Records of anthropogenic plutonium isotopes in wind-blown sand deposits: Tracing global fallout in northern China's semi-arid dune fields

This study investigates plutonium (Pu) isotopes preserved in nebkhas--aeolian dunes formed by shrubs intercepting wind-blown sands to reconstruct environmental changes in the semi-arid Mu Us dune field, northern China. Analysis results of two nebkha profiles reveal that the ²⁴⁰Pu/²³⁹Pu atom ratios consistently approximate 0.18, indicating a dominant source from global fallout, with no significant local contributions from the Lop Nor or Semipalatinsk nuclear tests or the Chernobyl accident. Total Pu inventories (308 ± 3 Bq/m² and 402 ± 3 Bq/m²) highly exceed the direct atmospheric fallout value (66 Bq/m²), suggesting accumulation of both distant and proximal Pu-bearing sediments transported by wind. Depth distributions of ^239+240Pu activities (0.005–0.387 mBq/g) show a single-peak corresponding to 1963 and an onset around 1952, consistent with previous ¹³⁷Cs and optically stimulated luminescence (OSL) dating results, validating Pu isotopes as reliable chronostratigraphic markers. Sediment deposition rates have declined over the past 20 years compared to the 1960s–1970s, likely due to reduced sandstorm activity and wind speed, potentially linked to regional afforestation and land-use changes. This study demonstrates the widespread nature of global Pu contamination—even in remote deserts, and highlights nebkhas as a novel geological archive for reconstructing atmospheric deposition and environmental changes. By providing a direct record of Pu deposition, this work advances understanding of Pu sources, transport, and behavior in arid regions, with broader implications for using radionuclides to study aeolian processes and environmental evolution.