Decoupling between circulation pattern and dust path since the last glacial in the Songnen Plain, NE China: Insights from quantitative provenance reconstruction of the Harbin dust sediments

Abstract

Knowledge of the provenance of dust deposits in the easternmost margin of the Eurasian loess belt is essential for understanding the connection between circulation patterns and dust source-to-sink route in the Songnen Plain, NE China. Here, a total of 131 samples, from the loess-paleosol sequence since the last glacial (20) and the modern dust-storm sediments (7) in Harbin area together with potential dust source areas (104), were collected for elemental geochemical analysis to quantify the source apportionment and compare the performance of the Frequentist and Bayesian models. Fourteen geochemical properties (V, Zn, Ga, Sr, Mo, Ba, Pb, Y/Ta, MREE_N/MREE_N*, Th/Sc, Th/U, La/Sc, Zr/Hf and Co/Th) were selected as the optimum composite fingerprint after a range test, non-parametric Kruskal-Wallis H-test and stepwise discriminant function analysis. Based on both the models, the source contributions to the loess sequence and dust-storm deposits were in the following order: southwestern Songnen Sandy Land (57–95%, 49–97%), Horqin Sandy Land and Onqin Daga Sandy Land (2–43%, 0–31%), northwestern Songnen Sandy Land (0–21%, 0–20%) and Hulun Buir Sandy Land (0%, 0–8%). Following the goodness-of-fit and virtual mixtures, combined with root mean square error and mean absolute error, we argue that the Frequentist model is slightly more accurate than the Bayesian model in quantifying dust sources. The sandy lands figure importantly in acting as a dust transfer station. The comparison between the loess sequence and modern dust-storm source reconstructions reveals a decoupling between circulation pattern (northwesterly wind domination in the glacial) and dust path (dominantly southwestern direction), and small areas, high vegetation coverage and topographical barrier are considered to be the main reasons for the significantly limited dust emission in the NW-direction source area. Finally, the study highlights that improving land management practices in the SW-direction but not NW-direction sandy land may help ameliorate the effects of the Harbin dust pollution.