Adam Clarke on Revelation 20:13

The sea gave up the dead - Those who had been drowned in it, and those millions slain in naval contests, who had no other grave.

And death - All who died by any kind of disease. Death is here personified, and represented as a keeper of defunct human beings; probably no more than earth or the grave is meant, as properly belonging to the empire of death.

And hell - Ἁιδης, Hades, the place of separate spirits. The sea and death have the bodies of all human beings; hades has their spirits. That they may be judged, and punished or rewarded according to their works, their bodies and souls must be reunited; hades, therefore, gives up the spirits; and the sea and the earth give up the bodies.