Classified documents obtained by a group of former workers at Thule, an Arctic air and radar base built by the United States in 1951-52, suggest that one of four hydrogen bombs on a B-52 bomber that crashed there in 1968 was never found, the daily Jyllands-Posten said 'Detective work by a group of former Thule workers indicates that an unexploded nuclear bomb probably still lies on the seabed off Thule' the newspaper said.
The crash, on January 21, 1968 led to a crisis in relations between the United States and NATO ally Denmark, which is responsible for Greenland’s foreign, security and defence policy and at the time prohibited nuclear weapons on its territory, including Greenland.
A U.S. state department document dated August 31, 1968 said all weapons on board the crashed aircraft had been accounted for but did not spell out whether they had been recovered. The United States assured the Danish government in spring 1968 that clean-up work after the B-52 crash had been completed and gave up searching for the lost bomb in August that year.
I'm sure it will turn up at some point.