Atmospheric Iodine (127I and 129I) Record in Spruce Tree Rings in the Northeast Qinghai-Tibet Plateau.

Atmospheric iodine isotopes have a significant impact on climate change and human health. However, the sources, transport pathways, and transfer processes of atmospheric iodine are still not well understood. Tree rings of spruce collected from the east edge of the Qinghai-Tibet Plateau were analyzed for iodine isotopes (127I and 129I). The results show that the levels and temporal variation of atmospheric iodine were well recorded in the spruce tree rings, and stable iodine concentrations in tree rings increased three times from 1960 to 2015, reflecting the increased releases of iodine to the atmosphere in the past decades due to human activities. The anthropogenic 129I in the tree rings represents the record of the human nuclear activities in the past 55 years. The sources and the transport pathways of radioactive substances could be extracted from the 129I recorded in the tree rings in the Qinghai-Tibet region. They are fallout from the global nuclear weapons tests in 1961-1962, releases of the Chinese atmospheric nuclear weapons tests in 1964-1980 transported through the tropospheric northwest wind, the releases of the Chernobyl accident dispersed through westerlies, and the continuous air releases before 1997 and the re-emission of marine discharges from the European nuclear fuel reprocessing plants transported through westerlies.