In Kingdom Hearts 1 and 2 Sora must become a mermaid to breathe in Atlantica. In Chain of memories he walks into the Atlantica door like it's nothing. If he still needs to be a mermaid to breathe underwater then there's no way he has an ability to breathe under it in Chain of memories (in between 1 and 2). If C.O's doors do indeed drive off of Sora's memories for each card then Atlantica would go by the same rules as before. 

 

In conclusion, gathering all of this, the only logical explanation seems to be that Atlantica's water is fake in some way.

 

Since its a memory, I dont think it will be real water. He just remembers atlantica, he is not actually there.

Hmmm. I'm going to chalk this one up to 'magic'.

Sora was granted gills by aquaman

In Kingdom Hearts 1 and 2 Sora must become a mermaid to breathe in Atlantica. In Chain of memories he walks into the Atlantica door like it's nothing. If he still needs to be a mermaid to breathe underwater then there's no way he has an ability to breathe under it in Chain of memories (in between 1 and 2). If C.O's doors do indeed drive off of Sora's memories for each card then Atlantica would go by the same rules as before. 

 

In conclusion, gathering all of this, the only logical explanation seems to be that Atlantica's water is fake in some way.

the White rooms take the apparnce of the world.but your not phisyaly there.like an illsiouion(bad spelling ><)

It was Sora's memories that he was seeing. He was basically in a white room somewhere in the castle at all times. Every world in COM is a memory projected in a white room with them not being real at all. It is like seeing a virtual world in real life where you can interact with the characters, but you only stay within the room you were in to begin with. So since it is just like a 5D element projection of Sora's memories, then they are basically talking to no one in a little white room that leds to more white rooms that they believe to be worlds, but they are seeing fake images. So Sora and the gang can survive in an area like that because of the whole not being really there thing.

Also, it is like that part in Zoroark Master of Illusions when the bad guy thought he succeeded in his plans on getting the power from the time gate.

It was Sora's memories that he was seeing. He was basically in a white room somewhere in the castle at all times. Every world in COM is a memory projected in a white room with them not being real at all. It is like seeing a virtual world in real life where you can interact with the characters, but you only stay within the room you were in to begin with. So since it is just like a 5D element projection of Sora's memories, then they are basically talking to no one in a little white room that leds to more white rooms that they believe to be worlds, but they are seeing fake images. So Sora and the gang can survive in an area like that because of the whole not being really there thing.

Also, it is like that part in Zoroark Master of Illusions when the bad guy thought he succeeded in his plans on getting the power from the time gate.

pretty much i said but in more detail

 

I believe in magic.

sora is king he makes and breaks rules like how nomura owns your brain

Don't forget you can also cast Fire, and it'll have the exact same physical properties as if you cast it anywhere else.  There's also how characters can speak properly despite how water distorts sound.  So yeah, magic water.

Nomura logic at it's best!~

If you want to get technical, the water is fake since Square Enix did not program any kind of water, and just added effects. So what you are actually doing in the games is simply flying through the area, like you can in Neverland in the first game.

Sora remembered breathing underwater and so he could?

But yours is the more likely conclusion.

I believe in magic.

Sora remembered breathing underwater and so he could?But yours is the more likely conclusion.

This.