“Then I stood still, forgetting war in Middle-Earth; for their wailing voices spoke to me of the Sea. The Sea! Alas! I have not yet beheld it. But deep in the hearts of all my kindred lies the sea-longing, which is perilous to stir. Alas! for the gulls. No peace shall I have again under beech or under elm.”
–-Legolas, The Return of the King, The Last Debate
The Sea is an extremely large biome surrounding Middle-Earth and is, as the name suggests, an ocean. This biome represents Belegaer, the Sundering Seas, the great western ocean of Arda. It surrounds all of Middle Earth, and is infinite.
It is mostly entirely made of water, and home to Fish, Seagull and squid, but there are islands that may contain mobs in the future. These islands are barren, with the exception of small Númenórean ruins scattered around. The colour of the water in the ocean will change depending on the player's latitude. Ice will also start forming as the player travels far north.
Upon reaching this vast body of water the player gains the achievement"To the Sea!" and the title of Mariner.
North of z -60000 the sea is completely frozen over, south of that small gaps in the ice become gradually more common until z -45000 where small ice burgs fill the sea and larger areas of open water are visible, with the ice again gradually becoming less common until z -30000, where it stops appearing at all. Snow placement on island biomes in the northern ocean appears to follow a similar pattern.
Islands are randomly generated in the sea as well as in specific locations, representing a few very specific islands. No people are known to currently inhabit these islands, although at a time they were part of Beleriand. oak, birch and beech trees dominate the flora.
This biome generates where the sea meets the land. It's mostly sand. Most of Middle-earth's coastlines consist of this biome, although there are also some rocky coastlines. There is also a white beach variant, made of white sand and a gravel beach.
The arctic zone is characterised by an area where part to all of the top layer of the sea is frozen and covered under a sheet of sea ice. This zone is situated north of the area bordered by z coordinate -30000. The farther north one travels, the denser the coverage of ice. North of z coordinate -60000, the ice shelf is fully closed.
The subtropical zone is characterised by the presence of palm trees, both on the beaches and islands in the sea. This zone stretches from z coordinate 64000 down to the farthest southern tip of Far Harad. The presence of palm trees gradually increases while going further south from z coordinates 64000 to 130000.
One structure spawns in the sea, and one on the beaches and islands (except Meneltarma).
Underwater Elven Ruin (submerged only) - These ruins are composed of Elven brick, with some glowstone and a chest, containing valuable loot. Despite the risk it would take to dive down, the reward is often worth it, as these ruins have been known to contain mithril.
Númenórean Ruin (on land only) - Dilapidated towers of stone brick, remnants of Númenórean colonies. They are hollow and often contain a single tree.
No sentient creatures inhabit the oceans and islands. The waters are alive and host many shoals of squid and Fish. And its shores are dominated by the ever presence noise and flapping of seagulls.
The many scattered islands, including the three islands visible on the map, host many types of non-domesticated common animal wildlife, survivors of ages past. Notably there is no Rabbit, Bird or Butterfly of any kind.
The Sea is an excellent place to find Rock Salt, which is more common here and in other coastal biomes than anywhere else in Middle-Earth. It is two and a half times as common underground, and additionally can be found in stone at levels up to Y=80, as opposed to most biomes, where it only generates up to Y=64. The same is true for all beach biomes.
Additionally, the Sea is also an excellent source of coral, which can be found growing on coral reef blocks, especially on the coasts. The Sea is also home to sponges, which can be found uncommonly on the seafloor.