Random pockets of air are floating mid ocean. I have seen this in older versions of MineCraft, but don't have any specific examples of old generation to show.
Here is where I have found this generation anomaly so far:
Seed: 8632520611045298466 (-33 55 926) / (87 55 1057) / (1147 54 -475)
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duplicates
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migrated
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Confirmed
EDIT: Duplicate of MC-954
Please do not mark unreleased versions (anything starting with "Future Version") as affected. You don't have access to them yet.
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.
Sorry for not doing my research on this matter.... 😉