Climate control of sulfate influx to Lake Hovsgol, northwest Mongolia, during the last glacial-postglacial transition: Constraints from sulfur geochemistry

摘要

Changes in sulfur cycles in Lake Hovsgol (northwest Mongolia) are discussed on the basis of total organic carbon (TOC), total sulfur (TS) concentrations and stable sulfur isotope ratios (δ~(34)S) in two sediment cores (X104 and X106) covering the last glacial to the present. Correlation plots of TOC and TS (C-S plots) of the sediment cores indicate dissolved sulfate enrichment in sediment pore water and high sulfate reducing bacteria (SRB) activity during the climate transition from the last glacial to postglacial period (LG-PG transition, from ca. 21 to 11.6calka BP). In addition, positive shifts of δ~(34)S values (from +3.7‰ to +32.6‰) were observed during the LG-PG transition. These results suggest a large influx of ~(34)S-rich dissolved sulfate into the lake during this period. The ~(34)S-rich dissolved sulfate may have accumulated on the shore (wetlands and marshes) of Lake Hovsgol during the last glacial period. Owing to the increase in atmospheric precipitation and lake level rise during the LG-PG transition, the ~(34)S-rich dissolved sulfate may have been supplied from the shore to the lake. Increased sulfate influx during the LG-PG transition has also been observed in a Lake Baikal sediment core. Our new sulfur geochemical data shows past-environmental changes, particularly moisture changes, within continental Asia during the climate transition.