What is the main conflict in Pacific Vortex by Clive Cussler?

Pacific Vortex is a thriller that opens with the main character, Dirk Pitt, lying on a beautiful Hawaiian beach. Gazing out over the sea, he spots something glistening in the waves. He swims out to retrieve the item, which turns out to be a communications capsule from a missing nuclear submarine. He opens the capsule and reads the contents, a missing twenty-six page section of the ship's log. In it, the captain, who has apparently gone over the brink of madness, tells of the strange goings-on in the Pacific Vortex, an area of the Pacific that is like the Bermuda Triangle with strange disappearance of ships.