Dian
Description
Continuous lacustrine records of the Indian Summer Monsoon that span the Pleistocene-Holocene transition to the present are relatively rare, yet crucial to providing context to future changes in hydroclimate. We summarize here a 17,000 year continuous multi-proxy record of hydroclimate and primary productivity from Lake Dian in the central Yunnan Province of China. Analysis of sediment composition, opal, carbon to nitrogen ratios, carbon and nitrogen stable isotope ratios, and magnetic susceptibility (MS) are used to identify four distinct lithologic units in the sediment record. Unit I sediments from 17,000 to 11,500 years BP are characterized by high MS and uniformly low organic and opal content interupted by a decrease in MS during the Bølling-Allerød indicating the influence of the North Atlantic on the Indian Monsoon. We interpret this to reflect cold, dry, and windy conditions during the transition out of the Last Glacial Maximum. Unit II from 11,500 to 5,000 years BP is marked by a pronounced decrease in MS, increase in opal, and decrease in 13Corg of organic carbon driven by peak warmth and wet conditions increasing productivity. Unit III from 5,000 to 1,800 years BP shows further increases in primary productivity, marked by lower carbon to nitrogen ratios and carbonate precipitation, possibly driven by a drop in lake level. A period of aridity is in wide agreement with a number of other records from the region. Unit IV from 1,800 years BP to present is dominated by anthropogenic impacts and hallmark signs of catchment soil erosion and cultural eutrophication. Our interpretations of the Dian sediment record agree well with previous palynological work and add a new dimension to our understanding of lake hydrology and productivity over the past 17,000 years.