of Mountain Fanjingshan, the high content of Fagus suggested 5.5°C lower in temperature, and less 540mm in precipitation during this period than nowadays. Interesting, both pollen records portrayed a coldest and driest climate condition during this period which correlated to the contemporaneous oxygen isotope data (δ18O/δ16O) from Hulu and Dongge caves and Greenland ice core, as well as consistent with the lowest summer insolation of 65°N. This indicated that the reginal vegetation change correlated to the solar insolation of Northern Hemisphere and intensity of Asian monsoon evoked by the simultaneous orbital parameter variability.