" there was no longer any sea " would indicate that what was seen as the canopy , sky , between heaven and earth had gone . Sea was used to depict the heavens in the sense of the sky . So the boundary between heaven and earth was removed ."
Or it could be literal in another sense. John wrote Revelation while on the island of Patmos in the Aegean Sea. He probably had a vision of an empty Aegean Sea or even the whole Mediterranean Sea. The Pacific and Atlantic oceans could still be present. Bible writers never saw the earth from outer space in their visions. If this were true the Jews and Christians would have had globes of earth thousands of years ago.