Abstract
The climate history of the source area of the Yellow River (SAYR) is important to understanding the pacing and processes of climate evolution on the northeastern Qinghai-Tibetan Plateau (QTP). To date, results of research in this alpine region are limited. Herein, we provide a first lacustrine record from the largest freshwater lake on the QTP that archives climatic and environmental variations in the SAYR for the last 1500 yr. The bulk organic carbon and nitrogen isotopic compositions (δ 13 C org and δ 15 N tot ) are combined with atomic carbon/nitrogen (C/N) ratios to indicate that the sedimentary organic matter in Lake Ngoring originates from autochthonous algae and that the terrestrial input is minor. Comparison of the record of organic carbon isotope values with published records of ice accumulation rate (IAR) of Dunde and Guliya glaciers from the northern QTP, the total solar irradiance (TSI), δ 18 O variations in the Greenland ice core and biologically sensitive indicators (C 37:4 alkenone, crenarchaeol and bGDGT concentrations) from Lake Qinghai indicate that variations in the δ 13 C org values in Lake Ngoring sediments reflect lake level fluctuations that are associated with variations in the amount of precipitation and glacier meltwater on the SAYR. High lake level phases indicated by positive shifts of δ 13 C org values correspond to higher values of the North Atlantic Oscillation Index (NAOI) and lower values of the Southern Oscillation Index (SOI pr ). This relation suggests that the hydrologic history in the SAYR is linked to changes in the Indian monsoon and the Westerlies and that both air masses delivered more moisture to the SAYR during high TSI stages. In contrast, variations in the δ 15 N tot values resemble the multiple paleoclimate proxy records obtained from ice cores, peat sequences, lake sediments, and integrated paleo-records from other QTP sites, suggesting that the δ 15 N tot values archived in Lake Ngoring sediments provide a history of past lake-water temperature variations that is consistent with the variation history of the temperature-dependent parameters from regional paleo-climatic studies. Global climatic events including the Dark Ages Cold Period, the Medieval Climate Anomaly, the Little Ice Age and Modern Warming in 20th century could be clearly observed in the δ 15 N tot variations. In general, the δ 13 C org and δ 15 N tot values in Lake Ngoring sediments appear to be useful indicators for paleo-environment and paleo-climate reconstructions in alpine oligotrophic freshwater lakes such as this one. • The first paleolimnological record of a modern lake in the SAYR is reported. • The δ 13 C org proxy in Lake Ngoring sediments can reflect lake level fluctuations. • The δ 15 N tot is a good indicator for variations in summer lake-water temperatures. • Monsoon and Westerlies bring more precipitation to the SAYR under high insolation.
Accepted Version (
Free)
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call