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Published September 13, 1996 | public
Journal Article

Iridium in Natural Waters


Iridium, commonly used as a tracer of extraterrestrial material, was measured in rivers, oceans, and an estuarine environment. The concentration of iridium in the oceans ranges from 3.0 (±1.3) × 10^8 to 5.7 (±0.8) × 10^8 atoms per kilogram. Rivers contain from 17.4 (±0.9) × 10^8 to 92.9 (±2.2) × 10^8 atoms per kilogram and supply more dissolved iridium to the oceans than do extraterrestrial sources. In the Baltic Sea, ∼75% of riverine iridium is removed from solution. Iron-manganese oxyhydroxides scavenge iridium under oxidizing conditions, but anoxic environments are not a major sink for iridium. The ocean residence time of iridium is between 2 × 10^3 and 2 × 10^4 years.

Additional Information

© 1996 American Association for the Advancement of Science. Received 26 April 1996; accepted 17 July 1996. R. A. Creaser contributed to the development of the analytical methods. We thank D. Karl and others involved in the HOT program for help in sampling the Pacific Ocean, M. Roy-Barman and D. Porcelli for their assistance in the field, and G. Ravizza for his thoughtful comments. Supported by U.S. Department of Energy grant DE-FG03-88ER13851, NASA grant NAGW-3337, and an NSF Graduate Research Fellowship to A.D.A. Ship time on the R.V. Moana Wave was supported by NSF OCE-9303094 (R. Lukas) and OCE-9301368 (D. Karl). Division contribution number 5669 (931).

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