That show truly is amazing.
My thoughts when I saw them zoom down into the ocean was that island is what we would call Atlantis.
Comments any one?
What if the underwater island is actually how the series ends? It seems like we're being bounced back and forth between at least two different times or parallel universes - Jack on the island and Jack on the plane (and at the airport). Maybe the writers just gave us a glimpse of their ending with the island ending up buried underwater...