In deep ocean biomes (possibly normal oceans as well) there are randomly generated air pockets that are best spotted when doing a fly-over.
MC-37601
Random Air Pockets in Deep Oceans
Resolved
Duplicate
0
Platypus
(Unassigned)
Unconfirmed
air, ocean, pockets
Minecraft 1.7.2
Retrieved
Duplicate of MC-954 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.