Environment Variation in North Margin of East Asian Summer Monsoon Record in Dali Lake over Past 168 Years

Abstract

Lakes close to the limit of East Asia summer monsoon (EASM) are sensitive to the climate changes, which record significant information about environmental changes and human activities. One sediment core was collected from Dali Lake in north EASM margin of China and high-resolution multi-proxies are analyzed. The constant rate of supply (CRS) model based on 137Cs and 210Pb contents is established and provides a detail history of EASM variability and environmental changes over past ~168 years. The period from ~1847 to 1900 AD was characterized by the steady values of total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC) and C/N and decrease in δ13Corg values reflected slightly enhanced EASM. The period between ~1901 to 1944 AD, δ13Corg values indicated EASM first decrease and then increase. The gradually increased TN, TP and TOC values and the decreased C/N ratios indicated the shrink of the lake area caused by the higher evaporation and autochthonous OM increased. From ~1945 to 2015 AD, the increased values in TN, TP and TOC may be mainly caused by the shrink of the lake area and the enhanced human activities, and δ13Corg values suggested a fluctuant EASM in this period. Mercury (Hg) element in Dali Lake sediments gradually increased since 1847 AD while it was constant in the interval of ~1944−1959 AD and then kept increasing, which may be caused by the increased Hg content in atmosphere from Europe and other industrial area. The EASM variability over past ~168 years showed the trends were similar to EASM records in other regions of China. Furthermore, our findings indicated that the variability of the EASM was forced by changes in oceanic-atmospheric circulation interaction.