It is based on the 1997 science fiction book Meg: A Novel of Deep Terror by Steve Alten.
" the species has indeed survived, but is trapped in the Mariana Trench due to the 'cold water barrier' (the bottom of the Trench is heated by geothermal ducts, keeping the water warm, but that warmth has limited range and the far colder water above it keeps the sharks trapped there as the cold water would apparently have highly negative effects on the giant sharks unless traversed properly)."