City Beneath the Sea (1971)

In the 21st-century, a former underwater scientific installation has been repurposed as a city, known as Pacifica to the colonists who inhabit it. Now the U. S. government has plans to store the Ft. Knox gold reserves there, along with a fantastic new radioactive element. But, someone has plans of stealing the gold, and to make matters worse;, the city faces imminent destruction by an asteroid heading towards it.