Molecular records of continental air temperature and monsoon precipitation variability in East Asia spanning the past 130,000 years

摘要

Our current understanding of past changes in East Asian summer monsoon (EASM) precipitation intensity derives from several loessepaleosol sequences and oxygen isotope (δ~(18)O) records of well-dated stalagmites. Although temperature is generally presumed to have had minimal impact on EASM records, past air temperature dynamics over East Asia are, so far, relatively poorly understood, mainly due to the lack of tools to reconstruct continental paleotemperatures. Here we report a high-resolution record of East Asian air temperature over the past 130,000 years, based on soil bacterial lipid signatures preserved in a loessepaleosol sequence from the Mangshan loess plateau in China. We find that maximum local insolation is the main driver of air temperature, although greenhouse gas concentrations and southern hemisphere climate may influence temperature at times when insolation is weak, causing a decoupling with EASM precipitation intensity. Direct comparison of our temperature record with precipitation-induced changes in past soil pH, derived from the same suite of lipids confirms this decoupling. Subsequent cross-spectral analysis of the two molecular proxy records reveals that variations in monsoon precipitation consistently lag those in air temperature throughout the whole record at the dominant precession band. The length of this lag is variable however, and increases as glaciation develops. This observation is consistent with an increasing influence of northern hemisphere ice sheets on the modulation of EASM response to insolation forcing during ice ages.