[driggs]

What makes blue holes so fascinating, in my opinion, is the historical perspective they provide.

These were once deep air-filled vertical shafts, formed by the longterm erosional/dissolutional power of falling water under the influence of gravity. Speleothems like stalactites prove that they formed in an air-filled environment.

In other words, the present-day sea level at the Yucatan Peninsula was formerly at least 275m lower; and/or the present-day surface was at least 275m higher. The paper attributes this to "glacio-eustatic changes", which is the equal-and-opposite-reaction involving lowered sea level (increased global glaciation) and the buoyant rising of the regional continental crust since the mass of additional sea water has been removed.