Iodine-129 enrichment in sediment of the Baltic Sea

Sediments are an excellent archive for evaluation of time-series environmental contamination of water systems. Measurements of ultra-trace radioactive species, such as ¹²⁹I, provide information for both chronologic calibration and anthropogenic emissions during the nuclear era. Here data are presented on ¹²⁹I and other chemical parameters from two sediment cores collected in the Baltic Sea during 1997. The sediment sections have a relatively uniform grain size (clay–mud) and cover a period of about 50 a. Distribution of ¹²⁹I in the sediment strongly relates to the liquid release records from the nuclear reprocessing facilities at Sellafield and La Hague. However, syn- and post-depositional alteration of organic matter at the sediment–water interface and within the sediment column may have contributed to slightly obliterating the anthropogenic ¹²⁹I signals. Indication of Chernobyl-derived ¹²⁹I occurs in the sediment profile, but is apparently overridden by the overwhelming flux from the nuclear reprocessing facilities. Although the record did not cover the pre-nuclear era (before 1945) sections, the ultra sensitive ¹²⁹I profile provides a potential tool for relative dating and monitoring sources of water and sediment to the region.