Reconstructing atmospheric I deposition over 170 years with the varved sediment in the Sihailongwan Maar Lake, northeast China.

Long-term deposition of atmospheric radioactive iodine-129 (I) is important for assessing the impact of human nuclear activities (HNAs), but still not well understood in East Asia. In this study, we quantitatively reconstructed the deposition history of airborne I using varved sediment from Sihailongwan Maar Lake (SHLW) in northeast China. Our results revealed significant increases in I concentrations and I/I atomic ratios since the 1950s, indicating the influence of HNAs on the environment and marking the onset of the Anthropocene. The variation of I in the investigated site can be primarily attributed to the global fallout of ANWT as well as nuclear fuel reprocessing in Europe, Russia and the USA. Notably, neither the Chernobyl nor the Fukushima nuclear accidents have had any discernable impact on the SHLW Lake. Over the past 170 years (1846-2021), the reconstructed fluxes indicate a rapid increase in I deposition from the early 1950s until the 1970s followed by dramatic changes thereafter. The measured I fluxes range between (1.26-349) × 10 atoms m yr in the SHLW Lake, which are consistent with similar latitude zones across East Asia, but differ significantly from those observed in high-elevation glaciers within the Northern Hemisphere due to prevailing atmospheric circulation patterns. The total I inventory was calculated to be 11.9 × 10 atoms m, with natural and anthropogenic I accounting for 2.86 % and 97.1 %, respectively, suggesting an overwhelming artificial contribution. The reconstructed fluxes and inventory of atmospheric I deposition quantitatively distinguish the natural and artificial contributions, and provide a novel insight into the historical environmental impact of HNAs in East Asia and the characteristics of the Anthropocene.