Deep Cold Ocean

Cold water, deep water. The darkest blue the game gives an unfrozen sea, over gravel far enough down that the light barely reaches it.

Monuments generate here, which puts elder guardians and sponge rooms under some of the coldest water in the Overworld, and guardians circle outside them. Salmon and cod swim above, drowned below, and kelp climbs from the gravel.

Temperature 0.5 with 0.5 humidity is the mild temperate climate every ocean shares, so rainfall at the surface. minecraft:deep_cold_ocean is uncommon, was split off in 1.13, and 1.21 still sinks it beside the cold shelf.

Deep cold water in the Overworld, further out than the shelf. Cold Ocean, Deep Ocean and Deep Frozen Ocean border it, so it begins where a cold sea stops being shallow.

Sail cold waters until the floor drops away; monuments can appear in the depths.

Uncommon rather than hidden: sail cold water until the floor disappears from under the boat. Guardians mean a monument is down there, and that monument is usually the whole reason for the trip. Sail through the cold shallows before anything else: nothing in the ordinary sea marks the change except the light, which reaches nowhere near this floor, and the water turns dark long before you reach the ice. Those neighbours will reveal it soon enough, and once the light under the hull goes you are nearly there.

The cold ocean list, one monster heavier. Squid take 60 percent of the spawn attempts, cod and salmon 50 percent each, the drowned about 1 in 100, and the guardian arrives with the monument.

A guardian fires a charging laser and inflicts Mining Fatigue near that monument, which is the whole reason a deep dive here goes wrong. Around it, cod is the common food fish and salmon the cold-water one, both easy to net in a bucket, and the squid drop ink sacs for a book and quill as well as black dye. The drowned brings its trident and its nautilus shells as usual. Behind it, salmon half and squid 60%. Cod hand over cod and bone meal, squid drop ink sacs, used for black dye and for books and quill, and on the peaceful side that is the lot; turn your back on the wrong shape and the drowned, underwater and a zombie, trident included if you are unlucky, is behind it. Watch the beam from the guardian while you are at it. A cod, for example, shoals three to six at a time. A drowned will wield whatever it picked up.

Squid

CodSalmon

Drowned

Guardian

Gravel, Seagrass and Kelp over a floor that sits far enough down to need a plan. Cold and deep is where ocean monuments stand, so a trip here is usually about the building rather than the blocks.

You can carry out gravel by the stack on the way, and the seagrass follows the deep cold rule: sparse, like the shallow cold sea, but spread over a much bigger floor.

People come for the monument that stands out here and leave with a full inventory of prismarine, but what sets this floor apart is the pattern its seagrass is laid down in over so much ground.

Kelp still grows at this depth, which is the one thing the cold water does not take away from you.

Gravel

Seagrass

Kelp

Cold, deep, and holding all three. An ocean monument can generate on this floor, one of four biomes on this site deep enough for the prismarine temple, its Elder Guardians and the hidden gold blocks inside it.

Ocean ruins are the sunken stone version of the same idea, found in nine biomes here, with chests of loot and buried treasure maps. A shipwreck adds an eleventh option, its chests packed with emeralds, treasure maps and supplies.

The gravel floor lies far enough down that the swim itself is the risk, and the kelp does nothing to shorten it. Deeper still, mineshaft tunnels with dungeon rooms cut off them and a stronghold on occasion generate with no attention paid to the cold water on top. A temple guarded by Elder Guardians and concealing gold, a vessel whose chests hold supplies, a ruin of sunken stone: exploring all three offers loot and challenges in one dive. Each of these is thoroughly guarded in its own way, as well as being able to sit within sight of the next, which is worth planning for.

The deep cold sea gets 40 seagrass tries per chunk, eight more than the shallow version and eight fewer than an ordinary deep ocean, which is as fine a distinction as world generation makes anywhere. Kelp runs on noise. Forty eight passes, and the rest of them are the ore and spring lists every Overworld chunk gets.

Cold classification, deep water and a monument: the deep cold ocean is on the cold farm animal list and on the map outline list, and it spawns squid, cod, salmon and drowned.

Nothing here takes a winter coat, because the fox and rabbit rules need snow on the ground rather than cold water over it.

A monument can stand on this floor, which the shallow cold ocean cannot manage, and it brings its own guardian spawn list and blocks the axolotls inside its walls.

Cold ocean ruins and shipwrecks fill in around it.