Assessing Potential South Asian Fossil-Fuel CO2 Influence in Southeastern Tibet Using Tree-Ring Δ14C

Transboundary fossil-fuel CO2 transport may affect regional atmospheric-background estimates, yet its isotope signal along China’s southwestern border remains poorly constrained. We analyzed annual tree-ring ∆14C records from one tree at each of two sites in Linzhi, southeastern Tibet. The 2014–2023 series provides one AMS determination per site-year (10 per site; 20 in total), but no within-site tree replication. AMS measurements were evaluated alongside HYSPLIT trajectory clustering and isotope mass-balance calculations. Mean Δ14C was 12.03‰ at Linzhi 1 and 14.86‰ at Linzhi 2. Across the nine years with background data (2015–2023), Type I South Asian terrestrial trajectory frequency was not significantly correlated with background deviation at Linzhi 1 (Spearman rS = −0.18, p = 0.644) or Linzhi 2 (rS = 0.30, p = 0.437). These nonsignificant associations, based on a short record and single-tree samples, do not establish that no relationship exists. Isotope mass balance estimated a fossil-fuel CO2 contribution of approximately 2.8 ppm under the selected background and mass-balance assumptions; this is an approximate estimate, not a direct in situ measurement. HYSPLIT frequency indicates potential transport pathways, not transport intensity or the fossil-fuel CO2 concentration of air masses. Linzhi 1 may be a candidate sentinel site, but this status requires validation with longer, replicated tree-ring records and continuous atmospheric observations.