Climatic and environmental changes in the Baidunzi wetland, Northwest China, over the last 800 years inferred from glycerol dialkyl glycerol tetraethers

Abstract

To help understand the temperature and moisture variations in the semiarid and semi-humid regions of China that lie a transitional zone between the Westerlies and the East Asian monsoon, reconstruction of the regional climatic changes over the last millennium is useful. However, high-resolution time-series data related to the histories of climatic changes in these areas are limited. Therefore, this multiproxy analysis of a sediment core from the Baidunzi wetland, northwest China, was conducted using grain size, total organic carbon, glycerol dialkyl glycerol tetraethers (GDGTs), and molecular biomarkers. The results show that GDGTs can reliably reconstruct paleoclimate changes recorded in sediments in salt marsh environments. The climate and environment history of the past 800 years can be divided into the three stages: the end of the dry Medieval Warm Period (MWP) (1278–1366 CE), a humid Little Ice Age (LIA) (1366–1896 CE), and the humid Current Warm Period (CWP) (1896–1999 CE). The Baidunzi setting during the end of the MWP was a warm and dry wetland with high salinity, low water levels, and emersed aquatic plants, and the depositional environment transitioned from fluvial facies to shore lake facies. In contrast, the local climate during the LIA was cold and humid, and the era was characterized by the appearance of vascular flora and two short-term flooding events, that caused a rise in water levels. The lowest temperatures and highest salinities of the period were correlated, which was likely caused by seasonal freeze-thaw cycles. During the CWP, the local climate was warm and humid, with a higher water level than during the LIA, and emersed plants again developed in shallow lagoon facies. Generally, salinity was positively correlated with temperature, except for freezing and thawing salinization resulting from episodes of extremely low temperatures. The warm–dry to cold–humid climate changes of the area were like those of arid Central Asia, which indicates that the Baidunzi region was affected mainly by the Westerlies and was impacted by southward intrusions of that system. The area was also affected by the North Atlantic Oscillation and experienced diminished evaporation during periods of cold climate.