At times we gasped for breath at an elevation beyond the Albatross—at times became dizzy with the velocity of our descent into some watery hell, where the air grew stagnant, and no sound disturbed the slumbers of the Kraken. (8)
The slumbers of the who? The what? The Kraken is a mythical sea monster, which the narrator evokes even though it never actually appears. The description helps blur the line between the natural world and the supernatural world. The Kraken's the kind of thing that pops up in adventure stories all the time, but here it never rears its ugly head. Just the hint of it is enough to inspire terror in our poor narrator.
Superstitious terror crept by degrees into the spirit of the old Swede, and my own soul was wrapped up in silent wonder. (8)
"I ain't afraid of no ghosts!" We get a glimpse into the narrator's personality and self-regard here: unafraid, even when others are. And not only is he not afraid here (where the Swede is), he's actually in awe—wonder, even—at what he's seeing.
She rose up, like a demon of the deep, slowly from the dim and horrible gulf beyond her. (9)
For a second time, Poe evokes a supernatural sea monster without actually revealing evidence of the supernatural. It keeps alive the question of whether the black galleon is otherworldly, or perfectly natural (though perhaps a little weird). Could it be that all the weird stuff is just in his head?
All around was horror, and thick gloom, and a black sweltering desert of ebony. (8)
The setting becomes the source of terror here, and the landscape reflects the narrator's generally freaked-out state of mind. And check out Poe's clever diction here: he refers to the sea as a desert. What's that all about?
I beheld a spectacle which froze the current of my blood. (9)
Anytime one's blood is frozen, scary things are likely going on: in this case, it's the arrival of the black galleon.
The crew glide to and fro like the ghosts of buried centuries, their eyes have an eager and uneasy meaning. (22)
Shiver us timbers, Shmoopers. We find these zombie sailors with the uneasy eyes to be the most terrifying thing in this whole terrifying tale. Are they ghosts? Are they just really rude? And why don't we ever get the full story? The mystery surrounding these guys makes them even scarier than the whirlpool. At least you know what's waiting for you at the bottom—death.
We are surely doomed to hover continually upon the brink of Eternity, without taking a final plunge into the abyss. (20)
The fear here is one of purgatory: of never going forward or backward, but just being stuck. It may describe the narrator's state of being as much as the position of the ship. But it also might point to the reason these zombie sailors are so bent on diving headfirst into a whirlpool. Through the narrator's many descriptions, we get the idea that these guys have been sailing the seven seas for far too long, and at the end of the story, they'll finally get the sweet release of—whatever it is that's at the bottom of the whirlpool.
About a league on either side of us, may be seen, indistinctly and at intervals, stupendous ramparts of ice, towering away into the desolate sky, and looking like the walls of the universe. (23)
Poe throws the narrator up against the big, bad universe here: scary because it's so much larger than him… and probably couldn't care less if he lives or dies.
Oh, horror upon horror! The ice opens suddenly to the right, and to the left, and we are whirling dizzily. (27)
The finale arrives and the whirlpool gets ready to swallow up the narrator, punctuating Poe's idea that not every exploration story has a happy ending. And since this is a message this guy is writing down as all this goes down, we'll never know the real ending, which makes everything all the more mysterious and creepy.