Tree-ring Δ14C time series from 1948 to 2018 at a regional background site, China: Influences of atmospheric nuclear weapons tests and fossil fuel emissions

Abstract Δ14C values were measured from tree-rings (1948–2018) of Pinus tabuliformis Carr. that grew at the Shangdianzi (SDZ) regional background site in China. The objectives of this study are to establish a record of atmospheric Δ14C, and to evaluate the influences of Chinese atmospheric nuclear tests and fossil carbon emissions on atmospheric Δ14C variations. The SDZ tree-ring Δ14C values are negative before 1956, and increase dramatically in response to global atmospheric nuclear tests, with a peak value of 844.0 ± 4.2‰ in 1964. After the Partial Test Ban Treaty in 1963, the Δ14C values at SDZ decrease exponentially during 1964–2018. The half-life of the Δ14C decrease was protracted by approximately 2.7 yr during 1964–1984, due to Chinese atmospheric nuclear tests as well as Chinese forests as a carbon source during that period. Massive fossil carbon emissions in China lead to the SDZ decrease rate that is about 1.8‰ yr−1 faster than that for the Northern Hemisphere background region during 2000–2010. SDZ Δ14C since 2000 show strong negative correlations with fossil carbon emissions from the Beijing-Tianjin-Hebei (BTH) region (r2 = 0.954) and China (r2 = 0.950), and a 1‰ decrease in SDZ Δ14C indicates an increase of 2.3 ± 0.2 Mt C and 23.3 ± 1.7 Mt C fossil carbon emissions from the BTH region and China, respectively.