There is a popular YA fantasy book titled Sea of Shadows by Kelley Armstrong. If you were searching for that specifically, it isn't related to Tolkien's universe, though the titles are very similar!
The Lord of the Rings: Sea of Longing or The Sundering Seas . A Shadow of the PastThe Lord of the Rings : Sea...
Alternatively, you might be referencing the "sea-longing" that many characters (like Legolas) feel as the Third Age ends. There is a popular YA fantasy book titled
The Lord of the Rings: Sea of Rhûn or Shadows of the East . 3. "To the Sea" (The Elven Longing) it isn't related to Tolkien's universe
The second part of your draft, "The Lord of the Rings: Sea...", could refer to a few different things in Middle-earth: 1. The Sea of Núrnen (Mordor)