Aeolian dust provenance across the Eurasian Asian steppe from grain-size dependent quartz δ18O in surface soils

Aeolian dust from the Eurasian interior significantly impacts climate, ecosystems, and soil formation, but the role of the Eurasian steppe as a dust source remains uncertain. We present grain-size-sorted quartz δ18O values in topsoil at 24 sites across the Eurasian steppe, from Ukraine and Kazakhstan to Xinjiang, Mongolia, and Inner Mongolia. Quartz fractions were separated from four fine soil classes (<2, 2–10, 10–20, 20–50 μm) at all sites, with additional coarse classes (50–200, 200–500, 500–2000 μm) at lithologically distinct locations. Coarse quartz grains in the Mongolian–Inner Mongolian Highlands show a relatively low and narrow δ18O range (7.6–9.0‰) over plutonic bedrocks and more variable higher values (8.9–17.8‰) over sedimentary bedrocks, indicating dependence on local lithology. In contrast, fine quartz grains (2–50 μm) exhibit a δ18O trend independent of bedrock lithology, indicating the values of regionally homogenized dust components. The δ18O values of the finest quartz fractions, exhibiting the highest at each site, decreased from the Western Steppe Plain (19.0 ± 0.8‰) through the Central Upland Steppe (18.0 ± 0.7‰) to the Mongolian–Inner Mongolian Highlands (13.8 ± 1.0‰), reflecting the distal dust input. Comparison with published quartz δ18O values for Mongolian and Northern China deserts and East Asian soils suggests that variable mixtures of these steppe end-members with Gobi and northern Chinese desert sources, along different atmospheric pathways of the East Asian winter monsoon, mid-latitude westerlies, and subtropical jets, can explain the aerosol-sized quartz in Japan and Korea.