A study on the AMS 14C chronology of late pleistocene lacustrine sediments and related proxies of organic carbon in northwest China

Abstract

Lake sediment is an effective archive containing information about past climate change, and accurately determining the deposition age of lake sediment is crucial to investigating past environmental variation. To elucidate the historical climate change modes in the northeastern Qinghai-Tibet Plateau (QTP), the sedimentary profile of a paleolake deposit on the western Qilian Mountains was examined. However, the profile exhibits notable age reversals due to the reservoir effect, as determined by analyzing 46 accelerator mass spectrometry carbon-14 (AMS 14C) dates of bulk organic matter. We therefore conduct a comprehensive examination of carbon-related indicators, including total organic carbon content (TOC), carbon/nitrogen ratio (C/N), and organic carbon isotope (δ13C). And combining with the changing patterns of them in topsoil samples around the northeastern QTP, this study determines that the formation age of the lacustrine sedimentary profile is 16278∼20662 cal a BP, corresponding to the Last Glacial Maximum (LGM) and the last deglaciation. The results of sedimentary facies identified by grain size and carbonate oxygen isotope (δ18O) suggest that this profile was developed near the paleolake shoreline, resulting from a transition in lake environment from deep to shallow during the LGM and the last deglaciation. The corresponding reconstructed lake area and precipitation are 642 km2 and 238 mm, respectively, indicating a wet and cold climate mode in the northeastern QTP during this time. Furthermore, the wetter state in the northeastern QTP can be attributed to a combination of reduced evaporation caused by colder conditions and enhanced precipitation driven by stronger southerly westerly jet streams.