| Summary: | During January–March 2011, 29 atmospheric Δ14CO2 samples were measured along the R/V Xuelong cruise track from Zhongshan Station (69.37°S, 76.38°E; Antarctica) to Shanghai. The extent of fossil fuel contamination in the samples was evaluated by comparison with contemporary hemispheric-scale averages of Δ14CO2, together with transport analysis and consideration of the δ13CO2 levels in the samples. Generally, the Δ14CO2 levels along the route south to 40.67°S were lower than the hemispheric-scale average. Circumpolar deep water (CDW) upwelling, stratosphere–troposphere transport (STT), and regional transport associated with the Fukushima nuclear power plant (NPP) accident in Japan on 12 March 2011 were found to have influenced Δ14CO2 levels at the sampling sites. In comparison with the atmospheric Δ14CO2 level (45.7 ± 3.5‰ (1σ)) measured in the coastal region of East Antarctica, CDW upwelling caused reduction of ∼10‰ in Δ14CO2 in two cross sections: 62.0°–64.0°S along 74.0°E and 51.7°–54.0°S along 80.5°–84.0°E. Conversely, STT-enhanced Δ14CO2 was ∼7‰ (∼3‰) at Zhongshan (around 45.0°S). The linkage was supported by a certain Model-3/CMAQ simulation that indicated dispersion of radionuclides from the Fukushima NPP accident over the East Asian region, which explained the individual high Δ14CO2 (52‰) level on 29 March 2011 in Shanghai.
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