Have you ever wondered what a "sea change" was? The easy answer is that it is a transformation of large proportion. It comes from Shakespeare's The Tempest in which Ariel sings:
Full fathom five thy father lies:
Of his bones are coral made:
Those are pearls that were his eyes:
Nothing of him that doth fade
But doth suffer a sea-change
Into something rich and strange.
In short, Ariel is saying that the sea has changed Ferdinand's father's body from flesh and blood to coral, pearls and things rich and strange. We have adapted the phrase and made it mean change of significance, any large change.
Now you know!
