Temperature Variations and Possible Forcing Mechanisms over the Past 300 Years Recorded at Lake Chaonaqiu in the Western Loess Plateau

Understanding the synchronicity of and discrepancy among temperature variations on the western Loess Plateau (WLP), China, is critical for establishing the drivers of regional temperature variability. Here we present an authigenic carbonate-content timeseries spanning the last 300 years from sediments collected from Lake Chaonaqiu in the Liupan Mountains, WLP, as a decadal-scale record of temperature. Our results reveal six periods of relatively low temperature, during the intervals AD 1743–1750, 1770–1780, 1792–1803, 1834–1898, 1930–1946, and 1970–1995, and three periods of relatively high temperature during 1813–1822, 1910–1928, and since 2000. These findings are consistent with tree-ring datasets from the WLP and correlate well with extreme cold and warm events documented in historical literature. Our temperature reconstruction is also potentially representative of large-scale climate patterns over northern China and more broadly over the Northern Hemisphere. The Pacific Decadal Oscillation (PDO) might be the dominant factor affecting temperature variations over the WLP on decadal timescales.

HUMAN RESPONSES TO CLIMATE CHANGE IN THE LATE PREHISTORIC WESTERN LOESS PLATEAU, NORTHWEST CHINA

ABSTRACTIn order to assess late prehistoric human responses to climate change in the Western Loess Plateau (WLP), we investigated 13,567 charred plant seeds and 19 radiocarbon (14C) dates obtained from 41 late prehistoric sites in the upper Wei River valley. Based on these new dating results as well as their cultural attributes, these sites could be confidently divided into four chronological phases (Phase 1: Late Yangshao and Majiayao culture; Phase 2: Qijia culture; Phases 3 and 4: Siwa culture) but a significant gap was identified at ca. 3600–3000 cal yr BP in this region. Comparison of this interval to high-resolution paleoclimate records from Tianchi Lake suggests it could be attributed to the dramatic drop in temperature at this time. Accordingly, archaeobotanical evidence with a refined chronology shows the adoption of cold-tolerant subsistence cereal grains such as barley on the NETP (Northeast Tibetan Plateau). Drawing from various lines of knowledge (chronology, palaeoclimate, archaeobotany, and archaeology), it is reasonable to conclude that, even when confronting a similar magnitude of climate change, local human societies could vary tremendously. Different subsistence strategies were brought in by the trans-Eurasia culture exchange of prehistoric times.

Characterization of DOC and CDOM and their relationship in turbid waters of a high-altitude area on the western Loess Plateau, China

Dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) in rivers and reservoirs on the western Loess Plateau, which is an area of severe soil erosion, were investigated in September 2017 to analyze the CDOM characteristics and composition, DOC distribution and influence of environmental factors on these parameters. Great differences of water parameters were exhibited between different groups based on the analysis of variance (p < 0.01). The results indicated that rivers exhibited higher DOC concentrations (mean: 3.70 mg/L) than reservoir waters (mean: 2.04 mg/L). Artificial and agricultural lands exert a large influence on DOC concentrations, which verifies the hypothesis that intense anthropogenic activity results in high DOC concentrations. The CDOM absorption at 350 nm [aCDOM(350)] of tributary water samples was 2.73 m−1, which was higher than that in the Yellow River (1.71 m−1) and reservoir waters (1.33 m−1). The effects of DOC, TC and turbulence (Tur) on CDOM are positive and significant (p < 0.05) according to the multiple linear regressions. An analysis of the optical characteristics of CDOM indicated that waters on the Loess Plateau contained abundant humic acid and higher levels of allochthonous DOM with a higher molecular weight (MW) based on the spectral slopes (S) and specific UV absorbance (SUVA254) values.