Nuclear weaponry and power generation have released far more129I onto the Earth's surface than was formerly present. The effects of this release are clearly visible in the waters of the Gulf of Mexico, far from the major sources. New129I is found down to at least 500 m, and probably to 1000 m. Surface values are approximately 60 times the pre-nuclear era levels. The129I penetration depth of 470 m agrees well with that determined from bomb fallout isotopes3H and Δ14C during the 1970s and 1980s in the Gulf of Mexico and in the western North Atlantic at similar latitudes. The observed levels exceed amounts expected from globally distributed nuclear test fallout. The observed surplus must come primarily from spent fuel reprocessing plants in the eastern North Atlantic, followed by rapid circulation of the North Atlantic gyre, and subsequent delivery into the Caribbean Sea and thence into the Gulf of Mexico. Airborne transport also appears significant.
