I-129: A New Biogeochemical Tracer of Oceanographic Processes

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9529351 Edmond It is very important to develop non-conservative tracers, i.e. transient anthropogenic species sensitive to biological and geochemical processes going on in the oceanic water column. At present the only such species for which information is available is anthropogenic lead (Shen and Boyle, 1988). It is derived from automobile exhaust and, to a much lesser extent, from the smelting of sulfide ores and other high temperature processes. Thus its atmospheric sources is predominantly confined to the Northern Hemisphere. Lead is strongly reactive with biogenic particles. Hence the fate of the transient can be used to study solute- particle scavenging reactions with a high degree of resolution ( Sherrell and Boyle, 1986). What is lacking is a tracer directly involved in the cycle of organic carbon with a strong signal. 129I, which is released in tremendous quantity from nuclear fuel reprocessing plants, has the potential to fill this role. Initial results from measurements in the Norwegian-Greenland Sea, the overflows around Iceland, the Labrador Sea and the North Atlantic show that the isotope is enriched in surface waters, the overflows and the deep Greenland, Norwegian and Labrador Seas, i.e. similar to 3H at a comparable stage in its evolution. However the penetration depth into the main thermocline in the North Atlantic appears significantly greater suggesting biogenic diapycnal transport, consistent with the biophilic nature of iodine. Measurements of I-129/I-127 ratios in selected archived samples will be made to develop I-129 as a non-conservative tracer and establish limits for its interpretation in biologically active environments.