The inorganic geochemistry of a peat deposit on the eastern Qinghai-Tibetan Plateau and insights into changing atmospheric circulation in central Asia during the Holocene

• Published in: Geochimica et cosmochimica acta 2012-08, Vol.91, p.7-31
• Main Authors: Ferrat, Marion, Weiss, Dominik J., Spiro, Baruch, Large, David
• Format: Article
• Language: English
• Subjects: altitude; Assessments; Atmospheric circulation; climate change; Dust; Geochemistry; hydrochemistry; Hydrology; mineral content; Minerals; monsoon season; Peat; Rare earth elements; tracer techniques; wind
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/j.gca.2012.05.028

Peat records enable the reconstruction of changes in the global biogeochemical mineral dust cycle and the detection of variations in atmospheric circulation patterns during the Holocene. They can therefore provide a key tool for understanding the relationship between the geochemical dust cycle and past climate change. Here, we present the first detailed study of the inorganic geochemistry of a peat core collected at an altitude of 3500m from the Hongyuan peatland, on the eastern Qinghai-Tibetan Plateau, and test its potential as an archive of atmospheric dust deposition. We find that the low accumulation rates of the peat and the presence of the extensive dust sources of northern China in the vicinity of the study site lead to approximately five times higher concentrations of mineral matter compared to temperate ombrotrophic peats. A detailed geochemical assessment of the core and surface samples from local and non-local dust sources, as well as of the hydrology and hydrochemistry of the surrounding waters, suggests that external and internal post-depositional processes have not affected the record of lithogenic elements, including the rare earth elements (REE), Sc, Y and Th. Changes in Ti-normalized major element profiles, La/Yb, Y/Tb and the Eu anomaly identify seven major shifts among the dominant dust sources and therefore potential changes in atmospheric circulation patterns. Bivariate plots using the REE-based tracers La/Yb, Y/Tb, La/Th, Y/Er, Sc/La, Th/Sc and Th/ΣREE suggest that the Taklamakan desert and the Chinese loess plateau in northern China were the dominant non-local dust sources to the peat. Local dust input dominated throughout the early Holocene until 4.9kyr BP. Increased dust input from the non-local sources thereafter suggests an enhanced influence of winds associated with the East Asian winter monsoon and the Westerly jet throughout most of the late Holocene. Sharp increases in non-local dust fluxes between 3.1–2.7 and between 1.3–0.9kyr BP suggest a particular strengthening of these wind systems during these times, in agreement with the organic characteristics of the core. Our results show that the Hongyuan peat is a reliable archive to study dust deposition in central Asia and allows the identification of changes in atmospheric circulation patterns and in the larger climatic arrangements of the monsoon system in this region during the Holocene.