Records of iodine isotopes (I-129, I-127) in the Barkol peat bog from northwest China and their sources, transport and preservation

The research on geochemical behaviors of iodine is significant for deep understanding of the source and distribution of iodine on the earth. However, as one of the most important sources, the ocean emissions and relative transport pathways of iodine, as well as the preservation after deposition are still not well known, especially in the arid areas of central Asia. A peat sediment core collected nearby Barkol Lake from northwest China was analyzed for iodine isotopes (I-127 and I-129). The observed high I-127 concentration in the top 2 cm indicated a significant accumulation of iodine in the surface oxic conditions due to the continuous sources of incompletely decomposed organic matter. Dissociation of iodine into pore waters occurred once the anoxic conditions established beneath the surface by a serial reduction reaction during the degradation of organic matter. The temporal variation of anthropogenic I-129 in the peat sediment recorded its sources and transport pathways. Besides the global fallout I-129 during late 1950s and early 1960s, the significantly increased air releases from the European nuclear fuel reprocessing plants during 1975-1997 and the increased marine discharges since 1990s contributed the major portion of I-129 in the peat core. The major transport pathway of I-129 from the Europe was through Westerlies following the re-emission of the marine discharged I-129 to the atmosphere, indicating a clearly ocean emitted iodine in the concerned central Asia. (C) 2021 Elsevier Ltd. All rights reserved