Environmental changes during the past 13500 cal. a BP deduced from lacustrine sediment records of Lake Qinghai,China

A 475-cm long sediment core (QH-2005) from Lake Qinghai was used to carry out multi-proxy analysis of δ¹⁸O and body length of ostracod valves and redness and grain size of sediments, in order to reconstruct environmental changes during the past 13500 cal. a BP. The age model was based on 6 ¹⁴C dates for bulk orgnic carbon (BOC) and 2 ¹⁴C dates for lignin. The lignin ¹⁴C dates are apparently younger than the corresponding layers’ BOC ¹⁴C dates, indicating that the reservoir age varied from 728 to 1222 a since the Late Glacial and from 2390 to 2490 a immediately before the pre-bomb era. Hence, the ¹⁴C age model for Core QH-2005 was corrected by the changing reservoir age. Ostracod δ¹⁸O values were primarily related to dilution and evaporative enrichment of the lake water. The reconstructed salinity based on ostracod body length coincides well with ostracod δ¹⁸O values. High redness and mean grain size (MZ) values indicate increased riverine supply to Lake Qinghai associated with increasing monsoon rainfall. Multi-proxy results show that climate during 13500–10900 cal. a BP was relatively cold and dry with frequent short-term fluctuations; a warm and wet climate began at about 10900 cal. a BP and culminated around 6500 cal. a BP as a result of monsoon strengthening; the climate became cold and dry afterwards and has remained relatively stable since 3400 cal. a BP. Our data also reveal short-term (millennial/centennial timescales) climatic fluctuations including: Younger Dryas events, ice-rafting events 8 and 1 (by ∼11000 cal. a BP and ∼1600 cal. a BP respectively), 8200 cal. a BP cold event, Little Ice Age and the Medieval Warm Period.