When the survivor is pulled out of the life raft and placed into the helicopter, her jumper is completely dry,
The taxi that Kendra takes to go home has the registration 3ZR 492A which is not a valid UK registration, nor is it a legal registration plate with no visible manufacturer's mark.
After the submersible implodes, Janet says on the phone that "there's no chance that the black boxes can be recovered now". Submersibles have been to the deepest parts of the oceans (Challenger Deep, Marianas Trench, Pacific), so it's perfectly possible to dive to the bottom of the Atlantic.