Fig. 1: Continental-scale impact of bomb ¹⁴C.

The impact of bomb ¹⁴C from Lop Nor: ΔΔ¹⁴C values at different Chinese background stations relative to either latitudinal zone compilations (a) or European atmospheric backgrounds (b). Specifically, black squares indicate Huangzhong (~1300 km from Lop Nor)²⁵; pruple diamonds represent Mingyin (~2000km)¹⁴; red circles correspond to Shangdianzi (~2400 km)¹¹; blue upward triangles denote Nanling (~3000 km, this study); and green downward triangles indicate Dailing (~3200 km)¹². Vertical bars indicate the annual yields of nuclear bomb tests²², with orange representing fission tests and green representing fusion tests conducted at the Semipalatinsk (left light blue shaded region) and Lop Nor (right lilac shaded region) test sites. Solid lines represent linear trends in ΔΔ¹⁴C for Huangzhong (black) and Shangdianzi (red), fitted from 1965 onward. The horizontal gray shaded band denotes a ± 10‰ range in ΔΔ¹⁴C, with the central gray solid line indicating 0‰. Vertical dashed lines mark the year when each fitted trend line (black for Huangzhong, red for Shangdianzi) crosses the +10‰ threshold. The latitudinal compilation data includes NH-3, NH-2, and NH-1 data from Hua et al.¹⁰. The European backgrounds include Vermunt data (1959–1983) and the Jungfraujoch data (JFJ, 1986–2015)^23,24. All the Chinese stations use tree-ring samples, with comparisons conducted during the tree-ring growth periods: March–October at Nanling and Mingyin, May–August at Huangzhong, and May–September at Shangdianzi and Dailing. c The impact of bomb ¹⁴C from Novaya Zemlya: ΔΔ¹⁴C at different European background stations relative to either latitudinal zone compilations or European atmospheric backgrounds. Black squares represent Fruholmen (air, ~1100 km from Novaya Zemlya)²⁸; red circles denote Trondheim (air, ~2100 km)²⁸; blue upward triangles show Trøndelag (tree-ring, ~2100 km)³⁷; green downward triangles represent Lindesnes (air, ~2650 km)²⁸; purple diamonds indicate Eastern Jutland (tree-ring, ~2700 km)³⁸; and goldenrod left-pointing triangles denote Niepołomice (tree-ring, ~3100 km)³⁶, each compared to the corresponding latitudinal zone compilations. Relative to the Vermunt/JFJ European background: cyan circles represent Fruholmen; dark brown hexagons, Trondheim; dark khaki stars, Trøndelag; orange pentagons, Lindesnes; cronflower blue diamonds, Eastern Jutland; and green right-pointing triangles, Niepołomice. Annual air sampling data are shown as means with standard error bars, while tree-ring data are based on species-specific growing seasons (May–August for Trøndelag and Niepołomice, and June–August for latewood in Eastern Jutland). Vertical bars indicate fission (orange) and fusion (green) bomb test yields at Novaya Zemlya (light blue shaded region)²². Cyan solid line represents linear fit of Fruholmen ΔΔ¹⁴C (relative to Vermunt/JFJ). Vertical gray dashed lines mark the year when the fitted trend line crosses the +10‰ threshold. Gray shading and other annotations follow the conventions of (a).