The 14C reservoir effects and paleoclimatic reconstructions in Lake Qinghai, northeastern Tibet

Lake Qinghai located in the northeastern Tibetan Plateau provides ideal Holocene paleoclimatic records to explore the climatic and environmental changes controlled by the Asian summer monsoon and the westerlies. Radiocarbon (C-14) is commonly used to constrain the sediment chronology, however, the C-14 reservoir effects in Lake Qinghai are still under debate. Here, we firstly carry out multiple C-14 dating (plant remains, authigenic carbonate and bulk organic matter) and multi-proxy analyses (mineralogy, major elements, total organic carbon (TOC), total nitrogen (TN), total inorganic carbon (TIC), carbon isotopic composition of bulk organic matter (delta C-13(org)) and inorganic matter (delta C-13(inorg)), and oxygen isotopic composition of inorganic matter (delta C-13(inorg))) on a 3.5 m-long core (QH1) in Lake Qinghai to illustrate the C-14 reservoir effects and paleoclimate changes during the last 6000 yr. The C-14 age-depth linear regressions of plant remains, authigenic carbonate and bulk organic matter present similar sediment accumulation rates of 17.59 +/- 0.21, 17.74 +/- 0.17 and 17.07 +/- 0.22 yr cm(-1) but different reservoir effects of 910 +/- 41, 1661 +/- 35 and 1031 +/- 49 yr, respectively. This evidence suggests that the new C-14 age-depth model used in this study is valid to estimate sediment accumulation rate and to distinguish different reservoir effects between multiple dating materials. Combing with the geochemical proxies, the paleoclimate fluctuated with a light drying trend from similar to 6,000 to similar to 4,000 cal yr BP. After the abrupt shift at similar to 4,000 cal yr BP, the paleoclimate became colder and drier. Since the Mid-Holocene millennial-timescale warm and humid periods occurred at similar to 5,900, similar to 4,800, similar to 4,000, similar to 1,800, similar to 1,100, similar to 600 and similar to 100 cal yr BP and relative droughts occurred at similar to 5,200, similar to 4,600, 4,000-2,000, similar to 1,500, similar to 900 and similar to 300 cal yr BP. These features can be attributed to the rapid strengthening and weakening of the summer monsoon circulation in the northeastern Tibetan Plateau.