Where are we? In the great, big sea—that's where. Naw, we're not talking about the band by the same name. We're talking about the actual ocean here. From the very get-go, Pound plunges us into a scene of "spray-whited circles of cliff wash" (6), filling our ears with the sound of the same sea that featured so strongly in "Canto I." But when we wonder why Pound focuses so much on the sea, he gives us a bit of an answer in line 13, where he says that the poet Homer had an "ear for the sea-surge" (13).
In other words, the sea is a gigantic, unstoppable force that has its own natural rhythms and beauty, and the great poets of history have taken inspiration from this. Further, Pound seems to directly compare the sea and the human imagination, since both are sources of endless creation from nothing. For example, there is a direct link between the sea and the imagination of the god Dionysius in lines 67-68, where living vines grow out from the ocean (under the god's command) and we discover that "where was gunwale, there now was vine-trunk,/ And tenthril where cordage had been" (68).
Whenever we start to forget where we are, Pound also has a rhythmic way of returning to certain phrases that invoke the sea, like in line 130: "And So-shu churned in the sea." The inclusion of "And" here reminds us that the washing of the sea has been going on throughout our reading of this poem. It's an eternal process that's witnessed by mortals (us) who aren't eternal. It's a bit like art in that way, don't you think? We're witnesses to a process that has been going on long before us, and will continue long after we're in the ground (or among the waves).