“Tehom” means “ocean.” It’s the deep sea that was too deep and scary and out of sight of land, so Mediterranean seafarers didn’t venture upon it. (And that’s also why it was associated with chaos and void, as well as with sea monsters.)
(It’s not “the bottom of the sea that we’ve never seen except maybe for about two seconds right before a tsunami,* because we’re ancient Israelites who don’t have diving gear.” Ancient people didn’t normally think about the bottom of the sea.)
Jonah 2:5/6 is another good example of this, with its parallelism:
“The waters encompassed me, even to the soul [or “breath”].
The deep closed around me.”
Now he does actually hit bottom, apparently, although it may be a figurative way of saying that he died:
“I went down to the roots of the mountains.
The bars of the earth were around me forever.
And yet You have brought my life out from the pit,
O Lord my God!”
“The face of the deep” is the surface of the ocean, where the waves are.
Here’s a bit from Job 38:29-30 that you may have forgotten, when God is asking Job rhetorical questions:
“Out of whose womb came the ice?
And the frost from heaven - who has engendered it?
The waters are hardened like a stone,
and the face of the deep is frozen.”
“The waters” are rivers, streams, and ponds. Since they are shallower, they can freeze completely in the winter. But only “the face of the deep” [pene tehom] is frozen, which is usually the case even in the Antarctic.
In the 3rd year of the persecutions under Maximinus, Eusebius (the church historian) was a student living in Caesarea Maritima at the house of a learned priest named Pamphilus, along with other students of his, including a guy named Apphianus. Apphianus secretly went off and confronted the governor, telling him not to make sacrifices to false gods. He was tortured in private, imprisoned, publicly burned (one of Maximinus’ favorite punishments for both Christians and pagans who disagreed with him), and then since he didn’t die or apostatize, thrown into the sea.
"But that wonderful thing which happened after this act, I know will not be believed by those who did not witness the wonder with their own eyes, as I myself did: for men are not wont to give the same credence to the hearing of the ear as to the seeing of eye. It is not, however, right for us also, like those who are in error and deficient in faith, to conceal that prodigy which took place at the death of this martyr of God; and we also call as witnesses to you of these things, which we have written, the whole of the inhabitants of the city of Caesarea, for there was not even one of the inhabitants of this city absent from this terrific sight.
For after this man of God had been cast into the depths of the terrible sea, with stones tied to his feet, forthwith a great storm and frequent commotions and mighty waves troubled the vast sea, and a severe earthquake made even the city itself tremble, and everyone’s hands were raised towards heaven in fear and trembling, for they supposed that the whole place, together with its inhabitants, was about to be destroyed on that day.
And at the same time, the sea, even as if it were unable to endure it, vomited back the holy body of the martyr of God, and carried it with the waves and laid it before the gate of the city. And there was at that time vast affliction and commotion, for it seemed like a messenger sent from God to threaten all men with great anger.
And this which took place was proclaimed to all the inhabitants of the city, and they all ran at once and pushed against each other in order that they might obtain a sight, both boys and men and old men together, and all grades of women, so that even the modest virgins, who kept to their own apartments, went out to see this sight. And the whole city together, even the very children as well, gave glory to the God of the Christians alone, confessing with a loud voice the name of Christ, who had given strength to the martyr in his lifetime to endure such afflictions, and at his death had showed prodigies to all who beheld."