(129)I and its species in the East China Sea: level, distribution, sources and tracing water masses exchange and movement

Anthropogenic (129)I as a long-lived radioisotope of iodine has been considered as an ideal oceanographic tracer due to its high residence time and conservative property in the ocean. Surface water samples collected from the East China Sea (ECS) in August 2013 were analyzed for (129)I, (127)I and their inorganic chemical species in the first time. The measured (129)I/(127)I ratio is 1–3 orders of magnitude higher than the pre-nuclear level, indicating its dominantly anthropogenic sources. Relatively high (129)I levels were observed in the Yangtze River and its estuary, as well as in the southern Yellow Sea, and (129)I level in seawater declines towards the ECS shelf. In the open sea, (129)I and (127)I in surface water exists mainly as iodate, while in Yangtze River estuary and some locations, iodide is dominated. The results indicate that the Fukushima nuclear accident has no detectable effects in the ECS until August 2013. The obtained results are used for investigation of interaction of various water masses and water circulation in the ECS, as well as the marine environment in this region. Meanwhile this work provides essential data for evaluation of the possible influence of the increasing NPPs along the coast of the ECS in the future.