When it comes to describing the vast, mysterious expanse of the ocean, there are a few possible synonyms for "deep blue sea." Some options include "azure waters," "navy depths," or "cobalt currents." Another option might be to refer to the ocean by name, such as the "Pacific" or "Atlantic," which evoke a sense of the immense size of these bodies of water. Or, for a more poetic or metaphorical approach, you could use phrases like "the abyss" or "the fathomless deep," which hint at the unknown depths that lie below the surface of the waves. Regardless of which synonym you choose, the sea will always remain a source of fascination and wonder.