On January 21, 1968, a U. S. Air Force B-52G Stratofortress carrying four thermonuclear weapons caught fire over Baffin Bay and crashed onto the sea ice near Thule Air Base, Greenland.
The high-explosive components of all four nuclear weapons detonated upon impact, fragmenting the nuclear cores and scattering radioactive material over a four-mile radius. While the massive cleanup effort known as Project Crested Ice managed to scrape away tons of contaminated snow, ice, and wreckage, a significant fraction of plutonium-239 and plutonium-240 sank through the melting ice into the benthic environment. Oceanographic studies conducted in the decades following the crash revealed a fascinating chemical interaction: finely grained marine silt in the Arctic sediment rapidly adsorbed the hydrophobic plutonium particles.
Rather than dissolving or dispersing uniformly through the water column, the radioactive isotopes bonded to fine clay minerals and organic matter in the seabed sediment. This particle fixation effectively locked high concentrations of plutonium into a thin layer of Arctic mud. Benthic organisms, including marine worms and bivalves, ingest these sediments, creating a localized bioaccumulation pathway in the cold-water benthic food chain.
Although the insoluble nature of sediment-bound plutonium limits its atmospheric spread, marine core sampling continues to detect distinct isotopic signatures from the 1968 accident trapped within the frozen silt layers of Bylot Sound, serving as a permanent geological marker of the Cold War.