Holocene monsoonal climate changes tracked by multiproxy approach from a lacustrine sediment core of the subalpine Retreat Lake in Taiwan

摘要

The aim of this study is to improve the understanding of environmental changes and the linkages with the dynamics of the East Asian Monsoon (EAM) during the Holocene in the western North Pacific. We analyzed the pollen, diatom, and weak acid-leachable fractions associated with extracted organic compounds of lacustrine sediments retrieved from the subalpine Retreat Lake in northwestern Taiwan. During the early Holocene (10,100-8600 cal BP), cool climate was inferred by the dominance of grass pollen with poor preservation of diatom valves in the record. At that time, derived biomarkers were also dominated by long-chain alkanes originating from herbs. The following Holocene Optimum (8600-6400 cal BP) was characterized by a remarkable increase of tree pollen, indicating the warmer and humid climate and a stronger summer EAM. The possible enhanced monsoon-driven precipitation resulted in higher contents of total organic carbon buried in sediments. However, the climate and precipitation of the alpine area in Taiwan might have been unstable. The high variability of wetland pollen and diatom abundance reveals weak periods of EAM during the late Holocene Optimum (6400-4500 cal BP). The hiatus in the deposit during 4500-2100 cal BP suggests the continuously decline of the EAM. During the last 2100 years, dominated wetland plant pollen accompanying stable diatom abundance indicated humid climatic conditions and a stable increase of the EAM. The climatic condition of study area was similar with modern situation during this late Holocene.