Prospects for “iodine-129 dating” of marine organic matter using AMS

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Natural levels of iodine 129 have been overwhelmed by a build-up of “new” iodine-129, a product of our nuclear age. Much of this new iodine-129 has entered the ocean and is now found in its upper layers. During primary production, marine organic matter incorporates iodine, which then moves through the food chain. The 129I 127I ratio in marine organics therefore represents the value found in the ocean's photic zone when the organic matter formed. Because the 129I 127I ratio in any well-mixed marine basin has increased rapidly since the advent of the nuclear age, establishing the build up pattern of 129I in that basin's surface waters would allow us to “date” the time of formation of any organics formed there, provided that we can obtain an adequate amount of iodine from samples. Measurement of this ratio requires the use of AMS.