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 δ 18 O 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 δ 18 O 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 δ 18 O trend independent of bedrock lithology, indicating the values of regionally homogenized dust components. The δ 18 O 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 δ 18 O 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. • The quartz content and δ 18 O in Eurasian steppe surface soils were measured. • Coarse quartz reflects local bedrock; fine quartz reveals regional dust signals. • Three distinct steppe dust end-members were defined by fine quartz δ 18 O. • Mixing of steppe and desert sources explains aerosol quartz δ 18 O in East Asia. • Steppe end-members contribute significantly to dust found in Japan and Korea.