Davy Jones's locker 
noun informal
The bottom of the sea, especially regarded as the grave of those drowned at sea: the reef will consign us all to Davy Jones’s locker...
- A dinosaur-era Davy Jones's locker of large, predatory sea reptiles has been discovered by fossil hunters on an Arctic island.
- Have my officer, Johnny; send him to Davy Jones's locker if he fights.
- And you'd have thought they'd at least shed a tear or two when their old man vanishes into Davy Jones's locker.
Origin
Extension of early 18th-century nautical slang Davy Jones, denoting the evil spirit of the sea.